JPH0832089A - Electrostatic capacitance pressure sensor - Google Patents

Abstract

PURPOSE:To provide an electrostatic capacitance pressure sensor, which can compensate an irregularity in the output characteristics of capacitors, which is due to an irregularity in the temperature characteristics of the capacitors. CONSTITUTION:A pressure sensing capacitor 41, a reference capacitor 42 and a storage capacitor 43 are constituted as an integrally formed sensor chip and the sensor chip has a silicon substrate 21 and a glass substrate 22, which are substantially equal in thermal expansion coefficient, so that the characteristics of the capacitors 41, 42 and 43 do not depend upon a temperature change. In the substrate 21, a diaphragm 23, which is deformed by a pressure, a cavity part 24, which is formed between the substrates 21 and 22, and a common electrode 20 are formed. In the substrate 22, three electrodes 25, 26 and 27 and a through hole 28 are formed. When a pressure is applied to the diaphragm 23 through a pressure introducing hole 34, the diaphragm 23 is deformed, the interval between the diaphragm 23 and the electrode 25 becomes narrow and the electrostatic capacity of the capacitor 41 is increased, but the interval between the electrode 20 and the electrodes 26 and 27 is not changed and each electrostatic capacitance of the capacitors 42 and 43 is constant.

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.

[0002]

2. Description of the Related Art A conventional capacitance type pressure sensor has a predetermined capacitance as a pressure sensitive capacitor 41 of a sensor detection circuit shown in FIG. 3 whose capacitance varies according to pressure and a reference capacitor. The reference capacitor 42 having the electrostatic capacitance of is provided. More specifically, the conventional electrostatic capacitance type pressure sensor is connected between the non-inverting input terminal to the operational amplifier 11 having the reference potential connected thereto and the pulse generating circuit 13 and the inverting input terminal of the operational amplifier 11 and is externally applied. A predetermined electrostatic capacitance connected between the pressure-sensitive capacitor 41 whose electrostatic capacity changes according to the applied pressure, the inverting circuit 14 for inverting the signal from the pulse generating circuit 13, and the inverting input terminal of the operational amplifier 11. Reference capacitor 4 having capacity
2, a switch 15 connected between the inverting input terminal and the output terminal of the operational amplifier 11 and turned on / off by a signal of the pulse generation circuit 13, and a predetermined electrostatic capacitance connected between the inverting input terminal and the output terminal of the operational amplifier 11. Is connected to the capacitor 16.

It should be noted that the pressure-sensitive capacitor 41 shown in FIG.
As shown in, the electrode 25 formed on the glass substrate 22.
And a silicon substrate 21 are provided so as to face each other with a predetermined gap, and a pressure sensitive capacitor is used. Further, as the reference capacitor 42, a reference capacitor in which the electrode 26 formed on the glass substrate 22 and the silicon substrate 21 are arranged so as to face each other with a predetermined gap is used.

[0004]

In the conventional capacitance type pressure sensor, the temperature characteristics of the capacitor (pressure sensitive capacitor, reference capacitor) inside the sensor and the capacitor 16 which is the external capacitor of the sensor detection circuit are different. However, there is a drawback that the output characteristics vary.

An object of the present invention is to provide a capacitance type pressure sensor capable of compensating for variations in output characteristics due to variations in temperature characteristics of capacitors.

[0006]

In order to solve the above problems, the present invention provides a first operational amplifier having a reference potential connected to a non-inverting input terminal, a pulse generating circuit, and an inverting input of the first operational amplifier. A pressure-sensitive capacitor connected between the terminal and a terminal, the capacitance of which changes according to the pressure applied from the outside; an inverting circuit for inverting the signal from the pulse generating circuit; and an inverting input terminal of the first operational amplifier. A reference capacitor having a predetermined electrostatic capacity connected between the first and second operational amplifiers, a switch connected between the inverting input terminal and the output terminal of the first operational amplifier and turned on / off by a signal from a pulse generation circuit, and the first capacitor. In a capacitance type pressure sensor having a storage capacitor having a predetermined capacitance connected between an inverting input terminal and an output terminal of an operational amplifier, a diaphragm portion that deforms according to pressure While being formed, the silicon substrate forming the first electrode on one surface including the diaphragm portion,
And a glass substrate on each surface of which electrically independent second, third and fourth electrodes are formed, and the first electrode and the second, third and fourth electrodes are mutually isolated. The first electrode is provided with a capacitor in which the silicon substrate and the glass substrate are fixed to each other such that they are opposed to each other with a predetermined distance and the second electrode is opposed to the diaphragm portion. And the second electrode as the pressure sensitive capacitor, the first electrode and the third electrode as the reference capacitor, and the first electrode and the fourth electrode as the storage capacitor. As the above, an electrostatic capacity type pressure sensor formed on one chip substrate is adopted as a means.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An operational amplifier 11 having a reference potential connected to a non-inverting input terminal, a pulse generation circuit 13, and an operational amplifier 1.
1 is connected to the inverting input terminal of No. 1 and has a capacitance that changes in accordance with the pressure applied from the outside.
A reference capacitor 42 having a predetermined capacitance connected between the inverting circuit 14 for inverting the signal from the pulse generating circuit 13 and the inverting input terminal of the operational amplifier 11, and the inverting input terminal and output terminal of the operational amplifier 11. A switch 1 which is connected in between and is turned on / off by a signal from the pulse generation circuit 13.
5 and a storage capacitor 43 having a predetermined capacitance connected between the inverting input terminal and the output terminal of the operational amplifier 11.

The electrostatic capacitance C _S of the pressure sensitive capacitor 41 changes in value when pressure is applied. On the other hand, the electrostatic capacitance C _R of the reference capacitor 42 does not change in value due to pressure. These C _S and C _R are driven by the pulse signal V _P from the pulse generating circuit 13 and the pulse signal from the inverting circuit 14 having the opposite phase, respectively. The output pulse V ₀ of the sensor detection circuit is represented by the following equation.

V ₀ = V _P (C _S -C _R ) / C _C Here, C _C is the capacitance of the storage capacitor 43 arranged in parallel in the operational amplifier 11. The output voltage V ₀ is the change in the electrostatic capacitance of the pressure sensitive capacitor 41 and the reference capacitor 42 (C
Proportional to the reciprocal of the applied pressure is proportional to the _S -C _R).

Next, the pressure sensitive capacitor 41, the reference capacitor 42 and the storage capacitor 43 used in the capacitance type piezoelectric sensor of this embodiment will be described with reference to FIG. The pressure sensitive capacitor 41, the reference capacitor 42 and the storage capacitor 43 are configured as an integrated sensor chip as shown in FIG. This sensor chip has a silicon substrate 21 and a glass substrate 22 having substantially the same coefficient of thermal expansion so that its characteristics do not depend on temperature changes. The silicon substrate 21 is provided with a diaphragm 23 that deforms due to pressure and a cavity portion 24 that forms a gap between the glass substrate 22 and the common electrode 20 by diffusing impurities such as boron. . Further, three electrodes 25, 26 and 27 and a through hole 28 are formed on the glass substrate 22.

The silicon substrate 21 and the glass substrate 22 are
The common electrode 20 and the electrodes 25, 26, and 27 are adhered so as to face each other, and a sealant 30 is applied around the cavity 24 and fixed to each other. Further, the glass substrate 22 is fixed to a pedestal 33 in which the lead terminals 32 are arranged and the through holes 29 are provided, and the pedestal 33 is fixed to a cap portion 35 in which a pressure introducing hole 34 is formed. The common electrode 20, the electrode 25, and the electrode 26
The lead wires 31 connected to the electrodes 27 and the electrodes 27 are connected to the lead terminals 32, respectively.

When pressure is applied from the pressure introducing hole 34 by a pressure transmitting substance such as gas or liquid, the diaphragm 23 is deformed. That is, the common electrode 20 in the diaphragm 23 portion
The distance between the electrode and the electrode 25 becomes narrower, and the capacitance of the capacitor formed by the common electrode 20 and the electrode 25 in the diaphragm 23 portion increases. On the other hand, the common electrode 20 and the electrode 2
The distance from 6, 27 is constant regardless of the pressure. That is, the capacitance of the capacitor composed of the common electrode 20 and the electrodes 26 and 27 is constant regardless of the pressure. Therefore, the capacitor composed of the common electrode 20 and the electrode 25 of the diaphragm 23 can be used as the pressure sensitive capacitor 41 of FIG. 1, and the capacitor composed of the common electrode 20 and the electrodes 26 and 27 is the reference capacitor 42. , Can be used as the storage capacitor 43.

From the above equation, the output of the sensor detection circuit is C
_Although it is determined by _S , C _R , and C _C , conventionally C _C uses an external capacitor, and if the temperature coefficient of C _C varies, the temperature characteristic of the output pulse V ₀ of the sensor detection circuit also varies. there was however, the use of integrated three capacitors as in the present invention, that the temperature coefficient of C _C is coincident with the temperature coefficient of C _S, C _R, provide excellent pressure sensor temperature characteristic it can.

[0015]

According to the present invention, since the pressure sensitive capacitor, the reference capacitor, and the storage capacitor are formed on one chip substrate, it is possible to compensate for variations in output characteristics due to variations in temperature characteristics of the capacitors. A mold pressure sensor can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a sectional view of a sensor chip used in the capacitance type pressure sensor of FIG.

FIG. 3 is a circuit diagram of a conventional capacitance type pressure sensor.

FIG. 4 is a sectional view of a sensor chip used in the capacitance type pressure sensor of FIG.

[Explanation of symbols]

 11 Operational Amplifier 12 External Output Terminal 13 Pulse Generation Circuit 14 Inversion Circuit 15 Switch 16 Capacitor 20 Common Electrode 21 Silicon Substrate 22 Glass Substrate 23 Diaphragm 24 Cavity 25, 26, 27 Electrode 28, 29 Through Hole 30 Sealant 31 Lead Wire 32 Lead terminal 33 Pedestal 34 Pressure introduction hole 35 Cap portion 41 Pressure sensitive capacitor 42 Reference capacitor 43 Storage capacitor

Claims (2)

[Claims] 1. A non-inverting input terminal connected to a first operational amplifier to which a reference potential is connected, and a pulse generator circuit and an inverting input terminal of the first operational amplifier, which responds to pressure applied from the outside. And a reference capacitor having a predetermined capacitance connected between the pressure-sensitive capacitor whose capacitance changes, the inverting circuit that inverts the signal from the pulse generating circuit, and the inverting input terminal of the first operational amplifier. And the first
A switch that is connected between the inverting input terminal and the output terminal of the operational amplifier of and that turns on and off according to the signal of the pulse generation circuit,
In a capacitance type pressure sensor having a storage capacitor having a predetermined capacitance connected between an inverting input terminal and an output terminal of the first operational amplifier, the pressure sensitive capacitor, the reference capacitor and the storage capacitor are combined into one. An electrostatic capacitance type pressure sensor characterized by being configured on a chip substrate. 2. A diaphragm portion that deforms in response to pressure is formed, and a first surface is formed on the one surface including the diaphragm portion.
A silicon substrate having electrodes formed thereon and a glass substrate having second, third and fourth electrodes electrically independent of each other formed on one surface thereof, the first electrode and the second and third electrodes The silicon substrate and the glass substrate are fixed to each other such that the fourth electrode and the fourth electrode are arranged to face each other at a predetermined distance, and the second electrode is placed to face the diaphragm portion. A capacitor is provided, the first electrode and the second electrode are used as the pressure sensitive capacitor, the first electrode and the third electrode are used as the reference capacitor, and the first electrode is used. Electrode and the fourth
2. The electrostatic capacitance type pressure sensor according to claim 1, wherein the electrode and the electrode are used as the storage capacitor.