Capacitive microphone and method therefor

• US 5,889,872 A
• Filed: 07/02/1996
• Issued: 03/30/1999
• Est. Priority Date: 07/02/1996
• Status: Expired due to Fees

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Sooriakumar, Kathirgamasundaram, Koch, Daniel J., Goldman, Kenneth G.
• Primary Examiner(s): LE, HUYEN D
• Application Number:
  US08/674,382
• Time in Patent Office: 1,001 Days
• Field of Search: 381/113, 381/116, 381/168, 381/174, 381/191, 381/173, 437/209, 367/181, 310/324
• US Class Current: 381/174
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 19/016 for microphones

Abstract

A capacitive microphone (10) utilizes a polysilicon diaphragm (14) that overlies an atmospheric cavity (34). The diaphragm is doped and annealed to form a sensitivity of the microphone (10). A silicon cap covers and protects the diaphragm (14) and a fixed plate (18).

Claims

1. A capacitive microphone comprising:

a substrate having a first surface, a second surface opposite to the first surface, and an atmospheric opening extending through the substrate from the second surface;

a doped polysilicon diaphragm of the capacitive microphone overlying the atmospheric opening;

a fixed capacitor plate formed from polysilicon wherein the fixed capacitor plate is aligned to the diaphragm; and

a silicon cap overlying the diaphragm and the fixed capacitor plate, the silicon cap forming a cavity with the diaphragm and the fixed capacitor plate therein.

2. The capacitive microphone of claim 1 wherein the doped polysilicon and the fixed capacitor plate are annealed to establish a stress thereof.

3. The capacitive microphone of claim 1 further including a semiconductor device formed in the silicon cap.

4. The capacitive microphone of claim 1 further including the cap attached with frit glass.

5. A capacitive microphone comprising:

a silicon substrate having an atmospheric opening through the substrate;

an etch stop layer on the substrate, the etch stop layer having an opening aligned to the atmospheric opening;

a polysilicon diaphragm on the etch stop layer and overlying the atmospheric opening;

a polysilicon fixed plate overlying and spaced apart from the polysilicon diaphragm; and

a cap overlying and spaced apart from the polysilicon fixed plate, the cap fixedly attached by a frit glass seal.

6. The capacitive microphone of claim 5 wherein the etch stop layer is silicon dioxide.

7. The capacitive microphone of claim 5 wherein the polysilicon diaphragm is doped polysilicon having a sensitivity of 0.1 to 20 mv/pascal.

8. The capacitive microphone of claim 5 wherein the polysilicon diaphragm has a resistivity of 10 to 1000 ohms/square.

9. The capacitive microphone of claim 5 further including damping openings through the polysilicon fixed plate.

10. The capacitive microphone of claim 5 further including pressure relief openings through the cap.

11. The capacitive microphone of claim 5 wherein the polysilicon diaphragm seals the atmospheric opening in the etch stop layer.