Transverse excitation film body acoustic resonator with multi-pitch interdigital transducer

Abstract

Acoustic resonators and methods of manufacturing acoustic resonators are disclosed herein. The acoustic resonator includes a single crystal piezoelectric plate having a front side and a back side, the back side attached to a surface of the substrate, but a portion of the piezoelectric plate forming a diaphragm across a cavity in the substrate is not attached to the surface of the substrate. The front-side conductor pattern includes a multi-pitch interdigital transducer (IDT), and the IDT interleaved fingers are disposed on the diaphragm.

Description

[0001] This application is a divisional application of the Chinese invention patent application "A thin film bulk acoustic resonator with lateral excitation and multi-pitch interdigital transducer" with application date of February 22, 2021 and application number 202110197006.2. Technical Field

[0002] The present disclosure relates to radio frequency filters using acoustic wave resonators, and more particularly to bandpass filters with high power capabilities for use in 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 range of frequencies passed by a filter is called the "passband" of the filter. The range of frequencies 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 less 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 cell size, longer battery life, higher data rates, greater network capacity, lower cost, enhanced security, higher reliability, etc. These improvements can be achieved 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.

[0007] High-performance RF filters used in current communication systems typically 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.

[0008] To obtain a wider communication channel bandwidth, it is necessary to use a higher frequency communication band. 3GPP (3rd Generation Partnership Project) has standardized the radio access technology for mobile phone networks. The radio access technology for the fifth generation mobile network is 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 and n79, where n77 uses a frequency range of 3300MHz to 4200MHz and n79 uses a frequency range of 4400MHz to 5000MHz. Both band n77 and band n79 use time division duplexing (TDD), so communication devices operating in band n77 and / or band n79 use the same frequency for uplink and downlink transmissions. The bandpass filters of the n77 and n79 bands must be able to handle the transmit power of the communication device. The 5G NR standard also defines a millimeter wave communication band with a frequency between 24.25GHz and 40GHz. Summary of the invention

[0009] The present invention discloses an acoustic resonator, comprising: a single crystal piezoelectric plate having a front side and a back side, the back side being attached to the surface of a substrate, a portion of the piezoelectric plate forming a diaphragm, the diaphragm spanning a cavity in the substrate; a conductor pattern formed on the front side, the conductor pattern comprising a multi-pitch interdigital transducer (IDT), the staggered fingers of the IDT being arranged on the diaphragm.

[0010] Wherein the piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a principal shear acoustic mode in the diaphragm.

[0011] Therein, at any point along the length of the IDT, the pitch of the IDT is constant across the aperture of the IDT.

[0012] Wherein, the marking of the IDT fingers is constant across the entire IDT.

[0013] The multi-pitch IDT is divided into two or more parts along the length of the multi-pitch IDT, and the pitch of each part is different from the pitch of other parts.

[0014] wherein the maximum pitch of the multi-pitch IDT of each of the two or more parts is p(1+δ); and the minimum pitch of the multi-pitch IDT of each of the two or more parts is p(1-δ), wherein p is the nominal pitch and δ is greater than 0 and less than or equal to 5.0%.

[0015] Here, δ is less than or equal to 1.0%.

[0016] The multi-pitch IDT is divided into three parts, and the pitches of the three parts are p(1-δ) and p(1+δ) respectively.

[0017] Wherein, the pitch of the multi-pitch IDT changes continuously along the length of the IDT.

[0018] The pitch of the multi-pitch IDT varies continuously between p(1-δ) and p(1+δ), where p is the nominal pitch of the IDT, and δ is greater than 0 and less than or equal to 5.0%.

[0019] Here, δ is less than or equal to 1.0%.

[0020] The present invention also discloses a filter device, comprising: a single crystal piezoelectric plate having a front side and a back side, the back side being attached to the surface of a substrate, multiple parts of the piezoelectric plate forming multiple diaphragms, the multiple diaphragms spanning respective cavities in the substrate; a conductor pattern formed on the front side, the conductor pattern comprising multiple interdigital transducers (IDTs), the staggered fingers of the IDTs being arranged on a corresponding one of the multiple diaphragms, wherein the first IDT of the multiple IDTs is a multi-pitch IDT.

[0021] Wherein the piezoelectric plate and the plurality of IDTs are configured such that each radio frequency signal applied to the IDT excites a principal shear acoustic mode in the corresponding diaphragm.

[0022] Wherein, all of the plurality of IDTs are multi-pitch IDTs.

[0023] The first IDT is divided into two or more parts along the length of the first IDT, and each pitch of each part is different from the pitch of other parts.

[0024] wherein the maximum pitch of the first IDT of each of the plurality of parts is p(1+δ); and the minimum pitch of the first IDT of another part of the plurality of parts is p(1-δ), wherein p is the nominal pitch and δ is greater than 0 and less than or equal to 5.0%.

[0025] Here, δ is less than or equal to 1.0%.

[0026] The first IDT is divided into three parts, and the pitches of the three parts are p(1-δ) and p(1+δ) respectively.

[0027] The pitch of the first IDT changes continuously along the length of the first IDT.

[0028] The pitch of the first IDT varies continuously between p(1-δ) and p(1+δ), where p is the nominal pitch of the IDT, and δ is greater than 0 and less than or equal to 5.0%.

[0029] Here, δ is less than or equal to 1.0%.

[0030] The second IDT among the plurality of IDTs is a multi-pitch IDT, and a pitch variation of the second IDT is different from a pitch variation of the first IDT.

[0031] The second IDT is a part of a parallel resonator, and the first IDT is a part of a series resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Included are a schematic plan view and two schematic cross-sectional views of a laterally excited film bulk acoustic resonator (XBAR).

[0033] Figure 2 yes Figure 1 A partially enlarged schematic cross-sectional view of an XBAR.

[0034] Figure 3 is an alternative enlarged schematic cross-sectional view of an XBAR.

[0035] Figure 4 is a diagram showing shear-horizontal acoustic modes in XBAR.

[0036] Figure 5 FIG. 1 is a graph showing the relationship between the admittance magnitude of an XBAR having a conventional interdigital transducer (IDT) and frequency.

[0037] Figure 6 yes Figure 5 The expanded portion of the graph.

[0038] Figure 7 It is a plan view of a multi-pitch IDT.

[0039] Figure 8 is a plan view of another multi-pitch IDT.

[0040] Fig. 9 FIG. 4 is a graph showing the relationship between the admittance of an XBAR with multi-pitch IDT and the frequency.

[0041] Fig.10 yes Figure 8 The expanded portion of the graph.

[0042] Fig.11 It is a graph of the input-output transfer function (S2, 1) of a bandpass filter implemented using an XBAR having a multi-pitch IDT.

[0043] 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

[0044] Description of the device

[0045] 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.

[0046] 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 orientation of the X, Y, and Z crystal axes relative to the direction of the front and back sides is 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 front and back sides 112, 114. However, XBARs can be made on piezoelectric plates with other crystal orientations.

[0047] The back side 114 of the piezoelectric plate 110 is attached to the surface of the substrate 120, but a portion of the piezoelectric plate 110 that forms a diaphragm 115 spanning a cavity 140 formed in the substrate is not attached to the surface of the substrate 120. The portion of the piezoelectric plate spanning the cavity is referred to herein as a "diaphragm" 115 because this portion is physically similar to the diaphragm of a microphone. Figure 1 As shown, the diaphragm 115 abuts the rest of the piezoelectric plate 110 around the entire perimeter 145 of the cavity 140. In this case, "abut" means "contiguously connected without anything in between." In other configurations, the diaphragm 115 can abut the piezoelectric plate around at least 50% of the perimeter 145 of the cavity 140.

[0048] Substrate 120 provides mechanical support for piezoelectric plate 110. Substrate 120 can be, for example, silicon, sapphire, quartz, or some other material, or a combination of these materials. The back side 114 of piezoelectric plate 110 can be bonded to substrate 120 using a wafer bonding process. Alternatively, piezoelectric plate 110 is grown on substrate 120, or piezoelectric plate 110 is attached to the substrate in some other manner. Piezoelectric plate 110 can be attached directly to the substrate, or can be attached to the substrate via one or more intermediate material layers ( Figure 1 (not shown) is attached to the substrate 120.

[0049] The conventional meaning of "cavity" is "empty space within a solid." Cavity 140 may be a hole that passes completely through substrate 120 (as shown in cross sections AA and BB), or may be a groove in substrate 120 below diaphragm 115. For example, cavity 140 may be formed before or after piezoelectric plate 110 is attached to substrate 120, such as by selectively etching substrate 120.

[0050] 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, which is generally 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.

[0051] 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 a primary acoustic mode within the piezoelectric plate 110. As will be discussed in detail below, the primary acoustic mode is a bulk shear mode that propagates in a direction substantially 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 laterally excited thin film bulk wave resonator.

[0052] The IDT 130 is placed on the piezoelectric plate 110 such that at least the fingers of the IDT 130 are disposed on a diaphragm 115 of the piezoelectric plate, which spans or is suspended over the cavity 140. Figure 1 As shown, cavity 140 is rectangular, the size of which is larger than aperture AP and length L of IDT 130. The cavity of XBAR can have different shapes, such as regular or irregular polygons. The cavity of XBAR can have more or less than four sides, which can be straight or curved.

[0053] In order to facilitate Figure 11, the geometric pitch 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 of parallel fingers in the IDT 110. Similarly, the finger thickness is greatly exaggerated in the cross-sectional view.

[0054] Figure 2 A detailed schematic cross-sectional view of XBAR 100 is shown. Piezoelectric plate 110 is a single crystalline layer of piezoelectric material having 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, n79, n77), the thickness ts can be, for example, 200 nm to 1000 nm.

[0055] Optionally, a front dielectric layer 214 can 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 only between the IDT fingers (e.g., IDT fingers 238b), or the front dielectric layer 214 can also be deposited as a capping layer so that the dielectric layer is formed between and on the IDT fingers (e.g., IDT fingers 238a). The front dielectric layer 214 can be a non-piezoelectric dielectric material, such as silicon dioxide or silicon nitride. Tfd can be, for example, 0 to 500 nm. Tfd is typically less than the thickness ts of the piezoelectric plate. The front dielectric layer 214 can be formed of a multilayer consisting of two or more materials.

[0056] The IDT fingers 238a and 238b may be aluminum, an aluminum alloy, copper, a copper alloy, beryllium, gold, tungsten, molybdenum, or some other conductive material. The IDT fingers are considered "substantially aluminum" if they are made of aluminum or an alloy containing at least 50% aluminum. The IDT fingers are considered "substantially copper" if they are made of copper or an alloy containing at least 50% copper. Thin (relative to the total thickness of the conductor) layers of other metals (e.g., chromium or titanium) may be formed beneath and / or over the fingers and / or as layers within the fingers to improve adhesion between the fingers and the piezoelectric plate 110 and / or to passivate or encapsulate the fingers and / or to improve power handling. The busbars ( Figure 1 132, 134) can be made of the same or different material as the fingers.

[0057] Dimension p is the center-to-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 geometry of 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. For example, the width of an XBAR IDT finger may be 500 nm or greater, so that the IDT may be easily manufactured using photolithography techniques. 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.

[0058] Figure 3 A detailed schematic cross-sectional view of a securely mounted XBAR (SM XBAR) 300 is shown. The SM XBAR was first described in application Ser. No. 16 / 381,141. The SM XBAR 300 includes a piezoelectric plate 110, an IDT (of which only fingers 336 and 338 are visible). The piezoelectric layer 110 has parallel front and back faces 112, 114. Dimension ts is the thickness of the piezoelectric plate 110. The width of the IDT fingers 336, 338 is dimension w, the thickness of the IDT fingers is dimension tm, and the IDT pitch is dimension p.

[0059] and Figure 1 and Figure 2 Unlike the XBAR device shown, the IDT of the SM XBAR is formed on a diaphragm that spans a cavity in the substrate 120. In contrast, the acoustic Bragg reflector 340 is sandwiched between the surface 222 of the substrate 220 and the back side 114 of the piezoelectric plate 110. The term "sandwiched between" means that the acoustic Bragg reflector 340 is both disposed between the surface 222 of the substrate 220 and the back side 114 of the piezoelectric plate 110 and mechanically attached to the surface 222 of the substrate 220 and the back side 114 of the piezoelectric plate 110. In some cases, a thin additional layer of material may be disposed between the acoustic Bragg reflector 340 and the surface 222 of the substrate 220, and / or between the Bragg reflector 340 and the back side 114 of the piezoelectric plate 110. For example, such an additional layer of material may be present to facilitate bonding of the piezoelectric plate 110, the acoustic Bragg reflector 340, and the substrate 220.

[0060] The acoustic Bragg reflector 340 includes a plurality of dielectric layers alternating between a material having a high acoustic impedance and a material having a low acoustic impedance. "High" and "low" are relative terms. For each layer, the standard of comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent low acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent high acoustic impedance layers. As will be discussed later, the main acoustic mode in the XBAR piezoelectric plate is a shear bulk wave. The thickness of each layer of the acoustic Bragg reflector 340 is equal to or about one-quarter of the wavelength of a shear bulk wave having the same polarization as the main acoustic mode at or near the resonant frequency of the SM XBAR 300. Dielectric materials with relatively low acoustic impedance include silicon dioxide, carbon-containing silicon oxides, and certain plastics, such as cross-linked polyphenylene polymers. Materials with relatively high acoustic impedance include hafnium oxide, silicon nitride, aluminum nitride, and silicon carbide. All high acoustic impedance layers of the acoustic Bragg reflector 340 do not have to be the same material, and all low acoustic impedance layers do not have to be the same material. Figure 3 In the example of , the acoustic Bragg reflector 340 has a total of six layers. The acoustic Bragg reflector may have more or less than six layers.

[0061] Figure 4 is a graphical representation of the main acoustic modes 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 that alternate between electrical polarity from finger to finger. An RF voltage is applied to the interlaced fingers 430. The voltage generates a time-varying electric field between the fingers. As shown by the arrows labeled "Electric Field", the direction of the electric field is primarily transverse or parallel to the surface of the piezoelectric plate 410. Due to the high dielectric constant of the piezoelectric plate, the RF electrical energy is highly concentrated in the plate relative to air. The transverse electric field induces shear deformation in the piezoelectric plate 410, which (at the resonant frequency defined by the acoustic cavity, where the acoustic cavity is formed by the volume between the two surfaces of the piezoelectric plate) is strongly connected to the shear primary acoustic mode. In this article, "shear deformation" is defined as a deformation in a material where parallel planes remain substantially parallel and maintain a constant separation when translated relative to each other. A "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 400 is represented by curve 460, with the adjacent small arrows indicating the direction and relative magnitude of atomic motion at the resonant frequency. The extent of atomic motion and the thickness of piezoelectric plate 410 are greatly exaggerated for ease of viewing. Although the atomic motion is primarily lateral (i.e., Figure 4 465 , the direction of acoustic energy flow of the main acoustic mode excited is basically perpendicular to the surface of the piezoelectric plate, as shown by arrow 465 .

[0062] 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.

[0063] Acoustic resonators based on shear acoustic wave resonances outperform current state-of-the-art film bulk acoustic resonators (FBARs) and firmly mounted resonator bulk acoustic wave (SMR BAW) devices, where the electric field is applied through the thickness. In such devices, the acoustic modes are compressive in the direction of atomic motion and acoustic energy flow through the thickness. Furthermore, the piezoelectric coupling for shear wave XBAR resonances can be higher (>20%) than for other acoustic resonators. Thus, high-voltage electrical coupling allows the design and implementation of microwave and millimeter-wave filters with appreciable bandwidths.

[0064] Figure 5 5 is a graph 500 of the admittance magnitude versus frequency of a first XBAR including a conventional (i.e., uniform pitch) IDT. The admittance was determined by simulating the first XBAR using a finite element method. Line 510 is a graph of the admittance magnitude. The shear primary acoustic mode of the first XBAR has a maximum admittance at a resonant frequency FR and a minimum admittance at an anti-resonant frequency FAR. The admittance graph 510 also exhibits a plurality of spurious modes or secondary resonances, including a substantial spurious mode at a frequency of approximately 1.825 GHz.

[0065] At least some of the spurious modes found in XBARs are propagating plate waves. The frequencies of propagating plate wave modes are proportional to the IDT finger pitch. In contrast, XBAR resonant and antiresonant frequencies have only a small dependence on the IDT pitch. For example, changing the IDT pitch from 7.5 times the piezoelectric plate thickness to 15 times the piezoelectric plate thickness (i.e., a 2:1 change) results in an approximately 3% change in the resonant frequency of the XBAR.

[0066] Small changes in the IDT pitch in an XBAR can lead to cancellation or destructive interference of spurious modes, while having negligible impact on the sheared main mode. Figure 6 This effect is shown, Figure 6 yes Figure 5 A zoomed-in view of a portion of the graph containing the largest spurious modes. Figure 6 , solid line 610 is a graph of the magnitude of the admittance of an XBAR with a conventional IDT as a function of frequency, as previously described in Figure 5. The dashed curve 620 is a graph of the admittance magnitude of the XBAR versus frequency for a 0.5% increase in the IDT pitch. Increasing the IDT pitch by this amount lowers the frequency of the spurious mode by about 10 MHz, aligning the maximum admittance of curve 610 with the minimum admittance of curve 620. If two resonators with these admittance characteristics were placed in parallel, the two spurious modes would cancel each other, at least to some extent. Increasing the IDT pitch by 0.5% has a negligible effect on the resonant and antiresonant frequencies of the shear principal acoustic modes of the XBAR.

[0067] Figure 7 is a plan view of an exemplary multi-pitch IDT 700. A "multi-pitch IDT" is an IDT in which the pitch between the IDT fingers varies along the length of the IDT. At any given point along the length, the pitch does not vary across the aperture of the IDT. In addition, the mark or finger width of the multi-pitch IDT is typically constant across the entire IDT.

[0068] The multi-pitch IDT 700 includes a first busbar 732 and a second busbar 734, and a plurality of staggered fingers, such as finger 736. The staggered fingers extend alternately from the first and second busbars 732, 734. The multi-pitch IDT 700 is divided into three parts along the length L of the IDT, identified as part A, part B, and part C, respectively. Each of parts A, B, and C includes 20 fingers, for a total of 60 fingers in the multi-pitch IDT 700. The use of three parts and 60 fingers is exemplary. The total number of fingers of the IDT may be more or less than 60. The IDT may be divided into two or more parts along its length, each part including a plurality of adjacent fingers. The total number of fingers may be substantially evenly divided between the two or more parts. In this case, "substantially" means "as close as possible." For example, an IDT having 100 fingers is substantially equally divided, wherein the 100 fingers are divided into three parts, and the three parts have the number of fingers respectively being 33, 34, and 33. The total number of fingers may be unequally divided between two or more parts.

[0069] In this example, the pitch p of section B is the nominal pitch of the IDT. The pitch of section A is p(1-δ) and the pitch of section C is p(1+δ). δ is greater than 0 and less than or equal to 5%. δ is typically less than 1%. δ can be selected during filter design to most effectively reduce spurious modes. At any point along the length L of the IDT 700, the pitch is constant across the aperture A. The markings or widths of the IDT fingers are constant and the same in all sections. When the IDT is divided into two or more than three sections, the maximum pitch can be p(1+δ) and the minimum pitch can be p(1+δ).

[0070] In the example multi-pitch IDT 700, the pitch increases monotonically from left (as shown) to right. This is not necessarily the case in all multi-pitch IDTs. The portions of the multi-pitch IDT may be arranged in other orders. In addition, in the multi-pitch IDT 700, the pitch variation between adjacent portions is constant. This is not necessarily the case in all multi-pitch IDTs. The pitch variation between adjacent portions may be the same or different.

[0071] Figure 8 8 is a plan view of another multi-pitch IDT 800 having a continuously varying pitch. IDT 800 includes a first busbar 832 and a second busbar 834, and a plurality of staggered fingers, such as finger 836. The staggered fingers extend alternately from the first busbar 832 and the second busbar 834. IDT 800 is not divided into a plurality of sections, but continuously changes pitch along its length. IDT 800 has 60 fingers, which is exemplary. The total number of fingers of the IDT may be more or less than 60.

[0072] like Figure 8 As shown, the pitch of the left edge of IDT 800 is p(1-δ), and the pitch of the right edge of IDT 800 is p(1+δ). The pitch varies continuously between these two extremes. The variation in pitch is usually, but not necessarily, a linear function of the position along the length L of the IDT. δ is greater than 0, less than or equal to 5%, and typically less than 1%. δ can be selected during filter design to most effectively reduce spurious modes. At any point along the length of IDT 800, the pitch is constant across the aperture A. The mark or width of the IDT fingers is constant across the entire IDT.

[0073] IDT 700 and 800 can be combined with Figure 1 and Figure 2 XBAR or Figure 3 SMXBAR shown.

[0074] Fig. 9 is included with Figure 7 The relationship between the admittance magnitude and frequency of a second XBAR with an IDT having a variable pitch similar to the IDT 700 is shown in FIG900. The IDT is divided into three sections along its length. The pitches of the three sections are 3.589, 3.6, and 3.611 μm (δ=0.3%), respectively. In addition to the IDT pitch, the second XBAR is similar to the previously described IDT with a variable pitch. Figure 59. The admittance characteristic of the first XBAR shown in FIG. 9 is the same. The admittance is determined by simulating the second XBAR using the finite element method. Line 910 is a graph of the magnitude of the admittance of the second XBAR. The shear primary acoustic mode of the second XBAR has a maximum admittance at the resonant frequency FR and a minimum admittance at the anti-resonant frequency FAR. The resonant and anti-resonant frequencies are the same as those of the XBAR with uniform pitch IDT. The admittance graph 910 also shows a variety of spurious modes or secondary resonances. Figure 5 and Fig. 9 A comparison of shows that the size of all spurious modes is reduced in the second XBAR due to the use of IDTs with varying pitches.

[0075] Fig.10 Shows Fig. 9 Expanded portion of the graph of , which contains the largest spurious modes. Fig.10 In FIG. 1 , the solid line 1010 is a graph showing the relationship between the magnitude of the admittance and the frequency for an XBAR including an IDT with a varying pitch, such as Fig. 9 The dashed line 1020 is Figure 6 The relationship between the admittance of the XBAR of the conventional uniform pitch IDT and the frequency is shown. The addition of multi-pitch IDT reduces the peak of the spurious mode by 5dB.

[0076] Fig.11 is a graph of the magnitude of S2,1 for two bandpass filters implemented using XBAR devices, where S2,1 is the input / output transfer function. The S2,1 data was determined by simulating the two filters using the finite element method. Solid line 1110 is a graph of S2,1 for the first filter using an XBAR with a multi-pitch IDT. The first filter uses a ladder circuit with four series and four parallel resonators. Figure 7 As shown, each resonator includes an IDT divided into three equal parts along its length. For the series resonator, the parameter δ is 0.3%, and for the parallel resonator, the parameter δ is 0.4%.

[0077] Dashed line 1120 is a plot of S2,1 for a second bandpass filter having a uniform pitch IDT, but otherwise identical to the first bandpass filter. Comparison of curves 1110 and 1120 shows that the passbands of the two filters are virtually identical. The spurious mode peak admittance of the first filter having multi-pitch IDTs is reduced by up to 8 dB compared to the second filter.

[0078] Used to generate Fig.11The filters of the data shown are exemplary. The filter may have less than or more than five resonators, and less than or more than three series resonators and two parallel resonators. The multi-pitch IDT may be divided into two parts or more than three parts, or may be continuous. The number of parts may not be the same for all resonators in the filter, and the filter may include segmented and continuous multi-pitch IDTs. The value δ may be different for some or all resonators. The filter may contain a combination of resonators with uniform pitch and multi-pitch resonators.

[0079] All the examples discussed above are for Figure 1 and Figure 2 As shown in the conventional XBAR. Figure 3 As shown, multi-pitch IDTs can also be used to reduce spurious modes in rigidly mounted XBARs. A similar reduction in spurious mode amplitudes can be expected.

[0080] Conclusion

[0081] Throughout the specification, the embodiments and examples shown should be considered as examples, rather than limitations on the disclosed or claimed 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.

[0082] 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 bulk acoustic wave resonator, comprising: a piezoelectric layer attached to the substrate either directly or through one or more intermediate layers of material, a portion of the piezoelectric layer being located above the cavity below the piezoelectric layer; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the portion of the piezoelectric layer, wherein the center-to-center spacing between the staggered fingers varies along the length of the IDT such that a pitch of one portion of the IDT is constant but varies relative to a constant pitch of an immediately adjacent portion of the IDT, the pitch being the center-to-center spacing between the staggered fingers, and Wherein, the width of the staggered fingers in the one portion is the same as the width of the staggered fingers in the immediately adjacent portion.

2. The BAW resonator according to claim 1, wherein: The piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear acoustic mode in the piezoelectric layer.

3. The BAW resonator according to claim 1, wherein: The piezoelectric layer and the IDT are configured to excite an acoustic wave having an electric field excited transversely in a thickness direction of the piezoelectric layer, wherein propagation of the acoustic wave is perpendicular to a direction of the electric field.

4. The BAW resonator according to claim 1, wherein: A pitch variation between the one portion and the immediately adjacent portion is less than or equal to 5%.

5. The BAW resonator according to claim 1, wherein: The one portion of the IDT has a nominal pitch p, and the pitch of the immediately adjacent portion is increased relative to the nominal pitch.

6. The BAW resonator according to claim 1, wherein: The one portion of the IDT has a nominal pitch p, and the pitch of an immediately adjacent IDT portion is reduced relative to the nominal pitch.

7. The BAW resonator according to claim 1, wherein: The IDT includes the one portion, the immediately adjacent portion, and an additional portion, each portion including a plurality of adjacent fingers.

8. The BAW resonator according to claim 1, wherein: The width of the staggered fingers is constant across the length L of the IDT, which is the distance between the outermost fingers of the IDT.

9. The BAW resonator according to claim 1, wherein: The conductor pattern further includes a first busbar and a second busbar, and wherein the staggered fingers extend alternately from the first busbar and the second busbar.

10. The BAW resonator according to claim 9, wherein: The first busbar and the second busbar are made of a different material than the interlaced fingers.

11. The BAW resonator according to claim 9, wherein: The first busbar and the second busbar are thicker than a thickness tm of the interleaved fingers.

12. The BAW resonator of claim 1 further comprising a dielectric layer over and between the interlaced fingers.

13. The BAW resonator according to claim 1, wherein: The pitch of the one portion of the IDT is substantially constant but varies relative to the substantially constant pitch of the immediately adjacent portion of the IDT.

14. The BAW resonator according to claim 1, wherein: The width of the staggered fingers in the one section is substantially the same as the width of the staggered fingers in the immediately adjacent section.

15. A bulk acoustic wave resonator filter comprising: A first BAW resonator in a ladder filter circuit, wherein the first BAW resonator comprises: a piezoelectric layer attached to the substrate either directly or through one or more intermediate layers of material, a portion of the piezoelectric layer being located above the cavity below the piezoelectric layer; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the portion of the piezoelectric layer, wherein the center-to-center spacing between the staggered fingers varies along the length of the IDT such that a pitch of one portion of the IDT is constant but different from a constant pitch of an immediately adjacent portion of the IDT; and A second BAW resonator in a ladder filter circuit, wherein the second BAW resonator comprises: a piezoelectric layer attached to the substrate either directly or through one or more intermediate layers of material, a portion of the piezoelectric layer being located above the cavity below the piezoelectric layer; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the portion of the piezoelectric layer, wherein the center-to-center spacing between the staggered fingers varies along the length of the IDT such that a pitch of one portion of the IDT is constant but different from a constant pitch of an immediately adjacent portion of the IDT, the pitch being the center-to-center spacing between the staggered fingers, wherein a pitch variation between the one portion of the first BAW resonator and the immediately adjacent portion of the first BAW resonator is different from a pitch variation between the one portion of the second BAW resonator and the immediately adjacent portion of the second BAW resonator.

16. The BAW resonator filter according to claim 15, wherein: The first BAW resonator is a series resonator in the ladder filter circuit.

17. The BAW resonator filter according to claim 16, wherein: The second BAW resonator is a parallel resonator in the ladder filter circuit.

18. The BAW resonator filter according to claim 15, wherein: The value δ is a variation between the parts, and wherein δ is different between the first BAW resonator and the second BAW resonator.

19. The BAW resonator filter according to claim 15, wherein: The width of the interleaved fingers in the one portion of the first BAW resonator is the same as the width of the interleaved fingers in the immediately adjacent portion.

20. The BAW resonator filter according to claim 15, wherein: The width of the interleaved fingers in the one portion of the second BAW resonator is the same as the width of the interleaved fingers in the immediately adjacent portion.

21. A bulk acoustic wave resonator, comprising: a piezoelectric layer attached to the substrate directly or through one or more intermediate material layers; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the piezoelectric layer, wherein the center-to-center spacing between the staggered fingers varies along the length of the IDT such that a pitch of one portion of the IDT is constant but varies relative to a constant pitch of an immediately adjacent portion of the IDT, the pitch being the center-to-center spacing between the staggered fingers, and Wherein, the width of the staggered fingers in the one portion is the same as the width of the staggered fingers in the immediately adjacent portion.

22. The BAW resonator according to claim 21, wherein: The piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear acoustic mode in the piezoelectric layer.

23. The BAW resonator of claim 21, wherein: The piezoelectric layer and the IDT are configured to excite an acoustic wave having an electric field excited transversely in a thickness direction of the piezoelectric layer, wherein propagation of the acoustic wave is perpendicular to a direction of the electric field.

24. The BAW resonator of claim 21, wherein: A pitch variation between the one portion and the immediately adjacent portion is less than or equal to 5%.

25. The BAW resonator of claim 21, wherein: The one portion of the IDT has a nominal pitch p, and the pitch of the immediately adjacent portion is increased relative to the nominal pitch.

26. The BAW resonator of claim 21, wherein: The one portion of the IDT has a nominal pitch p, and the pitch of the immediately adjacent portion is reduced relative to the nominal pitch.

27. The BAW resonator of claim 21, wherein: The IDT includes the one portion, the immediately adjacent portion, and an additional portion, each portion including a plurality of adjacent fingers.

28. The BAW resonator of claim 21, wherein: The width of the staggered fingers is constant across the length L of the IDT, which is the distance between the outermost fingers of the IDT.

29. The BAW resonator of claim 21, wherein: The conductor pattern further includes a first busbar and a second busbar, and wherein the staggered fingers extend alternately from the first busbar and the second busbar.

30. The BAW resonator of claim 29, wherein: The first busbar and the second busbar are made of a different material than the interlaced fingers.

31. The BAW resonator of claim 29, wherein: The first busbar and the second busbar are thicker than a thickness tm of the interleaved fingers.

32. The BAW resonator of claim 21 further comprising a dielectric layer over and between the interlaced fingers.

33. The BAW resonator of claim 21, further comprising a cavity of the BAW resonator, wherein: A portion of the piezoelectric layer and the interlaced fingers are located over the cavity.

34. The BAW resonator of claim 21 further comprising an acoustic reflector between the piezoelectric layer and the substrate.

35. The BAW resonator of claim 34, wherein: The piezoelectric layer and the interlaced fingers are located above the acoustic reflector.

36. The BAW resonator of claim 34, wherein: The acoustic reflector is an acoustic Bragg reflector.

37. The BAW resonator of claim 34, wherein: The acoustic reflector comprises a plurality of layers alternating between layers of high acoustic impedance and layers of low acoustic impedance.

38. A bulk acoustic wave resonator, comprising: a piezoelectric layer attached to the substrate either directly or through one or more intermediate layers of material, a portion of the piezoelectric layer being located above the cavity below the piezoelectric layer; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the portion of the piezoelectric layer, wherein a pitch is defined as the center-to-center spacing between the interleaved fingers, wherein the pitch varies along the length of the IDT such that a nominal pitch of a first portion of the IDT is constant but varies relative to a constant nominal pitch of an immediately adjacent portion of the IDT, and Wherein a width of the staggered fingers in the first portion is the same as a width of the staggered fingers in the adjacent portion.

39. The BAW resonator of claim 38, wherein: Portions of the IDT include three or more consecutive interleaved fingers.

40. A bulk acoustic wave resonator, comprising: a piezoelectric layer attached to the substrate either directly or through one or more intermediate layers of material, a portion of the piezoelectric layer being located above the cavity below the piezoelectric layer; a conductor pattern, at the piezoelectric layer, comprising an interdigital transducer IDT having interleaved fingers on the portion of the piezoelectric layer, wherein the center-to-center spacing between the interleaved fingers varies along the length of the IDT, and The width of the staggered fingers is constant throughout the IDT.

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