PCT Patent Application No. PCT/IL2008/000743 "Gimbaled scanning micro-mirror apparatus", published on December 10, 2009, is co-pending.

Priority is claimed from US Provisional Application No. USSN 61,242,813 entitled "MICRO COIL APPARATUS, DESIGN AND MANUFACTURING METHODS OF" and filed 16 September 2009.

FIELD OF THE INVENTION

The present invention relates to the field of micro-electro-mechanical systems (MEMS) and to micro-coil apparatus.

BACKGROUND OF THE INVENTION State of the art micro-coil apparatus and related technologies are described in the following publications and documents:

1. United States Patent US5724015 to Tai et al.

2. United States Patent US6535098 to Yeo et al.

3. United States Patent US6493861 to Li et al.

4. United States Patent US4818966 to Miyamoto et al.

5. United States Patent US5711912 to Chatterjee et al.

6. United States Patent US5610433 to Merrill et al.

7. United States Patent US5912608 to Asada.

8. United States Patent 6171886 to Ghosh et al

9. United States Patent 5543956 to Nakagawa et al

10. Published PCT Application WO/2008/072248 to Ramot

Since image sensor production has been achieved using TSV technology, more and more TSV technology development and demonstration of different function block integration are reported, e.g. in: Sitaram R Arkalgud et al., in VLSI Tech.Dig.,2009, p. 68

K-W Lee et al., in IEDM Tech. Dig., 2009, p. 531.

Wei-Chung Lo et al, in IEDM Tech. Dig., 2009, p. 70

3D interconnects by the Cu TSV are described in D.Y. Chen et al., in IEDM Tech. Dig., 2009, p. 353. TSV technology can be designed as a functional device. For example, J. H. Klootwijk et al„ in IEEE EDL 2008 Vol.29, p.740, reported TSV designed at ultra-high capacitance density. Another important application of TSV technology is the integration of different functional devices e.g. as described in Mitsumasa Koyanagi, in VLSI Tech. Dig. 2009, p. 64.

The disclosures of all publications and patent documents mentioned in the specification, and of the publications and patent documents cited therein directly or indirectly, are hereby incorporated by reference.

SUMMARY OF CERTAIN EMBODIMENTS OF THE INVENTION

Many applications employ coils as electronic devices. In particular, there are applications with the need of very small coils (i.e., micro-coils) to be operated as electrical inducers for various electrical circuits or as part of very small electro-magneto apparatuses. One such application is a coil for the inductance of magnetic flux for a MEMS micro-electro- magneto actuator.

Electro-magneto actuators offer numerous advantages in realizing micro-actuators for many applications. Their high force-density, resulting in a device that can operate in extreme conditions, along with their linear electro-mechanical response and small size is advantageous in many applications. In such applications, coils may be critical components as they determine the magnetic flux and inductance of the actuator results in an operating regime.

There is thus provided, in accordance with certain embodiments of the present invention, an electric coil device comprising a spiral comprising a plurality of electro- conductive turns and an isolation layer between the turns, the isolation layer comprising a spiral trench formed of a surrounding electrically isolating bulk, the electro-conductive turns comprising an electro-conductive material at least partly filling the spiral trench; and Connection feeds in and out of the spiral. Further in accordance with certain embodiments of the present invention, the bulk is formed of one of the following group of materials: Silicon, Pyrex, and Polymer.

Also provided, in accordance with certain embodiments of the present invention, is electronic circuitry apparatus including a coil device as described above.

Further provided, in accordance with certain embodiments of the present invention, is electronic circuitry apparatus as described above which includes a plurality of coils and is operative to induce electromagnetic flux coupling.

Further provided, in accordance with certain embodiments of the present invention, is multi-level electrical coil apparatus comprising a stack of electrically connected electric coil devices as described above.

Yet further provided, in accordance with certain embodiments of the present invention, is a method for manufacturing an electric coil device, the method comprising providing a spiral comprising a plurality of electro-conductive turns and an isolation layer between the turns, including forming the isolation layer by forming a spiral trench of a surrounding electrically isolating bulk, and forming the electro-conductive turns by at least partly filling the spiral trench with an electro-conductive material; and providing connection feeds in and out of the spiral.

Further in accordance with certain embodiments of the present invention, the spiral trench is formed by micromachining the bulk.

Still further in accordance with certain embodiments of the present invention, the apparatus also comprises isolated electrical feeds between the layers which are formed by micro-machining.

Additionally in accordance with certain embodiments of the present invention, an air gap which is generally parallel to the turns is provided in the conductive material.

Further in accordance with certain embodiments of the present invention, the connection feeds are formed by Through Silicon Via (TSV) technology.

Still further in accordance with certain embodiments of the present invention, the trench is completely filled with the electro-conductive material.

Further in accordance with certain embodiments of the present invention, a BGA (ball grid array) process is used to connect the coil devices. Still further in accordance with certain embodiments of the present invention, the method also uses a Silicon etch process to form the spiral trench.

Additionally in accordance with certain embodiments of the present invention, the bulk comprises bulk Silicon patterned using deep Si etch according to at least one spiral geometry specification, the turns are isolated, the coils are metallized; and in and out connection feeds are patterned at two ends of the spiral.

Further in accordance with certain embodiments of the present invention, the connection feeds are formed by micromachining.

Still further in accordance with certain embodiments of the present invention, the coils are metallized using a seed layer process, an electroplating process and a front side polishing process.

Additionally in accordance with certain embodiments of the present invention, at least one step uses a semiconductor fabrication process.

Further in accordance with certain embodiments of the present invention, at least one step uses a TSV semiconductor fabrication process.

Still further in accordance with certain embodiments of the present invention, the spiral geometry specification includes at least one of the following characteristics of the spiral: cross-section of each turn, number of turns, and pitch.

Yet further in accordance with certain embodiments of the present invention, the trench has spiral walls and the air gap is provided by deposition of the conductive material only adjacent the spiral walls rather than in the entirety of the trench.

Still further in accordance with certain embodiments of the present invention, the spiral has a central head end and a peripheral tail end and wherein the using includes fabricating at least one electrical connector by generating at least one through-silicon via for the spiral.

Additionally in accordance with certain embodiments of the present invention, the method also comprises using the semiconductor fabrication process to manufacture a second planar spiral conductive coil thereby to define at least first and second through-silicon vias for the first and second coils respectively, and using the vias to electrically connect the head end of the first coil to the tail end of the second coil. Further in accordance with certain embodiments of the present invention, the semiconductor fabrication process is used to manufacture a first plurality of clockwise spiral conductive coils and a second plurality of counterclockwise spiral conductive coils thereby to define through-silicon vias for the coils, and using the vias to at least once electrically connect a head end of an individual one of the first plurality of clockwise coils to an end of an individual one of the second plurality of counterclockwise coils and to connect the head end of the individual one of the second plurality of counterclockwise coils to an end of another individual one of the first plurality of clockwise coils and to generate a stack of conductive coils in which each pair of adjacent coils includes a clockwise coil and a counterclockwise coil.

Further in accordance with certain embodiments of the present invention, the method also comprises connecting at least one through-silicon via to a controlling electronic circuit.

Still further in accordance with certain embodiments of the present invention, the coil comprises trenches defined in a bulk and wherein the trenches are at least 40 microns deep.

Additionally in accordance with certain embodiments of the present invention, the spiral trench has spiral walls and wherein providing a spiral comprises extending effective coil length by manufacturing a pair of intertwined spiral conductive coils, wherein the trench has a trench cross-sectional width and the walls are coated with first and second conductive coatings respectively which are together thinner than the trench cross-sectional width thereby to form a non-conductive gap between the conductive coatings so as to define the intertwined spiral conductive coils.

Further in accordance with certain embodiments of the present invention, the apparatus comprises an electromagnetic actuator.

Still further in accordance with certain embodiments of the present invention, the connection feeds are patterned using Front side passivation thereby to generate a front passivation layer, Opening of a contact in the front passivation layer, Wafer polishing/etching, Back side passivation thereby to generate a back passivation layer, and Opening a contact in the back passivation layer.

Further in accordance with certain embodiments of the present invention, the spiral comprises a planar spiral. Still further in accordance with certain embodiments of the present invention, the coating of the walls is effected by an electroplating process.

The turns of the spiral planar coil provided herein may be round e.g. generally circular but may also be of any other suitable shape such as oblong which may include straight line segments.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention are illustrated in the following drawings:

FIG. 1 is a simplified cross-sectional view of a prior art electromagnetic actuator; FIGs. 2A - 2B, taken together, form a simplified flow diagram of steps of a method for fabricating Through Silicon Via (TSV) coils according to certain embodiments of the present invention.

Fig. 2C is a key to Figs. 2A - 2B .

Fig. 3 is a simplified flowchart illustration of a general method for manufacturing an electric coil device operative according to certain embodiments of the present invention;

FIG. 4 is a simplified cross-sectional view of a coil structure with 4 layers of coils constructed and operative according to certain embodiments of the present invention;

FIG. 5 is a simplified cross-sectional view of a coil structure with a double turn design constructed and operative according to certain embodiments of the present invention.

Figs. 6 - 8 are respective isometric cut-away, cross-sectional and top view illustrations of an electric coil device constructed and operative in accordance with certain embodiments of the present invention.

Fig. 9 is a simplified top view illustration of a spiral 710 comprising a plurality of electro-conductive turns 720 and an isolation layer 730 between the turns, the isolation layer being fabricated by forming a spiral trench of a surrounding electrically isolating bulk, and forming the electro-conductive turns by only partly filling the spiral trench with an electro- conductive material, thereby to form a spiral air gap 740 as shown.

Fig. 10 is a simplified isometric illustration of a stack of coils including a first plurality of clockwise spiral conductive coils and a second plurality of counterclockwise spiral conductive coils wherein each pair of adjacent coils includes a clockwise coil and a counter-clockwise coil.

Figs. 11A and 1 IB are top view simplified illustrations of respectively clockwise and counterclockwise spiral conductive coils, constructed and operative in accordance with certain embodiments of the present invention.

Figs. 12A - 12B are side view illustrations of BGA (ball grid array) process-formed connectors used to connect a coil device in a stack to a coil below it and above it, respectively, in the stack.

Figs. 13 - 17 are useful in understanding example methods for dense TSV coil process development and 8 TSV coil stacking for MEMs applications which methods are operative according to certain embodiments of the present invention, in particular:

Fig. 13 is a graph of Current and magnetic field change with applied voltage.

Fig. 14 is a graph of modification of current and magnetic field with time under

1.679volts.

Fig. 15 is a graph of Inductance performance with frequency of 8 stacking coils. Fig. 16 is a table of Coil resistances of wafer level after front-side UBM patterning. Fig. 17 is a table of resistance values for 4 example coils.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

Reference is made to Fig. 1 (Prior art), which illustrates a typical prior art electromagnetic actuation mechanism in cross-section. The electromagnetic actuator comprises a stator (i.e., non-rotating portion) and a rotor pivoting about an axis 30 along a route having a length of less than several dozen microns, the rotor comprising a flexure element fixedly associated with the stator, the flexure element comprising a magnetic portion 40; the stator comprising a Ferro-magnetic core 50 having a curved configuration which is almost closed thereby to define an air-gap 60 closing the curved configuration and having a width exceeding the route length by only a few microns and a conductive coil 70 wrapped around at least a portion of the almost closed curved configuration of the Ferro-magnetic core 50. At least the magnetic portion 40 of the flexure element is disposed within the air-gap 60, thereby to generate a first magnetic field in the air-gap 60 and an alternating current flows through the conductive coil 70 thereby to generate a second, alternating magnetic field within the air gap 60, the magnetic fields being indicated by arrows 75. The magnetic portion 40 is oriented such that the first magnetic field generated thereby in the air-gap 60, when interacting with the second, alternating magnetic field within the air-gap, generates a movement about the axis 30.

The conductive coil 70 of the electromagnetic actuator of prior art Fig. 1 induces electromagnetic flux, as indicated by arrows 85, which is typically directed by a flux director 90 and which drives the actuator.

The general model of the electromagnetic circuit can be deduced by Ampere law as an equilibrium of the applied electromagnetic force (on the left hand side) and the induced magnetic flux multi lied by the circuit reluctance (right hand side).

Whereas N is the number of coil turns and i is the applied current. The dissipative power of the operation of the motor can be described by:

p = iV = fR _{cot! (2)}

Whereas R is the coil impedance that can be computed as: c ^a " ^~ A

(3) Whereas L _c is the coil length, A _c is the coil cross-section area and p is the coil specific density. Hence the length of the coil is a function of the coil number of turns, estimating the length of each turn as a circumferential of a circle; the resistivity of a coil with N turns may be expressed as:

N-l

p∑2 (r _Q + jp)

- ^ - = + (N-l)p]

^A c ^A c ^A c (4) and the overall power, per one layer of coil, with initial radius of rO and pitch p as:

ρτιΝ

[2r ₀ +(N-l)p]

A. (5) A prevalent method of making coil devices is by turning a conductive wire. An alternative method is by utilizing well known semiconductors compatible with processing of thin film. By using such processes for manufacturing coils, the cost of such devices can be reduced; better electromagnetic response and reliability can be achieved along with a simplified assembly process for other components, such as for electromagnetic actuators, as is known in the art. In current state-of-the-art fabrication methods for creation of such coils, thin layers are utilized for the creation of metal strips (the coil itself) and the surrounding substance material in which the coil is fabricated (usually, a passivation layer). The design of the coil is limited by this fabrication process e.g., thickness of metal cross-section is limited by the deposition thickness of the isolation layer (passivation layer e.g.).

However, in some applications, there is a need for high currents, low resistance and high inductance. In order to achieve these, a larger cross section of the coil is needed along with increasing number of coil turns. This is not trivially achieved in current state-of-the-art semiconductor thin layer compatible manufacturing techniques.

According to certain embodiments of the present invention, bulk micro-machining technology is used to create such coils, in various bulks, whose bulks may for example be formed of Silicon, Pyrex, or suitable polymers. In particular, Through Silicon Via (TSV) technology is utilized in a manner compatible with semiconductor processes. TSV realizes electrical contacts from one side of wafers to the other. The conductive contacts may be realized either (a) by using through wafer patterning (e.g., deep Silicon etch, or laser drilling) and filling with electroplated or deposited metal or conductive material (e.g., doped Poly- Silicon), or (b) by realizing a through via and covering the side walls with a conformal conductive layer.

In TSV processes the bulk material of the wafer is utilized as the surrounding substance of the coil, along with via making processes (e.g., TSV technology) to pattern the coils, allowing wire cross-section to be increased to desired parameters, and the coils to be engineered accordingly.

The conventional TSV process employs a temporary support wafer which is temporarily bonded to the processed wafer and de-bonded, after the process is completed, for further treatment such as dicing, packaging and assembly. A fabrication process for TSV coils in accordance with certain embodiments of the present invention is now described with reference to Figs. 2A - 2B which, taken together, form a simplified flow diagram of a process flow for fabricating Through Silicon Via (TSV) coils, using bulk Silicon as the surrounding substance of the coil. The third, rightmost column of Figs. 2A - 2B provides illustrations of the outcome of each stage in the process flow. The fabrication process typically includes some or all of the following stages and steps, suitably ordered e.g. as shown:

aa. Step 310— Initially, the surrounding substance material is patterned using deep Si etch, according to coil specifications such as but not limited to metal cross-section, number of turns, and pitch.

bb. Subsequently, in step 320, turns are isolated.

cc. Metallization of the coils (steps 330 to 350).

dd. In steps 360 to 400, connection feeds to the coil are patterned on both sides of the coil (in and out connections).

Steps 310 - 410 are now described in detail:

310: Performing deep Si etch

320: Passivation of the etched trenches

330: Seed layer process

340: Electroplating

350: Front side CMP

360: Front side passivation

370: Open contact in the passivation layer

380: Wafer polish/etch

390: Back side passivation

400: Open contact in the passivation layer

410: BGA process

Fig. 2C is a key for the flow diagram of Figs. 2A - 2B

Fig. 3 is a simplified flowchart illustration of a general method for manufacturing an electric coil device operative according to certain embodiments of the present invention.

In order to increase the number of turns, multiple structures of coils can be assembled one on top of the other as illustrated in Fig. 4 which is a simplified cross-sectional view of a coil structure with 4 (say) layers of coils. Alternatively or in addition, an air gap can be provided in the middle of the conductive material's cross-section, so as to provide additional turns which are intertwined in one another, e.g. as shown in Fig. 5 which is a simplified cross-sectional view of a coil structure with double turns design which uses the same notation (e.g. for air and silicon) as Fig. 4.

Referring again to Fig. 3, the method for manufacturing an electric coil device according to certain embodiments of the present invention may include some or all of the following steps, suitably ordered e.g. as follows:

Step 510: forming a spiral trench , typically at least 40 microns deep, of a surrounding electrically isolating bulk e.g. by micromachining the bulk or using a silicon etch process to achieve a predetermined typically planar spiral geometry specification typically including at least one of the following characteristics: cross-section of each turn, number of turns, and pitch.

Step 520: forming electro-conductive turns by partly or fully filling the spiral trench with an electro-conductive material (if material is deposited only adjacent the spiral walls, e.g. by electroplating, an air gap which is generally parallel to the turns is provided in the conductive material).

Step 530: providing connection feeds in and out of the spiral e.g. using TSV technology or micromachining.

Step 540: optionally, fabricating other coils using the above steps, stacking them, e.g. using a BGA (ball grid array) process to connect the coils being stacked as shown in Figs. 12A - 12B, and providing isolated electrical feeds between the layers e.g. by micromachining such that the head end of each coil is electrically connected to the tail end of an adjacent coil and each pair of adjacent coils includes a clockwise coil and a counterclockwise coil.

Step 550: optionally, connecting at least one connection feed to a controlling electronic circuit e.g. so as to generate an actuator.

Figs. 6 - 8 are simplified respective isometric cut-away, cross-sectional and top view illustrations of an electric coil device constructed and operative in accordance with certain embodiments of the present invention and including a spiral 610 comprising a plurality of electro-conductive turns 620 and an isolation layer 630 between the turns, the isolation layer comprising a spiral trench formed of a surrounding electrically isolating bulk 640, the electro-conductive turns comprising an electro-conductive material at least partly filling the spiral trench; and connection feeds 650 in and out of the spiral. The cross-sectional and cutaway views are cut along the axis connecting the connection feeds in Fig. 8.

Fig. 9 is a simplified top view illustration of a spiral 710 comprising a plurality of electro-conductive turns 720 and an isolation layer 730 between the turns, the isolation layer being fabricated by forming a spiral trench of a surrounding electrically isolating bulk, and forming the electro-conductive turns by only partly filling the spiral trench with an electro- conductive material, thereby to form a spiral air gap 740 as shown.

Fig. 10 is a simplified isometric illustration of a stack of coils including a first plurality of clockwise spiral conductive coils 800, e.g. as shown in top view in Fig. 11 A, and a second plurality of counterclockwise spiral conductive coils 810, e.g. as shown in top view in Fig. 1 IB, wherein each pair of adjacent coils includes a clockwise coil and a counterclockwise coil. Through-silicon vias 820 electrically connect an end, such as a head end 830 or tail end 840 (Fig. 11A) of each individual one of the first plurality of clockwise coils to an end, typically the same end (head or tail) of an individual one of the second plurality of counterclockwise coils and connect the other end of the individual one of the first plurality of clockwise coils to an end, typically the same end (tail or head), of another individual one of the second plurality of counterclockwise coils.

Figs. 12A - 12B are side view illustrations of BGA (ball grid array) process-formed connectors 910 used to connect a coil device in a stack to a coil below it and above it, respectively, in the stack. Isolation material is denoted by reference numeral 920 and the balls formed by the BGA process are denoted by reference numeral 930.

Example methods for dense TSV coil process development and 8 TSV coil stacking for MEMs applications are now described in detail.

In the illustrated example, a dense TSV coil and stacking process suitable for MEMs applications is shown. The dense TSV coils (20um width, lOum space, 90um depth, in the illustrated example) are void-free filled by Cu. 8 layer coil stacking is provided, using conductive adhesive. The resistance, inductance, magnetic field, and basic reliability of 8 dense coils stacking in the illustrated example are described. In the illustrated example, higher resistivity (30 - 40 Ohm.cm) substrates were used in the dense TS V coil process development for the reduction of RF substrate loss in the MEMs application. The full process included TSV coil process development, back side thin wafer process, bonding and de-bonding for the dense TSV coil, laser drilling for the center cavity formation and die stacking. Dense TSV coil is etched by the DREE. Two step etching was applied for the TSV coil and coil stacking connection.

Multiple DC plating steps were developed for the Cu void-free plating in deep TSV trench. High polishing rate CuCMP process was setup and applied in this development work. The coil performance in the wafer level was tested after front-side UBM process by probe station and HP 34401 A multi-meter. The electric performance of coil is shown in the table of Fig. 16. Adhesive polymer is used for the bonding of carrier wafer with TSV coil wafers after front side UBM processing.

After back-grinding to 120um and exposing back side coil contact for the following on stacking, low temperature (150°C) SiN was deposited and patterned at the passivation layer. Following the back side UBM process, laser drilling was used for the formation of middle of cavity. After de-bonding from EVG supporting and dicing, conductive adhesive was used for 8 chip stacking, thereby to generate a void-free Cu filling TSV coil.

The resistances of coils after 8 layer stacking are measured and shown in Fig. 17. The measured resistances include contact resistance and conductive adhesive resistance. The 8 coils stacking resistance is matched with wafer level coil O.90hm. I-V performance and magnetic field of 8 layer coil stacking were measured using an Agilent E3631A Triple Out DC Power supply and a 475 DSP Gauss-meter. The distance between the magnet field detection and the 8 coil stacking center is around 2mm. The magnetic field and current changing with applied voltage are shown in Fig. 13. The magnetic field of the 8 layer coils stacking saturates from 4V. The linear I-V curve of 8 stacking coils is shown in Fig. 13. The breakdown voltage of 8 stacking coils is 4.6V from this coil measurement. This system was used to measure the basic reliability performance of 8 layer stacking coils. 1.697V was applied on the 8 stacking coils and the current and magnetic field was measured with the time. The measurement results are shown in Fig. 14. After 66 hours testing, the variation of current and magnetic fields are ~5-%, -10% respectively. The reliability of 8 dense TSV coil stacking is improved. The inductance is believed to be an important factor for the 8 stacking coils. The inductance of 8 coils stacking is measured by 4285A 75KHZ-300MHZ Precision LCR Meter under IV voltage. The variation of inductance with the frequency is shown in Fig. 15. The maximum value of 8 stacking coils inductance is 389uH at 80KHz. But inductance of 8 dense TSV coils stacking reduces to ~ 30uH from 0.8MHz to 1.3MHz.

In the illustrated example of a dense TSV coil process with void-free Cu filling, then, a thin wafer process is applied on the back side of dense TSV coil. Laser drilling is used for the deep cavity formation. An 8 dense TSV coils stacking functionality is provided. The electric and magnetic fields of 8 stacking coils were measured as described above. The 8 layer coils stacking can pass 66 hours electric stress testing under 0.19A.

Features of the present invention which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, features of the invention, including method steps, which are described for brevity in the context of a single embodiment or in a certain order may be provided separately or in any suitable subcombination or in a different order, "e.g." is used herein in the sense of a specific example which is not intended to be limiting. It is appreciated that in the description and drawings shown and described herein, functionalities described or illustrated as systems and sub-units thereof can also be provided as methods and steps therewithin, and functionalities described or illustrated as methods and steps therewithin can also be provided as systems and sub-units thereof. The scale used to illustrate various elements in the drawings is merely exemplary and/or appropriate for clarity of presentation and is not intended to be limiting.