Transversely excited film bulk acoustic resonator

Abstract

The invention discloses an acoustic resonator device and a filter. A filter includes a substrate, and a piezoelectric plate having parallel front and back surfaces, the back surface attached to the substrate. A conductive pattern is formed on the front side, the conductive pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, with interleaved fingers of each of the plurality of IDTs disposed on respective portions of the piezoelectric plate, the piezoelectric plate suspended over one or more cavities formed in the substrate. The plurality of resonators includes parallel resonators and series resonators. A first thickness of a first dielectric layer disposed between the fingers of the IDT of the parallel resonator is greater than a second thickness of a second dielectric layer disposed between the fingers of the IDT of the series resonator.

Description

[0001] This application is a divisional application of the Chinese invention patent application "A laterally excited thin film bulk acoustic resonator" with application number 201980039853.7 and application date June 11, 2019. Technical Field

[0002] The present disclosure relates to radio frequency filters using acoustic wave resonators, and more particularly to filters for communication devices. Background Art

[0003] Radio frequency (RF) filters are two-terminal devices that are configured to pass some frequencies and block other frequencies, where "pass" means transmission with relatively low signal loss, and "block" means blocking or substantially attenuating. The frequency range passed by a filter is called the "passband" of the filter. The frequency range blocked by such a filter is called the "stopband" of the filter. Typical RF filters have at least one passband and at least one stopband. The specific requirements of the passband or stopband depend on the specific application. For example, a "passband" can be defined as a frequency range where the insertion loss of the filter is better than a defined value such as 1dB, 2dB, or 3dB. A "stopband" can be defined as a frequency range where the rejection of the filter is greater than a defined value, such as 20dB, 30dB, 40dB, or more, depending on the specific application.

[0004] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in the RF front end of cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, Internet of Things (IoT) devices, laptops and tablets, fixed-point radio links, and other communication systems. RF filters are also used in radar and electronic and information warfare systems.

[0005] RF filters typically require many design trade-offs to achieve the best compromise between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing methods and enhancements can benefit one or several of these requirements simultaneously.

[0006] Enhancements in the performance of RF filters in wireless systems can have a wide range of impacts on system performance. Improvements in RF filters can lead to improvements in system performance, such as larger unit sizes, longer battery life, higher data rates, greater network capacity, lower costs, enhanced security, higher reliability, etc.

[0007] These improvements can be implemented individually or in combination at various levels of the wireless system, such as at the RF module, RF transceiver, mobile or fixed subsystem or network level.

[0008] To obtain a wider communication channel bandwidth, it is necessary to use a higher frequency communication band. TM The (Long Term Evolution) specification defines frequency bands between 3.3 GHz and 5.9 GHz. These bands are currently unused. Future proposals for wireless communications include millimeter wave communication bands with frequencies up to 28 GHz.

[0009] High-performance RF filters used in current communication systems often incorporate acoustic wave resonators, including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR) and other types of acoustic wave resonators. However, these existing technologies are not suitable for use at higher frequencies, which will be required for future communication networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Included are a schematic plan view and two schematic cross-sectional views of a laterally excited film bulk acoustic resonator (XBAR).

[0011] Figure 2 yes Figure 1 A partially enlarged schematic cross-sectional view of an XBAR.

[0012] Figure 3A yes Figure 1 Alternative schematic cross-sectional view of an XBAR.

[0013] Figure 3B yes Figure 1 Another alternative schematic cross-sectional diagram of an XBAR.

[0014] Figure 3C is an alternative schematic plan view of an XBAR.

[0015] Figure 4 is a diagram showing the shear horizontal acoustic mode in XBAR.

[0016] Figure 5 is a graph of the admittance of the simulated XBAR.

[0017] Figure 6 is a graph comparing the admittance of three simulated XBARs with different dielectric layers.

[0018] Figure 7 is a graph comparing the admittance of four simulated XBARs with different dielectric layer thicknesses.

[0019] Figure 8 Graph showing the effect of the thickness of a piezoelectric plate on the resonance frequency of an XBAR.

[0020] Fig. 9 is a graph showing the effect of the front dielectric layer thickness on the resonant frequency of the XBAR.

[0021] Fig.10 is a graph showing the effect of the IDT finger pitch on the resonant frequency of the XBAR.

[0022] Fig.11 is a graph comparing the admittance of XBAR on LiNb03 and LiTa03 plates.

[0023] Fig.12 is a graph of the measured admittance of the XBAR.

[0024] Fig.13 is another graph of the measured admittance of the XBAR.

[0025] Fig.14 is a schematic circuit diagram and layout of a filter using XBAR.

[0026] Fig.15 yes Fig.12 A diagram of a transfer curve (S21) of an embodiment of a filter.

[0027] Fig.16 yes Fig.12 Graph of a transfer curve (S21) of another embodiment of a filter.

[0028] Fig.17 is a flow chart of a method of manufacturing an XBAR.

[0029] Throughout the specification, elements appearing in the drawings are assigned three-digit or four-digit reference numerals, of which the two least significant digits are specific to the element and the one or two most significant digits are the figure number in which the element is first shown. Elements not described in conjunction with a drawing may be assumed to have the same characteristics and functions as previously described elements having the same reference numeral. DETAILED DESCRIPTION

[0030] Description of the device

[0031] Figure 1 A simplified schematic top view and orthogonal cross-sectional view of a laterally excited film bulk acoustic resonator (XBAR) 100 are shown. XBAR resonators such as resonator 100 can be used in a variety of RF filters, including band-stop filters, band-pass filters, duplexers, and multiplexers. XBARs are particularly suitable for use in filters in the communication band with frequencies above 3 GHz.

[0032] The XBAR 100 consists of a thin film conductor pattern formed on the surface of a piezoelectric plate 110, which has parallel front and back sides 112, 114, respectively. The piezoelectric plate is a thin single crystal layer of a piezoelectric material, such as lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride. The piezoelectric plate is cut so that the directions of the X, Y, and Z crystal axes relative to the front and back sides are known and consistent. In the example presented in the patent, the piezoelectric plate is Z-cut, that is, the Z axis is perpendicular to the surface. However, XBARs can be made on piezoelectric plates with other crystallographic orientations.

[0033] The back side 114 of the piezoelectric plate 110 is attached to a substrate 120, which provides mechanical support for the piezoelectric plate 110. The substrate 120 may be, for example, silicon, sapphire, quartz, or some other material. The piezoelectric plate 110 may be bonded to the substrate 120 using a wafer bonding process, or the piezoelectric plate 110 may be grown on the substrate 120, or the piezoelectric plate 110 may be attached to the substrate in some other manner. The piezoelectric plate may be attached directly to the substrate, or may be attached to the substrate via one or more intermediate material layers.

[0034] The conductor pattern of XBAR 100 includes an interdigital transducer (IDT) 130. IDT 130 includes a first plurality of parallel fingers, such as finger 136, and a second plurality of fingers, wherein the first plurality of parallel fingers extend from a first bus bar 132 and the second plurality of fingers extend from a second bus bar 134. The first and second plurality of parallel fingers are staggered. The staggered fingers overlap a distance AP, commonly referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of IDT 130 is the "length" of the IDT.

[0035] The first and second busbars 132, 134 serve as terminals of the XBAR 100. A radio frequency or microwave signal applied between the two busbars 132, 134 of the IDT 130 excites acoustic waves within the piezoelectric plate 110. As will be discussed in detail below, the excited acoustic waves are bulk shear waves that propagate in a direction perpendicular to the surface of the piezoelectric plate 110, which is also perpendicular or transverse to the direction of the electric field generated by the IDT fingers. Therefore, the XBAR is considered to be a transversely excited thin film bulk wave resonator.

[0036] A cavity 125 is formed in the substrate 120 so that the portion of the piezoelectric plate 110 containing the IDT 130 is suspended above the cavity 125 without contacting the substrate 120. The conventional meaning of "cavity" is "empty space within a solid." The cavity 125 can be a hole that passes completely through the substrate 120 (as shown in the AA and BB cross sections) or a groove in the substrate 120. The cavity 125 can be formed before or after the piezoelectric plate 110 and the substrate 120 are attached together, for example, by selectively etching the substrate 120. Figure 1As shown, cavity 125 is rectangular, with an extent greater than aperture AP and length L of IDT 130. The cavity of an XBAR can have different shapes, such as regular or irregular polygons. The cavity of an XBAR can have more or less than four sides, and the sides can be straight or curved.

[0037] In order to facilitate Figure 1 1, the geometric spacing and width of the IDT fingers are greatly exaggerated relative to the length (dimension L) and aperture (dimension AP) of the XBAR. A typical XBAR has more than ten parallel fingers in the IDT 110. An XBAR may have hundreds (possibly thousands) of parallel fingers in the IDT 110. Similarly, the finger thickness in the cross-sectional view is greatly exaggerated.

[0038] Figure 2 A detailed schematic cross-sectional view of XBAR 100 is shown. Piezoelectric plate 110 is a single crystalline layer of piezoelectric material with a thickness ts. ts may be, for example, 100 nm to 1500 nm. When used for LTE from 3.4 GHZ to 6 GHz TM When used in filters of frequency bands (e.g., frequency bands 42, 43, 46), the thickness ts can be, for example, 200 nm to 1000 nm.

[0039] Optionally, a front dielectric layer 214 may be formed on the front side of the piezoelectric plate 110. By definition, the "front side" of an XBAR refers to the surface facing away from the substrate. The front dielectric layer 214 has a thickness tfd. The front dielectric layer 214 is formed between the IDT fingers 238. Although Figure 2 23. Although not shown in the drawings, the front dielectric layer 214 may also be deposited on the IDT fingers 238. A back dielectric layer 216 may optionally be formed on the back side of the piezoelectric plate 110. The back dielectric layer 216 has a thickness tbd. The front dielectric layer 214 and the back dielectric layer 216 may be non-piezoelectric dielectric materials, such as silicon dioxide or silicon nitride. tfd and tbd may be, for example, 0 to 500 nm. tfd and tbd are typically less than the thickness ts of the piezoelectric plate. tfd and tbd do not have to be equal, and the front and back dielectric layers 214, 216 do not have to be the same material. The front dielectric layer 214 and / or the back dielectric layer 216 may be formed of multiple layers of two or more materials.

[0040] The IDT fingers 238 may be aluminum or a substantially aluminum alloy, copper or a substantially copper alloy, beryllium, gold, or some other conductive material. A thin (relative to the total thickness of the conductor) layer of another metal (e.g., chromium or titanium) may be formed under and / or over the fingers to improve adhesion between the fingers and the piezoelectric plate 110 and / or to passivate or encapsulate the fingers. The busbars ( Figure 1 132, 134) can be made of the same or different material as the fingers.

[0041] Dimension p is the center spacing or "pitch" of the IDT fingers, which may be referred to as the pitch of the IDT and / or the pitch of the XBAR. Dimension w is the width or "mark" of the IDT fingers. The IDT of an XBAR is significantly different from the IDT used in a surface acoustic wave (SAW) resonator. In a SAW resonator, the pitch of the IDT is half the wavelength of the acoustic wave at the resonant frequency. In addition, the mark-to-pitch ratio of a SAW resonator IDT is typically close to 0.5 (i.e., the width of the mark or finger is approximately one-quarter the wavelength of the acoustic wave at resonance). In an XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of the finger. In addition, the pitch p of the IDT is typically 2 to 20 times the thickness ts of the piezoelectric plate 110. The width of the IDT fingers in an XBAR is not limited to one-quarter the wavelength of the acoustic wave at resonance.

[0042] For example, the width of the XBAR IDT finger can be 500nm or more, so that the IDT can be manufactured using photolithography. The thickness tm of the IDT finger can be from 100nm to approximately equal to the width w. Figure 1 The thickness of 132, 134) in the IDT finger can be equal to or greater than the thickness tm of the IDT finger.

[0043] Figure 3A and Figure 3B Shown along Figure 1 Two alternative cross-sectional views of section AA defined in . Figure 3A , a piezoelectric plate 310 is attached to a substrate 320. A cavity 325 that does not completely penetrate the substrate 320 is formed in the substrate below a portion of the piezoelectric plate 310 containing the IDT of the XBAR. The cavity 325 may be formed, for example, by etching the substrate 320 before attaching the piezoelectric plate 310. Alternatively, the cavity 325 may be formed by etching the substrate 320 using a selective etchant that reaches the substrate through one or more openings provided in the piezoelectric plate 310.

[0044] exist Figure 3B , substrate 320 includes base 322 and intermediate layer 324 disposed between piezoelectric plate 310 and base 322. For example, base 322 may be silicon, and intermediate layer 324 may be silicon dioxide or silicon nitride or some other material. A cavity 325 is formed in intermediate layer 324 beneath the portion of piezoelectric plate 310 containing the XBAR. Cavity 325 may be formed, for example, by etching intermediate layer 324 prior to attaching piezoelectric plate 310. Alternatively, cavity 325 may be formed by etching intermediate layer 324 using a selective etchant that reaches the substrate through one or more openings disposed in piezoelectric plate 310.

[0045] Figure 3C3 is a schematic plan view of another XBAR 350. XBAR 350 includes an IDT formed on a piezoelectric plate 310. Piezoelectric plate 310 is disposed over a cavity 380 in a substrate. In this example, cavity 380 has an irregular polygonal shape such that none of the edges of the cavity are parallel or parallel to the conductors of the IDT. The cavity may have a different shape with straight or curved edges.

[0046] Figure 4 is a graphic representation of the primary acoustic mode of interest in the XBAR. Figure 4 A small portion of an XBAR 400 is shown, which includes a piezoelectric plate 410 and three interlaced IDT fingers 430. An RF voltage is applied to the interlaced fingers 430. This voltage generates a time-varying electric field between the fingers. As indicated by the arrow labeled "Electric Field," the direction of the electric field is transverse, or parallel to the surface of the piezoelectric plate 410. Due to the high dielectric constant of the piezoelectric plate, the electric field is highly concentrated in the plate relative to air. The transverse electric field induces shear deformation in the piezoelectric plate 410, thereby strongly exciting shear mode acoustic waves. In this article, "shear deformation" is defined as deformation in a material in which parallel planes remain parallel and maintain a constant distance when translated relative to each other. "Shear acoustic waves" are defined as acoustic waves in a medium that cause shear deformation of the medium. The shear deformation in the XBAR 400 is represented by curve 460, with the adjacent small arrows indicating the direction and magnitude of atomic motion. For ease of viewing, the extent of atomic motion and the thickness of the piezoelectric plate 410 are greatly exaggerated. Although the atomic motion is primarily transverse (i.e., as shown in FIG. 4B ), the shear deformation in the XBAR 400 is represented by curve 460, with the adjacent small arrows indicating the direction and magnitude of atomic motion. For ease of viewing, the extent of atomic motion and the thickness of the piezoelectric plate 410 are greatly exaggerated. Although the atomic motion is primarily transverse (i.e., as shown in FIG. 4B ), the atomic motion is primarily transverse (i.e., as shown in FIG. 4B ). Figure 4 465 , but the direction of the acoustic energy flow of the excited shear acoustic wave is mainly perpendicular to the vertical direction of the piezoelectric plate surface, as shown by arrow 465 .

[0047] like Figure 4 As shown, there is essentially no electric field directly under the IDT fingers 430, so acoustic modes are only minimally excited in the region 470 under the fingers. Transient acoustic motions may occur in these regions. Since no acoustic vibrations are excited under the IDT fingers 430, the acoustic energy coupled to the IDT fingers 430 is low (e.g., compared to IDT fingers in a SAW resonator), which minimizes viscous losses in the IDT fingers.

[0048] Acoustic wave resonators based on shear acoustic wave resonances have shown superior performance compared to the current state-of-the-art film bulk acoustic wave resonators (FBAR) and solid mounted resonator bulk acoustic wave (SMR BAW) devices, where the electric field is applied through the thickness direction. In such devices, the acoustic modes are compressive in the direction of atomic motion and acoustic energy flow through the thickness direction. In addition, the piezoelectric coupling for shear wave XBAR resonances can be higher (>20%) than for other acoustic wave resonators. Therefore, high voltage electrical coupling allows the design and realization of microwave and millimeter wave filters with considerable bandwidth.

[0049] Figure 5 5 is a graph 500 with a graphical representation 510 of the normalized magnitude (on a logarithmic scale) of the admittance as a function of frequency for an XBAR simulated using a finite element method (FEM) simulation technique. In the simulated XBAR, the piezoelectric plate is lithium niobate with a Z-cut (i.e., the Z-axis is perpendicular to the plate). The IDT fingers are aluminum. The IDTs are oriented so that the y-axis of the piezoelectric plate is perpendicular to the IDT fingers. The substrate supporting the piezoelectric plate is silicon with a cavity (e.g., Figure 1 The losses of the piezoelectric plate and the IDT fingers were simulated using standard material parameters. The physical dimensions of the simulation are as follows: ts = 400nm; tfd = 0; tbd = 0; tm = 100nm; p = 5um; w = 500nm. The admittance is normalized for a single pair of IDT fingers and an aperture of 1 meter. The admittance of an XBAR with N IDT fingers and an aperture A (in meters) can be calculated by using Figure 5 The normalized admittance provided in is estimated by multiplying it by (N-1)·A.

[0050] The simulated XBAR exhibits resonance at a frequency FR of 4693 MHz and anti-resonance at a frequency FAR of 5306 MHz. The Q of the resonant QR is 2645 and the Q of the anti-resonant QAR is 4455. The absolute difference between FAR and FR is about 600 MHz and the fractional difference is about 0.12. The acoustic coupling can be roughly estimated to be 24%. The secondary resonances can be clearly seen in the admittance curves at frequencies below FR and above FAR.

[0051] Acoustic RF filters typically contain multiple acoustic resonators. Typically, these resonators have at least two different resonant frequencies. For example, an RF filter using the well-known "ladder" filter architecture includes parallel resonators and series resonators. The parallel resonator typically has a resonant frequency below the passband of the filter and an anti-resonant frequency within the passband. The series resonator typically has a resonant frequency within the passband and an anti-resonant frequency above the passband. In many filters, each resonator has a unique resonant frequency. The ability to obtain different resonant frequencies for XBARs made on the same piezoelectric plate greatly simplifies the design and manufacture of RF filters using XBARs.

[0052] Figure 66 is a graph 600 comparing the normalized admittance of three XBARs with different dielectric layers as a function of frequency. The admittance data is from a two-dimensional simulation of an XBAR structure using the same materials and dimensions (except for the dielectric layer) as the previous example. The admittance is normalized for a single pair of IDT fingers and an aperture of 1 μm. The solid line 610 is a plot of the normalized admittance per unit aperture for an XBAR with tfd=tbd=0 (i.e., an XBAR without a dielectric layer). The normalized admittance of this XBAR is plotted against Figure 5 The normalized admittance plots in are comparable but slightly different, primarily due to the different simulation methods used. Dashed line 620 is a plot of the normalized admittance of an XBAR with 100 nm of SiO2 on the front side of the piezoelectric slab between the IDT fingers (tfd=100 nm, tbd=0). Adding a SiO2 layer on the front side of the piezoelectric slab reduces the resonant frequency by about 500 MHz, or about 11%, compared to an XBAR without a dielectric layer. Dotted line 630 is a plot of the normalized admittance of an XBAR with 100 nm SiO2 on the front side of the piezoelectric slab between the IDT fingers and 100 nm SiO2 on the back side of the piezoelectric slab (tfd=tbd=100 nm). Adding SiO2 layers on both surfaces of the piezoelectric slab reduces the resonant frequency by about 900 MHz, or 20%, compared to an XBAR without a dielectric layer.

[0053] Figure 7 700 is a graph comparing the variation of admittance versus frequency for four XBARs with different front dielectric layer thicknesses. The admittance data is from a three-dimensional simulation of an XBAR with the following parameters: ts = 400 nm; tfd = 0, 30, 60, 90 nm; tbd = 0; tm = 100 nm; p = 4.2 um; w = 500 nm; AP = 20 um; N (total number of IDT fingers) = 51. The substrate is Z-cut lithium niobate, the IDT conductor is aluminum, and the dielectric layer is SiO2.

[0054] The solid line 710 is a graph of the admittance of an XBAR with tfd=0 (i.e., an XBAR without a dielectric layer). The dashed line 720 is a graph of the admittance of an XBAR with tfd=30 nm. Adding a 30 nm dielectric layer can reduce the resonant frequency by about 145 MHz compared to an XBAR without a dielectric layer. The dot-dash line 730 is a graph of the admittance of an XBAR with tfd=60 nm. Adding a 60 nm dielectric layer can reduce the resonant frequency by about 305 MHz compared to an XBAR without a dielectric layer. The double-dash-dot line 740 is a graph of the admittance of an XBAR with tfd=90 nm. Adding a 90 nm dielectric layer can reduce the resonant frequency by about 475 MHz compared to an XBAR without a dielectric layer. The frequency and amplitude of the secondary resonances are affected differently than the primary shear mode resonances.

[0055] Importantly, the presence of dielectric layers of various thicknesses has little or no effect on the piezoelectric coupling, as evidenced by the nearly constant frequency shift between the resonance and antiresonance of each XBAR.

[0056] Figure 8 , Fig. 9 and Fig.10 is a graph showing the dependence of the resonant frequency determined by simulation on the physical properties of the XBAR. Specifically, Figure 8 is a graph showing the resonant frequency versus piezoelectric plate thickness when the IDT finger pitch P=3 μm and there is no front or back dielectric layer (tfd=tbd=0). Fig. 9 It is a graph showing the resonance frequency as a function of the thickness of the front dielectric layer tfd when the piezoelectric plate thickness ts = 400 nm and the IDT finger pitch P = 3 microns. Fig.10 is a graph of the resonant frequency as a function of the IDT finger pitch p for a piezoelectric plate thickness of ts = 400 nm and tfd = tbd = 0. In all cases, the piezoelectric substrate is Z-cut lithium niobate, while the IDT fingers are aluminum with a width of w = 500 nm and a thickness of tm = 100 nm. When a front dielectric layer is present, it is SiO2.

[0057] Fig.11 1100 is a graphical representation comparing the admittance versus frequency change of two XBARs with different piezoelectric plate materials. The admittance data is from a three-dimensional simulation of an XBAR with the following parameters: ts = 415 nm; tfd = 120 nm; tbd = 0; tm = 460 nm; p = 4.5 um; w = 700 nm; AP = 71 um; and N (total number of IDT fingers) = 221. The substrate is Z-cut lithium niobate or Z-cut lithium tantalate, the IDT electrode is copper, and the dielectric layer is SiO2.

[0058] The solid line 1110 is a plot of the admittance of the XBAR on a lithium niobate plate. The dashed line 1120 is a plot of the admittance of the XBAR on a lithium tantalate plate. It is noteworthy that the difference between the resonant and anti-resonant frequencies of the lithium tantalate XBAR is about 5%, or half the frequency difference of the lithium niobate XBAR. The lower frequency difference of the lithium tantalate XBAR is due to the weaker piezoelectric coupling of the material. The temperature coefficient of the resonant frequency of the lithium niobate XBAR was measured to be about -71 parts per million per degree Celsius. The temperature coefficient of frequency (TCF) of the lithium tantalate XBAR is about half that of the lithium niobate XBAR. The lithium tantalate XBAR can be used in applications that do not require the large filter bandwidth that a lithium niobate XBAR may have, and in these applications, the reduced TCF is advantageous.

[0059] Fig.12is a graph showing the measured admittance of an experimental XBAR fabricated on a Z-cut lithium niobate plate 400nm thick. The IDT has a 5um pitch, a 40um aperture, and has 101 IDT fingers. The IDT fingers are aluminum and 100nm thick. The device does not include a dielectric layer. The solid line 1210 is the magnitude of the admittance as a function of frequency. The resonant frequency is 4617MHz and the anti-resonant frequency is 5138MHz. The frequency difference is 521MHz or more than 11% of the resonant frequency. The measurement data has not been corrected for the effects of the measurement system. Typically, correcting the measurement system increases the anti-resonant frequency and the difference between the anti-resonant and resonant frequencies.

[0060] Fig.13 is a graph showing the measured admittance of another experimental XBAR fabricated on a Z-cut lithium niobate plate 400 nm thick. The IDT has a pitch of 5 um, an aperture of 20 um, and 51 fingers. The IDT fingers are aluminum and 100 nm thick. The device does not include a dielectric layer. The solid line 1310 is the magnitude of the admittance as a function of frequency. The third and fifth harmonics of the primary XBAR resonance are visible at approximately 13.5 GHz and 22.5 GHz, respectively. Resonances as high as 60 GHz have been measured in other XBARs.

[0061] Fig.14 1 is a schematic circuit diagram and layout of a high frequency bandpass filter 1200 using XBAR. The filter 1400 has a conventional ladder filter architecture, which includes three series resonators 1410A, 14110B, 1410C and two parallel resonators 1420A, 1420B. The three series resonators 1410A, 1410B and 1410C are connected in series between the first port and the second port. Fig.14 In FIG. 14, the first and second ports are labeled "In" and "Out", respectively. However, the filter 1400 is symmetrical and either port is used as the input or output of the filter. The two parallel resonators 1420A, 1420B are grounded from the node between the series resonators. All parallel resonators and series resonators are XBARs.

[0062] The three series resonators 1410A, 1410B, 1410C and two parallel resonators 1420A, 1420B of the filter 1400 are formed on a single plate 1430 of piezoelectric material bonded to a silicon substrate (not visible). Each resonator includes a corresponding IDT (not shown), at least the fingers of the IDT are disposed above a cavity in the substrate. In this and similar contexts, the term "corresponding" means "associating things with one another," that is, having a one-to-one correspondence. Fig.14In the example, the cavity is schematically shown as a dashed rectangle (such as rectangle 1435). In this example, each IDT is arranged above a corresponding cavity. In other filters, the IDTs of two or more resonators can be arranged on a single cavity.

[0063] Fig.15 is a diagram showing the results of simulating a first bandpass filter incorporating five XBARs. Fig.14 The XBAR is formed on a Z-cut lithium niobate plate with a thickness of 0.4 microns. The substrate is silicon, the IDT conductor is aluminum, and there is no dielectric layer. The following table provides other physical parameters of the resonator (all dimensions are in microns):

[0064]

[0065] The performance of the first filter was simulated using a 3D finite element modeling tool. Curve 1510 is a graph of the magnitude of S21 (input-output transfer function) of the first filter as a function of frequency. The filter bandwidth is approximately 800 MHz, centered at 5.15 GHz. The simulated filter performance includes resistive and viscous losses. Tuning of the resonant frequencies of the individual resonators is achieved by varying only the spacing and width of the IDT fingers.

[0066] Fig.16 is a diagram showing the results of simulating the second filter using five XBARs. Fig.14 The filter 1400 is identical to the one in Figure 1. The XBAR is formed on a Z-cut lithium niobate (0.4um thick) piezoelectric plate. The substrate is silicon and the IDT electrodes are copper. Adjusting the resonant frequency of the resonator is achieved by varying the spacing and width of the IDT fingers and providing a front dielectric layer on the parallel resonator to lower its frequency. The following table provides other physical parameters of the resonator (all dimensions are in microns):

[0067]

[0068] The performance of the filter was simulated using a 3D finite element modeling tool. Curve 1610 is a graph of the S21 (input-output transfer function) of the simulated filter 1400 as a function of frequency. The filter bandwidth is approximately 800 MHz, centered at 4.75 GHz. The simulated performance does not include resistive or viscous losses.

[0069] The first and second filters (whose S21 transfer function is Fig.15 and Fig.16) is an example of a filter using XBARs. The filter can use more or less than two parallel resonators, more or less than three series resonators, and more or less than a total of five resonators. In addition to XBARs, the filter can also use reactive components such as capacitors, inductors, and delay lines. Further fine-tuning of the individual resonators of these filters can improve the filter performance.

[0070] Method Description

[0071] Fig.17 is a simplified flow chart of a method 1700 for making an XBAR or a filter incorporating an XBAR. The method 1700 begins at 1705 with a substrate and a plate of piezoelectric material and ends at 1795 with a completed XBAR or filter. Fig.17 The flowchart only includes the main processing steps. Fig.17 Various conventional processing steps (eg, surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) are performed before, between, after, and during the steps shown.

[0072] The piezoelectric plate may be a Z-cut lithium niobate or lithium tantalate such as used in the previous embodiments. The piezoelectric plate may be other materials and / or other cuts. The substrate may preferably be silicon. The substrate may be other materials that allow deep cavities to be formed by etching or other processing.

[0073] At 1710, the piezoelectric plate is bonded to the substrate. The piezoelectric plate and substrate may be bonded by a wafer bonding process. Typically, the mating surfaces of the substrate and piezoelectric plate are highly polished. One or more layers of an intermediate material, such as an oxide or a metal, may be formed or deposited on the piezoelectric plate and / or substrate mating surfaces. One or both mating surfaces may be activated using, for example, a plasma process. The mating surfaces may then be pressed together with considerable force to establish a molecular bond between the piezoelectric plate and the substrate or intermediate material layer.

[0074] A variation of method 1700 is to grow the piezoelectric plate in situ on the substrate. In this method variation, bonding is not required, and the action at 1710 will be redefined as "growing a piezoelectric plate on a substrate".

[0075] At 1720, one or more cavities are formed in the substrate. A separate cavity may be formed for each resonator in the filter device. The one or more cavities may be formed using anisotropic or orientation-dependent dry or wet etching to open from the back side of the substrate to the piezoelectric plate. Alternatively, the cavities may be formed in the form of depressions in the substrate by etching the substrate using an etchant introduced through the openings in the piezoelectric plate.

[0076] A variation of method 1700 is to form one or more cavities in the substrate before attaching the piezoelectric plate to the substrate. In this method variation, the actions at 1720 and 1730 occur before the action at 1710.

[0077] At 1730, a back dielectric layer may be formed. In the case where the cavity formed at 1720 is a hole through the substrate, the back dielectric layer may be deposited through the cavity using conventional deposition techniques, such as sputtering, evaporation, or chemical vapor deposition. When the cavity formed at 1720 is a recess that does not completely penetrate the substrate, the back dielectric layer must be formed on the piezoelectric plate or substrate before bonding the piezoelectric plate to the substrate. In that case, the actions at 1730 occur before the actions at 1710.

[0078] At 1740, a conductor pattern of an IDT including each XBAR is formed by depositing and patterning one or more conductor layers on the front side of the piezoelectric plate. The conductor layer can be, for example, aluminum, an aluminum alloy, copper, a copper alloy, or some other conductive metal. Optionally, one or more layers of other materials can be disposed below the conductor layer (i.e., between the conductor layer and the piezoelectric plate) and / or on top of the conductor layer. For example, a thin film of titanium, chromium, or other metal can be used to improve the adhesion between the conductor layer and the piezoelectric plate. A conductive enhancement layer of gold, aluminum, copper, or other metal with higher conductivity can be formed over a portion of the conductor pattern (e.g., the interconnection between the IDT busbar and the IDT).

[0079] A conductor pattern may be formed at 1740 by sequentially depositing a conductor layer and optionally one or more other metal layers on the surface of the piezoelectric plate. Excess metal may then be removed by etching through the patterned photoresist. The conductor layer may be etched, for example, by plasma etching, reactive ion etching, wet chemical etching, and other etching techniques.

[0080] Alternatively, a lift-off process may be used to form the conductor pattern at 1740. A photoresist may be deposited on the piezoelectric plate. And patterned to define the conductor pattern. A conductor layer and optionally one or more other layers may be sequentially deposited on the surface of the piezoelectric plate. The photoresist may then be removed, which removes excess material, leaving behind the conductor pattern.

[0081] At 1750, a front dielectric layer may be formed by depositing one or more layers of dielectric material on the front side of the piezoelectric plate. Conventional deposition techniques such as sputtering, evaporation, or chemical vapor deposition may be used to deposit the one or more dielectric layers. The one or more dielectric layers may be deposited over the entire surface of the piezoelectric plate, including on top of the conductor pattern. Alternatively, one or more photolithographic processes (using photomasks) may be used to limit the deposition of the dielectric layer to selected areas of the piezoelectric plate, such as only between the interlaced fingers of the IDT. Masks may also be used to allow different thicknesses of dielectric material to be deposited on different portions of the piezoelectric plate.

[0082] After forming the front and back dielectric layers at 1750 and 1730, the filter device may be completed at 1760. Actions that may occur at 1760 include: depositing and patterning other metal layers to form conductors other than the IDT conductor pattern; depositing a dielectric layer such as SiO on all or part of the device; 2 or Si 3 O 4 The process may be performed by forming a packaging / passivation layer of the device; forming pads or solder bumps or other means for establishing a connection between the device and external circuitry; cutting individual devices from a wafer containing multiple devices; other packaging steps; and testing. Another action that may occur at 1760 is tuning the resonant frequency of a resonator within the device by adding or removing metal or dielectric material from the front side of the device. Once the filter device is complete, the process ends at 1795.

[0083] Conclusion

[0084] Throughout the specification, the embodiments and examples shown should be considered as examples, rather than limitations on the disclosed or required devices and processes. Although many of the examples provided herein relate to specific combinations of method actions or system elements, it should be understood that those actions and those elements can be combined in other ways to achieve the same goals. With respect to the flow charts, additional steps and fewer steps can be taken, and the steps shown can be combined or further refined to achieve the methods described herein. The actions, elements, and features discussed only in conjunction with one embodiment are not intended to exclude similar effects in other embodiments.

[0085] As used herein, "plurality" refers to two or more. As used herein, a "group" of items may include one or more such items. As used herein, whether in a written embodiment or in a claim, the terms "include", "comprising", "carrying", "having", "containing", "involving", etc. should be understood as open-ended, that is, referring to including but not limited to. With respect to the claims, only the transition phrases "consisting of..." and "consisting essentially of..." are closed or semi-closed transition phrases. Ordinal numbers used in the claims, such as "first", "second", "third", etc., are used to modify claim elements, which themselves do not indicate the priority of one claim element over another claim element, or the order, or the order of execution of method actions, but are only used to distinguish one claim element with the same name from another element with the same name (but with ordinal numbers), thereby distinguishing claim elements. As used herein, "and / or" means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

Claims

1. A filter device, comprising: substrate; a piezoelectric layer coupled to the substrate directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interlaced fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric layer and having interlaced fingers over a second cavity of the second BAR device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; as well as a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT, Wherein, the first thickness is greater than the second thickness.

2. The filter device according to claim 1, wherein A difference between a resonant frequency of the first bulk acoustic resonator device and a resonant frequency of the second bulk acoustic resonator device is based in part on a difference between the first thickness and the second thickness.

3. The filter device according to claim 1, wherein: The first thickness is less than or equal to 500 nm, and the second thickness is greater than zero.

4. The filter device according to claim 1, wherein: The first bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of a main lateral excitation electric field generated by the first IDT.

5. The filter device according to claim 4, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

6. The filter device according to claim 4, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

7. The filter device according to claim 1, wherein: The second bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of the main lateral excitation electric field generated by the second IDT.

8. The filter device according to claim 7, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

9. The filter device according to claim 7, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

10. The filter device according to claim 1, wherein: The thickness between the front and back surfaces of the piezoelectric layer is greater than or equal to 200 nm and less than or equal to 1000 nm.

11. The filter device according to claim 1, wherein: A pitch of the first IDT is greater than or equal to 2 times the thickness of the piezoelectric layer and less than or equal to 20 times the thickness of the piezoelectric layer, wherein the pitch is a center-to-center spacing of two adjacent IDT fingers.

12. The filter device according to claim 1, wherein: A pitch of the second IDT is greater than or equal to 2 times the thickness of the piezoelectric layer and less than or equal to 20 times the thickness of the piezoelectric layer, wherein the pitch is a center-to-center spacing of two adjacent IDT fingers.

13. The filter device according to claim 1, wherein: The first dielectric layer and the second dielectric layer include at least one of silicon oxide and silicon nitride.

14. The filter device according to claim 1, wherein: The first IDT includes one of aluminum, aluminum alloy, copper, copper alloy, beryllium, and gold.

15. The filter device according to claim 1, wherein: The z-axis of the piezoelectric layer is perpendicular to the surface of the piezoelectric layer.

16. The filter device according to claim 15, wherein The fingers of the first IDT and the fingers of the second IDT are substantially parallel to the x-axis of the piezoelectric layer.

17. The filter device according to claim 1, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are resonators in a ladder filter structure.

18. The filter device according to claim 1, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are series resonators in a ladder filter structure.

19. The filter device according to claim 1, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are parallel resonators in a ladder filter structure.

20. The filter device according to claim 1, wherein The first bulk acoustic resonator is a parallel resonator in a ladder filter structure, and the second bulk acoustic resonator is a series resonator in the ladder filter structure.

21. The filter device according to claim 1, wherein: The first dielectric layer is a front dielectric layer disposed between the interleaved fingers of the first IDT, and wherein the filter device further comprises a first back dielectric layer disposed on a surface of the piezoelectric layer facing the substrate.

22. The filter device according to claim 1, wherein: The second dielectric layer is a front dielectric layer disposed between the interleaved fingers of the second IDT, and wherein the filter device further comprises a second back dielectric layer disposed on a surface of the piezoelectric layer facing the substrate.

23. The filter device according to claim 1, wherein: The first dielectric layer is disposed between and over the staggered fingers of the first IDT.

24. The filter device according to claim 1, wherein: The second dielectric layer is disposed between and over the interleaved fingers of the second IDT.

25. The filter device according to claim 1, wherein: The first cavity is disposed in an intermediate layer between the piezoelectric layer and the substrate.

26. The filter device according to claim 1, wherein The second cavity is disposed in an intermediate layer between the piezoelectric layer and the substrate.

27. The filter device according to claim 1, wherein: The intermediate layer is a dielectric material.

28. The filter device according to claim 1, wherein: The intermediate layer is a non-piezoelectric material.

29. The filter device according to claim 27, wherein: The intermediate layer includes multiple layers of dielectric material.

30. The filter device according to claim 1, wherein: The first dielectric layer and the second dielectric layer are non-piezoelectric materials.

31. The filter device according to claim 1, wherein: The first IDT is located on a front surface of the piezoelectric layer facing away from the substrate.

32. The filter device according to claim 1, wherein: The second IDT is located on a front surface of the piezoelectric layer facing away from the substrate.

33. The filter device of claim 1, further comprising a first opening through the piezoelectric layer and to the first cavity.

34. The filter device of claim 1 further comprising a second opening through the piezoelectric layer and to the second cavity.

35. A filter device comprising: a substrate, including a base and an intermediate layer; a piezoelectric layer coupled to the substrate; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interlaced fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric layer and having interlaced fingers over a second cavity of the second BAR device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; as well as a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT, Wherein, the first thickness is greater than the second thickness.

36. The filter device of claim 35, wherein: The first bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of a main lateral excitation electric field generated by the first IDT.

37. The filter device of claim 36, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

38. The filter device of claim 36, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

39. The filter device of claim 35, wherein: The second bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of the main lateral excitation electric field generated by the second IDT.

40. The filter device of claim 39, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

41. The filter device of claim 39, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

42. A filter device comprising: A first bulk acoustic resonator device, comprising: substrate; a piezoelectric layer coupled to the substrate; a first interdigital transducer (IDT) on the piezoelectric layer and having interlaced fingers on the piezoelectric layer of the first bulk acoustic resonator device; and a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; A second body acoustic resonator device, comprising: substrate; a piezoelectric layer coupled to the substrate; a second interdigital transducer IDT on the piezoelectric layer and having interlaced fingers on the piezoelectric layer of the second BAR device; and a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT; wherein the first thickness is greater than the second thickness, and The spacing of the first IDT is greater than or equal to twice the thickness of the piezoelectric layer of the first bulk acoustic resonator device and less than 20 times the thickness of the piezoelectric layer of the first bulk acoustic resonator device, and the spacing is the center-to-center spacing of two adjacent IDT fingers of the first bulk acoustic resonator device.

43. The filter device according to claim 42, wherein The first bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of a main lateral excitation electric field generated by the first IDT.

44. The filter device of claim 43, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

45. The filter device of claim 43, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

46. ​​The filter device of claim 42, wherein: The second bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of the main lateral excitation electric field generated by the second IDT.

47. The filter device of claim 46, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

48. The filter device of claim 46, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

49. A filter device comprising: substrate; a piezoelectric plate coupled to the substrate directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric plate and having staggered fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric plate and having staggered fingers over a second cavity of the second BAR device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; as well as a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT, wherein the first thickness is greater than the second thickness, wherein the first bulk acoustic resonator device is configured to excite a first bulk shear wave, the propagation direction of the first bulk shear wave being perpendicular to the direction of a first electric field laterally excited in the piezoelectric plate by the first IDT, and The second bulk acoustic resonator device is configured to excite a second bulk shear wave, the propagation direction of the second bulk shear wave being perpendicular to a direction of a second electric field laterally excited in the piezoelectric plate by the second IDT.

50. A filter device comprising: substrate; a piezoelectric plate coupled to the substrate directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric plate and having staggered fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric plate and having staggered fingers over a second cavity of the second BAR device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; as well as a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT, wherein the first thickness is greater than the second thickness, The first bulk acoustic resonator and the second bulk acoustic resonator are series resonators in a ladder filter structure.

51. A filter device comprising: substrate; a piezoelectric plate coupled to the substrate directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric plate and having staggered fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric plate and having staggered fingers over a second cavity of the second BAR device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; as well as a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT, wherein the first thickness is greater than the second thickness, The first bulk acoustic resonator and the second bulk acoustic resonator are parallel resonators in a ladder filter structure.

52. A filter device comprising: substrate; a piezoelectric layer coupled to the substrate via one or more intermediate layers; a plurality of interdigital transducers (IDTs) on the piezoelectric layer and having interleaved fingers over corresponding cavities in the one or more intermediate layers; The dielectric layer, on the piezoelectric layer at each corresponding IDT, The thickness of the dielectric layer at one IDT is different from the thickness of the dielectric layer at another IDT.

53. The filter device of claim 52, wherein: A difference between a resonant frequency of the first bulk acoustic resonator device and a resonant frequency of the second bulk acoustic resonator device is based in part on a difference between the first thickness and the second thickness.

54. The filter device of claim 52, wherein: The first thickness is less than or equal to 500 nm, and the second thickness is greater than zero.

55. The filter device of claim 52, wherein: At least one of the plurality of IDTs is configured to excite a bulk shear wave having a propagation direction perpendicular to a direction of a primary lateral excitation electric field generated by the at least one of the plurality of IDTs.

56. The filter device of claim 55, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

57. The filter device of claim 55, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

58. A method of manufacturing a filter device on a piezoelectric layer having a front side and a back side, the back side being supported by a substrate, the method comprising: forming one or more cavities such that portions of the piezoelectric layer are located above the cavities; forming a conductor pattern on the piezoelectric layer, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a corresponding plurality of bulk acoustic resonators, the plurality of bulk acoustic resonators comprising a first bulk acoustic resonator and a second bulk acoustic resonator, wherein the interleaved fingers of each of the plurality of IDTs are disposed over a cavity beneath each of the plurality of IDTs; forming a first dielectric layer having a first thickness on the first bulk acoustic resonator, and A second dielectric layer having a second thickness is formed on the second bulk acoustic resonator, wherein The piezoelectric layer and all of the IDTs in the plurality of IDTs are configured such that a radio frequency signal applied to the IDT excites a shear acoustic wave in the piezoelectric layer, and The first thickness is greater than the second thickness.

59. A filter device comprising: substrate; a piezoelectric layer coupled to the substrate directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interlaced fingers over a first cavity of the first bulk acoustic resonator device; a second IDT of a second BAR device on the piezoelectric layer and having interlaced fingers over a second cavity of the second BAR device; a dielectric layer having a first thickness disposed between the staggered fingers of the first IDT and a second thickness disposed between the staggered fingers of the second IDT, Wherein, the first thickness is greater than the second thickness.

60. The filter device of claim 59, wherein: A difference between a resonant frequency of the first bulk acoustic resonator device and a resonant frequency of the second bulk acoustic resonator device is based in part on a difference between the first thickness and the second thickness.

61. The filter device of claim 59, wherein: The first thickness is less than or equal to 500 nm, and the second thickness is greater than zero.

62. The filter device of claim 59, wherein: The first bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of a main lateral excitation electric field generated by the first IDT.

63. The filter device of claim 62, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

64. The filter device of claim 62, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

65. The filter device of claim 59, wherein: The second bulk acoustic resonator device is configured to excite bulk shear waves, the propagation direction of which is perpendicular to the direction of the main lateral excitation electric field generated by the second IDT.

66. A filter device according to claim 65, wherein When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

67. The filter device of claim 65, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

68. The filter device of claim 59, wherein: The thickness between the front and back surfaces of the piezoelectric layer is greater than or equal to 200 nm and less than or equal to 1000 nm.

69. The filter device of claim 59, wherein: A pitch of the first IDT is greater than or equal to 2 times the thickness of the piezoelectric layer and less than or equal to 20 times the thickness of the piezoelectric layer, wherein the pitch is a center-to-center spacing of two adjacent IDT fingers.

70. The filter device of claim 59, wherein: A pitch of the second IDT is greater than or equal to 2 times the thickness of the piezoelectric layer and less than or equal to 20 times the thickness of the piezoelectric layer, wherein the pitch is a center-to-center spacing of two adjacent IDT fingers.

71. The filter device of claim 59, wherein: The dielectric layer includes at least one of silicon oxide and silicon nitride.

72. The filter device of claim 59, wherein: The first IDT includes one of aluminum, aluminum alloy, copper, copper alloy, beryllium, and gold.

73. The filter device of claim 59, wherein: The z-axis of the piezoelectric layer is perpendicular to the surface of the piezoelectric layer.

74. A filter device according to claim 73, wherein: The fingers of the first IDT and the fingers of the second IDT are substantially parallel to the x-axis of the piezoelectric layer.

75. The filter device of claim 59, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are resonators in a ladder filter structure.

76. The filter device of claim 59, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are series resonators in a ladder filter structure.

77. The filter device of claim 59, wherein: The first bulk acoustic resonator and the second bulk acoustic resonator are parallel resonators in a ladder filter structure.

78. The filter device of claim 59, wherein: The first bulk acoustic resonator is a parallel resonator in a ladder filter structure, and the second bulk acoustic resonator is a series resonator in the ladder filter structure.

79. The filter device of claim 59, wherein: The dielectric layer is a front dielectric layer, and wherein the filter device further comprises a back dielectric layer arranged on a surface of the piezoelectric layer facing the substrate.

80. The filter device of claim 59, wherein: The dielectric layer is disposed between and over the interleaved fingers of the first and second IDTs.

81. The filter device of claim 59, wherein: The first cavity is disposed in an intermediate layer between the piezoelectric layer and the substrate.

82. The filter device of claim 59, wherein: The second cavity is disposed in an intermediate layer between the piezoelectric layer and the substrate.

83. The filter device of claim 59, wherein: The intermediate layer is a dielectric material.

84. The filter device of claim 59, wherein: The intermediate layer is a non-piezoelectric material.

85. The filter device of claim 83, wherein: The intermediate layer includes multiple layers of dielectric material.

86. The filter device of claim 59, wherein: The dielectric layer is a non-piezoelectric material.

87. The filter device of claim 59, wherein: The first IDT is located on a front surface of the piezoelectric layer facing away from the substrate.

88. The filter device of claim 59, wherein: The second IDT is located on a front surface of the piezoelectric layer facing away from the substrate.

89. The filter device of claim 59, further comprising a first opening through the piezoelectric layer and to the first cavity.

90. The filter device of claim 59, further comprising a second opening through the piezoelectric layer and to the second cavity.

91. A filter device comprising: substrate; a piezoelectric layer coupled to the substrate; an interdigital transducer (IDT) of a bulk acoustic resonator device on the piezoelectric layer and having interlaced fingers over the cavity of the bulk acoustic resonator device; as well as A dielectric layer is disposed between the interleaved fingers of the IDT to change the frequency of the bulk acoustic resonator device.

92. The filter device of claim 91, wherein: The substrate includes a silicon wafer.

93. The filter device of claim 91, wherein: The dielectric layer includes silicon oxide.

94. The filter device of claim 91, wherein: The cavity of the bulk acoustic resonator device extends into the substrate.

95. The filter device of claim 91, wherein: The bulk acoustic resonator device is configured to excite bulk shear waves whose propagation direction is perpendicular to the direction of the main lateral excitation electric field generated by the IDT.

96. The filter device of claim 95, wherein: When the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

97. The filter device of claim 95, wherein: When the atomic motion of the bulk shear wave is primarily parallel to the surface of the piezoelectric layer, the electric field is primarily excited in the transverse direction.

98. The filter device of claim 95, wherein: Acoustic vibrations are minimally excited beneath the fingers of the IDT.

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