JP2010112934A - Apparatus and method for measuring membrane stiffness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for measuring membrane stiffness, which can measure the stiffness of a vibrating diaphragm of an ECM or MEMS microphone inexpensively, simply, and nondestructively. <P>SOLUTION: The apparatus includes: a vacuum container 10 that retains a completed ECM 20 in vacuum; a voltage source 30 that functions to overlap an excitation voltage with a direct-current voltage for operating the ECM 20; an input-output response measuring unit 40 for measuring the voltage and phase of a power supply terminal B that is connected to an FET 72 of the ECM 20 with respect to the excitation voltage; and a stiffness calculation unit 50 for calculating a resonant frequency from the frequency response characteristic thus measured, and for calculating the membrane stiffness of the vibrating diaphragm 105 from the resonant frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a measuring method for measuring the hardness (stiffness) of a diaphragm of a condenser microphone and a measuring apparatus therefor, and particularly to provide a highly reproducible film stiffness measuring method.

  An electrostatic electroacoustic transducer is an electroacoustic transducer that converts sound into an electric signal by using electrostatic energy as an intermediary, and conversely converts an electric signal into sound. An electret condenser microphone (ECM), a MEMS microphone, and an electret condenser speaker are classified into this electrostatic electroacoustic transducer.

  The ECM can be miniaturized and is widely used in mobile phones. As shown in FIG. 13, the conventional ECM includes an electret vibrating film 105 in which a metal conductor is formed on a film by metal deposition or the like in a case 103 having a sound hole 102, a metal fixed electrode 107, an FET, and the like. A printed circuit board 112 on which circuit elements are mounted is disposed, and the space between the vibration film 105 and the fixed electrode 107 is held by the spacer 106, and the back air chamber 108 is interposed between the fixed electrode 107 and the printed circuit board 112. Is formed. In addition, a face cloth 101 serving as an acoustic element is attached to the case sound hole while preventing foreign matters from being mixed.

  The electret vibrating film 105 is usually formed using FEP (fluorinated ethylene propylene resin), and keeps a given charge. In this ECM, when the vibrating membrane 105 vibrates due to sound pressure, the capacitance of the flat plate capacitor formed by the vibrating membrane 105 and the fixed electrode 107 changes and is converted into a voltage change, and the converted signal is amplified by the FET 109. And output from the terminal 113.

  Reference numeral 104 denotes a diaphragm ring, reference numeral 110 denotes an insulator, and reference numeral 111 denotes a cushion sheet.

  FEP, which is a polymer film, has the property of retaining charge semipermanently, but the charge retention property tends to deteriorate when exposed to high temperatures.

  In recent years, in order to realize a heat-resistant microphone that can be reflowed, a technology for manufacturing an ultra-small MEMS (Micro Electro Mechanical Systems) microphone has been developed by applying an ultra-precision processing technology used in a semiconductor process to a silicon substrate. Yes.

  FIG. 14 shows an example of a MEMS microphone. On the silicon substrate, a large number of microphone chips are simultaneously manufactured using a semiconductor manufacturing technique, and finally divided into individual pieces. FIG. 14 shows a side view of one divided microphone chip. This MEMS microphone has a vibrating membrane electrode 123 and an electret film 124 on a silicon substrate 121 with a first insulating layer 122 interposed therebetween, and has a second insulating layer 125 interposed thereon. And a fixed electrode 126 in which a sound hole 127 is formed. In addition, a back air chamber 128 is formed on the back surface of the vibrating membrane electrode 123 by etching the silicon substrate 121. Reference numeral G denotes an air gap, and reference numeral H denotes a contact hole for electrical connection.

  The vibrating membrane electrode 123 is made of conductive polysilicon, the electret film 124 is made of a silicon nitride film or a silicon oxide film, and the fixed electrode 126 is made of conductive polysilicon and a silicon oxide film or silicon nitride. It is formed by laminating a film.

  In this MEMS microphone, when the vibrating membrane electrode 123 vibrates due to the sound pressure, the capacitance of the flat plate capacitor formed by the vibrating membrane electrode 123 and the fixed electrode 126 changes and is taken out as a voltage change, like the ECM.

  By the way, at the manufacturing site of the microphone, the film strength (stiffness) of the vibrating membrane is measured in order to identify the quality uniformity, goodness, and failure of the product. Conventionally, the vibration membrane is vibrated, the resonance frequency of the displacement is measured with an optical interferometer, and the value is substituted into the following equation (Equation 1) to calculate the membrane stiffness. This equation can be commonly used in electrostatic electroacoustic transducers including ECM and MEMS microphones.

ここで、
ｆ０：振動膜の共振周波数[Hz]
ｓ０：膜強さ（スチフネス）[N/m]
ｍ０：振動膜の質量[kg]
である。

here,
f0: Resonance frequency of vibrating membrane [Hz]
s0: Film strength (stiffness) [N / m]
m0: Mass of vibrating membrane [kg]
It is.

  The mass m0 can be uniquely derived if the structure of the diaphragm is determined. Therefore, the film stiffness can be calculated from (Equation 1) by measuring the resonance frequency f0 with an optical interferometer (see Non-Patent Documents 1 and 2).

optonor catalog micromap5000 Vibration / displacement measurement and surface shape measurement device Hisao Hayasaka et al. Introduction to Acoustical Engineering Nikkan Kogyo Shimbun

  However, the optical interferometer used in the conventional film stiffness measurement method is extremely expensive, and it takes a lot of cost to prepare a set of measurement devices of this method.

  Further, in the above conventional measurement method, it is necessary to irradiate the FEP electret film, which is a film to be measured, or the vibration film of the MEMS microphone with interference light.

  However, in the case of the ECM, when the microphone is completed, a face cloth for protecting the vibration film, which is an acoustic characteristic element, is pasted on the metal case. Since irradiation cannot be performed, measurement can be performed only in the state of the FEP electret film alone before being incorporated into the microphone, and cannot be performed in the completed state of the microphone.

  On the other hand, even in the case of a MEMS microphone, as described above, when the microphone is completed, since the fixed film is formed on the vibration film, the fixed film hinders light irradiation, and measurement is performed. Therefore, the measurement is performed after removing the fixed film. Therefore, the measurement in this case is performed by destroying the MEMS chip alone, and cannot be performed when the microphone is completed.

  The present invention has been made in view of the above circumstances, and a film stiffness measuring apparatus and a film stiffness measuring method that can measure the stiffness of a microphone in a completed state inexpensively, easily, and non-destructively. The purpose is to provide.

  The film stiffness measuring apparatus of the present invention includes a vacuum container for holding a completed condenser microphone in a vacuum, a DC voltage for operating the condenser microphone, and a voltage source having a function of superimposing an excitation voltage on the DC voltage. A frequency response characteristic measuring unit that measures a voltage and a phase of a power supply terminal connected to the amplifier of the condenser microphone with respect to the excitation voltage; and a resonance frequency is calculated from the frequency response characteristic measured by the frequency characteristic measuring unit, and the resonance A stiffness calculation unit that calculates the film stiffness of the vibrating membrane from the frequency.

  With this configuration, even when the microphone is completed, the stiffness of the diaphragm can be measured non-destructively without using an expensive measuring instrument, and can be measured at low cost. Rather than directly measuring the vibration displacement of the vibrating membrane, the membrane stiffness is determined from the frequency response characteristics of the excitation voltage.

  When the condenser microphone is an ECM, the upper part of the diaphragm is covered with a face cloth when the microphone is completed, and in the method of directly measuring the vibration displacement of the diaphragm, the stiffness of the diaphragm can be measured. Can not. Further, when the condenser microphone is a MEMS microphone, when the microphone is completed, the MEMS chip is not disposed under the sound hole or even if it is disposed, the vibrating membrane is positioned below the fixed membrane, The method of directly measuring the vibration displacement of the vibration film cannot measure the stiffness of the vibration film. However, the membrane stiffness measuring apparatus of the present invention can measure the stiffness of the diaphragm without breaking even when the microphone is completed.

  In the film stiffness measuring apparatus according to the present invention, the voltage source includes a DC voltage source and an excitation voltage source.

  With these configurations, by applying the excitation voltage of the excitation voltage source to the DC voltage source in a superimposed manner, a minute amplitude displacement corresponding to the excitation voltage source is generated in the vibration film. This minute amplitude displacement becomes large at the resonance frequency point of the diaphragm, and this change can be confirmed by the voltage change at the response point. In this way, film stiffness measurement can be performed by using a DC voltage source and an excitation voltage source.

  In the membrane stiffness measuring apparatus of the present invention, the excitation voltage source supplies a sinusoidal voltage.

In this configuration, the frequency response is measured by running the frequency. At this time, if the frequency f1 at the start point and the frequency f2 at the end point in the frequency band are set, the frequency band is divided into N,
Δf = (f2−f1) / N
Steps cover this frequency band. This makes it possible to perform film stiffness measurement.

  In the film stiffness measuring apparatus of the present invention, the excitation voltage source supplies a white noise wave voltage.

  With this configuration, since white noise includes all the frequencies in the band that is necessary for broadband noise, film stiffness measurement can be performed without running through the frequency.

  In the film stiffness measuring apparatus of the present invention, the excitation voltage source supplies a voltage in the form of an M-sequence signal waveform.

  With this configuration, since the M-sequence signal includes all frequencies in the band necessary for broadband noise, film stiffness measurement can be performed without running through the frequency.

  In the membrane stiffness measuring apparatus of the present invention, one end that is the reference potential of the voltage source is connected to a reference potential terminal that is connected to a capacitor portion having a vibrating membrane of the capacitor microphone, and the other end of the voltage source. Is connected to the power supply terminal of the condenser microphone.

  In the membrane stiffness measuring apparatus of the present invention, the other end of the voltage source is connected to the power supply terminal of the condenser microphone via a predetermined load resistor.

  In the membrane stiffness measuring apparatus according to the present invention, the first terminal of the frequency characteristic measuring unit is connected to the reference potential terminal of the capacitor microphone, and the second terminal of the frequency characteristic calculating unit is connected to the capacitor microphone. Connected to the power terminal.

  With these configurations, in the stiffness measurement, with the microphone completed, the terminal for normal use is used for the terminal connection for power supply and the terminal connection for measuring the frequency characteristics of the input and output. Non-destructive measurement is possible with the microphone completed.

  In addition, the film stiffness measuring apparatus of the present invention includes a display unit that displays information indicating a measurement result by the frequency characteristic measuring unit.

  With this configuration, the frequency characteristics can be intuitively recognized.

  In the membrane stiffness measuring apparatus of the present invention, the frequency characteristic measuring unit extracts an inflection point in the frequency characteristic as the resonance frequency.

  With this configuration, it is possible to determine the resonance frequency by extracting the inflection point and measure the film stiffness.

In the membrane stiffness measuring apparatus of the present invention, the vacuum vessel holds the inside of the vacuum vessel at a vacuum degree of 10 ⁻¹ to 10 ⁻² (Torr).

  With this configuration, it is possible to measure the film stiffness in a vacuum and with the condenser microphone completed. By setting it as a vacuum state, it can prevent receiving the impedance by the air around a diaphragm.

  The membrane stiffness measurement method of the present invention is a membrane stiffness measurement method for measuring the stiffness of a diaphragm film of a condenser microphone, wherein an excitation voltage is superimposed on a DC voltage for operating a condenser microphone held in a vacuum. Measuring the frequency characteristics by measuring the voltage and phase of the power supply terminal connected to the amplifier of the capacitor microphone with respect to the excitation voltage, Calculating a resonance frequency from frequency response characteristics, and calculating a membrane stiffness of the vibrating membrane from the resonance frequency.

  According to this method, even when the condenser microphone is completed, the stiffness of the diaphragm of the condenser microphone can be measured inexpensively and without using an expensive measuring instrument.

  In the present invention, even when the condenser microphone is completed, the stiffness of the diaphragm of the condenser microphone can be measured inexpensively and non-destructively without using an expensive measuring instrument. Further, since the film stiffness is measured without directly detecting the vibration displacement, the reproducible measurement of the film stiffness can be performed in a short time.

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

(First embodiment)
FIG. 1 is a diagram schematically showing a configuration of a film stiffness measuring apparatus according to the first embodiment of the present invention. The film stiffness measuring apparatus of the present embodiment holds the completed condenser microphone in a vacuum when measuring the film stiffness. A voltage source having a function of superimposing an excitation voltage on the DC voltage and the DC voltage for operating the condenser microphone is provided. The voltage and phase of the power supply terminal connected to the amplifier of the condenser microphone with respect to this excitation voltage are measured, the resonance frequency is calculated from the measured frequency response characteristics, and the membrane stiffness of the diaphragm is calculated from the resonance frequency. When measuring the film stiffness, the power supply terminal and the reference potential terminal that are used when the microphone is actually used are used, so that there is no need to provide a separate measurement terminal. Therefore, the film stiffness can be measured non-destructively in the completed state of the microphone. In the present embodiment, it is assumed that the ECM shown in FIG. 13 is used as the condenser microphone.

  In this membrane stiffness measuring apparatus, the measurement object is the vibration membrane 105 of the ECM, and as shown in FIG. 1, the vacuum vessel 10 containing the ECM 20, the voltage source 30, and the vacuum were placed while changing the measurement frequency. The input / output response measuring unit 40 that measures the input / output response characteristics of the ECM 20 with respect to the excitation voltage of the voltage source 30 and the stiffness calculation that calculates the film stiffness of the ECM 20 by obtaining the resonance frequency of the vibration film 105 from the frequency-input / output response characteristic curve. And a display unit 60 for displaying a frequency-input / output response characteristic curve and the like.

  The vacuum vessel 10 includes a mounting table for setting the completed ECM 20 therein, and also includes a voltage supply terminal and a reference potential terminal as a terminal mechanism that enables voltage supply from the voltage source 30 to the ECM 20. The voltage supply terminal is connected to the power supply terminal B of the ECM 20, and the reference potential terminal is connected to the reference potential terminal A of the ECM 20.

Further, the vacuum container 10 is maintained in a vacuum state of about 10 ⁻¹ Torr or less (about 10 ⁻² Torr, that is, a state where no sound is transmitted) by a vacuum pump when measuring the frequency response characteristics. Since the degree of vacuum is not so high, the state can be reached in about 30 seconds after starting the vacuum pump.

  The voltage source 30 includes a DC voltage source for operating the ECM 20, an excitation voltage source that generates an AC excitation voltage, which is an excitation voltage, and various excitation voltages to be described later in order to measure input / output response characteristics. And has a function of superimposing an excitation voltage on a DC voltage. Then, this voltage is supplied to the ECM 20.

  The input / output response characteristic measurement unit 40 measures the input / output response characteristic with respect to the excitation voltage of the ECM 20 in vacuum while sweeping the measurement frequency of the excitation voltage.

  The stiffness calculation unit 50 obtains the resonance frequency of the vibrating membrane 105 from the frequency-input / output response characteristic curve measured by the input / output response characteristic measurement unit 40, and substitutes this resonance frequency into the above (Equation 1) to vibrate the ECM 20. Calculate the stiffness of the film.

  In the film stiffness measuring apparatus of the present embodiment, the resonance frequency to be substituted into (Equation 1) is obtained from the measurement result of the input / output response characteristics with respect to the excitation voltage of the ECM 20.

  The ECM 20 is normally used in a basic circuit configuration as shown in FIG. The ECM 20 includes a capacitor unit 71 having a vibration film 105 and an FET 72 as an amplifier that amplifies a signal output from the capacitor unit 71. In addition, a reference potential terminal A and a power supply terminal B that can be connected from the outside in the completed state are provided. As shown in FIG. 2, the power supply terminal B is connected to the FET 72, and the reference potential terminal A is connected to the capacitor unit 71. Each terminal A, B is connected to a terminal of the DC voltage source 62 and receives voltage supply through the load resistor 63, so that the ECM 20 is in an operating state. In addition, the dashed-dotted line in FIG. 2 represents the metal case of ECM20.

  FIG. 3 shows an example of a circuit configuration when measuring the input / output response characteristics with respect to the excitation voltage of the ECM 20 according to the present invention. In this circuit, the external reference potential point is the positive-side ground point of the DC voltage source 62, but the operation of the FET 72 is the same as in FIG.

In the present embodiment, an AC voltage source 61 as an excitation voltage source is superimposed on the DC voltage source 62 in order to vibrate the vibrating membrane 105 when measuring the input / output response characteristics as the voltage source 30. As the excitation voltage source, an AC voltage source that supplies a sinusoidal voltage, a voltage source that supplies a white noise wave voltage, a voltage source that supplies an M-sequence signal wave voltage, or the like is used. When a sinusoidal voltage is used, the frequency response is measured by running the frequency. At this time, if the frequency f1 at the start point and the frequency f2 at the end point in the frequency band are set, the frequency band is divided into N,
Δf = (f2−f1) / N
Steps cover this frequency band. In addition, when using a white noise wave-shaped voltage or an M-sequence signal waveform voltage, the white noise or M-sequence signal includes all the necessary bands for high-band noise, and thus the frequency is shifted. The frequency response can be measured without

  Further, as described above, one end of the DC voltage source 62 is grounded, and is connected to the power supply terminal B of the ECM 20 via a predetermined load resistor 63 provided arbitrarily. On the other hand, one end of the AC voltage source 61 is connected to the other end of the DC voltage source 62, and the other end of the AC voltage source 61 is set to the reference potential from the external reference potential point via the voltage source 30, and the ECM 20 Are connected to the reference potential terminal A.

  As shown in FIG. 3, the terminals of the input / output response characteristic measuring unit 40 that performs the input / output response characteristic measurement are connected to the AC voltage source 61 end and the load resistance 63 end to the ECM 20, respectively. That is, the first terminal of the input / output response characteristic measurement unit 40 is connected to the reference potential terminal A of the ECM 20, and the second terminal is connected to the power supply terminal B of the ECM 20. The input / output response characteristic measurement unit 40 includes a voltmeter that measures each voltage and a phase meter that measures the phase difference between the input and the voltage.

  Moreover, you may comprise as FIG. 4 as another example. FIG. 4 shows a configuration in which the external reference potential point is the same as that in FIG. That is, in this circuit, the external reference potential point is a negative-side ground point of the DC voltage source 62.

  Specifically, one end of the direct-current voltage source 62 is set as an external reference potential to be a reference potential, and is connected to the reference potential terminal A of the ECM 20. On the other hand, one end of the AC voltage source 61 is connected to the other end of the DC voltage source 62, and the other end of the AC voltage source 61 is connected to a power supply terminal B of the ECM 20 via a predetermined load resistor 63 provided arbitrarily. It is connected.

  The connection relationship between the terminals of the input / output response characteristic measurement unit 40 and the ECM is the same as that in FIG.

Next, a description will be given of what equivalent circuit the capacitor portion is represented in under reduced pressure.
An acoustic equivalent circuit of the ECM 20 in the air is expressed as shown in FIG.

  Here, A is the mechanical impedance constituted by the volume of the face cloth 101 of the ECM 20 shown in FIG. C1 is the compliance of the air chamber composed of the volume of the front surface of the case 103 and the vibrating membrane 105 (that is, the reciprocal of stiffness). B is the mechanical impedance of the vibrating membrane 105, m0 is the mass of the vibrating membrane 105, c0 (= 1 / so) is the compliance of the vibrating membrane 105, and r0 is the damping resistance of the vibrating membrane 105 itself. . Further, r2 and m2 are the combined impedance in series of the impedance of the hole of the fixed electrode 107 and the impedance of the thin fluid layer between the vibrating membrane 105 and the fixed electrode, C2 is the compliance of the thin fluid layer, and C3 is the back air chamber 108. Air compliance of the air chamber composed of

  As described above, since the capacitor unit 71 of the ECM 20 in the air has mechanical impedance due to air in addition to the mechanical impedance between the vibrating membrane 105 and the fixed electrode 107, input / output with respect to the excitation voltage of the ECM 20 is performed. When the response characteristic is measured in air, it is extremely difficult to measure the mechanical impedance effect of the diaphragm itself due to the influence.

Ｃ：音響コンプライアンス[m⁵/N]
γ：空気の体積比熱[J/m³K]
Ｖ：気室の容積[m³]
Ｐ０：気圧[N/m²] Compliances c1, c2, and c3 caused by the air in the front air chamber and the back air chamber 108 of the vibrating membrane 105 are expressed by the following (Equation 2).

C: Acoustic compliance [m ⁵ / N]
γ: Volume specific heat of air [J / m ³ K]
V: Volume of air chamber [m ³ ]
P0: Barometric pressure [N / m ² ]

In this measuring apparatus, since the ECM 20 is disposed in a vacuum, the value of C (= c1, c2, c3) becomes a very large value and is in a short circuit state. Therefore, the equivalent circuit of the capacitor unit 71 in the vacuum vessel 10 is represented only by the mechanical impedance of the vibrating membrane 105 itself.
The reversible equation of this capacitor part is expressed by the following equations (Equation 3) (Equation 4) (written by Masaaki Kawamura “
"Introduction to electroacoustic engineering", published by Shoshodo Co., Ltd.)

Ｖ１：励振源の交流電圧[V]
Ｚｍ：被測定振動板の機械インピーダンス
Ｅ_Ｂ：ＤＣ成極電圧[V]
Ａ：力係数
ε０：真空の誘電率 8.85E-12[F/m]
Ｓ：コンデンサ部の面積[m²]
Ｃｍ：コンデンサ部の電気容量[F]
ｄ０：エアギャップ間隔[m]
Ｖ：振動板の速度[m/sec]
ｓｎ：負スチフネス[N/m]

V1: Excitation source AC voltage [V]
Zm: Mechanical impedance of diaphragm to be measured E _B : DC polarization voltage [V]
A: Force coefficient ε0: Dielectric constant of vacuum 8.85E-12 [F / m]
S: Capacitor area [m ² ]
Cm: Capacitor capacitance [F]
d0: Air gap interval [m]
V: Speed of diaphragm [m / sec]
sn: Negative stiffness [N / m]

Here, the mechanical impedance of the diaphragm to be measured is

The force coefficient is

The capacitance Cm of the capacitor unit 71 is

で表される。 Negative stiffness is

It is represented by

This (Equation 3) is an equation that focuses on the relationship between the mechanical forces of the diaphragm, and (Equation 4) is an equation that focuses on the electrical relationship of the diaphragm.
In this measuring apparatus, since the vibration film 105 of the ECM 20 is driven by an excitation source, the external force F is 0, and (Equation 3) is expressed as (Equation 9).

Therefore, (Equation 4) can be transformed into the following equation (Equation 10) using (Equation 9).

Therefore, the impedance of the capacitor portion of the ECM 20 under a reduced-pressure vacuum environment is expressed by the following equation (Equation 11).

  As shown in FIG. 6, this impedance is expressed as a resonance equivalent circuit in which the electric capacitance Cm and the diaphragm mechanical impedance are arranged in parallel, and the mechanical resonance frequency of the diaphragm 105 is expressed as the electric resonance frequency. I understand that. Further, in the structure of the ECM 20, a minute fixed floating / parasitic capacitance that does not contribute to vibration is generated due to a structural factor, and is added in parallel to Cm.

  Since the expression of the capacitor unit 71 under a reduced-pressure vacuum environment is obtained, the equivalent circuit of the circuit configuration shown in FIG. 3 is shown in FIG. 7, and the equivalent circuit of the circuit configuration shown in FIG. 4 is shown in FIG. Is done.

  The input / output response to the excitation voltage shown in FIGS. 7 and 8 incorporating the equivalent circuit of the capacitor unit 71 under a reduced-pressure vacuum environment can be obtained by a general-purpose circuit simulator SPICE that simulates the operation of the electronic circuit.

FIG. 9 is a gain-phase response curve with respect to the excitation voltage of FIG. 7 (the actual circuit is FIG. 3).
7 shows that a response curve having the resonance frequency f0 of the vibration film 105, phase information of the resonance depth, and gain resonance information can be obtained at point B in FIG. 7 (point B in FIG. 3). The gain curve shows the simulation results at points B, C, and D in FIG. 7, and the phase curve shows only the simulation results at point B in FIG.

FIG. 10 is a gain-phase response curve with respect to the excitation voltage of FIG. 8 (the actual circuit is FIG. 4).
8 shows that a response curve having the resonance frequency f0 of the vibration film 105, phase information of the resonance depth, and gain resonance information is obtained at point B (point B in FIG. 4). The gain curve shows the simulation results at points B, C, and D in FIG. 8, and the phase curve shows only the simulation results at point B in FIG. The voltage and phase at point B become the voltage and phase of terminal B as the output terminal of ECM 20.

  The gain-phase response curve shown in FIG. 12 which is a partially enlarged view of FIG. 11 and FIG. 11 is a measurement result when the frequency of the alternating voltage of the excitation voltage source is run in the measurement circuit of FIG. This shows that a response curve having the resonance frequency f0 of the vibration film 105, the phase information of the resonance depth, and the gain resonance information can be obtained.

  The excitation voltage frequency-input / output response curve a has a voltage for each frequency at the reference potential terminal A of the ECM 20 as an input characteristic, a voltage for each frequency at the power supply terminal B as an output characteristic, and a gain of the output characteristic with respect to the input characteristic. Is shown. The excitation voltage frequency-phase curve b shows the phase difference for each frequency of the input characteristics and the output characteristics.

For example, the excitation voltage frequency-input / output response curve shown in FIG. 11 is displayed on the display unit 60.
The stiffness calculation unit 50 searches the frequency of the antiresonance point and the frequency of the resonance point from this curve, obtains the resonance frequency f0 by taking the average of the two frequencies, and substitutes this value in (Equation 1). The stiffness of the diaphragm of the ECM 20 is calculated.

  Alternatively, the stiffness calculation unit 50 obtains an intersection between the curve portion of the resonance-antiresonance unit of the excitation voltage frequency-input / output response curve and the constant gain curve, and substitutes the value into (Equation 1) to calculate the vibration film. Calculate the stiffness.

  For example, the excitation voltage frequency-phase curve shown in FIG. The stiffness calculation unit 50 obtains the peak of the curve, that is, the inflection point as the resonance frequency f0, and substitutes this value into (Equation 1) to calculate the stiffness of the diaphragm 105 of the ECM 20.

  As described above, in the film stiffness measurement method of the present embodiment, the excitation voltage source is superimposed on the DC voltage source to generate a minute amplitude displacement corresponding to the excitation voltage source on the vibration film. The minute vibration displacement becomes large at the resonance frequency point of the vibration film, and the change causes a voltage change at the response point. As shown in FIGS. 9 to 12, simulation data and actual data (measurement data) are generated near the resonance point. The resonance curve can be obtained as shown in Fig. 2).

  Since the resonance frequency is obtained from the excitation voltage frequency-input / output response curve a and the excitation voltage frequency-phase curve b shown in FIG. 11 of the ECM 20 by such a film stiffness measurement method, it can be measured at low cost. Further, a reproducible measurement result can be obtained in a short time with a microphone in a finished product state like the ECM 20.

  In addition, in the measurement apparatus that measures in the completed state of the microphone according to the present embodiment, the measurement object is placed in a vacuum and the input / output stress is measured, so that the influence of the air around the diaphragm can be eliminated. It is possible to accurately measure the input / output response of only the vibrating membrane.

The vacuum level at this time may be about 10 ⁻¹ to 10 ⁻² Torr, and can be set in a short time by a vacuum pump.

  Further, in this measuring apparatus, since the input / output response measuring unit 40 measures the absolute value | G | of the gain and the phase angle, an accurate measurement result equivalent to the impedance measurement in the equivalent circuit of FIG. Can be obtained.

  In addition, the input / output response may be measured using a commercially available frequency response measuring device.

  Moreover, the display part 60 and the stiffness calculation part 50 are realizable using the function of a personal computer (PC). In this case, when the measurement frequency band is designated from the PC to the input / output response measurement unit 40, and the input / output response measurement unit 40 scans the designated frequency band and outputs the input / output measurement result to the PC, the screen of the PC is displayed. The absolute value | G | of the gain and the phase angle can be displayed.

  In the present embodiment, the case where the stiffness of the vibration film 105 of the ECM 20 is measured has been described. However, the present invention can also use other electrostatic electroacoustic transducers (for example, MEMS microphones) as measurement targets. is there.

  In the present embodiment, the excitation voltage input / output response characteristic is measured by voltage. However, the stiffness of the diaphragm may be measured by detecting the current at point B.

  INDUSTRIAL APPLICABILITY The present invention is useful as a membrane stiffness measuring apparatus and a membrane stiffness measuring method that can easily and inexpensively measure the stiffness of diaphragms of ECM and MEMS microphones even when these microphones are completed. It is.

The figure which shows the outline | summary of the film | membrane stiffness measuring apparatus in embodiment of this invention. The figure which shows an example of the circuit structure at the time of actually using ECM in embodiment of this invention The figure which shows an example of the circuit structure at the time of measuring the input-output response characteristic of ECM in embodiment of this invention The figure which shows another example of the circuit structure at the time of measuring the input-output response characteristic of ECM in embodiment of this invention The figure which shows the equivalent circuit of the mechanical impedance of ECM in embodiment of this invention The figure which shows the equivalent circuit of the film | membrane stiffness measuring circuit in embodiment of this invention FIG. 3 is an equivalent circuit diagram when the circuit configuration when measuring the input / output response characteristics of the ECM in the embodiment of the present invention is as shown in FIG. 4 is an equivalent circuit diagram when the circuit configuration when measuring the input / output response characteristics of the ECM in the embodiment of the present invention is as shown in FIG. The figure which shows the simulation result of the frequency-input / output response curve in each point on the FIG. 3 measurement circuit in embodiment of this invention, and the frequency-phase curve in B point. The figure which shows the simulation result of the frequency-input / output response curve in each point on the measurement circuit of FIG. 4 in embodiment of this invention, and the frequency-phase curve in B point. The figure which shows the frequency-input / output response curve and frequency-phase curve which are measured with the film | membrane stiffness measuring method in embodiment of this invention. The principal part enlarged view of the curve shown in FIG. 11 in embodiment of this invention Diagram showing ECM configuration The figure which shows the structure of a MEMS microphone

Explanation of symbols

10 Vacuum vessel 20 ECM
30 Voltage Source 40 Input / Output Response Measurement Unit 50 Stiffness Calculation Unit 60 Display Unit 61 AC Voltage Source 62 DC Voltage Source 63 Load Resistor 71 Capacitor Unit 72 FET
101 Face cloth 102 Sound hole 103 Case 104 Vibration film ring 105 Electret vibration film 106 Spacer 107 Fixed electrode 108 Back air chamber 109 FET
110 Insulator 111 Cushion Sheet 112 Printed Circuit Board 113 Terminal 121 Silicon Substrate 122 First Insulating Layer 123 Vibrating Membrane Electrode 124 Electret Membrane 125 Second Insulating Layer 126 Fixed Electrode 127 Sound Hole 128 Back Air Chamber

Claims (12)

A vacuum container for holding the completed condenser microphone in a vacuum;
A voltage source having a function of superimposing an excitation voltage on the DC voltage and the DC voltage for operating the condenser microphone;
A frequency response characteristic measuring unit that measures a voltage and a phase of a power supply terminal connected to an amplifier of the condenser microphone with respect to the excitation voltage;
A membrane stiffness measurement apparatus comprising: a stiffness calculation unit that calculates a resonance frequency from a frequency response characteristic measured by the frequency characteristic measurement unit, and calculates a membrane stiffness of the vibrating membrane from the resonance frequency. The film stiffness measuring device according to claim 1,
The voltage source comprises a DC voltage source and an excitation voltage source. The film stiffness measuring device according to claim 2,
The excitation voltage source supplies a sinusoidal voltage. The film stiffness measuring device according to claim 2,
The excitation voltage source supplies a white noise wave-shaped voltage. The film stiffness measuring device according to claim 2,
The excitation voltage source supplies a voltage in the form of an M-sequence signal waveform. The film stiffness measuring device according to any one of claims 1 to 5,
One end to be a reference potential of the voltage source is connected to a reference potential terminal connected to a capacitor unit having a vibrating membrane of the capacitor microphone,
The other end of the voltage source is connected to the power supply terminal of the condenser microphone. The film stiffness measuring device according to claim 6,
The other end of the voltage source is connected to the power supply terminal of the condenser microphone via a predetermined load resistance. The film stiffness measuring device according to any one of claims 1 to 7,
The first terminal of the frequency characteristic measurement unit is connected to the reference potential terminal of the condenser microphone,
The second terminal of the frequency characteristic calculation unit is connected to the power supply terminal of the condenser microphone. The film stiffness measuring device according to any one of claims 1 to 8, further comprising:
A film stiffness measurement device comprising a display unit for displaying information indicating a measurement result obtained by the frequency characteristic measurement unit. The film stiffness measuring device according to any one of claims 1 to 9,
The frequency characteristic measurement unit extracts an inflection point in the frequency characteristic as the resonance frequency. It is a film | membrane stiffness measuring apparatus of any one of Claim 1 thru | or 10, Comprising:
The said vacuum vessel is a film | membrane stiffness measuring apparatus which hold | maintains the inside of the said vacuum vessel to the vacuum degree of 10 ^{< -1} > -10 ^<-2 > (Torr). A film stiffness measurement method for measuring the stiffness of a diaphragm of a condenser microphone,
Supplying a voltage obtained by superimposing an excitation voltage on a DC voltage for operating a condenser microphone held in a vacuum to the condenser microphone in a completed state;
Measuring a frequency characteristic by measuring a voltage and a phase of a power supply terminal connected to an amplifier of the condenser microphone with respect to the excitation voltage;
Obtaining a resonance frequency from the measured frequency response characteristics, and calculating a film stiffness of the vibration film from the resonance frequency.

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