Laterally excited thin film bulk acoustic resonator with anti-chirp interdigital transducer (IDT) for mechanical and process compensation

Abstract

The acoustic wave resonator has a piezoelectric plate having a first surface and a second surface, the second surface facing the substrate, and a diaphragm of the piezoelectric plate spanning the cavity. A conductor pattern is formed on at least one of the first surface and the second surface and has an interdigital transducer (IDT) having interleaved fingers on a diaphragm portion of the piezoelectric plate. At least one of a pitch of the interleaved IDT fingers or a mark of the interleaved IDT fingers varies over a region of the IDT to compensate for process-induced deformation of a diaphragm portion of the piezoelectric plate.

Description

[0001] This application is a divisional application of the patent application filed on December 9, 2022, with application number 202211585923.9 and invention title "LATERALLY EXCITED THIN FILM BULK ACOUSTIC WAVE RESONATOR WITH COUNTER CHIRPED INTERDIGITAL TRANSDUCER (IDT) FOR MECHANICAL AND PROCESS COMPENSATION". Cross - reference to related applications

[0002] This patent claims the priority of co - pending U.S. Provisional Patent Application No. 63 / 287,927, titled "COUNTER CHIRPED XBAR RESONATORS FOR MECHANICAL AND PROCESS COMPENSATION", filed on December 9, 2021. Technical field

[0003] The present disclosure relates to radio frequency (RF) filters using acoustic wave resonators, and more particularly to filters for communication devices. Background art

[0004] An RF filter is a two - port device configured to pass certain frequencies and block others, where "pass" means transmission with relatively low signal loss and "stop" means blocking or substantially attenuating. The frequency range that the filter passes is called the "passband" of the filter. The frequency range that such a filter stops is called the "stopband" of the filter. A typical RF filter has at least one passband and at least one stopband. Specific requirements for the passband or stopband depend on the specific application. For example, the "passband" can be defined as the frequency range where the insertion loss of the filter is better than a defined value such as 1 dB, 2 dB, or 3 dB. The "stopband" can be defined as the frequency range where the rejection of the filter is greater than a defined value such as 20 dB, 30 dB, 40 dB or more, depending on the application.

[0005] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in the RF front - ends of cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptop computers and tablet computers, point - to - point radio links, and other communication systems. RF filters are also used in radar, electronic, and information warfare systems.

[0006] 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, etc. and cost for each specific application. Specific design and manufacturing methods and enhancements can benefit from one or more of these requirements simultaneously.

[0007] Performance enhancement of RF filters in wireless systems can have a wide impact on system performance. Improvements to RF filters can be used to provide system performance improvements such as larger cell sizes, longer battery life, higher data rates, greater network capacity, lower costs, enhanced security, higher reliability, etc. These improvements can be achieved individually and in combination at multiple levels of a wireless system (e.g., at the RF module, RF transceiver, mobile or fixed subsystem, or network level).

[0008] High-performance RF filters for current communication systems typically include acoustic wave resonators, which include surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, thin film bulk acoustic wave resonators (FBAR), and other types of acoustic wave resonators. However, these existing technologies are not very suitable for use at the higher frequencies and bandwidths proposed for future communication networks.

[0009] The desire for wider communication channel bandwidths will inevitably lead to the use of higher frequency communication bands. The radio access technologies for mobile phone networks have been standardized by 3GPP (Third Generation Partnership Project). The radio access technologies for the 5th generation mobile network are defined in the 5G NR (New Radio) standard. The 5G NR standard defines several new communication bands. Two of these new communication bands are: n77, which uses a frequency range from 3300 MHz to 4200 MHz; and n79, which uses a frequency range from 4400 MHz to 5000 MHz. Both band n77 and band n79 use time division duplex (TDD), such that communication devices operating in band n77 and / or band n79 use the same frequency for uplink and downlink transmissions. The bandpass filters for bands n77 and n79 must be able to handle the transmission power of the communication devices. The 5 GHz and 6 GHz WiFi bands also require high frequencies and wide bandwidths. The 5G NR standard also defines millimeter wave communication bands with frequencies between 24.25 GHz and 40 GHz.

[0010] A laterally excited film bulk acoustic resonator (XBAR) is an acoustic resonator structure for microwave filters. The XBAR is described in the patent US 10,491,291 entitled "TRANSVERSELY EXCITED FILM BULK ACOUSTIC RESONATOR". The XBAR resonator includes an interdigital transducer (IDT) formed on a thin floating layer or diaphragm of a single crystal piezoelectric material, or formed on a substrate having a thin floating layer or diaphragm of a single crystal piezoelectric material. The IDT includes a first set of parallel fingers extending from a first bus bar and a second set of parallel fingers extending from a second bus bar. The first set of parallel fingers and the second set of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear dominant acoustic wave in the piezoelectric diaphragm. The XBAR resonator provides very high electromechanical coupling and high frequency capabilities. The XBAR resonator can be used in various RF filters including band-stop filters, band-pass filters, diplexers and multiplexers. The XBAR is well suited for filters in communication frequency bands above 3 GHz. Summary of the Invention

[0011] According to a first aspect of the present application, there is provided an acoustic resonator, comprising: a piezoelectric plate having a first surface and a second surface facing each other, the second surface facing a substrate, a diaphragm of the piezoelectric plate spanning a cavity; and a conductor pattern provided on at least one of the first surface and the second surface, the conductor pattern including an interdigital transducer IDT having interleaved fingers on the diaphragm of the piezoelectric plate, wherein at least one of a pitch of the interleaved IDT fingers or a mark of the interleaved IDT fingers varies over a region of the IDT to compensate for a process-induced deformation of the diaphragm of the piezoelectric plate.

[0012] According to a second aspect of the present application, there is provided a filter device, comprising: a piezoelectric plate having a first surface and a second surface facing each other, the second surface facing a substrate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in an intermediate layer of the substrate; a conductor pattern on at least one of the first surface and the second surface, the conductor pattern including a plurality of interdigital transducers IDT, the interleaved fingers of each IDT being on a respective diaphragm of the plurality of diaphragms, wherein at least one of a pitch of the interleaved fingers of each IDT or a mark varies on the respective diaphragm to compensate for a process-induced deformation of the respective diaphragm.

[0013] According to a third aspect of the present application, there is provided a method of manufacturing an acoustic resonator device, comprising: attaching an intermediate layer of a substrate to a piezoelectric plate; and forming an interdigital transducer (IDT) on at least one surface of the piezoelectric plate, the IDT comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device; forming at least one of a pitch of the interleaved IDT fingers or a mark of the interleaved IDT fingers that varies over the aperture to compensate for a process-induced deformation of the diaphragm; and forming a cavity below the aperture, wherein forming the cavity creates a process-induced deformation of the diaphragm and results in a constant pitch and mark of the IDT fingers. Description of the Drawings

[0014] Figure 1 Schematic plan view and two schematic cross-sectional views of a laterally excited thin film bulk acoustic resonator (XBAR).

[0015] Figure 2 is Figure 1 An enlarged schematic cross-sectional view of a part of the XBAR.

[0016] Figure 3A An alternative schematic cross-sectional view of the XBAR.

[0017] Figure 3B Illustration of the main acoustic mode of interest in the XBAR.

[0018] Figure 4A A simplified schematic cross-sectional side view of an XBAR showing an interdigital transducer (IDT) without anti-chirp for mechanical and process compensation.

[0019] Figure 4B Shows Figure 4A A simplified schematic cross-sectional side view of the XBAR after forming the cavity or during use.

[0020] Figure 4C A simplified schematic cross-sectional side view of an XBAR showing an IDT with anti-chirp for mechanical and process compensation.

[0021] Figure 4D Shows Figure 4C A simplified schematic cross-sectional side view of the XBAR after forming the cavity or during use.

[0022] Figure 4E and Figure 4F Shows Figure 4A and Figure 4B A simplified schematic plan view of the XBAR.

[0023] Figure 4G and Figure 4H Shows Figure 4Cand Figure 4D Simplified schematic plan view of the XBAR.

[0024] Figure 5 Schematic block diagram of a filter using the XBAR.

[0025] Figure 6 Flow chart of a conventional process for fabricating the XBAR.

[0026] Figure 7 Graph showing the definition of the curvature of a straight or curved shape.

[0027] Throughout this specification, the elements shown in the figures are assigned three - digit or four - digit reference numerals, where the two least - significant digits are specific to the element, and one or two of the most - significant digits are the figure number in which the element is first introduced. It can be assumed that the characteristics and functions of elements not described in conjunction with the figures are the same as those of previously described elements with the same reference numerals. Detailed Description Description of the Device

[0028] The laterally - excited film bulk acoustic resonator (XBAR) is a new resonator structure for microwave filters. The XBAR is described in U.S. Patent No. 10,491,291 entitled "TRANSVERSELY EXCITED FILM BULK ACOUSTIC RESONATOR", the entire content of which is incorporated herein by reference. The XBAR resonator includes a conductor pattern having interdigital transducers (IDTs) formed on a thin floating layer or diaphragm of a piezoelectric material. The IDT has two bus bars, each bus bar attached to a set of fingers, and the two sets of fingers are interleaved on the diaphragm above a cavity formed in a substrate on which the resonator is mounted. The diaphragm spans the cavity and may include front - side and / or back - side dielectric layers. A microwave signal applied to the IDT excites a shear - dominant acoustic wave in the piezoelectric diaphragm such that the acoustic energy flows substantially perpendicular to the surface of the layer, which is orthogonal or transverse to the direction of the electric field generated by the IDT. The XBAR resonator provides very high electromechanical coupling and high - frequency capabilities.

[0029] In this context, the coupling can be the frequency separation between the resonance and anti - resonance of the resonator. The frequency separation can be proportional to the "electromechanical coupling", which is the ratio of mechanical energy (e.g., the energy input to the A1 mode of the resonator for an A1 mode resonator) to the electrical input energy. In this sense, the "electromechanical coupling" is the degree to which the input electrical energy is "coupled" to the mechanical A1 XBAR mode that is to be excited.

[0030] The piezoelectric diaphragm can be part of a single crystal piezoelectric material plate spanning a cavity in a substrate. The piezoelectric membrane can be a diaphragm and can include a front side and / or a back side dielectric layer. The XBAR resonator can be a membrane or diaphragm having an IDT formed on the membrane or diaphragm.

[0031] The membrane of the XBAR can be deformed or bent due to stresses accumulated during the process of manufacturing the resonator and due to temperature variations during operation or use. In either case, the deformation of the membrane will result in a corresponding deformation of the IDT, which includes changes in the pitch and width of the interleaved IDT fingers. Since the deformation due to process stresses is somewhat predictable, the deformation of the IDT can be compensated by pre-deforming the IDT, e.g., by anti-chirping the IDT to mechanically and process compensate for the deformation due to process stresses.

[0032] Improved XBAR resonators, filters, and fabrication techniques for XBAR resonators are described below, which have an anti-chirped IDT for mechanically and process compensating for membrane deformation or bending due to process stresses. The pitch of the interleaved IDT fingers along the length (dimension L) direction of the XBAR and / or the markings (e.g., line width) of the interleaved IDT fingers along the aperture (dimension AP) direction of the XBAR can vary over the region of the IDT (e.g., the aperture or the membrane) to compensate for process-induced deformation of the membrane.

[0033] Anti-chirping the IDT can include: anti-chirping or pre-chirping the finger pitch and / or markings of adjacent fingers to have different pitches and / or markings on the plate in one processing step such that the adjacent fingers will have a constant pitch and / or marking after a later processing step, resulting in deformation along the length (dimension L) direction and / or aperture (dimension AP) direction of the XBAR due to process stresses. Anti-chirping the IDT provides mechanical and process compensation for deformation due to later process stresses (e.g., due to forming the cavity, etching the cavity, and / or releasing the membrane).

[0034] Figure 1 A simplified schematic top view and an 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 various RF filters including bandstop filters, bandpass filters, diplexers, and multiplexers. XBARs are particularly suitable for filters in communication frequency bands above 3 GHz.

[0035] The XBAR 100 is composed of thin-film conductor patterns formed on the surfaces of a piezoelectric plate 110 having parallel front surface 112 and rear surface 114. The front surface 112 and the rear surface 114 can also be more generally regarded as the first surface and the second surface. In addition, 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 such that the orientations of the X, Y, and Z crystal axes with respect to the front and rear surfaces are known and consistent. The piezoelectric plate can be Z-cut (i.e., the Z-axis is perpendicular to the front surface 112 and the rear surface 114), rotationally Z-cut, or rotationally YX-cut. The piezoelectric plate can be Y-cut (i.e., the Y-axis is perpendicular to the front surface 112 and the rear surface 114), rotationally Y-cut. The XBAR can be fabricated on piezoelectric plates with other crystal orientations.

[0036] The rear surface 114 of the piezoelectric plate 110 is attached to a substrate 120 that provides mechanical support to the piezoelectric plate 110. The substrate 120 can be, for example, silicon, sapphire, quartz, or some other material. The substrate can have a layer of silicon thermal oxide (TOX) and crystalline silicon. The rear surface 114 of the piezoelectric plate 110 can be bonded to the substrate 120 using a wafer bonding process, grown on the substrate 120, or attached to the substrate in some other way. The piezoelectric plate is directly attached to the substrate or can be attached to the substrate via a buried oxide (BOX) layer or an intermediate layer 122 (e.g., a layer of SiO2 or another oxide such as Al2O3).

[0037] As Figure 1 shown, the diaphragm 115 abuts the remainder of all the peripheries 145 of the piezoelectric plate 110 surrounding the cavity 1. In this context, "abut" means "connected continuously without any intermediary". However, a buried oxide layer (BOX) can bond the plate 110 to the substrate 120. The BOX layer can be present between the plate and the substrate around the periphery 145 and can extend away from the cavity rather than only within the periphery itself. In the process without removing the BOX layer (i.e., the present invention), the BOX is ubiquitous between the piezoelectric plate and the substrate. As part of forming the cavity, the BOX is typically removed from the rear side of the diaphragm 115.

[0038] The conductor pattern of the XBAR 100 includes an interdigital transducer (IDT) 130. The IDT 130 includes a first plurality of parallel fingers (e.g., finger 136) extending from a first bus bar 132 and a second plurality of fingers extending from a second bus bar 134. The first plurality of parallel fingers and the second plurality of parallel fingers are interleaved. The interleaved fingers 136 overlap a distance AP, and the distance AP is generally referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of the IDT 130 is the "length" of the IDT. As Figure 1As shown, the IDT 130 can be formed on the upper surface 112 (i.e., the first surface of the plate 110) facing away from the cavity 140, as described below. However, in an alternative aspect, the IDT 130 can be disposed on the bottom surface 114 (i.e., the second surface of the plate 110) directly facing the cavity 110. Thus, according to an exemplary aspect, the exemplary configuration of the IDT 130 can be applied to either (or both) surfaces of the piezoelectric plate 110.

[0039] There is a gap distance gd from the tip of the IDT finger end to the nearest surface of the opposing busbar. The distance gd can be in the range between 1 and 10 um. The gap distance gd can be in a direction tangential to the tip of the finger end. The gap distance gd can be between 1 and 5 um. The gap distance gd can be between 2 um and 4 um. The gap distance gd can be 3 um. The gap distance gd can be the pitch p minus the finger mark m or width.

[0040] The first busbar 132 and the second busbar 134 serve as terminals or electrodes of the XBAR 100. A radio frequency or microwave signal applied between the two busbars 132, 134 of the IDT 130 excites a primary acoustic wave mode within the piezoelectric plate 110. As will be discussed in further detail, the excited primary acoustic wave mode is a bulk shear mode, where the acoustic energy propagates in a direction substantially orthogonal 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. Thus, the XBAR is regarded as a laterally excited thin-film bulk acoustic wave resonator.

[0041] The cavity 140 is formed in the substrate 120 such that the portion 115 of the piezoelectric plate 110 containing the IDT 130 is suspended above the cavity 140 without contacting the substrate 120 or the bottom of the cavity. The conventional meaning of "cavity" is "an empty space within a solid body". The cavity can contain gas, air, or a vacuum. In some cases, there is also a second substrate, package, or other material having a cavity (not shown) above the plate 110, which can be a mirror image of the substrate 120 and the cavity 140. The cavity above the plate 110 can have a depth of empty space greater than that of the cavity 140. The fingers (and optionally portions of the busbars) extend over (or between) the cavities. The cavity 140 can be a hole that completely penetrates the substrate 120 (as shown in the A-A cross-section and B-B cross-section of Figure 1 ), or a groove in the substrate 120 (as shown subsequently Figure 3A ). The cavity 140 can be formed, for example, by selectively etching the substrate 120 before or after attaching the piezoelectric plate 110 and the substrate 120. As Figure 1As shown, the cavity 140 has a rectangular shape, which is larger in extent than the aperture AP and length L of the IDT 130. The cavity of the XBAR can have different shapes, such as regular or irregular polygons. The cavity of the XBAR can have more or fewer than four side surfaces, and these side surfaces can be straight or curved.

[0042] Since the portion 115 of the piezoelectric plate that is suspended above the cavity 140 is physically similar to the diaphragm of a microphone, it will be referred to herein as the "diaphragm" (for lack of a better term). The diaphragm can be continuously and seamlessly connected to the remainder of the piezoelectric plate 110 that surrounds all or substantially all of the perimeter of the cavity 140. In this context, "adjacent" means "connected continuously without any intermediary". In some cases, the BOX layer can bond the plate 110 to the substrate 120 around the perimeter.

[0043] For ease of presentation in Figure 1 the geometric pitch and width of the IDT 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. The XBAR can have hundreds or even thousands of parallel fingers in the IDT 110. Similarly, the thickness of the fingers in the cross-sectional view is greatly exaggerated.

[0044] Figure 2 Shows Figure 1 A detailed schematic cross-sectional view of the XBAR 100. The cross-sectional view can be a portion of the XBAR 100 that includes the IDT fingers. The piezoelectric plate 110 is a layer of single-crystal piezoelectric material having a thickness ts. Ts can be, for example, 100 nm to 1500 nm. When used in a filter for the LTE TM bands from 3.4 GHz to 6 GHz (e.g., bands 42, 43, 46), the thickness ts can be, for example, 200 nm to 1000 nm.

[0045] The plate 110 can be Z-cut LN, 82-Y-cut LN, 120-Y-cut LN, or 128-Y-cut LN. In some cases, the plate 110 can be cut within the following ranges: between 82-Y-cut and Z-cut; or between 110-Y-cut and 157-Y-cut. The plate 110 can have a thickness ts between 70 nm and 500 nm. The plate 110 can have a thickness ts between 350 nm and 450 nm.

[0046] The front-side dielectric layer 214 can optionally be formed on the front side of the piezoelectric plate 110. By definition, the "front side" of the XBAR is the surface facing away from the substrate. The front-side dielectric layer 214 has a thickness tfd. The front-side dielectric layer 214 is formed between the IDT fingers 236. Although not shown in Figure 2As shown, the front-side dielectric layer 214 can also be deposited over the IDT fingers 236. The back-side dielectric layer 216 can optionally be formed on the back side of the piezoelectric plate 110. The back-side dielectric layer 216 has a thickness tbd. The front-side dielectric layer 214 and the back-side dielectric layer 216 can be non-piezoelectric dielectric materials such as silicon dioxide or silicon nitride. tfd and tbd can be, for example, from 0 to 500 nm. tfd and tbd are generally less than the thickness ts of the piezoelectric plate. tfd and tbd are not necessarily equal, and the front-side dielectric layer 214 and the back-side dielectric layer 216 are not necessarily the same material. Either or both of the front-side dielectric layer 214 and the back-side dielectric layer 216 can be formed of a multi-layer of two or more materials.

[0047] The front-side dielectric layer 214 can be formed over the IDT of some (e.g., selected) XBAR devices in the filter. The front-side dielectric layer 214 can be formed between and cover the IDT fingers of some XBAR devices, but not formed on other XBAR devices. For example, the front-side frequency-setting dielectric layer can be formed over the IDT of a parallel resonator to reduce the resonance frequency of the parallel resonator relative to the resonance frequency of a series resonator having a thinner front-side dielectric layer or no front-side dielectric layer. Some filters can include two or more different thickness front-side dielectric layers over various resonators. The resonance frequency of the resonator can be set such that the resonator is "tuned" at least in part by selecting the thickness of the front-side dielectric layer.

[0048] In addition, a passivation layer can be formed over the entire surface of the XBAR device 100 except at the contact pads where electrical connection is made to a circuit external to the XBAR device. The passivation layer is a thin dielectric layer that is intended to seal and protect the surface of the XBAR device when the XBAR device is incorporated into a package. The front-side dielectric layer and / or the passivation layer can be SiO2, Si3N4, Al2O3, some other dielectric material, or a combination of these materials.

[0049] The thickness of the passivation layer can be selected to protect the piezoelectric plate and the metal electrodes from water and chemical corrosion, particularly for power durability purposes. The thickness of the passivation layer can be in the range of 10 nm to 100 nm. The passivation material can consist of multiple oxide and / or nitride coatings (e.g., SiO2 and Si3N4 materials).

[0050] The IDT fingers 236 can be one or more layers of aluminum or substantially aluminum alloy, copper or substantially copper alloy, beryllium, tungsten, molybdenum, gold, or some other conductive material. Thin (relative to the total thickness of the conductor) layers of other metals such as chromium or titanium can be formed under and / or over the fingers to improve the adhesion between the fingers and the piezoelectric plate 110, and / or passivate or encapsulate the fingers. The busbars of the IDT ( Figure 1132 and 134) in can be made of the same or different materials as these fingers.

[0051] The dimension p is the center-to-center spacing or "pitch" of the IDT fingers, which can be referred to as the pitch of the IDT and / or the pitch of the XBAR. When the center-to-center spacing of the IDT fingers varies along the length of the IDT, the "pitch" is the average of the center-to-center spacings of all adjacent finger pairs. The dimension w is the width or "finger" of the IDT fingers. The IDT of the XBAR is significantly different from the IDT used in surface acoustic wave (SAW) resonators. In a SAW resonator, the pitch of the IDT is one-half of the acoustic wavelength at the resonance frequency. Additionally, the finger pitch of the SAW resonator IDT is typically close to 0.5 (i.e., the finger or finger width is approximately one-quarter of the acoustic wavelength at resonance). In the XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of these fingers. Additionally, the pitch p of the IDT is typically 2 to 20 times the thickness ts of the piezoelectric plate 212. The pitch p can be between 3 um and 8 um. The pitch p can be between 4 um and 5 um. The plate thickness ts can be between 300 nm and 500 nm. The plate thickness ts can be 400 nm. The finger width w can be between 0.5 um and 7.5 um. The finger width w can be 1 um. The width of the IDT fingers in the XBAR is not limited to one-quarter of the acoustic wavelength at resonance. For example, the width of the XBAR IDT fingers can be 500 nm or greater, such that the IDT can be fabricated using optical lithography. The thickness tm of the IDT fingers can range from 100 nm to approximately equal to the width w. The busbars ( Figure 1 of 132, 134) in can have a thickness equal to or greater than the thickness tm of the IDT fingers.

[0052] Figure 3A is an alternative cross-sectional view of the XBAR device 300 along Figure 1 the cross-section A-A defined in. In Figure 3A the piezoelectric plate 310 is attached to the intermediate layer 322 of the substrate 320. A portion of the piezoelectric plate 310 forms a diaphragm 315 spanning the cavity 340 in the substrate. The cavity 340 does not completely penetrate the intermediate layer 322 but is formed in the layer 322 below the portion of the piezoelectric plate 310 that contains the IDT 330 of the XBAR's conductor pattern (e.g., the first metal or M1 layer). The IDT fingers (e.g., finger 336) are disposed on the diaphragm 315. The interconnection of the IDT (e.g., busbars) 330 to the signal and ground paths can pass through a second conductor pattern (e.g., the M2 metal layer, not shown in Figures 1 to 3A to other conductor patterns and / or to electrical contacts on the package.

[0053] The plate 310, diaphragm 315, and fingers 336 can be the plate 110, diaphragm 115, and fingers 136 (or 236). The cavity 340 can be formed, for example, by etching the layer 322 before attaching the piezoelectric plate 310. Alternatively, the cavity 340 can be formed by etching the layer 322 with a selective etchant that reaches the layer 322 through one or more holes or openings 342 provided in the piezoelectric plate 310. The diaphragm 315 can be adjacent to most of the remainder of the piezoelectric plate 310 around the perimeter 345 of the cavity 340. For example, the diaphragm 315 can be adjacent to at least 50% of the remainder of the perimeter of the piezoelectric plate 310 around the cavity 340.

[0054] The intermediate layer 322 can be one or more intermediate material layers attached between the plate 310 and the substrate 320. The intermediate layer can be or include a bonding layer, BOX layer, etch stop layer, sealing layer, adhesive layer, or other material layers attached or bonded to the plate 310 and the substrate 320. The layers of the layer 322 can be dielectrics, oxides, silicon oxides, silicon nitrides, aluminum oxides, silicon dioxides, or silicon nitrides. The layer 322 can be one or more of any of these layers or a combination of these layers.

[0055] Although the cavity 340 is shown in cross-section, it should be understood that the lateral extent of the cavity is a continuous closed belt region of the layer 322 that surrounds and defines the dimensions of the cavity 340 in a direction perpendicular to the plane of the drawing. The lateral (i.e., left and right as shown in the figure) extent of the cavity 340 is defined by the lateral edge layer 322. The vertical (i.e., downward from the plate 310 as shown) extent or depth of the cavity 340 into the layer 322. In this case, the cavity 340 has a rectangular or approximately rectangular side cross-section.

[0056] Figure 3A The XBAR 300 shown will be referred to herein as a "front-side etch" configuration because the cavity 340 is etched (before or after attaching the piezoelectric plate 310) from the front side of the layer 322. Figure 1 The XBAR 100 will be referred to herein as a "back-side etch" configuration because the cavity 140 is etched from the back side of the substrate 120 after attaching the piezoelectric plate 110. The XBAR 300 shows one or more openings 342 in the piezoelectric plate 310 at the left and right sides of the cavity 340. However, in some cases, the openings 342 in the piezoelectric plate 310 are only at the left or right side of the cavity 340.

[0057] In some cases, the layer 322 is absent, and the plate is directly bonded to the substrate 320; and the cavity is formed in and etched into the substrate 320.

[0058] In some cases, although not shown in the figure, layer 322 is a layer thinner than the cavity depth such that the plate is directly bonded to layer 322; and the cavity is formed in and etched into layer 322 and substrate 320. Here, the cavity extends completely through layer 322 and has a cavity bottom in substrate 320.

[0059] Figure 3B is a diagram of the main acoustic wave mode of interest in the XBAR. Figure 3B Shows a small portion of XBAR 350, including piezoelectric plate 310 and three interleaved IDT fingers 336. XBAR 350 can be part of any XBAR in this document. An RF voltage is applied to the interleaved fingers 336. This voltage creates a time-varying electric field between these fingers. The direction of the electric field is mainly lateral, or parallel to the surface of piezoelectric plate 310, as indicated by the arrow labeled "Electric Field". Due to the high dielectric constant of the piezoelectric plate, the electric field is highly concentrated in the plate relative to air. The lateral electric field creates a shear deformation in piezoelectric plate 310 and thus strongly excites the main shear mode acoustic wave mode. In this context, "shear deformation" is defined as a deformation in which parallel planes in a material remain parallel and maintain a constant distance while translating relative to each other. "Shear acoustic mode" is defined as an acoustic vibration mode in a medium that causes shear deformation of the medium. The shear deformation in XBAR 350 is represented by curve 360, where adjacent small arrows provide a schematic indication of the direction and magnitude of atomic motion. For ease of visualization, the degree of atomic motion and the thickness of piezoelectric plate 310 have been greatly exaggerated. Although the atomic motion is mainly lateral (i.e., in the horizontal direction as Figure 3B shown), the direction of the acoustic energy flow of the excited main shear acoustic wave mode is substantially orthogonal to the front and back surfaces of the piezoelectric plate, as indicated by arrow 365.

[0060] Acoustic wave resonators based on shear acoustic wave resonance can achieve better performance than current state-of-the-art thin film bulk acoustic wave resonators (FBARs) and solidly mounted resonator bulk acoustic wave (SMR BAW) devices in which the electric field is applied in the thickness direction. Compared with other acoustic wave resonators, the piezoelectric coupling of shear wave XBAR resonance can be relatively high (>20%). The high piezoelectric coupling enables the design and implementation of microwave and millimeter-wave filters with a significant bandwidth.

[0061] Figure 4A Shows a simplified schematic cross-sectional side view of XBAR 400 without an interleaved finger transducer (IDT) with anti-chirping for mechanical and process compensation. Figures 4A to 4D Shows regarding Figure 1Or a view of cross-section A-A of FIG. 3. Device 400 may represent a version of devices 100, 300, and / or 350 without an anti-chirp IDT 433. Device 400 is shown to have a constant pitch p of interleaved IDT fingers 437 in the length (dimension L) direction of the XBAR and a constant pitch w of interleaved IDT fingers 437 in the aperture (dimension AP) direction of the XBAR, where the constant pitch p and constant pitch w do not vary over the region of the IDT to compensate for process-induced deformation of the diaphragm portion of the piezoelectric plate 417. Figure 4A All or part of the diaphragm portion is shown, for example, by showing only part or all of the diaphragm 315.

[0062] XBAR 400 may be a version of the XBAR before the diaphragm portion of the plate 417 is deformed due to process-induced mechanical displacement and / or stress that varies in a direction tangent to the length of the fingers or in the direction of the width w and pitch p. XBAR 400 may be a version of the XBAR before the formation of the cavity 340 causes mechanical or process-driven spatial variations in the plate, or after the formation of the cavity 340 (e.g., during use of the XBAR in a filter) and before compensating for temperature variations in the plate.

[0063] Figure 4B A simplified schematic cross-sectional side view of XBAR 425 is shown, which is XBAR 400 after the formation of the cavity 340 or during use and without mechanical and process compensation. Device 425 is shown to have a varying pitch p_i of interleaved IDT fingers 438 and / or a varying pitch wi of interleaved IDT fingers 438, where the varying pitch p_i and varying pitch wi vary over the region of the IDT 435 because Figure 4A the constant pitch p and constant pitch w do not compensate for process-induced deformation of the diaphragm portion of the piezoelectric plate 418.

[0064] Compared to the deformation of the diaphragm of the plate 417, due to the deformation of the diaphragm of the plate 418, the pitch p_i and pitch wi vary in XBAR 425, as shown by increasing the height dd of the plate 418 (compared to the height of the plate 417) before the diaphragm portion is deformed due to the process. In some cases, only one of the pitch or pitch varies in XBAR 425 compared to XBAR 400.

[0065] XBAR 425 can be a version of XBAR 400 after the diaphragm portion of plate 418 has been deformed due to process-induced mechanical displacement and / or stress that varies in a direction tangential to the length of the finger or in the direction of width wi and pitch pi. XBAR 425 can be a version of XBAR 400 after compensating for temperature variations in plate 418 after mechanical or process-driven spatial variations dd caused by the formation of cavity 340 or after the formation of cavity 340 (e.g., during the use of XBAR 425 in a filter).

[0066] As Figure 4B shown in equation 405, the pitch (and markings) of the IDT of XBAR 425 can vary according to p i = (p 2 + h i 2 ) 1 / 2 vary in the direction of the pitch and markings (e.g., perpendicular to the finger length), where i is an integer representing the pitch between adjacent fingers or the marking of a finger, p i is the pitch or marking variation of the finger, p is the length in the direction of the pitch or the process-induced deformation of the finger, and h is the height of the pitch or the process-induced deformation of the finger. The sum of all h i on the diaphragm can be equal to the distance of variation dd.

[0067] XBAR 425 can be an example of mechanically inducing IDT chirping. For example, XBAR 400 can be a synchronous resonator on a flat substrate (e.g., an unreleased piezoelectric plate or piezoelectric wafer without cavity 340 beneath it), which will have a uniform pitch. However, the released diaphragm of XBAR 425 (e.g., after the formation of cavity 340) will have a deflection curvature that slightly disturbs the pitch of each electrode, thereby causing a gradient of the acoustic wave vector, or simply chirping in the pitch and possibly the markings. Residual stress that disturbs the diaphragm stiffness has a similar effect in causing a gradient of the speed of sound or chirping of the speed of sound. The gradients caused by the released diaphragm and / or residual stress can be the sum of variation dd or h i .

[0068] Thus, it is known that XBAR diaphragms have mechanical displacements and stresses that vary with position along the length of the resonator or diaphragm. In addition, processing can also introduce variations with systematic size gradients. These spurious tones cause "process deviations" that simulate the IDT chirping effect in the released diaphragm or during use. Figure 4A and Figure 4B show this variation as the sum of variation dd or h i and this chirping as an example of pitch pi and marking wi.

[0069] However, if this analog effect of the IDT chirp is not desired, an IDT pitch "anti-chirp" can be used to compensate for these mechanically and process-driven spatial variations and chirp. When a physical mechanism (e.g., diaphragm deflection) causes an IDT chirp with a spatial distribution, the resonator can be drawn and / or designed in its computer-aided design (CAD) layout to have an equal magnitude and opposite polarity chirp, or be pre-chirped for compensation. Given the sum of the known variations dd or hi, the anti-chirp can compensate for the chirped pitch pi and mark wi. This effectively extends the "process deviation" correction from spatially uniform correction to correction with a spatial gradient. Process deviation is the small dimensional variation used to draw a pattern on a CAD layout that results in the best or expected dimensions in the as-built dimensions of a fabricated microstructure or nanostructure. Optical lithography and etching, for example, can both result in a microstructure or nanostructure on a mask reticle that is different from the CAD dimensions. For an IDT on a flat surface with uniform piezoelectric properties, a constant process deviation would be required for the drawn dimensions in the CAD layout for all pitch and mark sizes. According to an exemplary aspect, a process deviation that depends on the position of the IDT on the diaphragm is used since the diaphragm has some curvature or other non-uniformity that can be predicted from the position of the IDT on the diaphragm.

[0070] Figure 4C A simplified schematic cross-sectional side view of an XBAR 450 with an interdigital transducer (IDT) having an anti-chirp for mechanical and process compensation is shown. Device 450 can represent a version of devices 100, 300, and / or 350 having an IDT with an anti-chirp. Device 450 is shown having a varying pitch p'_i–p'_i+6 of the interleaved IDT fingers 467 in the length (dimension L) direction of the XBAR and / or a varying mark wi' of the interleaved IDT fingers 467 in the aperture (dimension AP) direction of the XBAR, which varies over the region of the IDT 463 to compensate for process-induced deformation of the diaphragm portion of the piezoelectric plate 457. The varying pitch p'_i–p'_i+6 and / or mark wi of the interleaved IDT fingers 467 can be an anti-chirp or pre-chirp of the IDT 463. The fingers 467 and pitch p'_i–p'_i+6 can represent a portion of the IDT fingers and pitch. There can be fewer or more than the 8 fingers shown. In some cases, there can be dozens or hundreds of fingers. Figure 4C For example, all or part of the diaphragm portion is shown by showing only part or all of the diaphragm 315.

[0071] XBAR 450 can be a version of the XBAR before the diaphragm portion of the plate 457 is deformed due to process-induced mechanical displacement and / or stress that varies in a direction tangent to the length of the finger or along the direction of the markers wi and the pitch p'_i–p'_i+6. XBAR 450 can be a version of the XBAR before compensating for temperature variations in the plate 458 before or after the mechanical or process-driven spatial variations dd caused by the formation of the cavity 340 (e.g., during the use of the XBAR in a filter).

[0072] Figure 4D A simplified schematic cross-sectional side view of the XBAR 475 is shown, which is the XBAR 450 after the formation of the cavity 340 or during use and with mechanical and process compensation. The device 475 is shown to have a constant pitch p' of the interleaved IDT fingers 468 and a constant marker w' of the interleaved IDT fingers 468, and the constant pitch p' and the constant marker w' do not vary over the region of the IDT 465 because Figure 4C the variation of the inverse pitch p'_i–p'_i+6 and / or the marker wi' compensates for the process-induced deformation of the diaphragm portion of the piezoelectric plate 458.

[0073] Compared to the deformation of the diaphragm of the plate 457, due to the deformation of the diaphragm of the plate 458, the variation of the inverse pitch and / or the marker of the XBAR 475 before the process-induced deformation of the diaphragm portion keeps the pitch p' and the marker w' constant in the XBAR 475, as shown by increasing the height dd of the plate 418 (compared to the height of the plate 457). In some cases, only one of the pitch or the marker varies in the XBAR 475 compared to the XBAR 450. In other cases, both the pitch and the marker vary. For example, Figure 4A and Figure 4C can show an XBAR with an unreleased (flat) small plate or plates; while Figure 4B and Figure 4D can show an XBAR with a released (curved) small plate or plates.

[0074] XBAR 475 can be a version of the XBAR 450 after the process-induced deformation dd of the diaphragm portion of the plate 458 caused by mechanical displacement and / or stress that varies in a direction tangent to the length of the finger or along the width wi and the pitch p'. XBAR 475 can be a version of the XBAR 450 after the mechanical or process-driven spatial variation dd caused by the formation of the cavity 340 or after compensating for temperature variations in the plate 458 after the formation of the cavity 340 (e.g., during the use of the XBAR 475 in a filter).

[0075] As Figure 4CAs shown in Equation 455, the pitch p' (and / or the mark w') of the IDT of the XBAR 475 can be anti-chirped according to p' i = (p' 2 – h i 2 ) 1 / 2 varies along the direction of the pitch and the mark, where i is an integer representing the pitch between adjacent fingers or the mark of a finger, p' i is the anti-pitch or mark variation of the finger, p' is the length along the direction of the pitch or the deformation of the finger caused by the process, and h is the height of the deformation of the pitch or the finger caused by the process. The sum of all h i on the diaphragm can be equal to the distance of the variation dd.

[0076] Therefore, once the physical effects (which may include stress gradients) of the diaphragm deflection or variation dd can be defined, such as those mentioned for the XBAR 425, then an "anti-chirp" can be designed, such as those mentioned for the XBAR 450. The resonator CAD layout and thus the IDT on the unreleased diaphragm of the XBAR 450 will have an anti-chirp that compensates for the chirped pitch p_i and mark wi of the XBAR 425 given a known sum of the variation dd or hi. Then, when the diaphragm is released by forming the cavity 340 of the XBAR 475, the anti-chirp signal designed for the XBAR 450 and the chirp signal caused by the XBAR 425 will cancel each other out, such that a constant pitch p and a constant mark w exist on the diaphragm of the XBAR 475.

[0077] Figure 4C and Figure 4D show the resonators 450 and 475 with piezoelectric plates 457 and 458 having parallel front and back surfaces. Except that a portion of the piezoelectric plate 458 forms a diaphragm portion spanning the cavity 340 in the intermediate layer, the back surface of the plate faces a substrate (not shown) and can be bonded to the intermediate layer of the substrate. The diaphragm portion can be a part of the diaphragm 315, and the cavity can be the cavity as shown in Figure 1 or Figure 3A shown. At least one of the pitch p'_i of the interleaved IDT fingers 467 or the mark wi' of the interleaved IDT fingers 467 varies over the region of the IDT 463 to compensate for the process-induced deformation of the diaphragm portion of the piezoelectric plate. The varying pitch and mark of the interleaved IDT fingers 467 can be anti-chirped on the diaphragm 315 of the IDT 463 to compensate for the process-induced deformation of the diaphragm portion of the piezoelectric plate 458 during or after the formation of the cavity 340.

[0078] The pitch and the mark can vary on the diaphragm portion to compensate for the bending of the diaphragm portion caused by process stress during the manufacture of the XBAR 475 and / or temperature variations during the use of the XBAR 475. In some cases, bending due to process stress or temperature variations during use occurs when the increase in the plate temperature causes the plate to have a concave curvature of the plate 475 (e.g., a hollow and curved line that looks like the inside of a bowl from the perspective of the cavity 340 or the substrate). The concave shape can also be the bottom surface of the plate 475, a part of which is a straight line where the central portion is recessed by having a "dent" or an upward dent at an inner angle greater than 5°.

[0079] The pitch and the mark vary on the diaphragm portion in the following manner: Before forming the cavity 340, the pitch p'i and the mark wi' of adjacent finger pairs 467 of the pre-chirped IDT 463 are varied to have different pitches and marks on the plate 457, such that after forming the cavity 340, the adjacent finger pairs 468 have a constant pitch p' and mark w'. The pitch p'i of the interleaved IDT fingers 467 varies over the region of the IDT 463 to compensate for the process-induced deformation of the diaphragm portion of the piezoelectric plate 457 when the piezoelectric plate 457 becomes the plate 458.

[0080] The overlap distance of the interleaved fingers 467 and 468 defines the aperture AP of the devices 450 and 475. At any point along the length of the IDT 463, at least one of the pitch or the mark of this IDT varies over the aperture AP of the IDT. Both the pitch and the mark of the IDT 463 can vary along the aperture AP, and the mark varies along the diaphragm because the mark exists even if the pitch is not in the gap between the ends of one set of fingers and the opposite bus bar.

[0081] At least one of the pitch p'i or the mark wi' of the IDT 463 varies over all of the plurality of fingers in a certain direction (e.g., the direction shown by the diaphragm 315). At least one of the pitch p'i and the mark wi' (e.g., the line width of the fingers) of the interleaved IDT 463 varies along a direction that can be tangent to the length of the fingers and / or along the direction of the pitch and the mark.

[0082] The process-induced deformation of the diaphragm portion can be a mechanical displacement and / or stress that varies in the said direction. It is known that an XBAR has mechanical displacements and stresses that vary with the position in the said direction of the resonator. Therefore, in some cases, the process-induced deformation of the diaphragm portion is divided into two or more parts along the said direction, where each part has a different deformation from each other part.

[0083] For example, any two or more of the adjacent spacings p'_1 - p'_i+6 can represent portions between 3 fingers and 10 fingers, each portion having a deformation different from each adjacent portion. Accordingly, each portion has a different anti-chirp spacing p'i and a label wi' from each adjacent portion. For these two or more portions, the process-induced deformation of the diaphragm portion can be p' i = (p' 2 – h i 2 ) 1 / 2 .

[0084] The piezoelectric plate has a plate thickness ts between the front and back surfaces of the piezoelectric plate (not shown but extending into the page, also see Figure 2 ). For Figure 4A and Figure 4C , the thickness ts can be a constant thickness. For Figure 4B and Figure 4D , as shown, the thickness ts can not be a constant thickness.

[0085] During the use of the XBAR 475, the piezoelectric plate 458 and the IDT are configured such that a radio frequency signal applied to the IDT 465 excites a principal shear acoustic mode in the piezoelectric plate above the cavity. The thickness of the piezoelectric plate or the diaphragm can be selected to tune the principal shear acoustic mode in the piezoelectric plate. As Figure 5 shown, the XBAR 475 can be used as a parallel resonator or a series resonator. In addition, the anti-chirp IDT concept herein can be applied to multiple XBARs, such as the series and / or parallel XBARs of the filter shown in Figure 5 . Each of these XBARs can have a piezoelectric plate having a front surface and a back surface, the back surface facing the substrate, and portions of the piezoelectric plate forming a plurality of diaphragms spanning corresponding cavities in an intermediate layer of the substrate.

[0086] In one exemplary aspect, the anti-chirp can be "digitized" to have an approximate, discrete distribution that best simulates the compensated parasitic chirp. This will generally be necessary because the IDTs do not sample the diaphragm continuously, i.e., they are at discrete positions. In cases where chirp spacing is still desired, the magnitude of the chirp can be increased to compensate for the "built-in" chirp: this forms a "chirp process deviation". According to one exemplary aspect, chirp may be desired to control acoustic spurs, so anti-chirp can be used to apply a "chirp process deviation" to achieve a desired chirp distribution. In addition, the anti-chirp can have purely dimensional characteristics, but can be used to address both dimensional and physical property gradients. The spatial variation of the speed of sound caused by mechanical stress gradients, for example, can be compensated using anti-chirp. The optimal anti-chirp under this condition can be derived by empirical measurement or DOE, and can take a functional form different from the definition in Figure 4C .

[0087] As described above, the diaphragm deflection of the plate can stretch the IDT in the width direction or the aperture AP direction (e.g., along the Figure 1 cross-section B-B). In some cases, the process-induced deformation of the diaphragm portion of the plate 418 or 458 caused by mechanical displacement and / or stress varies along the length direction of the fingers (e.g., along the direction tangent to the width w' and the pitch p'). To a certain extent, this results in a continuous change in the finger thickness along the finger length, and the mark wi' can also be anti-chirped to mitigate the situation where extreme bending will narrow the IDT fingers.

[0088] Figure 4E and Figure 4F show Figure 4A and Figure 4B simplified schematic plan views or top perspective views of the XBARs 400 and 425 of Figure 4G and Figure 4H show Figure 4C and Figure 4D simplified schematic plan views of the XBARs 450 and 475 of Figures 4E to 4D shows a plan view of a portion of the diaphragm having an IDT on or above the piezoelectric plate but not the entire width or distance L of the IDT with respect to Figure 1 the diaphragm.

[0089] Figure 4E shows that the fingers 437 of the IDT 433 of the XBAR 400 have a mark w of the staggered IDT fingers 437 that does not change in the region of the IDT 433, the aperture AP direction, or the diaphragm 315 to compensate for the process-induced deformation of the diaphragm portion 315 of the piezoelectric plate 417 with respect to Figure 1 the direction of the cross-section B-B. Figure 4F shows that the mark wi of the fingers 438 of the IDT 435 of the XBAR 425 is stretched along the region of the IDT 435, the aperture AP direction, or the diaphragm 315 due to the process-induced deformation of the diaphragm portion 315 of the piezoelectric plate 418 with respect to Figure 1 the direction of the cross-section B-B. If this is not desired, anti-chirping can be used to avoid the stretched shape of the fingers.

[0090] For example, Figure 4G shows that the fingers 467 of the IDT 463 of the XBAR 450 are anti-chirped along the region of the IDT 463, the aperture AP direction, or the diaphragm 315 and thicken along the plate 457. The fingers 467 have a mark wi' that varies in the region of the IDT 463, the aperture AP direction, or the diaphragm 315 to compensate for the process-induced deformation of the diaphragm portion 315 of the piezoelectric plate 457 with respect to Figure 1 the direction of the cross-section B-B. Figure 4HIt is shown that the finger 468 of the IDT 465 of the XBAR 475 has a mark w', due to the process-induced deformation of the diaphragm portion 315 of the IDT 465 of the piezoelectric plate 458 with respect to Figure 1 the direction of the cross-section B-B, and this mark w' does not change in the region of the IDT 465, the aperture AP direction, or the diaphragm 315. Here, for example, the anti-chirp mentioned for Figures 4A to 4D can be used to avoid Figure 4F the stretching shape of the fingers. The mark wi' of the interleaved IDT fingers 467 changes in the region of the IDT 463 to compensate for the process-induced deformation of its diaphragm portion when the piezoelectric plate 457 becomes the plate 458.

[0091] Figure 5 FIG. 10 is a schematic circuit diagram and layout of a high-frequency bandpass filter 500 using an XBAR, where the two connections shown to the XBAR are connections to the two busbars of the XBAR. The filter 500 has a conventional ladder filter architecture, including three series resonators 510A, 510B, 510C and two parallel resonators 520A, 520B. The three series resonators 510A, 510B and 510C are connected in series between the first port and the second port (thus being called "series resonators"). Any number of resonators of the filter 500 can be the XBAR 425, the XBAR 475, or an example of this XBAR. In Figure 5 FIG. 10, the first port and the second port are respectively labeled "In" and "Out". However, the filter 500 is bi-directional and either port can be used as the input or output end of the filter. The two parallel resonators 520A, 520B are connected to ground from the nodes between the series resonators. The filter can include additional reactance components (such as inductors) not shown in Figure 5 FIG. 10. All the parallel resonators and series resonators are XBARs. Including three series resonators and two parallel resonators is exemplary. The filter can have more or fewer than five total resonators, more or fewer than three series resonators, and more or fewer than two parallel resonators. Generally, all the series resonators are connected in series between the input end and the output end of the filter. All the parallel resonators are generally connected between ground and the input end, the output end, or the node located between two series resonators.

[0092] In an exemplary filter 500, three series resonators 510A, 510B, 510C and two parallel resonators 520A, 520B of the filter 500 are formed on a single plate 530 of a piezoelectric material bonded to a silicon substrate (not visible). Each resonator includes a corresponding IDT (not shown), wherein at least the fingers of the IDT are disposed above a cavity in the substrate. In this context and similar contexts, the term "corresponding" means "relating things to each other", i.e., having a one-to-one correspondence. In Figure 5 the cavity is schematically shown as a dashed rectangle (e.g., rectangle 535). In this example, each IDT is disposed on a corresponding cavity. In other filters, the IDTs of two or more resonators may be disposed above a single cavity.

[0093] Each of the resonators 510A, 510B, 510C, 520A, 520B in the filter 500 has a resonance at which the admittance of the resonator is very high and an anti-resonance at which the admittance of the resonator is very low. The resonance and anti-resonance occur at the resonance frequency and anti-resonance frequency, respectively, and for the various resonators in the filter 500, the resonance frequency and anti-resonance frequency may be the same or different. In short, each resonator can be considered as a short circuit at its resonance frequency and an open circuit at its anti-resonance frequency. At the resonance frequency of the parallel resonator and the anti-resonance frequency of the series resonator, the input-output transfer function will be close to zero. In a typical filter, the resonance frequency of the parallel resonator is below the lower edge of the filter passband, while the anti-resonance frequency of the series resonator is above the upper edge of the passband.

[0094] Description of the method

[0095] Figure 6 is a simplified flowchart showing a process 600 for manufacturing an XBAR or a filter including an XBAR. The process 600 can form an XBAR 400, 425, 450, 457, or an example of such an XBAR. The process 600 begins at 605 with a substrate and a piezoelectric material plate and ends at 695 with a completed XBAR or filter. As will be described subsequently, the piezoelectric plate may be mounted on a sacrificial substrate or may be part of a wafer of piezoelectric material. Figure 6 The flowchart of only includes the main process steps. Various conventional process steps (e.g., surface preparation, chemical mechanical polishing (CMP), cleaning, inspection, deposition, lithography, baking, annealing, monitoring, testing, etc.) may be performed before, between, after, and during the steps shown in Figure 6 the steps shown.

[0096] Figure 6The flowchart captures three variants of process 600 for manufacturing an XBAR, which differ in when and how cavities are formed in a substrate. A cavity can be formed at step 610A, 610B, or 610C. Only one of these steps is performed in each of the three variants of process 600.

[0097] The piezoelectric plate can be, for example, Z-cut, rotated Z-cut, or rotated Y-cut lithium niobate or lithium tantalate. In some cases, it is Y-cut or rotated Y-cut lithium niobate. The piezoelectric plate can be some other material and / or some other cut. The substrate can be silicon. The substrate or an intermediate layer of the substrate can be some material that allows deep cavities to be formed by etching or other processing. The silicon substrate can have a silicon TOX layer and a polysilicon layer.

[0098] In one variant of process 600, one or more cavities are formed at 610A in the substrate 120 or 320 or an intermediate layer of the substrate before the piezoelectric plate is bonded to the substrate at 620. Separate cavities can be formed for each resonator in the filter device. Conventional lithography and etching techniques can be used to form one or more cavities. These techniques can be isotropic or anisotropic; and deep reactive ion etching (DRIE) can be used. Generally, the cavities formed at 610A will not penetrate the substrate or layer 322, and the resulting resonator device will have a cross-section as shown in Figure 3A the figure.

[0099] At 620, the piezoelectric plate is bonded to the substrate. The piezoelectric plate and the substrate can be bonded by a wafer bonding process. Generally, the mating surfaces of the substrate and the piezoelectric plate are highly polished. One or more layers of an intermediate material (e.g., oxide or metal) can be formed or deposited on the mating surface of one or both of the piezoelectric plate and the substrate. One or both of the mating surfaces can be activated using, for example, a plasma process. The mating surfaces can then be pressed together with a significant force to establish a molecular bond between the piezoelectric plate and the substrate or the intermediate material layer.

[0100] In a first variant of 620, the piezoelectric plate is initially mounted on a sacrificial substrate. After the piezoelectric plate and the substrate are bonded, the sacrificial substrate and any intermediate layer are removed to expose the surface of the piezoelectric plate (the surface that previously faced the sacrificial substrate). The sacrificial substrate can be removed, for example, by material-related wet or dry etching or some other process.

[0101] In a second variant of 620, starting from a single-crystal piezoelectric wafer, ions are implanted to a controlled depth below the surface of the piezoelectric wafer ( Figure 6(not shown). The portion of the wafer from the surface to the ion implantation depth is (or will be) a thin piezoelectric plate, and the remainder of the wafer is effectively a sacrificial substrate. After the implantation surface of the piezoelectric wafer and the device substrate are bonded, the piezoelectric wafer can be split at the plane of the implanted ions (e.g., using a thermal shock), leaving a thin sheet of piezoelectric material exposed to and bonded to the substrate. The thickness of the thin sheet of piezoelectric material is determined by the energy (and depth) of the implanted ions. The process of ion implantation and subsequent separation of the thin sheet is generally referred to as "ion slicing". The exposed surface of the thin piezoelectric plate can be polished or planarized after splitting the piezoelectric wafer.

[0102] At 630, a conductor pattern and a dielectric layer defining one or more XBAR devices are formed on the surface of the piezoelectric plate. Typically, a filter device will have two or more conductor layers that are deposited and patterned sequentially. The conductor layer can include bonding pads, gold or solder bumps, or other means for establishing a connection between the device and an external circuit. The conductor layer can be, for example, aluminum, aluminum alloy, copper, copper alloy, molybdenum, tungsten, beryllium, gold, or some other conductive metal. Optionally, one or more layers of other materials can be disposed beneath 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. The conductor layer can include bonding pads, gold or solder bumps, or other means for establishing a connection between the device and an external circuit.

[0103] At 630, the conductor pattern can be formed by depositing a conductor layer on the surface of the piezoelectric plate and removing the excess metal by etching through a patterned photoresist. Alternatively, at 630, a lift-off process can be used to form the conductor pattern. The photoresist can be deposited on the piezoelectric plate and patterned to define the conductor pattern. The conductor layer can be deposited sequentially on the surface of the piezoelectric plate. The photoresist can then be removed, thereby removing the excess material and leaving the conductor pattern. In some cases, the formation at 630 occurs prior to the bonding at 620, e.g., forming an IDT before bonding the plate to the substrate.

[0104] Forming the conductor pattern at 630 can include forming an IDT 130 having at least one of the pitch pi of the interleaved IDT fingers or the mark wi of the interleaved IDT fingers varying over the aperture to compensate for process-induced deformation of the diaphragm. The formation at 630 includes anti-chirping of the device 450 as described herein. For example, at 630, the pitch pi and the mark wi vary over the diaphragm portion such that, before forming the cavity, the pitch and the mark of adjacent finger pairs of the pre-chirped IDT are different on the piezoelectric plate so that after forming the cavity at 610B or 610C, the adjacent finger pairs have a constant pitch and mark.

[0105] For example, the anti-chirping at 630 may include selecting the pitch pi of the staggered IDT fingers and / or the mark wi of the staggered IDT fingers to compensate for the process-induced deformation of the diaphragm. This selection may be based on compensating for the mechanical and / or process-driven spatial variations due to the formation of the cavity, or compensating for the temperature variations of the plate after the formation of the cavity (e.g., during the use of the resonator). This selection may be based on empirical measurements, design of experiments (DOE), or computer-aided design (CAD). The measurement may be of the variation dd or hi' of the actual or simulated plate or XBAR of the interdigital transducer (IDT) without anti-chirping for mechanical and process compensation, e.g., the measurement of the variation dd or hi' of the XBAR 425.

[0106] Design of experiments (DOE) is a systematic method for improving operating processes by analyzing the relationship between inputs and outcomes. Design of experiments (DOE) is a systematic method for determining the relationship between the factors that affect a process and the output of that process. In other words, design of experiments (DOE) is used to find cause-and-effect relationships. This information is needed to manage process inputs to optimize outputs. Design of experiments is a collection of controlled tests that are designed to model and explore the relationship between factors and one or more responses.

[0107] At 640, one or more front-side dielectric layers may be formed on one or more desired conductor patterns of the IDT or XBAR device 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 on the entire surface of the piezoelectric plate including the top of the conductor pattern. Alternatively, one or more lithography processes (using photomasks) may be used to limit the deposition of the dielectric layer to selected areas of the piezoelectric plate, e.g., only between the staggered fingers of the IDT. The mask may also be used to allow the deposition of different thicknesses of dielectric material on different parts of the piezoelectric plate. In some cases, the deposition at 640 includes depositing at least one dielectric layer of a first thickness above the front-side surface of the selected IDT, but not depositing a dielectric layer or depositing at least one dielectric layer of a second thickness less than the first thickness above other IDTs. Another alternative is that these dielectric layers are only between the staggered fingers of the IDT.

[0108] One or more dielectric layers may include, for example, a dielectric layer selectively formed above the IDT of a parallel resonator to shift the resonance frequency of the parallel resonator relative to the resonance frequency of the series resonator, as described in U.S. Patent No. 10,491,192. One or more dielectric layers may include an encapsulation / passivation layer deposited on all or most of the device.

[0109] Compared with other XBARs, these dielectric layers with different thicknesses cause the selected XBAR to be tuned to different frequencies. For example, the resonant frequency of the XBAR in the filter can be tuned using different front-side dielectric layer thicknesses on certain XBARs.

[0110] Compared with the admittance of the XBAR with tfd = 0 (i.e., the XBAR without a dielectric layer), the admittance of the XBAR with a dielectric layer of tfd = 30 nm has a resonant frequency reduced by approximately 145 MHz compared to the XBAR without a dielectric layer. Compared with the XBAR without a dielectric layer, the admittance of the XBAR with a dielectric layer of tfd = 60 nm has a resonant frequency reduced by approximately 305 MHz. Compared with the XBAR without a dielectric layer, the admittance of the XBAR with a dielectric layer of tfd = 90 nm has a resonant frequency reduced by approximately 475 MHz. Importantly, the presence of dielectric layers with different thicknesses has little or no effect on the piezoelectric coupling.

[0111] In the second variant of process 600, after forming all conductor patterns and dielectric layers at 630, at 610B, one or more cavities are formed in the back side of the substrate. Separate cavities can be formed for each resonator in the filter device. One or more cavities can be formed using anisotropic or orientation-dependent dry or wet etching to open holes through the back side of the substrate until the piezoelectric plate. In this case, the resulting resonator device will have a cross-section as Figure 1 shown.

[0112] In the third variant of process 600, at 610C, by etching a sacrificial layer formed on the front side of the substrate using an etchant introduced through an opening in the piezoelectric plate, one or more cavities in the form of grooves can be formed in the substrate or the top layer 322. Separate cavities can be formed for each resonator in the filter device. One or more cavities can be formed using isotropic or orientation-independent dry etching that passes through holes in the piezoelectric plate and etches the sacrificial layer formed in grooves on the front side of the substrate. The one or more cavities formed at 610C will not completely penetrate the substrate top layer 322, and the resulting resonator device will have a cross-section as Figure 3A shown in.

[0113] In variant 610B or 610C, forming the cavities results in process-induced deformation of the diaphragm, and due to the anti-chirping of device 450, the pitch and marking of the IDT fingers are constant for XBAR 475. Therefore, by pre-chirping the pitch and marking of adjacent finger pairs of the IDT at 630 before forming the cavities to have different pitches and markings on the plate, the etching at 610B or 610C results in adjacent finger pairs having a constant pitch p and marking w after forming the cavities at 610B or 610C.

[0114] In all variations of process 600, a filter or XBAR device is completed at 660. Actions that can occur at 660 include: depositing a encapsulation / passivation layer, such as SiO2 or Si3O4, on all or part of the device; forming bond pads, or solder bumps, or other means for establishing connections between the device and an external circuit; singulating the devices from a wafer containing multiple devices; other packaging steps; and testing. Another action that can occur at 660 is to tune the resonant frequency of resonators within the filter device by adding or removing metal or dielectric material from the front side of the device. After the filter device is completed, the process ends at 695. Figure 1 FIG. 4 may show an example of the fingers of the selected IDT after completion at 660.

[0115] Forming a cavity at 610A may require the fewest total process steps, but has the disadvantage that the XBAR diaphragm will not be supported in all subsequent process steps. This can lead to damage or unacceptable deformation of the diaphragm during subsequent processing.

[0116] Using backside etching to form a cavity at 610B requires additional processing inherent in double-sided wafer processing. Forming a cavity from the backside also greatly complicates the packaging of the XBAR device because both the front and back sides of the device must be sealed by the packaging.

[0117] Forming a cavity by etching from the front side at 610C does not require double-sided wafer processing and has the advantage that the XBAR diaphragm is supported during all previous process steps. However, the etching process capable of forming a cavity through an opening in the piezoelectric plate needs to be isotropic. However, as Figure 3A shown, such an etching process using a sacrificial material allows for controlled etching of the cavity both laterally (i.e., parallel to the substrate surface) and perpendicular to the substrate surface.

[0118] Figure 7 is a graph showing the definition of the curvature of a straight or curved shape. Line 710 is a two-dimensional closed curve of arbitrary shape. Circle 720 is the so-called "osculating circle", which is the circle that is closest to curve 710 at point P. More precisely, given a point P on curve 710, each other point X (not shown) of curve 710 defines a circle (or sometimes a line) that passes through X and is tangent to the curve at P. The osculating circle is the limit (if it exists) of this circle as X approaches P. Radial line 730 connects point P to the center 725 of the osculating circle 720. The length Rc of the radial line 730 is the "radius of curvature" of curve 710 at point P. The curvature C at point P Pis the reciprocal of Rc. If the radial line connecting this point and the center of the corresponding osculating circle is within the cavity or passes through the cavity, the curvature at a point on the perimeter of the cavity is positive. Conversely, if the radial line connecting this point and the center of the corresponding osculating circle is outside the cavity, the curvature at a point on the perimeter of the cavity is negative. For example, the curvature of line 710 at point Q is negative.

[0119] Since the radius of curvature of a straight line is infinite, the curvature of a straight line is zero. Conversely, since the radius of a sharp corner (e.g., an angle formed by the intersection of two straight lines) is zero, the curvature of such an angle is infinite.

[0120] In this patent, if the curvature of at least one point on the perimeter is non-zero and finite, the perimeter of the cavity is "curved". Figure 1 The perimeter 145 of the cavity 140 in [reference] is not curved. The curvature of the perimeter 145 is zero along the straight top, bottom, left, and right sides of the cavity (as shown), and is infinite at the angles where the sides intersect. There is no point on the perimeter 145 that has a curvature that is both non-zero and finite. This is true for any perimeter that has only straight edges.

[0121] If the curvature at each point along the perimeter is non-zero and finite, the perimeter of the cavity is "continuously curved". If the curvature at all points along the perimeter is finite, the perimeter of the cavity is "cornerless".

[0122] The part of the perimeter with positive curvature is "convex", while the part of the perimeter with negative curvature is "concave". If the curvature at each point on the perimeter is finite and greater than zero, the perimeter of the cavity is continuously convex. If the curvature at each point on the perimeter is finite and greater than or equal to zero, the perimeter of the cavity is "non-concave".

[0123] The "elliptical" shape is curved, cornerless, continuously curved, and non-concave, as these terms were defined previously.

[0124] End of comments

[0125] Throughout this specification, the illustrated embodiments and examples should be regarded as illustrative, rather than limiting, of the disclosed or claimed devices and processes. Although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that these acts and these elements may be combined in other ways to achieve the same objective. With regard to flowcharts, additional and fewer steps may be taken, and the steps shown may be combined or further refined to implement the methods described herein. Acts, elements, and features discussed only in connection with one embodiment are not intended to be excluded from similar roles in other embodiments.

[0126] As used herein, "a plurality" means two or more. As used herein, a "set" of items can include one or more such items. As used herein, whether in the written description or claims, the terms "comprising," "including," "carrying," "having," "containing," "involving," etc. shall be understood to be open-ended, i.e., meaning including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" are, respectively, closed or semi-closed transitional phrases with respect to claims. The use of sequential terms such as "first," "second," "third," etc. in claims to modify the claim elements themselves does not mean any priority, precedence, or order of one claim element with respect to another claim element or the chronological order of acts of a method of performing, but is only used as a label to distinguish one claim element having a particular name from another element having the same name (but using an ordinal term) to distinguish these 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. An acoustic resonator, comprising: A piezoelectric plate having a first surface and a second surface facing each other, the second surface facing a substrate, the piezoelectric plate having a diaphragm located above a cavity; And A conductor pattern disposed on at least one of the first surface and the second surface, the conductor pattern including an interdigital transducer having interleaved fingers on the diaphragm of the piezoelectric plate, Wherein at least one of the pitch of the interleaved fingers or the markings of the interleaved fingers varies over the area of the interdigital transducer to compensate for process-induced deformation of the diaphragm of the piezoelectric plate.

2. The acoustic resonator according to claim 1, wherein The piezoelectric plate and the interdigital transducer are configured such that a radio frequency signal applied to the interdigital transducer excites a main shear acoustic mode in the diaphragm, such that the direction of acoustic energy flow of the main shear acoustic mode is substantially perpendicular to the front and rear surfaces of the piezoelectric plate, and The pitch and markings of the interleaved fingers vary over the diaphragm to compensate for bending of the diaphragm due to process stress or temperature changes during use.

3. The acoustic resonator according to claim 1, wherein, The pitch and markings of the interleaved fingers vary over the diaphragm by pre-chirping the pitch and markings of adjacent finger pairs of the interdigital transducer to have different pitches and markings on the piezoelectric plate before forming the cavity, such that the adjacent finger pairs have a constant pitch and markings after forming the cavity.

4. The acoustic resonator according to claim 1, wherein, The overlapping distance of the interleaved fingers defines the aperture of the acoustic resonator, and At any point along the length of the interdigital transducer, at least one of the pitch or the markings of the interdigital transducer varies over the aperture of the interdigital transducer.

5. The acoustic resonator according to claim 3, wherein, At least one of the pitch or the markings varies over all of the plurality of interleaved fingers.

6. The acoustic resonator according to claim 1, wherein, At least one of the pitch of the interleaved fingers and the markings of the interleaved fingers varies in a direction tangential to the length of the interleaved fingers.

7. The acoustic resonator according to claim 6, wherein, At least one of the pitch of the interdigital transducer or the mark varies according to p i = (p 2 – h i 2 ) 1 / 2 varies along the direction, where i is an integer representing the finger along the direction, p i is the pitch or mark variation of the finger, p is the length of the finger along the direction due to process-induced deformation, and h is the height of the finger due to process-induced deformation.

8. The acoustic resonator according to claim 6, wherein The process-induced deformation of the diaphragm is one of mechanical displacement or stress that varies in said direction.

9. The acoustic resonator according to claim 6, wherein, The process-induced deformation of the diaphragm is divided along the length of the diaphragm into two or more portions, wherein the deformation of each portion is different from the deformation of each other portion.

10. The acoustic resonator according to claim 9, wherein, For the two or more parts, the diaphragm deformation caused by the process is p i = (p 2 – h i 2 ) 1 / 2 , where i is an integer representing the finger along the direction, p i is the pitch or mark change of the finger, p is the length of the finger deformation caused by the process, and h is the height of the finger deformation caused by the process.

11. A filter device, comprising: A piezoelectric plate having a first surface and a second surface facing each other, the second surface facing a substrate, a portion of the piezoelectric plate forming a plurality of diaphragms above corresponding cavities in an intermediate layer of the substrate; A conductor pattern on at least one of the first surface and the second surface, the conductor pattern including a plurality of interdigital transducers, the interleaved fingers of each interdigital transducer being on a corresponding one of the plurality of diaphragms, Wherein at least one of the pitch or the markings of the interleaved fingers of each interdigital transducer varies over the corresponding diaphragm to compensate for process-induced deformation of the corresponding diaphragm.

12. The filter device according to claim 11, wherein, The piezoelectric plate and the plurality of interdigital transducers are configured such that a respective radio frequency signal applied to each interdigital transducer excites a principal shear acoustic mode in the respective diaphragm such that the direction of acoustic energy flow of the principal shear acoustic mode is substantially perpendicular to the front and back surfaces of the piezoelectric plate.

13. The filter device according to claim 11, wherein the piezoelectric plate and the interdigital transducers are configured such that a radio frequency signal applied to each interdigital transducer excites a principal shear acoustic mode in the respective diaphragm, and the pitch and mark of the respective interdigital transducers vary on the diaphragm to compensate for bending of the diaphragm due to process stress or temperature variations during use.

14. The filter device according to claim 11, wherein, The pitch and mark of each interdigital transducer vary on the respective diaphragm by pre-chirping the pitch and mark of adjacent finger pairs of the interdigital transducer to have different pitches and marks on the piezoelectric plate before forming the cavity such that the adjacent finger pairs have a constant pitch and mark after forming the cavity.

15. The filter device according to claim 11, wherein the overlapping distance of the interleaved fingers of each interdigital transducer defines the aperture of the respective acoustic wave resonator device, and at any point along the length of the interdigital transducer, at least one of the pitch or mark of the interdigital transducer varies across the aperture of the interdigital transducer.

16. A method of manufacturing an acoustic wave resonator device, comprising: attaching an intermediate layer of a substrate to a piezoelectric plate; and forming interdigital transducers on at least one surface of the piezoelectric plate, the interdigital transducers including interleaved fingers, the overlapping distance of the interleaved fingers defining the aperture of the acoustic wave resonator device; forming at least one of the pitch of the interleaved fingers or the mark of the interleaved fingers that varies across the aperture to compensate for process-induced deformation of the diaphragm; and forming a cavity below the aperture, wherein forming the cavity creates process-induced deformation of the diaphragm and causes the pitch and mark of the interleaved fingers to be constant.

17. The method according to claim 16, wherein, The pitch and mark of the interdigital transducers vary on the diaphragm by pre-chirping the pitch and mark of adjacent finger pairs of the interdigital transducer to have different pitches and marks on the piezoelectric plate before forming the cavity such that the adjacent finger pairs have a constant pitch and mark after forming the cavity.

18. The method according to claim 16, further comprising: Selecting at least one of the pitch of the interleaved fingers or the mark of the interleaved fingers to compensate for process-induced deformation of the diaphragm.

19. The method according to claim 16, wherein, Selecting at least one of the pitch of the interleaved fingers or the mark of the interleaved fingers is based on one of: compensating for mechanically or process-driven spatial variations due to forming the cavity, or compensating for temperature variations in the piezoelectric plate after forming the cavity.

20. The method according to claim 16, wherein The piezoelectric plate and the interdigital transducers are configured such that a radio frequency signal applied to the interdigital transducers excites a principal shear acoustic mode in the piezoelectric plate such that the direction of acoustic energy flow of the principal shear acoustic mode is substantially perpendicular to the at least one surface of the piezoelectric plate.

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