Condenser microphone

Abstract

An electret condenser microphone (ECM) forms an air-gap capacitor structure in which an upper electrode and a lower electrode are opposed to each other with its hollow portion interposed therebetween, and an electret film made of a charge retention material is formed between the electrodes. The ECM is formed continuously with a semiconductor substrate, and the electret film is made of an amorphous perfluoropolymeric resin. The electret film made of such a material can be formed on the substrate by spin coating. This facilitates reducing the thickness of the electret film. In addition, the film can be easily etched by a fluorine based gas used in a semiconductor process. This permits fine patterning, resulting in the reduced area of a condenser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating the structure of an electret condenser microphone (acoustic sensor) according to an embodiment of the present invention.

FIG. 2A through 2D are cross-sectional views illustrating process steps for fabricating an electret condenser microphone (acoustic sensor) according to the embodiment of the present invention.

FIG. 3 is a plan view illustrating the structure of the electret condenser microphone immediately after the process step illustrated in FIG. 2B.

FIG. 4 is a plan view illustrating the structure of the electret condenser microphone immediately after the process step illustrated in FIG. 2D.

FIG. 5 is a cross-sectional view illustrating the structure of a known electret condenser microphone.

Claims

1. A condenser microphone comprising a vibrating electrode, a fixed electrode, and an electret film formed between the vibrating electrode and the fixed electrode, the condenser microphone being formed continuously with a semiconductor substrate, andthe electret film being made of one of an amorphous perfluoropolymeric resin and benzocyclobutene.

2. The condenser microphone of claim 1, wherein the vibrating electrode, the fixed electrode and the electret film are stacked on the semiconductor substrate, andthe electret film is formed by applying a solution containing one of the amorphous perfluoropolymeric resin and benzocyclobutene onto the semiconductor substrate and patterning a film made of the applied solution.

3. The condenser microphone of claim 1, wherein a hollow portion is formed in a portion of the condenser microphone located between the vibrating electrode and the fixed electrode.

4. The condenser microphone of claim 3, wherein the hollow portion is formed by partially removing a film formed on the semiconductor substrate.

5. The condenser microphone of claim 1, wherein the electret film is covered with a hydrophobic insulating film.

6. The condenser microphone of claim 5, wherein the hydrophobic insulating film is a silicon nitride film.

7. The condenser microphone of claim 1, wherein a signal processing circuit for processing a signal detected by the condenser microphone is integrated on the semiconductor substrate.