JPS59163514A - Electrostatic capacity type sensor - Google Patents

Abstract

PURPOSE:To improve accuracy in measurement and to make negligible the floating capacity between two electrodes by forming a support and a diaphragm (including a base plate) of fused quartz, quartz crystal, glass, ceramics, sapphire, etc. and providing an adhesive layer and a supporting part between the two electrodes which are formed into a concentrical shape. CONSTITUTION:An electrode support 21 consists of a material such as, for example, fused quartz, quartz crystal, glass, ceramics, sapphire, or the like, and two concentrical electrodes 22, 24 are formed on the surface thereof. These electrodes 22, 24 are formed by vapor deposition, etc. in the prescribed depth position of the support. A measuring diaphragm 26 consists of the material similar to the material of the support 21, and a prescribed metal is deposited by a means such as vapor deposition over the entire surface of the diaphragm facing the support 21, by which an electrode 23 is formed. The support 21 and the diaphragm 26 are joined by an adhesive layer 25 such as low melting glass, glass, org. adhesive agent, metal or the like in such a way that the electrodes face each other.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a detection unit that capacitively detects physical factors such as pressure, differential pressure, load, or level (hereinafter referred to as pressure). (sensor) structure.

[Prior art and its problems]

Figure 1 is a sectional view showing a conventional example of a capacitive pressure sensor.
FIG. 1A is a top view showing the structure of the electrode section, and FIG. 1B is a circuit diagram showing the electrical circuits of the sensor. In FIG. 4, 1 is a housing, 2.3 is an electrode, 4 is a pressure measuring diaphragm, 5 is an insulator, 6 and 9 are communicating holes, 7 and 8 are electrode tubes, and 10 to 12 are terminals. That is, electrode 2,
The insulator 5 to which the insulator 3 is attached is attached to the metal housing 1
The housing 1 is attached to a metal measuring diaphragm 4 by electron beam welding or the like. As shown in FIG. 1A, electrodes 2 and 3 are arranged concentrically with each other and their cross-sectional areas S 1 r 82 are chosen to be equal to each other (S1=82=S). And the center electrode 3
An electrode tube 7 having a communication hole 6 leading to the outside is attached to the electrode tube 7, which is configured to transmit pressure to the pressure measuring diaphragm 4, and the electrode 2 on the outer periphery also has a communication hole 9. An electrode tube 8 having a diameter is attached. Note that the electrode 3 and the diaphragm 4 and the electrode 2 and the diaphragm 4 form capacitors having capacitances C1 and C2, respectively. Therefore, for example, when pressure is introduced through the communication hole 6, the diaphragm 4 will be displaced.
Conventionally, this displacement is large near the center of the measurement diaphragm 4, but almost non-existent at the outer periphery.Considering that the capacitance C2 remains unchanged as shown in the equinodal circuit of Figure 1B, we consider the following: I was trying to find it from an arithmetic expression.

(1), (From Equation 21, C0 is the dielectric constant between the electrodes, S is the area of the electrodes, do is the gap between the electrodes, and Δd is the average displacement of the measurement diaphragm.

However, in reality, displacement also occurs near the fixed end of the diaphragm 4 and the capacitance C2 changes, so there are not only drawbacks such as poor linearity and reduced measurement accuracy, but also the following drawbacks: There is.

b) Since the two electrodes are arranged adjacent to each other, stray capacitance is likely to be formed between them.

Since two electrodes are provided facing the measurement diaphragm, their capacitance values are small, and as a result, they are easily affected by stray capacitance as described above.

c) It is generally expensive because a composite of metal and insulator must be provided.

2) Since the pressure is measured using a metal diaphragm, the hysteresis of the metal diaphragm is included in the measurement results, making it difficult to measure with high precision.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a capacitive sensor that can perform highly accurate measurements and is easy to downsize.

[Key points of the invention]

Its feature is that the first concentric circles have the same area.
A support body on which a second electrode part is formed, a third electrode part on a surface facing the support body, and at least the first electrode part of the third electrode part.
A first bonding portion is used to connect the second electrode portion and a substrate on which a diaphragm portion that responds to physical force is formed at a position facing each other with a predetermined gap between them. This is because the substrate is arranged between the second electrodes, and at least the material of the substrate has good physical properties and can be microfabricated.

[Embodiments of the invention]

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

FIG. 2 is a structural diagram showing an embodiment of this invention, and FIG.
1 is a cross-sectional view showing the overall structure, (b) is a top view showing the structure of the electrode part, and (c) is a cross-sectional view thereof.

In the figure, 21 is, for example, molten lime, crystal, glass,
It is made of a material such as ceramics or sapphire, and there are two concentric electrodes 22.2 on its surface as shown in the same figure (b).
4, these electrodes 22.2
4 is formed at a predetermined depth on the support 210 by vapor deposition or the like. The support body 21 is provided with a ring-shaped protrusion 21' as shown in FIG. 2
Reference numeral 6 denotes a measuring diaphragm made of the same material as the support 21, and a predetermined metal is attached to the entire surface facing the support 21 by means such as vapor deposition.
3 is formed. The support body 21 and the measurement diaphragm 26 are bonded to each other by an adhesive layer 25 made of low melting point glass, glass, an organic adhesive, metal, or the like, with the electrodes facing each other. Note that for this bonding, a known method such as a method utilizing a eutectic reaction or an anodic bonding method may be used depending on the substance used. In this way, a flat plate capacitor c1 is formed on electrodes 23 and 24, and a flat plate capacitor c2 is formed on electrodes 22 and 23, respectively. In this case, the capacitance of the capacitor c2 changes depending on the pressure and the like, whereas the capacitor C1 does not respond to the pressure and the like, so it can be used as a reference capacitor.

In addition, in the same figure (a), 28-3o are terminals connected to each electrode by means of bonding, soldering, etc.

Now, if a pressure difference occurs across the measuring diaphragm,
Since the measuring diaphragm 26 deflects in proportion to the pressure difference, the electrode spacing of the electrodes 22.23 and the capacitance C2 change, but the electrode spacing of the electrodes 23.24 does not change. Now, the gap between the electrodes (between 23 and 22.24) is d
Assuming that the dielectric constant between the os electrodes is ε, and the area of the electrodes (22', 24) is A1Δd, which is a quantity proportional to the differential pressure, the relationship between these quantities and the capacitances C1 and C2 is expressed by the above equations (1) to ( Similar to 3), the following relational expression holds true.

C1-a, ......(4) C2-d
o-Δ, -°-(51(4)) According to equation (5), by measuring the capacitances of capacitors cl and c2, a quantity proportional to the differential pressure can be obtained from equation (6). Note that the above equations (4) to (6) are exactly the same as equations (1) to (3) if the directions of pressure and the like are matched.

Figures 3, 4 and 5 are cross-sectional views showing different embodiments of the present invention, and Figure 6 shows the structure of the electrode section used in the embodiment of Figures 4 and 5. FIG.

1. In the device shown in FIG. 3, instead of forming the measurement diaphragm in a flat plate shape as shown in FIG. By doing this, the thin part is made to function as the measuring diaphragm 26. As a result, the second
Compared to the case shown in the figure, the influence of hysteresis of the diaphragm material is reduced (this point is
It has been confirmed experimentally. ). Note that, assuming that the thickness of the thick part of the substrate 20 is '(il-hl) and the thickness of the thin part is h2, the ratio γ (=hx/h2) is preferably set such that γ≧3. This has also been experimentally confirmed.

The one shown in FIG. 4 is configured to be connected to the diaphragm 26 via a ring-shaped projection 21' formed on the support 21, whereas the one shown in FIGS. 2 and 3 is As shown in FIG. 6, electrodes 22 and 24 are formed by vapor deposition on a planar support from which the protrusions have been removed, and organic adhesive and low-melting glass are applied to the portion 21' between the electrodes 22 and 24. Or create an adhesive layer made of an insulator such as glass,
The support body 21 and the diaphragm 26 are bonded together using this portion 25. By doing so, processing of the support body 21 can be facilitated. In addition, the 6th
As shown in the figure, by providing the electrode 22 with a lead-out portion 22', the terminal can be easily taken out. Further, the diaphragm 26 in this embodiment can be replaced with a diaphragm as shown in FIG. 3 having a thinner part in the center.

In all of the examples shown in FIGS. 2 to 4, concentric electrodes are provided only on the support side, but it is now clear that similar electrodes may be formed on the diaphragm side. As will be clear from the description, an embodiment based on this point of view is shown in FIG.

That is, in this example, electrodes as shown in FIG. 6 are formed on both the support 21 and the measurement diaphragm, and these are bonded together with an adhesive layer 25 facing each other, and the capacitance values are taken out individually. Suitable for cases where

Fig. 7 is a circuit diagram showing the electrical equivalent circuit of a capacitive sensor, in which (a) shows each sensor shown in Figs. 2 to 4, and (b) shows a sensor shown in Fig. 5. These correspond to the following. In addition, 28~30°28', 32,
32' represent terminals, cl represents a reference capacitor, and C2 represents a measurement capacitor.

〔Effect of the invention〕

According to this invention, since the support and the diaphragm (including the substrate) are made of fused silica, crystal, glass, ceramics, sapphire, etc., their physical properties (elastic properties) are better than those made of metal. ), the measurement accuracy can be improved. In addition, such materials are suitable for microfabrication,
In particular, it can be processed to a size of several microns using semiconductor manufacturing technology, so it has the advantage of being able to be made into a shed. Furthermore, according to the present invention, the following effects can be expected.

b) An adhesive layer and a support part are provided between two concentric electrodes, and the capacitance of the outer reference capacitor does not change even if the diaphragm is displaced, so the linearity of the measured value is improved. Improved.

(Example) Since an adhesive layer is provided between two concentric electrodes to separate the electrodes, stray capacitance between them can be ignored.

c) Since the entire surface of the diaphragm on which the electrode portion is formed can be used as an electrode, the capacitance is not large, and therefore the influence of stray capacitance can be ignored.

2) There is no need to use a composite of metal and insulator,
Cost can be reduced.

e) Since the measurement diaphragm is made of a material other than metal with excellent elastic properties, the linearity of diaphragm displacement is improved and hysteresis can be reduced.

In addition, in the above explanation, the support body and the diamond waller 6. Although materials such as fused silica, crystal, glass, ceramics, or sapphire are used for both the diaphragm (substrate), it is sufficient to use a material that is flexible only toward the diaphragm portion.

Further, the present invention can be widely applied not only to pressure measurement as described above but also as a sensor for measuring various mechanical or physical quantities.

[Brief explanation of drawings]

Figure 1 is a structural cross-sectional view showing a conventional example of a capacitive pressure sensor, Figure 1A is a top view showing the structure of an electrode, and Figure 1B is an electrical equivalent circuit of the sensor shown in Figure 1. 2 is a block diagram showing an embodiment of the present invention, FIGS. 3 to 5 are cross-sectional views showing other embodiments of the invention, and FIG. 6 is a diagram showing an electrode structure formed on a support. A top view showing an example of
FIG. 7 is a circuit diagram showing an electrical equivalent circuit of a capacitive sensor. Code explanation l...Housing, 2, 3.22, 23.24...
Electrode, 4, 26... diaphragm, 5... insulator,
6゜9, 27,..., communicating hole, 7, 8, 31-...
・Electrode tube, 10-12, 28-30, 28', 3
2, 32'...Terminal, 21...Support, 21' protruding part, 21' flat part between electrodes, 25...Adhesive layer agent Patent attorney Akio Namiki Patent attorney Matsuzaki Qing Figure 1 Figure 1A Figure 1B Figure 2 Figure 3, 6244EJ □□□□□ 2'2 north Figure 5 Figure 6 Figure 1 Figure 7 (B)

Claims (1)

[Scope of Claims] 1) A support body formed with concentric first and second electrode parts having the same area and the same area, and a third electrode part provided on a surface facing the support body, and the third electrode part. At least the first of the three electrode parts
or a substrate on which a diaphragm part that responds to physical force is formed at a position corresponding to one of the second electrode parts; The first joint is for joining with a gap.
A capacitive sensor formed between an electrode and a second electrode. 2. The capacitive sensor according to claim 1, characterized in that only the substrate or both the substrate and the support are made of a material such as fused silica, crystal, glass, ceramics, or sapphire. capacitive sensor. 3) The capacitive sensor according to claim 1 or 2, characterized in that a counterbore portion is formed on the substrate, and a diaphragm portion is formed by the counterbore portion. capacitive sensor. 4) In the capacitive sensor according to any one of claims 1 to 3, the thickness of the substrate is set to a predetermined thickness, and the entire substrate is a diaphragm portion. capacitive sensor.