Optimal acoustic impedance materials for polished substrate coating to suppress passband ripple in BAW resonators and filters

• US 8,952,768 B2
• Filed: 08/20/2013
• Issued: 02/10/2015
• Est. Priority Date: 12/04/2007
• Status: Active Grant

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: TriQuint Semiconductor Incorporated (Qorvo, Inc.)
• Inventors: Godshalk, Edward Martin, Lutz, Rick D., Hannan, Masud, Wall, Ralph N., Sridhar, Uppili
• Primary Examiner(s): Cleveland, Michael
• Assistant Examiner(s): Murata, Austin
• Application Number:
  US13/971,721
• Publication Number:
  US 20130335169A1
• Time in Patent Office: 539 Days
• Field of Search: 333/187, 427/100
• US Class Current: 333/187
• CPC Class Codes: H03H 9/02055 of the surface including the back surface
• CPC Class Codes: H03H 9/0211 of reflections
• CPC Class Codes: H03H 9/15 Constructional features of resonators consisting of piezoelectric or electrostrictive material H03H9/25 takes precedence
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

A bulk acoustic wave (BAW) resonator is constructed to reduce phase and amplitude ripples in a frequency response. The BAW resonator is fabricated on a substrate 400 μm thick or less, preferably approximately 325 μm, having a first side and a polished second side with a peak-to-peak roughness of approximately 1000 A. A Bragg mirror having alternate layers of a high acoustic impedance material, such as tungsten, and a low acoustic impedance material is fabricated on the first side of the substrate. A BAW resonator is fabricated on the Bragg mirror. A lossy material, such as epoxy, coats the second side of the substrate opposite the first side. The lossy material has an acoustic impedance in the range of 0.01× to 1.0× the acoustic impedance of the layers of high acoustic impedance material.

Claims

1. A BAW resonator with reduced phase and amplitude ripples in a frequency response, the BAW resonator comprising:

a substrate having a first side, a second side opposite the first side, and a thickness of 400 μ

m or less, the second side of the substrate being a polished surface with a peak-to-peak roughness of approximately 1000 A;

a Bragg mirror having alternate layers of a high acoustic impedance material and a low acoustic impedance material fabricated on the first side of the substrate;

a BAW resonator fabricated on the Bragg mirror; and

a lossy material coating the second side of the substrate, the lossy material having an acoustic impedance in the range of 0.01×

to 1.0×

the acoustic impedance of the layers of high acoustic impedance material.

2. The BAW resonator of claim 1 wherein the lossy material is epoxy.

3. The BAW resonator of claim 1 wherein the substrate is approximately 325 μ

m thick.

4. The BAW resonator of claim 1 wherein the layers of high acoustic impedance material are tungsten.

5. A BAW resonator with reduced phase and amplitude ripples in a frequency response, the BAW resonator comprising:

a substrate having a first side, a second side opposite the first side, and a thickness of 400 μ

m or less, the second side of the substrate being a polished surface with a peak-to-peak roughness of approximately 1000 A;

a Bragg mirror having alternate layers of tungsten and a low acoustic impedance material fabricated on the first side of the substrate;

a BAW resonator fabricated on the Bragg mirror;

a lossy epoxy material coating the second side of the substrate, the lossy epoxy material having an acoustic impedance in the range of 0.01×

to 1.0×

the acoustic impedance of the layers of tungsten.

6. The BAW resonator of claim 5 wherein the substrate is approximately 325 μ

m thick.