JPH08285714A - Capacitive pressure sensor - Google Patents

Abstract

PURPOSE: To obtain a pressure sensor substantially unsusceptible to the humidity. CONSTITUTION: The capacitive pressure sensor comprises a diaphragm 1 made of an electric insulating material provided with a first electrode 4 on the surface thereof, a fixed substrate 2 made of an electric insulating material provided with a second electrode 5 on the surface thereof, an adhesive layer 3 for bonding the diaphragm 1 and the fixed substrate 2 at the outer circumferential parts of the electrodes 4, 5 while being sandwiched between them, and a waterproof layer 6 provided on the outer surface of the diaphragm 1, the fixed substrate 2 and the adhesive layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type pressure sensor for converting a pressure change into a capacitance change of an electrode provided on a diaphragm and further converting it into an electric output.

[0002]

2. Description of the Related Art A conventional capacitance type pressure sensor takes advantage of the fact that the change in the dielectric constant of air due to temperature is small, and the diaphragm is deformed by the pressure to change the distance between the electrodes, which causes static electricity between the electrodes. It utilizes the fact that the capacitance changes. In particular, a capacitive pressure sensor in which a metal thin film electrode is formed on the side opposite to the diaphragm pressure receiving surface is generally known, but a bimetal action occurs due to the difference in thermal expansion coefficient between the diaphragm and the electrode, and the capacitance changes depending on the temperature. There was a problem. In order to improve this, as shown in FIG. 5, a dummy electrode made of a metal thin film 7 having substantially the same material and substantially the same material as the metal thin film electrode 4 is formed on the pressure receiving surface of the diaphragm 1 to form a temperature dependence of the capacitance. Was reduced (Japanese Patent Laid-Open No. 61-99383).
Issue).

[0003]

However, the above-mentioned structure has the following problems. That is, in the conventional capacitance type pressure sensor having the dummy electrode, the bimetal action due to the difference in thermal expansion coefficient between the diaphragm 1 made of ceramics and the electrodes 4a, 4b is reduced, so that it is effective for the temperature characteristic, but the small pressure is applied. If the diaphragm 1 is made thin to detect the temperature, when it is kept in a high-humidity environment for a long time, it becomes easy for water vapor to pass through due to pores and defects in the ceramics, which makes it very susceptible to humidity and other factors. The rate was easy to change. In other words, in the conventional element, since the metal thin films 7a and 7b having substantially the same outer shape as the electrodes 4a and 4b are formed on the diaphragm pressure receiving surface made of thin ceramics such as alumina, dew condensation occurs on the portion where the electrodes are not formed. When water vapor adheres due to the influence of, the water vapor may penetrate into the thin ceramic diaphragm 1 and reach the inside of the sensor. Therefore, there is a problem in that the output capacitance changes greatly.

FIG. 6 shows a conventional pressure sensor element of about 90-9.
The capacity value after standing for about 60 hours in a high humidity condition of 5% RH is shown using the plate thickness as a parameter. For the sensor element at this time, a diaphragm 1 made of 96% alumina and a fixed substrate 2 are prepared, and gold diaphragm is screened on the diaphragm 1 and the fixed substrate 2 as the first electrodes 4a and 4b and the second electrodes 5a and 5b, respectively. It was formed to a thickness of 0.1 μm by a printing method. Further, a gold resinate, which is the same material as the first electrode 4, was formed on the surface opposite to the surface on which the first electrode 4 was formed in a shape substantially the same as that of the first electrode 4. Next, with the first electrode 4 and the second electrode 5 arranged so as to face each other, the adhesive layer 3
Joined together. Further, the thickness of this diaphragm 1 was changed to 0.15 to 1.0 mm. From this result, in the conventional element, the thickness of the diaphragm 1 is about 0.8 mm.
Since then, the capacity has increased rapidly. That is, since the smaller the thickness of the diaphragm 1 is, the larger the change in capacitance is, it is considered that dew condensation occurs on the surface of the diaphragm 1 due to the influence of humidity and the water vapor permeates into the inside of the diaphragm 1. Therefore, the conventional pressure sensor is easily affected by humidity, and this tendency is strong especially for the thin diaphragm 1 having a thickness of 0.8 mm or less.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a structure which is not easily affected by humidity, that is, dielectric constant.

[0006]

In order to solve the above-mentioned problems, the capacitance type pressure sensor of the present invention has the following constitution.

That is, a diaphragm having a first electrode formed on the surface thereof, a fixed substrate having a second electrode formed on the surface thereof, and the first electrode and the second electrode arranged to face each other. An adhesive layer for holding and adhering the diaphragm and the fixed substrate at a constant interval on the outer peripheral portion of the above, and a waterproof layer on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer.

Further, a diaphragm made of alumina having a thickness of less than 0.8 mm and having a first electrode formed on the surface, a fixed substrate having a second electrode formed on the surface, the first electrode and the first electrode An adhesive layer that is disposed so as to face two electrodes and that holds the diaphragm and the fixed substrate at a constant interval at the outer peripheral portion of the electrode and adheres them, and a waterproof layer on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer. It was configured with.

A diaphragm made of alumina having a first electrode formed on the surface and having a thickness smaller than 0.8 mm, a fixed substrate having a second electrode formed on the surface, the first electrode and the first electrode An adhesive layer that is disposed so as to face two electrodes and that holds the diaphragm and the fixed substrate at a constant interval at the outer peripheral portion of the electrode and adheres them, and a metal thin film on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer. , A ceramics or a hydrophobic resin layer is provided.

Further, a diaphragm having a first electrode formed on the surface thereof, a fixed substrate having a second electrode formed on the surface thereof, and the first electrode and the second electrode arranged to face each other. An adhesive layer for holding and adhering the diaphragm and the fixed substrate at a constant distance at the outer peripheral part of the device, an element having a waterproof layer on at least the outer surface of the diaphragm, the fixed substrate and the adhesive layer, and caused by a pressure change Also, a conversion means for converting a capacitance change between the diaphragm and the fixed substrate into an electric signal is provided.

A diaphragm made of alumina having a thickness of less than 0.8 mm and having a first electrode formed on the surface, a fixed substrate having a second electrode formed on the surface, the first electrode and the first electrode An adhesive layer that is disposed so as to face two electrodes and that holds the diaphragm and the fixed substrate at a constant interval at the outer peripheral portion of the electrode and adheres them, and an adhesive layer on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer. And a conversion means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal.

Further, the first electrode is formed on the surface of the diaphragm made of alumina having a thickness smaller than 0.8 mm, the fixed substrate having the second electrode formed on the surface, the first electrode and the first electrode. An adhesive layer that is disposed so as to face two electrodes and that holds the diaphragm and the fixed substrate at a constant interval at the outer peripheral portion of the electrode and adheres them, and a metal thin film on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer. , A device provided with a layer of ceramics or a hydrophobic resin, and a conversion means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal.

[0013]

The pressure sensor of the present invention has the following actions due to the above configuration.

That is, by forming a waterproof layer on at least the outer surface of the diaphragm, the fixed substrate and the adhesive layer,
It is possible to realize a pressure sensor that prevents moisture from penetrating due to the influence of dew condensation and is not affected by humidity, that is, the dielectric constant.

Moreover, if the diaphragm thickness is reduced to increase the sensitivity, the water permeability also increases. However, by forming the waterproof layer on at least the outer surface of the diaphragm pressure receiving surface, the sensitivity remains high and humidity is maintained. It has become possible to make it less susceptible.

Further, since the bimetal effect can be reduced by forming the waterproof layer on the surface opposite to the first electrode, it is possible to reduce the influence of temperature at the same time.

Further, a capacitance type pressure sensor which is not affected by humidity, that is, a dielectric constant is provided by providing a conversion means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal. Easy to use and widely used.

Further, by providing the pressure sensor having high sensitivity and being hardly influenced by humidity with the converting means for converting the capacitance change into the electric signal, the pressure sensor having high sensitivity and not being easily influenced by humidity can be used easily and widely. it can.

Further, by providing the pressure sensor capable of reducing the bimetal effect with the converting means for converting the capacitance change into the electric signal, the pressure sensor which hardly causes the bimetal effect can be used easily and widely.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the capacitance type pressure sensor according to the present invention, in which the same components as those in the conventional example are designated by the same reference numerals.

As shown in FIG. 1, a diaphragm 1 made of an electrically insulating elastic material having a first electrode 4 formed on the surface thereof.
And a fixed substrate 2 made of an electrically insulating material having a second electrode 5 formed on the surface thereof, the first electrode 4 and the second electrode 5 are arranged to face each other, and the diaphragm is provided on the outer peripheral portion of the electrode. An adhesive layer 3 for adhering 1 to the fixed substrate 2 and a waterproof layer 6 are formed on the outer surfaces of the diaphragm 1, the fixed substrate 2 and the adhesive layer 3. Here, the measurement electrodes 4a and 5a and the reference electrodes 4b and 5b are used as the first electrode 4 and the second electrode 5, respectively. The measurement electrodes 4a, 5a and the reference electrodes 4b, 5b are used to prevent a change in the sensor characteristics due to a change in the distance between the electrodes due to a disturbance such as a temperature change. Zero shift and span shift can be eliminated by calculating and compensating for the storage capacity.

The capacitance C, which is the output of the capacitance type pressure sensor, is represented by C = εAX ^-1 (where A is the electrode area, ε is the dielectric constant, and X is the electrode spacing), and the electrode spacing is The smaller the size, the larger the capacity. Further, dC / dX = −εAX ⁻² , and it can be seen that the smaller the electrode interval, the better the sensitivity. The height of the gap formed by the adhesive layer is usually 0.1 μ
m to several tens of μm is preferable, and about 0.1 to 10 μm is more preferable for high capacity and high precision. Further, the thinner the plate thickness of the diaphragm 1, the better the displacement. Therefore, the electrode interval also changes greatly, and the plate thickness of the diaphragm is also a major factor in improving the accuracy of the pressure sensor. Specific examples will be shown below.

(Example 1) A diaphragm 1 and a fixed substrate 2 made of 96% alumina were prepared, and the first electrode 4a, 4b and the second electrode 5 were formed on the diaphragm 1 and the fixed substrate 2, respectively.
Gold resinates as a and b were formed to a thickness of 0.1 μm by a screen printing method. Next, the first electrode 4 and the second electrode 5 were arranged so as to face each other, and were integrally joined by the adhesive layer 3. Further, the outer surfaces of the diaphragm 2, the fixed substrate 2 and the adhesive layer 3 were sprayed with SiO ₂ which is ceramics to a thickness of 1 μm and coated to a thickness of 1 μm. As shown in FIG. 2, the thickness of the diaphragm 1 is 0.
It was changed from 15 to 1.0 mm. The capacitance value was measured after the pressure sensor element manufactured in the above process was left for about 60 hours in a high humidity condition of about 90 to 95% RH. The result is shown in FIG. As a result, in the element in which the pressure-receiving surface and the side surface of the diaphragm 1 are coated with SiO ₂ which is the ceramics of the present invention, even if the thickness of the diaphragm 1 is reduced to 0.8 mm or less, it is left in a high humidity as shown by ○. It can be seen that there is almost no difference from the capacity value before (temperature 25 degrees, humidity 40%) and there is no change. Therefore diaphragm 2
It can be said that forming a waterproof layer on the outer surfaces of the fixed substrate and the adhesive layer is very effective in improving the humidity characteristics in order to make it more difficult to be affected by the pressure receiving surface and the side surface and further by the humidity. Furthermore, even if the thickness of the diaphragm 1 is made thin, the humidity characteristics are not affected, so that it is possible to realize a highly sensitive pressure sensor element.

Example 2 A diaphragm 1 made of 96% alumina and a fixed substrate 2 were prepared.
And the first electrode 4a, 4b and the second electrode 5 on the fixed substrate 2.
Gold resinates as a and b were formed in a thickness of 0.1 μm by a screen printing method. Further, a gold resinate was formed in the same manner on the entire surface and the side surface opposite to the surface on which the first electrode 4 and the second electrode 5 were formed. Then the first electrode 4
And the second electrode 5 are arranged so as to face each other, and they are integrally joined while being held at a constant interval by the adhesive layer 3. The diaphragm 1 has a thickness of 0.15 to 0.15 as shown in FIG.
It was changed to 1.0 mm. The capacitance value was measured after the pressure sensor element manufactured in the above process was left in a high humidity condition of about 90 to 95% for about 60 hours. The result is shown in FIG. In the device of the present invention, the diaphragm 1 has a thickness of 0.1.
It can be seen that even when the thickness is very thin as 5 mm, there is almost no difference from the capacity value before being left at high humidity (temperature 25 ° C., humidity 40%) as shown by ◯, and there is no change. Therefore, it is understood that forming the waterproof layer on the outer surfaces of the diaphragm 1 and the fixed substrate 2 is very effective in improving the humidity characteristics. Furthermore, even if the thickness of the diaphragm 1 is made thin, the humidity characteristics are not affected, so that it is possible to realize a highly sensitive pressure sensor element.

The zero-point change rate with respect to temperature change was measured using the element of the present invention used in Example 2 with the diaphragm 1 having a thickness of 0.15 mm. As a result, even if the temperature rises, there is almost no change in the zero point, and almost the same result as the conventional element was obtained. This is presumably because the waterproof layer was formed of a material having substantially the same quality as that of the first electrode, so that the coefficients of thermal expansion of the diaphragm 1 and the electrode 4 cancel each other out. Therefore, by forming the electrode on the entire pressure receiving surface, the bimetal effect can be reduced and the capacitance change due to temperature can be improved. That is, a capacitance type pressure sensor that is hardly affected by humidity and temperature can be realized, and stable sensor characteristics can be obtained.

(Example 3) A diaphragm 1 made of 96% alumina and a fixed substrate 2 were prepared.
And the first electrode 4a, 4b and the second electrode 5 on the fixed substrate 2.
Gold resinates as a and b were formed in a thickness of 0.1 μm by a screen printing method. Next, the first electrode 4 and the second electrode 5 were arranged so as to face each other, and were integrally joined by the adhesive layer 3. Further, the diaphragm 2 and the fixed substrate 2
The polyimide / amide resin, which is a hydrophobic resin, was applied to the outer surface of the adhesive layer 3 with a thickness of 3 μm and then heat-treated for coating. The thickness of the diaphragm 1 was changed to 0.15 to 1.0 mm as shown in FIG. The capacitance value was measured after the pressure sensor element manufactured in the above process was left for about 60 hours in a high humidity condition of about 95% RH. The result is shown in FIG. As a result, in the element in which the polyimide-amide resin which is the hydrophobic resin of the present invention is coated on the pressure-receiving surface and the side surface of the diaphragm 1, even if the thickness of the diaphragm 1 becomes thin, the element is left in high humidity as shown by ○. Before (Temperature 2
It can be seen that there is almost no difference from the capacity value at 5 degrees and humidity 40%), and there is no change. Therefore, it can be said that forming the waterproof layer on the outer surfaces of the fixed substrate and the adhesive layer is very effective in improving the humidity characteristics in order to make the diaphragm 2 less susceptible to the pressure receiving surface and the side surface and to the humidity. Furthermore, even if the thickness of the diaphragm 1 is made thin, the humidity characteristics are not affected, so that it is possible to realize a highly sensitive pressure sensor element.

(Example 4) Die made of 96% alumina
Prepare the diaphragm 1 and the fixed substrate 2, and
The ceramic is formed on the entire outer surface of the ram 2, the fixed substrate 2, and the adhesive layer 3.
SiO which is a box ₂With a thickness of 1 μm
It was coated so that Spray these ceramics
The first electrode on the diaphragm 1 and the fixed substrate 2 on one side
4a and 4b and second electrodes 5a and 5b are made of gold, respectively.
Of the resinate of 0.1 μm by screen printing
Was. Next, so that the first electrode 4 and the second electrode 5 face each other.
In the state of being arranged in
I joined them together. The thickness of the diaphragm 1 at this time is shown in FIG.
As shown in FIG. Since
About 90-95% R of the pressure sensor element produced in the above process
Measure the capacity value after leaving for 60 hours in the high humidity condition of H
Decided As a result, the ceramic of the present invention, SiO
₂Spray the first electrode 4 and the second electrode 5 before printing
Therefore, even in a pressure sensor equipped with a waterproof layer, the diaphragm
Even if the plate thickness of Mumu 1 becomes thin, the capacity does not change, and
The same effect as the case described in Example 1 was obtained.

(Embodiment 5) A diaphragm 1 made of 96% alumina and a fixed substrate 2 were prepared.
And the first electrode 4a, 4b and the second electrode 5 on the fixed substrate 2.
Gold resinates as a and b were formed to a thickness of 0.1 μm by a screen printing method. Next, the first electrode 4 and the second electrode 5 were arranged so as to face each other, and were integrally joined by the adhesive layer 3. Further, the pressure sensor simple substance formed in the above process was dipped in a polyimide / amide resin and dried in a vacuum dryer at about 100 ° C. for 1 hour to remove water that had penetrated into the electrode. This makes it possible to provide a waterproof layer on the surfaces of the first electrode 4 and the second electrode 5 and on the inner surface of the adhesive container 3. The plate thickness of the diaphragm 1 at this time is 0.15 to 1.0 m as in the first embodiment.
It was changed to m. The capacitance value was measured after the pressure sensor element manufactured in the above process was left for about 60 hours in a high humidity condition of about 90 to 95% RH. As a result, even if the thickness of the diaphragm 1 is reduced, the diaphragm 1 is left at a high humidity (temperature 25
The same results as in Example 1 were obtained, with almost no difference from the capacity value (degrees, humidity 40%).

In the capacitance type pressure sensor of the present invention, 96% alumina was used as the material of the diaphragm and gold, ceramics and polyimide / amide resin were used as the dense thin film, but these are not limited to this embodiment. Not something.

Further, in this embodiment, the waterproof layer is provided only on the outer surfaces of the diaphragm, the fixed substrate and the adhesive layer, but the effect is further obtained by providing the waterproof layer on the surfaces of the first electrode and the second electrode. To be

Further, even if a waterproof layer is provided on the surfaces of the diaphragm and the fixed substrate and the first electrode and the second electrode are provided on the surfaces, the same effect as that of the first embodiment can be obtained.

[0033]

As described above, according to the capacitance type pressure sensor of the present invention, the following effects can be obtained.

(1) By forming a waterproof layer on the outer surfaces of the diaphragm, the fixed substrate and the adhesive layer, it is possible to prevent moisture from permeating due to the influence of dew condensation and to realize a pressure sensor which is not affected by humidity.

(2) If the thickness of the diaphragm is made thinner than 0.8 mm in order to increase the sensitivity, the water permeability also increases, but by forming the waterproof layer on the outer surface of the diaphragm pressure receiving surface, high sensitivity can be obtained. It has become possible to reduce the influence of humidity.

(3) Since the bimetal effect can be reduced by forming the waterproof layer on the surface opposite to the first electrode, it is possible to reduce the influence of temperature at the same time.

(4) A pressure sensor which prevents moisture from penetrating due to the influence of dew condensation and the like and which is not affected by humidity is provided with a converting means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal. Therefore, the pressure sensor that is not affected by humidity can be widely used.

(5) A pressure sensor having a diaphragm plate thickness of 0.8 mm or less is provided with a conversion means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal, whereby the influence of humidity is exerted. A pressure sensor that is not subjected to pressure can be easily and widely used.

(6) A pressure sensor which is not affected by humidity by providing the pressure sensor capable of reducing the bimetal action with a conversion means for converting a capacitance change between the diaphragm and the fixed substrate caused by a pressure change into an electric signal. Can be easily and widely used.

[Brief description of drawings]

FIG. 1 is a sectional view of a capacitive pressure sensor according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of an example of the same capacitive pressure sensor.

FIG. 3 is a characteristic diagram of a capacitance type pressure sensor according to another embodiment of the present invention.

FIG. 4 is a characteristic diagram of an embodiment of the present invention.

FIG. 5 is a sectional view of a conventional capacitance type pressure sensor.

FIG. 6 is a characteristic diagram of a conventional capacitive pressure sensor.

[Explanation of symbols]

 1 Diaphragm 2 Fixed Substrate 3 Adhesive Layer 4 First Electrode 5 Second Electrode 6 Waterproof Layer

Claims (6)

[Claims] 1. A diaphragm having a first electrode formed on the surface thereof, a fixed substrate having a second electrode formed on the surface thereof, and the first electrode and the second electrode arranged to face each other. An adhesive layer for holding and adhering the diaphragm and the fixed substrate at a constant interval at the outer peripheral portion of the diaphragm, and a capacitive pressure structure in which a waterproof layer is provided on at least the outer surface of the diaphragm, the fixed substrate and the adhesive layer. Sensor. 2. The thickness of the first electrode formed on the surface is 0.
A diaphragm made of alumina smaller than 8 mm, a fixed substrate having a second electrode formed on the surface thereof, the first electrode and the second electrode are arranged to face each other, and the diaphragm and the fixed portion are provided at the outer peripheral portion of the electrode. An electrostatic capacitance type pressure sensor having a structure in which an adhesive layer for holding and adhering a substrate at a constant interval and a waterproof layer are provided on at least the outer surface of the diaphragm, the fixed substrate and the adhesive layer. 3. The thickness of the first electrode formed on the surface is 0.
A diaphragm made of alumina smaller than 8 mm, a fixed substrate having a second electrode formed on the surface thereof, the first electrode and the second electrode are arranged to face each other, and the diaphragm and the fixed portion are provided at the outer peripheral portion of the electrode. An electrostatic capacitance type pressure sensor comprising: an adhesive layer for holding and adhering a substrate at a constant interval; and a layer of a metal thin film, ceramics, or a hydrophobic resin on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer. 4. A diaphragm having a first electrode formed on the surface thereof, a fixed substrate having a second electrode formed on the surface thereof, and the first electrode and the second electrode arranged to face each other. An adhesive layer for holding and adhering the diaphragm and the fixed substrate at a constant distance at the outer peripheral part of the device, an element having a waterproof layer on at least the outer surface of the diaphragm, the fixed substrate and the adhesive layer, and caused by a pressure change A capacitance type pressure sensor comprising: a conversion unit that converts a capacitance change between the diaphragm and the fixed substrate into an electric signal. 5. The thickness of the first electrode formed on the surface is 0.
A diaphragm made of alumina smaller than 8 mm, a fixed substrate having a second electrode formed on the surface thereof, the first electrode and the second electrode are arranged to face each other, and the diaphragm and the fixed portion are provided at the outer peripheral portion of the electrode. An adhesive layer for holding and adhering the substrate at a constant interval, an element having an adhesive layer on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer, and the diaphragm and the fixed substrate caused by a pressure change And a conversion unit that converts a change in capacitance between the two into an electric signal. 6. The thickness of the first electrode formed on the surface is 0.
A diaphragm made of alumina smaller than 8 mm, a fixed substrate having a second electrode formed on the surface thereof, the first electrode and the second electrode are arranged to face each other, and the diaphragm and the fixed portion are provided at the outer peripheral portion of the electrode. An adhesive layer for holding and adhering the substrate at a constant interval, an element in which a layer of a metal thin film, ceramics, or a hydrophobic resin is provided on at least the outer surface of the diaphragm, the fixed substrate, and the adhesive layer; A capacitance type pressure sensor comprising: a conversion unit that converts a capacitance change between the diaphragm and the fixed substrate into an electric signal.