JP2000350296A - Microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone which is easily made small-sized and lightweight. SOLUTION: The microphone is a diaphragm member 1 formed of a silicon wafer and the diaphragm member 1 is formed by forming a trapezoidally- sectioned recessed part 1c which is downward open by carrying out anisotropic etching from the lower face side. This diaphragm member 1 is composed of a ring-shaped base la and a silicon diaphragm 1b supported on the base 1a. On the silicon diaphragm 1b, four piezoresistance elements 2a and 2c constitute a resistor bridge circuit and an insulating thin film 3 is formed on the silicon diaphragm 1b while covering an exposed surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone.

[0002]

2. Description of the Related Art Representative typical microphones include a condenser microphone and a dynamic microphone. A condenser microphone is provided so that a movable electrode formed on a plastic diaphragm serving as a diaphragm and a fixed electrode facing the movable electrode face each other at a certain distance to form a parallel plate capacitor. have. With this microphone,
When sound arrives at the diaphragm, the diaphragm vibrates due to sound pressure. Then, the distance between the movable electrode and the fixed electrode of the diaphragm changes, and the capacitance of the parallel plate capacitor changes. Then, the change in the capacitance is converted into an electric signal to obtain an audio signal.

On the other hand, a dynamic microphone has a structure in which a voice coil is fixed to a diaphragm that vibrates due to sound pressure, and a permanent magnet is provided so as to penetrate the voice coil. When the sound reaches the diaphragm and the diaphragm vibrates due to the sound pressure, the voice coil works together with the diaphragm to cut off the magnetic flux emitted from the permanent magnet, and an induced current flows through the voice coil. Then, an audio signal is obtained based on the induced current. The condenser microphone and the dynamic microphone described above are required to have excellent frequency characteristics, easy handling, small size and light weight, and the like.

[0004]

However, in satisfying the above requirements, there are the following problems.

First, both the condenser microphone and the dynamic microphone make up the microphone body, which has many mechanical parts and many parts. Further, since the structure is complicated, it is difficult to reduce the size and weight of the microphone body.

In addition, since the size of the diaphragm is large, a mechanical resonance point tends to appear near the audible band, and the frequency characteristic is limited to the resonance point. Further, when a plastic diaphragm is used, the plastic is deteriorated by being exposed to ultraviolet rays, and is not suitable for long-time outdoor use in which the characteristics of the diaphragm change. Further, when used in a liquid, a thick and hard diaphragm is used so that the diaphragm does not deform or malfunction. This degrades various characteristics of the microphone, such as sensitivity, frequency characteristics, and temperature characteristics.

An object of the present invention is to provide a microphone that can be easily reduced in size and weight.

[0008]

SUMMARY OF THE INVENTION A microphone according to the present invention comprises a silicon diaphragm vibrating under a sound pressure, one or more piezoresistive elements formed by diffusing impurities into a part of the silicon diaphragm, and a piezoresistive element. An insulating thin film formed on the silicon diaphragm so as to cover the exposed surface of the element. Here, the silicon diaphragm is a diaphragm formed from a silicon wafer using a known semiconductor processing technique. The diaphragm vibrates when receiving a sound pressure, and the vibration of the diaphragm is regarded as a change in the electric resistance of the crystal of the piezoresistive element. A microphone is established by converting an electric signal based on the change in the electric resistance into an audio signal. As the insulating thin film, SiON, SiO2, SiN, or the like can be used.

In this case, by using a silicon diaphragm as the diaphragm, a conventional semiconductor manufacturing technique can be applied to the manufacturing process of the diaphragm, and the diaphragm can be reduced in size, weight, and thickness. Also, the piezoresistive element can be formed small and thin using a known semiconductor manufacturing technique. Further, by forming an insulating thin film on the silicon diaphragm, the exposed surface of the piezoresistive element is protected. The silicon wafer used for the silicon diaphragm is, in addition to a normal silicon wafer, an SI in which an oxide film is embedded in the wafer in advance in a bare wafer state.
MOX wafers may be used.

Typically, it is preferable to form four piezoresistive elements constituting a bridge circuit on a silicon diaphragm. By adopting such a configuration, by combining the respective piezoresistive elements so as to maximize the output, the vibration of the silicon diaphragm vibrating under the sound pressure is efficiently converted into a change in electric resistance, that is, a change in electric signal. be able to.

[0011]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing a structure of a main part of a microphone, which is an example of an embodiment of the present invention. As shown in FIG. 1, the microphone is a diaphragm member 1 formed from a silicon wafer. The diaphragm member 1 includes an annular base 1a and a silicon diaphragm 1b supported by the base 1a. Four piezoresistive elements 2a to 2d are formed on the silicon diaphragm 1b so as to form a resistance bridge circuit as shown in FIG.

The four piezoresistive elements 2a to 2d are formed so that when the silicon diaphragm 1b vibrates in a direction orthogonal to the plane direction, a voltage change in a direction indicated by an arrow in FIG. Have been. Although not shown, on the surface of the diaphragm member 1,
A connection pattern for connecting the piezoresistive elements to each other and a connection pattern for connecting a connection point of the bridge circuit to an output electrode (not shown) are formed by using a known semiconductor forming technique. An insulating thin film 3 made of SiO2, SiN, SiON or the like is formed on the surface of the base 1a and the surface of the silicon diaphragm 1b so as to cover the exposed surface of the piezoresistive element 2.

Next, a method of manufacturing the above-described microphone will be described in the order of manufacturing steps. First, the diaphragm member 1 is formed by performing anisotropic etching from the lower surface side of the silicon wafer to form a concave portion 1c which is opened downward as shown in FIG. 1 and has a trapezoidal vertical sectional shape.

Next, the entire surface of the diaphragm member 1 is
A process for converting into iO2, SiN, and SiON is performed. Next, silicon is epitaxially grown on the silicon diaphragm 1b using single crystal silicon, polycrystal silicon, amorphous silicon, or the like. The piezoresistive element 2 is formed by diffusing impurities into the epitaxially grown silicon. Finally, SiO 2 is coated on the entire upper surface of the diaphragm member 1 so as to cover the exposed surface of the piezoresistive element 2.
An insulating film 3 such as SiN or SiON is formed by using a thin film forming technique such as sputtering.

It should be noted that the formation of the concave portion 1c may be made last, contrary to the order of the manufacturing steps described above. That is, first, a piezoresistive element is formed on a silicon wafer, and an insulating thin film is formed so as to cover an exposed surface of the piezoresistive element. Thereafter, anisotropic etching may be performed from the lower surface of the silicon wafer to form a concave portion 1c having a shape as shown in FIG.

The piezoresistive element 2 is preferably formed on the maximum sensitivity region when the silicon diaphragm 1b vibrates. For example, when the silicon diaphragm 1b is formed using a (100) plane silicon wafer, the piezoresistive element 2 is formed in the peripheral portion of the silicon diaphragm 1b, that is, in the region from the base 1a. Also, (1
When the silicon diaphragm 1b is formed using the silicon wafer having the 10) surface, the piezoresistive element 2 is provided in the central region of the silicon diaphragm 1b. The embodiment shown in FIG. 1 shows the positions where the piezoresistive elements 2a to 2d are formed when a (110) plane silicon wafer is used.

Further, as the silicon wafer used for the diaphragm member 1, a silicon wafer in which an oxide film is formed in a bare wafer state, for example, a SIMOX wafer may be used.

As described above, the piezoresistive elements 2a to 2d formed on the silicon diaphragm 1b are formed so as to form a resistance bridge circuit as shown in FIG. 2 when formed on the silicon diagram 1b. I have.
The resistance value of each piezoresistive element is determined so that the voltage signal output from the bridge circuit becomes as large as possible when the silicon diaphragm 1b vibrates due to sound pressure. By configuring such a bridge circuit, the vibration of the silicon diaphragm 1b can be efficiently converted into an electric signal.

In the above embodiment, four piezoresistive elements are used, but the number of piezoresistive elements may be one or more, and the circuit configuration is arbitrary.

[0021]

According to the present invention, a piezoresistive element detects a vibration of a silicon diaphragm as a change in a resistance value to obtain an audio signal. Therefore, it is possible to eliminate a problem which occurs in a microphone having a mechanical vibration system. In particular, a small and lightweight microphone can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a main part of a microphone according to the present invention.

FIG. 2 is a circuit diagram when four piezoresistive elements are used as a bridge circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diaphragm member 1a Base 1b Silicon diaphragm 1c Diaphragm recess 2a-2d Piezoresistive element 3 Insulating thin film

Claims (2)

[Claims] 1. A silicon diaphragm that vibrates under a sound pressure, at least one piezoresistive element formed by diffusing an impurity into a part of the silicon diaphragm, and an exposed surface of the piezoresistive element. A microphone comprising an insulating thin film formed on the silicon diaphragm. 2. The microphone according to claim 1, wherein the four piezoresistive elements forming a bridge circuit are formed in the silicon diaphragm.