BACKGROUND

[0001] Multiple exploratory logic devices are based on ferromagnetic (FM) elements.

AC (Alternating Current) perturbations of magnetization in FM are spin waves (e.g., propagating disturbances in the ordering of magnetic materials). One spin wave switch is described with reference to Figs. 1A-B. Fig. 1A illustrates scheme 100 of spin wave field transistor where transmitted or reflected spin waves are formed depending on the gate voltage VG. In this scheme, the spin wave switching mechanism is based on switching magnetic anisotropy in a FM wire (i.e., switching based on magnetostrictive change of anisotropy). The principle of operation is based on a piezoelectric (PZ) material which is placed adjacent to an FM wire.

[0002] As voltage is applied to the PZ layer, it exerts stress on the FM wire. As a result, magnetic anisotropy changes (i.e., magnetostriction effect). When the applied voltage is equal to zero (i.e., VG=0), Incident spin wave (SW) propagates as Transmitted SW as shown by scheme 100, and when the applied voltage is greater than zero (i.e., VG>0), Incident SW is reflected back as Reflected SW as shown by scheme 110. Fig. IB illustrates a set of plots 120 and 130 showing magnetic anisotropy versus position in the FM wire according to the applied voltage VG. Plot 120 illustrates the case when VG is greater than zero, and plot 130 illustrates athe case when VG is less than zero. This spin wave switching scheme is a volatile scheme (i.e., data is lost when applied voltage is removed).

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The embodiments of the disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the disclosure, which, however, should not be taken to limit the disclosure to the specific embodiments, but are for explanation and understanding only.

[0004] Fig. 1A illustrates a scheme with spin wave field transistor where transmitted or reflected spin waves are formed depending on a gate voltage VG.

[0005] Fig. IB illustrates a set of plots showing magnetic anisotropy versus position in a Ferromagnetic (FM) wire.

[0006] Figs. 2A illustrates a bi-stable magnetic element and quad-stable magnetic elements which can form building blocks of a spin wave switch scheme, according to some embodiments of the disclosure. [0007] Fig. 2B illustrates bi-stable elements, with piezoelectric layers, which can form building blocks of a spin wave switch scheme, according to some embodiments of the disclosure.

[0008] Fig. 2C illustrates a quad-stable element, with a piezoelectric layer, which can form building blocks of a spin wave switch scheme, according to some embodiments of the disclosure.

[0009] Fig. 2D illustrates quad-stable elements, with Spin Orbit Coupling layers, which can form building blocks of a spin wave switch scheme, according to some embodiments of the disclosure.

[0010] Fig. 2E illustrates a quad-stable element with a wire to provide magnetic field, according to some embodiments of the disclosure.

[0011] Fig. 3A illustrates a top view of a spin wave switch scheme with in-plane magnets, according to some embodiments of the disclosure.

[0012] Fig. 3B illustrates a spin wave switch scheme with a quad-stable element, according to some embodiments of the disclosure.

[0013] Fig. 4 illustrates a top view of a spin wave switch scheme with in-plane magnets, according to some embodiments of the disclosure.

[0014] Fig. 5A illustrates a top view of the spin wave switch scheme of Fig. 3A in which the propagation of spin wave is controlled to generate a low logic state at a spin wave detector, according to some embodiments of the disclosure.

[0015] Fig. 5B illustrates a top view of the spin wave switch scheme of Fig. 3A in which the propagation of spin wave is controlled to generate a high logic state at the spin wave detector, according to some embodiments of the disclosure.

[0016] Fig. 6 illustrates a spin wave switch scheme with out-of-plane magnets and controllable by a magnetic junction, according to some embodiments of the disclosure.

[0017] Fig. 7 illustrates a side view of a spin wave switch scheme controllable by a magnetic junction, according to some embodiments of the disclosure.

[0018] Fig. 8 illustrates micro-magnetic simulation based plots for the spin wave switch scheme of Fig. 3B showing spin wave propagation (in the x, y, and -z directions, respectively) at an initial state with the nanomagnets and FM wires having parallel magnetizations, according to some embodiments of the disclosure.

[0019] Fig. 9 illustrates micro-magnetic simulation based simulation plots for the spin wave switch scheme of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at a final state with the nanomagnets and FM wires having parallel

magnetizations, according to some embodiments of the disclosure.

[0020] Fig. 10 illustrates micro-magnetic simulation based plots for the spin wave switch of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at an initial state with the nanomagnets having perpendicular magnetizations relative to the magnetizations of the FM wires, according to some embodiments of the disclosure.

[0021] Fig. 11 illustrates micro-magnetic simulation based plots for the spin wave switch scheme of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at a final state with the nanomagnets having perpendicular magnetizations relative to magnetizations of the FM wires, according to some embodiments of the disclosure.

[0022] Fig. 12 illustrates a flowchart of a method of using the spin wave switch scheme, according to some embodiments of the disclosure.

[0023] Fig. 13 illustrates a smart device or a computer system or a SoC (System-on-

Chip) with a spin wave switch scheme, according to some embodiments of the disclosure.

DETAILED DESCRIPTION

[0024] Some embodiments describe a spin wave switch (or scheme) formed by introducing a break (or gap) in a ferromagnet (FM) wire (also referred to as FM nanowire) and inserting a nonmagnetic element (also referred to as a nanomagnet) in the break. In some embodiments, the FM wire and the nanomagnet can be coupled by exchange interaction. For example, an exchange coupling layer formed of Ru, Cu, or Mo can be used for exchange interaction between the FM nanowire and the nanomagnet. In some embodiments, when the magnetization of the nanomagnet is parallel to that of the FM wire (or nanowire), the transmission of spin waves is high (e.g., the spin waves traverse through the nonmagnetic element and the nanomagnet). In some embodiments, when the magnetization of the nanomagnet is perpendicular to that of the FM nanowire, the transmission of spin waves is low (e.g., most spin waves do no traverse through the exchange coupling layer and the nanomagnet).

[0025] The spin wave switch of the various embodiments is a non-volatile switch.

For example, if power is switched off, the magnetization state persists. Conversely, the spin wave switch of Figs. 1A-B are volatile. Multiple mechanisms of switching the magnetization are possible with the spin wave switch of the various embodiments. In contrast, the switching mechanism of the switch of Figs. 1A-B is a single switching mechanism. As such, any FM material can be switched with the spin wave switch scheme of the various embodiments and is not limited to merely materials with high magnetostriction coefficients, in accordance with some embodiments.

[0026] In the following description, numerous details are discussed to provide a more thorough explanation of embodiments of the present disclosure. It will be apparent, however, to one skilled in the art, that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring embodiments of the present disclosure.

[0027] Note that in the corresponding drawings of the embodiments, signals are represented with lines. Some lines may be thicker, to indicate more constituent signal paths, and/or have arrows at one or more ends, to indicate primary information flow direction. Such indications are not intended to be limiting. Rather, the lines are used in connection with one or more exemplary embodiments to facilitate easier understanding of a circuit or a logical unit. Any represented signal, as dictated by design needs or preferences, may actually comprise one or more signals that may travel in either direction and may be implemented with any suitable type of signal scheme.

[0028] Throughout the specification, and in the claims, the term "connected" means a direct connection, such as electrical, mechanical, or magnetic connection between the things that are connected, without any intermediary devices. The term "coupled" means a direct or indirect connection, such as a direct electrical, mechanical, or magnetic connection between the things that are connected or an indirect connection, through one or more passive or active intermediary devices. The term "circuit" or "module" may refer to one or more passive and/or active components that are arranged to cooperate with one another to provide a desired function. The term "signal" may refer to at least one current signal, voltage signal, magnetic signal, or data/clock signal. The meaning of "a," "an," and "the" include plural references. The meaning of "in" includes "in" and "on."

[0029] The term "scaling" generally refers to converting a design (schematic and layout) from one process technology to another process technology and subsequently being reduced in layout area. The term "scaling" generally also refers to downsizing layout and devices within the same technology node. The term "scaling" may also refer to adjusting (e.g., slowing down or speeding up - i.e. scaling down, or scaling up respectively) of a signal frequency relative to another parameter, for example, power supply level. The terms "substantially," "close," "approximately," "near," and "about," generally refer to being within +/- 10% of a target value. [0030] Unless otherwise specified the use of the ordinal adjectives "first," "second," and "third," etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner.

[0031] For the purposes of the present disclosure, phrases "A and/or B" and "A or B" mean (A), (B), or (A and B). For the purposes of the present disclosure, the phrase "A, B, and/or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0032] The terms "left," "right," "front," "back," "top," "bottom," "over," "under," and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions.

[0033] For purposes of the embodiments, the transistors in various circuits and logic blocks described here are metal oxide semiconductor (MOS) transistors or their derivatives, where the MOS transistors include drain, source, gate, and bulk terminals. The transistors and/or the MOS transistor derivatives also include Tri-Gate and FinFET transistors, Gate All Around Cylindrical Transistors, Tunneling FET (TFET), Square Wire, or Rectangular Ribbon Transistors, ferroelectric FET (FeFETs), or other devices implementing transistor functionality like carbon nanotubes or spintronic devices. MOSFET symmetrical source and drain terminals i.e., are identical terminals and are interchangeably used here. A TFET device, on the other hand, has asymmetric Source and Drain terminals. Those skilled in the art will appreciate that other transistors, for example, Bi-polar junction transistors (BJT PNP/NPN), BiCMOS, CMOS, etc., may be used without departing from the scope of the disclosure.

[0034] Figs. 2A illustrates a bi-stable magnetic element 200a and quad-stable magnetic elements 200b and 200c which can form building blocks of a spin wave switch scheme, according to some embodiments. In some embodiments, bi-stable magnetic element 200a is a ferromagnet 201 that has non-volatile states along the long axis as shown by the arrow indicating magnetization. In some embodiments, quad-stable magnetic element 200b has non-volatile states along every arm of the cross 202. In this example, the magnetization direction of quad-stable magnetic element 200b extends along a direction indicated by the arrow in Fig. 2A. In some embodiments, quad-stable magnetic element 200c has non-volatile states along every arm of cross 203. The magnetization direction of quad-stable magnetic element 200c extends from south to north, in this example.

[0035] In some embodiments, the magnets of the bi-stable and quad-stable elements

200a, 200b, and 200c are formed of from CFGG (i.e., Cobalt (Co), Iron (Fe), Germanium (Ge), or Gallium (Ga) or a combination of them). In some embodiments, the magnets of bistable and quad-stable elements 200a, 200b, and 200c are formed from Heusler alloys.

Heusler alloys are ferromagnetic metal alloys based on a Heusler phase. Heusler phases are intermetallic with certain composition and face-centered cubic crystal structure. The ferromagnetic property of the Heusler alloys are a result of a double-exchange mechanism between neighboring magnetic ions.

[0036] In some embodiments, the magnets of the bi-stable and quad-stable elements

200a, 200b, and 200c are formed of one of: Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, Yttrium Iron Garnet (YIG), or a combination of them. In some embodiments, Heusler alloys are one of: Cu ₂ MnAl, Cu ₂ MnIn, Cu ₂ MnSn, Ni ₂ MnAl, Ni ₂ MnIn, Ni ₂ MnSn, Ni ₂ MnSb, Ni ₂ MnGa Co ₂ MnAl, Co ₂ MnSi, Co ₂ MnGa, Co ₂ MnGe, Pd ₂ MnAl, Pd ₂ MnIn, Pd ₂ MnSn, Pd ₂ MnSb, Co ₂ FeSi, Co ₂ FeAl, Fe ₂ VAl, Mn ₂ VGa, Co ₂ FeGe, MnGa, or MnGaRu.

[0037] In some embodiments, the magnets of the bi-stable and quad-stable elements are formed with a sufficiently high anisotropy (Hk) and sufficiently low magnetic saturation (Ms) to increase injection of spin currents. Magnetic saturation M _s is generally the state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material (i.e., total magnetic flux density B substantially levels off). Here, sufficiently low M _s refers to M _s less than 200 kA/m (kilo- Amperes per meter).

Anisotropy Hk generally refers to the material property which is directionally dependent. Materials with high Hk are materials with material properties that are highly directionally dependent. Here, sufficiently high Hk in context of Heusler alloys is considered to be greater than 2000 Oe (Oersted).

[0038] Fig. 2B illustrates bi-stable elements 220a and 220b, with piezoelectric layers, which can form building blocks of a spin wave switch scheme, according to some embodiments. It is pointed out that those elements of Fig. 2B having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0039] In some embodiments, bi-stable element 220a/b is formed of layers of ferromagnet (FM) 221, Piezoelectric layer 222, and metal contact 223 coupled together as shown. In some embodiments, FM 221 and FM 221b are made of the same materials as FM 201 of Fig. 2B (i.e., bi-stable element 200a). Referring back to Fig. 2B, Piezoelectric layer 222 provides a piezoelectric effect upon applied voltage. In some embodiments,

Piezoelectric layer 222 is formed of poly crystalline ferroelectric ceramics. In some embodiments, Piezoelectric layer 222 is formed of: zirconate titanate PZT (e.g., Pb(Zro.2 Tio.sXb); BaTiC , or CoFeO. In other embodiments, other materials may be used for forming Piezoelectric layer 222. For example, materials such as PZT-5, PZT-4, PZNPT, PMNPT, BiFeCb; Βΐ4Τΐ3θΐ2; Polyvinylidene fluoride, and PVDF can be used for forming Piezoelectric layer 222. In some embodiments, metal contact 223 is made of non-magnetic metals such as Copper (Cu).

[0040] In some embodiments, a switching device (e.g., an n-type transistor MNl) is provided with its source terminal coupled to metal contact 223, drain terminal coupled to a supply (e.g., Vdd), and gate terminal controllable by a swathing signal (e.g., clock signal (elk)). In some embodiments, FM 221 of bi-stable element 220a/b switches between in-plane (see magnetization direction of FM 221) to out-of-plane (see magnetic direction of FM 221b) depending on the applied voltage on metal contact 223. This change in property of FM 221 (and 221b) is because of magnetostriction. Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. In some embodiments, FM 221 of bi-stable element 220a/b stays in an unstable switched state while the stimulus is on, and returns to a stable non-volatile stage when the stimulus is off.

[0041] Fig. 2C illustrates quad-stable element 230, with piezoelectric layers, which can form building blocks of a spin wave switch scheme, according to some embodiments. It is pointed out that those elements of Fig. 2C having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0042] Here, quad-stable element 230 is similar to bi-stable element 220 except that

FM 221/221b is replaced with quad-stable FM 203. In some embodiments, bi-axial magnetostriction strain is applied to FM 203 by Piezoelectric layer 222 when a voltage is applied to Piezoelectric layer 222 via the transistor MNl. As such, magnetization of FM 203 can be switched by magnetostriction strain. In some embodiments, FM 203 of the quad- stable element 230 stays in an unstable switched state while the stimulus is on, and returns to a stable non-volatile state when the stimulus is off, where the stimulus is provided by transistor MNl .

[0043] Fig. 2D illustrates quad-stable elements 240a/b, with Spin Orbit Coupling

(SOC) layers, which can form building blocks of a spin wave switch scheme, according to some embodiments. It is pointed out that those elements of Fig. 2D having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such. [0044] In some embodiments, quad-stable elements 240a/b include quad-stable FM

203/203b, layer 241 of SOC material deposited over quad-stable FM 203, and metal contacts 242, 243, 244, and 245 formed on the corners of layer 241. In quad-stable element 240a, positive voltage Vdd is applied to metal contact 242 and negative voltage -Vdd is applied to metal contact 244, while in quad-stable elements 240b positive voltage Vdd is applied to metal contact 242 and negative voltage -Vdd is applied to metal contact 244.

[0045] In some embodiments, SOC layer 241 is a layer that is operable to exhibit spin

Hall effect (SHE). In some embodiments, SOC layer 241 is made of one or more of β- Tantalum (β-Ta), Ta, β-Tungsten (β-W), W, Pt, Copper (Cu) doped with elements such as Iridium, Bismuth and any of the elements of 3d, 4d, 5d, 4f, and 5f periodic groups in the Periodic Table which may exhibit high spin orbit coupling. In some embodiments, SOC layer 241 is coupled to high conductivity non-magnetic metal(s) 242-245 to reduce the resistance of SOC layer 241. In some embodiments, non-magnetic metals 242-245 are formed from one or more of: Cu, Co, a-Ta, Al, CuSi, or NiSi.

[0046] In some embodiments, spin-to-charge conversion is achieved by SOC layer

241 via spin orbit interaction in metallic interfaces (i.e., using Inverse Rashba-Edelstein Effect (IREE) and/or Inverse SHE (ISHE), where a spin current injected from an input magnet produces a charge current Ic.

[0047] Table 1 summarizes transduction mechanisms for converting spin current to charge current and charge current to spin current for bulk materials and interfaces.

Table 1: Transduction mechanisms for Spin to Charge and Charge to Spin Conversion using SOC

[0048] In some embodiments, SOC layer 241 comprises layers of materials exhibiting inverse spin orbit coupling (ISOC) such as one of inverse SHE (ISHE) or inverse Rashba- Edelstein effect (IREE). In some embodiments, SOC layer 241 comprises a stack of layers with materials exhibiting IREE and ISHE effects. In some embodiments, SOC layer 241 comprises a metal layer, such as a layer of Copper (Cu), Silver (Ag), or Gold (Au), which is coupled to FM 203. In some embodiments, the metal layer is a non-alloy metal layer.

[0049] In some embodiments, SOC layer 241 also comprises layer(s) of a surface alloy, e.g. Bismuth (Bi) on Ag coupled to the metal layer. In some embodiments, the surface alloy is a templating metal layer to provide a template for forming FM 203. In some embodiments, the metal of the metal layer which is directly coupled to FM 203 is a noble metal (e.g., Ag, Cu, or Au) doped with other elements for group 4d and/or 5d of the Periodic Table.

[0050] In some embodiments, the surface alloy is one of: Bi-Ag, Antimony-Bismuth

(Sb-Bi), Sb-Ag, Lead-Nickel (Pb-Ni), Bi-Au, Pb-Ag, Pb-Au, β-Ta; β-W; Pt; or Bi ₂ Te ₃ . In some embodiments, one of the metals of the surface alloy is an alloy of heavy metal or of materials with high SOC strength, where the SOC strength is directly proportional to the fourth power of the atomic number of the metal.

[0051] Here, the crystals of Ag and Bi of SOC layer 241 have lattice mismatch (i.e., the distance between neighboring atoms of Ag and Bi is different). In some embodiments, the surface alloy is formed with surface corrugation resulting from the lattice mismatch, (i.e., the positions of Bi atoms are offset by varying distance from a plane parallel to a crystal plane of the underlying metal). In some embodiments, the surface alloy is a structure not symmetric relative to the mirror inversion defined by a crystal plane. This inversion asymmetry and/or material properties lead to spin-orbit coupling in electrons near the surface (also referred to as the Rashba effect).

[0052] In some embodiments, when the spin current from FM 203 flows through the 2D (two dimensional) electron gas between Bi and Ag in SOC layer 241 with high SOC, charge current L is generated. In some embodiments, the interface surface alloy of

BiAg2/PbAg2 of SOC layer 241 comprises of a high density 2D electron gas with high Rashba SOC. The spin orbit mechanism responsible for spin-to-charge conversion is described by Rashba effect in 2D electron gases. In some embodiments, 2D electron gases are formed between Bi and Ag, and when current flows through the 2D electron gases, it becomes a 2D spin gas because as charge flows, electrons get polarized.

[0053] The Hamiltonian energy HR of the SOC electrons in the 2D electron gas corresponding to the Rashba effect is expressed as:

H _R = a _R (k x ζ). σ . . . (3)

where i¾is the Rashba coefficient, 'k' is the operator of momentum of electrons, z is a unit vector perpendicular to the 2D electron gas, and σ is the operator of spin of electrons.

[0054] The spin polarized electrons with direction of polarization in-plane (in the xy- plane) experience an effective magnetic field dependent on the spin direction which is given as: where i _B is the Bohr magneton.

[0055] This results in the generation of a charge current in the interconnect proportional to the spin current / _s . The spin orbit interaction at the Ag/Bi interface (i.e., the Inverse Rashba-Edelstein Effect (IREE)) produces a charge current I _c in the horizontal direction which is expressed as:

j = biSSS . . . ₍₅₎

W _M

where w _m is width of the magnet, and λ _ΙΚΕΕ is the IREE constant (with units of length) proportional to a _R .

[0056] The IREE effect produces spin-to-charge current conversion around 0.1 with existing materials at lOnm magnet width. For scaled nanomagnets (e.g., 5nm width) and exploratory SHE materials such as Bi2Se3, the spin-to-charge conversion efficiency can be between 1 and 2.5, in accordance with some embodiments. The net conversion of the drive charge current / _d to magnetization dependent charge current is:

where P is the spin polarization. The charge current I _c propagates through non-magnetic metal contacts coupled to SOC layer 241.

[0057] Fig. 2E illustrates quad-stable element 250, with a wire to provide magnetic field, which can form building blocks of a spin wave switch scheme, according to some embodiments. It is pointed out that those elements of Fig. 2E having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0058] In some embodiments, two layers 251 and 252 of non-magnetic metals (e.g.,

Cu) are positioned over quad-stable magnet FM 203. In some embodiments, layers 251 and 252 are orthogonal to each other. So as not to obscure the embodiments, portion of layers 251 and 252 are shown. Layers 251 and 252 are coupled to a current source (not shown) that causes current to flow through layers 251 and 252. As current flows through layers 251 and/or 252, magnetic field 'FT is produced which switches the magnetization of FM 203.

[0059] The direction of magnetization switching of FM 203 depends on the direction of current flow through layers 251 and/or 252. In some embodiments, the magnetic state of FM 203 remains the previous state when stimulus is removed (e.g., when current is no longer flowing through layers 251 and/or 252). In some embodiments, the direction of current flow depends on the applied voltage (e.g., Vdd and -Vdd) on the terminals of layer 251. [0060] Fig. 3A illustrates top view 300 of a spin wave switch scheme with in-plane magnets, according to some embodiments of the disclosure. In some embodiments, spin wave switch scheme comprises a first FM (FMl) nanowire 301, second FM (FM2) nanowire 302, third FM (FM3) 303, first Exchange Coupling Layer 304, second Exchange Coupling Layer 305, Spin Wave Generator 306, and Spin Wave Detector 307.

[0061] In some embodiments, Spin Wave Generator 306 is coupled to FMl nanowire

301. In some embodiments, Spin Wave Generator 306 generates spin waves that traverse towards first Exchange Coupling Layer 304. In some embodiments, depending on the impedance of the block or stack including first and second Exchange Coupling Layers 304 and 305 and FM3 303, the generated spin waves are either reflected back towards Spin Wave Generator 306 or allowed to pass through towards FM2 nanowire 302. Here, FMl nanowire 301 and FM2 nanowire 302 are also referred to as spin waveguides.

[0062] In the embodiment of Fig. 3A, FMl nanowire 301, FM2 nanowire 302, and

FM3 303 are in-plane magnets (e.g., the magnetization direction is along the plane of the substrate on which FMl and FM2 nanowires are formed). In some embodiments, FM3 303 is a free magnetic layer. The thickness of a ferromagnetic layer may determine its

magnetization direction.

[0063] For example, when the thickness of the ferromagnetic layer is above a certain threshold (depending on the material of the magnet, e.g., approximately 1.5nm for CoFe), then the ferromagnetic layer exhibits magnetization direction which is in-plane. Likewise, when the thickness of the ferromagnetic layer is below a certain threshold (depending on the material of the magnet), then the ferromagnetic layer exhibits magnetization direction which is perpendicular to the plane of the magnetic layer. Other factors may also determine the direction of magnetization.

[0064] For example, factors such as surface anisotropy (depending on the adjacent layers or a multi-layer composition of the ferromagnetic layer) and/or crystalline anisotropy (depending on stress and the crystal lattice structure modification such as FCC, BCC, or L10- type of crystals, where LI 0 is a type of crystal class which exhibits perpendicular magnetizations), can also determine the direction of magnetization.

[0065] In some embodiments, FMl nanowire 301, FM2 nanowire 302, and/or FM3

303 are made from CFGG (i.e., Cobalt (Co), Iron (Fe), Germanium (Ge), or Gallium (Ga) or a combination of them). In some embodiments, FMl nanowire 301, FM2 nanowire 302, and/or FM3 303 are formed from Heusler alloys. Heusler alloys are ferromagnetic metal alloys based on a Heusler phase. Heusler phases are intermetallic with certain composition and face-centered cubic crystal structure. The ferromagnetic property of the Heusler alloys are a result of a double-exchange mechanism between neighboring magnetic ions.

[0066] In some embodiments, FMl nanowire 301, FM2 nanowire 302, and/or FM3

303 are formed of one of: Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, Yttrium Iron Garnet (YIG), or a combination of them. In some embodiments, Heusler alloys are one of: CiteMnAl, Cu ₂ MnIn, Cu ₂ MnSn, Ni ₂ MnAl, Ni ₂ MnIn, Ni ₂ MnSn, Ni ₂ MnSb, Ni ₂ MnGa

Co ₂ MnAl, Co ₂ MnSi, Co ₂ MnGa, Co ₂ MnGe, PdJVInAl, PdJVInln, Pd ₂ MnSn, Pd ₂ MnSb, Co ₂ FeSi, Co ₂ FeAl, Fe ₂ VAl, Mn ₂ VGa, Co ₂ FeGe, MnGa, or MnGaRu.

[0067] In some embodiments, first and second Exchange Coupling Layers 304 and

305, respectively, are non-magnetic layers of metal. In some embodiments, first and second Exchange Coupling Layers 304 and 305, respectively, are formed of one of: Ru, Cu, Mo, etc. In some embodiments, first and second Exchange Coupling Layers 304 and 305, respectively, are thin layers (e.g., lnm to 2nm in thickness). Exchange coupling is a way in which two magnetic atoms (or ions) in a material interact with each other. Here, first exchange coupling occurs between FMl nanowire 301 and FM3 303 via first Exchange Coupling Layer 304. Depending on the magnetization direction of FM3 303, a second exchange coupling occurs between FM3 303 and FM2 nanowire 302.

[0068] For example, when the magnetization of FM3 303 is perpendicular relative to the magnetizations of FMl nanowire 301 and/or FM2 nanowire 302, then little or no exchange coupling occurs between FMl nanowire 301 and FM3 303, and between FM3 303 and FM2 nanowire 302 as illustrated by Fig. 5A.

[0069] Fig. 5A illustrates top view 500 of the spin wave switch scheme of Fig. 3A in which the spin wave switch scheme is controlled to generate a low logic state at Spin Wave Detector 307, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 5A having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0070] In some embodiments, Spin Wave Generator 306 generates a spin wave which propagates along FMl nanowire 301 towards the first Exchange Coupling Layer 304. This spin wave is called the incident spin wave (SW) and as shown by wave propagation 501. In some embodiments, when the magnetization of FM3 303 is perpendicular relative to the magnetizations of FMl nanowire 301 and FM2 nanowire 302, no exchange of spin waves occurs between FMl nanowire 301 and FM2 nanowire 302. As such, incident spin wave 501 is reflected back as shown by spin wave propagation 502 in Fig. 5A. In this case, substantially zero or none of the incident spin wave makes it to FM2 nanowire 302.

[0071] For example, the amplitude of the spin waves that make it to FM2 nanowire

302 have drastically suppressed amplitudes (e.g., suppressed by lOx). This practically means no spin waves reach Spin Wave Detector 307. When no spin wave reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 0 state (e.g., phase zero state), in accordance with some embodiments. While the output state detected by Spin Wave Detector 307 is indicated as a digital state of logic 0 when phase is zero, the state detected by Spin Wave Detector 307 does not have to be a digital state in accordance with some embodiments. For example, in some embodiments, Spin Wave Detector 307 detects an AC signal with phase and amplitude.

[0072] Referring back to Fig. 3A, in some embodiments, when the magnetization of

FM3 303 is parallel (like the magnetizations of FMl nanowire 301 and FM2 nanowire 302), then exchange coupling occurs between FMl nanowire 301 and FM3 303, and between FM3

303 and FM2 nanowire 302 as illustrated by Fig. 5B.

[0073] Fig. 5B illustrates top view 520 of the spin wave switch scheme of Fig. 3A in which the spin wave propagation is controlled to generate a high logic state at Spin Wave Detector 307, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 5B having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0074] In some embodiments, Spin Wave Generator 306 generates spin wave 501

(e.g., incident spin wave) which propagates along FMl nanowire 301 towards first Exchange Coupling Layer 304. When the magnetization of FM3 303 is parallel relative to the magnetizations of FMl nanowire 301 and FM2 nanowire 302, exchange of spin waves occurs between FMl nanowire 301 and FM2 nanowire 302. As such, incident spin wave 501 propagates through FM3 303 and Second Exchange Coupling Layer 305 to FM2 nanowire 302. In this case, incident spin wave 501 makes it to FM2 nanowire 302 as indicated by spin wave propagation 522.

[0075] The amplitude of the spin waves 522 may not be the same as the amplitude of the incident spin wave 501. For example, the amplitude of transmitted spin waves 522 is about half the amplitude of incident spin wave 501. But the amplitude of transmitted spin wave 522 is high enough to be detected by Spin Wave Detector 307, in accordance with some embodiments. When spin wave 522 reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 1 state (e.g., phase Pi), in accordance with some embodiments. While the output state is indicated as a digital state of logic 1 when phase is Pi (π), the state detected by Spin Wave Detector 307 does not have to be a digital state, in accordance with some embodiments. For example, in some embodiments, Spin Wave Detector 307 detects an AC signal with phase and amplitude.

[0076] Referring back to Fig. 3A, in some embodiments, FM3 303 forms a spin wave impedance modulator in that an external stimulus can cause change in the spin wave impedance associated with FM3 303. According to various embodiments, it is the direction of magnetization in the (middle) switched element FM3 303 that changes or modulates the impedance, and hence determines what Spin Wave Detector 307 detects. In various embodiments, exchange layers 304 and 305 mediate interaction of magnetizations in FMl 301 to FM3 303 and FM3 303 to FM2 302.

[0077] In other embodiments, an external stimulus is used to modulate the impedance of FM3 303. In some embodiments, the external stimulus is based on domain wall motion. In other embodiments, the external stimulus is provided by one of: spin Hall effect (or Spin Orbit Coupling), spin polarization, spin current reversal, magnetic junction (e.g., magnetic tunnel junction or spin valve), antenna or current carrying wire, magnetostriction, etc. to change the magnetization direction of FM3 303 to affect propagation of spin waves through FM3 303 towards FM2 nanowire 302.

[0078] In some embodiments, Spin Wave Generator 306 comprises an excitation antenna that converts an RF (Radio Frequency) current into an RF field, which in turn generates spin waves in FMl 301. In some embodiments, Spin Wave Generator 306 comprises a magnetic junction (e.g., a magnetic tunnel junction or a spin valve) with a free magnetic layer coupled to FMl nanowire 301. In one such embodiment, upon application of an excitation voltage to the magnetic junction, spin waves are generated in FMl nanowire 301.

[0079] In some embodiments, Spin Wave Generator 306 comprises magnetostrictive device which includes a Piezoelectric layer and a magnetostrictive layer, where the magnetostrictive layer is coupled to FMl nanowire 301. In some embodiments, when a voltage is applied to the Piezoelectric layer, an electric field is formed in the magnetostrictive layer which in turn generates spin wave in FMl nanowire 301. In other embodiments, other types of spin wave generators may be used for implementing Spin Wave Generator 306.

[0080] In some embodiments, Spin Wave Detector 307 comprises a detection antenna that converts the spin waves in FM2 nanowire 302 into representative current. In some embodiments, the spin waves in FM2 nanowire 302 generate an RF field around the detection antenna, and this RF field causes current to flow through the detection antenna. In some embodiments, if current is detected by the detection antenna, then spin waves are considered to have traversed from FM1 nanowire 301 to FM2 nanowire 302. In some embodiments, if current is not detected by the antenna or if the current is too small (e.g., below a threshold), then spin waves are considered to be blocked from traversing from FM1 nanowire 301 to FM2 nanowire 302.

[0081] In some embodiments, Spin Wave Detector 307 comprises a magnetic junction (e.g., a magnetic tunnel junction or a spin valve) with a free magnetic layer coupled to FM2 nanowire 302. In one such embodiment, spin waves in FM2 nanowire 302 can switch magnetization of FM2 nanowire 302 and the resistance of the magnetic junction is detected using tunnel magnetoresistance (TMR) effect. In some embodiments, Spin Wave Detector 307 comprises magnetostrictive device which includes a Piezoelectric layer and a magnetostrictive layer, where the magnetostrictive layer is coupled to FM2 nanowire 302. In other embodiments, other types of spin wave detectors may be used for implementing Spin Wave Detector 307.

[0082] Fig. 3B illustrates a spin wave switch scheme 320 with a quad-stable element, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 3B having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0083] Spin wave switch scheme 320 is a three-dimensional (3D) view of one embodiment of spin wave switch scheme 300. In this embodiment, FM 303 is a quad-stable magnetic device as described with reference to Fig. 2A. In some embodiments, an external stimulus is provided by a magnetic junction (e.g., MTJ or spin valve) to FM3 303. An MTJ comprises stacking of a ferromagnetic layer (e.g., Free Magnet) with a tunneling dielectric (e.g., MgO) and another ferromagnetic layer (e.g., Fixed Magnet). In some embodiments, FM3 303 forms the free magnetic layer of the MTJ or spin valve, and a voltage applied to the MTJ or spin valve can switch the magnetization of FM3 303.

[0084] In some embodiments, the external stimulus is provided by an excitation antenna or wires as described with reference to Fig. 2E. For example, quad-stable FM 203 of Fig. 2E can be the same as quad-stable element 303 of Fig. 3B, and then depending on the direction of current flowing through antenna element 251, magnetic field is generated around the wires or antenna element 251 and so magnetization of FM3 303 can be switched parallel or perpendicular relative to FMl nanowire 301 and FM2 nanowire 302 in accordance with some embodiments.

[0085] Depending on the direction of current T in antenna element 251, the magnetic field 'FT can be clockwise or counter clock wise, according to some embodiments. For example, the direction of magnetic field 'FT (e.g., clockwise of counter clockwise) can change the magnetization direction of FM3 303 to parallel relative to the magnetization direction of FMl nanowire 301 and FM2 nanowire 302, or perpendicular relative to the magnetization directions of FMl nanowire 301 and FM2 nanowire 302.

[0086] In some embodiments, when the magnetization direction of FM3 303 is parallel relative to the magnetization directions of FMl nanowire 301 and FM2 nanowire 302, spin waves traverse from FMl nanowire 301 to FM2 nanowire 302. As such, Spin Wave Detector 307 detects a spin wave, in accordance with some embodiments. In some embodiments, when the magnetization direction of FM3 303 is perpendicular relative to the magnetization directions of FMl nanowire 301 and FM2 nanowire 302, spin waves are unable to traverse through FMl nanowire 301 to FM2 nanowire 302. In this case, the incoming spin waves generated by Spin Wave Generator 306 are reflected back from

Exchange Layer 304 back towards Spin Wave Generator 306. As such, Spin Wave Detector 307 detects does not detect spin wave(s), in accordance with some embodiments.

[0087] Referring back to Fig. 3B, in some embodiments, the external stimulus is provided by magnetostriction via a Piezoelectric layer as described with reference to Figs. 2B-C. For example, quad-stable FM 203 of Fig. 2C can be the same as quad-stable element 303 of Fig. 3B, and then depending on the polarity of the clock signal elk applied to the gate terminal of transistor MNl, Piezoelectric layer 222 applies strain (e.g., electric field) on FM3 303 which can change its magnetization direction according to the applied strain. As such, depending on whether the clock signal elk is logic high or low, magnetization of FM3 303 can be switched to parallel or perpendicular relative to the magnetizations of FMl nanaowire 301 and FM2 nanowire 302, in accordance with some embodiments.

[0088] In the case where FM3 303 is a bi-stable magnetic element, as described with reference to Fig. 3A, magnetostriction effect as described with reference to Fig. 2B can be used to provide the external stimulus to FM3 303, in accordance with some embodiments. In some embodiments, FM layers 221 or 221b are the same as FM3 303, while other layers of the bi-stable elements are formed over FM3 303.

[0089] Referring back to Fig. 3B, in some embodiments, the external stimulus is provided by Spin Orbit Coupling (SOC) as described with reference to Fig. 2D. For example, quad-stable FM 203 of Fig. 2D can be the same as quad-stable element 303 of Fig. 3B, and then depending on the voltage applied on metal contacts 242-245, magnetization of FM3 303 can be switched to parallel or perpendicular relative to the magnetizations of FM1 nanowire 301 and FM2 nanowire 302 via SOC, in accordance with some embodiments.

[0090] Referring back to Fig. 3B, in other embodiments, other types of stimulus may be used. For example, stimulus based on domain wall motion, spin Hall effect, spin polarization, spin current reversal, etc. may be used to change the magnetization direction of FM3 303 to affect propagation of spin waves through FM3 303 towards FM2 nanowire 302.

[0091] Fig. 4 illustrates top view 400 of a spin wave switch scheme with in-plane magnets, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 4 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such. So as not to obscure the embodiments, differences between Fig. 3A and Fig. 4 are described.

[0092] In some embodiments, instead of two Exchange Coupling Layers 304 and 305,

FM3 403 is embedded in a single Exchange Coupling Layer 404. Material wise, FM3 403 is the same as FM3 303, and Exchange Coupling Layer 404 is the same as Exchange Coupling Layers 303 and 304. In some embodiments, FM3 403 is formed on top of Exchange

Coupling Layer 404. Functionally, spin wave switch scheme of Fig. 4 works the same as the spin wave switch scheme of Figs. 3A-B, but may have at least one less fabrication step, according to some embodiments.

[0093] Fig. 6 illustrates side view 600 of a spin wave switch scheme with out-of- plane magnets and controllable by a magnetic junction, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 6 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[0094] In some embodiments, FM1 nanowire 601 (first FM), FM2 nanowire 602

(second FM), and quad-stable FM3 603 (third FM) are magnets with perpendicular magnetic anisotropy. In some embodiments, magnets with perpendicular magnetic anisotropy (PMA) are formed with multiple layers in a stack. The multiple thin layers can be layers of Cobalt and Platinum (i.e., Co/Pt), for example. Other examples of the multiple thin layers include: Co and Pd; Co and Ni; MgO, CoFeB, Ta, CoFeB, and MgO; MgO, CoFeB, W, CoFeB, and MgO; MgO, CoFeB, V, CoFeB, and MgO; MgO, CoFeB, Mo, CoFeB, MgO; Mn _x Ga _y ;

Materials with L10 crystal symmetry; or materials with tetragonal crystal structure. In some embodiments, the perpendicular magnetic layer is formed of a single layer of one or more materials. In some embodiments, the single layer is formed of MnGa. In some

embodiments, the perpendicular magnetic layer is formed of one of: a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, YIG, or a combination of them.

[0095] In some embodiments, a break (or gap) is formed between FM1 nanowire 601 and FM2 nanowire 602, and an Exchange Layer 604 is formed over FM1 nanowire 601 and FM2 nanowire 602 as shown. In some embodiments, FM3 603 is formed above Exchange Layer 604. In some embodiments, FM3 603 is a free magnet. In some embodiments, FM3 603 is a quad-stable element which is formed over a quad-shaped Exchange Layer 604.

[0096] In some embodiments, magnetization direction of FM3 603 is controlled or modulated relative to the magnetization directions of the FM1 nanowire 601 and FM2 nanowire 602 by a spin transfer torque (STT). For example, a magnetic junction (an MTJ or spin valve) is formed using FM3 603 as the free magnetic layer.

[0097] In some embodiments, a first exchange coupling occurs between FM1 nanowire 601 and FM3 603 via Exchange Coupling Layer 604. Depending on the magnetization direction of FM3 603, a second exchange coupling occurs between FM3 603 and FM2 nanowire 602. For example, when the magnetization of FM3 603 is perpendicular relative to the magnetizations of FM1 nanowire 601 and FM2 nanowire 602, then little or no exchange coupling occurs between FM1 nanowire 601 and FM3 603, and between FM3 603 and FM2 nanowire 602.

[0098] In some embodiments, Spin Wave Generator 306 generates a spin wave which propagates along FM1 nanowire 601 towards the Exchange Coupling Layer 604. This spin wave is called the incident spin wave (SW). When the magnetization of FM3 603 is perpendicular relative to the magnetizations of FM1 nanowire 601 and FM2 nanowire 602, no exchange of spin waves occurs between FM1 nanowire 601 and FM2 nanowire 602. As such, the incident spin wave is reflected back towards Spin Wave Generator 306. In this case, substantially zero or none of the incident spin wave makes it to FM2 nanowire 602. For example, the amplitude of the spin waves that make it to FM2 nanowire 602 have drastically suppressed amplitudes (e.g., suppressed by lOx). This practically means no spin waves reach Spin Wave Detector 307. When no spin wave reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 0 state, a phase zero state, or AC signal with amplitude below a threshold, etc., in accordance with some embodiments.

[0099] In some embodiments, when the magnetization of FM3 603 is parallel (like the magnetizations of FM1 nanowire 601 and FM2 nanowire 602), then exchange coupling occurs between FMl nanowire 601 and FM3 603, and between FM3 603 and FM2 nanowire 602. In some embodiments, Spin Wave Generator 306 generates spin wave (e.g., incident spin wave) which propagates along FMl nanowire 601 towards Exchange Coupling Layer 604. When the magnetization of FM3 603 is parallel relative to the magnetizations of FMl nanowire 601 and FM2 nanowire 602, exchange of spin waves occurs between FMl nanowire 601 and FM2 nanowire 602. As such, incident spin wave is propagates through FM3 603 and Exchange Coupling Layer 604 to FM2 nanowire 602.

[00100] The amplitude of the spin waves on FM2 602 may not be the same as the amplitude of the incident spin wave. For example, the amplitude of the transmitted spin waves on FM2 602 is about half the amplitude of incident spin wave. But the amplitude of the transmitted spin wave on FM2 nanowire 602 is high enough to be detected by Spin Wave Detector 307. When spin wave reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 1 state, a phase Pi state, or AC signal with amplitude above a threshold, etc. in accordance with some embodiments.

[00101] Fig. 7 illustrates side view 700 of a spin wave switch scheme controllable by a magnetic junction, according to some embodiments of the disclosure. It is pointed out that those elements of Fig. 7 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such. Fig. 7 is described with reference to Fig. 6.

[00102] In some embodiments, spin wave switch scheme of Fig. 7 comprises a Spin

Wave Generator 306, Spin Wave Detector 307, FMl nanowire 701, FM2 nanowire 702, FM3 703, and first and second Exchange coupling layers 704 and 705, respectively. In some embodiments, FMl nanowire 701 and FM2 nanowire 702 are in different layers. For example, in a stack, FMl nanowire 701 and FM2 nanowire 702 are at different levels, one being above or below the other. In some embodiments, FMl nanowire 701 and FM2 nanowire 702 are formed of the same ferromagnetic materials.

[00103] In some embodiments, Exchange Coupling Layer 704 is formed over part of

FMl nanowire 701 as shown. In some embodiments, FM3 703 is sandwiched between Exchange Coupling Layers 704 and 705. In some embodiments, FM2 nanowire 702 is formed over part of Exchange Coupling Layer 705. In some embodiments, magnetization direction of FM3 703 is controlled or modulated relative to the magnetization directions of FMl nanowire 701 and FM2 nanowire 702 by STT, domain wall motion, spin Hall effect, Spin current reversal, etc. [00104] In some embodiments, a first exchange coupling occurs between FMl nanowire 701 and FM3 703 via Exchange Coupling Layer 704. Depending on the magnetization direction of FM3 703, second exchange coupling occurs between FM3 703 and FM2 nanowire 702. For example, when the magnetization of FM3 703 is perpendicular relative to the magnetizations of FMl nanowire 701 and FM2 nanowire 702, then little or no exchange coupling occurs between FMl nanowire 701 and FM3 703, and between FM3 703 and FM2 nanowire 702.

[00105] In some embodiments, Spin Wave Generator 306 generates a spin wave which propagates along FMl nanowire 701 towards the Exchange Coupling Layer 704. This spin wave is the incident spin wave. When the magnetization of FM3 703 is perpendicular relative to the magnetizations of FMl nanowire 701 and FM2 nanowire 702, no exchange of spin waves occurs between FMl 701 and FM2 nanowire 702. As such, the incident spin wave is reflected back towards Spin Wave Generator 306. In this case, substantially zero or none of the incident spin wave makes it to FM2 nanowire 702. For example, the amplitude of the spin waves that make it to FM2 nanowire 702 have drastically suppressed amplitudes (e.g., suppressed by lOx). This practically means no spin waves reach Spin Wave Detector 307. When no spin wave reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 0 state, a phase zero state, or AC signal with amplitude below a threshold, etc., in accordance with some embodiments.

[00106] In some embodiments, when the magnetization of FM3 703 is parallel (like the magnetizations of FMl nanowire 701 and FM2 nanowire 702), then exchange coupling occurs between FMl nanowire 701 and FM3 703, and between FM3 703 and FM2 nanowire 702. In some embodiments, Spin Wave Generator 306 generates spin wave (e.g., incident spin wave) which propagates along FMl nanowire 701 towards Exchange Coupling Layer 704. When the magnetization of FM3 703 is parallel relative to the magnetizations of FMl nanowire 701 and FM2 nanowire 702, exchange of spin waves occurs between FMl nanowire 701 and FM2 nanowire 702. As such, incident spin wave propagates through FM3 703 and Exchange Coupling Layer 704 to FM2 nanowire 702.

[00107] The amplitude of the spin waves on FM2 nanowire 702 may not be the same as the amplitude of the incident spin wave. For example, the amplitude of the transmitted spin waves on FM2 nanowire 702 is about half the amplitude of the incident spin wave. But the amplitude of transmitted spin wave on FM2 nanowire 702 is high enough to be detected by Spin Wave Detector 307. When the spin wave reaches Spin Wave Detector 307, Spin Wave Detector 307 indicates a logic 1 state, a phase Pi state, or AC signal with amplitude above a threshold, etc., in accordance with some embodiments.

[00108] Figs. 8-11 illustrate micro-magnetic simulation results for the spin wave switch scheme of Fig. 3B showing spin wave propagation (in the x, y, and -z directions, respectively) at various states. It is pointed out that those elements of Figs. 8-11 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[00109] With reference to Figs. 8-11, spin waves are generated by a magnetic field oscillation with frequency of 20.5 GHz acting on the leftmost 40nm of the FM nanowire (FM1 301) and propagate left to right (towards FM2 nanowire 302). Here, the width of nanowires FM1 301 and FM2 302 is 40nm with thickness 5nm, the length of FM1 nanowire 301 and FM2 nanowire 302 is 60nm, coupling length to the magnet is 20nm on each side, material properties of FM1 nanowire 301 , FM2 nanowire 302, and FM3 303 correspond to permalloy (e.g., 80% Ni, 20% Fe), and exchange coupling strength of Exchange Coupling Layers 304 and 305 is 3mJ/m ² .

[00110] Here, coupling length generally refers to the length of the interface between FM nanowire and exchange layer. For example, with reference to Fig. 6, coupling length is the length of the interface between FM 601 and exchange layer 604, and between exchange layer 604 and FM2 602 nanowire.

[00111] Arrows in plots 800, 830, 900, 930, 1000, 1030, 1100, and 1130 designate the in-plane dominant direction of magnetization. The transverse (e.g., y and z) projections are designated by a gray-scale map. The darker shades correspond to plus values and minus values. Deep dark shade corresponds to 10,000 A/m, while white or no shade corresponds to values close to zero.

[00112] Fig. 8 illustrates micro-magnetic simulation results as plots 800 and 830 for the spin wave switch scheme of Fig. 3B showing spin wave propagation (in the x, y, and -z directions, respectively) at an initial state with the nanomagnets and FM wire having parallel magnetizations, according to one embodiment of the disclosure. Plots 800 and 830 show the initial state of magnetization with FM3 303 (or nanomagnet) and FM1 nanowire 301 and FM2 nanowire 302 (i.e., FM wires) having parallel magnetizations. Plot 800 shows propagation of spin waves in the x-direction with projections towards the y-direction near the edges as shown by the gray-scale shades. Plot 830 shows the initial state of magnetization in the -z direction. [00113] Fig. 9 illustrates micro-magnetic simulation results as plots 900 and 930 for the spin wave switch scheme of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at a final state with the nanomagnets and FM wire having parallel magnetizations, according to one embodiment of the disclosure.

[00114] Plots 900 and 930 show the final state (e.g., after 0.5ns) of the magnetization with FM3 303 (or nanomagnet) and FMl nanowire 301 and FM2 nanowire 302 having parallel magnetizations. Plot 900 shows propagation of spin waves in the x-direction with projections towards the y-direction near the edges as shown by the gray-scale shades. Plot 930 shows the final state of magnetization in the -z direction. Plots 900 and 930 show propagation of spin waves (as discussed with reference to Fig. 5B) from FMl nanowire 301 to FM2 nanowire 302.

[00115] Fig. 10 illustrates micro-magnetic simulation results as plots 1000 and 1030 for the spin wave switch scheme of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at an initial state with the nanomagnets having perpendicular magnetizations relative to the FM wires, according to one embodiment of the disclosure. Plots 1000 and 1030 show the initial state of magnetization of FM3 303 (or nanomagnet) relative to FMl nanowire 301 and FM2 nanowire 202, where FM3 303 has perpendicular magnetization compared to FMl nanowire 301 and FM2 nanowire 302.

[00116] Plot 1000 shows propagation of spin waves in the x-direction with projections towards the y-direction near the edges as shown by the gray-scale shades. Plot 1030 shows the initial state of magnetization in the -z direction. Because magnetization of FM3 303 is perpendicular relative to magnetizations of FMl nanowire 301 and FM2 nanowire 302, the edges of the magnets and the exchange coupling layers have dark gray shades.

[00117] Fig. 11 illustrates micro-magnetic simulation results as plots 1100 and 1130 for the spin wave switch scheme of Fig. 3B showing magnetization (in the x, y, and -z directions, respectively) at a final state with the nanomagnets having perpendicular magnetizations relative to the FM wires, according to one embodiment of the disclosure.

[00118] Plots 1100 and 1130 show the final state (e.g., after 0.5ns) of magnetization with FM3 303 (or nanomagnet) having perpendicular magnetization relative to

magnetizations of FMl nanowire 301 and FM2 nanowire 302. Plot 1000 shows the propagation of spin waves in the x-direction with projections towards the y-direction near the edges as shown by the gray-scale shades. Plot 1130 shows the final state of magnetization in the -z direction. Plots 1100 and 1130 show propagation of spin waves being halted (as discussed with reference to Fig. 5A) from FMl nanowire 301 to FM2 nanowire 302 due to FM3 303.

[00119] Fig. 12 illustrates flowchart 1200 of a method of using the spin wave switch scheme, according to some embodiments. It is pointed out that those elements of Fig. 12 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[00120] Although the blocks in the flowchart with reference to Fig. 12 are shown in a particular order, the order of the actions can be modified. Thus, the illustrated embodiments can be performed in a different order, and some actions/blocks may be performed in parallel. Some of the blocks and/or operations listed in Fig. 12 are optional in accordance with certain embodiments. The numbering of the blocks presented is for the sake of clarity and is not intended to prescribe an order of operations in which the various blocks must occur.

Additionally, operations from the various flows may be utilized in a variety of combinations.

[00121] At block 1201, Spin Wave Generator 306 generates an incident spin wave using any of the schemes described with reference to the various embodiments. The incident spin wave traverses along FMl nanowire 301 towards the exchange coupling layer (e.g., first Exchange Coupling layer 304, Exchange Coupling layer 404, Exchange Coupling layer 604, or Exchange Coupling layer 704). At block 1202, the incident spin wave is exchanged coupled to FM2 nanowire 302 depending on the magnetization direction of FM3 303.

[00122] For example, if the magnetization of FM3 303 is parallel with reference to the magnetization directions of FMl nanowire 301 and FM2 nanowire 302 (e.g., the

magnetizations of FMl nanowire 301, FM2 nanowire 302, and FM3 303 are the same), then exchange coupling results in the incident wave propagating from FMl nanowire 301 to FM2 nanowire 302 via FM3 303. In another example, if the magnetization of FM3 303 is perpendicular with reference to the magnetization directions of FMl nanowire 301 and FM2 nanowire 302, then exchange coupling is very weak and the incident wave is reflected back and may not propagate from FMl nanowire 301 to FM2 nanowire 302 via FM3 303.

[00123] At block 1203, the impedance of the stack having FM3 303 and the Exchange

Coupling Layer is modulated by an external stimulus (e.g., STT, Spin current reversal, domain wall motion, spin Hall effect, etc.). For example, when the magnetization of FM3 303 is modulated to be parallel (or same) relative to the magnetizations of FMl nanowire 301 and FM2 nanowire 302, then the impedance of the stack is low (which allows spin wave propagation through the stack). In another example, when the magnetization of FM3 303 is modulated to be perpendicular (or opposite) relative to magnetizations of FMl nanowire 301 and FM2 nanowire 302, then the impedance of the stack is high (which substantially halts spin wave propagation through the stack).

[00124] Depending on the impedance of the stack, the process either proceeds to block 1204 or 1205. At block 1204, Spin Wave Detector 307 detects spin wave on FM2 nanowire 302 as logic one when the magnetization of FM3 303 is the same as the magnetization of FM1 301 and FM2 302. At block 1205, Spin Wave Detector 307 detects no spin wave (or spin wave with very small amplitude, e.g., 10 times smaller than the amplitude of the incident spin wave) on FM2 nanowire 302 as logic zero when the magnetization of FM3 303 is the opposite as the magnetization of FM1 nanowire 301 and FM2 nanowire 302.

[00125] The FM materials and materials for exchange coupling layers for the various embodiments are not repeated and are same as those described with reference to Figs.2A-E and Figs. 3A-B.

[00126] Fig. 13 illustrates a smart device or a computer system or a SoC (System-on-

Chip) with a spin wave switch, according to some embodiments. It is pointed out that those elements of Fig. 13 having the same reference numbers (or names) as the elements of any other figure can operate or function in any manner similar to that described, but are not limited to such.

[00127] Fig. 13 illustrates a block diagram of an embodiment of a mobile device in which flat surface interface connectors could be used. In some embodiments, computing device 1600 represents a mobile computing device, such as a computing tablet, a mobile phone or smart-phone, a wireless-enabled e-reader, or other wireless mobile device. It will be understood that certain components are shown generally, and not all components of such a device are shown in computing device 1600.

[00128] In some embodiments, computing device 1600 includes first processor 1610 with a spin wave switch, according to some embodiments discussed. Other blocks of the computing device 1600 may also include a spin wave switch, according to some

embodiments. The various embodiments of the present disclosure may also comprise a network interface within 1670 such as a wireless interface so that a system embodiment may be incorporated into a wireless device, for example, cell phone or personal digital assistant.

[00129] In some embodiments, processor 1610 (and/or processor 1690) can include one or more physical devices, such as microprocessors, application processors,

microcontrollers, programmable logic devices, or other processing means. The processing operations performed by processor 1610 include the execution of an operating platform or operating system on which applications and/or device functions are executed. The processing operations include operations related to I/O (input/output) with a human user or with other devices, operations related to power management, and/or operations related to connecting the computing device 1600 to another device. The processing operations may also include operations related to audio I/O and/or display I/O.

[00130] In some embodiments, computing device 1600 includes audio subsystem

1620, which represents hardware (e.g., audio hardware and audio circuits) and software (e.g., drivers, codecs) components associated with providing audio functions to the computing device. Audio functions can include speaker and/or headphone output, as well as microphone input. Devices for such functions can be integrated into computing device 1600, or connected to the computing device 1600. In one embodiment, a user interacts with the computing device 1600 by providing audio commands that are received and processed by processor 1610.

[00131] In some embodiments, computing device 1600 comprises display subsystem

1630. Display subsystem 1630 represents hardware (e.g., display devices) and software (e.g., drivers) components that provide a visual and/or tactile display for a user to interact with the computing device 1600. Display subsystem 1630 includes display interface 1632, which includes the particular screen or hardware device used to provide a display to a user. In one embodiment, display interface 1632 includes logic separate from processor 1610 to perform at least some processing related to the display. In one embodiment, display subsystem 1630 includes a touch screen (or touch pad) device that provides both output and input to a user.

[00132] In some embodiments, computing device 1600 comprises I/O controller 1640.

I/O controller 1640 represents hardware devices and software components related to interaction with a user. I/O controller 1640 is operable to manage hardware that is part of audio subsystem 1620 and/or display subsystem 1630. Additionally, I/O controller 1640 illustrates a connection point for additional devices that connect to computing device 1600 through which a user might interact with the system. For example, devices that can be attached to the computing device 1600 might include microphone devices, speaker or stereo systems, video systems or other display devices, keyboard or keypad devices, or other I/O devices for use with specific applications such as card readers or other devices.

[00133] As mentioned above, I/O controller 1640 can interact with audio subsystem

1620 and/or display subsystem 1630. For example, input through a microphone or other audio device can provide input or commands for one or more applications or functions of the computing device 1600. Additionally, audio output can be provided instead of, or in addition to display output. In another example, if display subsystem 1630 includes a touch screen, the display device also acts as an input device, which can be at least partially managed by I/O controller 1640. There can also be additional buttons or switches on the computing device 1600 to provide I/O functions managed by I/O controller 1640.

[00134] In some embodiments, I/O controller 1640 manages devices such as accelerometers, cameras, light sensors or other environmental sensors, or other hardware that can be included in the computing device 1600. The input can be part of direct user interaction, as well as providing environmental input to the system to influence its operations (such as filtering for noise, adjusting displays for brightness detection, applying a flash for a camera, or other features).

[00135] In some embodiments, computing device 1600 includes power management

1650 that manages battery power usage, charging of the battery, and features related to power saving operation. Memory subsystem 1660 includes memory devices for storing information in computing device 1600. Memory can include nonvolatile (state does not change if power to the memory device is interrupted) and/or volatile (state is indeterminate if power to the memory device is interrupted) memory devices. Memory subsystem 1660 can store application data, user data, music, photos, documents, or other data, as well as system data (whether long-term or temporary) related to the execution of the applications and functions of the computing device 1600.

[00136] Elements of embodiments are also provided as a machine-readable medium (e.g., memory 1660) for storing the computer-executable instructions (e.g., instructions to implement any other processes discussed herein). The machine-readable medium (e.g., memory 1660) may include, but is not limited to, flash memory, optical disks, CD-ROMs, DVD ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, phase change memory (PCM), or other types of machine-readable media suitable for storing electronic or computer- executable instructions. For example, embodiments of the disclosure may be downloaded as a computer program (e.g., BIOS) which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals via a communication link (e.g., a modem or network connection).

[00137] In some embodiments, computing device 1600 comprises connectivity 1670.

Connectivity 1670 includes hardware devices (e.g., wireless and/or wired connectors and communication hardware) and software components (e.g., drivers, protocol stacks) to enable the computing device 1600 to communicate with external devices. The computing device 1600 could be separate devices, such as other computing devices, wireless access points or base stations, as well as peripherals such as headsets, printers, or other devices. [00138] Connectivity 1670 can include multiple different types of connectivity. To generalize, the computing device 1600 is illustrated with cellular connectivity 1672 and wireless connectivity 1674. Cellular connectivity 1672 refers generally to cellular network connectivity provided by wireless carriers, such as provided via GSM (global system for mobile communications) or variations or derivatives, CDMA (code division multiple access) or variations or derivatives, TDM (time division multiplexing) or variations or derivatives, or other cellular service standards. Wireless connectivity (or wireless interface) 1674 refers to wireless connectivity that is not cellular, and can include personal area networks (such as Bluetooth, Near Field, etc.), local area networks (such as Wi-Fi), and/or wide area networks (such as WiMax), or other wireless communication. In some embodiments, Connectivity 1670 includes parallel sensing arrays as described with reference to Figs. 10-13.

[00139] In some embodiments, computing device 1600 comprises peripheral connections 1680. Peripheral connections 1680 include hardware interfaces and connectors, as well as software components (e.g., drivers, protocol stacks) to make peripheral connections. It will be understood that the computing device 1600 could both be a peripheral device ("to" 1682) to other computing devices, as well as have peripheral devices ("from" 1684) connected to it. The computing device 1600 commonly has a "docking" connector to connect to other computing devices for purposes such as managing (e.g., downloading and/or uploading, changing, synchronizing) content on computing device 1600. Additionally, a docking connector can allow computing device 1600 to connect to certain peripherals that allow the computing device 1600 to control content output, for example, to audiovisual or other systems.

[00140] In addition to a proprietary docking connector or other proprietary connection hardware, the computing device 1600 can make peripheral connections 1680 via common or standards-based connectors. Common types can include a Universal Serial Bus (USB) connector (which can include any of a number of different hardware interfaces), DisplayPort including MiniDisplayPort (MDP), High Definition Multimedia Interface (HDMI), Firewire, or other types.

[00141] Reference in the specification to "an embodiment," "one embodiment," "some embodiments," or "other embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments. The various appearances of "an embodiment," "one embodiment," or "some embodiments" are not necessarily all referring to the same embodiments. If the specification states a component, feature, structure, or characteristic "may," "might," or "could" be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to "a" or "an" element, that does not mean there is only one of the elements. If the specification or claims refer to "an additional" element, that does not preclude there being more than one of the additional element.

[00142] Furthermore, the particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment may be combined with a second embodiment anywhere the particular features, structures, functions, or characteristics associated with the two embodiments are not mutually exclusive.

[00143] While the disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of such embodiments will be apparent to those of ordinary skill in the art in light of the foregoing description. The embodiments of the disclosure are intended to embrace all such alternatives, modifications, and variations as to fall within the broad scope of the appended claims.

[00144] In addition, well known power/ground connections to integrated circuit (IC) chips and other components may or may not be shown within the presented figures, for simplicity of illustration and discussion, and so as not to obscure the disclosure. Further, arrangements may be shown in block diagram form in order to avoid obscuring the disclosure, and also in view of the fact that specifics with respect to implementation of such block diagram arrangements are highly dependent upon the platform within which the present disclosure is to be implemented (i.e., such specifics should be well within purview of one skilled in the art). Where specific details (e.g., circuits) are set forth in order to describe example embodiments of the disclosure, it should be apparent to one skilled in the art that the disclosure can be practiced without, or with variation of, these specific details. The description is thus to be regarded as illustrative instead of limiting.

[00145] The following examples pertain to further embodiments. Specifics in the examples may be used anywhere in one or more embodiments. All optional features of the apparatus described herein may also be implemented with respect to a method or process.

[00146] For example, an apparatus is provided which comprises: a first ferromagnet

(FM) layer; a second FM layer; an exchange coupling layer adjacent to the first and second FM layers; and a third FM layer adjacent to the exchange coupling layer. In some embodiments, the apparatus comprises a magnetic junction adjacent to the exchange coupling layer, wherein the third FM layer is to form a free magnet layer of the magnetic junction. In some embodiments, the magnetic junction is one of a spin valve or a magnetic tunneling junction (MTJ).

[00147] In some embodiments, the first FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG); the second FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG); and the third FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG). In some embodiments, the Heusler alloy is a material selected from a group consisting of: Cu ₂ MnAl, Cu ₂ MnIn,

Cu ₂ MnSn, Ni ₂ MnAl, Ni ₂ MnIn, Ni ₂ MnSn, Ni ₂ MnSb, Ni ₂ MnGa Co ₂ MnAl, Co ₂ MnSi,

Co ₂ MnGa, CoJVInGe, Pd ₂ MnAl, PdJVInln, Pd ₂ MnSn, Pd ₂ MnSb, Co ₂ FeSi, Co ₂ FeAl, Fe ₂ VAl, Mn ₂ VGa, Co ₂ FeGe, MnGa, and MnGaRu.

[00148] In some embodiments, the exchange coupling layer is formed of a material selected from a group consisting of: Ru, Cu, and Mo. In some embodiments, the third FM layer has a thickness in the range of lnm to 2nm. In some embodiments, the apparatus comprises a spin wave generator coupled to the first FM layer. In some embodiments, the spin wave generator comprises at least one of: an antenna, a tunneling magnetoresistance (TMR) device, or a magnetoelectric device. In some embodiments, the apparatus comprises a spin wave detector adjacent to the second FM layer. In some embodiments, the spin wave generator comprises at least one of: an antenna, a tunneling magnetoresistance (TMR) device, or a magnetoelectric device. In some embodiments, the apparatus comprises a spin wave impedance modulator which is operable to modulate an impedance of a stack which includes the third FM layer.

[00149] In another example, a system is provided which comprises: a memory; a processor coupled to the memory, the processor having a spin wave switch which comprises an apparatus according to the apparatus described above; and a wireless interface for allowing the processor to communicate with another device.

[00150] In another example, an apparatus is provided which comprises: a first ferromagnet (FM) layer; a second FM layer; a first exchange coupling layer adjacent to the first FM layer; a third FM layer adjacent to first exchange coupling layer; and a second exchange coupling layer adjacent to the third FM layer and to the second FM layer. In some embodiments, wherein: the first FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG); the second FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG); and the third FM layer comprises one or a combination of materials selected from a group consisting of a Heusler alloy, Co, Fe, Ni, Gd, B, Ge, Ga, permalloy, and Yttrium Iron Garnet (YIG).

[00151] In some embodiments, the Heusler alloy is formed of a material selected from a group consisting of: Cu ₂ MnAl, Cu ₂ MnIn, Cu ₂ MnSn, Ni ₂ MnAl, Ni ₂ MnIn, Ni ₂ MnSn, Ni ₂ MnSb, Ni ₂ MnGa Co ₂ MnAl, Co ₂ MnSi, Co ₂ MnGa, Co ₂ MnGe, Pd ₂ MnAl, Pd ₂ MnIn, Pd ₂ MnSn, Pd ₂ MnSb, Co ₂ FeSi, Co ₂ FeAl, Fe ₂ VAl, Mn ₂ VGa, Co ₂ FeGe, MnGa, and MnGaRu. In some embodiments, the first and second exchange coupling layers are formed of a material selected from a group consisting of: Ru, Cu, and Mo. In some embodiments, the apparatus comprises a spin wave impedance modulator which is operable to modulate an impedance of a stack which includes the third FM layer. In some embodiments, the apparatus comprises a magnetic junction, wherein the third FM layer forms a free magnet layer of the magnetic junction. In some embodiments, the magnetic junction is one of a spin valve or a magnetic tunneling junction (MTJ).

[00152] In another example, a system is provided which comprises: a memory; a processor coupled to the memory, the processor having a spin wave switch which comprises an apparatus according to the apparatus described above; and a wireless interface for allowing the processor to communicate with another device.

[00153] In another example, a method is provided which comprises: generating a spin wave, wherein the spin wave is to propagate through a first ferromagnet (FM); and exchange coupling the spin wave to a second FM according to the magnetization direction of a third FM, wherein the third FM is adjacent to a layer providing the exchange coupling. In some embodiments, the method comprises: detecting a spin wave on the second FM as logic one when the magnetization of the third FM is same as the magnetization of the first or second FM. In some embodiments, the method comprises detecting a spin wave on the second FM as logic zero when the magnetization of the third FM is opposite as the magnetization of the first or second FM. In some embodiments, the method comprises modulating an impedance of a stack which includes the third FM layer.

[00154] In another example, an apparatus is provided which comprises: means for generating a spin wave, wherein the spin wave is to propagate through a first ferromagnet (FM); and means for exchange coupling the spin wave to a second FM according to the magnetization direction of a third FM, wherein the third FM is adjacent to a layer providing the exchange coupling. In some embodiments, the apparatus comprises means for detecting a spin wave on the second FM as logic one when the magnetization of the third FM is same as the magnetization of the first or second FM. In some embodiments, the apparatus comprises: means for detecting a spin wave on the second FM as logic zero when the magnetization of the third FM is opposite as the magnetization of the first or second FM. In some

embodiments, the apparatus comprises means for modulating an impedance of a stack which includes the third FM layer.

[00155] In another example, a system is provided which comprises: a memory; a processor coupled to the memory, the processor having a spin wave switch which comprises an apparatus according to the apparatus described above; and a wireless interface for allowing the processor to communicate with another device.

[00156] An abstract is provided that will allow the reader to ascertain the nature and gist of the technical disclosure. The abstract is submitted with the understanding that it will not be used to limit the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.