JPH036433A - Capacitance-type pressure transducer - Google Patents

Abstract

PURPOSE:To improve the precision in detection of pressure by providing an insulating plate opposite to a diaphragm on the base side and by forming a fixed electrode on the insulating plate. CONSTITUTION:By applying a pressure to be measured onto a diaphragm 10 from outside, the diaphragm 10 is displaced by the pressure, a space between the diaphragm 10 and a fixed electrode 20 on an insulating plate 21 changes, and an electrostatic capacity between them changes in accordance with the pressure applied. Accordingly, the pressure applied onto the diaphragm 10 can be measured by connecting electrode terminals 24 and 25 to the diaphragm 10 or a surface plate 11 operating as a moving electrode and to the electrode 20 respectively and by measuring the electrostatic capacity between them. Herein the electrode 20 is formed in the shape of the insulating plate 21 disposed in a measuring chamber 16 and is made opposite at prescribed spacing to the diaphragm 10. Since there is no interposition of a part causing a large electrostatic capacity not contributing to measurement between the electrode 20 and the diaphragm 10, on the occasion, the electrostatic capacity measured can be made to show a change in pressure between the electrode 20 and the diaphragm 10 exclusively, and thus highly-precise pressure measurement can be executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a capacitance pressure transducer whose capacitance changes depending on applied pressure, and is suitable for measuring fluid pressure and contact pressure. Available.

[Background technology]

Conventionally, various types of pressure sensors have been used to measure fluid pressure in pipes and containers, contact pressure between members, and the like. Among these, capacitive pressure transducers detect the amount of deformation according to applied pressure as a change in capacitance, and have become popular in recent years because they have a simple structure, can be miniaturized, and have high measurement accuracy. It is used for.

As an example of such a capacitive pressure transducer, a capacitive pressure sensor 50 as shown in FIG. 5 is known.

In the figure, a silicone surface plate 51 has a diaphragm 52 formed on one side thereof with a thick central portion processed by an etching technique or the like.

A silicon substrate 53 is laminated on the surface plate 51 via a bonding layer 54 made of a silicon oxide film, low melting point glass, or the like. The silicon used for the surface plate 51 and the substrate 53 are both highly conductive and low resistivity silicon.
The bonding layer 54 has an insulating function between the surface plate 51 and the substrate 53.

A measurement chamber 55 is formed in the gap between the diaphragm 52 and the substrate 53. This measurement chamber 55 is configured to release back pressure to the outside through a through hole 56 formed in the substrate 53, and the diaphragm 52 is displaced in the thickness direction according to external pressure, and the distance between the diaphragm 52 and the substrate 53 is changes.

Therefore, if the surface plate 51 is used as a moving electrode and the substrate 53 is used as a fixed electrode, and the capacitance between them is measured using the electrode terminals 57 and 58, the value will depend on the displacement of the diaphragm 52 due to external pressure. The pressure applied to the diaphragm 52 can be measured based on the obtained capacitance.

On the other hand, FIG. 6 shows another type of capacitive pressure sensor 60.
It is shown.

In the figure, this capacitive pressure sensor 6o uses an insulating material for a substrate 63 laminated on a surface plate 61 having a silicon diaphragm 62.

A fixed electrode 69 is arranged in the center of the substrate 63 on the diaphragm 62 side, and this fixed electrode 69 is connected to the through ball 62.
It is connected to the electrode terminal 68 via a conductive pattern 698, which extends outward through the electrode terminal 68. Therefore, the capacitance between this electrode terminal 68 and the electrode terminal 67 on the surface plate 61 side,
That is, the applied pressure can be measured by detecting the capacitance depending on the distance between the diaphragm 62 and the fixed electrode 69.

[Problems to be Solved by the Invention] By the way, the capacitive pressure sensor 5 shown in FIG.
0, the insulating bonding layer 54 interposed between the surface plate 51, which is a moving electrode, and the substrate 53, which is a fixed electrode, is thin and has a large dielectric constant, so the capacitance (so-called parasitic The capacitance (capacitance) becomes extremely large compared to the capacitance between the diaphragm 52 and the substrate 53 that contributes to the original pressure measurement. In other words, considering the entire capacitance between the electrode terminals 57 and 58, that is, between the surface plate 51 and the substrate 53,
There is a problem in that the rate of change in capacitance in response to applied pressure becomes small, resulting in poor pressure measurement accuracy.

On the other hand, in the capacitive pressure sensor 60 shown in FIG. 6, there is almost no capacitance that does not contribute to pressure measurement in the space between the diaphragm 62 and the fixed electrode 69, so highly accurate measurement is possible. becomes.

However, since the laminated silicon diaphragm 62 and insulating material substrate 63 are made of different materials, the difference in thermal expansion coefficients causes distortion due to temperature changes, and the temperature characteristics of the sensor are different from those when the same materials are used. The problem was that it got worse.

An object of the present invention is to provide a capacitive pressure transducer with high measurement accuracy and good temperature characteristics.

[Means to solve the problem]

In the present invention, a silicon substrate is laminated on a silicon surface plate having a diaphragm, and a measurement chamber is formed between the substrate and the diaphragm. A capacitive pressure transducer is constructed by arranging an insulating plate and providing at least one fixed electrode on the surface of the insulating plate on the diaphragm side.

Here, as the material for the surface plate and the substrate, a thin plate of low resistivity silicon, which is normally used for semiconductor devices, etc., may be used.

In addition, when forming a diaphragm on the surface plate,
A method can be adopted in which a predetermined portion of the surface plate is processed and removed by etching or the like to form a diaphragm.

Furthermore, when forming a measurement chamber between the substrate and the diaphragm, it is sufficient to use a recess in the diaphragm part, and if necessary, a recess can also be formed on the substrate side to accommodate the insulating plate when stacked. As long as there is enough space to do so.

In addition, in order to eliminate the back pressure of the diaphragm, a through hole or a through hole may be formed in the substrate, etc., to open the measurement chamber to the outside. Furthermore, a lead pattern may be provided on the surface of the insulating plate, one end of which is connected to the fixed electrode, and the other end of which extends through the through hole to a position where it can be contacted from the outside.

At this time, the fixed electrodes and lead patterns provided on the insulating plate are
Be careful not to touch the silicon part of the top plate or substrate.
It is electrically insulated from these silicon parts.

[Operation] According to the present invention, by applying a pressure to be measured from the outside to the diaphragm, the diaphragm is displaced by the pressure, and the distance between the diaphragm and the fixed electrode on the insulating material changes, and the distance between them changes. Capacitance changes in response to applied pressure. Therefore, the pressure applied to the diaphragm can be measured by connecting electrode terminals to the diaphragm or surface plate serving as the moving electrode and the fixed electrode and measuring the capacitance between them.

Here, the fixed electrode is formed in the shape of an insulating plate placed in the measurement chamber and is opposed to the diaphragm at a predetermined interval, and there is no intervening part between the fixed electrode and the diaphragm that produces a large capacitance that does not contribute to measurement. Therefore, the measured capacitance can exclusively represent the pressure change between the fixed electrode and the diaphragm, allowing highly accurate pressure measurement.

In addition, by using the same silicon, etc. for the surface plate with the diaphragm and the substrate laminated to this surface plate, the thermal expansion coefficients of each are made to match, reducing distortions caused by temperature. . In addition, at this time, the insulating plate is fixed to a part of the board without being bonded to the top plate, so the diaphragm suffers almost no distortion due to temperature changes caused by the difference in thermal expansion coefficient between the insulating board and the board. It doesn't get across. This maintains good temperature characteristics.

Therefore, in the capacitive pressure transducer of the present invention, highly accurate pressure measurement and good temperature characteristics can be satisfied at the same time, thereby achieving the above object.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

1 and 2 show a capacitive pressure sensor 1 according to the invention.

In the figure, a front plate 11 is a silicon wafer plate having a <100> crystal plane as its main plane, and a recess 12 is formed in the center of the back surface by etching. The central portion of the surface plate 11 is thinned by the recess 12, and the diaphragm 10 is constituted by the thin portion.

A substrate 14 is laminated on the concave portion 12 side of the surface plate 11 with a thin bonding layer 13 made of glass or the like interposed therebetween.

Similar to the surface plate 11, this substrate 14 has a crystal plane <100>
This device uses a silicon wafer with a main plane of
A recess 15 corresponding to the recess 12 of No. 1 is provided. Therefore, there is a gap between the laminated top plate 11 and the substrate 14.
A space is formed by the recesses 12 and 15, and a measurement chamber 16 surrounded by the substrate 14 and the diaphragm 10 is configured in this space.

Further, four through parts 18 are formed by etching on the bottom surface of the recess formed in the substrate 14 so as to leave a cross-shaped beam 17, and each of these through parts 18 connects the measurement chamber 1.
6 is open to the outside.

On the other hand, an insulating plate 21 made of glass having an appropriate size to fit within the recess 15 is fixed to the beam 17 of the substrate 14 via a bonding layer 22 made of low melting point glass or the like.

This insulating plate 21 is accommodated in the measurement chamber 16 as the substrate 14 and the surface plate 11 are laminated, and is arranged opposite to the diaphragm 10 at a constant interval.
By adjusting the thickness of the bonding layer 22, a predetermined distance is maintained between the two.

Here, a fixed electrode 20 is formed by vapor deposition on the surface of the insulating plate 21 on the diaphragm 10 side, and a part of the fixed electrode 20 is continuous with the lead pattern 23 . This lead pattern 23
is extended so as to wrap around the back surface of the insulating plate 21, and its tip is disposed at a position where it can be contacted from the outside through the through portion 18, and a fixed side electrode terminal 24 is formed at the tip. These fixed electrodes 20 and lead patterns 23
, the fixed side electrode terminals 24 are each electrically insulated from the substrate 14.

Note that a moving side electrode terminal 25 is formed on the surface of the surface plate 11, and this electrode terminal 25 is electrically connected to the diaphragm 10 through the surface plate 11. Therefore, by measuring the capacitance between these electrode terminals 24 and 25, the capacitance between the diaphragm 10 and the fixed electrode 20 can be measured.

In this embodiment configured as described above, the pressure to be measured is applied to the surface of the diaphragm 10, and one pole of a capacitance detector (not shown) is connected to the fixed side electrode terminal 24 via the lead wire 26. Then, the other pole is connected to the movable electrode terminal 25 via the lead wire 27, and the capacitance between the diaphragm 10 and the fixed electrode 20 is measured.

At this time, the diaphragm 10 bends depending on the pressure difference between the pressure applied from the front side and the pressure on the back side (measurement chamber 16), and the distance from the fixed electrode 20 changes. As this distance changes, the capacitance between the diaphragm 10 and the fixed electrode 20 changes, and its value is measured by capacitance detectors connected to the fixed and moving electrode terminals 24 and 25. Ru.

Therefore, if you measure the capacitance value corresponding to a known pressure in advance and determine the relationship between the measured capacitance value and the applied pressure, you can make measurements based on the measured capacitance. The power pressure can be calculated.

According to this embodiment, the diaphragm 1
It is possible to accurately measure the pressure applied to zero.

Moreover, since there is almost no part between the diaphragm 10 and the fixed electrode 20 where electrostatic capacitance (parasitic capacitance) is generated, which is detected regardless of pressure measurement, The capacitance generated is caused by the diaphragm 10 and the fixed electrode 20, which contribute exclusively to pressure measurement.
This is the capacitance between.

Therefore, even subtle changes in the pressure applied to the diaphragm 10 can be reliably detected without being disturbed by other capacitances, and highly accurate pressure measurement can be performed.

Furthermore, since the surface plate 11 having the diaphragm 10 and the base 1 2 temporary 14 are made of the same material (silicon), the effects of temperature changes on each are also the same. Therefore, it is possible to reduce the possibility of distortion etc. occurring due to changes in the environmental temperature, ensure stable measurement operation even in a variety of measurement environments, and maintain good temperature characteristics. .

Note that the present invention is not limited to the above embodiments,
It also includes the following modifications.

That is, in the embodiment described above, the recess 1 is formed in the surface plate 11.
2 is provided, and a recess 15 is provided in the substrate 14, and when the surface plate 11 and the substrate 14 are stacked, the recess 12) 1
5 to form the measurement chamber 16, the depth of either the recess 12 or the recess 15 may be increased and the other may be made shallower or omitted. In short, the diaphragm 10 that is displaced by the pressure to be measured on the surface plate 11 At the same time, a measurement chamber 16 that can accommodate an insulating plate 21 and a fixed electrode 20 facing the diaphragm 1o is formed.

Another embodiment of the invention is shown in FIG. In the figure, a recess 12A is formed in the surface plate 11A, and the recess 12A has a deep peripheral part 12B, while a central part 12A has a deep recess 12A.
2C is formed shallowly. Therefore, the diaphragm 10^ formed on the surface plate 11A is thin at the periphery, but relatively thick at the center. On the other hand, the configurations of the substrate 14 side, fixed electrode 20, etc. are the same as in the previous embodiment. According to such an embodiment, in addition to obtaining the same effects as the above-mentioned embodiment, since the peripheral portion of the diaphragm 10A is thin,
In addition to being able to increase displacement in response to applied pressure,
Since the central portion is thick and approaches the fixed electrode 20 in parallel, it is possible to increase the change in capacitance due to displacement to the diaphragm 10, and it is possible to measure even minute pressures. In addition, the diaphragm 10^ and the fixed electrode 20
As in the previous embodiment, the distance between the two electrodes can be adjusted by appropriately setting the thicknesses of the insulating plate 21 and the bonding layer 22.

Further, in each of the embodiments described above, a bonding layer 13 made of glass or the like is interposed between the surface plate 11 and the substrate 14, but in the sensor 341, insulation between the fixed electrode 20 and the substrate 14 is ensured by the insulating plate 21. Therefore, direct bonding without intervening a bonding layer may be used.

Furthermore, the fixed electrode 20 or lead pattern 23 formed on the insulating plate 21, the fixed side electrode terminal 24, and the surface plate 1
The shape, position, etc. of the moving side electrode terminal 25 formed in 1 are not limited to the form of the above embodiment, and may be changed as appropriate in implementation. Further, the electrode configuration is not limited to the two poles on the fixed side and the movable side as described above, but may be configured such that a measurement electrode and a reference electrode are respectively provided to perform error correction at LJ.

FIG. 4 shows a different example of the electrode pattern of the insulating plate 21 in the above embodiment. This embodiment includes a surface plate 11 (not shown), a substrate 14, a diaphragm 10 (not shown), and an insulating plate 21 similar to those of the previous embodiment, but the structure of the fixed side electrode formed on the insulating plate 21 is different. It is something. That is, in the figure, on the surface of the insulating plate 21, a measuring electrode 20^ is formed on the inside, and a reference electrode 20B is formed around the periphery. Connected to the electrode on the back side. Therefore, each diaphragm 10
It is possible to detect the capacitance between each of these electrodes 2
By using a well-known correction method such as taking the difference between the outputs from 0^ and 20B, more accurate measurements can be made by canceling out noise components and temperature errors.

〔Effect of the invention〕

As explained above, according to the capacitance type pressure transducer of the present invention, the 1! ! By providing an edge plate and forming fixed electrodes on this insulating plate, it is possible to almost eliminate the influence of parasitic capacitance between the diaphragm and the detection electrode, improving pressure detection accuracy, and forming a diaphragm. Since the surface plate and the substrate are made of the same material, the temperature characteristics can be made better than when different materials are used for each, and the stability of the sensor can be improved.

[Brief explanation of drawings]

5 6 Fig. 1 is a longitudinal sectional view showing one embodiment of the present invention, Fig. 2 is a bottom view showing the embodiment, Fig. 3 is a longitudinal sectional view showing another embodiment of the invention, and Fig. 4. 5 is a plan view of an insulating plate showing still another embodiment of the present invention, FIG. 5 is a longitudinal sectional view showing a conventional example, and FIG. 6 is a longitudinal sectional view showing another conventional example. DESCRIPTION OF SYMBOLS 1... Capacitance type pressure sensor, 10... Diaphragm, 11... Surface plate, 12... Recessed part, 13... Bonding layer, 14... Substrate, 15... Recessed part, 16 ...Measurement chamber, 20...Fixed electrode, 21...Insulating plate, 22...
... Bonding layer, 23... Lead pattern, 24... Fixed side electrode terminal, 25... Moving side electrode terminal.

Claims (2)

[Claims] (1) A silicon substrate is laminated on a silicon surface plate on which a diaphragm is formed, a measurement chamber is formed between this substrate and the diaphragm, and a measurement chamber is formed on the inside of the measurement chamber of the substrate, facing the diaphragm at a predetermined interval. A diaphragm-side insulating plate is placed on the diaphragm side surface of the insulating plate.
Two fixed electrodes were installed. (2) The capacitive pressure transducer according to claim 1, characterized in that at least one through portion is formed in any one of the silicon substrates to communicate the inside and outside of the measurement chamber.