JP4358697B2 - Manufacturing method of electret condenser microphone - Google Patents

Description

  The present invention relates to a method of manufacturing an electret condenser microphone, and more particularly, to an electret layer generation process thereof.

  In general, an electret condenser microphone has a configuration including a capacitor structure portion in which a diaphragm and a back electrode plate are arranged to face each other, and an impedance conversion element that converts a change in capacitance of the capacitor structure portion into an electrical impedance. ing. At that time, the back electrode plate has a structure in which an electret layer is disposed on the surface of the metal electrode plate main body, and this electret layer has a predetermined charge on the insulating film formed on the surface of the electrode plate main body. It is generated by applying a polarization process with voltage.

  And in the manufacturing process of this electret condenser microphone, in order to obtain a product having a required sensitivity characteristic, a device for selecting the back electrode plate whose surface potential is within a certain range has been devised. Yes.

  Further, as described in “Patent Document 1”, a device has been devised in which the surface potential of the electret layer of the back electrode plate is reduced and adjusted by irradiating the completed electret condenser microphone with ionizing radiation. .

JP 2000-32596 A

  In recent years, downsizing of electret condenser microphones has progressed, but with this, the variation in sensitivity tends to increase. When the inventor of this application analyzed about this cause, it became clear that the variation in the thickness of the electret layer of a back electrode plate has contributed greatly.

  That is, the electret layer of the back electrode plate does not have a uniform film thickness over the entire region, and the film thickness continuously changes so as to swell greatly. At this time, if the size of the back electrode plate is large to some extent, the film thickness of the electret layer is averaged within the size range, so that it becomes a substantially constant value between the mass-produced back electrode plates. On the other hand, if the size of the back electrode plate is extremely small, the undulation of the change in the thickness of the electret layer cannot be sufficiently averaged within the size range. Variations in film thickness occur. Therefore, even if the polarization process is performed at the same charge voltage, the electret condenser microphone having the back electrode plate with the thick electret layer is more in comparison with the electret condenser microphone having the back electrode plate with the thin electret layer. Sensitivity will decrease.

  According to such knowledge, it is difficult to suppress the variation in sensitivity sufficiently small simply by selecting the back electrode plate in which the surface potential of the electret layer is within a certain range as in the prior art.

  On the other hand, if the electret condenser microphone is irradiated with ionizing radiation and the surface potential of the electret layer of the back electrode plate is reduced and adjusted as described in the above-mentioned "Patent Document 1," the sensitivity of the electret condenser microphone is lowered. However, there is a problem that the sensitivity cannot be improved, and additional work is required after completion of the electret condenser microphone.

  The present invention has been made in view of such circumstances, and even when the electret condenser microphone is miniaturized, the required sensitivity characteristic can be obtained with sufficiently small variation in sensitivity. An object of the present invention is to provide a method for manufacturing an electret condenser microphone.

  In the present invention, when the polarization treatment is performed on the insulating film, the above object is achieved by changing the charge voltage according to the film thickness.

That is, the manufacturing method of the electret condenser microphone according to the present invention is as follows:
A capacitor structure having a diaphragm and a back electrode plate facing each other; and an impedance conversion element for converting the capacitance of the capacitor structure into an electrical impedance, the back electrode plate being a metal electrode In a method of manufacturing an electret condenser microphone in which an electret layer is disposed on the surface of a plate body,
Including an electret layer generating step for generating the electret layer by subjecting the insulating film formed on the surface of the electrode plate body to a polarization treatment at a predetermined charge voltage;
In the electret layer generation step, when the insulating film is subjected to polarization treatment, the charge voltage is changed in accordance with the film thickness of the insulating film.

  The specific configuration of the “insulating film” such as the material and film thickness is not particularly limited.

  The specific amount of change in the charge voltage at the time of “changing the charge voltage in accordance with the film thickness of the insulating film” is not particularly limited. Further, the value of the “charge voltage” itself is not particularly limited.

  As shown in the above configuration, the method for manufacturing an electret condenser microphone according to the present invention includes applying an electret layer to an insulating film formed on the surface of the electrode plate body of the back electrode plate with a predetermined charge voltage. In this case, since the charge voltage is changed according to the film thickness of the insulating film, the following effects can be obtained.

  That is, as described above, when the polarization process is performed with a constant charge voltage, the analysis of the inventor of the present application has revealed that the sensitivity of the electret condenser microphone decreases as the thickness of the insulating film increases. On the other hand, it is conventionally known that the sensitivity of the electret condenser microphone changes when the insulating film is subjected to polarization treatment with different charge voltages.

  Therefore, if the charge voltage is changed according to the film thickness of the insulating film (specifically, if the charge voltage is increased as the film thickness of the insulating film is increased), it is compared with the film thickness of the electret layer. Even if there is a large variation, the change in sensitivity due to the change in film thickness can be substantially canceled by the change in sensitivity due to the change in charge voltage, and thus the variation in sensitivity of the electret condenser microphone can be kept small.

  As described above, according to the present invention, even when the electret condenser microphone is downsized, variation in sensitivity can be sufficiently reduced, and thus required sensitivity characteristics can be obtained. In addition, since the processing for suppressing the variation in sensitivity is performed within the manufacturing process of the electret condenser microphone, the sensitivity characteristics can be made uniform at the completion stage, thereby improving the process capability.

  In the above configuration, as described above, the specific change amount of the charge voltage when changing the charge voltage according to the thickness of the insulating film is not particularly limited, but the thickness of the insulating film increases by 1 μm. Accordingly, if the charge voltage is increased by 1 to 3 V in absolute value, variations in sensitivity of the electret condenser microphone can be effectively suppressed to some extent.

  At this time, if the charge voltage is increased by 1.5 to 2.5 V in absolute value as the film thickness of the insulating film increases by 1 μm, the variation in sensitivity of the electret condenser microphone can be more effectively suppressed. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side cross-sectional view showing an electret condenser microphone to be applied to a manufacturing method according to an embodiment of the present invention in an upwardly arranged state.

  As shown in the figure, the electret condenser microphone 10 according to the present embodiment is an ultra-small microphone having an outer diameter of about 3 mm and a height of about 1.2 to 1.5 mm. The diaphragm subassembly 14, the spacer 16, the back electrode plate 18, the coil spring 20, the insulating bush 22 and the JFET board 24 are accommodated. The target sensitivity of the electret condenser microphone 10 is set to -41.5 dB.

  The case 12 is made of metal (for example, aluminum), and has a sound hole 12a formed in the upper end wall thereof, and is caulked and fixed to the JFET board 24 at the open lower end portion 12b.

  The vibrating membrane subassembly 14 has a circular vibrating membrane 26 stretched and fixed to a support ring 28. The vibration film 26 is formed by forming a metal vapor deposition film such as a nickel alloy on the upper surface of a PET (polyethylene terephthalate) film having a thickness of about 1.5 μm, and its outer diameter is set to be substantially the same as the inner diameter of the case 12. ing. On the other hand, the support ring 28 is a metal pressed product and has substantially the same outer diameter as that of the vibration film 26.

  The spacer 16 is formed of a thin plate ring made of stainless steel having an outer diameter substantially the same as the inner diameter of the case 12, and the thickness thereof is set to about 25 μm.

  The back electrode plate 18 includes an electrode plate body 18A and an electret layer 18B disposed on the upper surface of the electrode plate body 18A, and through holes 18a are formed at a plurality of locations.

  The electrode plate body 18A is made of a stainless steel plate having a thickness of about 0.15 mm, and has an outer diameter that is substantially the same as the inner diameter of the insulating bush 22.

  The electret layer 18B is generated by subjecting an insulating film formed on the upper surface of the electrode plate body 18A to a polarization treatment at a predetermined charge voltage (for example, about −100 V). Has been granted. In that case, the said insulating film is formed by heat-seal | fusing the FEP (fluorinated ethylene propylene) film which has a film thickness of about 12.5 micrometers on the upper surface of 18 A of electrode plate main bodies.

  In the case 12, the electret layer 18 </ b> B and the vibration film 26 are disposed to face each other with a predetermined minute interval through the spacer 16, thereby constituting a capacitor structure.

  The insulating bush 22 is a cylindrical member having an outer diameter substantially the same as the inner diameter of the case 12, and the back electrode plate 18 and the coil spring 20 are disposed on the inner peripheral side thereof. At that time, the back electrode plate 18 is elastically pressed toward the spacer 16 by the coil spring 20.

  The JFET board 24 includes a board main body 32 having an outer diameter substantially the same as the inner diameter of the case 12, and an impedance conversion element 34 and a capacitor 36 mounted on the upper surface of the board main body 32.

  A conductive layer 32a is formed in a predetermined pattern on the upper surface of the board main body 32, and a conductive layer 32b serving as a plus terminal is formed at the center of the lower surface of the board main body 32. A conductive layer 32c serving as a ground terminal is formed at the peripheral edge.

  The impedance conversion element 34 is a junction field effect transistor (JFET), and its gate electrode is electrically connected to the back electrode plate 18 via the conductive layer 32a and the coil spring 20, and its drain electrode is conductive. The source electrode is electrically connected to the metal vapor deposition film of the vibration film 16 via the conductive layers 32a and 32c, the case 12 and the support ring 28 through the layer 32a. Yes.

  Next, the manufacturing process of the electret condenser microphone 10 according to the present embodiment will be described.

  The electret condenser microphone 10 includes a vibrating membrane subassembly in a case 12 in a state in which a case 12 (a case shown by a two-dot chain line in FIG. 1) before being caulked and fixed is arranged upside down. 14, spacer 16, insulating bush 22, back electrode plate 18, coil spring 20, and JFET board 24 are assembled in this order, and then the open lower end 12 b of case 12 is caulked and fixed to JFET board 24. Is to be done.

  At that time, the back electrode plate 18 is incorporated in the case 12 in a state where the surface potential of the electret layer 18B is adjusted.

  That is, as described above, the electret layer 18B is generated by subjecting the insulating film formed on the upper surface of the electrode plate body 18A to polarization treatment at a predetermined charge voltage. In this electret layer generating step, the insulating film is formed. When a polarization process is applied to the film, the charge voltage is changed according to the film thickness. Specifically, as the thickness of the insulating film increases by 1 μm, the charge voltage is increased by 2V in absolute value.

  This is based on the following findings.

  That is, the insulating film constituting the electret layer 18B is formed by thermally fusing the FEP film on the upper surface of the electrode plate body 18A. At that time, the FEP film is stretched and becomes thinner than the original film thickness. The film thickness continuously changes in a wavy manner. At this time, if the back electrode plate 18 is somewhat large, the film thickness of the electret layer 18B is averaged within the size range, so that the back electrode plates 18 that are mass-produced have a substantially constant value. On the other hand, when the size of the back electrode plate 18 becomes extremely small as in the present embodiment, the undulation of the change in the thickness of the electret layer 18B cannot be sufficiently averaged within the size range. Variations in the thickness of the electret layer 18B occur between the back electrode plates 18. If there is such variation, the sensitivity of the electret condenser microphone 10 changes even if the polarization process is performed with the same charge voltage.

  FIG. 2 shows the results of measuring the relationship between the thickness of the electret layer 18B and the sensitivity of the electret condenser microphone 10 for the electret condenser microphone 10 in which the back electrode plate 18 subjected to polarization treatment with a constant charge voltage is incorporated. It is a graph to show. At that time, the number of samples measured was 20, and the measured sensitivity was the sensitivity at 1 kHz.

  As is clear from this graph, the thickness of the electret layer 18B varies in the range of 6 to 12 μm, and the influence on the sensitivity of the electret condenser microphone 10 is about 2.2 dB. When the film thickness of the electret layer 18B increases by 1 μm, the sensitivity of the electret condenser microphone 10 decreases by about 0.37 dB.

  On the other hand, even if the thickness of the electret layer 18B is constant, the sensitivity of the electret condenser microphone 10 can be changed if the insulating film is subjected to polarization treatment with different charge voltages. As a result of quantitative measurement using an electrostatic potentiometer, it was found that the sensitivity of the electret condenser microphone 10 is improved by about 0.36 dB when the charge voltage is increased by 2 V in absolute value.

  Therefore, if the charge voltage is increased by about 2V in absolute value as the thickness of the insulating film increases by 1 μm, the sensitivity decrease due to the increase in film thickness is substantially offset by the sensitivity improvement due to the increase in charge voltage. Accordingly, variation in sensitivity of the electret condenser microphone 10 can be suppressed to a very small level. Thereby, the sensitivity of the electret condenser microphone 10 can be maintained at a value close to the target sensitivity of −41.5 dB.

  3 and 4 are graphs showing sensitivity characteristics of the electret condenser microphone 10 manufactured by the manufacturing method according to the present embodiment.

  FIG. 3 is a graph showing data of ten samples of the electret condenser microphone 10 having the back electrode plate 18 having a thin film thickness of the electret layer 18B. On the other hand, FIG. 4 is a graph showing data of 10 samples of the electret condenser microphone 10 having the back electrode plate 18 having a thick electret layer 18B.

  At that time, as a sample of the back electrode plate 18 having a thin film thickness of the electret layer 18B, a sample having a film thickness of the electret layer 18B of 6 μm is used, and as a sample of the back electrode plate 18 having a large film thickness of the electret layer 18B. Uses an electret layer 18B having a thickness of 12 μm. Further, with respect to the back electrode plate 18 having the thick electret layer 18B, the electret layer 18B has a thickness of 6 μm thicker than the back electrode plate 18 having the thin electret layer 18B. The charge voltage at the time of applying is increased by 12V (= 6 × 2V) in absolute value.

  As is apparent from these figures, the sensitivity of the electret condenser microphone 10 is maintained at a value close to the target sensitivity of −41.5 dB by changing the charge voltage in accordance with the film thickness of the insulating film.

  That is, the sensitivity of the electret condenser microphone 10 having the back electrode plate 18 having a thin film thickness of the electret layer 18B is −42.05 to −41.10 dB, and its average value is −41.59 dB. Moreover, the sensitivity of the electret condenser microphone 10 having the back electrode plate 18 having the thick electret layer 18B is −42.06 to −41.19 dB, and its average value is −41.55 dB.

  On the other hand, FIG. 5 shows not the electret condenser microphone 10 manufactured by the manufacturing method according to the present embodiment, but the electret condenser microphone having the back electrode plate 18 having a thick electret layer 18B (specifically, a film thickness of 12 μm). 8 shows sensitivity characteristic data of eight samples when the charge voltage is not changed according to the film thickness of the insulating film (specifically, when the charge voltage is set to be the same as the film thickness of 6 μm). It is.

  As shown in the figure, when the charge voltage is not changed according to the film thickness of the insulating film, the sensitivity of the electret condenser microphone is −44.14 to −43.11 dB, and the average value is −43. .68 dB, which is about 2 dB lower than the target sensitivity of -41.5 dB.

  As described above in detail, the method of manufacturing the electret condenser microphone according to the present embodiment performs a polarization process on the insulating film formed on the surface of the electrode plate body 18A of the back electrode plate 18 at a predetermined charge voltage. The electret layer 18B is generated by the above, but at this time, the charge voltage is increased as the thickness of the insulating film increases, so that there is a large variation in the thickness of the electret layer 18B. However, the change in sensitivity due to the change in the film thickness can be substantially canceled by the change in sensitivity due to the change in the charge voltage, whereby the variation in sensitivity of the electret condenser microphone 10 can be kept small.

  Therefore, according to the present embodiment, even though the electret condenser microphone 10 is configured as an ultra-small microphone, the sensitivity variation can be sufficiently reduced, and thus the required sensitivity characteristic can be obtained. . In addition, since the processing for suppressing the variation in sensitivity is performed in the manufacturing process of the electret condenser microphone 10, the sensitivity characteristics can be made uniform at the completion stage, thereby improving the process capability.

  At this time, in the present embodiment, the charge voltage is increased by 2V in absolute value as the thickness of the insulating film increases by 1 μm, so that variation in sensitivity of the electret condenser microphone 10 can be suppressed to a very small value. it can.

  Instead of increasing the charge voltage by 2V in absolute value as the film thickness of the insulating film increases by 1 μm as in this embodiment, the charge voltage is increased by 1 to 3V in absolute value as the film thickness of the insulating film increases by 1 μm. Even in the case where it is increased, variations in sensitivity of the electret condenser microphone 10 can be suppressed within an allowable range. At this time, if the charge voltage is increased by 1.5 to 2.5 V in absolute value as the thickness of the insulating film increases by 1 μm, the range of sensitivity of the electret condenser microphone 10 is narrower than the allowable range. Can be suppressed within.

  In the above embodiment, the case where the value of about −100 V is exemplified as the charge voltage and the target sensitivity of the electret condenser microphone 10 is set to −41.5 dB, the surface potential of the electret layer 18B and Even when the target sensitivity of the electret condenser microphone 10 is set to a value other than the above, the same effect as that of the above embodiment can be obtained by performing the polarization process under the same conditions as in the above embodiment.

  Moreover, in the said embodiment, although the case where the insulating film was comprised with the FEP film was demonstrated, also when comprised with the film of materials other than this, a polarization process is carried out on the conditions similar to the said embodiment. By applying, the same effect as the above embodiment can be obtained.

Sectional side view which shows the state which has arrange | positioned the electret condenser microphone used as the application object of the manufacturing method which concerns on one Embodiment of this invention upwards The graph which shows the result of having measured the relation between the film thickness of the electret layer and the sensitivity for the electret condenser microphone in which the back electrode plate which has been polarized with the charge voltage kept constant The graph which shows the sensitivity characteristic of the electret condenser microphone manufactured by the manufacturing method which concerns on this embodiment, Comprising: The graph which shows the data in the case of having a back electrode board with a thin film thickness of an electret layer The graph which shows the sensitivity characteristic of the electret condenser microphone manufactured by the manufacturing method which concerns on this embodiment, Comprising: The graph which shows data in case it has a back electrode board with a thick film thickness of an electret layer The graph which shows the sensitivity characteristic of the electret condenser microphone manufactured by methods other than the manufacturing method which concerns on this embodiment, Comprising: The graph which shows the data in the case of having a back electrode board with a thick film thickness of an electret layer

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electret condenser microphone 12 Case 12a Sound hole 12b Open lower end part 14 Vibration membrane subassembly 16 Spacer 18 Back electrode plate 18A Electrode plate main body 18B Electret layer 18a Through-hole 20 Coil spring 22 Insulating bush 24 JFET board 26 Vibration membrane 28 Support ring 32 Board body 32a, 32b, 32c Conductive layer 34 Impedance conversion element 36 Capacitor

Claims (3)

A capacitor structure having a diaphragm and a back electrode plate facing each other; and an impedance conversion element for converting the capacitance of the capacitor structure into an electrical impedance, the back electrode plate being a metal electrode In a method of manufacturing an electret condenser microphone in which an electret layer is disposed on the surface of a plate body,
Including an electret layer generating step for generating the electret layer by subjecting the insulating film formed on the surface of the electrode plate body to a polarization treatment at a predetermined charge voltage;
A method of manufacturing an electret condenser microphone, characterized in that, when a polarization process is performed on the insulating film in the electret layer generating step, a charge voltage is changed in accordance with a film thickness of the insulating film.   2. The method of manufacturing an electret condenser microphone according to claim 1, wherein the charge voltage is increased by 1 to 3 V in absolute value as the thickness of the insulating film increases by 1 [mu] m.   2. The method of manufacturing an electret condenser microphone according to claim 1, wherein the charge voltage is increased by 1.5 to 2.5 V in absolute value as the thickness of the insulating film increases by 1 [mu] m.

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