JP2009200740A - Composite sensor and composite microphone device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, thin and light-weight composite sensor capable of detecting light as well together with sound, vibrations and pressure by a single acoustic sensor in a MEMS microphone as an acoustic sensor. <P>SOLUTION: The composite sensor includes: a capacitor part provided with a vibration film as a first electrode, a dielectric film fixed to the vibration film and a second electrode disposed facing the first electrode; an amplifier connected to the first electrode of the capacitor part, for amplifying signals from the capacitor part; a capacitor electrode terminal connected to the second electrode of the capacitor part; a voltage supply terminal connected to the amplifier; a grounding terminal; an output terminal from the amplifier; and a signal separation part connected to the output terminal and provided with a band division filter for dividing the output of the amplifier into optical signals and acoustic signals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite sensor and a composite microphone device using the same, and more particularly to a composite device having an optical sensor function in addition to an acoustic sensor function.

A multivariate detection sensor capable of detecting a physical quantity such as sound, vibration, pressure, and acceleration, and a physical quantity such as light is described in Patent Document 1, for example.
In the multivariate detection sensor described in Patent Document 1, an electret condenser and an optical sensor are used in combination.
That is, physical quantities such as sound, vibration, pressure, and acceleration are obtained by converting a change in capacitance into a voltage, and the physical quantities of each parameter are detected based on this. Further, the physical quantity of light is detected using a sensor different from the electret condenser type sensor.

JP 2004-354199 A (first page, FIG. 1)

In the prior art, the following two problems may occur.
(1) A single electret condenser sensor having a conventional structure can detect sound, vibration, and pressure, but cannot detect light at the same time.
(2) Therefore, when detecting light, it is necessary to use another sensor in combination. For example, it is possible to provide a sensor that converts light into heat and converts it into pressure, and the pressure value can be detected and output by an electret condenser sensor. However, in this case, conversion from light to heat is very poor in conversion efficiency, and it is difficult to detect a small amount of light. In addition, the structure tends to be complicated and large.

  FIG. 6 shows an example of the MEMS microphone M. The MEMS microphone M is formed by forming a large number of microphone chips on a silicon substrate at the same time using a semiconductor manufacturing technique, and finally dividing them into individual pieces. FIG. 6 shows a side view of one divided microphone chip. This MEMS microphone M has, for example, a vibrating membrane electrode 23 and an electret film 24 on a p-type silicon substrate 21 with a first insulating layer 22 interposed therebetween. A fixed electrode 26 in which a sound hole 27 is formed is provided via an insulating layer 25. Further, a back air chamber 28 is formed on the back surface of the vibrating membrane electrode 23 by etching the silicon substrate 21.

  The vibrating membrane electrode 23 is made of polysilicon made conductive by n doping, the electret film 24 is made of a silicon nitride film or a silicon oxide film, and the fixed electrode 26 made conductive by n doping. The polysilicon is formed by laminating a silicon oxide film and a silicon nitride film.

  In the MEMS microphone M, when the vibrating membrane electrode 23 vibrates due to the sound pressure, the capacitance of the plate capacitor formed by the vibrating membrane electrode 23 and the fixed electrode 26 changes and is taken out as a voltage change.

  By the way, in the manufacturing site of microphones and speakers, sensitivity has become an extremely important issue. As a result of various verifications, the present inventors have steadily flickered fluorescent lamps (the blink is a frequency twice the commercial frequency). I found that a MEMS microphone placed in the public (to become publicly known) picks up noise. This was a periodic output at a frequency twice the commercial frequency, and it was found that the light was detected by a fluorescent lamp.

The present invention has been made in view of the above circumstances, and pays attention to the above discovery, and can detect light as well as sound, vibration, and pressure by a single acoustic sensor in a MEMS microphone, that is, a MEMS microphone as an acoustic sensor. An object of the present invention is to provide a composite sensor that is small, thin, and lightweight.
It is another object of the present invention to provide a composite microphone device having an optical sensor function.

Therefore, the composite sensor of the present invention includes a vibration film as a first electrode, a dielectric film fixed to the vibration film, and a second electrode disposed to face the first electrode. A capacitor unit, an amplifier connected to the first electrode of the capacitor unit for amplifying a signal from the capacitor unit, a capacitor electrode terminal connected to the second electrode of the capacitor unit, and the amplifier A band division filter that includes a voltage supply terminal to be connected, a ground terminal, and an output terminal from the amplifier, and is connected to the output terminal and divides the output of the amplifier into an optical signal and an acoustic signal. And a signal separation unit including
The composite sensor may be a composite sensor in which a capacitor electrode terminal connected to the second electrode of the capacitor unit and a ground terminal are connected internally or externally.
As described above, the present inventors paid attention to the discovery that the output of the capacitor unit includes a signal output of the same frequency as that of the fluorescent lamp, and as a result of consideration, the first electrode and the second electrode In addition to the mechanical-electrical conversion output due to vibration caused by the signal caused by sound, vibration, and pressure (hereinafter referred to as acoustic signal) The insight that the photoelectric conversion output to be able to be obtained can be obtained. Therefore, various experiments were performed, and the signal corresponding to the sound of the speaker that did not emit light was confirmed by confirming the signal completely synchronized with the on / off modulation of the LED with LED light that does not emit light. It was found that a signal corresponding to light and sound can be obtained on one output signal line of one sensor.
By dividing the signal on this single output signal line into an optical signal and an acoustic signal using a band division filter, we succeeded in extracting both the optical signal and the acoustic signal with one sensor.
Therefore, according to the above configuration, both the optical signal and the acoustic signal can be extracted by one sensor by dividing the optical signal and the acoustic signal using the band division filter. This band division filter may be provided outside the sensor.

The band dividing filter divides the signal into 100 Hz or more and less than 100 Hz.
The frequency audible to the human ear is usually from 20Hz to 15000Hz to 20000Hz, although there are individual differences. This frequency band is called the audible range. Furthermore, it is known from Fletcher Manson's loudness characteristics that the frequency on the low frequency side of the audible range is 200 Hz to 300 Hz when human hearing characteristics are taken into consideration.
On the other hand, the flickering of fluorescent lamps is twice the commercial frequency. Therefore, by dividing the band dividing filter into 100 Hz or more and less than 100 Hz, the acoustic signal and the optical signal can be efficiently separated and extracted.

  According to the present invention, in the composite sensor, the capacitor unit, the amplifier, and the signal separation unit are housed in a container, and the voltage supply terminal, the output terminal, the capacitor electrode terminal, and the ground terminal are included in the container. And is connected to the signal separation unit.

  In the composite sensor, the capacitor unit and the amplifier are mounted on a first surface of the same substrate, and the capacitor electrode terminal, the voltage supply terminal, the ground terminal, and the output terminal are Including those arranged as surface mount terminals on the second surface of the substrate.

  The composite sensor includes one in which a capacitor electrode terminal connected to the second electrode of the capacitor unit and a ground terminal are connected internally or externally.

  According to the present invention, in the composite sensor, the capacitor unit includes a MEMS microphone.

In the composite sensor, the silicon substrate of the MEMS microphone includes a first conductivity type silicon substrate, and an electrode includes a second conductivity type silicon.
From various experimental results, it was found that when a p-type silicon substrate was processed by a MEMS process and an n-doped polysilicon layer was used as an electrode, good photoelectric conversion efficiency could be obtained. Further, as a result of further experiments, it has been found that this is effective when the first conductive type silicon substrate is used as a starting material and the electrode is made of reverse conductive type, that is, second conductive type silicon.

According to the present invention, in the composite sensor, the capacitor unit, the amplifier, and the signal separation unit are formed on the same silicon substrate, and the signal separation unit is an active filter.
With this configuration, by forming the signal separation unit on the silicon substrate, it is possible to perform filtering efficiently while minimizing transmission loss.
In addition, the MEMS microphone includes a dielectric film that retains a permanent charge.

The present invention also provides a composite microphone device using the composite sensor.
According to this configuration, various uses such as providing a microphone device having a switching function using light are possible.

  According to the present invention, both a light signal and an acoustic signal can be detected by a single sensor, and a small and highly sensitive output can be obtained. When this is used as a composite microphone device, it is possible to detect both small and highly sensitive optical signals and acoustic signals, and it is possible to provide a highly functional microphone device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a device configuration of a microphone device with an optical remote controller using a composite sensor according to an embodiment of the present invention.
In the present embodiment, as shown in FIG. 1, the output Eo (see FIG. 2) of the composite microphone device 10 is transmitted through a transmission path such as a cable, and the band division filter 20 is connected to the receiving end. The signal output S _out is obtained via the signal processing circuit 30 on the basis of the photoelectric conversion signal S _light divided by 20 and the acoustic signal S _audio . In this configuration, as shown in FIG. 1, by turning on an LED of about 20 Hz to 40 Hz as the remote control switch 40, the photoelectric conversion unit of the composite microphone device 10 outputs an optical signal, while the capacitor of the composite microphone device 10 An acoustic signal can be output as the signal output _Sout output by the unit.

  This composite microphone device is composed of a MEMS microphone chip M that forms a capacitor portion and a photoelectric conversion portion in which an electrode is formed of n-doped polysilicon while processing a shape of a p-type silicon substrate, and this MEMS microphone chip M The capacitor electrode terminal connected to the second electrode and the ground terminal are separately derived, and a desired voltage can be applied between the capacitor electrode terminal and the ground terminal so that the sensitivity can be adjusted. It is configured.

FIG. 2 is a block diagram including the composite microphone device, FIGS. 3A to 3C are a top view, a side view and a bottom view of the composite microphone device, and FIGS. 4A and 4B. Fig. 5 shows a top view and a cross-sectional view showing the internal configuration of the composite microphone device, and Fig. 5 shows a cross-sectional view of the MEMS chip, and a MEMS microphone (chip) M constituting a usual capacitor unit and an amplifier connected thereto. The CMOS amplifier A to be configured is mounted on a circuit board 100 for mounting and sealed with a metal cap 101. In the equivalent circuit diagram of this microphone device, as shown in FIGS. 2 to 4, the capacitor part M and the CMOS amplifier A are connected, and the capacitor electrode terminal E _i that is the second electrode of the capacitor part and the ground of the CMOS amplifier A are connected. and the terminal E _G, the capacitor electrode pad P _{i respectively,} is taken out independently as a ground pad P _G, constitutes an external terminal. Although described later in detail, the sensitivity between the capacitor electrode terminals E _i as shown in FIG. 2, separately taken out and ground terminal E _G of CMOS amplifier A, and the capacitor electrode pad P _i, and the ground pad P _G A sensitivity control voltage composed of the variable voltage VR of the adjustment unit is connected and used as a sensitivity variable microphone.

Further, as shown in FIG. 5, the microphone device is connected to the capacitor electrode terminals E _i is a second electrode of the capacitor portion, and a ground terminal E _G of CMOS amplifier A with the microphone device inside example own circuit board Or it can also take the structure connected with the circuit board of the other party at the time of mounting.
In this case, a capacitor electrode pad P _i, a film that holds the sensitivity instead of the variable voltage configured sensitivity control voltage VR adjustment unit, a permanent charge a dielectric film of the microphone between the ground pad P _G By doing so, a fixed-sensitivity microphone device can be configured.

That is, the composite microphone device of the present invention is an n-doped polysilicon which is a vibration film 23 formed on a base 21 as a support portion made of a p-type silicon substrate through a silicon oxide film as an insulating film 22. And a capacitor portion (FIG. 2) composed of a microphone including a first electrode made of n and a second electrode made of n-doped polysilicon as a fixed electrode 26 disposed opposite to the first electrode. 6) and an amplifier A that is connected to the first electrode of the capacitor unit and amplifies the signal from the capacitor unit are mounted in a container made of a metal cap 101. FIGS. ) Shows an external view (a top view, a side view, and a bottom view), a capacitor electrode terminal E _i connected to the second electrode of the capacitor section, and a voltage supply connected to the amplifier A And the terminal E _V, a ground terminal E _G, wherein the output terminal E _O from the amplifier A is derived from the container, and the pad (capacitor electrode pad P _i, respectively on the back side of the circuit board 100, the voltage supply pad P _V If forms a ground pad _{P G,} the output pad _{P O} from the amplifier (CMOS amplifier) a.

As shown in FIG. 4, the inside of the composite microphone device is mounted on a printed wiring board (circuit board) 100 in which a capacitor part M and a CMOS amplifier A form a circuit pattern, and sealed with a metal cap 101. and, four pads described above on the back side of the circuit board 100 i.e., the capacitor electrode pad P _i, and the voltage supply pad P _V, a ground pad P _G, the output pad P _O are formed.

As shown in FIG. 6, this silicon microphone chip M is composed of a p-type silicon substrate 21 and an n-doped polysilicon film formed on the surface thereof through a silicon oxide film 22, and serves as one capacitor. A vibrating film 23 as a functioning first electrode, a silicon oxide film as an electret film (film to be electretized) 24, a spacer portion 25 made of a silicon oxide film, and a fixed electrode 26 functioning as the other electrode of the capacitor And a back air chamber 28 formed by etching the silicon substrate 21. The fixed electrode 26 is provided with a plurality of sound holes (openings for guiding sound waves to the vibration film 23) 27. Reference symbol G indicates an air gap, and H indicates a contact hole for electrical connection.
The fixed electrode 26 is formed by laminating polysilicon made conductive by n doping and a silicon oxide film or silicon nitride film.

  The vibration film 23, the fixed electrode 26, and the inorganic dielectric film 24 constituting the microphone are a silicon microfabrication technique using a p-type silicon substrate 21 as a starting material and a CMOS (complementary field effect transistor) manufacturing process technique. Is used to form a so-called MEMS element.

FIG. 7 is a diagram showing the result of measuring the output signal of the MEMS microphone when the fluorescent lamp is turned on and off, and FIG. 8 is a diagram showing the output by turning on / off the LED light. In FIG. 7, the vertical axis shows the spectrum of the microphone output voltage when the fluorescent lamp in the audio room is turned on and off, and it can be seen from this figure that the output can be seen at the flicker frequency of the light fluorescent lamp. According to FIG. 7, the output signal is a complicated output signal including noise, but the signal appears at a frequency corresponding to a frequency twice the commercial frequency, which is the striking frequency of the fluorescent lamp, and becomes a remarkable light detection signal. Yes. FIG. 8 shows an output by ON / OFF of the LED light used for signal generation of the optical remote controller, and a signal synchronized with the ON / OFF signal indispensable to the remote controller is obtained.
FIG. 9 shows the magnitude and frequency characteristics of the optical signal when the magnitude and polarity of the sensitivity control voltage are changed.
It shows characteristics with respect to the magnitude and polarity of the sensitivity control voltage.

On the other hand, for a sound signal, FIG. 10 shows sensitivity characteristics when the polarity of the sensitivity control voltage and the magnitude of the voltage are changed. A voltage adjustment unit composed of a variable voltage VR is connected to the applied voltage. As a result, the sensitivity can be made variable.
Accordingly, it is possible to adjust the sensitivity variation by this voltage control after completion. Also, when it is desired to change the sensitivity at the time of use, the desired sensitivity can be obtained very easily by only voltage control.
Further, the sensitivity frequency characteristic is sufficient as a microphone as shown in FIG.

  Here, according to the present embodiment, as shown in FIG. 6, for example, the film thickness is between the p-type silicon substrate 21 and the n-doped polysilicon film constituting the first electrode 23 formed on this surface. An insulating film 22 made of a silicon oxide film of about 700 nm is formed. It can be considered that a MOS structure is formed between the first electrode 23 and the second electrode 26 sandwiching the insulating layer 25 of about 3 μm and the p-type silicon substrate 21. It is thought that there is a depletion layer in some form. Also, considering that the thickness of the depletion layer is modulated by the ON / OFF light of a fluorescent lamp or LED, the capacitance is modulated, and the capacitance modulation with this light changes the capacitance with sound and the output voltage appears. It is estimated that an optical modulation output may be obtained as an output. Therefore, from the composite microphone according to the present embodiment, the output corresponding to the modulated light and the output corresponding to the sound input appear on the same output line. By separating this optical signal from the output signal by the band division filter, it is possible to separate and extract the acoustic signal and the optical signal.

  Using this composite microphone device, an optical remote control signal and an acoustic signal are separated by a band division filter connected to the outside, and the optical remote control signal and the acoustic signal are applied to an AND circuit by the signal processing circuit 30, so that the optical remote control An acoustic signal can be output only when the switch is on.

  In the above-described embodiment, it is particularly easy to take out an optical signal when an n-doped polysilicon layer is used as an electrode on a p-type silicon substrate. Conversely, when a p-doped polysilicon layer is used as an electrode on an n-type silicon substrate, it is easy to take out an optical signal. The crystal types of silicon constituting these are not particularly limited to this combination, and can be selected from amorphous silicon, μ crystal silicon, polysilicon, single crystal silicon, and combinations thereof.

  In the above embodiment, the case where the substrate and the first electrode are of the reverse conductivity type has been described. However, the substrate and the second electrode or the first electrode and the second electrode are of the reverse conductivity type. In some cases, the composite sensor of the present invention may be applicable.

  In the above embodiment, the case where the DC bias type MEMS microphone device is used has been described. However, the present invention can also be applied to an electret type electrostatic electroacoustic transducer.

  According to the composite microphone device of the present invention, since both the optical signal and the acoustic signal can be detected by one sensor, it is small and highly reliable, and thus can be widely used for an electret condenser microphone device and the like. .

Conceptual explanatory diagram of the composite microphone device according to the first embodiment of the present invention. Equivalent circuit diagram of the composite microphone device used in Embodiment 1 of the present invention The figure which shows the microphone apparatus used by embodiment of this invention, (a) is a top view, (b) is a side view, (c) is a bottom view The figure which shows the internal structure of the microphone apparatus used by embodiment of this invention. The figure which shows the microphone apparatus used by embodiment of this invention Cross-sectional view of MEMS chip The figure which shows the result of having measured the output signal of a MEMS microphone The figure which shows the output by ON / OFF of LED light Diagram showing optical signal magnitude and frequency characteristics when sensitivity control voltage magnitude and polarity are changed A diagram showing the sensitivity characteristics when the polarity of the sensitivity control voltage and the voltage magnitude are changed. Diagram showing sensitivity frequency characteristics

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Composite microphone apparatus 20 Band-division filter 30 Signal processing circuit 40 Optical remote control 21 Silicon substrate 22 Insulating layer 23 Vibration film electrode 24 Electret film 25 Second insulating layer 26 Fixed electrode 27 Sound hole 28 Back air chamber M MEMS microphone

Claims (10)

A capacitor unit including a vibration film as a first electrode, a dielectric film fixed to the vibration film, and a second electrode disposed to face the first electrode;
An amplifier connected to the first electrode of the capacitor unit and amplifying a signal from the capacitor unit;
A capacitor electrode terminal connected to the second electrode of the capacitor unit; a voltage supply terminal connected to the amplifier; a ground terminal; and an output terminal from the amplifier; connected to the output terminal; A composite sensor comprising an optical signal and a signal separation unit that branches into an acoustic signal.  2. The composite sensor according to claim 1, wherein a capacitor electrode terminal connected to the second electrode of the capacitor unit and a ground terminal are connected internally or externally. The composite sensor according to claim 1,
A composite sensor using an output signal having a frequency of 100 Hz or more as a sound signal among the output signals, and using an output signal of less than 100 Hz as an optical sensor signal. The composite sensor according to any one of claims 1 to 3,
The capacitor unit and the amplifier are stored in a container,
The composite sensor in which the voltage supply terminal, the output terminal, the capacitor electrode terminal, and the ground terminal are led out from the container and connected to the signal separation unit. The composite sensor according to any one of claims 1 to 4,
The capacitor unit, the amplifier and the signal separation unit are mounted on the first surface of the same substrate,
A composite sensor in which the capacitor electrode terminal, the voltage supply terminal, the ground terminal, and the output terminal are disposed on the second surface of the substrate as surface mount terminals. The composite sensor according to any one of claims 1 to 5,
The capacitor unit is a composite sensor composed of a MEMS microphone. The composite sensor according to claim 6,
The MEMS microphone includes a first conductivity type silicon substrate, and at least one of the first and second electrodes is a second conductivity type silicon. The composite sensor according to claim 7,
The composite sensor in which the capacitor unit, the amplifier, and the signal separation unit are formed on the same silicon substrate, the signal separation unit is an active filter, and the dielectric film of the MEMS microphone is a film that holds a permanent charge.   A composite microphone device using the composite sensor according to claim 1. A capacitor unit including a vibration film as a first electrode, a dielectric film fixed to the vibration film, and a second electrode disposed to face the first electrode;
An amplifier connected to the first electrode of the capacitor unit and amplifying a signal from the capacitor unit;
A capacitor electrode terminal connected to the second electrode of the capacitor unit; a voltage supply terminal connected to the amplifier; a ground terminal; and an output terminal from the amplifier. The output of the amplifier is an optical signal. A composite sensor that is an acoustic signal.

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