JPH0937382A - Microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to highly sensitively detect a sound even by a microminiaturized microphone by detecting a change in a resistance value obtained when a heat sensitive resistor formed on a diaphragm formed on a base board 1 by micromachining work is oscillated as an electric signal. SOLUTION: A diaphragm 2 consisting of a thin film is formed on a base board 1 by micromachining work. A heat sensitive resistor consisting of a heat wire 3 having a large resistance temperature coefficient is formed on the surface of the diaphragm 2 and electrode parts 4 are formed on the end parts of the diaphragm 2. A constant current power supply 5 is connected to the heat wire 3 through the electrode part 4 to heat the wire 3 always at a fixed temperature. When the diaphragm 2 is oscillated by the input of a sound from the upper face, the wire 3 is cooled by air and its resistance value is changed. Thereby the terminal voltage of the wire 3 is changed and the change is detected by a voltage variation forming circuit 6, so that an output signal Vo corresponding to the input sound is obtained. Thus a microminiaturized micro∥phone can be attained by micromachining work and a sound can be highly accurately detected.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Recently, a thin film diaphragm is formed by etching a semiconductor substrate by using a micromachining process of a semiconductor device, and then a vibration of a diaphragm is caused by a piezoresistive effect and a change in capacitance. Microminiaturized microphones have been developed that convert a signal into an electric signal (reference document 1994 Elsevie).
r Science Review Paper "A
review of silicon microph
ones ").

[0003]

The problem to be solved by the present invention is to solve the problem in the microminiature microphone in which the vibration due to the sound of the diaphragm is converted into an electric signal by utilizing the piezoresistive effect and the change of the electrostatic capacity. Since it is miniaturized, it is impossible to sufficiently oscillate the diaphragm with respect to the sound, so that the SN ratio is lowered and the sound detection sensitivity is deteriorated.

[0004]

According to the present invention, it is possible to detect a sound with high sensitivity even if it is miniaturized.
It has a diaphragm formed on the substrate and a thermosensitive resistor formed on the diaphragm so that the change in the resistance value of the thermosensitive resistor when the diaphragm vibrates due to sound can be detected as an electric signal. .

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A microphone according to the present invention has a diaphragm 2 whose basic constituent parts are formed as a thin film on a base 1 made of silicon or glass, as shown in FIGS. 1 and 2, and a diaphragm 2 thereof. A heat wire 3 made of a material such as platinum Pt, nickel Ni, or tungsten W having a large temperature coefficient of resistance as a heat-sensitive resistor is formed in the portion. In the figure, 4 is an electrode portion of the heat wire 3.

[0006] In such a structure, a constant current power source 5 is connected to the heat wire 3 to constantly supply current, and the heat wire 3 is heated to a constant temperature of about 200 to 300 ° C. Keep it.

When the diaphragm 2 vibrates due to the sound input from the upper surface, the heat wire 3 is cooled by the air, the resistance value of the heat wire 3 changes, and the terminal voltage of the heat wire 3 changes. By taking out the amount of change in the terminal voltage of the heat wire 3 by the voltage change detection circuit 6, an output signal Vo corresponding to the input sound can be obtained.

At this time, the heat wire 3 is formed in a predetermined pattern so as to obtain the entire length so that a larger air cooling effect can be obtained when the diaphragm 2 vibrates due to the input sound.

The output signal Vo of the sound as the change of the terminal voltage based on the temperature change of the heat wire 3 is expressed by the following equation (1) where ΔT is the temperature change of the heat wire 3 and η is the resistance temperature coefficient of the heat wire 3. ).

[0010]

[Equation 1]

Therefore, according to the present invention, it is possible to obtain a large gain as compared with the conventional one in which the vibration caused by the sound of the diaphragm is converted into an electric signal by the piezoresistive effect or the change of the electrostatic capacitance. The sound detection sensitivity is significantly improved.

The structure consisting of the base 1, the diaphragm 2 and the heat wire 3 is manufactured, for example, by micromachining a semiconductor device as shown in FIG.

First, on the upper and lower surfaces of a semiconductor substrate 7 made of Si or the like, layers 8, 9 made of SiN, SiON, SiO ₂ or the like are formed.
Is formed by sputtering or CVD (step S1). Next, a heat wire material is formed into a thin film on the upper layer 8 and then patterned into a predetermined pattern to form the heat wire 3 and the electrode portion 4 (step S2). Then, in order to protect the heat wire 3, a layer 10 of SiN, SiON, SiO ₂ or the like is further formed thereon (step S3), and then the base 1 is etched (eg, KOH etching) from the upper surface and the lower surface. And the diaphragm 2 is formed (step S4).

Further, according to the present invention, it becomes possible to easily manufacture microminiature microphones having various structures by micromachining the semiconductor device.

FIG. 4 shows an example thereof, and here,
Formed on the base 1 are cantilevers 11 to 14 as a plurality of thin film diaphragms having different resonance frequencies by changing the length and the width, instead of the diaphragm 2, which selectively detects the input sound by its frequency. However, by forming the heat wires 3 on the cantilevers 11 to 14 respectively, it is possible to selectively obtain the output signals Vo to Vo ₄ of specific sounds that resonate with the sounds input from the upper surface. I am trying.

Resonance frequency f of each cantilever 11-14
_Q is given by the following equation (2) according to the lever length 1, width t, density p, and elastic constant S.

[0017]

[Equation 2]

With this structure, the vibrations of the cantilevers 11 to 14 resonate with the frequency of the input sound, so that specific sounds of different tones can be selectively detected with high sensitivity. become able to.

By installing the required number of cantilevers, it becomes possible to directly obtain the output signal of the frequency-converted (Fourier-converted) sound, which is applicable to voice recognition and digital recording. Becomes

It is also possible to convert a sound source such as an ultrasonic wave into a digital signal and perform sound wave communication by utilizing the characteristic that the sound can be selectively detected depending on the frequency.

For example, as shown in FIG. 5, a specific frequency f is obtained by using a plurality of cantilever structures that resonate at the same frequency on the transmitting side A and the receiving side B, respectively.
It becomes possible to receive a digital signal of a plurality of bits by binary values of "1" and "0" by combining the turning on and off of the dial tone by 1, f2, f3 and f4.

In that case, at the originating side A, for example,
Electric power having a frequency f1 having a resonance relationship with the receiving side B is supplied to the heat wire 31 formed on the cantilever 11 to repeatedly generate heat at the frequency f1, and the cantilever 11 is vibrated by the bimetal effect.
The signal "1" is emitted.

In the case of performing sound wave communication by ultrasonic waves or the like, noise due to reflected waves generally poses a problem, but the use of the present invention does not cause the problem of noise due to reflected waves.

[0024]

As described above, in the microphone according to the present invention,
A thermosensitive resistor is provided on a diaphragm that vibrates by sound, and changes in the resistance value of the thermosensitive resistor when the diaphragm vibrates are detected as an electrical signal. Microminiaturized by semiconductor device micromachining processing. It is possible to easily achieve the above, and there is an advantage that the sound can be detected with high sensitivity even if the size is reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing a basic configuration of a microphone according to the present invention.

FIG. 2 is a front view showing a basic configuration of a microphone according to the present invention.

FIG. 3 is a diagram showing an example of a manufacturing process of a microphone according to the present invention.

FIG. 4 is a plan view showing another configuration example of the microphone according to the present invention.

FIG. 5 is a plan view showing a configuration example when sound wave communication is performed using the present invention.

[Explanation of symbols]

 1 Base 2 Diaphragm 3 Heat wire 4 Electrode part 5 Constant current power supply 6 Voltage fluctuation detection circuit 11-14 Cantilever 31-34 Heat wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiro Fueki 1-4-1 Chuo, Wako, Saitama Prefecture Honda R & D Co., Ltd. (72) Inventor Hiroshi Yamakawa 1-4-1 Chuo, Wako, Saitama Stock Company Honda Technical Research Institute

Claims (4)

[Claims] 1. A vibrating plate formed on a substrate and a thermosensitive resistor formed on the vibrating plate, wherein a change in resistance value of the thermosensitive resistor when the vibrating plate vibrates due to sound is used as an electric signal. A microphone characterized by being designed to be captured. 2. The method according to claim 1, wherein the diaphragm is formed into a thin film on the substrate by a micromachining process of the semiconductor device, and the thermal resistor is formed into a thin film on the diaphragm. Microphone. 3. The microphone according to claim 1, wherein a plurality of diaphragms having different resonance frequencies are formed. 4. The microphone according to claim 1, wherein the thermosensitive resistor is formed into a wire shape and patterned.