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US-20260128723-A1 - MULTILAYER PIEZOELECTRIC DEVICE WITH PIEZO-LAYER TRENCH WITH WIDER IDT EDGE REGION

US20260128723A1US 20260128723 A1US20260128723 A1US 20260128723A1US-20260128723-A1

Abstract

An acoustic wave device, a radio frequency filter, and an electronics module are provided. The acoustic wave device includes a layer of carrier substrate, a layer of dielectric material, a layer of piezoelectric material, a pair of interdigital transducer electrodes, each interdigital transducer electrode including a bus bar and a plurality of electrode fingers extending from the bus bar to the distal ends of the electrode fingers at an edge region of the interdigital transducer electrode, and trench portions located in the upper surface of the layer of piezoelectric material, said trench portions being overlapped by the edge regions of the interdigital transducer electrodes, the electrode fingers having a width at their distal end that is greater than the width of the rest of the electrode finger. The acoustic wave device provides effective suppression of transverse modes.

Inventors

  • Rei GOTO
  • Shoji Okamoto

Assignees

  • SKYWORKS SOLUTIONS, INC.

Dates

Publication Date
20260507
Application Date
20251103

Claims (20)

  1. 1 . An acoustic wave device, comprising: a layer of carrier substrate; a layer of dielectric material, the layer of dielectric material having a lower surface disposed against an upper surface of the layer of carrier substrate; a layer of piezoelectric material, the layer of piezoelectric material having a lower surface disposed against an upper surface of the layer of dielectric material; a pair of interdigital transducer electrodes disposed on an upper surface of the layer of piezoelectric material, each interdigital transducer electrode including a bus bar, and a plurality of electrode fingers extending from the bus bar to distal ends of the plurality of electrode fingers at an edge region of the interdigital transducer electrode; and trench portions located in the upper surface of the layer of piezoelectric material, said trench portions being overlapped by the edge regions of the interdigital transducer electrodes, the plurality of electrode fingers having a width at their distal end that is greater than the width of the rest of the electrode finger.
  2. 2 . The acoustic wave device of claim 1 wherein the trench portions each have a depth relative to the upper surface of the layer of piezoelectric material of between about 0.004λ and 0.02λ, where λ is a wavelength of an acoustic wave generated by the pair of interdigital transducer electrodes during operation.
  3. 3 . The acoustic wave device of claim 1 wherein the trench portions are located in the areas of the upper surface of the layer of piezoelectric material that are overlapped by the edge regions of the interdigital transducer electrodes and are not covered by the material of the interdigital transducer electrodes.
  4. 4 . The acoustic wave device of claim 1 wherein the trench portions extend discontinuously in a direction of propagation of an acoustic wave to be generated by the pair of interdigital transducer electrodes.
  5. 5 . The acoustic wave device of claim 1 wherein the trench portions each have a length of between about 0.5λ and 1λ, where λ is a wavelength of the acoustic wave to be generated.
  6. 6 . The acoustic wave device of claim 1 wherein the bus bars of the pair of interdigital transducer electrodes are opposing and the plurality of electrode fingers of each interdigital transducer electrode extend towards the bus bar of the other electrode.
  7. 7 . The acoustic wave device of claim 1 wherein the plurality of electrode fingers of each interdigital transducer electrode interleave with one another in an active region of the pair of interdigital transducer electrodes, and form gap regions between the ends of the plurality of fingers of one of the electrodes and the bus bar of the other electrode.
  8. 8 . The acoustic wave device of claim 7 wherein the edge regions of the pair of interdigital transducer electrodes are located within the active region and on opposing sides of the active region.
  9. 9 . The acoustic wave device of claim 8 wherein the active region includes a central region and the edge regions of the interdigital transducer electrodes, each edge region extending from tips of the plurality of electrode fingers of one of the interdigital transducer electrodes towards a center of the central region.
  10. 10 . The acoustic wave device of claim 9 wherein a duty factor of the pair of interdigital transducer electrodes in the edge regions of the interdigital transducer electrodes is larger than a duty factor of the pair of interdigital transducer electrodes in the central region of the active region.
  11. 11 . The acoustic wave device of claim 1 wherein a duty factor at the distal end of the plurality of electrode fingers is between about 0.5 and 0.64.
  12. 12 . The acoustic wave device of claim 1 wherein the portion of the interdigital transducer electrode with greater width is contiguous with one or more adjacent trench portions in the layer of piezoelectric material and has the same length as the length of the one or more trench portions.
  13. 13 . The acoustic wave device of claim 1 wherein the bus bars of the pair of interdigital transducer electrodes are opposing and the plurality of electrode fingers of each interdigital transducer electrode extend towards the bus bar of the other electrode.
  14. 14 . The acoustic wave device of claim 7 wherein the trench portions in the upper surface of the layer of piezoelectric material are also overlapped with at least part of the gap regions.
  15. 15 . The acoustic wave device of claim 14 wherein the trench portions each have a length in a direction perpendicular to the direction of propagation of an acoustic wave to be generated by the pair of interdigital transducer electrodes that extends from the respective edge region to the bus bar of the other electrode.
  16. 16 . The acoustic wave device of claim 14 wherein each of the interdigital transducer electrodes includes a second bus bar that is located within the gap region.
  17. 17 . The acoustic wave device of claim 16 wherein the trench portions each have a length that extends from the respective edge region to the second bus bar of the other electrode.
  18. 18 . A radio frequency filter comprising at least one acoustic wave device, the at least one acoustic wave device including: a layer of carrier substrate; a layer of dielectric material, the layer of dielectric material having a lower surface disposed against an upper surface of the layer of carrier substrate; a layer of piezoelectric material, the layer of piezoelectric material having a lower surface disposed against an upper surface of the layer of dielectric material; a pair of interdigital transducer electrodes disposed on an upper surface of the layer of piezoelectric material, each interdigital transducer electrode including a bus bar, and a plurality of electrode fingers extending from the bus bar to distal ends of the plurality of electrode fingers at an edge region of the interdigital transducer electrode; and trench portions located in the upper surface of the layer of piezoelectric material, said trench portions being overlapped by the edge regions of the interdigital transducer electrodes, the plurality of electrode fingers having a width at their distal end that is greater than the width of the rest of the electrode finger.
  19. 19 . The radio frequency filter of claim 18 wherein the at least one acoustic wave device includes a first acoustic wave device and a second acoustic wave device, the plurality of electrode fingers of the first acoustic wave device having a different duty cycle at their distal ends than the plurality of electrode fingers of the second acoustic wave device.
  20. 20 . The radio frequency filter of claim 19 wherein the trench portions of the first acoustic wave device have a same trench depth as the trench portions of the second acoustic wave device.

Description

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. BACKGROUND Field Embodiments of the disclosure relate to an acoustic wave device, a radio frequency filter including the same, and an electronics module comprising at least one radio frequency filter including the same. In particular, embodiments of the disclosure relate to an acoustic wave device including trench portions in a piezoelectric layer and electrode fingers having a width at their distal end that is greater than the width of the rest of the electrode finger for transverse mode suppression. Description of the Related Technology Multilayer piezoelectric substrates (MPSs) are often used in acoustic wave devices, such as surface acoustic wave (SAW) devices. Several structures for suppressing unwanted transverse modes in such devices are known. However, the various known structures each have different drawbacks. FIGS. 1A and 1B show one type of acoustic wave device 100. FIG. 1A is a cross section through the line marked A on the plan view of FIG. 1B. The acoustic wave device 100 has a multilayer piezoelectric substrate (MPS) including a carrier substrate 102, a layer of dielectric material 104 disposed on an upper surface of the carrier substrate 102, and a layer of piezoelectric material 106 disposed on the layer of dielectric material 104. An interdigital transducer (IDT) 108 is disposed on top of the layer of piezoelectric material 106. In the acoustic wave device 100 of FIGS. 1A and 1B, the electrode fingers in the IDT 108 include hammer head portions 110 to suppress the transverse modes. The hammer head portions 110 are sections of the electrode fingers in edge regions E of the IDT that have a width (in a direction perpendicular to the lengthwise extension of the electrode fingers) larger than the width of each finger in a central region C of the IDT 108. In other words, a duty factor (DF) of the IDT 108 is greater in the edge regions E of the IDT compared to the duty factor of the IDT in the central region C of the IDT. An illustrative diagram showing what is meant by the term Duty Factor is provided in FIG. 4. In general, the width of the IDT fingers (w) compared to the width of the spacing between the same part of the IDT fingers (p) sets the duty factor (DF). Specifically, the duty factor is defined as the fraction of the IDT width spanned by the width of the IDT fingers (in the direction of propagation of the main surface acoustic wave to be generated). Increasing the width of the IDT fingers, whilst maintaining the position of the center of each IDT finger, increases the duty factor. The DF can be expressed as: DF=wp The hammer head portions 110 of the device of FIGS. 1A and 1B reduce the acoustic velocity in the edge regions E compared to the central region C. This velocity reduction creates a piston mode distribution to reduce transverse modes. In order to obtain a large enough velocity difference for transverse mode suppression through a larger DF in the edge regions E, the DF of the central region C of the IDT needs to be less than 0.5. This is because the velocity of the main acoustic mode changes rapidly with DF when the DF is less than 0.5, compared to when DF is greater than 0.5 and the velocity of the main acoustic mode does not vary with DF as much. The requirement of a DF smaller than 0.5 in the central region C leads to a decrease in the static capacitance. A smaller static capacitance leads to a larger size device for a given impedance, as static capacitance sets the limit on the IDT size. Therefore, the hammer head structure of FIGS. 1A and 1B can lead to an undesirable increase in size of the acoustic wave device 100. FIG. 2A is a plan view of a surface acoustic wave (SAW) device (e.g., a SAW resonator). As shown in FIGS. 2C and 2E, the SAW device includes a trench region 210. FIGS. 2B and 2C show cross sections through the lines in FIG. 2A labeled A and B respectively. FIGS. 2D and 2E show partial cross sections through the lines in FIG. 2A labeled X and Y respectively (with only two IDT fingers shown in FIGS. 2D and 2E for clarity). The acoustic wave device 200 includes a carrier substrate 202, a layer of dielectric material 204 disposed on an upper surface of the carrier substrate 202, and a layer of piezoelectric material 206 disposed above the layer of dielectric material 204 on the upper surface of the carrier substrate 202. Together the carrier substrate 202, layer of dielectric material 204, and layer of piezoelectric material 206 may be referred to as a multilayer piezoelectric substrate (MPS). As can be seen in FIG. 2A, the IDT fingers of acoustic wave device 200 have a uniform width along their length. The acoustic wave device also includes electrodes 208a and 208b disposed above the layer of piezoelect