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DE-112020001227-B4 - Transversely excited acoustic film resonator with lambda-half dielectric layer

DE112020001227B4DE 112020001227 B4DE112020001227 B4DE 112020001227B4DE-112020001227-B4

Abstract

Acoustic resonator device, comprising: a substrate (120) with a surface; a piezoelectric plate (310, 510) with a front and a back surface, wherein the back surface is attached to the surface of the substrate (120), except for a part of the piezoelectric plate (310, 510) which forms a membrane (115) spanning a cavity (140) in the substrate (120); an interdigital converter, IDT, (130) on the front surface of the piezoelectric plate (310, 510), such that nested fingers (338, 538) of the IDT (130) are arranged on the membrane (115), wherein the piezoelectric plate (310, 510) and the IDT (130) are configured such that a high-frequency signal applied to the IDT (130) excites a primary acoustic shear mode in the membrane (115); and a dielectric layer (350, 550) arranged either on the front surface or on the back surface of the piezoelectric plate (310, 510), where a thickness td of the dielectric layer (350, 550) is defined as: 0.85 λ 0,d ≤ 2 td ≤ 1.15 λ 0,d , and where λ 0,d is a wavelength of the fundamental resonance of the acoustic volume shear wave in the dielectric layer (350, 550).

Inventors

  • Ventsislav Yantchev

Assignees

  • MURATA MANUFACTURING CO., LTD.

Dates

Publication Date
20260513
Application Date
20200316
Priority Date
20200316

Claims (12)

  1. Acoustic resonator device comprising: a substrate (120) with a surface; a piezoelectric plate (310, 510) with a front and a back surface, wherein the back surface is attached to the surface of the substrate (120), except for a portion of the piezoelectric plate (310, 510) which forms a membrane (115) spanning a cavity (140) in the substrate (120); an interdigital transducer, IDT, (130) on the front surface of the piezoelectric plate (310, 510), such that nested fingers (338, 538) of the IDT (130) are arranged on the membrane (115), wherein the piezoelectric plate (310, 510) and the IDT (130) are arranged such that a high-frequency signal applied to the IDT (130) excites a primary acoustic shear mode in the membrane (115); and a dielectric layer (350, 550) arranged either on the front surface or on the back surface of the piezoelectric plate (310, 510), wherein a thickness td of the dielectric layer (350, 550) is defined as: 0.85 λ 0,d ≤ 2 td ≤ 1.15 λ 0,d , and wherein λ 0,d is a wavelength of the fundamental resonance of the acoustic volume shear wave in the dielectric layer (350, 550).
  2. Acoustic resonator device according to Claim 1 , where a thickness ts of the piezoelectric plate (310, 510) is defined as follows: 2 ts = λ 0, s where λ 0,s is a wavelength of a fundamental resonance of the acoustic volume shear wave in the piezoelectric plate (310, 510).
  3. Acoustic resonator device according to Claim 1 , wherein the dielectric layer (350, 550) is one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 and AlN.
  4. Acoustic resonator device according to Claim 1 , where the piezoelectric plate (310, 510) is lithium niobate, the dielectric layer (350, 550) is SiO2 , and a thickness ts of the piezoelectric plate (310, 510) and the thickness td of the dielectric layer (350, 550) is defined by the relationship: 0.875 ts ≤ td ≤ 1.25 ts
  5. Acoustic resonator device according to Claim 4 , wherein a temperature coefficient of the frequency of the acoustic resonator device is between -32 ppm/C° and -42 ppm/C° at a resonance frequency and between -20 ppm/C° and -36 ppm/C° at an antiresonance frequency.
  6. Filter device comprising: a substrate (120); a piezoelectric plate (310, 510) with parallel front and back surfaces and a thickness ts, the back surface being attached to the substrate (120); a conductor structure formed on the front surface, the conductor structure comprising a plurality of interdigital transducers, IDTs, (130) of a respective plurality of resonators comprising a shunt resonator and a series resonator, with nested fingers of each of the plurality of IDTs (130) arranged on respective parts of the piezoelectric plate (310, 510) that are above one or more cavities formed in the substrate (120); a first dielectric layer (350, 550) having a thickness tds, deposited between the fingers of the series resonator; and a second dielectric layer (350, 550) with a thickness tdp deposited between the fingers of the shunt resonator, where ts, tds and tdp are related to each other by the equations: 2 ts = λ 0, s , and 0,85 λ 0, d ≤ 2 tds < 2 tdp ≤ 1,15 λ 0, d , where λ 0,s is a wavelength of a fundamental resonance of the acoustic volume shear wave in the piezoelectric plate (310, 510), and λ 0,d is a wavelength of the fundamental resonance of the acoustic volume shear wave in the dielectric layer (350, 550).
  7. Filter device comprising: a substrate (120); a lithium niobate piezoelectric plate (310, 510) with parallel front and back surfaces and a thickness ts, the back surface being attached to the substrate (120); a conductor structure formed on the front surface, the conductor structure comprising a plurality of interdigital transducers, IDTs, (130) of a respective plurality of resonators comprising a shunt resonator and a series resonator, with nested fingers of each of the plurality of IDTs (130) arranged on respective parts of the piezoelectric plate (310, 510) that are above one or more cavities formed in the substrate (120); a first SiO₂ layer of a thickness tds deposited between the fingers of the series resonator; and a second SiO2 layer with a thickness tdp deposited between the fingers of the shunt resonator, where ts, tds and tdp are related to each other by the equation: 0,875 ts ≤ tds < tdp ≤ 1,25 ts .
  8. Acoustic resonator device according to Claim 7 , wherein a temperature coefficient of the frequency of the acoustic resonator device lies between -20 ppm/C° and -42 ppm/C° at the resonance frequencies and the antiresonance frequencies of all of the plurality of resonators.
  9. Method for manufacturing an acoustic resonator device on a piezoelectric plate (310, 510) having parallel front and back surfaces, wherein the back surface is attached to a substrate (120), the method comprising: forming (1310A, 1310B, 1310C) a cavity (140) in the substrate (120) such that part of the piezoelectric plate (310, 510) forms a membrane (115) spanning the cavity (140); Forming (1350) an interdigital transducer, IDT, (130) on the front surface of the piezoelectric plate (310, 510) such that nested fingers of the IDT (130) are arranged on the membrane (115), wherein the piezoelectric plate (310, 510) and the IDT (130) are arranged such that a high-frequency signal applied to the IDT (130) excites a primary acoustic shear mode within the membrane (115); and forming (1360) a dielectric layer (350, 550) on the front or back surface of the piezoelectric plate (310, 510), wherein a thickness td of the dielectric layer (350, 550) is defined as: 0.85 λ 0,d ≤ 2 td ≤ 1.15 λ 0,d , and wherein λ 0,d is a wavelength of the fundamental resonance of the acoustic volume shear wave in the dielectric layer (350, 550).
  10. Procedure according to Claim 9 , where a thickness ts of the piezoelectric plate (310, 510) is defined as follows: 2 ts = λ 0, s where λ 0,s is a wavelength of a fundamental resonance of the acoustic volume shear wave in the piezoelectric plate (310, 510).
  11. Procedure according to Claim 9 , wherein the formation of the dielectric layer (350, 550) further comprises: depositing one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 and AlN.
  12. Procedure according to Claim 9 , wherein the piezoelectric plate (310, 510) is lithium niobate, and the formation of the dielectric layer (350, 550) comprises depositing SiO2 to a thickness td, where td is greater than or equal to 0.875 ts and less than or equal to 1.25 ts, where ts is a thickness of the piezoelectric plate (310, 510).

Description

BACKGROUND Area This disclosure relates to high-frequency filters that use acoustic wave resonators, and in particular to filters for use in communication equipment. Description of the related prior art A high-frequency filter (HF filter) is a two-port device configured to pass some frequencies and block others, where "pass" means transmission with relatively little signal loss and "block" means blocking or significant attenuation. The range of frequencies passed by a filter is called the filter's "passband." The range of frequencies blocked by such a filter is called the filter's "stopband." A typical RF filter has at least one passband and at least one stopband. Specific requirements for a passband or stopband depend on the specific application. For example, a "passband" might be defined as a frequency range in which the insertion loss of a filter is better than a defined value such as 1 dB, 2 dB, or 3 dB. A "stopband" can be defined as a frequency range in which the suppression of a filter is greater than a defined value such as 20 dB, 30 dB, 40 dB or more, depending on the application. RF filters are used in communication systems where information is transmitted wirelessly. Examples include the RF front ends of cellular base stations, mobile phones and computers, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptops and tablets, fixed-point radio links, and other communication systems. RF filters are also used in radar and electronic warfare systems. RF filters typically require many design compromises to achieve the best balance between performance parameters such as insertion loss, suppression, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing methods and improvements can simultaneously benefit one or more of these requirements. Improvements to the RF filters in a wireless system can have a broad impact on system performance. RF filter enhancements can be used to provide system performance improvements such as larger cells, longer battery life, higher data rates, greater network capacity, lower costs, improved security, and higher reliability. These improvements can be implemented at many levels of the wireless system, both individually and in combination, such as the RF module, RF transceiver, mobile or fixed subsystem, or network level. The desire for greater bandwidth for communication channels will inevitably lead to the use of higher frequency bands. The current LTE™ (Long Term Evolution) specification defines frequency bands from 3.3 GHz to 5.9 GHz. Some of these bands are currently unused. Future proposals for wireless communications include millimeter-wave communication bands with frequencies up to 28 GHz. High-performance RF filters for current communication systems typically incorporate acoustic wave resonators, including surface acoustic wave resonators (SAW resonators), bulk acoustic wave resonators (BAW resonators), film bulk acoustic wave resonators (FBAR resonators), and other types of acoustic resonators. However, these existing technologies are not well-suited for use at the higher frequencies proposed for future communication networks. The WO 2016 / 147 687 A1 discloses a resonator comprising a support substrate with a recess in its top surface, a thin film which may consist of a dielectric and which is arranged on the support substrate, a piezoelectric substrate which is arranged on the thin film, and an IDT electrode which is provided on the piezoelectric substrate. DESCRIPTION OF THE DRAWINGS 1 contains a schematic top view and two schematic cross-sectional views of a transversely excited acoustic film volume resonator (XBAR).2 is an extended schematic cross-sectional view of a part of the XBAR of 1 .3 is an extended schematic cross-sectional view of part of an improved XBAR with a "lambda-half" dielectric layer.4 is a diagram comparing the admittances of an XBAR with a lambda-half dielectric layer and a conventional XBAR.5 is a cross-sectional view of an XBAR with a half-wave dielectric layer with contours representing the voltage at the resonant frequency.6 is a diagram comparing the admittances of three XBAR with lambda-half-AlN layers.7 is a diagram comparing the admittances of three XBAR with lambda-half- SiO2 layers.8 is a diagram comparing the admittances of three other XBARs with lambda-half- SiO2 layers.9 is a diagram of the admittance of an XBAR with an excessively thin lambda-half- SiO2 layer.10 is a diagram of the admittance of an XBAR with an excessively thick lambda-half- SiO2 layer.11 is a diagram of the temperature coefficient of the frequency of an XBAR as a function of the SiO2 thickness.12 This is a schematic circuit diagram and the layout of a filter using XBAR.13 This is a flowchart of a process for manufacturing an XBAR with a lambda-half dielectric layer. In this description, elements appearing in drawings are assigned three- or four-digit reference identifier