A filter using a piezoelectric thin film bonded to a high-resistivity silicon substrate with a trap-rich layer

Abstract

An acoustic resonator device and filter are disclosed. The acoustic resonator includes a substrate having a trap-rich region adjacent a surface, and a single crystal piezoelectric plate having parallel front and back faces, the back face being attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity formed in the substrate. Interdigital transducers (IDTs) are formed on the front face of the single crystal piezoelectric plate such that interleaved fingers of the IDTs are disposed on the diaphragm. The single crystal piezoelectric plate and the IDTs are configured such that a radio frequency signal applied to the IDTs excites a shear primary acoustic mode in the diaphragm.

Description

Technical Field

[0001] This disclosure relates to radio frequency filters using acoustic resonators, and more particularly to filters used in communication equipment. Background Technology

[0002] Radio frequency (RF) filters are two-ended devices configured to allow some frequencies to pass while blocking others. "Passing" means transmitting with relatively low signal loss, while "blocking" means blocking or essentially attenuating the signal. The range of frequencies a filter can pass through is called its "passband." The range of frequencies blocked by such a filter is called its "stopband." A typical RF filter has at least one passband and at least one stopband. The specific requirements for the passband or stopband depend on the application. For example, a "passband" can be defined as a frequency range where the filter's insertion loss is better than defined values ​​such as 1 dB, 2 dB, or 3 dB. A "stopband" can be defined as a frequency range where the filter's rejection is greater than defined values, such as 20 dB, 30 dB, 40 dB, or greater, depending on the application.

[0003] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in 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 the RF front end of other communication systems. RF filters are also used in radar and electronic and information warfare systems.

[0004] RF filters typically require numerous design trade-offs to achieve the optimal balance between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing approaches and enhancements can simultaneously benefit one or more of these requirements.

[0005] Enhancements to the performance of RF filters in wireless systems can have a wide-ranging impact on system performance. Improvements to RF filters can lead to improvements such as larger cell size, longer battery life, higher data rates, greater network capacity, lower cost, enhanced security, and higher reliability. These improvements can be implemented individually or in combination at various levels of the wireless system, including at the RF module, RF transceiver, mobile or fixed subsystem, or network level.

[0006] To obtain a wider communication channel bandwidth, it is necessary to use a higher frequency communication band. Current LTE... TM （The Long Term Evolution (LTE) specification defines frequency bands between 3.3 GHz and 5.9 GHz. These bands are currently unused. Future proposals for wireless communications include millimeter-wave communication bands up to 28 GHz.

[0007] High-performance RF filters used in current communication systems typically incorporate acoustic resonators, including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, thin-film bulk acoustic wave (FBAR) resonators, and other types of acoustic resonators. However, these existing technologies are not suitable for use at higher frequencies, which future communication networks will require. Summary of the Invention

[0008] This invention discloses an acoustic resonator device, comprising: a substrate having a trap-rich region adjacent to a surface; a single-crystal piezoelectric plate having parallel front and back sides, except for a piezoelectric plate portion forming a diaphragm, wherein the diaphragm spans a cavity formed in the substrate, and the back side is attached to a surface of the substrate; and an interdigital transducer (IDT) formed on the front side of the single-crystal piezoelectric plate, such that interlaced fingers of the IDT are disposed on the diaphragm, the single-crystal piezoelectric plate and the IDT being configured such that a radio frequency signal applied to the IDT excites a shear-dominant acoustic mode within the diaphragm.

[0009] The diaphragm is adjacent to the piezoelectric plate at least 50% of the periphery of the cavity.

[0010] The substrate includes a single-crystal silicon plate.

[0011] The trap enrichment region is a portion of the silicon slab that has been irradiated to create defects in the crystal structure.

[0012] The trap-rich region is a portion of the silicon substrate containing deep trap impurities.

[0013] The trap enrichment region is a layer of trap enrichment material formed on the surface of the silicon substrate.

[0014] The trap enrichment material is amorphous silicon or polycrystalline silicon.

[0015] The depth of the trap-rich region is greater than the depth of the inversion layer formed in the substrate in the absence of the trap-rich region.

[0016] The present invention also discloses a filter device comprising: a substrate having a trap enrichment region adjacent to a surface; a single-crystal piezoelectric plate having a parallel front and a back side, the back side being attached to a surface of the substrate, a portion of the single-crystal piezoelectric plate forming one or more diaphragms spanning various cavities in the substrate; and a conductor pattern formed on the front side, the conductor pattern including a plurality of interdigital transducers (IDTs) of a plurality of corresponding acoustic resonators, staggered fingers of each of the plurality of IDTs being disposed on one of the one or more diaphragms, wherein the single-crystal piezoelectric plate and all IDTs are configured such that a corresponding radio frequency signal applied to each IDT excites a corresponding shearing principal acoustic mode within the corresponding diaphragm.

[0017] Each of the one or more diaphragms is adjacent to the piezoelectric plate at least 50% of the periphery of the respective cavity.

[0018] The substrate includes a single-crystal silicon plate.

[0019] The trap enrichment region is a portion of the silicon slab that has been irradiated to create defects in the crystal structure.

[0020] The trap-rich region is a portion of the silicon substrate containing deep trap impurities.

[0021] The trap enrichment region is a layer of trap enrichment material formed on the surface of the silicon substrate.

[0022] The trap enrichment material is amorphous silicon or polycrystalline silicon.

[0023] The depth of the trap-rich region is greater than the depth of the inversion layer formed in the substrate in the absence of the trap-rich region.

[0024] The present invention further discloses a method for fabricating an acoustic resonator device on a substrate having a trap-rich region adjacent to a surface, the method comprising: attaching a back side of a single-crystal piezoelectric plate to a surface of the substrate; forming a cavity in the substrate such that a portion of the single-crystal piezoelectric plate forms a diaphragm spanning the cavity; and forming interdigitated transducers (IDTs) on the front side of the single-crystal piezoelectric plate such that the interlaced fingers of the IDTs are disposed on the diaphragm, the single-crystal piezoelectric plate and all IDTs being configured such that a radio frequency signal applied to the IDTs excites a shear-dominant acoustic mode within the diaphragm. According to the method, the diaphragm is adjacent to the piezoelectric plate for at least 50% of the periphery of the cavity.

[0025] The cavity is formed before the single-crystal piezoelectric plate is attached to the surface of the substrate.

[0026] The cavity is formed after the single-crystal piezoelectric plate is attached to the surface of the substrate. Attached Figure Description

[0027] Figure 1 Includes a schematic plan view and two schematic cross-sectional views of a transversely excited thin-film bulk acoustic resonator (XBAR).

[0028] Figure 2 yes Figure 1 A partially enlarged schematic cross-sectional view of the XBAR.

[0029] Figure 3 yes Figure 1 Alternative schematic cross-sectional view of XBAR.

[0030] Figure 4 This is a diagram showing the shear level acoustic modes in XBAR.

[0031] Figure 5 Here is a schematic cross-sectional view and two detailed cross-sectional views of a filter using XBAR.

[0032] Figure 6 This is a graph comparing the input / output transfer functions of filters fabricated using high-resistivity and low-resistivity substrates.

[0033] Figure 7 This is a flowchart of the process for fabricating a filter on a piezoelectric plate bonded to a silicon substrate with a trap enrichment layer.

[0034] Throughout the specification, elements appearing in the accompanying drawings are assigned three- or four-digit reference numerals, where the two least significant digits are unique to that element, and one or two most significant digits are the drawing number in which the element is first shown. Elements not described in conjunction with the accompanying drawings may be assumed to have the same characteristics and functions as previously described elements with the same reference numerals. Detailed Implementation

[0035] Description of the device

[0036] Figure 1 A simplified schematic top view and orthogonal cross-sectional view of a laterally excited thin-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 communication frequency bands above 3 GHz.

[0037] XBAR 100 consists of a thin-film conductor pattern formed on the surface of a piezoelectric plate 110, which has parallel front and back faces 112 and 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 X, Y, and Z crystal axes are known and aligned with respect to the front and back faces. In the example presented in this patent, the piezoelectric plate is Z-shaped cut, meaning the Z-axis is perpendicular to the front and back faces 112 and 114. However, XBARs can be fabricated on piezoelectric plates with other crystallographic orientations, including rotated Z-shaped cuts and rotated YX-shaped cuts.

[0038] Except for the portion of piezoelectric plate 110 that forms diaphragm 115 (wherein diaphragm 115 spans a cavity 140 formed in the substrate), the back surface 114 of piezoelectric plate 110 is attached to the surface of substrate 120. The portion of piezoelectric plate spanning the cavity is referred to herein as "diaphragm" 115 due to its physical similarity to the diaphragm of a microphone. Figure 1 As shown, the diaphragm 115 is adjacent to the rest of the piezoelectric plate 110 around the entire periphery 145 of the cavity 140. In this case, "adjacent" means "continuous connection without any intermediate items".

[0039] Substrate 120 provides mechanical support for piezoelectric plate 110. Substrate 120 may be, for example, silicon, sapphire, quartz, or some other material or combination of materials. The back side 114 of piezoelectric plate 110 may be bonded to substrate 120 using wafer bonding processes. Alternatively, piezoelectric plate 110 may be grown on substrate 120 or otherwise attached to the substrate. Piezoelectric plate 110 may be directly attached to the substrate or may be attached to substrate 120 via one or more intermediate material layers.

[0040] The term "cavity" has its conventional meaning, namely, "empty space within a solid." Cavity 140 can be a hole that completely penetrates the substrate 120 (as shown in sections AA and BB), or it can be a recess in the substrate 120 (as will be shown later in...). Figure 3 A and Figure 3 (as shown in B). For example, the cavity 140 can be formed by selectively etching the substrate 120 before or after attaching the piezoelectric plate 110 and the substrate 120.

[0041] The conductor pattern of XBAR 100 includes an interdigitated transducer (IDT) 130. IDT 130 includes a first plurality of parallel fingers, such as fingers 136, and a second plurality of fingers, wherein the first plurality of parallel fingers extend from a first busbar 132, and the second plurality of fingers extend from a second busbar 134. The first and second plurality of parallel fingers are staggered. The staggered fingers overlap by a distance AP, which is commonly referred to as the “aperture” of the IDT. The center-to-center distance L between the outermost fingers of IDT 130 is the “length” of the IDT.

[0042] The first and second buses 132 and 134 serve as terminals of the XBAR 100. An radio frequency or microwave signal applied between the two buses 132 and 134 of the IDT 130 excites the primary acoustic mode within the piezoelectric plate 110. As will be discussed in detail below, the primary acoustic mode is a bulk shear mode, in which acoustic energy 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 a transversely excited thin-film bulk resonator.

[0043] IDT 130 is disposed on piezoelectric plate 110 such that at least the fingers of IDT 130 are disposed on diaphragm 115 of piezoelectric plate, which spans or hangs over cavity 140. Figure 1 As shown, cavity 140 has a rectangular cross-section, which is larger than the aperture AP and length L of IDT 130. The cavity of the XBAR can have different cross-sectional shapes, such as regular or irregular polygons. The cavity of the XBAR can have more or fewer than four sides, which can be straight or curved.

[0044] To better illustrate Figure 1 Compared to the length (size L) and aperture (size AP) of the XBAR, the geometric spacing and width of the fingers in the IDT are greatly magnified. A typical XBAR in an IDT has more than ten parallel fingers. An XBAR in an IDT may have hundreds or even thousands of parallel fingers. Similarly, the thickness of the fingers in the cross-sectional view is greatly magnified.

[0045] Figure 2 It shows Figure 1 A detailed schematic cross-sectional view of XBAR 100. Piezoelectric plate 110 is a single-crystal layer of piezoelectric material with a thickness of ts. ts can be, for example, 100 nm to 1500 nm. When used for LTE from 3.4 GHz to 6 GHz... TM In filters for frequency bands (e.g., bands 42, 43, 46), the thickness ts can be, for example, 200 nm to 1000 nm.

[0046] Optionally, a front dielectric layer 214 may be formed on the front side of the piezoelectric plate 110. By definition, the "front side" of XBAR refers to the surface facing away from the substrate. The front dielectric layer 214 has a thickness tfd. The front dielectric layer 214 is formed between the IDT fingers 238. Although Figure 2 Not shown, but the front dielectric layer 214 may also be deposited on the IDT fingers 238. The back dielectric layer 216 may optionally be formed on the back side of the piezoelectric plate 110. The back dielectric layer 216 has a thickness tbd. The front dielectric layer 214 and the back dielectric layer 216 may be non-piezoelectric dielectric materials, such as silicon dioxide or silicon nitride. tfd and tbd may be, for example, 0 to 500 nm. tfd and tbd are typically less than the thickness ts of the piezoelectric plate. tfd and tbd need not be equal, and the front and back dielectric layers 214, 216 need not be the same material. The front dielectric layer 214 and / or the back dielectric layer 216 may be formed from multiple layers of two or more materials.

[0047] IDT fingers 238 can be aluminum or a basic aluminum alloy, copper or a basic copper alloy, beryllium, gold, or some other conductive material. A thin layer (relative to the total thickness of the conductor) of another metal (e.g., chromium or titanium) can be formed below and / or above the fingers to improve adhesion between the fingers and the piezoelectric plate 110 and / or passivate or encapsulate the fingers. The busbar of the IDT ( Figure 1 132 and 134 in the text can be made of the same or different material as the finger.

[0048] The dimension p is the center-to-center spacing or "pitch" of the IDT fingers, which can be referred to as the IDT pitch and / or XBAR pitch. The dimension w is the width or "mark" of the IDT fingers. The IDT in XBAR is significantly different from the IDT used in surface acoustic wave (SAW) resonators. In SAW resonators, the IDT pitch is half the wavelength of the acoustic wave at the resonant frequency. Additionally, the mark pitch ratio of SAW resonator IDTs is typically close to 0.5 (i.e., the width of the mark or finger is approximately one-quarter of the wavelength of the acoustic wave at resonance). In XBAR, the IDT pitch p is typically 2 to 20 times the finger width w. Furthermore, the IDT pitch p is typically 2 to 20 times the thickness ts of the piezoelectric plate 110. The width of the IDT fingers in XBAR is not limited to one-quarter of the wavelength of the acoustic wave at resonance. For example, the width of the XBAR IDT fingers can be 500 nm or greater, allowing the IDT to be fabricated using photolithography. The thickness tm of the IDT fingers can range from 100 nm to approximately equal to the width w. IDT bus ( Figure 1 The thickness of 132 and 134 in the figure can be equal to or greater than the thickness tm of the IDT finger.

[0049] Figure 3 It shows along Figure 1 An alternative cross-sectional view of section AA as defined in the diagram. Figure 3 In this configuration, a piezoelectric plate 310 is attached to a substrate 320. A portion of the piezoelectric plate 310 forms a diaphragm 315 spanning a cavity 340 in the substrate. The cavity 340 does not completely penetrate the substrate 320. IDT fingers are disposed on the diaphragm 315. For example, the cavity 340 can be formed by etching the substrate 320 prior to attaching the piezoelectric plate 310. Alternatively, the cavity 340 can be formed by etching the substrate 320 with a selective etchant that reaches the substrate through one or more openings (not shown) disposed in the piezoelectric plate 310. In this case, the diaphragm 315 may abut the remainder of the piezoelectric plate 310 around a large portion of the periphery 345 of the cavity 340. For example, the diaphragm 315 may abut the remainder of the piezoelectric plate 310 around at least 50% of the periphery of the cavity 340.

[0050] Figure 4 This is a diagram of the main acoustic modes of interest in XBAR. Figure 4 A small portion of the XBAR 400 is shown, comprising a piezoelectric plate 410 and three staggered IDT fingers 430. An RF voltage is applied to the staggered fingers 430. This voltage generates a time-varying electric field between the fingers. As indicated by the arrow labeled “Electric Field,” the direction of the electric field is transverse or parallel to the surface of the piezoelectric plate 410. Due to the high dielectric constant of the piezoelectric plate, the electric field is highly concentrated in the plate relative to air. The transverse electric field introduces shear deformation in the piezoelectric plate 410, thereby strongly exciting shear-mode acoustic modes. In this paper, “shear deformation” is defined as deformation in a material where parallel planes remain parallel and maintain a constant distance when translated 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 the XBAR 400 is represented by curve 460, with adjacent small arrows indicating the direction and magnitude of atomic motion. For ease of observation, the degree of atomic motion and the thickness of the piezoelectric plate 410 are greatly exaggerated. Although the atomic motion is primarily transverse (i.e., as shown by the arrows), the shear deformation in the XBAR 400 is not fully exaggerated. Figure 4 (As shown in the figure, it is horizontal), but the direction of the acoustic energy flow of the main shear acoustic mode is basically perpendicular to the surface of the piezoelectric plate, as shown by arrow 465.

[0051] like Figure 4 As shown, there is essentially no electric field directly beneath the IDT fingers 430, thus only minimal excitation of acoustic modes occurs in the region 470 beneath the fingers. Brief acoustic motions may occur in these regions. Because no acoustic vibrations are excited beneath the IDT fingers 430, the acoustic energy coupled to the IDT fingers 430 is very low (e.g., compared to IDT fingers in a SAW resonator), which minimizes viscous losses in the IDT fingers.

[0052] Shear wave resonators based on XBAR exhibit superior performance compared to current state-of-the-art thin-film bulk acoustic resonators (FBAR) and solid-mounted resonator bulk acoustic (SMR BAW) devices (where an electric field is applied along the thickness direction). In such devices, the acoustic modes are compressed in the direction of atomic motion and acoustic energy flow along the thickness. Furthermore, the piezoelectric coupling for shear wave XBAR resonances can be higher (>20%) compared to other acoustic resonators. Therefore, high-voltage electric coupling can be used to design and implement microwave and millimeter-wave filters with considerable bandwidth.

[0053] Figure 5 A schematic cross-sectional view and two detailed cross-sectional views of a filter 500 using XBAR are shown. A piezoelectric plate 510 is attached to a substrate 520. An optional dielectric layer 525 may be sandwiched between the piezoelectric plate 510 and the substrate 520. A portion of the piezoelectric plate 510 forms a diaphragm 515 spanning a cavity 540 in the substrate. As shown, the cavity 540 does not completely penetrate the substrate 520. Alternatively, as... Figure 1 As shown, cavity 540 can penetrate the substrate. IDT fingers are disposed on diaphragm 515. On the surface of piezoelectric plate 510, at the location where cavity 540 has been removed, two conductors 550 and 555 are formed. The two conductors 550 and 555 can be signal conductors interconnecting other components of XBAR and / or filter 500. Conductors 550 and 555 can be a signal conductor and a ground conductor. Although... Figure 5 Only a single XBAR and two conductors are shown, but a filter can include multiple XBARs as well as two or more signal conductors and ground conductors.

[0054] The preferred material for substrate 520 is silicon. Silicon wafers are readily available and inexpensive. Furthermore, processes and equipment for handling silicon wafers are well-developed. However, silicon is a semiconductor material. Silicon wafers can be doped or loaded with impurities to achieve a desired bulk resistivity. An undoped or intrinsic silicon wafer can form a conductive inversion layer along the boundary between silicon and some other material, for example, along the boundary between silicon wafer 520 and dielectric layer 525 of filter device 500. If dielectric layer 525 is not present, an inversion layer can be formed along the boundary between silicon wafer 520 and piezoelectric plate 510.

[0055] like Figure 5 As shown in the details, conductors 550 and 555 are capacitively coupled to substrate 520 via piezoelectric plate 510 and dielectric layer 525 (if present). If substrate 520 is conductive, or if a conductive inversion layer is formed in substrate 520, conductors 550 and 555 will be effectively connected at RF frequencies via parasitic resistance 560. The power dissipated in resistor 560 will contribute to the insertion loss of filter 500.

[0056] Figure 6 An amplified example of filter degradation due to substrate conductivity is shown. Figure 6 This is a graph showing the relationship between the magnitude of the S21 (input-output transfer function) and the frequencies of two filters, which are identical except for their substrate materials. Solid line 610 shows the S21 of a filter fabricated on a nearly insulating silicon substrate with a bulk resistivity of 5000 ohm-cm. Dashed line 620 shows the S21 of a filter fabricated on a conductive silicon substrate with a bulk resistivity of 15 ohm-cm. Both graphs are based on simulations of the filters using the finite element method. The differences between the two filters are significant. In the filter passband, substrate conductivity reduces S21 by 6 dB or more (i.e., increases insertion loss). The effect of the conductive inversion layer in the high-resistivity substrate on insertion loss is smaller, but still noticeable.

[0057] Back Figure 5 Detail B shows a partial cross-sectional view of a filter formed on substrate 520, which includes a high-resistivity silicon wafer 522 and a trap-rich region 524. The trap-rich region 524 may be a region within the high-resistivity silicon wafer 522 or a layer formed on the surface of the high-resistivity silicon wafer 522. In either case, if a dielectric layer 525 is absent, the trap-rich region is adjacent to the dielectric layer 525 or piezoelectric plate 510. The trap-rich region 522 has a large number of traps that trap free carriers and reduce carrier lifetime to a degree where the conductivity of the trap-rich region approaches zero.

[0058] Traps-rich regions can be formed within a silicon substrate by irradiating the substrate surface with neutrons, protons, or various ions (silicon, argon, nitrogen, neon, oxygen, etc.) to create defects in the substrate's crystal structure. Alternatively, trap-rich regions can be formed within the silicon substrate by introducing deep trap impurities, such as gold, copper, or other metal ions. Such impurities can be introduced via ion implantation, diffusion, or other methods. A combination of these techniques can be used to form trap-rich regions. When the filter 500 includes a dielectric layer 525, the trap-rich region 524 can be formed before the dielectric layer is formed on the substrate 520. Alternatively, the trap-rich region 524 can be formed by ion implantation through the dielectric layer 525.

[0059] Traps can be formed on a silicon substrate by depositing a trap-rich material, such as amorphous silicon or polycrystalline silicon (polysilicon). When the trap-rich region is polycrystalline silicon, the average grain size of the polycrystalline silicon should be substantially smaller than the minimum spacing between electrodes 550 and 555. The thickness of the trap-rich region formed on or within the high-resistivity silicon substrate should be greater than the thickness of the inversion layer that might be formed without a trap-rich layer.

[0060] Method description

[0061] Figure 7 This is a simplified flow chart illustrating process 700 for manufacturing a filter that incorporates an XBAR and a substrate with trap-rich regions. Process 700 begins at 705 with a substrate and a piezoelectric material plate and ends at 795 with the completed XBAR or filter. Figure 7 The flowchart only includes the main processing steps. (It can be found in...) Figure 7 Various routine process steps (e.g., surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) are performed before, between, after, and during the steps shown.

[0062] Figure 7 The flowchart captures three variations of process 700 for manufacturing XBARs, differing in when and how the cavity is formed in the substrate. The cavity can be formed at steps 715A, 715B, or 715C. In each of the three variations of process 700, only one of these steps is performed.

[0063] The piezoelectric plate can be, for example, Z-cut lithium niobate or lithium tantalate. The piezoelectric plate can be a rotary Z-cut or rotary YX-cut lithium niobate. The piezoelectric plate can be other materials and / or other cuts. The substrate can preferably be high-resistivity silicon. The substrate can be other materials that allow deep cavities to be formed by etching or other processes.

[0064] At 710, a trap-rich region can be formed on the substrate. This trap-rich region can be formed within the silicon substrate by irradiating the substrate surface with neutrons, protons, or various ions (silicon, argon, nitrogen, neon, oxygen, etc.) to disrupt the substrate's crystal structure. Alternatively, a trap-rich region can be formed within the silicon substrate by introducing deep trap impurities such as gold, copper, or other metal ions. Such impurities can be introduced via ion implantation, diffusion, or other methods. A combination of these techniques can be used to form the trap-rich region. When the filter 500 includes a dielectric layer 525, the trap-rich region 524 can be formed before the dielectric layer is formed on the substrate 520. Alternatively, the trap-rich region 524 can be formed by ion implantation through the dielectric layer 525.

[0065] Alternatively, at 710, a trap-rich region can be formed on the silicon substrate by depositing a trap-rich material such as amorphous silicon or polycrystalline silicon. When the trap-rich region is polycrystalline silicon, the average particle size of the polycrystalline silicon should be substantially smaller than the minimum spacing between electrodes 550 and 555.

[0066] In all cases, the thickness of the trap enrichment zone formed at 710 should be greater than the thickness of the inversion layer that can be formed in the absence of a trap enrichment zone.

[0067] In a variation of process 700, one or more cavities are formed in the substrate at 715A before the piezoelectric plate is bonded to the substrate at 720. Individual cavities can be formed for each resonator in the filter device. Conventional photolithography and etching techniques can be used to form the one or more cavities. Typically, the cavities formed at 715A will not penetrate the substrate, and the resulting resonator device will have, for example, [missing information - likely a specific feature or characteristic]. Figure 3 A and Figure 3 The cross-section shown in B.

[0068] At 720°, the piezoelectric plate is bonded to the substrate. The piezoelectric plate and substrate can be bonded using a wafer bonding process. Typically, the mating surfaces of the substrate and piezoelectric plate are highly polished. One or more layers of intermediate material, such as oxides or metals, can be formed or deposited on the mating surfaces of the piezoelectric plate and / or substrate. One or both mating surfaces can be activated using, for example, a plasma process. The mating surfaces can then be pressed together with considerable force to establish molecular bonds between the piezoelectric plate and the substrate or intermediate material layer.

[0069] At position 730, by depositing and constructing on the front side of the piezoelectric plate Figure 1 One or more conductor layers are used to form a conductor pattern for the IDT including each XBAR. The conductor layers can be, for example, aluminum, aluminum alloy, copper, copper alloy, or some other conductive metal. Optionally, one or more layers of other materials can be disposed below the conductor layers (i.e., between the conductor layers and the piezoelectric plate) and / or on top of the conductor layers. For example, a thin film of titanium, chromium, or other metals can be used to improve adhesion between the conductor layers and the piezoelectric plate. A conductive reinforcement layer of gold, aluminum, copper, or other metals with higher conductivity can be formed above portions of the conductor pattern (e.g., the IDT busbar and the interconnection between IDTs).

[0070] A conductor pattern can be formed at 730 by sequentially depositing a conductor layer and optionally one or more other metal layers on the surface of the piezoelectric plate. Excess metal can then be removed by etching with a patterned photoresist. The conductor layer can be etched, for example, by plasma etching, reactive ion etching, wet chemical etching, and other etching techniques.

[0071] Alternatively, a stripping process can be used at 730 to form the conductor pattern. A photoresist can be deposited on the piezoelectric plate and patterned to define the conductor pattern. A conductor layer, along with one or more optional additional layers, can be sequentially deposited on the surface of the piezoelectric plate. The photoresist can then be removed, removing excess material and leaving the conductor pattern.

[0072] At 740, a front dielectric layer can be formed by depositing one or more layers of dielectric material on the front side of the piezoelectric plate. Conventional deposition techniques such as sputtering, evaporation, or chemical vapor deposition can be used to deposit one or more dielectric layers. One or more dielectric layers can be deposited over the entire surface of the piezoelectric plate, including on top of the conductor pattern. Alternatively, one or more photolithography processes (using photomasks) can be used to confine the deposition of dielectric layers to selected areas of the piezoelectric plate, for example, confining it only between the interlaced fingers of the IDT. Masks can also be used to allow the deposition of dielectric material of different thicknesses on different portions of the piezoelectric plate.

[0073] In a second variation of process 700, one or more cavities are formed in the back side of the substrate at 715B. A separate cavity can be formed for each resonator in the filter device. Anisotropic or orientation-dependent dry or wet etching can be used to form one or more cavities to open holes through the back side of the substrate to reach the piezoelectric plate. In this case, the resulting resonator device will have, for example, […]. Figure 1 The cross-section shown.

[0074] In a second variation of process 700, a back dielectric layer can be formed at 750. When the cavity formed at 715B serves as a hole through the substrate, conventional deposition techniques, such as sputtering, evaporation, or chemical vapor deposition, can be used to deposit the back dielectric layer through the cavity.

[0075] In a third variation of process 700, one or more cavities in the form of grooves in the substrate can be formed at 715C by etching the substrate with an etchant introduced through an opening in the piezoelectric plate. A separate cavity can be formed for each resonator in the filter device. The one or more cavities formed at 715C will not penetrate the substrate, and the resulting resonator device will have... Figure 3 The cross-section shown.

[0076] In all variations of process 700, the filter device can be completed at 760. Actions that may occur at 760 include: depositing materials such as SiO2 or S on the entire or partial device. i3 The process includes: O4 encapsulation / passivation layer; forming pads or solder bumps or other means for establishing connections between the device and external circuitry; cutting individual devices from a wafer containing multiple devices; other packaging steps; and testing. Another action that may occur at 760 is tuning the resonant frequency of the resonator within the device by adding or removing metal or dielectric material from the front side of the device. Once the filter device is complete, the process ends at 795.

[0077] Summarize

[0078] Throughout this specification, the embodiments and examples shown should be considered as examples and not as limitations on the disclosed or claimed devices and processes. While many of the examples provided herein relate to specific combinations of method actions or system elements, it should be understood that those actions and elements can be combined in other ways to achieve the same objective. Regarding the flowcharts, additional and fewer steps may be taken, and the steps shown may be combined or further refined to implement the methods described herein. Actions, elements, and features discussed in connection with only one embodiment are not intended to exclude their similarity in other embodiments.

[0079] As used herein, “multiple” means two or more. As used herein, a “group” of items may include one or more such items. As used herein, whether in the written description or in the claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” etc., shall be understood as open-ended, i.e., referring to including but not limited to. Only the transitional phrases “consisting of…” and “substantially consisting of…” are closed or semi-closed transitional phrases relative to the claims. Ordinal numbers used in the claims, such as “first,” “second,” “third,” etc., are used to modify claim elements. This does not in itself indicate the priority, order, or sequence of action of one claim element over another, but is merely used to distinguish one claim element with the same name from another element with the same name (but with ordinal numbers), thereby differentiating claim elements. As used herein, “and / or” means that the listed items are alternatives, but alternatives also include any combination of the listed items.

Claims

1. An acoustic resonator device, comprising: A substrate having a trap-rich region adjacent to a surface; A piezoelectric plate having parallel front and back sides, except for a piezoelectric plate portion forming a diaphragm, wherein the diaphragm spans a cavity formed in the substrate, and the back side is attached to the surface of the substrate via an intermediate dielectric layer; and An interdigital transducer (IDT) is formed on the front side of the piezoelectric plate, such that the interlaced fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shearing primary acoustic mode within the diaphragm through a transverse electric field parallel to the front side of the piezoelectric plate, such that the direction of the acoustic energy flow of the shearing primary acoustic mode is substantially perpendicular to the front and back sides of the piezoelectric plate.

2. The apparatus according to claim 1, characterized in that, The diaphragm is adjacent to the piezoelectric plate at least 50% of the periphery of the cavity.

3. The apparatus according to claim 1, characterized in that, The substrate includes a silicon plate.

4. The apparatus according to claim 3, characterized in that, The trap enrichment region is a portion of the silicon substrate that has been irradiated to create defects in the crystal structure of the silicon substrate.

5. The apparatus according to claim 3, characterized in that, The trap-rich region is a portion of the silicon substrate containing deep trap impurities.

6. The apparatus according to claim 3, characterized in that, The trap enrichment zone is a layer of trap enrichment material formed on the surface of the silicon substrate.

7. The apparatus according to claim 6, characterized in that, The trap enrichment material is amorphous silicon or polycrystalline silicon.

8. The apparatus according to claim 1, characterized in that, The depth of the trap-rich region is greater than the depth of the inversion layer formed in the substrate in the absence of the trap-rich region.

9. A filter device, comprising: A substrate having a trap-rich region adjacent to a surface; A piezoelectric layer having parallel front and back sides, the back side being attached to the surface of the substrate via an intermediate dielectric layer, a portion of the piezoelectric layer forming one or more diaphragms above a respective cavity of a plurality of cavities between the substrate and the piezoelectric layer; and A conductor pattern is formed on the front side, the conductor pattern comprising multiple interdigitated transducers (IDTs) of corresponding multiple acoustic resonators, wherein the interlaced fingers of each of the multiple IDTs are disposed on one of one or more diaphragms, wherein The piezoelectric layer and all IDTs are configured such that a corresponding radio frequency signal applied to each IDT excites a corresponding shear principal acoustic mode within the corresponding diaphragm through a transverse electric field parallel to the front side of the piezoelectric layer, such that the direction of the acoustic energy flow of the corresponding shear principal acoustic mode is substantially perpendicular to the front and back sides of the piezoelectric layer.

10. The filter device according to claim 9, characterized in that, Each of the one or more diaphragms is adjacent to the piezoelectric layer at least 50% of the periphery of the corresponding cavity in the plurality of cavities.

11. The filter device according to claim 9, characterized in that, The substrate includes a silicon plate.

12. The filter device according to claim 11, characterized in that, The trap enrichment region is a portion of the silicon substrate that has been irradiated to create defects in the crystal structure of the silicon substrate.

13. The filter device according to claim 11, characterized in that, The trap-rich region is a portion of the silicon substrate containing deep trap impurities.

14. The filter device according to claim 11, characterized in that, The trap enrichment zone is a layer of trap enrichment material formed on the surface of the silicon substrate.

15. The filter device according to claim 14, characterized in that, The trap enrichment material is amorphous silicon or polycrystalline silicon.

16. The filter device according to claim 9, characterized in that, The depth of the trap-rich region is greater than the depth of the inversion layer formed in the substrate in the absence of the trap-rich region.

17. A method for fabricating an acoustic resonator device on a substrate having a trap-rich region adjacent to a surface, the method comprising: The back side of the piezoelectric plate is attached to the surface of the substrate via an intermediate dielectric layer; A cavity is formed in the substrate such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity; as well as An interdigitated transducer (IDT) is formed on the front side of the piezoelectric plate opposite to the back side, such that the interlaced fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shearing primary acoustic mode within the diaphragm through a transverse electric field parallel to the front side of the piezoelectric plate, such that the direction of the acoustic energy flow of the shearing primary acoustic mode is substantially perpendicular to the front and back sides of the piezoelectric plate.

18. The method according to claim 17, characterized in that, The diaphragm is adjacent to the piezoelectric plate at least 50% of the periphery of the cavity.

19. The method according to claim 17, characterized in that, The cavity is formed before the piezoelectric plate is attached to the surface of the substrate.

20. The method according to claim 17, characterized in that, The cavity is formed after the piezoelectric plate is attached to the surface of the substrate.

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