JP4889393B2 - Measuring method of electric potential between both electrodes of electret capacitor - Google Patents

Description

  The present invention relates to a method for measuring an electric potential between both electrodes of an electret capacitor, and more particularly to a method for nondestructively measuring an electric potential between both electrodes in an assembled state of an electret capacitor.

  FIG. 1 is a cross-sectional view for explaining an example of the structure of an electret condenser microphone (mechanical microphone formed by a diaphragm, a spacer, and a back electrode). FIG. 1 (a) shows the structure of the electret condenser microphone. Sectional drawing shown, (b) is a sectional view of an electronic component connected to the electret condenser microphone.

  As shown in FIG. 1A, in the electret condenser microphone, a front plate 101a is integrally formed on the front surface of a metal case 101, a sound hole 107 is formed on the front plate 101a, and the periphery of the inner surface of the front plate 101a. The diaphragm plate 102 made of metal is in contact with and electrically connected to the part, and the diaphragm 103 is attached to the surface of the diaphragm ring 102 opposite to the front plate. Metal is deposited on one surface of the film, and the deposited film is attached in contact with the diaphragm ring 102.

  The vibrating membrane 103 is closely opposed to the back electrode 105 via the spacer 104, and the back electrode 105 is held on the front surface of the cylindrical back electrode holder 106. An impedance conversion IC element 109 is disposed in a back chamber 110 configured inside the back electrode holder 106, an input terminal 109a of the IC element is connected to the back electrode, and an output terminal 109b protrudes from the back of the case. The wiring is connected to the wiring of the wiring board 108 that closes the back of the case. The rear terminal portion of the case is bent on the back surface of the wiring board 108, and the internal portions are pressed against the front plate 101a to be fixed as a whole.

  An electret material such as FEP is fused to the back electrode 110, and the electret material is converted into an electret, whereby a potential Vg is generated between the back electrode and the vibrating membrane. Reference numeral 120 is a connection part, reference numeral 120a is a spring contact, reference numeral 120b is a connection part housing, and reference numeral 121 is a rubber bush.

When a sound signal is input to the microphone of FIG. 1 (a), the capacitance of the capacitor formed by the diaphragm, the spacer, and the back pole changes, and is input to the impedance conversion IC element 109 as a voltage signal for impedance conversion. The electrical signal is output via the output terminal 109b. The signal output from the impedance conversion IC 109 is output to the wiring pattern through the through hole 111.
Here, since the microphone sensitivity is proportional to the potential Vg between the back electrode (109) and the vibrating membrane (103), the measurement technique of the interpolar electric potential Vg becomes a technique necessary for supplying stable Vg, and therefore It has become an important technology for the manufacture of electret microphones with precision and sensitivity with little variation.
As a conventional method of measuring Vg, as shown in Patent Document 1, instead of measuring Vg, it is common to measure the surface potential of the back electrode 105. When creating a microphone, the surface potential of the back electrode is measured. By controlling, a microphone having a desired sensitivity was created.

  In recent years, an electret condenser microphone formed by processing a silicon substrate using MEMS (micro electro mechanical system) technology has also appeared (for example, see Patent Document 2).

  FIG. 2 is a diagram showing a cross-sectional structure of a microphone on which an acoustic transducer formed by processing a silicon substrate is mounted.

  In FIG. 2, an acoustic transducer 300 and an impedance conversion IC 200 are mounted on a wiring board 404. Reference numeral 400 is a case, and reference numeral 402 is a case side plate.

  The impedance conversion IC 200 includes a signal output terminal 204a and a signal input terminal 204b, and the terminals 204a and 204b are connected to a wiring pattern on the wiring board 404 by, for example, solder 202.

  The acoustic transducer 300 includes a silicon substrate 300, a first electrode (for example, made of silicon) 302 provided with holes (sound holes) 304, and a second electrode (for example, made of a silicon oxide film) 307. The first electrode 302 and the second electrode 307 are provided to face each other with a predetermined air gap 306 therebetween. Reference numeral 308 is a spacer (for example, made of metal) that forms an air gap, and reference numeral 309 is a bonding wire.

  The wiring board 404 is provided with through holes 312a and 312b. A ground wiring pattern 314 a and a signal wiring pattern 314 b are formed on the back surface of the wiring substrate 404.

An electret condenser microphone manufactured by using the MEMS technology as shown in FIG. 2 is described in Patent Document 2, for example.
Japanese Patent Laid-Open No. 6-313782 (page 5, FIG. 1) Japanese Patent Laid-Open No. 2005-183437

However, in the conventional surface potential measurement method described in Patent Document 1, measurement with a microphone assembled is impossible.
Furthermore, in an electret condenser microphone mounted with an acoustic transducer (acoustic-electric conversion element) created by a semiconductor manufacturing process as shown in FIG. 2, for example, when an electret material is used for the second electrode, the second When measuring the surface potential applied to an electrode (for example, a silicon oxide film), the first electrode made of silicon becomes an obstacle, making it difficult to measure the surface potential non-destructively and accurately. Even when the first electrode is an electret material, the second electrode becomes an obstacle at this time, and it is therefore difficult to measure the surface potential accurately in a non-destructive manner.

  The present invention has been made on the basis of the above circumstances, and the object thereof is to measure the potential between the two electrodes of the electret capacitor in a state where the electret capacitor is assembled and non-destructively. There is.

  A method for measuring an electric potential between both electrodes of an electret capacitor according to the present invention includes a diaphragm and a fixed pole disposed opposite to the diaphragm, and one of the diaphragm and the fixed pole is electretized. A method for measuring a potential between both electrodes of an electret capacitor, which is an electret material, wherein a bias voltage is swept between the diaphragm and the fixed electrode while an impedance value between the diaphragm and the fixed electrode is measured. A first step of measuring, and a second step of identifying a potential between the diaphragm and the fixed pole based on a relationship between the measured impedance value and the bias voltage value.

  When a bias voltage is applied to both poles of the electret capacitor in the assembled state and the voltage value is linearly changed, the impedance between both poles changes accordingly. Here, since one pole of the electret capacitor is made of an electret material (a material having permanent electric polarization), a potential Vg is generated between the two poles. It will be different from when it is not. Since the behavior of the impedance variation is closely related to the potential Vg generated by electretization, based on the relationship between the measured impedance value and the bias voltage value applied at that time, It is possible to identify the potential between the diaphragm and the fixed pole.

  In one aspect of the method for measuring the potential between the two electrodes of the electret capacitor of the present invention, in the second step, the bias voltage value when the impedance value is minimized is used as the potential between the two electrodes.

  When the voltage between the two poles increases, the diaphragm approaches the fixed pole due to the electrostatic attraction, so that the measured impedance increases. When the fixed pole is not electretized, the bias voltage is 0V. In this case, the impedance value becomes the minimum value, but in the case where the fixed pole is electretized, when the bias voltage is 0 V, electrostatic attraction is generated by the potential Vg already obtained by electretization. The impedance value is not the lowest value. On the other hand, when the bias voltage is −Vg, which is opposite to the positive / negative, Vg, the bias voltage and Vg cancel each other, and the voltage between the two electrodes becomes 0V, so that the impedance value becomes the lowest value. Using this principle, the impedance between the two poles with the fixed pole electretized is measured while applying a sweep voltage, and the bias voltage (minimum voltage value) when the impedance becomes the minimum value is obtained. The potential between the two electrodes of the electret capacitor in the assembled state can be measured nondestructively. Therefore, it is possible to accurately obtain the electrification amount of the electret material when the microphone is assembled.

  In another aspect of the method for measuring a potential between both electrodes of an electret capacitor according to the present invention, in the second step, two voltage values at which the impedance value changes rapidly are obtained, and an average voltage of the two voltage values is obtained. Calculate the value and use the average voltage value as the potential between the two electrodes.

  When there is a material whose characteristics change due to the sweep bias voltage between the diaphragm and the fixed pole (or when the counter pole of the pole whose charge is to be measured is made of such a material), the material When the impedance value is the lowest, the electrostatic attractive force is not always zero. The measuring method of this aspect is a method applicable also in such a case. That is, when the voltage between the two electrodes increases, the vibrating membrane approaches the fixed electrode due to the electrostatic attractive force, and finally comes into contact. When the bias voltage when the vibrating membrane and the fixed pole are in contact is assumed to be Vt + and Vt−, the impedance value changes rapidly due to the contact between the vibrating membrane and the fixed pole before and after Vt + and Vt−. At Vt +, the vibrating membrane and the fixed pole are in contact with each other with a positive voltage. On the other hand, the Vt− part is in a state in which the vibrating membrane and the fixed electrode are in contact with each other with a negative voltage, and electrostatic attraction at Vt + and Vt−. Are equivalent. Therefore, the electrostatic attractive force at the average value Vc of Vt + and Vt− is 0, and therefore it can be estimated that the voltage between the two electrodes at that time is 0V. When the potential between the two electrodes is 0, the bias voltage is -Vg, which is opposite to the potential Vg between the two electrodes. Therefore, if this principle is applied, the potential between the two electrodes becomes 0V. Vc estimated to be (= average value of Vt + and Vt−) represents the potential between the two poles under the influence of the impedance change of the material interposed between the two poles. In this way, the potential between both electrodes of the electret capacitor can be measured nondestructively. Therefore, it is possible to accurately obtain the electrification amount of the electret material when the microphone is assembled.

  According to the potential measurement of the present invention, the potential between the two electrodes of the electret capacitor in a state assembled with the microphone can be measured nondestructively.

  Therefore, it is possible to accurately obtain the electrification amount of the electret material in a state where the microphone is assembled, and thereby it is possible to optimize the conditions for producing the electret and to optimize the manufacturing process conditions.

  Therefore, it is possible to manufacture a highly sensitive electret condenser microphone that is precise and has little variation.

Next, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 3 is a diagram showing a basic configuration for carrying out the impedance measuring method according to the embodiment of the present invention.

As shown in the figure, a sweep bias voltage generator 500 is connected to both poles of an electret capacitor 300 constituted by an electret first electrode (fixed pole) 302 and a second electrode (vibrating membrane) 306. The bias voltage Vb is swept and applied, and at the same time, the impedance measuring instrument 600 measures the impedance between the two electrodes.
FIG. 4 is a diagram showing an example of impedance-bias voltage characteristics obtained by impedance measurement in the embodiment of the present invention.

Here, the characteristic line L1 is the impedance bias voltage characteristic when the fixed pole is not electreted, and the characteristic line L2 is the impedance-bias voltage characteristic when the fixed pole is electretized.
Here, when the voltage between the two poles increases, the vibrating membrane 306 approaches the fixed pole 302 due to the electrostatic attractive force, and thus the measured impedance increases. Therefore, when the fixed pole is not electretized, the impedance value becomes the minimum value when the bias voltage is 0V.

On the other hand, when the fixed pole 306 is electretized, when the bias voltage is 0 V, the electrostatic attractive force is generated by the potential Vg already obtained by electretization, so that the impedance value is the lowest value. Not. On the other hand, when the bias voltage is −Vg, which is opposite to the positive / negative, Vg, the bias voltage and Vg cancel each other, and the voltage between the two electrodes becomes 0V, so that the impedance value becomes the lowest value.
Using the principle as described above, the impedance between two electretized fixed poles 302 is measured while applying a sweep voltage, and the bias voltage and the minimum voltage value when the impedance becomes the minimum value are obtained. Can measure the potential between two electrodes by the electret.
According to the present invention, the potential between two electrodes in a state assembled with a microphone can be measured nondestructively.
When measuring with a conventional surface potential meter, if there is a hole in the fixed pole 302 or if the sample is extremely small, a measurement error will occur due to misalignment of the measurement position, and the surface potential must be measured accurately. However, according to the potential measuring method of the present invention, it is possible to measure without such an error.
(Embodiment 2)

  In the case of an electret condenser microphone that uses an acoustic transducer (Fig. 2) made by a semiconductor process, a semiconductor material exists between the two electrodes (or the opposite electrode of the electrode whose charge amount is to be measured is made of a semiconductor material. Therefore, not only the impedance between the two electrodes but also the impedance of the semiconductor material is changed by the sweep voltage, so that the impedance-bias voltage characteristics in which both characteristics overlap each other are obtained. When such characteristics are exhibited, the semiconductor characteristics overlap in the vicinity of the minimum value of the bias voltage, and the electrostatic attractive force does not always become zero when the impedance value is the lowest.

  In order to measure the potential between two electrodes by the electret of an acoustic transducer produced by such a semiconductor process, the measurement method of the first embodiment cannot be used. In the present embodiment, a method for measuring a potential between two electrodes applicable to such a case will be described.

  FIG. 5 is a diagram illustrating an example of impedance-bias voltage characteristics obtained by impedance measurement in the embodiment of the present invention. Here, the characteristic line L3 indicates the impedance-bias voltage characteristic between the two poles in the case of a microphone using an acoustic transducer created by a semiconductor process.

  Here, when the voltage between the two electrodes is increased, the vibrating membrane approaches the back electrode due to the electrostatic attractive force, and finally comes into contact. Assuming that the bias voltage when the diaphragm and the back electrode are in contact is Vt + and Vt−, the impedance value changes abruptly before and after Vt + and Vt− due to the contact between the diaphragm and the back electrode.

  At Vt +, the vibrating membrane and the back electrode are in contact with each other with a positive voltage. On the other hand, the Vt− part is in a state in which the vibrating membrane and the back electrode are in contact with each other with a negative voltage. Are equivalent. Therefore, the electrostatic attractive force at the average value Vc of Vt + and Vt− is 0, and therefore it can be estimated that the voltage between the two electrodes at that time is 0V.

  As described in the first embodiment, the fact that the potential between the two electrodes is 0 means that the bias voltage is -Vg which is opposite to the potential Vg between the two electrodes. For example, Vc (= average value of Vt + and Vt−) estimated that the potential between the two electrodes becomes 0 V represents the potential between the two electrodes under the influence of the semiconductor material. In this way, the potential between the two electrodes constituting the electret capacitor can be identified with high accuracy.

  As described above, a microphone using an acoustic transducer created by a semiconductor process, especially when the semiconductor process is surface micromachining, and especially when the structure of forming the spacer with a semiconductor is unavoidable. Therefore, due to the sweep voltage, not only the impedance between the two electrodes but also the impedance of the semiconductor changes, resulting in an impedance bias voltage characteristic in which the characteristics of both are overlapped, as shown by a characteristic line L3 in FIG. As described above, when the characteristics of the semiconductor overlap in the vicinity of the minimum value and the impedance value is the lowest, the electrostatic attractive force does not always become zero.

  Therefore, the measurement method of the first embodiment cannot be used to measure the potential between the two electrodes by the electret of the acoustic transducer produced by such a semiconductor process, and the measurement method of the second embodiment is effective. According to the present embodiment, the potential between two electrodes of an acoustic transducer created by a semiconductor process can be measured nondestructively.

  Note that this embodiment is an effective measurement method not only for acoustic transducers produced by a semiconductor process, but also for materials whose characteristics change due to the sweep voltage between the diaphragm and the fixed pole.

  As described above, according to the present invention, the potential between the two electrodes of the electret capacitor in the state assembled with the microphone can be measured nondestructively.

  Therefore, it is possible to accurately obtain the electrification amount of the electret material in a state where the microphone is assembled, and thereby it is possible to optimize the conditions for producing the electret and to optimize the manufacturing process conditions.

  Therefore, it is possible to manufacture a highly sensitive electret condenser microphone that is precise and has little variation.

  INDUSTRIAL APPLICABILITY The present invention has an effect of enabling non-destructive measurement of the potential between the two electrodes of the electret capacitor in a state assembled in a microphone, and is therefore useful as a method for measuring the potential between both electrodes of the electret capacitor. .

It is sectional drawing for demonstrating an example of the structure of an electret condenser microphone (mechanical microphone formed with a diaphragm, a spacer, and a back pole), (a) is sectional drawing which shows the structure of an electret condenser microphone, (B) is sectional drawing of the electronic component connected to an electret condenser microphone The figure which shows the cross-section of the microphone carrying the acoustic transducer formed by processing a silicon substrate The figure which shows the basic composition for enforcing the impedance measuring method in embodiment of this invention The figure which shows an example of the impedance-bias voltage characteristic obtained by the impedance measurement in embodiment of this invention The figure which shows an example of the impedance-bias voltage characteristic obtained by the impedance measurement in embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Case 101a Front plate 102 Diaphragm ring 103 Vibration membrane 104 Spacer 105 Back pole 106 Back pole holding body 107 Sound hole 108 Wiring board 109 Impedance conversion IC
109a Impedance conversion IC input terminal 109b Impedance conversion IC output terminal 110 Back chamber 111 Through hole 120 Connection component 120a Spring contact 120b Connection component casing 121 Rubber bush 130 Mounting target component 130a Connection component input terminal 200 IC for impedance conversion
202 Solder 204a Impedance conversion IC input terminal 204b Impedance conversion IC output terminal 300 Electret capacitor (assembled state)
302 First electrode 304 Hole (sound hole)
306 Air gap 307 Second electrode 308 Joining material also serving as spacer 309 Boding wire 310 Silicon substrate 312a, 312b Through hole 314a Ground wiring pattern 314b Signal wiring pattern 400 Case 402 Case side plate 404 Wiring board 500 Sweep voltage applying device 600 Impedance measuring device

Claims (3)

A method for measuring an electric potential between both electrodes of an electret capacitor, which is an electret material that includes an oscillating plate and a fixed pole disposed opposite to the oscillating plate, and one of the oscillating plate and the fixed pole is electretized. There,
A first step of measuring an impedance value between the diaphragm and the fixed pole while sweeping and applying a bias voltage between the diaphragm and the fixed pole;
A second step of identifying a potential between the diaphragm and the fixed pole based on a relationship between the measured impedance value and the bias voltage value;
A method for measuring the electric potential between both electrodes of an electret capacitor. A method for measuring a potential between both electrodes of an electret capacitor according to claim 1,
In the second step, the potential between the two electrodes of the electret capacitor is measured using the bias voltage value when the impedance value is minimized as the potential between the two electrodes. A method for measuring a potential between both electrodes of an electret capacitor according to claim 1,
In the second step, two voltage values in which the impedance value changes rapidly are obtained, an average voltage value of the two voltage values is calculated, and the average voltage value is used as a potential between both electrodes. To measure the potential between both electrodes of an electret capacitor.

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