US-12620967-B2 - Enhanced bulk acoustic wave resonator performance using metallic bragg mirrors

US12620967B2US 12620967 B2US12620967 B2US 12620967B2US-12620967-B2

Abstract

Aspects and embodiments include a bulk acoustic wave resonator comprising a layer of piezoelectric material, an upper electrode disposed on top of the layer of piezoelectric material, the upper electrode including a metallic Bragg mirror having alternating layers of a first metal and a second metal, and a lower electrode disposed on a bottom of the layer of piezoelectric material, the lower electrode including a metallic Bragg mirror having alternating layers of a third metal and a fourth metal.

Inventors

Ahmed E. Hassanien
Scott J. Smith

Assignees

SKYWORKS SOLUTIONS, INC.

Dates

Publication Date: 20260505
Application Date: 20240308

Claims (20)

1 . A bulk acoustic wave resonator comprising: a layer of piezoelectric material; an upper electrode disposed on top of the layer of piezoelectric material, the upper electrode including a metallic Bragg mirror having multiple pairs of alternating layers of a first metal and a second metal, a metal layer of the upper electrode closest to the layer of piezoelectric material having a different thickness than other layers of that same metal; and a lower electrode disposed on a bottom of the layer of piezoelectric material, the lower electrode including a metallic Bragg mirror having alternating layers of a third metal and a fourth metal.
2 . The bulk acoustic wave resonator of claim 1 wherein the first metal is the same as the third metal and the second metal is the same as the fourth metal.
3 . The bulk acoustic wave resonator of claim 1 wherein the first metal has a different acoustic impedance than an acoustic impedance of the second metal and a different electrical conductivity than an electrical conductivity of the second metal.
4 . The bulk acoustic wave resonator of claim 3 wherein the first metal is titanium and the second metal is ruthenium.
5 . The bulk acoustic wave resonator of claim 1 wherein each of the layers of the first and second metals has a same thickness.
6 . The bulk acoustic wave resonator of claim 5 wherein each of the layers of the first and second metals has a thickness of λ4, λ being a wavelength of a main acoustic wave generated in the bulk acoustic wave resonator.
7 . The bulk acoustic wave resonator of claim 1 wherein a metal layer of the lower electrode closest to the layer of piezoelectric material has a different thickness than other layers of that same metal.
8 . The bulk acoustic wave resonator of claim 1 wherein the metal layer of the upper electrode closest to the layer of piezoelectric material is formed of the first metal and has a lower acoustic impedance than the second metal.
9 . The bulk acoustic wave resonator of claim 1 wherein the metal layer of the upper electrode closest to the layer of piezoelectric material is formed of the first metal and has a higher acoustic impedance than the second metal.
10 . The bulk acoustic wave resonator of claim 1 configured as a film bulk acoustic wave resonator.
11 . The bulk acoustic wave resonator of claim 1 configured as a solidly mounted resonator.
12 . The bulk acoustic wave resonator of claim 1 further comprising a layer of dielectric material disposed between the layer of piezoelectric material and at least one of the upper electrode or the lower electrode.
13 . The bulk acoustic wave resonator of claim 1 wherein a metal layer of the upper electrode closest to the layer of piezoelectric material is formed of a same metal as a metal layer of the lower electrode closest to the layer of piezoelectric material.
14 . The bulk acoustic wave resonator of claim 1 wherein a metal layer of the upper electrode closest to the layer of piezoelectric material is formed of a different metal than a metal layer of the lower electrode closest to the layer of piezoelectric material.
15 . The bulk acoustic wave resonator of claim 1 wherein the layers of the first metal have different thicknesses than the layers of the second metal.
16 . An acoustic wave filter including the bulk acoustic wave resonator of claim 1 .
17 . An electronics module including the acoustic wave filter of claim 16 .
18 . An electronic device including the electronics module of claim 17 .
19 . A bulk acoustic wave resonator comprising: a single layer of piezoelectric material; an upper electrode disposed on top of the single layer of piezoelectric material, the upper electrode including a metallic Bragg mirror having alternating layers of a first metal and a second metal, a metal layer of the upper electrode closest to the layer of piezoelectric material having a different thickness than other layers of that same metal; a lower electrode disposed on a bottom of the single layer of piezoelectric material, the lower electrode including a metallic Bragg mirror having alternating layers of a third metal and a fourth metal; and a layer dielectric material disposed between the single layer of piezoelectric material and at least one of the upper electrode of the lower electrode.
20 . A bulk acoustic wave resonator comprising: a layer of piezoelectric material; an upper electrode disposed on top of the layer of piezoelectric material, the upper electrode including a metallic Bragg mirror having alternating layers of a first metal and a second metal, a plurality of the layers of the first and second metals having a thickness of λ/4, λ being a wavelength of a main acoustic wave generated in the bulk acoustic wave resonator, a metal layer of the upper electrode closest to the layer of piezoelectric material having a different thickness than other layers of that same metal; and a lower electrode disposed on a bottom of the layer of piezoelectric material, the lower electrode including a metallic Bragg mirror having alternating layers of a third metal and a fourth metal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 63/452,808, titled “ENHANCED BULK ACOUSTIC WAVE RESONATOR PERFORMANCE USING METALLIC BRAGG MIRRORS,” filed Mar. 17, 2023, the subject matter which being incorporated herein by reference for all purposes. BACKGROUND Technical Field Embodiments of this disclosure relate to bulk acoustic wave resonators and to acoustic wave filters, electronic modules, and electronic devices including same. Description of Related Technology Acoustic wave filters can filter radio frequency signals. An acoustic wave filter can include a plurality of acoustic wave resonators arranged to filter a radio frequency signal. The resonators can be arranged as a ladder circuit. Example acoustic wave resonators include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators. A film bulk acoustic wave resonator is an example of a BAW resonator. A solidly mounted resonator (SMR) is another example of a BAW resonator. Acoustic wave filters can be implemented in radio frequency electronic systems. For instance, filters in a radio frequency front end of a mobile phone can include acoustic wave filters. Two acoustic wave filters can be arranged as a duplexer. SUMMARY In accordance with one aspect, there is provided a bulk acoustic wave resonator. The bulk acoustic wave resonator comprises a layer of piezoelectric material, an upper electrode disposed on top of the layer of piezoelectric material, the upper electrode including a metallic Bragg mirror having alternating layers of a first metal and a second metal, and a lower electrode disposed on a bottom of the layer of piezoelectric material, the lower electrode including a metallic Bragg mirror having alternating layers of a third metal and a fourth metal. In some embodiments, the upper electrode includes multiple pairs of the alternating layers of the first metal and the second metal. In some embodiments, the first metal is the same as the third metal and the second metal is the same as the fourth metal. In some embodiments, the first metal has a different acoustic impedance than an acoustic impedance of the second metal. In some embodiments, the first metal has a different electrical conductivity than an electrical conductivity of the second metal. In some embodiments, the first metal is titanium and the second metal is ruthenium. In some embodiments, each of the layers of the first and second metals has a same thickness. In some embodiments, each of the layers of the first and second metals has a thickness of λ/4, λ being a wavelength of a main acoustic wave generated in the bulk acoustic wave resonator. In some embodiments, a metal layer of the upper electrode closest to the layer of piezoelectric material has a different thickness than other layers of that same metal. In some embodiments, a metal layer of the lower electrode closest to the layer of piezoelectric material has a different thickness than other layers of that same metal. In some embodiments, the metal layer of the upper electrode closest to the layer of piezoelectric material is formed of the first metal and has a lower acoustic impedance than the second metal. In some embodiments, the metal layer of the upper electrode closest to the layer of piezoelectric material is formed of the first metal and has a higher acoustic impedance than the second metal. In some embodiments, the bulk acoustic wave resonator is configured as a film bulk acoustic wave resonator. In some embodiments, the bulk acoustic wave resonator is configured as a solidly mounted resonator. In some embodiments, the bulk acoustic wave resonator further comprises a layer of dielectric material disposed between the layer of piezoelectric material and at least one of the upper electrode or the lower electrode. In some embodiments, the bulk acoustic wave resonator further comprises a layer of dielectric material disposed between the layer of piezoelectric material and the upper electrode and a layer of dielectric material disposed between the layer of piezoelectric material and the lower electrode. In some embodiments, the layer of dielectric material is a temperature compensating layer. In some embodiments, a metal layer of the upper electrode closest to the layer of piezoelectric material is formed of a same metal as a metal layer of the lower electrode closest to the layer of piezoelectric material. In some embodiments, a metal layer of the upper electrode closest to the layer of piezoelectric material is formed of a different metal than a metal layer of the lower electrode closest to the layer of piezoelectric material. In some embodiments, the layers of the first metal have different thicknesses than the layers of the second metal. In some embodiments, the bulk acoustic wave resonator is included in an acoustic wave filter. In some embodiments, the acoustic wave filter is included in an electro