JPH0467344B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an electronic pressure sensor that converts mechanical pressure into an electrical signal using a piezoelectric element.

[Prior art]

Mechanical pressure sensors using Bourdon tubes, bellows, or diaphragms have been widely used in the past, but these pressure sensors
It has disadvantages such as having many mechanically moving parts, poor reliability and short lifespan, large volume and weight, which are often inconvenient for mounting, high cost, poor accuracy, and slow response speed.

On the other hand, in recent years, electronic pressure sensors have been researched and developed that utilize pressure-induced resistance changes in metal thin films, the piezoresistance effect of semiconductors, or the piezoelectric effect of insulators. Excellent pressure sensors that do not have this type of pressure are now being used in various fields. For example, pressure sensors that use the piezoresistance effect of Si can be manufactured from Si wafers, so batch processing is possible, and mass production is expected to reduce costs. Moreover, since it can be made small, it can be implemented even in a fairly narrow place. Furthermore, by integrating peripheral circuits on the same substrate, space for peripheral circuits can also be freed up. Furthermore, since Si is not easily attacked by anything other than strong acids and strong alkalis, it has the advantage of being less prone to malfunctions due to corrosion or malfunctions due to adhesion of dust.

A more important advantage of electronic pressure sensors is that they convert pressure directly into electrical signals, making them much more compatible with computer control or automatic measurement. For example, a pressure sensor using Si piezoresistance is
It is being incorporated into engine control systems linked to microprocessors as sensors for measuring negative air intake pressure and differential pressure for ignition timing control in automobiles. Further, a medical diagnostic system using a pressure sensor using a piezoelectric element as a detector for Korotkoff sounds for blood pressure measurement and fetal heart sounds has been prototyped. However, from now on,
These conventional electronic pressure sensors do not have sufficient potential for distribution measurement and sensor intelligent functions, which are important in fields such as computer control and automatic measurement. These functions can be realized by arraying pressure sensors, but with currently known electronic pressure sensors, arraying is either difficult or unavoidably increases the cost significantly. There are many things. For example, in a silicon diaphragm pressure sensor that utilizes the silicon piezoresistance effect, a diaphragm with a thickness of about 20 to 50 μm is formed by etching the back side of a silicon wafer. is extremely difficult, making integration nearly impossible. Furthermore, even if this could be done, the yield would be poor and the cost would be extremely high.

To give another example, a configuration of a piezoelectric polymer sheet and a printed wiring board has been proposed as a well-known integrated pressure sensor (Kitayama, Ueda, Sato, Namiki, "Piezoelectric printed circuit board (1)", "Showa 1951 National Conference of the Institute of Electronics and Communication Engineers, Paper No. 223, March 1976).
This pressure sensor can easily be made into a large area and its production cost is low, but as the number of integrated pressure sensor units increases, the S/N ratio drops rapidly, making it impossible to increase the degree of integration. .

〔the purpose〕

The purpose of the present invention is to realize many of the advantages of the electronic pressure sensor described above, to realize further lower costs, and to easily realize a high-density integration, large-area pressure sensor array with an excellent S/N ratio. It is an object of the present invention to provide a pressure sensor that can be tightened.

The pressure sensor of the present invention includes a field effect transistor element having a semiconductor layer provided in a matrix, and a gate electrode provided on the semiconductor layer via a gate insulating layer; A scanning device in which a plurality of unit elements each having a pair of electrodes coupled to each other and a piezoelectric element having a piezoelectric thin film provided between the electrodes are connected to the source (or drain) of the field effect transistor element. a parallel output signal line to which the drain (or source) of the field effect transistor element is connected, a shift register for matrix scanning connected to the scanning line, and a parallel output signal line connected to the parallel output signal line. a shift register for parallel-to-serial conversion, and an insulating layer for preventing crosstalk provided at least at the intersection of the scanning line and the parallel output signal line as a gate insulating layer of the field effect transistor element. It is characterized by the fact that it also serves as

The pressure sensor of the present invention has an equivalent circuit as shown in FIG. 1 as its basic circuit. In Figure 1,
101, 102, and 103 are terminals for electrical connection, 104 is a piezoelectric element, and 105 is a field effect transistor.

Normally, terminal 101 is at ground level, and terminal 10
2 connects to the power supply. The piezoelectric element 104 is polarized by externally applied pressure and raises (or lowers) the potential of the gate electrode of the field effect transistor element 105. When this potential becomes just above (or below) the threshold voltage V _t of the field effect transistor element 105, the drain current I _d is output from the output terminal 103 (or the output stops). The piezoelectric element 104 generates a voltage directly proportional to the applied pressure over a suitable pressure range;
Furthermore, by selecting the drain voltage V _d in the range of (V _g −V _t )>V _d in the field effect transistor element 105, the gate voltage and the drain current I _d are proportional to each other, and as a result, the voltage is proportional to the pressure input. It is possible to obtain a drain current I _d of the same magnitude. Therefore, although the pressure sensor according to the present invention is capable of measuring analog quantities with high precision, it is obvious that it can be applied to, for example, a keyboard as a simple pressure-sensitive switch. be.

Furthermore, in the pressure sensor according to the present invention,
Since the output of the piezoelectric element 104 is directly input to the gate electrode of the high-resistance field effect transistor element 105, it is possible to achieve good impedance matching, a wide operating frequency range, and a good S/N ratio.

[Example of implementation]

Hereinafter, the present invention will be explained using the drawings. Note that the present invention will be explained using a thin film field effect transistor element (hereinafter referred to as a TFT element) and a piezoelectric thin film as an example.

FIGS. 2 to 4 are diagrams for explaining a first preferred embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of this embodiment, FIGS. 3a to 3e are schematic diagrams showing the steps of manufacturing the pressure sensor of this embodiment shown in FIG. The figure is a schematic cross-sectional view showing a modification of this embodiment.

In FIG. 2, 201 is a substrate, 202 and 2
04 is an electrode, and 203 is a piezoelectric thin film. 205
and 207 are a source electrode and a drain electrode of the TFT (if 205 is a drain electrode, 207 is a source electrode), 206 is a semiconductor layer, and 208 is an insulating layer.

The substrate 201 serves as a common support substrate for the thin film piezoelectric element and the TFT element. The substrate 201 is an inorganic insulating material such as a fused quartz plate, a sapphire substrate, a silicon wafer whose surface is thermally oxidized, various glass plates, or an insulating material made of a polymeric material such as polyimide, polyethylene terephthalate, polyethylene naphthalate, or polycarbonate. Film can be used. When the polymer material is flexible, the amount of deformation of the piezoelectric thin film increases, making it possible to obtain a pressure sensor with even higher sensitivity.

The thin film piezoelectric element includes a piezoelectric thin film 203 and electrodes 202 and 2 provided to sandwich this from above and below.
Consists of 04. Examples of the piezoelectric thin film 203 include zinc oxide (ZnO), aluminum nitride (AN), lead zirconate titanate solid solution (PZT),
Alternatively, materials such as zircon lanthanum lead titanate solid solution (PLZT), quartz, etc. can be used.

These materials can be deposited on the substrate surface by means such as DC sputtering, high frequency sputtering, and reactive sputtering.

When zinc oxide (ZnO) was used as the piezoelectric thin film, the thin film could be formed at a relatively low substrate temperature of around 200°C by using the high-frequency sputtering method. It is desirable that the piezoelectric thin film 203 in the present invention has as high a resistivity and a piezoelectric constant as possible. In this example, high resistance ZnO was used as the target material.
By using the sintered body, we were able to form a thin film with a resistivity of 10 ¹⁰ Ω·cm or more. Moreover, at the same time, it was also possible to form a thin film with relatively well-aligned C-axis orientation.

The TFT element has an electrode 204 (this corresponds to a gate electrode), a drain (or source) electrode 205,
Source (or drain) electrode 207, semiconductor layer 2
06, an insulating layer 208. semiconductor layer 2
Materials such as amorphous silicon, polycrystalline silicon, cadmium sulfide, cadmium selenium, tellurium zinc oxide, gallium arsenide, etc. can be used for 06. These materials can be produced using deposition methods such as chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PCVD), electron beam thermal evaporation, sputtering, reactive sputtering, and molecular beam epitaxy (MBE). It can be formed by using a post-deposition annealing method such as a plasma annealing method, a laser annealing method, an electron beam annealing method, a furnace heating annealing method, etc., which are adopted as necessary. The gate insulating layer 208 is made of a material such as silicon dioxide, silicon nitride, or aluminum oxide, and these materials can be formed using a thermal oxidation method, a sputtering method, a reactive sputtering method, a chemical vapor deposition method (CVD), or a plasma chemical vapor deposition method. It can be formed by depositing using a method such as a growth method (PCVD) or an electron beam heating evaporation method.

This embodiment will be explained in more detail using the schematic process diagrams shown in FIGS. 3a to 3e. The numbers with dashes attached to the respective parts in FIGS. 3a to 3e correspond to the numbers without dashes in FIG. 2, respectively.

Corning #7059 glass (trade name; manufactured by Corning Inc.) was used for the substrate 201', and amorphous silicon (hereinafter referred to as a-Si) was used for the semiconductor layer 206'. The a-Si thin film is produced by introducing a mixed gas of silane gas (SiH ₄ ), which is a raw material gas, and hydrogen gas (H ₂ ) into the vacuum chamber of a plasma chemical vapor deposition (PCVD) device and adjusting the gas pressure to about 0.12 torr. The film was deposited on the substrate 201' by maintaining the temperature and applying high-frequency power of appropriate strength to generate glow discharge in the vacuum chamber. At this time, the mixing ratio of silane gas (SiH ₄ ) and hydrogen gas (H ₂ ), which are the raw material gases, can be any ratio in the range of 1:10 to 1:0, although there are differences in degree. , we were able to obtain the minimum required transistor characteristics. Further, it is desirable that the substrate temperature is about 150 to 300°C. Patterning of the semiconductor layer 206' could be performed using mask vapor deposition or etching with a hydrofluoric acid solution. Note that the typical thickness of the semiconductor layer 206' made of a-Si is 500 Å to 5000 Å (step (a)).

Next, the electrode 202' and the source or drain electrodes 205' and 207' of the TFT are formed by a common electrode forming method in the manufacture of semiconductor devices, such as vacuum deposition followed by etching. (Step (b)).

After that, an insulating layer 208' was formed.
Silicon nitride was used for the insulating layer 208'.
Silicon nitride is produced by introducing a mixture of silane gas (SiH ₄ ) and hydrogen gas (H ₂ ) and ammonia gas (NH ₃ ) as raw material gases into the vacuum chamber of a plasma chemical vapor deposition (PCVD) device, and controlling the gas pressure. A desired insulating layer could be formed by maintaining the temperature at about 0.1 Torr and applying high-frequency power of appropriate strength to generate glow discharge in the vacuum chamber. At this time, the temperature of the substrate was maintained at approximately 150 to 300°C. Patterning of the insulating layer 208' could be performed by mask vapor deposition or etching with a hydrofluoric acid solution. The typical thickness of the thin silicon nitride layer is 1000-5000 Å (step (c)).

After this, a piezoelectric thin film 203' and an electrode 204' are formed.
6' and the insulating layer 208' are composed of the a-Si and silicon nitride formed by the plasma chemical vapor deposition (PCVD) method, in the subsequent steps It is not desirable to maintain the substrate at a temperature exceeding 150 to 300° C. when forming a thin film.

Therefore, in this embodiment, this limiting condition could be satisfied by using zinc oxide (ZnO) as the piezoelectric thin film 203'. When sputtering was performed using a zinc oxide (ZnO) sintered body as a target while maintaining the substrate temperature at around 200°C, it was possible to obtain a piezoelectric thin film 203' with good C-axis orientation and high resistivity. (Step (d)).

Finally, an electrode 204', which will serve as the gate electrode of the TFT element and one electrode of the thin film piezoelectric element, was formed by vapor deposition (step (e)).

Although the pressure sensor was fabricated as described above, a protective film may be further provided thereon if necessary.

Similarly, in the case where the semiconductor layer 20 of the TFT element is made of polycrystalline silicon, the manufacturing process of the pressure sensor will be explained using FIGS. 3a to 3e.

FIG. 3a illustrates a semiconductor layer 206' deposited on a suitable substrate 201', such as a Corning 7059 glass or fused silica plate, the semiconductor layer being polycrystalline silicon.
A mixed gas of silane gas (SiH ₄ ) and hydrogen gas (H ₂ ), which is a raw material gas, is introduced into the vacuum chamber of a plasma chemical vapor deposition (PCVD) device, and the gas pressure is increased.
It was deposited on the substrate 201' by maintaining the temperature at about 0.05 Torr and applying high frequency power of appropriate strength to generate glow discharge in the vacuum chamber. At this time, it is desirable that the mixing ratio of the raw material gases, silane gas (SiH ₄ ) and hydrogen gas (H ₂ ), be at a volume ratio of about 1:100. Also, the substrate temperature is 450℃
The temperature was set to ~600℃. The desirable thickness of the semiconductor layer 206' made of polycrystalline silicon is 2000 to 5000 Å.
It was hot.

Patterning of the semiconductor layer 206' could be performed using etching using a hydrofluoric acid solution.

FIG. 3b shows that as the next step, the electrode 202' and the TFT source or drain electrode 205',
207' is shown formed by the same process.

FIG. 3c illustrates the formation of an insulating layer 208 as the next step. Insulating layer 2
The material of 08' is deposited on amorphous silicon in the embodiment described above, and a silicon nitride film can be formed under exactly the same conditions as in the embodiment described above. However, as already mentioned, when the semiconductor layer 206' is a polycrystalline silicon film formed at a relatively high substrate temperature of 450° C. to 600° C., a so-called plasma anodic oxide film can be used. Plasma anodic oxide film is produced by introducing oxygen gas into the vacuum chamber of a plasma chemical vapor deposition (PCVD) device to a pressure of approximately 0.1 Torr, and then applying high-frequency power of appropriate strength to create a glow discharge in the vacuum layer. In addition, approximately
This could be obtained by applying a voltage of 30V to oxidize the surface of the polycrystalline silicon layer. The substrate temperature at this time was maintained at 500 to 600°C. Insulating layer 20
Patterning of 8' could be performed by etching with a hydrofluoric acid solution. The typical thickness of the thin silicon oxide layer is 500-3000 Å.

FIG. 3d shows the thin film piezoelectric element formed. When zinc oxide (ZnO) is used as the piezoelectric thin film 203', sputtering is performed using a sintered body of zinc oxide (ZnO) as a target while maintaining the substrate temperature at around 200°C. Piezoelectric thin film 203' with excellent resistance and high resistivity
was able to obtain it.

A mixed gas of argon gas and oxygen gas is used as the atmospheric gas in the spatsuta, and the gas pressure is
Approximately 10 ^-3 to ^{10 -2} Torr was good.

FIG. 3e shows the formation of an electrode 204' as the next step. Electrode 204'
In this case, the gate electrode of the TFT element and one of the thin film piezoelectric elements are formed in the same process. In Figure 3e,
Although the pressure sensor process is completed, a protective film may be further provided thereon if necessary.

The TFT element in Fig. 2 has a so-called coplanar structure (electrode 2 serves as a source or drain electrode).
05, the electrode 207, and the electrode 204 are the semiconductor layer 2
06), but has a staggered structure as shown in FIG.
and the electrode 403 is connected to the semiconductor layer 405 and the insulating layer 407.
It is also possible to have a structure on the opposite side with the two in between.

In the configuration shown in FIG. 2, in the electrode 204,
A thin film piezoelectric element and a TFT element are electrically coupled. In the example embodiment shown in FIGS. 2 and 4,
By applying pressure to the thin film piezoelectric element portion from above, a polarized potential in the vertical direction is generated, and this voltage is applied to the electrode 204 or the electrode 403. In the configurations shown in FIGS. 2 and 4, if the polarization of the piezoelectric thin film 203 and the piezoelectric thin film 402 are the same, the electrodes of the configuration shown in FIG. 4 will respond to pressure applied from the same direction. 403 can be applied with a voltage of opposite polarity to that of the electrode 204 having the configuration shown in FIG. (By forming the pressure sensor shown in Fig. 2 and the pressure sensor shown in Fig. 4 on the same substrate and electrically connecting them, another pressure sensor with a new function can be constructed. (Also possible.) FIG. 5 is a schematic cross-sectional view for explaining the second embodiment of the present invention. In Figure 5, 5
01 is a substrate, 502 and 509 are electrodes for thin film piezoelectric elements, and 503 is a piezoelectric thin film. 504
is the gate electrode of TFT, 505 and 507 are TFT
506 is a semiconductor layer, and 508 is an insulating layer.

In this embodiment, two electrodes 202 and 204 for detecting the polarization potential of the piezoelectric thin film 203 are configured to vertically sandwich the piezoelectric thin film 203 as shown in FIG. 2 in the first embodiment. In contrast,
This embodiment differs from the first embodiment in that two electrodes 502 and 509 are configured to sandwich a piezoelectric thin film 503 laterally.

A pressure sensor configured as in this embodiment example is
To obtain a pressure sensor with high sensitivity when using a piezoelectric thin film that exhibits greater polarization in a direction perpendicular to the pressure input from above or below, that is, in a direction parallel to the substrate surface. was completed.

Further, in the configuration shown in FIG. 5, the piezoelectric thin film 50
The electrodes 502 and 509 sandwiching the thin film piezoelectric element can be avoided without shorting through the pinhole 3, and without increasing the thickness of the thin film piezoelectric element.
It was possible to increase the resistance between the two, and therefore, it was also possible to obtain a high polarization potential.

In the configuration shown in FIG. 5, the TFT element has a coplanar structure, but it is clear that it can have a staggered structure as shown in FIG.

FIG. 6 is a schematic cross-sectional view for explaining a third embodiment of the present invention. In Fig. 6, 601 is a substrate, and 606 is a piezoelectric thin film/TFT.
The insulating layer 602 at the gate of the element is one electrode of the thin film piezoelectric element. 603 and 605 are source electrodes or drain electrodes of the TFT elements, respectively, and 604 is a semiconductor layer.

In this embodiment example, as shown in FIG.
The insulating layer of the gate of the TFT element is composed of a piezoelectric thin film. Therefore, it is no longer necessary to form the gate insulating layer and the piezoelectric thin film separately, so that the manufacturing process can be shortened. Further, according to the configuration of this embodiment, it was possible to further increase the packaging density.

A fourth embodiment of the present invention will be described using FIGS. 7 to 9a and 9b. This example is an embodiment of a pressure sensor array using pressure sensors according to the present invention.

7 is an equivalent circuit diagram of this embodiment, FIG. 8 is a diagram showing a drive timing chart of this embodiment, FIG. 9a is a schematic partial plan view, and FIG. 9b is a diagram of FIG. 9a. 9 is a schematic cross-sectional partial view taken when FIG. 9a is cut along the dashed line A-A' shown in FIG.

In FIG. 7, 4 _1-1 to 4 _no are thin film piezoelectric elements, 5 _1-1 to 5 _no are TFT elements, and 701 _1-1 to 70
1 _no is a unit element, and 704 _-1 to 704 _-o are storage capacitors. 702 _-1 to 702 _-n are scanning lines,
703 _-1 to 703 _-o are parallel output signal lines, 70
5 is a shift register for matrix scanning, 70
6, 708, and 710 are clock lines, respectively. 7
07 is a transfer gate, 709 is a shift register for parallel-to-serial conversion, and 711 is a serial output line.

Unit element of pressure sensor 701 _1-1 ~ 701 _no
has a structure in which a thin film piezoelectric element and a TFT element are electrically coupled, and these unit elements 701 _1-1 to 70
1 _no are arranged in a matrix on the board. The source (or drain) and drain (or source) of the TFT element of each unit element are connected to a scanning line and a parallel output signal line, respectively.

The shift register 705 is synchronized with a clock line 706 and sends scanning pulse signals to scanning lines 702 _-1 to 702 .
702 Output to _-n . The transfer gate 707 is synchronized by a transfer gate clock line 708, and is used to time the signals on the parallel output signal lines _703-1 to 703 _-o to be taken into the shift register 709.

The shift register 709 is a shift register for converting the n parallel signals outputted to the parallel output signal lines 703 _-1 to 703 _-o into serial signals, and is synchronized by the clock line 710, and the serial signals are output as serial signals. It is output from line 711.

Next, the operation of the pressure sensor array shown in the equivalent circuit diagram of FIG. 7 will be explained using FIG. 8.

It is now assumed that mechanical pressure is applied to each unit element arranged within the substrate, and that a polarization voltage of the piezoelectric thin film corresponding to this pressure is applied to the gate electrode of the TFT element 5. Therefore, place it within the board.
The TFT element has a channel conductance that depends on pressure.

First, when the scanning line _17-1 goes to a high level during period _t1 , a channel is established in the n TFT elements _51-1 to _51-o connected to the scanning line _17-1 .
A drain current I _d flows according to the conductance,
The signals are stored in storage capacitors 704 ₁ to 704 _o , respectively. At this time, if t ₁ is sufficiently smaller than the time constant determined by the channel conductance and the storage capacitor capacity, a charge proportional to the mechanical pressure applied to each unit element can be stored.

The data stored in storage capacitors _704-1 to 704 _-o is transferred to transfer gate 707 at the end of period _t1 .
(signal φ _T of clock line 708
becomes high level), the signal is taken into the shift register 709. Next, transfer gate 70
7 closes (φ _T becomes Low-Level) and enters the next instantaneous period t ₂ . In period _t2 , the scanning line _702-2 becomes high level, and the scanning line _702-2
A drain current corresponding to the channel conductance flows through the n TFT elements 5 _2-1 to 5 _2-o connected to the channel conductance, and is stored in the storage capacitors 704 _-1 to 704 _-o . On the other hand, the data in the shift register 709 that has already been taken in is sequentially transferred in synchronization with the signal φ ₁ on the clock line 710, and is sequentially output from the output line 711 as a serial signal. At the same time as all the data in the shift register 709 is output, the transfer gate 707 is opened and the output signals from the unit elements 701 _2-1 to 701 _2-o are sequentially taken into the shift register 709.

Hereinafter, by repeating the same process, all the unit elements 701 of the pressure sensors distributed in a matrix are
Signals from _1-1 to 701 _no can be extracted as serial signals.

9a and 9b are schematic configuration diagrams of the pressure sensor array shown in the equivalent circuit diagram of FIG. 7, respectively.
FIG. 9b shows a schematic partial cross-sectional view taken along line A-A' in FIG. 9a.

906 is a semiconductor layer patterned into an island shape of a TFT element, 905 and 907 are a source (or drain) electrode and a drain (or source) electrode, respectively, and 904 is a gate electrode of a TFT element and an electrode of a thin film piezoelectric element. This layer also serves as a layer. Further, 910 is a scanning line, 914 is a parallel output signal line, and 913 is a ground line for applying a ground level to one electrode of the thin film piezoelectric element. Reference numeral 909 is an insulating layer for preventing crosstalk between the scanning line 910 and the ground line 913. The electrode that should provide the ground level of the thin film piezoelectric element is connected to a ground line 913 through a through hole 912 made in the insulating layer 909.
connected to. 918 is a gate insulating layer of the TFT element, which also serves as an insulating layer for preventing crosstalk between the scanning line 910 and the parallel output signal line 914.
It may be provided over the entire surface of the substrate, or it may be provided in an island shape at a necessary portion. A drain electrode (or source electrode) 907 is connected to a scanning line 910 through a through hole 911 formed in an insulating layer 908. Source electrode (or drain electrode) 905 is directly connected to parallel signal line 914. 903 is a piezoelectric thin film patterned into an island shape for each unit element. The piezoelectric thin film of each unit element may be connected to each other instead of being patterned into an island shape, but in this case, the mechanical pressure applied to a particular unit element is It propagates through the piezoelectric thin film as mechanical vibration, and tends to cause crosstalk to surrounding unit elements. Therefore, generally the piezoelectric thin film 9
03 is preferably separated for each unit element.

Materials for the substrate 901 include a fused quartz plate, a sapphire substrate, a silicon wafer whose surface is thermally oxidized,
Inorganic insulating materials such as various glass substrates, insulating films made of organic polymer materials such as polyimide, polyethylene, terephthalate, polyethylene naphthalate, polycarbonate, etc., as well as aluminum plates and steel plates, provided that an insulating layer 909 is provided. , metal plates such as iron plates, nickel plates, and stainless steel plates can be used. When a metal plate is used as the substrate, a ground level is applied to the substrate 901, and the piezoelectric thin film 9 is connected through the through hole 912.
By directly connecting the electrode 902 of 03 to the substrate 901, the ground wire 913 can be omitted.

As the piezoelectric thin film 903, zinc oxide (Zn0),
Materials such as aluminum nitride (AN), lead zircon titanate solid solution (PZT), zircon lanthalate lead titanate solid solution (PLZT), and crystal are used, and these materials can be processed by direct current sputtering method, high frequency sputtering method,
It can be deposited on the substrate surface by means such as chemical vapor deposition (CVD) or reactive sputtering.

The semiconductor layer 11 of the TFT element is made of amorphous silicon, polycrystalline silicon, cadmium sulfide (CdS), cadmium selenium (CdSe), tellurium (Te), zinc oxide (Zn0), gallium arsenide (GaAs).
These materials include chemical vapor deposition (CVD), plasma chemical vapor deposition (PCVD), electron beam heated evaporation, various sputtering methods,
Formed by a deposition method such as molecular beam epitaxial (MBE) method, and a post-deposition annealing method such as plasma annealing method, laser annealing method, electron beam annealing method, furnace heating annealing method, etc. adopted as necessary. .

Materials such as silicon dioxide, silicon nitride, and aluminum oxide are used for the gate insulating layer 908, and these materials can be processed by thermal oxidation, various sputtering methods, electron beam heated evaporation, chemical vapor deposition (CVD), and plasma. Deposited using methods such as chemical vapor deposition (PCVD).

As is clear from the equivalent circuit diagram in FIG. 7, this embodiment, which is a pressure sensor array using the pressure sensor according to the present invention, has a TFT element having a crosstalk prevention function and a signal amplification function for each unit element. is provided, so crosstalk is extremely low.
It was possible to provide a pressure sensor array with an excellent S/N ratio.

Therefore, by using the pressure sensor according to the present invention, it is possible to realize a large-area pressure sensor array with a high degree of integration in which a large number of pressure sensor unit elements are mounted on the same substrate.

For example, a case where hydrogenated amorphous silicon is used for the semiconductor layer of a TFT element of a pressure sensor, and silicon nitride or silicon dioxide is used for the insulating layer will be described in detail.

The semiconductor layer is formed by plasma chemical vapor deposition (PCVD) using a mixed gas of silane gas (SiH ₄ ) and hydrogen gas (H ₂ ) as a raw material gas at a gas pressure of 0.1 Torr and a substrate temperature of about 150 to 300°C. Hydrogenated amorphous silicon (a-Si:H) was deposited.

Next, a mixed gas of silane gas and hydrogen gas and ammonia gas (NH ₃ ) are used as raw material gas,
Silicon nitride was deposited on the semiconductor layer by plasma chemical vapor deposition while maintaining the gas pressure at 0.1 Torr and the substrate temperature at approximately 150 to 300°C.

In addition, a mixed gas of silane gas and hydrogen gas and oxygen gas (O ₂ ) are placed on another semiconductor layer as raw material gases.
, gas pressure 0.1Torr, substrate temperature 150~300℃
Silicon dioxide was deposited by plasma enhanced chemical vapor deposition at a constant temperature.

Note that the electrodes were formed using a method generally used for manufacturing TFT devices.

Silicon dioxide as an insulating layer with a thickness of approximately 1000-5000Å
The drain current I _d of a TFT device deposited to a film thickness of
The ON/OFF ratio of is about 6 orders of magnitude at a gate voltage of about 10 volts.

Therefore, if the required S/N ratio was 40 decibels, this TFT element could drive about 10,000 scanning lines.

Even when silicon nitride was used as the insulating layer, the TFT device had performance comparable to that when silicon dioxide was used.

〔effect〕

As described above in detail, according to the present invention, it is possible to realize a pressure sensor with high accuracy and fast response speed, which solves the problems of conventional pressure sensors. In addition, a pressure sensor that is low cost, easy to integrate, and easy to form into a large area matrix array can be realized.

Although the embodiments and examples of the present invention are described using thin film field effect transistors and thin film piezoelectric elements, it is of course possible to carry out the invention without using thin film transistors. be.

[Brief explanation of the drawing]

FIG. 1 is a basic equivalent circuit diagram of the present invention. FIGS. 2 to 4 are diagrams for explaining embodiment example 1 of the present invention, FIG. 2 is a schematic cross-sectional view, and FIG. 3 a
3e to 3e are schematic process diagrams for producing Example 1, and FIG. 4 is a schematic cross-sectional view showing a modification of Example 1. FIG. 5 is a schematic cross-sectional view for explaining the second embodiment of the present invention, and FIG. 6 is a schematic cross-sectional view for explaining the third embodiment of the present invention. 7 to 9a and 9b are diagrams for explaining the fourth embodiment of the present invention, in which FIG. 7 is an equivalent circuit diagram, FIG. 8 is a drive timing chart,
FIG. 9a is a schematic partial plan view, and FIG. 9b is a schematic partial cross-sectional view taken along the dashed line A-A' shown in FIG. 201, 201', 401, 501, 601,
901...Substrate, 203, 203', 402, 5
03,606,903...Piezoelectric thin film, 206,
206', 405, 506, 604, 906...
semiconductor layer, 208, 208', 407, 508,
906, 908...Insulating layer, 205, 207, 2
05'207',404,406,505,50
7,603,605,905,907...TFT
Source or drain electrode of the device.

Claims (1)

[Scope of Claims] 1. A field effect transistor element having a semiconductor layer provided in a matrix and a gate electrode provided to the semiconductor layer via a gate insulating layer; a plurality of unit elements comprising a pair of electrodes coupled to each other and a piezoelectric element having a piezoelectric thin film provided between the electrodes, and a scanning element in which the source (or drain) of the field effect transistor element is connected. a parallel output signal line connected to the drain (or source) of the field effect transistor element, a shift register for matrix scanning connected to the scanning line, and a parallel output signal line connected to the parallel output signal line. a shift register for parallel-to-serial conversion, and an insulating layer for preventing crosstalk provided at least at an intersection of the scanning line and the parallel output signal line as a gate insulating layer of the field effect transistor element. A pressure sensor that is characterized by having the following functions: 2. The pressure sensor according to claim 1, wherein the piezoelectric thin film is separated into each unit element.