TECHNICAL FIELD

The present disclosure relates to an acoustic resonator device. The acoustic resonator device comprises a piezoelectric layer arranged over a dielectric substrate, and comprises an interdigital transducer (IDT) structure arranged in-between the dielectric substrate and the piezoelectric layer, wherein the IDT structure may be solidly attached to both the piezoelectric layer and the dielectric substrate and is configured to resonantly excite an acoustic Al Lamb mode in the piezoelectric layer.

BACKGROUND

Recently, a transversely excited bulk acoustic resonator (XBAR) device has been proposed, which exploits a crystalline piezoelectric membrane (for example, made of lithium niobate (LN)) of sub-micron thickness as piezoelectric layer. The device can operate at 5 GHz frequency range, having critical dimensions CD>0.3 pm, which is manufacturable with optical lithography. However, the XBAR device has some drawbacks. For instance, the fabrication of the XBAR device is difficult, because the bottom side of the piezoelectric membrane is open and free. In particular, the piezoelectric membrane is suspended over a cavity for acoustic isolation. The XBAR device is thus fragile, specifically because the piezoelectric membrane is very thin. Further, the XBAR device shows poor powerhandling properties, because of a low thermal conductivity of lithium niobate material and the sub-micron thickness of the piezoelectric membrane - the only way for the heat evacuation from the membrane is to the sides of the cavity. Long and thin IDT electrodes have to be used to convert an electric AC voltage into an acoustic wave in the piezoelectric membrane. These IDT electrodes have a high electric resistivity and poor capability to evacuate generated heat that increases losses and causes overheating of the XBAR device.

An exemplary XBAR device comprises more thick electrodes (even thicker than the piezoelectric layer itself), in an attempt to improve the power-handling. Such thick electrodes, however, can result in additional acoustic resonances, which deteriorates the losses in the device, reduces its Q-factor, and creates unacceptable perturbations of the admittance curve. Another exemplary XBAR device comprises pedestals that support the suspended membrane, in an attempt to decrease the fragility of the device. However, this only partly mitigates the above-described drawbacks. In particular, the IDT electrodes, by which heat is generated, remain separated from the substrate of the device by the piezoelectric membrane, which has low thermal conductivity. In addition, also the pedestals have only a limited thermal conductivity. Thus, the power-handling properties of the exemplary XBAR device are still not optimal. Further, the fabrication of the exemplary XBAR device is difficult, because both sides of the piezoelectric membrane are used, one side for attaching the pedestals, and the other side for applying the IDT electrodes.

SUMMARY

In view of the above, this disclosure aims to provide an improved acoustic resonator device. An objective is to overcome the above-mentioned drawbacks of the XBAR devices. An objective is also to provide the acoustic resonator device with enhanced mechanical robustness compared to the XBAR devices. For example, a desire is to use a solid thick substrate to stabilize the device. Improving the power-handling properties of the acoustic resonator device compared to the XBAR devices is another objective. The acoustic resonator device of this disclosure should be suitable for operation at the 5 GHz frequency range. In addition, a critical dimension (CD) of the IDT electrodes should be CD > 0.3 pm.

These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

An aspect of this disclosure provides an acoustic resonator device comprising: a dielectric substrate; an IDT structure including a plurality of conductive first electrodes connected to a first busbar and a plurality of conductive second electrodes connected to a second busbar, wherein the first electrodes and the second electrodes are arranged periodically and altematingly one after the other on a surface of the dielectric substrate; and a piezoelectric layer arranged in a distance and parallel to the surface of the dielectric substrate; wherein the piezoelectric layer is arranged on the first and second electrodes of the IDT structure and on the first and second busbar; and wherein the IDT structure is configured to convert an electrical signal to an acoustic Lamb wave in the piezoelectric layer. The dielectric substrate may be non-piezoelectric or weakly piezoelectric. For instance, the dielectric substrate may comprise a weakly piezoelectric material, such as quartz.

The IDT structure may be created on the dielectric substrate, arranged in-between the dielectric substrate and the piezoelectric layer. The electrodes of the IDT structure may contact the piezoelectric layer without any intermediate dielectric, in order to have a good thermal coupling to the piezoelectric layer. The electrodes of the IDT structure may be mechanically and/or solidly attached to the piezoelectric layer. The electrodes of the IDT may be attached to the dielectric substrate through an adhesive dielectric or metal layer. However, the electrodes also have a good thermal coupling to the dielectric substrate. The busbars are configured to provide a voltage, in particular, an AC voltage between the first electrodes and the second electrodes. The AC voltage can be transformed by the electrodes into a vibration of the piezoelectric layer, which leads to the excitation of the acoustic Lamb wave in the piezoelectric layer. The resonance frequency may essentially be determined by the piezoelectric layer thickness.

The acoustic resonator device provides several advantages. The device is mechanically more robust than the conventional XBAR devices, since the thin piezoelectric layer is arranged on, and thus supported by, the electrodes of the IDT structure and also by the busbars. In particular, the part of the piezoelectric layer that overlaps with the busbars may be bonded to the busbars in order to increase the mechanical stability of the device. Further, the power-handling properties of the acoustic resonator device are radically improved over the conventional XBAR devices because the heat that is generated by the IDT electrodes can be directly evacuated through the large-area bottom side of the electrodes to the dielectric substrate, wherein the dielectric substrate may have a high thermal conductivity. Also resistive losses can be decreased compared to the conventional XBAR devices, since the IDT electrodes of the acoustic resonator device can be rather thick. Moreover, parasitic vibrations or resonances in the IDT electrodes can be reduced, because the electrodes are fixed to the dielectric substrate.

The acoustic resonator device of this disclosure may be used in a “ladder” filter network. For example, to provide a low loss wideband filter for 5G mobile devices, a resonator device beneficially has a low impedance at resonance, typically <1 Ohm, and has a high impedance at the anti-resonance (e.g., >1000 Ohm). This is achievable with the acoustic resonator device of this disclosure. Further, the resonance to anti-resonance relative frequency gap (R-a-R) is beneficially >10% or even up to 25%, and a static capacitance corresponds to around j* 50 Ohm at operating frequency. Also this is achievable with the acoustic resonator device of this disclosure. Notably, parasitic perturbation created by other propagating or resonating modes may be tolerated only on low level.

In an implementation form of the aspect, the acoustic Lamb wave comprises an Al Lamb mode and/or an A3 Lamb mode.

Notably, the excitation of the Lamb modes on the order n=5 and higher, although theoretically possible, may result in reduced piezo-coupling, proportional to 1/n ² . In any case, the acoustic resonator device of this disclosure can exploit the fundamental (n=l), second (n=2, with deposited additional layer) and 3 ^rd (n=3) order of the acoustic Lamb waves Al, quasi-S2, and A3, in the piezoelectric layer.

In an implementation form of the aspect, the electrodes of the IDT structure are attached to the piezoelectric layer at positions of amplitude nodes of the acoustic Lamb wave.

Thus, the leakage of vibration energy into the dielectric substrate is reduced. The electrodes support the generation of the acoustic Lamb wave in the piezoelectric layer. The piezoelectric layer can freely vibrate according to the acoustic Lamb wave, the piezoelectric layer being attached to the substrate through the electrodes situated in the nodes of vibration, or places with minimal and zero amplitude of vibrations.

Alternatively, the vibration between the electrodes can be described as a standing wave resonance with a resonance frequency determined by the condition that the membrane thickness dp = A/2 (corresponding to Al Lamb mode) or dp = 3/2*A (for A3 mode). The resonant frequency is thus determined mainly by the thickness of the piezoelectric layer, and may be only weakly dependent on the pitch p between the electrodes.

In an implementation form of the aspect, the dielectric substrate is made of diamond, or silicon carbide, or boron nitride. Thus, a material with high velocity of acoustic waves is used for the dielectric substrate. The dielectric substrate is also mechanically robust, and has a good thermal conductivity. The use of other similar materials is possible, such as sapphire, YAG, etc.

In an implementation form of the aspect, a thermal conductivity of the dielectric substrate is above 100 W/m*K.

For instance, the thermal conductivity may be equal to or above 300 W/m*K. The thermal conductivity of the piezoelectric layer may be 1-10 W/M*K, for instance, about 4.2 W/m*K for the lithium niobate layer. The heat generated by the electrodes can be directly evacuated to the dielectric substrate, which may act as a heat sink or may even be connected to an additional heat sink.

In an implementation form of the aspect the piezoelectric layer is made of crystalline lithium niobate, or lithium tantalate, or aluminum nitride.

Scandium doped Al _x Sci- _x N can also be used, however, lithium niobate having strong “shear” piezo-modules, such as eis or e24, is preferred, if a large resonance-anti-resonance frequency gap is desirable.

In an implementation form of the aspect, the piezoelectric layer made of crystalline lithium niobate is a rotated ZY-cut, 120°Y-cut, or 128°Y-cut of lithium niobate plate.

These piezoelectric materials, in particular, the indicated cuts of the lithium niobate, have enhanced coupling to the Al Lamb mode and/or A3 Lamb mode to horizontal electric fields. This may roughly correspond to a maximal value of the ei,i3 = ei,s piezoelectric-module. Alternative cuts may comprise a ZX-cut of lithium niobate, analogous cuts of lithium tantalite, and others.

In an implementation form of the aspect, a thickness of the piezoelectric layer is about half of the wavelength of a shear bulk acoustic wave in the piezoelectric layer propagating in the thickness direction and with displacements perpendicular to the electrodes of the IDT structure; and/or the thickness dp of the piezoelectric layer is in a range of 400-600 nm, and/or the thickness dp of the piezoelectric layer determines a resonance frequency FR roughly equal to Vs/(2* dp), where IA is the velocity of the shear bulk acoustic wave in the piezoelectric layer propagating in the thickness direction and with displacements perpendicular to the electrodes of the IDT structure.

For other frequencies the thickness dp can be in the range of 200nm-1500nm.

In an implementation form of the aspect, the electrodes of the IDT structure are arranged periodically with a pitch on the dielectric substrate, wherein the pitch is in a range of 1-10 times the wavelength of a shear bulk acoustic wave 2* dp in the piezoelectric layer.

In an implementation form of the aspect, the electrodes of the IDT structure are arranged periodically with a pitch on the dielectric substrate, wherein a periodicity of the first electrodes or the second electrodes of the IDT structure, which is determined by twice the pitch, is smaller than the wavelength of any bulk acoustic wave propagating in the dielectric substrate in a sagittal plane at an operation frequency of the acoustic resonator device.

According to the above implementation forms, on the one hand the pitch between the first and second electrodes is sufficiently small, and on the other hand the dielectric substrate (e.g., made of diamond) has a sufficiently high velocity of acoustic waves, so that acoustic loss to the dielectric substrate is suppressed.

In an implementation form of the aspect, the electrodes of the IDT structure are made of metal, for example, of copper (Cu), aluminum (Al), molybdenum (Mo), gold (Au), or any of their alloys.

The electrodes can also include two or more different metal layers or materials, in order to improve adhesion, and/or in order to prevent acoustic migration of the Al, Cu, etc.

In an implementation form of the aspect, the electrodes of the IDT structure are conductive pedestals configured to hold the piezoelectric layer in the distance to the surface of the substrate.

The conductive pedestals help to make the acoustic resonator device more robust mechanically. In combination with the first and second busbar, the conductive pedestals can support the piezoelectric layer in a stable manner, without affecting its ability to vibrate and resonate.

In an implementation form of the aspect, the electrodes of the IDT structure each comprise a first part and a second part having the same potential; the first parts of the electrodes are conductive pedestals arranged on the dielectric substrate, and the piezoelectric layer is arranged on the conductive pedestals; and the second parts of the electrodes are arranged on the opposite side of the piezoelectric layer than the first parts, wherein the second part of each electrode sandwiches the piezoelectric layer with the first part of the electrode.

The conductive pedestals may be made from a metal, for instance as described for the electrodes above, while the substrate is dielectric. This implementation form, although somewhat more complicated to fabricate, has the benefit of a more uniform horizontal electric field and an even stronger coupling. Thus, vertical electric fields under/between the IDT electrodes are reduced and, as a consequences, the generation of the parasitic modes is reduced as well.

In an implementation form of the first aspect, at least one foremost electrode and at least one last electrode of the periodically arranged electrodes of the IDT structure are at a floating potential.

The floating potential electrodes improve further the performance of the acoustic resonator device, since acoustic energy loss is avoided or reduced also through the ends of the structure (leading to a higher Q-factor).

In summary, this disclosure solves the above-mentioned drawbacks of the conventional XBAR devices, while keeping most of their advantages. Contrary to a conventional XBAR device, the acoustic resonator device of this disclosure comprises the IDT electrodes arranged between the piezoelectric layer (e.g., a plate or a crystalline membrane) and the dielectric substrate (e.g., a solid diamond or silicon carbide substrate with a high thermal conductivity and/or a high acoustic wave velocity). In particular, in the case that the dielectric substrate has a high acoustic wave velocity, relatively low losses caused by bulk wave radiation into the dielectric substrate may be further reduced or avoided. The electrodes serve both as stabilizing structures (e.g., pedestals) and simultaneously as IDT structure to convert the electrical signal into the acoustic Lamb wave in the piezoelectric layer. Notably, also the first and the second busbar, which may be arranged between the dielectric substrate and the piezoelectric layer, help in supporting the piezoelectric layer, and thus lead to a further enhancement of the mechanical stability of the acoustic resonator device.

For a relatively small pitch, described by the conditions above, the piezoelectric layer remain a perfect acoustic waveguide despite the attachment by the IDT structure to the substrate, since the radiation into the bulk of the substrate is suppressed due to destructive interference of the radiated bulk waves. The acoustic vibration may propagate exclusively in the piezoelectric layer, as if it would be suspended over a cavity.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

FIG. 1 shows an acoustic resonator device according to this disclosure in a sectional view. Only a small part of periodic electrode system is schematically shown.

FIG. 2 shows the acoustic resonator device of FIG. 1 in a perspective top view without the piezoelectric layer.

FIG. 3 shows the acoustic resonator device of FIG. 1 in a perspective top view with the piezoelectric layer.

FIG. 4 shows an acoustic resonator device according to this disclosure in a sectional view.

FIG. 5 shows an acoustic resonator device according to this disclosure in a sectional view.

FIG. 6 shows simulations of the admittance versus frequency of an exemplary acoustic resonator device according to this disclosure. FIG. 7 shows simulations of admitance versus frequency of another exemplary acoustic resonator device according to this disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1, FIG. 2, and FIG. 3 show an acoustic resonator device 100 according to this disclosure. FIG. 2 and FIG. 3 show the device 100 in a perspective top view while FIG. 1 shows the device 100 in a sectional view along the dashed cut-line A-A indicated in FIG. 2 and FIG. 3, respectively. FIG. 2 does not show the device 100 completely, but - for the purpose of a beter illustration - shows the device 100 without its piezoelectric layer 103. FIG. 3 shows the device 100 like in FIG. 2, but this time completely with the piezoelectric layer 103.

The acoustic resonator device 100 comprises a dielectric substrate 101. For example, the dielectric substrate 101 may be made of diamond, or of silicon carbide, or of boron nitride. Also combinations of these materials are possible. The dielectric substrate 101 may alternatively be made of a weakly piezoelectric material, for instance, of quartz. A thermal conductivity of the dielectric substrate 101 may be above 100 W/m*K, or even above 200 W/m*K, or even above 300 W/m*K.

The substrate 101 can be a thick substrate or can be composed of two or more substrate layers, where the top substrate layer may be of high acoustic velocity material, as described above. The thickness of the dielectric substrate 101 may be 4 to 20 times larger than that of piezoelectric layer. It can be atached to any thick handle dielectric substrate, Si, quartz, melted quartz, etc. not shown in FIG. 1-3, situated below the substrate 101.

The acoustic resonator device 100 further comprises an IDT structure 102, which includes a plurality of conductive first electrodes 102a (depicted in grey) and a plurality of conductive second electrodes 102b (depicted in white). The number of first electrodes 102a may be the same as the number of second electrodes 102b, and in total there may be 4-300 electrodes 102a, 102b. The electrodes 102a and 102b may each be made of a metal, wherein different metals may be used. The first electrodes 102a may be made of the same or of a different material, e.g., metal, than the second electrodes 102b. The first electrodes 102a are connected to a first busbar 105, and the plurality of conductive second electrodes 102b are connected to a second busbar 104, wherein the busbars 104, 105 are only well visible in FIG. 2, as they may be arranged between the dielectric substrate 101 and the piezoelectric layer 103. The first electrodes 102a and the second electrodes 102b of the IDT structure 102 are arranged periodically and altematingly one after the other on a surface of the dielectric substrate 101. They may be attached to the dielectric substrate 101, e.g., by a thermally conductive adhesive, and may also be attached to the piezoelectric layer 103. This holds similarly for the busbars 104, 105.

The device 100 further comprises the piezoelectric layer 103, which is shown in FIG. 1 and FIG. 3, but is omitted in FIG. 2, so that in FIG. 2 the IDT structure 102 and the busbars

104, 105 can be better seen, as they may be arranged on the dielectric substrate 101 below the piezoelectric layer 103. The piezoelectric layer 103 is arranged in a distance to the dielectric substrate 101. That is, there is a gap formed between the top surface of the dielectric substrate 101 and a bottom surface of the piezoelectric layer 103. Notably, “top” may denote the side of the acoustic resonator device 100, where the piezoelectric layer 103 is arranged, and “bottom” may denote the other side of the acoustic resonator device 100, where the dielectric substrate 101 is arranged. In this gap, the electrodes 102a, 102b are arranged. The surface of the piezoelectric layer 103 is parallel to the surface of the dielectric substrate 101.

The piezoelectric layer 103 is arranged on the first electrodes 102a and on the second electrodes 102b, respectively, as can be seen in FIG. 1. Further, the piezoelectric layer 103 is also arranged on the first busbar 105 and on the second busbar 104, respectively, as can be understood from FIG. 2 (without piezoelectric layer 103) and FIG. 3 (with the piezoelectric layer 103). The electrodes 102a and 102b of the IDT structure 102 are configured to convert an electrical signal to an acoustic Lamb wave propagating in the piezoelectric layer 103. This may be achieved by applying a differential AC voltage at a resonance frequency of the piezoelectric layer 103 between the first and the second busbar 104, 105, to which the first and the second electrodes 102a, 102b are connected, or applying an AC voltage at the resonance frequency to one of the first and the second busbar 104,

105, and keeping the other one of the first and the second busbar 104, 105 at ground potential. In addition the electrodes 102a, 102b and the busbars 104, 105 provide mechanical stability to the piezoelectric layer 103. Due to high thermal conductivities of the dielectric substrate 101 (see value above) and the electrodes 102a, 102b (e.g., they can be made of a metal), the power-handling properties of the acoustic resonator device 100 are improved over conventional XBAR devices.

As can be seen from the FIGs. 1-3, the geometry of the acoustic resonator device 100 is different from a conventional XBAR device. In particular, in that the piezoelectric layer 103, which may be a crystalline piezoelectric membrane, is attached to the dielectric substrate 101 by the electrodes 102a, 102a, which are, in addition to their functionality to create an acoustic Lamb wave in the piezoelectric layer 103, used as anchors or pedestals supporting the piezoelectric layer 103.

The electrodes 102a, 102b may be placed periodically at positons of amplitude nodes of the acoustic Lamb wave in the piezoelectric layer 103, for example, an Al Lamb mode standing wave. Power handling is radically improved in the acoustic resonator device 100 compared to conventional XBAR devices, because the heat that is generated mainly in the electrodes 102a, 102b can immediately be discharged through their bottom sides to the dielectric substrate 101, which may have a high thermal conductivity above 100 W/m*K. Also parasitic resonance generation in the electrodes 102a, 102b is significantly reduced. Parasitic propagating modes (such as the SO mode) are particularly reduced, since they are scattered on the electrodes 102a, 102b.

FIG. 4 shows an acoustic resonator device 100 according to this disclosure, which builds on the acoustic resonator device 100 of the FIGs. 1-3. Same elements in FIG. 4 and in the FIGs. 1-3 are labelled with the same reference signs.

The acoustic resonator device 100 of FIG. 4 is exemplarily shown with a different number of electrodes 102a, 102b than that in FIG. 1, to illustrate that the acoustic resonator device 100 is not limited to the number of electrodes 102a, 102b arranged on the dielectric substrate 101. A pitch 403 of the IDT structure 102 is indicated in FIG. 4. The electrodes 102a, 102b of the IDT structure 102 are arranged periodically with the pitch 403 on the dielectric substrate 101. The pitch 403 is the distance between the center of a first electrode 102a and the center of the neighboring second electrode 102b (in direction of the periodic electrode arrangement). The periodicity of the first electrodes 102a and the second electrodes 102b, respectively, is twice the pitch 403. For instance, the pitch 403 between the electrodes 102a, 102b may be sufficiently large compared to the thickness of the piezoelectric membrane dp, for example, the pitch 403 may be in a range of 1-10 times the wavelength of a shear bulk acoustic wave 2* dp in the piezoelectric layer 103, wherein rfpis the thickness 401 of the piezoelectric layer 103, and wherein the thickness 401 of the piezoelectric layer 103 may be in a range of 400-600 nm. That is, the thickness 401 of the piezoelectric layer 103 may be about half of the wavelength of the shear bulk acoustic wave in the piezoelectric layer 103 propagating in the thickness direction and with displacements perpendicular to the electrodes 102a, 102b of the IDT structure 102. The thickness 401 of the piezoelectric layer 103 may determine a resonance frequency FR of the piezoelectric layer 103, which is roughly equal to Vs/(2*dp), where Vs is the velocity of the shear bulk acoustic wave in the piezoelectric layer 103.

From the other side, to avoid the radiation of the bulk waves into the dielectric substrate 101, the pitch can be limited as described below. For example, the dielectric substrate 101 may have a comparatively high velocity of acoustic waves. This may prevent acoustic waves, for example, the Al Lamb modes of the acoustic Lamb wave in the piezoelectric layer 103, from radiating acoustic energy into the bulk of the dielectric substrate 101. In other words, the bulk waves or vibrations that are excited by the electrodes 102a, 102b may bounce up and down in the piezoelectric layer 103, and acoustic waves are not radiated into the dielectric substrate 101, in particular, exponentially decay in the depth of dielectric substrate 101. In these conditions even the piezoelectric layer 103 attached to the dielectric substrate 101 through the electrodes 102a, 102b may remain an ideal waveguide, which does not lose energy through the electrodes 102a, 102b. For example, a velocity 14/ of a slow-shear-bulk-wave propagating parallel to a surface in the dielectric substrate layer 102 in direction perpendicular to the electrodes 102a, 102b may be higher than the phase velocity Vph of the Lamb wave in the piezoelectric layer 103, Vph=2*p*FR. Notably, the resonance frequency FR may correspond to the operation frequency of the acoustic resonator device 100, and the pitch 403 (p) may satisfy the condition p < Vd/V _s *dp.

Moreover, FIG. 4 shows that a protective layer 402, for instance, a dielectric layer or an oxide layer may be arranged on top of the piezoelectric layer 103, since no electrodes 102a, 102b need to be arranged on the top surface of the piezoelectric layer 103. FIG. 5 shows an acoustic resonator device 100 according to this disclosure, which is further developed based on the acoustic resonator device 100 of the FIGs. 1-3. Same elements in FIG. 5 and in the FIGs. 1-3 are labelled with the same reference signs.

FIG. 5 shows that the first electrodes 102a of the IDT structure 102 may each comprise a first part 501 and a second part 502, and that also the second electrodes 102b may each comprise a first part 503 and a second part 504. The first parts 501 of the first electrodes 102a have the same potential as the second parts 502 of the first electrodes 102a, and the first parts 503 of the second electrodes 102b have the same potential as the second parts 504 of the second electrodes 102b. Both parts 501 and 502 are connected to the same busbar 105(not shown in Fig.5).

The first parts 501, 503 of the electrodes 102a, 102b may respectively be conductive pedestals, which are arranged on and protrude from the dielectric substrate 101. The piezoelectric layer 103 is in this case arranged on the conductive pedestals. The second parts 502, 504 of the electrodes 102a, 102b may respectively be arranged on the opposite side of the piezoelectric layer 103 than the first parts 501, 503, and the second part 502, 504 of each electrode 102a, 102b, and may sandwich the piezoelectric layer 103 with the first part 501, 503 of the same electrode 102a, 102b.

Exemplary acoustic resonator devices 100 according to this disclosure have been simulated using a two-dimensional (2D) finite element method (FEM) software. The results of wideband FEM simulations are shown for two examples in FIG. 6 and FIG. 7, respectively. In particular, the results comprise the admittance plotted versus the frequency as presented in the graphs of FIG. 6 and FIG. 7.

FIG. 6 relates to an exemplary acoustic resonator device 100 with a dielectric substrate 101 made of silicon carbide, and a piezoelectric layer 103 made of lithium niobate. The thickness 401 of the piezoelectric layer 103 is 400 nm. The electrodes 102a, 102b are aluminum electrodes with a height of 400 nm, wherein this height corresponds to a distance or gap between the dielectric substrate 101 and the piezoelectric layer 101. A pitch 403 of the electrodes 102a, 102b is 5 pm. The widths of each electrode 102a, 102b was taken to be 0.5pm in this simulation; in practice it may be equal or larger than about 0.5pm. The acoustic resonator device 100 of FIG. 6 shows a resonance frequency FR of 4595 MHz. The resonance Q-factor is 460. The resonance admitance is 0.044 (per two electrodes 102a, 102b). The anti-resonance frequency is 5167 MHz. The distance between resonance frequency and anti-resonance frequency is 570 MHz, or 12.6%. The anti-resonance Cofactor is 815. The anti -resonance impedance is about 40 kOhm calculated per one pair of electrodes and aperture W= 50 pm.

The acoustic resonator device 100 simulated in FIG. 6 has a robust design, enables high power handling, and exhibits high coupling to the acoustic Lamb modes. Further, the resistive loss is low in the device 100. The device 100 is suitable for 5GHz operation. In particular, operation on the A3 Lamb mode with 3x frequency is also possible (13 GHz in the example of FIG. 6). The device 100 also has an improved temperature coefficient of frequency (TCF).

FIG. 7 relates to an exemplary acoustic resonator device 100 with a piezoelectric layer 103 made of a 128°Y-cut of lithium niobate plate. The FEM-simulated curve is for the thickness 401 of the plate being 400 nm, and the pitch 403 of the electrodes 102a, 102b being 3.5 pm. The dielectric substrate 101 is again made of silicon carbide. The admitance is normalized to 50 pairs of electrodes 102a, 102b, and to an aperture of 50 pm.

The acoustic resonator device 100 of FIG. 7 shows a resonance frequency FR of 4695 MHz. The resonance Q-factor is about 400. The resonance admitance is 0.027 (per two electrodes 102a, 102b), and correspondingly for 50 pairs Zres is about 0.4 Ohm. The antiresonance frequency is 5282 MHz. The distance between resonance frequency and antiresonance frequency is 587 MHz, or 11.8%. The anti-resonance Q-factor is about 350. The anti-resonance impedance is about 5 kOhm.

The acoustic resonator device 100 simulated in FIG. 7 has similar advantages as the acoustic resonator device 100 simulated in FIG. 6. In both cases a SiC substrate was considered. A diamond substrate, or a sufficiently thick diamond layer on a dielectric substrate material shows in FEM-simulations even beter resonator parameters.

The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.