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

• US 8,512,800 B2
• Filed: 12/04/2007
• Issued: 08/20/2013
• Est. Priority Date: 12/04/2007
• Status: Expired due to Fees

• 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:
  US11/950,149
• Publication Number:
  US 20090142480A1
• Time in Patent Office: 2,086 Days
• Field of Search: 427/100
• US Class Current: 427/100
• 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

Methods of reducing phase and amplitude ripples in a BAW resonator frequency response by providing a substrate, fabricating a Bragg mirror having alternate layers of a high acoustic material and a low acoustic material on a first surface of the substrate, fabricating a BAW on the Bragg mirror, and coating a second side of the substrate opposite the first side with a lossy material having an acoustic impedance in the range of 0.01× to 1.0× the acoustic impedance of the layers of high impedance material, the second surface of the substrate being a polished surface. Various embodiments are disclosed.

Claims

1. A method of reducing phase and amplitude ripples in a BAW resonator frequency response comprising:

providing a substrate;

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

fabricating a BAW resonator on the Bragg mirror;

coating a second side of the substrate opposite the first side with a 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;

the substrate of the BAW resonator having 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.

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

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

m thick.

4. The method of claim 3 wherein the Bragg mirror and the BAW are fabricated on a thicker substrate and then material is removed from the second side to reduce the substrate thickness to approximately 325 μ

m and polish the second side.

5. The method of claim 4 wherein material is removed by grinding the second side of the substrate.

6. The method of claim 5 wherein the layers of high impedance material are Tungsten.

7. A method of reducing phase and amplitude ripples in a BAW resonator frequency response comprising:

providing a substrate;

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

fabricating a BAW on the Bragg mirror;

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

to 1.0×

the acoustic impedance of the layers of tungsten;

the substrate of the BAW resonator having a thickness of 400 μ

m or less;

the second side of the substrate being polished to a peak-to-peak roughness of less than approximately 1000 A.

8. The method of claim 7 wherein the Bragg mirror and the BAW are fabricated on a thicker substrate and then material is removed from the second side to reduce the substrate thickness to approximately 325 μ

m and polish the side surface.

9. The method of claim 8 wherein material is removed by grinding the second side of the substrate.