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JP2017118240

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DESCRIPTION JP2017118240
Abstract: The present invention provides an electret sensor element, a matrix sensor, and a
method of manufacturing the same, which can be reduced in thickness and size by a simple
process and can be easily matrixed. An electret sensor element for converting vibration into an
electric signal, comprising: a vibrating electrode having a flat vibrating surface at no load, a fixed
electrode formed on a substrate, and a space between the vibrating electrode and the fixed
electrode Comprising an insulating layer disposed in the air gap and an electret layer storing
charges, and an insulating layer insulated from the vibrating electrode and the fixed electrode,
and a thin film transistor for impedance conversion formed on the same surface as the fixed
electrode It is. [Selected figure] Figure 1
Electret sensor element, matrix sensor and method for manufacturing them, and matrix sensor
circuit
[0001]
The present invention relates to an electret sensor element for converting vibration into an
electrical signal, a matrix sensor in which the electret sensor elements are arranged in a matrix, a
method of manufacturing them, and a matrix sensor circuit using the matrix sensor.
[0002]
2. Description of the Related Art Electret sensor elements that convert vibrations into electrical
signals are known.
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Here, the electret sensor element has a capacitor structure in which an air gap and an electret
layer storing charges are disposed between the fixed electrode and the vibrating electrode, and
the change in the inter-electrode distance due to the vibration of the vibrating electrode , As a
change in the voltage between the electrodes.
[0003]
Although the electret sensor element can detect minute vibrations, the electric signal output from
the electret sensor element is weak. Therefore, in order to reduce the influence of noise
superimposed in the transmission path to the AD converter provided in the subsequent stage, an
FET (Field Effect Transistor) for impedance conversion is provided in the vicinity of the fixed
electrode, and the electric signal from the electret sensor element Is amplified.
[0004]
As such an electret sensor element, a vibrating electrode having a flat vibrating surface at no
load, a vibrating-layer insulating layer provided on the lower surface of the vibrating electrode,
and an electret layer facing the vibrating electrode via an air gap. There has been proposed an
ultrasonic probe provided with a back electrode (fixed electrode) in contact with the lower
surface of the electret layer and an amplifier (FET) connected between the vibrating electrode
and the back electrode (see, for example, Patent Document 1) ).
[0005]
WO 2009/125773
[0006]
However, the prior art has the following problems.
That is, in the electret sensor element of Patent Document 1, the back surface (surface opposite
to the vibration electrode) of the back electrode is a separate component from the sensor unit
including the vibration electrode, the vibration layer insulating layer, the electret layer and the
back electrode. And the FET for impedance conversion is connected by another process.
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2
[0007]
Therefore, there is a problem that the thickness of the electret sensor element is increased and
enlarged, and the manufacturing process of the electret sensor element is complicated.
In addition, when this electret sensor element is formed into a matrix to form a matrix sensor, an
FET is required for each sensor unit, and wiring crosses occur and a separate circuit board for
wiring is required, so the thickness is further increased. There is a problem of increasing in size
more than ever.
[0008]
The present invention has been made to solve the problems as described above, and it is possible
to realize thinning and downsizing by a simple process, and an electret sensor element, which is
easy to form into a matrix, a matrix sensor, and those The purpose is to obtain a manufacturing
method.
[0009]
An electret sensor element according to the present invention is an electret sensor element that
converts vibration into an electric signal, and includes a vibrating electrode having a flat
vibrating surface at no load, a fixed electrode formed on a substrate, and a vibrating electrode.
An insulating layer formed of an air gap and an electret layer storing charges, which is disposed
between the fixed electrode and the vibrating electrode and the fixed electrode, and a thin film
transistor for impedance conversion formed on the same surface as the fixed electrode. (TFT:
Thin Film Transistor).
[0010]
A matrix sensor according to the present invention has the above-described electret sensor
elements arranged in a matrix.
[0011]
A method of manufacturing an electret sensor element according to the present invention is a
method of manufacturing an electret sensor element for converting vibration into an electric
signal, and the steps of forming a fixed electrode and a thin film transistor for impedance
conversion in the same process on a substrate; Forming an air gap on the electrode and the thin
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film transistor, forming an electret layer storing charges on the spacer, forming an insulating
layer on the electret layer, and forming the insulating layer on the insulating layer Forming a
vibrating electrode having a flat vibrating surface at no load.
[0012]
A method of manufacturing a matrix sensor according to the present invention is a method of
manufacturing a matrix sensor in which electret sensor elements for converting vibrations into
electric signals are arranged in a matrix, and a set of fixed electrodes and thin film transistors for
impedance conversion is formed on a substrate. A plurality of steps of forming in the same
process, disposing a spacer forming an air gap on the plurality of fixed electrodes and thin film
transistors, and forming an electret layer on which the charge is stored. And forming an
insulating layer on the electret layer and forming a vibrating electrode having a flat vibration
surface at no load on the insulating layer.
[0013]
According to the electret sensor element, the matrix sensor, and the method of manufacturing
the same according to the present invention, the thin film transistor for impedance conversion is
formed on the same surface as the fixed electrode in the same process.
Therefore, it is possible to obtain an electret sensor element, a matrix sensor, and a method for
manufacturing them, which can realize thinning and downsizing with a simple process, and can
be easily matrixed.
[0014]
It is sectional drawing which shows the electret sensor element which concerns on Embodiment
1 of this invention.
It is a top view which shows typically the relationship of the fixed electrode and TFT of the
electret sensor element which concern on Embodiment 1 of this invention.
It is a top view which shows the matrix sensor which arrange ¦ positioned the electret sensor
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element which concerns on Embodiment 1 of this invention in a matrix form.
FIG. 6 is another cross-sectional view showing the electret sensor element in accordance with
Embodiment 1 of the present invention.
FIG. 6 is yet another cross-sectional view showing the electret sensor element in accordance with
Embodiment 1 of the present invention. It is a top view which shows the matrix sensor circuit
which used the matrix sensor. It is a top view which shows the matrix sensor circuit which
concerns on Embodiment 2 of this invention. It is the equivalent circuit schematic which extracts
and shows the electret sensor element of the matrix sensor circuit which concerns on
Embodiment 2 of this invention.
[0015]
Hereinafter, preferred embodiments of an electret sensor element, a matrix sensor and a method
for manufacturing them, and a matrix sensor circuit according to the present invention will be
described using the drawings, but the same or corresponding parts in the respective drawings
are identical A description will be given with reference numerals.
[0016]
The electret sensor element is a highly sensitive vibration sensor that can detect even ultrasonic
waves.
Specifically, it can realize the function of position (three-dimensional position) sensor using
ultrasonic waves and the function of heart rate sensor, and by using TFT, it integrates with the
current TFT type display device, It becomes possible to provide a functional display device.
[0017]
In addition, matrix formation can be applied to medical applications such as simple echo and
industrial applications such as failure point diagnosis. Further, in the case of using a transparent
electrode, it can be integrated with an LCD (Liquid Crystal Display), and can be applied to a
wearable display device with a sensor or the like.
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[0018]
Embodiment 1 FIG. 1 is a cross-sectional view showing an electret sensor element in accordance
with Embodiment 1 of the present invention. FIG. 2 is a schematic view showing the relationship
between the fixed electrode and the TFT of the electret sensor element in accordance with
Embodiment 1 of the present invention. This electret sensor element is obtained by integrating
the above-described FET for impedance conversion with a fixed electrode and a TFT at the same
time, and integrating it with a sensor unit.
[0019]
In FIGS. 1 and 2, the electret sensor element 1 is fixed to a vibrating electrode 11 having a flat
vibrating surface at no load, a fixed electrode 13 formed on a substrate 12 made of glass or a
film, and the vibrating electrode 11. An air gap 14 disposed between the electrode 13 and an
electret layer 15 storing electric charge, and connected to the insulating layer 16 insulated from
the vibrating electrode 11 and the fixed electrode 13 and the fixed electrode 13, the fixed
electrode 13 And a TFT 17 for impedance conversion formed on the same surface.
[0020]
Further, the insulating layer 16 includes a first insulating layer 18 provided on the surface on the
fixed electrode 13 side of the vibrating electrode 11, an electret layer 15 provided on the surface
on the fixed electrode 13 side of the first insulating layer 18, and an electret It has an air gap 14
disposed between the layer 15 and the fixed electrode 13.
The air gap 14 is formed by the spacer 19. Further, the substrate 12 and the electret layer 15 are
bonded by an adhesive 20.
[0021]
Here, for the vibrating electrode 11, the first insulating layer 18, and the electret layer 15, for
example, an electrode is provided on one side of a material having a high insulation resistance,
such as a PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer) film, and the other side.
Is formed of an electretized film of a three-layer structure which is electretized by irradiation of
an electron beam or the like.
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[0022]
The air gap 14 is formed between the fixed electrode 13 and the TFT 17 and the electret layer
15 at an interval of 10 nm to 100 μm.
Further, the spacer 19 is an insulating material having a high resistivity of about 10 <16> Ω so
that the fixed electrode 13 and the electret layer 15 charged do not conduct.
[0023]
Hereinafter, the manufacturing process of the electret sensor device 1 shown in FIG. 1 will be
described. First, the fixed electrode 13 and the TFT 17 are formed in the same process on the
substrate 12 made of glass or film. At this time, a wire connecting the fixed electrode 13 and the
TFT 17 is also formed simultaneously with the fixed electrode 13 and the TFT 17.
[0024]
Subsequently, the spacer 19 forming the air gap 14 is disposed on the fixed electrode 13 and the
TFT 17. Next, the electretized film having the vibrating electrode 11, the first insulating layer 18
and the electret layer 15 is placed on the spacer 19. Subsequently, the periphery of the substrate
12 is sealed with an adhesive 20.
[0025]
In the electret sensor element 1 manufactured in this manner, the vibrating electrode 11 is
connected to the ground, and the output from the TFT 17 is connected to an AD converter (not
shown). A change in distance can be detected as a change in inter-electrode voltage.
[0026]
Thus, the FET for impedance conversion necessary for the electret sensor element can be formed
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of a TFT and integrated with the sensor unit.
In addition, by forming the FET for impedance conversion with a TFT, it is possible to realize an
ultra-compact FET with almost the same thickness and on substantially the same plane as the
fixed electrode 13.
[0027]
FIG. 3 is a plan view showing a matrix sensor in which the electret sensor elements according to
Embodiment 1 of the present invention are arranged in a matrix. In FIG. 3, only the fixed
electrode 13 and the TFT 17 formed on the substrate 12 are shown. In FIG. 3, this matrix sensor
10 has a configuration in which a plurality of electret sensor elements 1 shown in FIG. 1 are
arranged in a matrix.
[0028]
Hereinafter, the manufacturing process of the matrix sensor 10 shown in FIG. 3 will be described.
First, a plurality of sets of fixed electrodes 13 and TFTs 17 are formed in a matrix on the
substrate 12 made of glass or film in the same process. At this time, a wire connecting the fixed
electrode 13 and the TFT 17 is also formed simultaneously with the fixed electrode 13 and the
TFT 17.
[0029]
Subsequently, the spacer 19 forming the air gap 14 is disposed on the plurality of sets of the
fixed electrode 13 and the TFT 17. Next, the electretized film having the vibrating electrode 11,
the first insulating layer 18 and the electret layer 15 is placed on the spacer 19. Subsequently,
the periphery of the substrate 12 is sealed with an adhesive 20.
[0030]
Thus, the spacer 19 forming the air gap 14 is disposed on the entire surface of the substrate 12
on which a plurality of sets of the fixed electrode 13 and the TFT 17 are formed, and the
electretized film is mounted on the spacer 19. The matrix sensor 10 can be configured by a
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simple process.
[0031]
As described above, according to the first embodiment, the TFT for impedance conversion is
formed on the same surface as the fixed electrode in the same process.
Therefore, it is possible to obtain an electret sensor element, a matrix sensor, and a method for
manufacturing them, which can realize thinning and downsizing with a simple process, and can
be easily matrixed.
[0032]
In the first embodiment, it has been described that the air gap 14 is disposed between the fixed
electrode 13 and the TFT 17 and the electret layer 15 in FIG. However, when a strong force is
applied to the vibrating electrode 11, the electret layer 15 may come into contact with the fixed
electrode 13 and a discharge may occur.
[0033]
Therefore, as shown in FIG. 4, by providing the second insulating layer 21 between the fixed
electrode 13 and the TFT 17 and the spacer 19, the electret layer is obtained even when a strong
force is applied to the vibrating electrode 11. The contact 15 can be prevented from contacting
the fixed electrode 13.
[0034]
Further, in FIG. 4, the electret layer 15 and the air gap 14 are disposed between the first
insulating layer 18 and the second insulating layer 21.
However, as shown in FIG. 5, the spacers forming the air gap 14 may be electretized electretized
spacers 22.
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[0035]
Second Embodiment FIG. 6 is a plan view showing a matrix sensor circuit using the matrix sensor
shown in FIG. As shown in FIG. 6, in this matrix sensor circuit, an AD converter 23 that digitizes
the output from the TFT 17 is required for each electret sensor element 1. Therefore, in this
embodiment, the reduction of the number of AD converters 23 will be described.
[0036]
FIG. 7 is a plan view showing a matrix sensor circuit according to Embodiment 2 of the present
invention. In FIG. 7, this matrix sensor circuit includes a matrix sensor 10, an AD converter 23, a
shift register 24 composed of a plurality of D-type flip flops (DFFs), and a logic circuit 25 for
signal processing.
[0037]
Here, with respect to the TFT 17 of each electret sensor element 1, a plurality of vertical wirings
26 and a plurality of horizontal wirings 27 which are insulated from the plurality of vertical
wirings 26 and are orthogonal to each other are provided. Further, at the intersections of the
plurality of vertical wires 26 and the plurality of horizontal wires 27, TFTs for switches are
provided.
[0038]
FIG. 8 is an equivalent circuit diagram showing an electret sensor element of a matrix sensor
circuit according to Embodiment 2 of the present invention. In FIG. 8, the electret sensor element
1 is connected to a switch TFT 28 formed at the intersection of the vertical wire 26 and the
horizontal wire 27.
[0039]
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In this equivalent circuit, when a selection signal is applied to the horizontal wiring 27 from the
shift register 24, a signal after impedance conversion, which is output from the TFT 17 according
to the change in inter-electrode voltage generated by the vibration of the vibrating electrode 11,
is , And the vertical wiring 26. As described above, by providing the vertical wires 26, the
horizontal wires 27 and the TFTs 28 for switches, it is possible to sense only the selected row,
and the number of AD converters 23 can be reduced.
[0040]
Further, in the matrix sensor circuit shown in FIG. 8, the TFT 17, the TFT 18 and the shift
register 24 can be formed in the same process as the fixed electrode 13. Therefore, the matrix
sensor circuit can be configured by a simple process.
[0041]
Reference Signs List 1 electret sensor element, 10 matrix sensor, 11 vibrating electrode, 12
substrate, 13 fixed electrode, 14 air gap, 15 electret layer, 16 insulating layer, 17 TFT, 18 first
insulating layer, 19 spacer, 20 adhesive, 21 first 2 insulating layers, 22 electret spacers, 23 AD
converters, 24 shift registers, 25 logic circuits, 26 vertical wires, 27 horizontal wires, 28 TFTs.
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