Acoustic resonator

Abstract

Various exemplary embodiments relate to an acoustic resonator. The acoustic wave resonator may include a substrate, a piezoelectric film attached to the substrate, and a plurality of electrodes. The piezoelectric film is provided with a plurality of grooves, and two adjacent grooves define a ridge between them. And each electrode is arranged in the corresponding groove. Each electrode includes two side portions, each side portion at least partially covering a respective sidewall of the recess.

Description

Technical Field

[0001] Various exemplary embodiments generally relate to the field of radio communications. In particular, some exemplary embodiments provide an acoustic wave resonator. In particular, some exemplary embodiments provide a thin film bulk acoustic wave resonator device.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to provisional application PCT / CN2022 / 110127 filed on August 4, 2022, with the invention name “AN ACOUSTIC RESONATOR SOLIDLY MOUNTED ON A HIGH ACOUSTIC VELOCITY SUBSTRATE”. Background Art

[0004] Radio frequency (RF) filters used in radio communication systems often contain acoustic wave resonators.

[0005] Some acoustic resonators, such as excited bulk acoustic resonators (XBARs), use suspended piezoelectric crystal membranes (such as sub-micron-thick lithium niobate (LN)) with a horizontal electric field to generate A1 mode resonances with a displacement in the horizontal direction. However, in the area near the top electrode, the electric field is mainly in the vertical direction, which greatly weakens the main resonant mode nearby, thereby limiting the overall piezoelectric coupling.

[0006] Another disadvantage is the use of suspended piezoelectric membranes. The manufacturing process required for such devices is difficult because the bottom side of the membrane must be open. BAW resonators need to be suspended above the cavity for acoustic isolation. Because the membrane is thin, these devices are fragile. In addition, due to the low thermal conductivity of thin piezoelectric membranes made of LN, the power handling properties of these devices are poor. Summary of the invention

[0007] The Summary briefly introduces some concepts that will be further described in the Detailed Description. The Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0008] Exemplary embodiments of the present invention provide an acoustic wave resonator. Some embodiments utilize a horizontal electric field to excite the A1 resonance mode in a thin film piezoelectric layer as an acoustic wave resonator.

[0009] Some embodiments provide a robust device.The present invention solves the brittleness problem of sub-micron thick LN films of XBAR resonators by attaching the film to a solid thick substrate.

[0010] Some embodiments can be manufactured using common optical lithography techniques and are comparable to surface acoustic wave resonators in the mid- to high-frequency band (1 to 3 GHz range) with a minimum critical dimension of 350 nm. Some embodiments are suitable for operation in the 5 GHz frequency range. Some embodiments can be manufactured using optical lithography techniques.

[0011] Some embodiments exhibit excellent power handling capabilities. In some embodiments, a high thermal conductivity substrate provides a heat dissipation path below the piezoelectric membrane, for example in a direction perpendicular to the membrane. This can avoid overheating and low power handling.

[0012] Some embodiments avoid bulk acoustic wave radiation and improve the quality (Q) factor of the resonator by using a high acoustic velocity substrate.

[0013] Some embodiments achieve strong piezoelectric coupling. In some embodiments, this is achieved by using embedded vertical electrodes to produce a uniform horizontal electric field, appropriate cutouts of the piezoelectric film, appropriate spacing, and appropriate geometry of the resonator. In some embodiments, cavities (e.g., grooves) in the electrodes allow the piezoelectric ridges to vibrate more freely, thereby increasing the piezoelectric coupling.

[0014] Some embodiments include vertical U-shaped electrodes to generate a horizontal electric field for A1 mode resonance. This effectively increases coupling and eliminates parasitic modes.

[0015] Some embodiments provide the possibility to change or tune the resonant frequency by varying the spacing and electrode geometry.

[0016] Some embodiments include an intermediate layer that reduces acoustic coupling between the piezoelectric membrane and the substrate. The intermediate layer reduces the effects of the rigid substrate, supports fundamental thickness resonances in the piezoelectric membrane, and thus increases piezoelectric coupling.

[0017] The above and other advantages can be achieved by means of the features of the independent claims. Further implementations are apparent from the dependent claims, the description and the accompanying drawings.

[0018] According to a first aspect, an acoustic wave resonator comprises: a substrate; a piezoelectric film attached to the substrate and a plurality of electrodes. The piezoelectric film has a plurality of grooves. Two adjacent grooves define a ridge between them. Each electrode is placed in a corresponding one of the grooves. Each electrode comprises two side portions, each side portion at least partially covering a corresponding side wall of the groove.

[0019] According to an exemplary embodiment, the acoustic wave resonator comprises a circuit for applying a radio frequency voltage across the at least two electrodes to induce an electric field in the ridges.

[0020] According to an exemplary embodiment, the side portions of each electrode are electrically connected.

[0021] According to an exemplary embodiment, each electrode includes a bottom portion at least partially covering a bottom of the groove, the bottom portion of the electrode being electrically connected to the side portion of the electrode.

[0022] According to one exemplary embodiment, a cavity is formed at the front surface of each electrode.

[0023] According to an exemplary embodiment, the cross section of the electrode is U-shaped.

[0024] According to an exemplary embodiment, the piezoelectric membrane is attached to the substrate via the intermediate layer.

[0025] According to an exemplary embodiment, the intermediate layer is made of SiO 2 .

[0026] According to an exemplary embodiment, the thickness of the intermediate layer is substantially equal to one quarter of the wavelength of a shear bulk acoustic wave in the intermediate layer at a resonance frequency of the acoustic wave resonator.

[0027] According to an exemplary embodiment, the substrate is made of a high-acoustic-velocity material, wherein the shear acoustic velocity in the high-acoustic-velocity material is higher than 7000 m / s.

[0028] According to an exemplary embodiment, the speed of sound in the substrate is at least twice the speed of sound in the piezoelectric film.

[0029] According to an exemplary embodiment, the substrate is made of diamond, silicon carbide or boron nitride.

[0030] According to an exemplary embodiment, the substrate is mounted on a support wafer.

[0031] According to an exemplary embodiment, the support wafer is made of silicon or glass.

[0032] According to an exemplary embodiment, the thickness of the substrate is greater than ten times the thickness of the piezoelectric film.

[0033] According to an exemplary embodiment, the depth of the groove is greater than one third of the thickness of the piezoelectric film.

[0034] According to an exemplary embodiment, the thickness of the piezoelectric film is substantially equal to half the wavelength of the shear acoustic wave in the piezoelectric film at the operating frequency of the acoustic wave resonator.

[0035] According to an exemplary embodiment, the electrodes are alternately connected to two bus bars, two adjacent electrodes are connected to different ones of the bus bars, and the circuit is used to apply the radio frequency to the two bus bars.

[0036] According to an exemplary embodiment, the bus bars are deposited directly on the substrate and do not cover the piezoelectric film.

[0037] According to an exemplary embodiment, the distance between the two electrodes is less than , is the shear velocity in the high-velocity substrate, is the operating frequency of the acoustic wave resonator.

[0038] According to an exemplary embodiment, the piezoelectric film is made of lithium niobate with a Y-cut of 120°±20° rotation or a Z-cut of ±20°.

[0039] According to a second aspect, a radio frequency filter comprises at least one acoustic wave resonator according to the first aspect.

[0040] Any implementation may be combined with one or more other implementations.These and other aspects of the invention are apparent from one or more exemplary implementations described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are used to help further understanding of the exemplary embodiments and constitute a part of this specification. These drawings illustrate exemplary embodiments and together with the description help explain the exemplary embodiments. In the drawings:

[0042] Figure 1A is a schematic top plan view of an exemplary acoustic wave resonator;

[0043] Figure 1B is a schematic top plan view of another exemplary acoustic wave resonator;

[0044] Figure 1C is a schematic top plan view of another exemplary acoustic wave resonator;

[0045] Figure 2 is a schematic three-dimensional view of a cross section of an exemplary acoustic wave resonator;

[0046] Figure 3 is a schematic cross-sectional view of a cross section of an exemplary acoustic wave resonator;

[0047] Figure 4 is a schematic exploded cross-sectional view of a cross section of an exemplary acoustic wave resonator;

[0048] Figure 5is a schematic cross-sectional view of a cross section of another exemplary acoustic wave resonator;

[0049] Figure 6 is a schematic cross-sectional view of an electrode of another exemplary acoustic wave resonator;

[0050] Figure 7 shows a resonant vibration mode A1 in a schematic cross-sectional view of a cross section of an exemplary resonator;

[0051] Figure 8 is a graph of piezoelectric coupling of an exemplary acoustic wave resonator as a function of intermediate layer thickness;

[0052] Fig. 9 is a graph of piezoelectric coupling of an exemplary acoustic wave resonator as a function of cavity depth in an electrode;

[0053] Fig.10 is a graph of the admittance of an exemplary acoustic wave resonator as a function of frequency;

[0054] Fig.11A and Fig. 11B are graphs of admittance versus frequency for two different exemplary acoustic wave resonators;

[0055] Fig.12 is a flow chart of an exemplary process for making an exemplary acoustic wave resonator.

[0056] In the drawings, the same reference numerals are used to designate the same components. DETAILED DESCRIPTION

[0057] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The detailed description provided below in conjunction with the accompanying drawings is intended as a description of the present examples and is not intended to be the only representation of the forms in which the present examples may be constructed or used. The description sets forth the functions of the examples and the sequence of steps for constructing and operating the examples. However, the same or equivalent functions and sequences may be implemented by different examples.

[0058] Figure 1A A schematic plan view of an exemplary acoustic wave resonator 100 is shown. Resonators such as resonator 100 may be used in a variety of RF filters, including band-stop filters, band-pass filters, duplexers, and multiplexers.

[0059] The resonator 100 includes a piezoelectric film 110 and at least two electrodes 120-1, 120-2. The electrodes 120-1, 120-2 are in contact with the piezoelectric film 110. The circuit 140 can be used to apply a radio frequency voltage to two adjacent electrodes 120-1, 120-2. Therefore, the two adjacent electrodes 120-1, 120-2 have opposite polarities.

[0060] In some embodiments, the resonator 100 includes an interdigital transducer (IDT) 150. The IDT 150 includes a first plurality of parallel electrodes or electrode fingers (e.g., electrode 120-1) connected to a first bus bar 121, and a second plurality of electrodes or electrode fingers (e.g., electrode 120-2) connected to a second bus bar 122. The first plurality of parallel electrodes and the second plurality of parallel electrodes are staggered (or crossed). Two adjacent electrodes 120-1, 120-2 are connected to different bus bars 121, 122. The staggered electrodes 120-1, 120-2 overlap a distance AP, which is generally referred to as the aperture of the IDT. The bus bars 121, 122 are spaced apart by a distance d. b The distance d between the bus bars 121 and 122 is b In some embodiments, the overlapping portion of the electrodes is located on the piezoelectric film 110 , while the bus bars 121 , 122 are directly located on the substrate 102 or on the intermediate layer 103 , but not on the piezoelectric film 110 .

[0061] The resonator 100 may include two terminals. The resonator 100 has a low impedance at a resonant frequency and a high impedance at an anti-resonant frequency. The first bus bar 121 and the second bus bar 122 may serve as terminals of the resonator 100. In this case, a radio frequency signal is applied between the two bus bars 121 and 122 of the IDT 130.

[0062] The main direction of the electric field generated between the two electrodes is in the plane of the piezoelectric film 110. In this sense, the electric field in the piezoelectric film 110 can be considered to be horizontal.

[0063] The RF signal excites the main acoustic mode in the piezoelectric film 110. The main acoustic mode can be an A1 Lamb mode or a close to A1 Lamb mode. The main acoustic mode can be a shear mode, in which the main displacement at resonance is the shear vibration in the piezoelectric film 110, the horizontal displacement is mainly in the area between the electrodes, and the amplitude of the displacement changes in the thickness direction of the film. At the same time, near the starting frequency, the main acoustic mode (such as the A1 Lamb mode) is mainly composed of two shear body waves, in which the sound energy bounces up and down in the thickness direction of the film. The wave is shear because the displacement in the wave is perpendicular to the propagation direction of the wave. The propagation direction is the vertical direction and the displacement direction is the horizontal direction. Due to the anisotropy of the piezoelectric effect, the horizontal electric field excites the wave to bounce up and down. At resonance, if the film thickness is λ / 2, the displacement phases on the top and bottom surfaces of the film are opposite. The amplitude of the displacement varies along the thickness direction. Shear deformation and shear stress are generated by the horizontal electric field caused by the corresponding piezoelectric module (for example, piezoelectric module e15).

[0064] The main acoustic mode or main resonant mode is similar to the A1 Lamb mode. The resonant frequency of the main acoustic mode is Depends on the thickness of the piezoelectric film t p and spacing (ie, the interval between the two electrodes 120 - 1 and 120 - 2 ). More specifically,

[0065]

[0066] in, is the transverse acoustic velocity of the piezoelectric material in the thickness (Z) direction, is the longitudinal sound velocity of the piezoelectric material in the horizontal (X) direction.

[0067] The piezoelectric film 110 may or may not extend under the bus bars 121 , 122 of the IDT 130 .

[0068] In some embodiments, Figure 1A As shown, the piezoelectric film 110 does not extend below the bus bars 121, 122 of the IDT 130. Figure 1A As shown, the width w of the piezoelectric film 110 m It can be greater than or equal to the aperture AP of the IDT, but less than the distance d between the bus bars 121 and 122 of the IDT 130. b This isolates the main resonance region from the bus bars 121, 122 on both sides, thereby suppressing the lateral mode to a great extent.

[0069] In some embodiments, Figure 1B As shown, the piezoelectric film 110 extends (eg, partially or completely) below the bus bars 121 , 122 of the IDT 130 . In this case, the width w of the piezoelectric film 110 is m The distance d between the bus bars 121 and 122 of the IDT 130 may be greater than b .

[0070] In some embodiments, Figure 1C As shown, the piezoelectric film 110 may have a hole 160 between the tips of the electrodes 120-1, 120-2 and the bus bars 121, 122. The hole 160 may have a rectangular, circular or other form. In this case, the piezoelectric film 110 may or may not extend under the bus bars 121, 122 of the IDT 130. The hole 160 reduces the acoustic energy loss in the lateral (aperture) direction. The hole 160 can be formed by removing (e.g., etching) the area of ​​the piezoelectric film 110 between the bus bars 121, 122 and the electrode 120. The hole 160 isolates the main resonance region from the bus bars 121, 122 on both sides, thereby suppressing the lateral mode to a large extent.

[0071] Piezoelectric films are made of piezoelectric materials such as lithium niobate (LN), lithium tantalate (LT), Al(Sc)N, and ZnO.

[0072] The electrodes 120-1, 120-2 may be aluminum, substantially aluminum alloy, copper, substantially copper alloy, beryllium, gold, tungsten, molybdenum or some other conductive material. The busbars 121, 122 of the IDT may be made of the same or different material as the electrodes. The busbars may have double or secondary metallization to reduce their resistivity.

[0073] Figure 2 1 shows a schematic three-dimensional view of a cross section of an exemplary acoustic wave resonator 100. Specifically, Figure 2 Shows Figure 1A Schematic three-dimensional view of a cross section S1 of an exemplary acoustic wave resonator 100 .

[0074] The thickness t of the piezoelectric film 110 p can be substantially equal to the operating frequency f of the acoustic wave resonator 100 r The thickness t is half the wavelength of the shear acoustic wave in the lower piezoelectric film 110, which propagates in the thickness direction (0Z) and has a displacement in the horizontal direction (0X). p It can be, for example, 400 nm. Figure 8 The effect of the interlayer thickness is described in more detail.

[0075] The piezoelectric film 110 can have different component values ​​of the piezoelectric tensor with different crystal orientations. The piezoelectric tensor components describe the excitation of the requested mode of resonant vibration by the applied electric field (for example, in an XBAR type structure, e15 is used for the A1 mode, and in an IHP type device, e16 is used for the SH0 mode). Generally, specific piezoelectric tensor components should be large and other components should be small to avoid the generation of parasitic modes. Specifically, the piezoelectric film 110 can be 120°±20° rotated Y-cut or Z-cut ±20°, Y-propagation. In some embodiments, the 120°±20° rotated Y-cut can provide maximum piezoelectric coupling based on the embedded vertical electrode structure and the resonant mode (A1), and have a larger corresponding piezoelectric module (for example, e 15 ). A Z-cut ±20° can be an alternative orientation, especially for a slightly weaker coupling.

[0076] The cut can be optimized to obtain the necessary size of the piezoelectric tensor components. The cut determines the size of the piezoelectric coupling and ultimately the relative width of the filter passband (e.g., ladder filter passband).

[0077] The resonator 100 includes a substrate 102. The substrate 102 provides mechanical support for the piezoelectric film 110.

[0078] The piezoelectric film 110 is attached to the substrate 102. In other words, the piezoelectric film 110 is firmly mounted on the substrate 102.

[0079] The piezoelectric film 110 has a front surface and a back surface in parallel. The front side is the surface facing away from the substrate 102. The back side is the surface facing the substrate 102. The back surface of the piezoelectric film 110 is attached to the substrate 102 or the intermediate layer 103.

[0080] The substrate 102 may be made of a high-acoustic-velocity material. The shear acoustic velocity of a high-acoustic-velocity material is generally higher than 7000 m / s. For example, the acoustic velocity of the substrate 102 The acoustic velocity of the piezoelectric film 110 may be For example, substrate 102 may be made of diamond, silicon carbide, boron nitride, or some other material or combination of materials having a high acoustic velocity.

[0081] When the distance between electrodes 120-1 and 120-2 is less than , the substrate 102 having a high velocity prevents the bulk acoustic wave from leaking into the substrate 102, wherein, is the thickness of the piezoelectric film, is the acoustic velocity of the substrate 102, is the acoustic velocity of the piezoelectric film 110. Such a robust substrate provides excellent power handling capability for the resonator due to the efficient evacuation of heat generated primarily in the electrodes to the substrate having high thermal conductivity.

[0082] The substrate 102 may be mounted on a support wafer 101. The support wafer 101 may be made of, for example, silicon or glass. The support wafer 101 provides mechanical stability and good heat dissipation.

[0083] The substrate 102 can be a relatively thin layer. However, it needs to be thick enough relative to the piezoelectric film 110 so that the A1 mode vibration is completely confined in the piezoelectric film 110 and strongly attenuated onto the supporting wafer. For example, the thickness of the substrate 102 can be more than ten times the thickness of the piezoelectric film 110. This reduces or avoids bulk acoustic radiation into the supporting wafer and improves the quality factor or Q-factor of the resonator.

[0084] The back surface of the piezoelectric film 110 (e.g., with the intermediate layer 103 underneath) can be bonded to the substrate 102 using a wafer bonding process. Alternatively, the piezoelectric film 110 can be grown on the substrate 102 or attached to the substrate in some other way. The piezoelectric film 110 can be attached directly to the substrate, or can be attached to the substrate via one or more intermediate material layers (e.g., Figure 3 The intermediate layer 103) is attached to the substrate.

[0085] Figure 3 A schematic cross-sectional view of a cross section of an exemplary resonator is shown. Specifically, Figure 3Shows Figure 2 Schematic two-dimensional view of plane P1 of an exemplary acoustic wave resonator 100. The resonator 100 may include a similar Figure 4 Parallel and periodic repetition of regularly spaced portions of the portions shown.

[0086] The piezoelectric film 110 may be attached to the substrate 102 via an intermediate layer 103. The thickness of the intermediate layer 103 may be substantially equal to one quarter of the wavelength of the shear bulk acoustic wave in the intermediate layer 103 at the resonant frequency of the acoustic wave resonator. The thickness of the piezoelectric film 110 reduces the acoustic coupling between the piezoelectric film 110 and the substrate 102, thereby increasing the piezoelectric coupling. The intermediate layer 103 can be made of SiO2. The SiO2 layer reduces the influence from the rigid substrate, supports the basic thickness resonance in the piezoelectric film 110, and thus further increases the piezoelectric coupling. The bus bar is deposited on the intermediate layer 103, or on the substrate 102. In some embodiments, less preferably, the bus bar can also be deposited on the piezoelectric layer 110.

[0087] Figure 4 is a schematic exploded cross-sectional view of a cross section of an exemplary acoustic wave resonator.

[0088] A plurality of grooves 130 are formed on the front surface of the piezoelectric film 110. The grooves 130 may be long, narrow cuts or depressions in the piezoelectric film 110.

[0089] like Figure 3 As shown, two adjacent grooves 130 define a ridge 111 therebetween.

[0090] The cross section of the groove 130 may be rectangular, or have a different shape, such as a regular or irregular polygon. The groove may have a bottom wall 303 and two side walls 301, 302. The side walls 301, 302 of the groove may be straight, inclined or curved.

[0091] The groove 130 may extend partially or completely through the piezoelectric film 110. The depth of the groove 130 formed in the piezoelectric film 110 is Can be less than, equal to, or greater than the thickness of the piezoelectric film In some embodiments, the depth of the groove 130 is Can be larger than the thickness of the piezoelectric film In some embodiments, the depth of the groove 130 is It can be in the range of 150 nm to 250 nm.

[0092] like Figure 5 As shown, if the depth of the groove Greater than the thickness of the piezoelectric film , the groove may extend in the intermediate layer 103 .

[0093] For example, the groove 130 may be formed by selectively etching the piezoelectric film 110 before or after the piezoelectric film 110 and the substrate 102 are attached.

[0094] like Figure 3 As shown, each electrode 120 - 1 , 120 - 2 is placed in a corresponding groove 130 .

[0095] The total width of the electrode 120-1 or 120-2 is equal to the width of the groove 130. Spacing is the spacing between the two electrodes 120 - 1 , 120 - 2 (eg, the center-to-center spacing). is the metallization ratio of the resonator.

[0096] In some embodiments, the spacing Less than (1), is the shear velocity of the substrate, is the operating frequency of the acoustic resonator.

[0097] In some embodiments, the spacing Less than (2), where is the speed of sound in the substrate, is the speed of sound in the piezoelectric film, is the thickness of the piezoelectric film.

[0098] The acoustic velocity may be about 4000 m / s in a piezoelectric film and as high as 9600 m / s in a high acoustic velocity substrate. Therefore, in the case of a diamond substrate, the spacing is smaller than the thickness t of the piezoelectric film 110. p This makes the frequency of the acoustic resonator Up to 5 GHz, spacing Less than 1.2 μm. This spacing Suitable for fabrication using optical lithography. Radiation of bulk acoustic waves into the bottom substrate is avoided or at least significantly limited.

[0099] Equations (1) and (2) are only reasonable estimates. Device simulations (e.g., based on the finite element method (FEM)) can be used to accurately determine whether the spacing is small enough to avoid bulk wave radiation into the substrate.

[0100] The electrodes 120-1, 120-2 extend perpendicular to the surface of the piezoelectric film 110. In this sense, the electrodes 120-1, 120-2 can be considered vertical. The vertical electrodes realize horizontal electric fields for A1 mode resonance. Therefore, the vertical electrodes effectively increase piezoelectric coupling and eliminate parasitic modes.

[0101] like Figure 4 As shown, the electrode 120 can be attached to the sidewall of the piezoelectric film. The electrode 120 can be adjacent to the sidewalls 301, 302 of the groove 130 over substantially all or part of the sidewalls 301, 302 of the groove 130. Specifically, the electrode 120 can be adjacent to the sidewalls 301, 302 of the groove 130 over at least 50% of the sidewalls 301, 302 of the groove 130.

[0102] like Figure 3 As shown, the radio frequency voltage applied to two adjacent electrodes 120 - 1 , 120 - 2 induces an electric field in a ridge 111 defined between the two adjacent electrodes 120 - 1 , 120 - 2 .

[0103] The electrodes 120-1, 120-2 are vertically embedded in the piezoelectric film 110. This provides a uniform horizontal electric field through the piezoelectric film 110 within the ridges 111, thereby providing optimal excitation of the A1 mode resonance. This helps to increase piezoelectric coupling and reduce parasitic modes.

[0104] like Figure 4 As shown, the electrode 120 has a front surface and a rear surface. The front surface is a surface facing away from the piezoelectric film 110. The rear surface is a surface facing the piezoelectric film 110. The rear surface of the electrode 120 is attached to the piezoelectric film 110.

[0105] In some embodiments, the height of electrode 120 can be in the range of 150 nm to 250 nm. IDT's busbars ( Figure 1A , Figure 1B , Figure 1C The height of electrodes 121 , 122 ) may be equal to or greater than the height of electrode 120 .

[0106] In some embodiments, there is a cavity 410 on the front surface of the electrode 120, such as Figure 4 The cavity 410 in the electrode 120 allows the ridge 111 to vibrate more freely, thereby increasing the piezoelectric coupling.

[0107] A separate cavity 410 is formed in each electrode 120. The cavity 410 in the electrode 120 may be formed by depositing the electrode 120 only on the sidewalls (and optionally on the bottom wall of the groove) of the groove 130. Alternatively, the cavity 410 in the electrode 120 may be formed by removing excess metal, such as by etching through a patterned photoresist.

[0108] The cavity 410 may be a groove, such as a long, narrow cut or depression in the electrode 120. The cavity 410 in the electrode 120 may be a groove substantially parallel to the groove 130 in the piezoelectric film 110 in which the electrode 120 is disposed. The cavity 410 in the electrode 120 extends substantially along the entire length of the electrode 120. Specifically, the cavity 410 may extend along more than 90% of the length of the electrode 120, at least in the region of the aperture AP of the electrode (e.g., Figure 1A ).

[0109] The cavity 410 may extend partially or completely through the electrode 120. The depth of the cavity formed in the electrode 120 may be It can be less than, equal to, or greater than the height of the electrode 120 In some embodiments, the depth of the cavity formed in the electrode 120 is Greater than the height of electrode 120 This achieves high voltage electrical coupling. In some embodiments, the depth of cavity 410 in electrode 120 is The width of the cavity 410 in the electrode 120 may be in the range of 100 nm to 250 nm. Can be in the range of 50 nm to 100 nm. Fig. 9 The effect of the cavity depth in the electrode is described in more detail.

[0110] like Figure 4 As shown, the cross-section of the electrode 120 may be U-shaped. The electrode 120 may include a first side portion 401 and a second side portion 402. The first side portion 401 and the second side portion 402 are separated by a cavity 410. The electrode 120 may also include a bottom portion 403. Figure 6 As shown, the electrode 120 may not include the bottom portion 403 .

[0111] like Figure 4 As shown, each side portion 401 at least partially covers the corresponding side wall of the groove 130. The first side portion 401 at least partially covers the side wall 301 of the groove. The second side portion 402 at least partially covers the side wall 302 of the groove 130. The electrode 120 may also include a bottom portion 403 at least partially covering the bottom wall 303 of the groove.

[0112] The side portions 121 and 122 of the electrode 120 are electrically connected. The side portions 121 and 122 may be connected via the bottom portion 403. Alternatively or additionally, the side portions 121 and 122 may be connected via the bus bar ( Figure 1A , Figure 1B , Figure 1CA bus bar connection is provided in 121, 122).

[0113] Figure 7 The resonant vibration mode in a schematic cross-sectional view of a cross section of an exemplary resonator is shown. In the piezoelectric film, the resonant vibration mode is close to the antisymmetric Lamb mode A1. In the example shown, the piezoelectric film is made of 120° Y-cut LN, has a thickness of 400 nm, a pitch p of 0.9 μm, and a metallization ratio m / p=0.33.

[0114] The A1 Lamb mode has a main vibration displacement in the horizontal direction x. The displacement is opposite on the top and bottom sides of the membrane. The displacement is generated by the horizontal electric field. Selective cutting of LN membranes provides high-value piezoelectric modules (e.g., piezoelectric modules e 15 The piezoelectric module is responsible for generating stress (for example, S5=S13), which excites the corresponding frequency Shear wave thickness resonance.

[0115] The vertical electrodes provide a uniform horizontal electric field near the electrode area, rather than a vertical field like electrodes on top of the piezoelectric film, providing greater coupling and weaker parasitic modes. The high-speed substrate support avoids body wave radiation and energy leakage downward. All acoustic energy is trapped in the piezoelectric film and partially in the intermediate layer, providing a high Q factor for the resonator.

[0116] Figure 8 is a graph of piezoelectric coupling of an exemplary acoustic wave resonator as a function of intermediate layer thickness.

[0117] In this example, the interlayer is made of SiO2, the piezoelectric film is made of LN and the substrate is made of diamond. The interlayer made of SiO2 reduces the acoustic coupling between LN and diamond. The coupling reaches a maximum of about 23% when the interlayer thickness is about half the thickness of the piezoelectric film. The shear wave speeds in LN and SiO2 are comparable, so, in other words, the interlayer thickness is about a quarter of the shear wave wavelength in their materials. In the example shown, the thickness of the interlayer is 200 nm and the thickness of the piezoelectric film is 400 nm. The thickness of the interlayer is about half the thickness of the piezoelectric film, which greatly reduces the acoustic effect from the hard diamond substrate, thereby supporting the fundamental A1 mode resonance in the LN and thus increasing the piezoelectric coupling.

[0118] Fig. 9 is a graph of piezoelectric coupling of an exemplary acoustic wave resonator as a function of cavity depth (or hollow depth) in the electrode.

[0119] In some embodiments, the depth of the cavity formed in the electrode 120 is Greater than the thickness of the piezoelectric film 110 This cavity 410 in the electrode 120 enables the ridge 111 to vibrate more freely in the horizontal direction, thereby increasing the piezoelectric coupling. For example, for a thickness of the piezoelectric film 110 of 600 nm , the depth of the cavity formed in the electrode 120 can be larger than 200 nm. This allows for a larger coupling K 2 (about 26%).

[0120] Fig.10 is a graph of the admittance of an exemplary acoustic wave resonator as a function of frequency. The admittance curve of the optimized structural parameters shows a large coupling (26.4%), no parasitic modes, and a high frequency (4.5 to 6 GHz) configuration. This shows that the effectiveness and correctness of the model await further practical applications.

[0121] Fig.11A and Fig. 11B is a plot of admittance versus frequency for two different exemplary acoustic wave resonators. Fig.11A In the exemplary resonator of FIG. 1 , bus bars 121 and 122 cover the piezoelectric film 110, and Fig. 11B In the exemplary resonator of , the bus bars 121 , 122 do not cover the piezoelectric film 110 . Fig.11A and Fig. 11B A comparison of φ 1 and φ 2 shows that isolating the piezoelectric film 110 from the bus bars 121 , 122 on both sides suppresses the lateral modes to a great extent.

[0122] Fig.12 is a simplified flow chart illustrating an exemplary process 1200 for manufacturing a resonator or a filter including a resonator. Fig.12 The flowchart only includes the main process steps. Additional steps including various traditional process steps (e.g., surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) can be found in Fig.12 Executed before, between, after, and during the steps shown.

[0123] In operation 1201, the piezoelectric film 110 is bonded to the substrate 102. The piezoelectric film 110 and the substrate 102 may be bonded by a wafer bonding process. One or more intermediate layers 103 may be formed or deposited on a surface of one or both of the piezoelectric film 110 and the substrate 102.

[0124] In operation 1202, grooves 130 are formed in the piezoelectric film 110. A separate groove 130 may be formed for each electrode 120. The grooves 130 may be formed using conventional photolithography and etching techniques.

[0125] In operation 1203, the electrodes 120 are formed by depositing one or more conductor layers in the grooves 130 formed in the piezoelectric film 110. The conductor layers may be, for example, aluminum, aluminum alloy, copper, copper alloy, or some other conductive metal.

[0126] A separate cavity 410 is formed in each electrode 120. The cavity 410 in the electrode 120 can be formed by depositing the electrode 120 only on the sidewalls of the groove 130 (and optionally on the bottom wall of the groove). Alternatively, the cavity 410 in the electrode 120 can be formed by removing excess metal, such as by etching through a patterned photoresist. For example, the conductor layer can be etched by plasma etching, reactive ion etching, wet chemical etching, and other etching techniques.

[0127] Any range or device value given herein may be expanded or changed without losing the effect sought. In addition, any embodiment may be combined with another embodiment unless expressly prohibited.

[0128] Although the subject matter has been described in structural features and / or action-specific language, it should be understood that the subject matter defined by the appended claims is not necessarily limited to the specific features or actions described above. On the contrary, the specific characteristics and actions described above are disclosed as examples of implementing the claims, and other equivalent features and actions are intended to be included in the scope of the claims.

[0129] It should be understood that the advantages and benefits described above may relate to one embodiment, or may relate to multiple embodiments. These embodiments are not limited to embodiments that solve any or all of the problems described, or those that have any or all of the advantages and benefits described. It should also be understood that reference to "an" item may refer to one or more of these items.

[0130] The steps or operations of the methods described herein may be performed in any appropriate order, or may be performed simultaneously where appropriate. In addition, separate frames may be deleted from any method without departing from the scope of the subject matter described herein. Aspects of any exemplary embodiment described above may be combined with aspects of any other exemplary embodiment described to form more exemplary embodiments without affecting the effects to be achieved.

[0131] The term "comprising" is used herein to mean including the identified methods, blocks or elements, but such blocks or elements do not include an exclusive list and the method or apparatus may contain additional blocks or elements.

[0132] Although a subject may be referred to as the "first" or "second" subject, this does not necessarily indicate any order or importance of the subjects. Rather, these attributes may be used merely to distinguish between subjects.

[0133] It should be understood that the above description is given by way of example only, and that various modifications may be made by those skilled in the art. The above description, examples, and data provide a complete description of the structure and use of the exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity or with reference to one or more separate embodiments, those skilled in the art may make various changes to the disclosed embodiments without departing from the scope of this specification.

Claims

1. An acoustic wave resonator (100), characterized in that: The acoustic wave resonator (100) comprises: Substrate (102); A piezoelectric film (110) attached to the substrate (102), wherein the piezoelectric film (110) has a plurality of grooves (130), wherein two adjacent grooves (130) define a ridge (111) therebetween; A plurality of electrodes (120), wherein each electrode (120) is disposed in a corresponding groove in the groove (130), each electrode (120) comprises two side portions (401, 402), and each side portion (401, 402) at least partially covers a corresponding side wall (301, 302) of the groove (130).

2. The acoustic wave resonator (100) according to the preceding claim, characterized in that The side portions (401, 402) of each electrode (120) are electrically connected.

3. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The acoustic wave resonator (100) comprises a circuit for applying a radio frequency voltage to the electrodes (120-1, 120-2) disposed in the adjacent grooves (130) to induce an electric field in the ridge (111).

4. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that Each electrode (120) includes a bottom portion (403) at least partially covering the bottom of the groove (303), and the bottom portion (403) of the electrode (120) is electrically connected to the side portions (401, 402) of the electrode (120).

5. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that A cavity (410) is formed on the front surface of each electrode (120).

6. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The cross section of each electrode (120) is U-shaped.

7. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The piezoelectric film (110) is attached to the substrate (102) via an intermediate layer (103).

8. The acoustic wave resonator (100) according to the preceding claim, characterized in that The intermediate layer (103) is made of SiO2.

9. The acoustic wave resonator (100) according to claim 6 or 7, characterized in that: The thickness of the intermediate layer (103) is substantially equal to one quarter of the wavelength of the shear bulk acoustic wave in the intermediate layer (103) at the resonance frequency of the acoustic wave resonator (100).

10. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The substrate (102) is made of a high-sound-velocity material, wherein the shear sound velocity in the high-sound-velocity material is higher than 7000 m / s.

11. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The speed of sound in the substrate (102) is at least twice the speed of sound in the piezoelectric film (110).

12. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The substrate (102) is made of diamond, silicon carbide or boron nitride.

13. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The thickness of the substrate (102) is greater than ten times the thickness of the piezoelectric film (110).

14. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The depth of the groove (130) is greater than one third of the thickness of the piezoelectric film (110).

15. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The thickness of the piezoelectric film (110) is substantially equal to half the wavelength of the shear acoustic wave in the piezoelectric film at the operating frequency of the acoustic wave resonator (100).

16. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The electrodes (120) are alternately connected to two bus bars (121, 122), and two adjacent electrodes (120) are connected to different bus bars among the bus bars.

17. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The piezoelectric film (110) covers only the area defined by the overlap of the electrodes (120).

18. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The distance between the two electrodes (120) is less than , is the shear sound velocity in the substrate (102), is the operating frequency of the acoustic wave resonator.

19. The acoustic wave resonator (100) according to any one of the preceding claims, characterized in that The piezoelectric film (110) is made of lithium niobate with a Y-cut rotated at 120°±20° or a Z-cut lithium niobate with a ±20° rotation.

20. A radio frequency filter, characterized in that: The radio frequency filter comprises at least one acoustic wave resonator (100) according to any one of the preceding claims.

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