JPH05145996A - Electrostatic acoustic transducer - Google Patents

Abstract

PURPOSE:To enable use under a high-temperature environment and to reduce a stray loss in the case of miniaturizing the device or improving an S/N by forming an oxide silicon thin film on a metal foil and using a diaphragm made into an electret. CONSTITUTION:The oxide silicon film is formed with the thickness from 1mum to 5mum on the surface of a fixed electrode 5 and made into the electret and a surface potential is kept at a prescribed potential. A fine gap 3 is changed by the oscillation of a diaphragm 1, and an electric signal is obtained corresponding to the change of electrostatic capacity between the diaphragm 1 and the fixed electrode 5. At such a time, since the oxide silicon has high heat resistance, the electret potential is not degraded even under the high-temperature environment but can maintain high sensitivity. Further, since the oxide silicon thin film can be formed extremely thin, the ratio of the electrostatic capacity and the effective capacity is increased, the device can be miniaturized and the S/N can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer for converting an acoustic signal into an electrical signal or an electrical signal into an acoustic signal, and more particularly to a diaphragm or a fixed electrode of an electrostatic (condenser type) acoustic transducer.

[0002]

2. Description of the Related Art Conventionally, this type of electrostatic acoustic transducer has, for example, the structure shown in FIG. That is, on the back side of the diaphragm 1, the fixed electrodes 5 are provided so as to face each other with a certain slit 3 interposed therebetween. A bias voltage is applied in advance between the diaphragm 1 and the fixed electrode 5. When the diaphragm 1 vibrates acoustically, the electrostatic capacitance formed between the two changes, and the fixed electrode takes out an electromotive voltage proportional to this change as an electric signal to act as a microphone. Alternatively, in the case of a speaker, conversely, the electromotive voltage between the two is changed by the electric signal applied to the fixed electrode 5, the diaphragm vibrates, and the basis is generated.

Generally, the diaphragm 1 is preferably light and has a high Young's modulus. For example, a FEP film 7 (copolymer of 4 Huccaethylene and 6 Huccapropylene) is used and semipermanently stored by corona discharge, electron beam or the like. To be retained. As a result, since the surface always has a potential, it is not necessary to apply a bias voltage from the outside, and the size and the size can be reduced.

Alternatively, as shown in FIGS. 6 and 7, a polyester film or a metal foil (titanium alloy foil, nickel alloy foil, etc.) is used for the diaphragm 1, and the FEP film 7 is heat-welded to the fixed electrode 5 side. Then, it becomes an electret.

By making the electret in this way,
Sound can be converted to electricity or electricity can be converted to sound without the need for externally applying a bias voltage.

[0006]

However, in the above-mentioned conventional electrostatic acoustic transducer, (1) the electret potential of the electric charge stored in the FEP deteriorates in a high temperature environment (about 90 ° C. or higher), so that It cannot be used for equipment used in a temperature environment.

(2) Since the thickness of the FEP film cannot be 10 μm or less due to its nature, downsizing of the converter,
When measuring a high S / N ratio, the ratio of stray loss (floating loss) increases compared to the external bias method of applying a bias voltage from the outside, and the electret-applied electrostatic sound that makes the diaphragm 1 or the fixed electrode 5 an electret. It was a problem of the converter.

The present invention solves such a conventional problem, enables use even in a high temperature environment of 90 ° C. or higher, and can reduce the proportion of stray loss in miniaturization and high S / N ratio. An object is to provide an excellent electrostatic acoustic transducer.

[0009]

In order to achieve the above object, the present invention provides an electrostatic acoustic transducer according to the present invention, wherein the invention according to claim 1 is characterized in that silicon oxide (Si
An O ₂ ) thin film having a thickness of 1 μm or more and 5 μm or less is formed and has an electretized vibration plate, and a fixed electrode facing the vibration plate and provided with a certain gap therebetween.

The invention according to claim 2 is constituted by a diaphragm and a silicon oxide (SiO ₂ ) thin film of 1 μm or more and 5 μm or less formed on the surface of the diaphragm, facing the diaphragm with a certain gap. And an electret fixed electrode diaphragm.

[0011]

Therefore, according to the present invention, (1) the conventional FEP
By using a silicon oxide thin film instead of a film,
Since the surface potential of the silicon oxide, that is, the electret potential, does not deteriorate due to the heat resistance of silicon oxide even at a high temperature (90 ° C. or higher), the bias voltage due to the electret potential can be kept constant without applying a bias voltage from the outside. It can be used in high temperature environment.
Further, (2) the silicon oxide thin film can be made to have a thickness of 5 μm or less by various vapor deposition methods, and the stray loss can be suppressed even when the size is reduced and the S / N ratio is increased.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows the configuration of the first embodiment of the present invention, and corresponds to FIG. 6 of the conventional example. In FIG. 1, a hole 11 for transmitting sound is provided on the front side of the case 9.
Are formed. Inside the case 9, the hole 1
The vibrating plate ring 13 is provided on the side of 1, and the vibrating plate 1 is supported and fixed by a constant tension, and the fixed electrode 5 is opposed by the spacer 15 via the constant slit 3. Fixed electrode 5
Is held by the insulator 16 with respect to the case 9, and is integrated as a whole.

On the surface of the fixed electrode 5, a silicon oxide (SiO ₂ ) thin film 17 having a thickness of 1 μm is formed by PVD method C or CVD method.
The thickness is 5 μm or less (FIG. 2). The thin film 17 is subjected to corona discharge and electron beam irradiation to accumulate electric charges and semi-permanently store the same to form an electret, and the surface potential is changed from 150V to 250V. The diaphragm 1 can be a polyester film or a metal foil (for example, titanium alloy foil or nickel alloy foil) as in the conventional case.

Next, the operation of the first embodiment will be described. When the acoustic transducer of this embodiment is used as a microphone, when the diaphragm 1 vibrates, the thickness of the slit 3 changes, and the electrostatic capacitance formed between the diaphragm 1 and the fixed electrode 5. Changes, and an electromotive voltage proportional to this change can be taken out as an electric signal. The bias voltage that causes this electrostatic capacitance is given by the surface potential (electret potential) obtained by the fixed electrode 5 being electretized. Therefore, even if a bias voltage is not applied from the outside, a high bias voltage can be maintained and a highly sensitive electric signal can be obtained. In addition, since silicon oxide has high heat resistance, the electret potential of the silicon oxide thin film 17 does not deteriorate even in an environment of a temperature higher than that of the related art (about 90 ° C. or more and 150 ° C. or less), and high sensitivity can be maintained. Furthermore, silicon oxide thin film 1
7 is very thin by PVD method or CVD method (5μ
Therefore, the ratio of the effective capacitance of the electrostatic capacitance formed between the diaphragm 1 and the fixed electrode 5 is high, and thus the ratio of the stray capacity (floating capacitance) can be reduced. Therefore, it has an effect of realizing miniaturization, high sensitivity, and high S / N.

FIG. 3 shows the configuration of the second embodiment of the present invention and corresponds to FIG. 5 of the conventional example. In FIG.
The vibrating plate 1 is made of a metal foil 19 and a silicon oxide thin film 17 PVD
By 1 μm or more and 5 μm or less by the CVD method or the CVD method. The thin film 17 is electretized by corona discharge or electron beam as in the first embodiment, and the surface potential is changed from 150V to 250V. As described above, the fixed electrode 5 is electretized in the above-described embodiment, whereas the diaphragm 1 is electretized in the present embodiment. Even in this case, the same effect as that of the above embodiment is obtained.

In the above embodiments, the electrostatic type acoustic device has been described as a microphone for converting sound into an electric signal, but in other embodiments, it can be implemented as a speaker for converting an electric signal into sound. Also in this case, it has the effects of being usable in a high temperature environment, having a small size, high S / N, and high sensitivity.

[0018]

As is apparent from the above-described embodiments, the present invention forms a silicon oxide thin film on a vibration plate or a fixed electrode to form an electret, so that the electret potential is not deteriorated even in a high temperature environment and the high temperature environment is maintained. Allows the use of electrostatic acoustic transducers below. further,
Since the silicon oxide thin film can be formed extremely thin (5 μm or less), miniaturization, high sensitivity, and high S / N can be realized.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an electrostatic acoustic transducer according to a first embodiment of the invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a vertical sectional view showing a second embodiment of the present invention.

FIG. 4 is an enlarged view of a main part of FIG.

FIG. 5 is a vertical sectional view showing a first conventional example.

FIG. 6 is a vertical cross-sectional view showing a second conventional example.

7 is an enlarged view of a main part of FIG.

[Explanation of symbols]

 1 Vibration Plate 3 Slit 5 Fixed Electrode 9 Case 11 Hole 13 Vibration Plate Ring 15 Spacer 16 Insulator 17 Silicon Oxide Thin Film

Claims (2)

[Claims] 1. A vibrating plate which is formed by forming a silicon oxide (SiO ₂ ) thin film on a metal foil in a thickness of 1 μm or more and 5 μm or less and is made into an electret, and a fixed electrode which faces the vibrating plate and is provided with a certain gap. And an electrostatic acoustic transducer having. 2. A vibrating plate, and a vibrating plate facing the vibrating plate and having a silicon oxide (SiO ₂ ) thin film of 1 μm or more and 5 μm or less provided on the surface with a certain gap provided therebetween. Electrostatic acoustic transducer.