Surface micromachined microphone with broadband signal detection

Patent metadata

Field	Value
Publication number	US-2016337761-A1
Application number	US-201515111080-A
Country	US
Kind code	A1
Filing date	Jan 12, 2015
Priority date	Jan 13, 2014
Publication date	Nov 17, 2016
Grant date	—

Abstract

A surface micromachined microphone with a 230 kHz bandwidth. The structure uses a 2.25 μm thick, 305 μm radius polysilicon diaphragm suspended above an 11 μm gap to form a variable parallel-plate capacitance. The backcavity of the microphone consists of the 11 μm thick air volume immediately behind the moving diaphragm, and also an extended larger cavity with a radius of 504 μm. The dynamic frequency response of the sensor in response to electrostatic signals is presented using laser Doppler vibrometry, and indicates a system compliance of 0.4 nm/Pa in the flat-band of the response. The sensor is configured for acoustic signal detection using a charge amplifier configuration, and signal to noise ratio measurements and simulations are presented herein. A resolution of 0.80 mPa/√Hz (32 dB SPL in a 1 Hz bin) is achieved in the flat-band portion of the response extending from 10 kHz to 230 kHz.

First claim

1 . An acoustic sensor, comprising:
a diaphragm attached to a substrate via a plurality of columns forming a cavity; and a plurality of structures shorter in length than said plurality of columns attached to said substrate, wherein said plurality of structures is electrically conductive forming a lower electrode.

2 . The acoustic sensor as recited in claim 1 , wherein said cavity contains a barometric vent to an outside world.

3 . An acoustic sensor, comprising:
a diaphragm attached to a substrate via a first set of sidewalls forming a first cavity; a lower electrode attached to said substrate that is capacitively coupled to said diaphragm; an upper electrode attached to said substrate via a second set of sidewalls, wherein said upper electrode has vents such that air pressure from sound waves deflect said diaphragm; and a second cavity formed between said upper electrode and said diaphragm forming a second capacitively coupled structure.

4 . The acoustic sensor as recited in claim 3 , wherein a first bias voltage is applied between said diaphragm and said lower electrode and a second bias voltage is applied between said diaphragm and said upper electrode.

5 . The acoustic sensor as recited in claim 4 , wherein said first and second bias voltages are balanced such that said diaphragm is physically centered between said upper and lower electrodes.

6 . The acoustic sensor as recited in claim 3 , wherein said first set of sidewalls contains at least one opening forming a barometric vent.

7 . An acoustic sensor, comprising:
a diaphragm attached to a substrate via a first set of sidewalls; a lower electrode attached to said substrate via a second set of sidewalls, wherein said lower electrode is formed below said diaphragm, wherein said lower electrode has vents to a cavity formed between said lower electrode and said substrate; and a second cavity formed between said lower electrode and said diaphragm.

8 . The acoustic sensor as recited in claim 7 , wherein said first set of sidewalls contains at least one opening forming a vent.

9 . An acoustic sensor, comprising:
a planar diaphragm with an active area; a cavity disposed at least partially above a substrate, wherein said cavity has a wall formed by said diaphragm, wherein said cavity has a planar area that is greater than said active area of said diaphragm; and one or more bottom electrodes.

10 . The acoustic sensor as recited in claim 9 , wherein said diaphragm comprises an approximately 2 μm thick polysilicon layer, wherein said cavity comprises an approximately 11 μm tall cylindrical air volume with an approximately 504 μm radius enclosed by said approximately 2 μm thick polysilicon diaphragm layer.

11 . The acoustic sensor as recited in claim 10 , wherein said polysilicon diaphragm layer has a clamped boundary condition at said approximately 504 μm radius perimeter.

12 . The acoustic sensor as recited in claim 10 , wherein said diaphragm is attached to a plurality of post structures from a radius of approximately 315 μm to said approximately 504 μm radius to prevent a portion of said diaphragm from moving during operation.

13 . The acoustic sensor as recited in claim 12 , wherein in a center region of said diaphragm from a radius of approximately 0 μm to said approximately 315 μm, there exists no post structures thereby allowing said diaphragm to move freely towards and away from said one or more bottom electrodes.

14 . The acoustic sensor as recited in claim 11 , wherein said clamped boundary condition is affixed to a sidewall that is attached to said substrate.

15 . The acoustic sensor as recited in claim 9 , wherein said diaphragm is attached to a plurality of post structures preventing a portion of said diaphragm from moving during operation.

16 . The acoustic sensor as recited in claim 9 , wherein said diaphragm comprises a conductively doped material acting as an electrode.

17 . The acoustic sensor as recited in claim 9 , wherein said diaphragm comprises a layer of conductive material deposited on it to form an electrode.

18 . The acoustic sensor as recited in claim 9 further comprising:
a release hole existing at a portion of said diaphragm.

19 . The acoustic sensor as recited in claim 18 further comprising:
a layer of polysilicon underneath said diaphragm configured to restrict airflow through said release hole or configured to collect a sealant when it is applied to a top surface of said sensor.

20 . The acoustic sensor as recited in claim 19 further comprising:
a sealing layer on said top surface of said sensor.

Assignees

• Univ Texas

Inventors

• Hall Neal A
• Kuntzman Michael L
• Sauceda Karen Kirk

Classifications

• H04R17/02 Primary

  Microphones · CPC title

• G01S3/801 Primary

  Details {(G01S3/82, G01S3/84, G01S3/86 take precedence)} · CPC title