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US-20260128730-A1 - TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATOR WITH MULTI-MARK INTERDIGITAL TRANSDUCER

US20260128730A1US 20260128730 A1US20260128730 A1US 20260128730A1US-20260128730-A1

Abstract

An acoustic resonator is provided that includes a piezoelectric layer having at least a portion attached to a substrate either directly or via one or more intermediate layers; and a conductor pattern on the piezoelectric layer. The conductor pattern includes a multi-mark interdigital transducer having a plurality of interleaved fingers extending from opposing busbars, and a length between outermost fingers of the interleaved fingers. The IDT is divided along the length into at least three sections. A change in the mark between the at least three sections has a smaller effect on a resonance frequency of a primary shear acoustic mode of all of the at least three sections of the acoustic resonator in comparison to an effect that the change in the mark has on a spurious acoustic mode other than the primary shear acoustic mode of all of the at least three sections.

Inventors

  • Greg Dyer
  • Bryant Garcia
  • Julius Koskela

Assignees

  • MURATA MANUFACTURING CO., LTD.

Dates

Publication Date
20260507
Application Date
20251027

Claims (20)

  1. 1 . An acoustic resonator comprising: a piezoelectric layer having at least a portion attached to a substrate either directly or via one or more intermediate layers; and a conductor pattern on the piezoelectric layer, the conductor pattern comprising a multi-mark interdigital transducer (IDT) having a plurality of interleaved fingers extending from opposing busbars, and a length between outermost fingers of the interleaved fingers, wherein the IDT is divided along the length into at least three sections, with each of a first section, a second section, and third section having multiple pairs of fingers of the plurality of interleaved fingers, wherein a mark and a pitch of the interleaved fingers in each of the first, second and third sections are constant in each section, wherein the mark in each section is different from the respective marks of the other sections, and wherein a change in the mark between the at least three sections has a smaller effect on a resonance frequency of a primary shear acoustic mode of all of the at least three sections of the acoustic resonator in comparison to an effect that the change in the mark has on a spurious acoustic mode other than the primary shear acoustic mode of all of the at least three sections.
  2. 2 . The acoustic resonator of claim 1 , further comprising a cavity between the piezoelectric layer and the substrate.
  3. 3 . The acoustic resonator of claim 2 , wherein the cavity is an irregular polygon in shape.
  4. 4 . The acoustic resonator of claim 1 , wherein the primary shear acoustic mode is excited in response to a radio frequency signal applied to the IDT.
  5. 5 . The acoustic resonator of claim 1 , further comprising an acoustic reflector of multiple layers between the substrate and the piezoelectric layer.
  6. 6 . The acoustic resonator of claim 1 , wherein the mark is a width of an interleaved finger of the plurality of interleaved fingers, and the mark is measured in a direction substantially perpendicular to a direction of extension of the IDT finger of the plurality of interleaved fingers from a respective busbar among the opposing busbars.
  7. 7 . The acoustic resonator of claim 1 , wherein the acoustic resonator is one of a plurality of acoustic resonators of a filter, and the spurious acoustic mode is an in-band acoustic mode in a passband of the filter.
  8. 8 . The acoustic resonator of claim 1 , wherein the smaller effect is a smaller change in a primary shear acoustic mode amplitude than a change in a spurious acoustic mode amplitude.
  9. 9 . The acoustic resonator of claim 1 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites the primary shear acoustic mode in the piezoelectric layer, the primary shear acoustic mode being a bulk shear mode where acoustic energy propagates along a direction substantially orthogonal to the surface of the piezoelectric layer and that is orthogonal to a direction of an electric field generated by the IDT.
  10. 10 . The acoustic resonator of claim 1 , wherein the IDT is a multi-pitch IDT and the pitch in each section is different from the respective pitches of the other sections, and wherein the pitch in each section is measured as a center-to-center-spacing between adjacent fingers extending from different busbars in the respective section.
  11. 11 . A filter device comprising: a piezoelectric layer having at least a portion attached to a substrate either directly or via one or more intermediate layers; and a conductor pattern on the piezoelectric layer, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a plurality of bulk acoustic resonators each having interleaved fingers extending from opposing busbars, wherein each of a first IDT and a second IDT from the plurality of IDTs is a multi-mark IDT, and each of the first IDT and the second IDT have a respective length between outermost fingers of the interleaved fingers of the respective IDT, wherein: the first IDT and second IDT are each divided along the length into at least three sections, with each of a first section, a second section, and third section having multiple pairs of fingers of the plurality of interleaved fingers, wherein a mark and a pitch of the interleaved fingers in each of the first, second and third sections are constant in each section of the respective IDT, wherein the mark in each section of the first and second IDTs is different from the respective marks of the other sections, and wherein a change in the mark between the at least three sections has a smaller effect on a resonance frequency of a primary shear acoustic mode of all of the at least three sections of all of the respective bulk acoustic resonators in comparison to an effect that the change in the mark has on a spurious acoustic mode of the filter device other than the primary shear acoustic mode of all of the at least three sections.
  12. 12 . The filter device of claim 11 , further comprising a cavity between the piezoelectric layer and the substrate.
  13. 13 . The filter device of claim 11 , wherein the change in mark between the at least three sections of the first IDT is different than the change in mark between the at least three sections of the second IDT.
  14. 14 . The filter device of claim 11 , further comprising an acoustic reflector of multiple layers between the substrate and the piezoelectric layer.
  15. 15 . The filter device of claim 11 , wherein the mark is a width of an interleaved finger of the interleaved fingers, and the mark is measured in a direction substantially perpendicular to a direction of extension of the interleaved finger from a respective busbar among the opposing busbars.
  16. 16 . The filter device of claim 11 , wherein the spurious acoustic mode is an in-band acoustic mode in a passband of the filter.
  17. 17 . The filter device of claim 11 , wherein the smaller effect is a smaller change in a primary shear acoustic mode amplitude than a change in a spurious acoustic mode amplitude.
  18. 18 . The filter device of claim 11 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites the primary shear acoustic mode in the piezoelectric layer, the primary shear acoustic mode being a bulk shear mode where acoustic energy propagates along a direction substantially orthogonal to a surface of the piezoelectric layer and that is orthogonal to a direction of an electric field generated by the IDT.
  19. 19 . The filter device of claim 11 , wherein the first IDT is a multi-pitch IDT, and the pitch in each section is different from the respective pitches of the other sections, and wherein the pitch in each section is measured as a center-to-center-spacing between adjacent fingers extending from different busbars in the respective section.
  20. 20 . The filter device of claim 19 , wherein the second IDT is a multi-pitch IDT, and the pitch in each section is different from the respective pitches of the other sections, and wherein the pitch is measured as a center-to-center-spacing between adjacent fingers extending from different busbars in the respective section, and the change in mark between the at least three sections of the first IDT is different than a change in mark between the at least three sections of the second IDT.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 17/950,019, filed Sep. 21, 2022, which is a continuation of U.S. patent application Ser. No. 17/388,745, filed Jul. 29, 2021, now issued as U.S. Pat. No. 12,088,281, which claims priority to U.S. Provisional Ser. No. 63/144,977, filed Feb. 3, 2021, entitled CHIRPED XBAR ELECTRODES, the entire content of each of which are incorporated herein by reference. This patent application is related to application Ser. No. 17/093,239, filed Nov. 9, 2020, entitled TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATOR WITH MULTI-PITCH INTERDIGITAL TRANSDUCER. TECHNICAL FIELD This disclosure relates to radio frequency filters using acoustic wave resonators, and specifically to filters for use in communications equipment. BACKGROUND A radio frequency (RF) filter is a two-port device configured to pass some frequencies and to stop other frequencies, where “pass” means transmit with relatively low signal loss and “stop” means block or substantially attenuate. The range of frequencies passed by a filter is referred to as the “pass-band” of the filter. The range of frequencies stopped by such a filter is referred to as the “stop-band” of the filter. A typical RF filter has at least one pass-band and at least one stop-band. Specific requirements on a pass-band or stop-band depend on the specific application. For example, a “pass-band” may be defined as a frequency range where the insertion loss of a filter is better than a defined value such as 1 dB, 2 dB, or 3 dB. A “stop-band” may be defined as a frequency range where the rejection of a filter is greater than a defined value such as 20 dB, 30 dB, 40 dB, or greater depending on application. RF filters are used in communications systems where information is transmitted over wireless links. For example, RF filters may be found in the RF front-ends of cellular base stations, mobile telephone and computing devices, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptop computers and tablets, fixed point radio links, and other communications systems. RF filters are also used in radar and electronic and information warfare systems. RF filters typically require many design trade-offs to achieve, for each specific application, the best compromise between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size and cost. Specific design and manufacturing methods and enhancements can benefit simultaneously one or several of these requirements. Performance enhancements to the RF filters in a wireless system can have broad impact to system performance. Improvements in RF filters can be leveraged to provide system performance improvements 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 realized at many levels of the wireless system both separately and in combination, for example at the RF module, RF transceiver, mobile or fixed sub-system, or network levels. High performance RF filters for present communication systems commonly 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 resonators. However, these existing technologies are not well-suited for use at the higher frequencies and bandwidths proposed for future communications networks. The desire for wider communication channel bandwidths will inevitably lead to the use of higher frequency communications bands. Radio access technology for mobile telephone networks has been standardized by the 3GPP (3rd Generation Partnership Project). Radio access technology for 5th generation mobile networks is defined in the 5G NR (new radio) standard. The 5G NR standard defines several new communications bands. Two of these new communications bands are n77, which uses the frequency range from 3300 MHz to 4200 MHz, and n79, which uses the frequency range from 4400 MHz to 5000 MHz. Both band n77 and band n79 use time-division duplexing (TDD), such that a communications device operating in band n77 and/or band n79 use the same frequencies for both uplink and downlink transmissions. Bandpass filters for bands n77 and n79 must be capable of handling the transmit power of the communications device. WiFi bands at 5 GHz and 6 GHz also require high frequency and wide bandwidth. The 5G NR standard also defines millimeter wave communication bands with frequencies between 24.25 GHz and 40 GHz. The Transversely-Excited Film Bulk Acoustic Resonator (XBAR) is an acoustic resonator structure for use in microwave filters. The XBAR is described in U.S. Pat. No. 10,491,291, titled TRANSVERSELY EXCITED FILM BULK ACOUSTIC RESONATOR. An XBAR resonator comprises an interdigital transducer (IDT) formed on a thin floating layer, or