US-12620974-B2 - Stacked resonators with shared reflector layers

Abstract

The present disclosure relates to a resonator structure including stacked resonators, which share a same reflector. The disclosed resonator structure includes a first resonator and a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator. Herein, the first resonator is at least composed of a first top electrode, a first piezoelectric layer underneath the first top electrode, and the common reflector underneath the first piezoelectric layer. The second resonator is at least composed of the common reflector, a second piezoelectric layer underneath the common reflector, and a second bottom electrode underneath the second piezoelectric layer. The first resonator and the second resonator are acoustically isolated from each other.

Inventors

• Mohammad J. Modarres-Zadeh
• Gernot Fattinger

Assignees

• QORVO US, INC.

Dates

Publication Date

20260505

Application Date

20230620

Claims (19)

1. 1 . A resonator structure comprising: a first resonator; and a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator, wherein: the first resonator is at least composed of a top reflector, a first top electrode underneath the top reflector, a first piezoelectric layer underneath the first top electrode, and the common reflector underneath the first piezoelectric layer; the top reflector is a non-conductive reflector and includes alternating high acoustic impedance layers and low acoustic impedance layers over the first top electrode; the second resonator is at least composed of the common reflector, a second piezoelectric layer underneath the common reflector, and a second bottom electrode underneath the second piezoelectric layer; and the first resonator and the second resonator are acoustically isolated from each other.
2. 2 . The resonator structure of claim 1 wherein the second resonator further includes a bottom reflector underneath the second bottom electrode.
3. 3 . The resonator structure of claim 2 wherein the bottom reflector is a non-conductive reflector and includes alternating high acoustic impedance layers and low acoustic impedance layers underneath the second bottom electrode.
4. 4 . The resonator structure of claim 3 wherein: the high acoustic impedance layers of the bottom reflector and the high acoustic impedance layers of the top reflector are formed of W, Mo, or Pt; the low acoustic impedance layers of the bottom reflector and the low acoustic impedance layers of the top reflector are formed of SiO 2 ; a total number of the alternating high acoustic impedance layers and low acoustic impedance layers of the bottom reflector is at least five; and a total number of the alternating high acoustic impedance layers and low acoustic impedance layers of the top reflector is at least five.
5. 5 . The resonator structure of claim 1 wherein the common reflector is a non-conductive reflector, and the first resonator and the second resonator are electrically connected with external wiring.
6. 6 . The resonator structure of claim 5 wherein: the first resonator further includes a first bottom electrode residing vertically between the common reflector and the first piezoelectric layer, while the second resonator further includes a second top electrode residing vertically between the common reflector and the second piezoelectric layer; and the common reflector includes alternating high acoustic impedance layers and low acoustic impedance layers residing vertically between first bottom electrode and the second top electrode.
7. 7 . The resonator structure of claim 6 wherein: the high acoustic impedance layers of the common reflector are formed of W, Mo, or Pt, and the low acoustic impedance layers of the common reflector are formed of SiO 2 ; the high acoustic impedance layers of the top reflector are formed of W, Mo, or Pt, and the low acoustic impedance layers of the top reflector are formed of SiO 2 ; a total number of the alternating high acoustic impedance layers and low acoustic impedance layers of the common reflector is at least five; and a total number of the alternating high acoustic impedance layers and low acoustic impedance layers of the top reflector is at least five.
8. 8 . The resonator structure of claim 1 wherein the first piezoelectric layer and the second piezoelectric layer are formed of different materials.
9. 9 . A resonator structure, comprising: a first resonator; and a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator, wherein: the common reflector is a conductive reflector and includes top common vias, bottom common vias, a top common dielectric layer, a bottom common dielectric layer underneath the top common dielectric layer, and alternating high acoustic impedance layers and low acoustic impedance layers residing vertically between the top common dielectric layer and the bottom common dielectric layer; the first resonator is at least composed of a first top electrode, a first piezoelectric layer underneath the first top electrode, a first bottom electrode underneath the first piezoelectric layer, and the common reflector underneath the first bottom electrode; the second resonator is at least composed of the common reflector, a second top electrode underneath the common reflector, a second piezoelectric layer underneath the second top electrode, and a second bottom electrode underneath the second piezoelectric layer; each of the top common vias extends through the top common dielectric layer and electrically connects the first bottom electrode and a top one of the high acoustic impedance layers, and each of the bottom common vias extends through the bottom common dielectric layer and electrically connects the second top electrode and a bottom one of the high acoustic impedance layers; and the first resonator and the second resonator are acoustically isolated from each other.
10. 10 . The resonator structure of claim 9 wherein: the top common dielectric layer and the bottom common dielectric layer are formed of silicon oxide (SiO 2 ); and the high acoustic impedance layers are formed of tungsten (W), molybdenum (Mo), or platinum (Pt), and the low acoustic impedance layers are formed of aluminum (Al).
11. 11 . The resonator structure of claim 9 wherein the first resonator further includes a top reflector over the first top electrode.
12. 12 . The resonator structure of claim 11 wherein: the top reflector is a conductive reflector and includes top vias, a top dielectric layer over the first top electrode, and alternating high acoustic impedance layers and low acoustic impedance layers over the top dielectric layer; and each of the top vias extends through the top dielectric layer and electrically connects the first top electrode and a bottom one of the high acoustic impedance layers.
13. 13 . The resonator structure of claim 11 wherein the second resonator further includes a bottom reflector underneath the second bottom electrode.
14. 14 . The resonator structure of claim 13 wherein: the top reflector is a conductive reflector and includes top vias, a top dielectric layer over the first top electrode, and alternating first high acoustic impedance layers and first low acoustic impedance layers over the top dielectric layer; each of the top vias extends through the top dielectric layer and electrically connects the first top electrode and a bottom one of the first high acoustic impedance layers; the bottom reflector is a conductive reflector and includes bottom vias, a bottom dielectric layer underneath the second bottom electrode, and alternating second high acoustic impedance layers and second low acoustic impedance layers underneath the bottom dielectric layer; and each of the bottom vias extends through the bottom dielectric layer and electrically connects the second bottom electrode and a top one of the second high acoustic impedance layers.
15. 15 . The resonator structure of claim 14 wherein: the top dielectric layer and the bottom dielectric layer are formed of SiO 2 ; the first high acoustic impedance layers and the second high acoustic impedance layers are formed of W, Mo, or Pt; and and the first low acoustic impedance layers and the second low acoustic impedance layers are formed of Al.
16. 16 . The resonator structure of claim 9 wherein the second resonator further includes a bottom reflector underneath the second bottom electrode.
17. 17 . The resonator structure of claim 16 wherein: the bottom reflector is a conductive reflector and includes bottom vias, a bottom dielectric layer underneath the second bottom electrode, and alternating high acoustic impedance layers and low acoustic impedance layers underneath the bottom dielectric layer; and each of the bottom vias extends through the bottom dielectric layer and electrically connects the second bottom electrode and a top one of the high acoustic impedance layers.
18. 18 . The resonator structure of claim 9 wherein the first piezoelectric layer and the second piezoelectric layer are formed of different materials.
19. 19 . A resonator structure comprising: a first resonator; a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator; and a third resonator, which is vertically stacked with the first resonator and the second resonator, and shares a second common reflector with the second resonator, wherein: the first resonator is at least composed of a first top electrode, a first piezoelectric layer underneath the first top electrode, and the common reflector underneath the first piezoelectric layer; the second resonator is at least composed of the common reflector, the second piezoelectric layer underneath the common reflector, the second bottom electrode underneath the second piezoelectric layer, and the second common reflector underneath the second bottom electrode; the third resonator is at least composed of the second common reflector, a third piezoelectric layer underneath the second common reflector, and a third bottom electrode underneath the third piezoelectric layer; and the first resonator, the second resonator, and the third resonator are acoustically isolated from each other.

Description

RELATED APPLICATIONS This application claims the benefit of provisional patent application Ser. No. 63/353,709, filed Jun. 20, 2022, the disclosure of which is hereby incorporated herein by reference in its entirety. FIELD OF THE DISCLOSURE The present disclosure relates to a resonator structure including stacked resonators, which share a same reflector. BACKGROUND Due to, among other things, their small size, high Q values, and very low insertion losses at microwave frequencies, particularly those above 1.5 Gigahertz (GHz), Bulk Acoustic Wave (BAW) resonators are widely used in many wireless communications devices. In particular, for many 3rd Generation (3G) and 4th Generation (4G) wireless devices, BAW resonators are used in filters to improve reception and transmission of signals. One example of a conventional solid mount BAW resonator (SMR) 100 is illustrated in FIG. 1. The SMR 100 is formed by sandwiching a piezoelectric layer 102 between a top reflector 104 and a bottom reflector 106. The top reflector 104 and the bottom reflector 106 are configured to keep the energy in the piezoelectric layer 102. Due to acoustic reasons (e.g., achieving different temperature coefficient frequency) or packaging reasons, the SMR 100 may only have one of the top and bottom reflectors 104 and 106. In addition, the SMR 100 also includes a top electrode 108 residing vertically between the piezoelectric layer 102 and the top reflector 104 and a bottom electrode 110 residing vertically between the piezoelectric layer 102 and the bottom reflector 106. The top electrode 108 and the bottom electrode 110 are used to electrically connect to external components. The SMR 100 may also include a substrate 112 underneath the bottom reflector 106. Typically, one device die may only accommodate one SMR 100, which has one piezoelectric coefficient (e.g., the piezoelectric layer 102 is formed of one piezoelectric material with one piezoelectric coefficient/electromechanical coupling coefficient Ke2). To implement a BAW filter with both series resonators and shunt resonators will consume a significant device area. Accordingly, there remains a need for improved resonator designs to achieve more than one piezoelectric coefficient without suffering a bulk volume of the final product. Further, there is also a need to keep the final product easy to implement and cost effective. SUMMARY The present disclosure relates to a resonator structure including stacked resonators, which share a same reflector. The disclosed resonator structure includes a first resonator and a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator. Herein, the first resonator is at least composed of a first top electrode, a first piezoelectric layer underneath the first top electrode, and the common reflector underneath the first piezoelectric layer. The second resonator is at least composed of the common reflector, a second piezoelectric layer underneath the common reflector, and a second bottom electrode underneath the second piezoelectric layer. The first resonator and the second resonator are acoustically isolated from each other. In one embodiment of the resonator structure, the common reflector is a conductive reflector, such that the first resonator and the second resonator are electrically connected without external wiring. In one embodiment of the resonator structure, the first resonator further includes a first bottom electrode residing vertically between the common reflector and the first piezoelectric layer, while the second resonator further includes a second top electrode residing vertically between the common reflector and the second piezoelectric layer. The common reflector includes top common vias, bottom common vias, a top common dielectric layer, a bottom common dielectric layer underneath the top common dielectric layer, and alternating high acoustic impedance layers and low acoustic impedance layers residing vertically between the top common dielectric layer and the bottom common dielectric layer. Each of the top common vias extends through the top common dielectric layer and electrically connects the first bottom electrode and a top one of the high acoustic impedance layers. Each of the bottom common vias extends through the bottom common dielectric layer and electrically connects the second top electrode and a bottom one of the high acoustic impedance layers. In one embodiment of the resonator structure, the top common dielectric layer and the bottom common dielectric layer are formed of silicon oxide (SiO2). The high acoustic impedance layers are formed of tungsten (W), molybdenum (Mo), or platinum (Pt), and the low acoustic impedance layers are formed of aluminum (Al). In one embodiment of the resonator structure, the common reflector is a non-conductive reflector, and the first resonator and the second resonator are electrically connected with external wiring. In one embodime