Optimal Acoustic Impedance Materials for Polished Substrate Coating to Suppress Passband Ripple in BAW Resonators and Filters

• US 20090142480A1
• Filed: 12/04/2007
• Published: 06/04/2009
• Est. Priority Date: 12/04/2007
• Status: Active Grant

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Hannan, Masud, Sridhar, Uppili, Godshalk, Edward Martin, Wall, Ralph N., Lutz, Rick D.
• Granted Patent: US 8,512,800 B2
• Time in Patent Office: Days
• 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 0.01x to 1.0x 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 material and a low acoustic material on a first surface of the substrate;

fabricating a BAW 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 0.01x to 1.0x the acoustic impedance of the layers of high impedance material;

the second surface of the substrate being a polished surface.

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 surface to reduce the substrate thickness to approximately 325 and polish the second surface.

5. The method of claim 4 wherein the second surface is polished to a peak-to-peak roughness of approximately 1000 A.

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

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

8. 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 material and a low acoustic material on a first surface of the substrate;

fabricating a BAW 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 0.01x to 1.0x the acoustic impedance of the layers of high impedance material;

the substrate being approximately 325 μ

m thick and the second surface of the substrate being polished.

9. The method of claim 8 wherein the lossy material is epoxy.

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

11. The method of claim 10 wherein the second surface is polished to a peak-to-peak roughness of approximately 1000 A.

12. The method of claim 11 wherein material is removed by grinding the second side of the substrate.

13. The method of claim 8 wherein the layers of high impedance material are Tungsten.

14. 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 material on a first surface 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 0.01x to 1.0x the acoustic impedance of the layers of high impedance material;

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

15. The method of claim 14 wherein the Bragg mirror and the BAW are fabricated on a thicker substrate and then material is removed from the second surface to reduce the substrate thickness to approximately 325 and polish the second surface.

16. The method of claim 15 wherein material is removed by grinding the second side of the substrate.