Granted Patent B2

US 12,744,512 · App. 17/878,819 · Granted Sep 22, 2026

Inventors: Andrew Kay (Provo, UT); Albert Cardona (Santa Barbara, CA); Chris O'Brien (San Diego, CA); Akanksha Saha (Santa Barbara, CA)

Assignee: Murata Manufacturing Co., Ltd.

H03H9/173H03H3/02H03H9/13H03H2003/021

Abstract

Claims (59)

1 . A method of fabricating an acoustic resonator using sacrificial pillars, the method comprising:

forming a sacrificial pillar on a bottom surface of a piezoelectric wafer;

depositing a blanket conforming dielectric layer on the bottom surface of the piezoelectric wafer and on the sacrificial pillar to cover the sacrificial pillar;

polishing a bottom surface of the blanket conforming dielectric layer to form a bottom planar surface of the blanket conforming dielectric layer and to leave a thickness of the blanket conforming dielectric that covers the sacrificial pillar;

bonding the planar bottom surface of the blanket conforming dielectric layer to a front surface of a substrate wafer;

forming at least one conductor pattern on a planar front surface of the piezoelectric wafer;

forming holes through the piezoelectric wafer to the sacrificial pillar; and

removing the sacrificial pillar using an etchant introduced through the holes in the piezoelectric wafer to form a cavity under a diaphragm of the piezoelectric wafer spanning the cavity,

wherein forming the sacrificial pillar includes:

depositing a blanket layer of pillar material on the bottom surface of the piezoelectric wafer;

masking and patterning a top of the blanket layer of pillar material;

etching through a resulting pattern of the blanket layer to remove areas of the blanket layer of pillar material to the piezoelectric wafer to leave the sacrificial pillar; and

using the piezoelectric wafer as an etch stop for the etching through the pattern to remove areas of the blanket layer of pillar material.

2 . The method of claim 1 , wherein the bonding comprises flip chip bonding the planar surface of the blanket conforming dielectric layer to a bonding oxide (BOX) layer of the substrate that is on a trap rich layer of the substrate wafer.

3 . The method of claim 2 , further comprising, prior to the bonding:

forming the trap rich layer on the substrate wafer; and

forming the BOX layer on the trap rich layer.

4 . The method of claim 1 , wherein the sacrificial pillar is a pillar material configured to be selectively etched with respect to a material of the blanket conforming dielectric layer and a material of the piezoelectric wafer.

5 . The method of claim 1 , wherein;

a thickness of the blanket conforming dielectric is between 1 nm and 10 μm; and

a thickness of the sacrificial pillar is between 0.2 nm and 7 μm.

6 . The method of claim 1 , wherein the removing of the sacrificial pillar includes front-side etching the sacrificial pillar through the holes in the piezoelectric wafer to form the cavity where the sacrificial pillar is removed in a frontside release of a piezoelectric membrane of the piezoelectric wafer to form the diaphragm over an etched cavity under the diaphragm.

7 . The method of claim 1 , wherein the forming of the at least one conductor pattern includes forming an interdigital transducer (IDT) with interleaved fingers disposed on the diaphragm spanning the cavity; and wherein the piezoelectric wafer forms a piezoelectric plate that with the IDT are configured such that radio frequency signals applied to the IDT excites a primary shear acoustic mode in the piezoelectric plate over the cavity.

8 . The method of claim 1 , wherein the polishing of the blanket conforming dielectric layer leaves a thickness of the dielectric layer that covers the sacrificial pillar so that the dielectric layer has a homogenous surface for bonding to the substrate wafer or an oxide layer of the substrate wafer.

9 . A method of fabricating an acoustic resonator, the method comprising:

depositing a blanket layer of a pillar material on a piezoelectric layer;

masking and patterning a top of the blanket layer of pillar material;

etching through the patterned top of the blanket layer of pillar material to remove areas of the blanket layer of pillar material to leave a pillar of the pillar material;

depositing a blanket dielectric layer to cover the pillar;

planarizing a surface of the dielectric layer;

polishing a bottom surface of the planarized dielectric layer to form a bottom planar surface of the dielectric layer and to leave a thickness of the dielectric layer that covers the pillar;

flip-chip bonding the planarized surface of the dielectric layer to a bonding oxide (BOX) layer of a substrate that is on a trap rich layer of the substrate;

forming a conductor pattern on the piezoelectric layer; and

removing the pillar through holes in the piezoelectric layer to form a cavity where the pillar was removed.

10 . The method of claim 9 , wherein the removing of the pillar includes front-side etching the pillar through the holes in the piezoelectric layer to form the cavity where the pillar is removed, to frontside release a piezoelectric membrane of the piezoelectric layer to form a diaphragm over the etched cavity that spans the cavity.

11 . The method of claim 10 , wherein the conductor pattern includes an interdigital transducer (IDT) with interleaved fingers disposed on the diaphragm spanning the cavity.

12 . The method of claim 11 , wherein the piezoelectric layer and the IDT are configured such that radio frequency signals applied to the IDT excite a primary shear acoustic mode in the piezoelectric layer over the cavity, wherein a thickness of the diaphragm is selected to tune the primary shear acoustic modes in the piezoelectric layer.

13 . The method of claim 9 , further comprising, prior to the bonding:

forming the trap rich layer on the substrate; and

forming the BOX layer on the trap rich layer.

14 . The method of claim 13 , wherein the substrate is a polycrystalline or crystalline silicon (Si) material having a thickness of 250-500 μm;

the pillar is polysilicon and has a thickness between 1 and 5 μm;

the BOX layer has a thickness between 3 and 5 μm; and

the trap rich layer is an oxide layer having a thickness between 1 and 5 μm; and

the piezoelectric layer is one of lithium niobate or lithium tantalate having a thickness between 150 and 1000 nm.

15 . A method of fabricating an acoustic resonator using sacrificial pillars, the method comprising:

forming a sacrificial pillar on a bottom surface of a piezoelectric wafer;

depositing a blanket conforming dielectric layer on the bottom surface of the piezoelectric wafer and on the sacrificial pillar to cover the sacrificial pillar;

polishing a bottom surface of the blanket conforming dielectric layer to form a bottom planar surface of the blanket conforming dielectric layer and to leave a thickness of the blanket conforming dielectric that covers the sacrificial pillar;

bonding the planar bottom surface of the blanket conforming dielectric layer to a front surface of a substrate wafer;

forming at least one conductor pattern on a planar front surface of the piezoelectric wafer;

forming holes through the piezoelectric wafer to the sacrificial pillar; and

removing the sacrificial pillar using an etchant introduced through the holes in the piezoelectric wafer to form a cavity under a diaphragm of the piezoelectric wafer spanning the cavity,

wherein:

the piezoelectric wafer is one of lithium niobate or lithium tantalate;

the sacrificial pillar is one of polycrystalline silicon, an amorphous silicon, a silicon oxide, or a silicon nitride;

the blanket conforming dielectric layer is one of phosphosilicate glass (PSG), silicon oxide borosilicate glass (BSG), silicon oxide borophosphosilicate glass (BPSG), silicon oxide spin on glass (SOG), undoped silicon oxide, or silicon nitride;

the BOX layer is one of polycrystalline silicon, silicon oxide or silicon nitride; and

the substrate wafer is one of silicon, sapphire or quartz.

Assignments (2)

Continuity (2)

References Cited (252)