JP3102595B2 - Capacitive pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive pressure sensor, and more particularly, to a capacitor comprising an electrode fixed to a substrate and an electrode fixed to a diaphragm,
The present invention relates to a capacitive pressure sensor that converts a pressure acting on the diaphragm into a capacitance between the two electrodes and outputs the capacitance.

[0002]

2. Description of the Related Art FIG. 6 is an exploded perspective view showing an example of a conventional capacitive pressure sensor, and FIG. 7 is a sectional view thereof. 6 and 7, the capacitive pressure sensor 50 includes an alumina circular substrate 51 and an alumina circular diaphragm 53 having substantially the same diameter as the substrate 51.
In the center of one surface (upper surface) of the substrate 51, the outer peripheral edge 5 is provided.
A disk-shaped electrode 52 is fixed inwardly away from 1a. The diameter of the electrode 52 is smaller than the diameter of the substrate 51. Therefore, an annular portion 51b is formed between the outer peripheral edge of the electrode 52 and the outer peripheral edge 51a of the substrate 51.

[0003] On one surface (lower surface) of the diaphragm 53, a disk-shaped electrode 5 is disposed inward from an outer peripheral edge 53a.
4 is fixed. The diameter of the electrode 54 is smaller than the diameter of the diaphragm 53. Therefore, the annular portion 5 is provided between the outer peripheral edge of the electrode 54 and the outer peripheral edge 53a of the diaphragm 53.
3b is formed. The diameter of the electrode 54 is substantially equal to the diameter of the electrode 52 on the substrate 51.

[0004] The joined body 55 is made of solder glass having a rectangular cross section, and joins and seals the periphery of the substrate 51 and the diaphragm 53 in an annular shape. A gap 56 is formed between the electrode 52 and the joined body 55, and a gap 57 is formed between the electrode 54 and the joined body 55. A gap g is formed between the two electrodes 52 and 54, and the gap g and the two electrodes 52 and 54 form a capacitor. Both electrodes 52 and 54 are connected to an electric circuit (not shown) via a lead wire (not shown).

When the diaphragm 53 is bonded to the substrate 51, a flow of solder glass is adhered onto the annular portion 51b of the substrate 51 by screen printing or the like, and then the diaphragm 53 is connected to the electrodes 52, 54 by the screen printing. They are overlapped so as to face each other, and are further cured and joined by applying pressure and baking.

The pressure medium to be detected is applied to the diaphragm 53 from the outside, and the pressure causes the diaphragm 53 to bend inward or outward. As a result, the gap g between the electrodes 52 and 54 changes, and the capacitance of the capacitor constituted by them changes. The capacitive pressure sensor 50 detects the pressure by converting the pressure into the capacitance.

As another related prior art, there is a "pressure sensor provided with a capacitive pressure transducer" disclosed in Japanese Patent Application Laid-Open No. 63-19527. In this pressure sensor, when the electrode of the diaphragm member (diaphragm) is fixed to face the electrode on the ceramic substrate, a fixing medium containing frit glass is used, and the fixing medium is coaxially mounted on the ceramic substrate. It is arranged between the two formed grooves.

[0008]

In the conventional capacitive pressure sensor 50, the effective range of the diaphragm 53 as a diaphragm, that is, the range in which the diaphragm 53 can bend under the action of pressure, is a joint body 55 made of solder glass. Is determined by the position of the inner peripheral edge 55a. For this reason, the position of the inner peripheral edge 55 a of the joined body 55 directly affects the size (diameter) of the effective range of the diaphragm 53.

In the above-described conventional capacitive pressure sensor 50, a flowable solder glass is used as the material of the joined body 55, and the gap g between the electrodes 52 and 54 is formed in the step of joining the diaphragm 53 to the substrate 51. Is pressed and baked until the liquid solder glass on the substrate 51 reaches a predetermined small value (for example, about 30 to 40 / μm). For this reason, at the time of pressurization and baking, there is a problem that the solder glass flows into the electrodes 52 and 54 and the radial width of the joined body 55 may be larger than a predetermined value. Such a variation in the radial width of the joined body 55 is directly linked to a variation in pressure-capacitance characteristics.

In the pressure sensor disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-19527, the size of the effective range of the diaphragm fluctuates when the fixing medium containing the frit glass spreads in the radial direction during curing. Do not consider. Therefore, this pressure sensor also has a problem that pressure-capacitance characteristics vary as in the pressure sensors shown in FIGS. 6 and 7.

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitive pressure sensor capable of reducing variation in pressure-capacitance characteristics with a simple structure.

[0012]

According to the present invention, there is provided a capacitive pressure sensor comprising: a substrate having electrodes; a diaphragm having other electrodes opposed to the electrodes at a predetermined interval; and a substrate having the electrodes and the diaphragm. Joining at the periphery
In capacitive pressure sensor for detecting a change in capacitance between the fluidized material to cure the result and a joint body formed by the two electrodes the pressure acting on the diaphragm to the outer peripheral edge of the substrate And the outer edge of the electrode on the substrate
An annular portion formed on the substrate between the
Having an annular groove formed on the substrate,
It is characterized in that it is provided close to the outer peripheral edge of the electrode .

[0013]

In the capacitive pressure sensor according to the present invention, since the annular groove is provided on the surface of the substrate on the electrode side so as to surround the electrode, the fluidized joint before curing tends to flow to the electrode side. Is not obstructed by the groove, and there is no danger of getting inside. For this reason, the width (radial length) of the joined body is substantially constant, and as a result, the diameter of the effective range of the diaphragm is also substantially constant. Therefore, it is possible to almost eliminate variations in pressure-capacitance characteristics. Also,
The structure is extremely simple because it is only necessary to provide an annular groove.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited by this. (Structure) FIG. 1 is an exploded perspective view showing an embodiment of a capacitive pressure sensor according to the present invention, and FIG. 2 is a sectional view thereof.

In FIGS. 1 and 2, the capacitive pressure sensor 10 includes a circular substrate 11 and a circular diaphragm 13 having substantially the same diameter as the substrate 11. A disk-shaped electrode 12 is fixed to the center of one surface (upper surface) of the substrate 11 so as to be inward from the outer peripheral edge 11a of the substrate 11. Since the diameter of the electrode 12 is smaller than the diameter of the substrate 11, an annular portion 11 b is formed on the upper surface of the substrate 11 between the outer peripheral edge 11 a and the outer peripheral edge 12 a of the electrode 12. Here, the substrate 11 and the diaphragm 13 are both made of alumina. However, other insulating materials can of course be used.

The outer peripheral edge 12 of the electrode 12 is
An annular groove 18 is formed near the electrode a so as to surround the electrode 12. This groove 18 has a V-shaped cross section,
This serves to suppress the flow of the bonding material 15 before being hardened from flowing inward in the radial direction.

The groove 18 has a V-shaped cross section here, but may have another shape (for example, a rectangular or U-shaped cross section). The groove 18 can be easily formed by forming an annular projection having a shape corresponding to the groove 18 in the die when the alumina substrate 11 is press-formed with a die, for example.

A disk-shaped electrode 14 is fixed to one surface (lower surface) of the diaphragm 13 so as to be inward from the outer peripheral edge 13a of the diaphragm 13. Since the diameter of the electrode 14 is smaller than the diameter of the diaphragm 13, an annular portion 13 b is formed on the lower surface of the diaphragm 13 between the outer peripheral edge 13 a and the outer peripheral edge 14 a of the electrode 14. The diameter of the electrode 14 is substantially equal to the diameter of the electrode 12 on the substrate 11.

The electrodes 12 and 14 can be fixed by, for example, screen printing a gold or silver paste on the surface of the substrate 11 or the diaphragm 13 and then baking or attaching the paste by sputtering. Electrode 1
Lead wires (not shown) are connected to 2 and 14, respectively, and a predetermined electric circuit is connected via these lead wires.

The joined body 15 is made of solder glass,
The substrate 11 is formed such that a predetermined gap g is formed between
And the outer peripheral portion of the diaphragm 13 and the space between them is sealed. The cross-sectional shape of the joined body 15 is substantially rectangular, and the lower surface thereof is bonded to the annular portion 11b of the substrate 11 between the outer peripheral edge 11a and the outer peripheral edge of the groove 18. An annular gap 16 is formed between the electrode 12 and the assembly 15. The upper surface of the bonded body 15 is bonded to the annular portion 13b of the diaphragm 13, and the radial width of the bonded surface is substantially the same as the radial width of the bonded surface of the lower surface of the bonded body 15. An annular gap 17 is also formed between the electrode 14 and the joined body 15.

The outer periphery of the diaphragm 13 is joined to a joined body 15.
Therefore, the range in which it can bend, that is, the effective range is a portion inside (center side) of the inner peripheral edge 15 a of the joined body 15. The diameter of the effective range is substantially equal to the diameter of the inner peripheral edge 15a of the joined body 15.

When the substrate 11 and the diaphragm 13 are joined by the joint 15, first, the annular portion 1 of the substrate 11 is joined.
Fluid solder glass is applied to 1b by screen printing or the like with a width substantially equal to the distance between the outer peripheral edge 11a and the outer peripheral edge of the groove 18. Next, the diaphragm 13 is overlaid on the solder glass with the electrode 14 facing downward. Thereafter, the diaphragm 13 is heated while being pressed at a constant pressure, and the solder glass is baked to bond and seal the substrate 11 and the diaphragm 13. At this time, electrode 1
The pressure and the like are adjusted so that the gap g between 2 and 14 has a predetermined value. Thus, the substrate 11 and the diaphragm 13 are
Are integrated as shown in FIG.

In this capacitive pressure sensor 10, the substrate 11
Since the groove 18 is provided on the outside of the electrode 12, the solder glass adhered on the annular portion 11b tends to flow toward the electrode 12 at the time of pressurization and heating, but the solder glass is It flows in and cannot flow any further inside due to its fluidity. For this reason, even if the amount of solder glass adhered on the annular portion 11b is slightly different,
The possibility that the solder glass flows inside the groove 18 is eliminated.

As a result, the diameter of the effective range of the diaphragm 13 can be kept substantially constant if the amount of the solder glass is slightly increased so that the inner peripheral edge 15a of the joined body 15 always comes to the position shown in FIG. Therefore, variation in pressure-capacitance characteristics is reduced. If the variation in the pressure-capacitance characteristics is small, the correction circuit becomes unnecessary, and the pressure sensor 1
There is an advantage that the driving circuit for the zero can be simplified.

(Operation) Next, the operation of the capacitive pressure sensor 10 having the above configuration will be described. When the capacitive pressure sensor 10 is used, the substrate 10 is fixed to a casing or the like, and a fluid pressure is applied to the diaphragm 13 from outside. Further, a predetermined electric circuit is connected to the lead wires connected to the electrodes 12 and 14.

When the fluid pressure acts, the diaphragm 13 bends and the gap g between the electrodes 12 and 14 changes. As a result, the capacitance of the capacitor formed by the electrodes 12, 14 and the gap g between them changes. By measuring this capacitance, the fluid pressure can be known.
Since the groove 18 is provided between the electrode 12 on the substrate 11 and the joined body 15, it has no adverse effect on the detection operation.

(Confirmation Test) In order to confirm the effect of the present invention, a test was conducted under the following conditions.

First, an alumina substrate having a diameter of 20 mm and a thickness of 0.8 mm and an alumina diaphragm having the same diameter and a thickness of 3 mm are formed.
mm electrode on an alumina diaphragm with a diameter of 11 mm.
Were fixed respectively. These electrodes were screen-printed circularly with silver paste and then fixed by baking at 750 ° C. The substrate groove has a diameter (measured at the center of the groove) of 12 mm, a radial width of 0.5 mm,
The section was V-shaped with a depth of about 0.3 mm.

Next, the electrode side of the substrate is placed upward, and a solder glass is formed on the upper surface of the substrate in a ring shape by screen printing with a width substantially equal to the distance between the outer peripheral edge of the substrate and the outer peripheral edge of the groove. Was applied, and a diaphragm was overlaid thereon with the electrode facing down.

Thereafter, the pressure is increased at a constant pressure, and is
Bake at 00 ° C for sealing, and set the gap between both electrodes to 30μ.
m. Thus, a grooved pressure sensor shown in FIGS. 1 and 2 was obtained.

Further, the same pressure sensor was manufactured in the same manner as in the above steps, and a total of ten pressure sensors were obtained.

On the other hand, an alumina substrate having the same shape and dimensions as the above substrate except that it had no groove was manufactured, and ten pressure sensors shown in FIGS. 6 and 7 were obtained in the same manner as above.

Then, the capacitance acting on each of the pressure sensors was measured while changing the pressure acting on the diaphragm, and the pressure-capacitance characteristics were investigated. The result is as shown in FIG. From FIG. 5, the variation is very large in the conventional pressure sensor without grooves (FIGS. 6 and 7), while the variation in capacitance is very small in the pressure sensor of the present invention (FIGS. 1 and 2). (About 1/3).

(Other Embodiments) FIGS. 3 and 4 show another embodiment of the present invention. In FIGS. 3 and 4, corresponding parts of the embodiment of FIGS. 1 and 2 are denoted by corresponding reference numerals. This embodiment is different from the embodiment shown in FIGS. 1 and 2 in that the substrate-side electrode is composed of a disk-shaped main electrode 22 and a ring-shaped auxiliary electrode 29 provided concentrically with the main electrode 22. It is different from the example. Main electrode 22 and auxiliary electrode 29
Are separated by a groove 30. Thus, the main electrode 2
In this case, the two electrodes 2 and the auxiliary electrode 29 are provided.
The stray capacitance between 2 and 29 can be greatly reduced,
29 can be electrically separated almost completely.

When the main electrode 22 and the auxiliary electrode 29 are provided as described above, the auxiliary electrode 2 is provided on the annular portion 21b of the substrate 21.
An annular groove 28 is provided adjacent to the groove 9. With this configuration,
The flow of the solder glass is suppressed by the grooves 28, and the variation in the pressure-capacitance characteristics can be reduced in the same manner as described above.

In the above embodiment, the solder glass is used as the joined body, but other fluid materials can be used. The groove 1 for suppressing the flow of the solder glass
8 and 28 are provided adjacent to the outside of the electrode 12 and the auxiliary electrode 29, but the annular portions 11 b and 2
If it is on 1b and inside the joined bodies 15, 25, its position can be changed as appropriate.

[0037]

According to the electrostatic pressure sensor of the present invention,
Variations in pressure-capacitance characteristics can be reduced with a simple configuration.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of an electrostatic pressure sensor according to the present invention.

FIG. 2 is a sectional view of the electrostatic pressure sensor of FIG.

FIG. 3 is an exploded perspective view showing another embodiment of the electrostatic pressure sensor of the present invention.

FIG. 4 is a sectional view of the electrostatic pressure sensor of FIG. 3;

FIG. 5 is a graph comparing the variation in pressure-capacitance characteristics between the electrostatic pressure sensor of the present invention and a conventional electrostatic pressure sensor.

FIG. 6 is an exploded perspective view showing an example of a conventional electrostatic pressure sensor.

FIG. 7 is a cross-sectional view of the conventional electrostatic pressure sensor of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Capacitive pressure sensor 11 Substrate 11a Outer edge 11b Annular part 12 Electrode 12a Outer edge 13 Diaphragm 13a Outer edge 13b Annular part 14 Electrode 14a Outer edge 15 Joint 15a Inner edge 16, 17 Gap 18 Groove 20 Capacitive pressure sensor 21 Substrate 21a Outer edge 21b Annular portion 22 Main electrode 23 Diaphragm 23a Outer edge 23b Annular portion 24 Electrode 24a Outer edge 25 Joint 25a Inner edge 26, 27 Gap 28 Groove 29 Auxiliary electrode 29a Outer edge 30 Groove 31 Gap G Gap

Claims (1)

(57) [Claims] 1. A substrate having an electrode, a diaphragm having another electrode opposed to the electrode at a predetermined interval, and a fluid material which joins the substrate and the diaphragm at their peripheral edges is formed by curing. Wherein the outer peripheral edge of the substrate and the outer peripheral edge of the electrode on the substrate are detected by detecting a pressure acting on the diaphragm as a change in capacitance between the two electrodes. Between
An annular portion formed on the substrate; and an annular portion formed on the annular portion.
An annular groove formed outside the electrode on the substrate.
A capacitive pressure sensor provided near a periphery .