JPH11241968A - Electrical capacitance pressure sensor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the dispersion of characteristic to enhance the stability and rate of good product and reduce the cost. SOLUTION: Insulating substrates 30a and 30b consisting of mullite-cordierite ceramics are connected to both sides of a silicon substrate 20 having a diaphragm (a thin part 212 and a flat part 211 as movable electrode) displaceable by pressure by electrostatic bonding. Fixed electrodes 31a and 31b and electrodes 32a and 32b are formed on the insulating substrates 30a and 30b, respectively, to form capacitors C1 and C2. A detecting circuit 6 is formed by a bear chip on the upper surface of the insulating substrate 30b of the area where the rigidity is enhanced by the connection of the silicon substrate 20 to the two insulating substrates 30a and 30b. The detecting circuit 6 are formed after the silicon substrate 20 is connected to the insulating substrates 30a and 30b.

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 detecting a displacement of a diaphragm caused by a pressure or a pressure difference applied to the diaphragm as a capacitance value of a capacitor formed by the diaphragm and a counter electrode. .

[0002]

2. Description of the Related Art In a capacitance type pressure sensor (hereinafter abbreviated as a pressure sensor), a capacitance value of a capacitor for measuring a pressure to be measured or a pressure difference is 10 to 10%.
Since the value is as small as 0 pF, the effect of the stray capacitance associated with the wiring is large, and the detection circuit is arranged near the capacitor to minimize the effect.

FIGS. 3 and 4 are sectional views showing the structure of a conventional pressure sensor. Pressure sensor shown in FIG.
Reference numeral 10a denotes a pressure sensor disclosed in Japanese Patent Application Laid-Open No. 1-253627, in which a diaphragm 21 is formed on a silicon substrate 2 by anisotropic etching, and a signal processing circuit 22 is provided in a region other than the diaphragm 21. Are formed. The glass substrate 3 is bonded to the upper surface of the silicon substrate 2 by electrostatic bonding (in the publication, anodic bonding) to completely seal the upper part of the diaphragm 21 and the signal processing circuit 22.
The signal line 4 from the signal processing circuit 22 is passed through a hole formed in the glass substrate 3, and the signal line 4 is fixed by filling the hole with an adhesive 5.

The pressure sensor 10b shown in FIG.
This is a pressure sensor disclosed in Japanese Patent No. 323941. In the pressure sensor 10b, a frame 2a and a cover 2b, both made of a single-crystal silicon wafer, are integrated by a low-temperature bonding technique using a glass material (heat treatment at about 100 to 200 ° C.). The frame 2a has a square diaphragm 21a whose periphery is elastically held, and a movable electrode 24 made of a sputtered aluminum film is formed on the upper surface of the diaphragm 21a. The diaphragm 21a is formed by anisotropic etching using an alkaline solution. At the same time as the formation of the movable electrode 24, the connection wiring 25a from the movable electrode 24 and the external lead-out wiring 26 are also formed. A detection circuit 22a is formed in the cover 2b by a normal semiconductor manufacturing process, and an oxide film 27 made of SiO ₂ is formed by a CVD method so as to cover the detection circuit 22a. On the oxide film 27, a fixed electrode 28 facing the movable electrode 24 and a connection wiring 25b are formed by a sputtered aluminum film. Detection circuit 22a and connection wiring 25a
And 25b are connected by a contact hole 29a and a not-shown 29b.

In the case where a diaphragm 21 and a detection circuit (signal processing circuit in FIG. 3) 22 are formed on a silicon substrate 2 as shown in FIG. Etching
It is necessary to take measures to eliminate the influence of alkali metal contamination, which complicates the process and increases the process cost. If the alkali metal remains, the detection circuit 22 becomes unstable and the reliability decreases. Further, since the diaphragm 21 and the detection circuit 22 are formed in different regions of the same silicon substrate 2, the chip size increases and the cost increases. In addition, in the electrostatic bonding in which the silicon substrate 2 and the glass substrate 3 are bonded, the substrate is heated to about 400 ° C. and a voltage of several hundred volts is applied. Care must be taken, which may reduce the non-defective product rate.

In the case of FIG. 4, the cover 2b on which the detection circuit 22a is formed is a silicon substrate different from the frame 2a on which the diaphragm 21a is formed. The problem of contamination is gone. However, when the probability that the characteristics of the detection circuit 22a deteriorates in the joining process of the frame 2a and the cover 2b increases, the non-defective rate as a pressure sensor decreases, which causes a cost increase.
In the case of a MOSIC, the storage temperature is said to be 125 ° C. or lower. If the junction temperature between the frame 2a and the cover 2b increases, the deterioration of the characteristics of the detection circuit 22a becomes a problem. In the case of the aforementioned low-temperature bonding technique (heat treatment at about 100 to 200 ° C.), it is expected that there will be relatively few problems. However, when the frame 2a and the cover 2b are joined by electrostatic joining that can be joined without an adhesive layer, as described above, since the temperature is high and a high voltage is applied, the characteristics of the detection circuit 22a Deterioration is likely to increase, and the yield rate is likely to decrease.

A detection circuit formed on the cover 2b
When the pressure of the object to be measured is high when the cover 22b is deformed when the pressure of the object to be measured is high, the detection circuit 22a is formed in the upper portion of the diaphragm 21a as shown in FIG.
a has the problem that the characteristics of
2b needs to be thicker. The pressure sensor shown in FIGS. 3 and 4 is a pressure sensor for measuring a certain range of pressure. However, depending on the application, there is a case where only one pressure sensor cannot cover the measurement range.
A pressure sensor integrally having a plurality of diaphragms having different sensitivities to pressure as described in Japanese Patent Application No. 8-12762 filed by the inventors of the present invention corresponding to such an application. There is also.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to manufacture a pressure sensor and a pressure sensor which are less scattered in characteristics, have good stability, have a high yield rate, and are inexpensive. Is to provide a way.

[0009]

According to the present invention, there is provided a conductive substrate having a diaphragm which is displaced in response to pressure, and an electrode at a position opposed to the diaphragm. A pressure sensor comprising an insulating substrate bonded to a conductive substrate, and measuring a pressure or a pressure difference applied to the diaphragm by a capacitance value of a capacitor formed by the diaphragm and an electrode opposed thereto. A detection circuit for detecting the capacitance value of the capacitor is formed on the surface of the insulating substrate which is not the bonding surface with the conductive substrate (the invention of claim 1).

Since the detection circuit is formed on the surface of the insulating substrate other than the bonding surface, after the conductive substrate and the insulating substrate are bonded, the detection circuit is mounted on the insulating substrate under the condition that there is no fear of deterioration. Can be configured. According to the first aspect of the present invention, the area of the surface of the insulating substrate on which the detection circuit is formed can be within the area corresponding to the bonding area with the conductive substrate (the second aspect of the invention). The rigidity of the region corresponding to the diaphragm formed on the conductive substrate is the rigidity of only the insulating substrate, while the region where the conductive substrate and the insulating substrate are joined has rigidity due to the combined effect of both. Larger, less distortion due to pressure.

According to the first and second aspects of the present invention, the detection circuit can be constituted by a bare chip (the third aspect of the invention).
When the detection circuit is configured by a bare chip, there are the following advantages as compared with the case where a packaged detection circuit is used. Corrosion of the package due to the pressure transmission medium to which the detection circuit is exposed, for example, silicone oil, cracking of the package due to pressure, and the like are avoided, the area occupied by the detection circuit is reduced, and the configuration of the detection circuit can be easily changed. Further, the manufacturing process of the pressure sensor can be reduced as compared with the case where the pressure sensor is formed in the silicon substrate as shown in FIGS.

According to the first to third aspects of the present invention, the insulating substrate can be made of ceramic (the fourth aspect of the invention). Since ceramic has high rigidity, distortion of the detection circuit due to pressure applied to the pressure sensor can be reduced. According to the invention of claim 4, the conductive material can be a single crystal silicon wafer, and the ceramic can be a mullite-cordierite ceramic (the invention of claim 5). Single-crystal silicon as a conductive material has a wide elastic deformation range, has little variation in the properties of the material, and a technology for processing the diaphragm has been established, and is ideal as a material for forming the diaphragm. Further, the mullite-cordierite ceramic as an insulating material can obtain a ceramic whose thermal expansion coefficient exactly matches that of single crystal silicon, and has high rigidity as a ceramic.

According to a sixth aspect of the present invention, there is provided the method for manufacturing a capacitance type pressure sensor according to the first aspect, wherein after the conductive substrate and the insulating substrate are joined, the detection circuit is connected to the insulating substrate. Configure on the outside surface. Since the detection circuit is formed after the two substrates are joined, the detection circuit is not affected by temperature, voltage, and the like accompanying the joining of the two substrates.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to examples. FIG. 1 is a sectional view showing the structure of the embodiment, and FIG. 2 is a block diagram showing the configuration of the signal processing circuit. The silicon substrate 20 as a conductive substrate has a suitable electric conductivity, for example, about 0.1 Ωcm,
0] A p-type silicon wafer having a crystal plane orientation, a circular recess corresponding to the cavities 23a and 23b, and a ring groove for forming a ring-shaped thin portion 212 outside thereof are formed twice on each surface. It is formed by the above plasma etching. The inside of the ring-shaped thin part 212 is a flat part that is thicker
211, which is a movable electrode of the pressure sensor 100 .
The flat portion 211 and the thin portion 212 constitute a diaphragm that is displaced by a pressure difference. The silicon substrate
The thickness of the thin portion 20 and the thickness of the thin portion 212 are determined by the magnitude of the pressure or the pressure difference to be measured.

[0015] Mullite-
Insulating substrate 30a made of cordierite ceramic
And 30b are joined by electrostatic joining, and the insulating substrate 30a
And 30b, fixed electrodes 31a and 31b and electrodes 32a and 32b are formed by mask sputtering of three layers of chromium, platinum, and gold, respectively. A fixed electrode is connected to the electrode through the inner wall. Although not shown, a 1.6 μm thick Pyrex glass sputtered film is formed on each of the electrostatic bonding surfaces of the insulating substrates 30a and 30b, and the Pyrex glass film enables electrostatic bonding. Becomes

A flat portion 21 as a movable electrode of a silicon substrate 20
One and two fixed electrodes 31a and 31b form a pair of capacitors whose capacitance value changes relatively. The reason why the mullite-cordierite ceramic is used as the insulating substrates 30a and 30b is that a ceramic having a thermal expansion coefficient very close to that of silicon and having high rigidity can be obtained.

On the lower surface of the insulating substrate 30a, an insulating member 7 made of a mullite-cordierite ceramic having a through hole in the center and positioned in a state of conducting to the pressure introducing port 33a is provided with a gold-tin eutectic. Joined by solder. On the upper and lower surfaces of the insulating member 7, chrome for soldering,
Three sputtered films of platinum and gold are formed. Similarly, a base 8 made of stainless steel and having a through hole in the center is joined to the lower surface of the insulating member 7 by a gold-tin eutectic solder. A three-layer sputtered film of chromium, platinum, and gold is also formed on the soldered portion of the base 8. Through these through holes, the sealed pressure transmitting fluid 9 is supplied to the first pressure P1.
To the lower surface of the diaphragm.

On the other hand, the insulating substrate 30b has a silicon substrate
A through-hole is formed at one corner of the joint portion with the substrate 20, and after joining the two substrates, an electrode 35 is formed by aluminum mask sputtering to serve as an extraction electrode from the silicon substrate 20. Further, a detection circuit 6 using a bare chip is formed in a region corresponding to a region bonded to the syringe board 20 on a surface which is not a bonding surface with the silicon substrate 20, and the electrodes 32a, 32b and 35 Each is connected to an aluminum wire. The region where the detection circuit 6 is configured is a region having the highest rigidity in the pressure sensor 100 , and is close to a pair of capacitors, and requires a small amount of stray capacitance due to wiring.

The periphery of the pressure sensor 100 and the upper surface of the diaphragm are shown for transmitting a second pressure P2 with respect to the pressure P1 guided through the through hole of the base 8 or the like to the upper surface of the diaphragm. No pressure transmitting fluid is sealed. Pressure P1 and pressure P2 applied to both sides of the diaphragm
The thin portion 212 is deformed by the difference from
The flat portion 21 which is displaced vertically to 32a and 32b and is a movable electrode
1 and the capacitance value C ₁ between the fixed electrode 31a, the flat portion 211
And the capacitance value C ₂ between the fixed electrode 31b is relatively changed, the difference between P1 and P2 by measuring its value is detected to. In this pressure sensor, if one of the pressures is set to the atmospheric pressure, it becomes a gauge pressure sensor, and if one is set to a vacuum, it becomes an absolute pressure sensor.

FIG. 2 shows an example of the detection circuit 6.
The circuit configuration is the same as that described in Japanese Patent Application No. 8-12762. Although only one diaphragm is shown in FIG. 1, the detection circuit 6 of FIG. 2 includes a pressure difference sensor having several diaphragms having different measurement pressure ranges, an absolute pressure sensor measuring with one capacitance, and Is applied to a composite pressure sensor having a temperature sensor and the like. The detection circuit 6 includes a switching unit 61 for sequentially switching a plurality of pairs of capacitors corresponding to the capacitance values C ₁ and C ₂ , a capacitor for absolute pressure, a capacitor for temperature measurement, and the like, and connecting to the detection unit 62, And means 62. The capacitance value corresponding to each capacitor is converted to a noise-resistant signal by the detection means 62 and sent to the calculation means 60.

In the above description, the paired capacitor and 1
A description has been given of the case where all the capacitors and the capacitor for temperature measurement are included.However, it is not a necessary condition that the pressure sensor 100 includes all the above-described capacitors, and the pressure sensor 100 is configured by appropriately combining them as necessary. It should be done. Therefore, in the minimum case, there may be one in which the switching means 61 is lacking with only one capacitor for absolute pressure.

FIG. 1 illustrates the case of a pressure sensor 100 having a circular diaphragm having a ring-shaped thin portion 212 at the peripheral portion and having both sides forming a capacitor. The present invention can be applied to a diaphragm having a square shape and a uniform thickness as shown in FIG. The present invention is not limited by the shape of the diaphragm, the configuration of the capacitor, and the like.

Also, an example in which a p-type silicon wafer having a [100] plane as a crystal plane direction is used as the silicon substrate 20 has been described.
It is not restricted by the crystal plane.

[0024]

According to the present invention, a conductive substrate having a diaphragm which is displaced in response to pressure and an insulating substrate having an electrode at a position facing the diaphragm and joined to the conductive substrate are provided. In the provided capacitance type pressure sensor, since the detection circuit for detecting the capacitance value is configured on the surface of the insulating substrate on the side other than the bonding surface with the conductive substrate,
After bonding the conductive substrate and the insulating substrate, the detection circuit can be formed on the insulating substrate under a condition in which there is no fear of deterioration. Therefore, the detection circuit does not deteriorate due to the joining of the conductive substrate and the insulating substrate, and the non-defective product rate does not decrease. Further, the detection circuit can be configured near the diaphragm.

When the surface region of the insulating substrate on which the detection circuit is formed is within a region corresponding to the bonding region with the conductive substrate, the region forming the detection circuit has high rigidity and less distortion due to pressure. Excellent characteristics can be obtained even under high pressure, and variations in characteristics can be reduced. As a result, the non-defective rate is improved, and the price is reduced (claim 2).

When the detection circuit is constituted by a bare chip, the package is corroded by a pressure transmission medium to which the detection circuit is exposed, for example, silicone oil, which is generated when a packaged product is used as the detection circuit, and the package is cracked by pressure. Can be avoided, so that the reliability of the detection circuit is improved. Further, the area occupied by the detection circuit is reduced, so that the cost is reduced and the size is reduced. Further, since the configuration of the detection circuit can be easily changed, the development time and the development cost can be significantly reduced. Further, as compared with the case where the detection circuit is formed on a silicon substrate, the number of manufacturing steps is reduced, and the process cost is reduced. (Claim 3).

When the insulating substrate is made of ceramic, distortion of the detection circuit due to the pressure applied to the pressure sensor can be reduced, so that even under high pressure, excellent characteristics with little influence of distortion can be obtained. Can be reduced (claim 4). When the conductive material is a single-crystal silicon wafer and the ceramic is a mullite-cordierite-based ceramic, silicon is ideal as a material forming the diaphragm, and has a coefficient of thermal expansion that exactly matches the coefficient of thermal expansion and has high rigidity. With the mullite-cordierite ceramic from which the ceramic can be obtained, a pressure sensor exhibiting the above various effects at the highest can be obtained (claim 5).

According to a sixth aspect of the present invention, there is provided the method of manufacturing a capacitance type pressure sensor according to the first aspect, wherein after the conductive substrate and the insulating substrate are joined, the detection circuit is connected to the insulating substrate. Since the detection circuit is provided on the outer side surface, the detection circuit is not affected by the temperature, voltage, and the like associated with the joining of the two substrates. Therefore, the detection circuit is not deteriorated due to the joining of the conductive substrate and the insulating substrate, and the non-defective product rate is not reduced.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a detection circuit.

FIG. 3 is a sectional view showing the structure of an example of a conventional pressure sensor.

FIG. 4 is a sectional view showing the structure of another example of the conventional pressure sensor.

[Description of Signs ] 10a , 10b , 100 Pressure sensor 2, 20 Silicon substrate 2a Frame 2b Cover 21, 21a Diaphragm 22 Signal processing circuit 22a Detection circuit 23 n ⁺ layer 24 Movable electrode 25a, 25b Connection wiring 26 External extraction wiring 27 Oxidation Membrane 28 Fixed electrode 29a Contact hole 3 Glass substrate 30a, 30b Insulating substrate 31, 31a, 31b Fixed electrode 32a, 32b, 35 Electrode 33a, 33b Pressure port 34 Through hole 4 Signal line 5 Adhesive 6 Detection circuit 61 Switching means 62 Detecting means 7 Insulating member 8 Base 9 Pressure transmitting fluid 60 Calculation means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Shuhisa Kato 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Kimihiro Nakamura 1, Tanabe-Nitta, Kawasaki-ku, Kawasaki, Kanagawa, Japan No. 1 Fuji Electric Co., Ltd.

Claims (6)

[Claims] A conductive substrate having a diaphragm that is displaced in response to pressure; and an insulating substrate joined to the conductive substrate having electrodes at positions facing the diaphragm. In a capacitance type pressure sensor for measuring a pressure or a pressure difference applied to a diaphragm based on a capacitance value of a capacitor formed by an opposing electrode, a detection circuit for detecting a capacitance value of the capacitor is electrically conductive. A capacitance-type pressure sensor, wherein the capacitance-type pressure sensor is formed on a surface of an insulating substrate which is not a bonding surface with the substrate. 2. The electrostatic capacitance type according to claim 1, wherein a region on the surface of the insulating substrate on which the detection circuit is formed is within a region corresponding to a bonding region with the conductive substrate. Pressure sensor. 3. The capacitance type pressure sensor according to claim 1, wherein said detection circuit is constituted by a bare chip. 4. The capacitance type pressure sensor according to claim 1, wherein said insulating substrate is made of ceramic. 5. The capacitance-type pressure sensor according to claim 4, wherein said conductive material is a single crystal silicon wafer, and said ceramic is a mullite-cordierite ceramic. 6. The method for manufacturing a capacitance type pressure sensor according to claim 1, wherein the detection circuit is formed on the surface of the insulating substrate after the conductive substrate and the insulating substrate are joined. A method for producing a capacitance type pressure sensor.