JPH08193903A - Capacitive pressure sensor - Google Patents

Abstract

PURPOSE: To obtain a capacitive pressure sensor in which the linearity is enhanced in the output characteristics while minimizing fluctuation in the output caused by an outer conductor by suppressing the parasitic capacitance formed by a conductor disposed closely to the outer circumference of the sensor. CONSTITUTION: The pressure sensor comprises a glass substrate 20 provided with electrodes, a silicon substrate 10 provided with a diaphragm part 11 being deformed by the pressure, a sensor chip 30 for bonding the glass substrate 20 and the silicon substrate 10 while facing the diaphragm part 11 and the electrode through a gap, upper and lower sealing housings 43, 41 having lead terminals 51, 52 for connecting the electrode output terminals of the sensor chip 30, conductors, and a resin case 71. The sensor chip 30 is arranged in the sealing housing, the lead terminals 51, 52 are connected with a signal processing circuit, and the sealing housings 43, 41 are encased, along with the signal processing circuit, in the resin case subjected to metal plating on the surface thereof.

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 change in capacitance of opposing electrode surfaces.

[0002]

2. Description of the Related Art As this type of capacitance type pressure sensor,
A pressure sensor as shown in FIG. 3 is generally known. In FIG. 3, a diaphragm portion 11 that deforms according to pressure is formed on a silicon substrate 10, and a fixed electrode 21 is formed on a glass substrate 20.

Further, the silicon substrate 10 and the glass substrate 20 are joined at a part thereof, whereby
The cavity 12 is formed below the diaphragm 11.

A sensor chip 30 is constituted by the silicon substrate 10 and the glass substrate 20, and the sensor chip 30 is bonded onto the lower sealing casing 41 by the glass substrate 20.

Further, in order to introduce a pressure for introducing atmospheric pressure, or for introducing a pressure to be compared with the measured pressure, into the glass substrate 20 constituting the sensor chip 30 and the lower sealed casing 41 in which the sensor chip 30 is arranged. A through hole 42 that serves as a passage is formed.

In the lower sealed casing 41, lead terminals 51 and 52, which are produced together at the time of molding, are arranged.

On the upper surface of the glass substrate 20, there are formed a bonding pad 23 from which the fixed electrode 21 is drawn out and a bonding pad 22 from which the movable electrode 13 formed on the diaphragm 11 is drawn out.

The lead terminal 52 and the bonding pad 23 are electrically connected by a lead wire 61, and the lead terminal 51 and the bonding pad 22 are connected by a lead wire 62.

The lower sealed casing 41 and the upper sealed casing 43 provided with a pressure introducing passage 44 for introducing the measured pressure are sealed by ultrasonic welding.

In the capacitance type pressure sensor of FIG. 3, when pressure is applied to the diaphragm portion 11, the diaphragm portion 11 is deformed according to the magnitude of the pressure. Due to the deformation of the diaphragm portion 11, the gap between the movable electrode 13 and the fixed electrode 21 changes.

Here, there is a relationship of c = ξ (A / d) between the movable electrode 13 and the fixed electrode 21. In addition, c: capacitance, ξ: dielectric constant of air, A: electrode area, d: gap between electrodes.

Therefore, the capacitance changes due to the change in the gap between the electrodes, and further, since there is a certain correlation between the pressure and the gap between the electrodes, by detecting the capacitance, You can know the pressure.

The lead terminals 51 and 52 are connected to a signal processing circuit board 81 for converting the electrostatic capacity into a voltage output to form an electrostatic capacity type pressure sensor.

[0014]

However, in the conventional capacitance type pressure sensor, as shown in the equivalent circuit of FIG. 4, the capacitance Cs of the sensor chip, which changes depending on the pressure to be detected.
Is as small as 1 and 2 pF, the sensor chip is arranged in a sealed casing, and the lead terminals 51 and 52 connected to the output terminal of the sensor chip are connected to the signal processing circuit board 81. 51, 52, when the outer conductor 91 approaches the periphery of the wiring pattern of the signal processing circuit board 81, the capacitance C formed through the conductor 91.
d1 and Cd2 are parasitic capacitances that exist in parallel with the electrostatic capacitance Cs of the sensor chip, and have a drawback that the linearity is lowered when the inverse characteristic of the electrostatic capacitance Cs of the sensor chip is used.

Further, when the approach distance of the outer conductor or the like in the periphery changes, the parasitic capacitance also changes, and the sensor output becomes unstable.

An object of the present invention is to suppress the parasitic capacitance formed by a conductor close to the outer periphery of the sensor, to have a good output characteristic linearity, and to reduce the output fluctuation due to the influence of the outer conductor. To provide a sensor.

[0017]

In order to achieve the above object, the present invention provides a first substrate having an electrode portion and a second substrate having a diaphragm portion which deforms in response to pressure. The first diaphragm so that the diaphragm portion and the electrode portion are opposed to each other with a gap.
And a second substrate to form a sensor chip, the width of the gap is changed according to the pressure applied to the diaphragm, and the diaphragm and the electrode are changed in accordance with the change of the width of the gap. Is configured to detect the pressure by a change in capacitance between the sensor chip, the sensor chip is arranged in a sealed housing having a lead terminal for connecting the electrode output terminal of the sensor chip, the lead terminal In a pressure sensor connected to a signal processing circuit and housing the sealed housing in a resin case, the sealed housing and the signal processing circuit are housed in a resin case whose surface is metal-plated. It is a characteristic electrostatic capacity type pressure sensor.

[0018]

[Function] The sealed casing in which the sensor chip is arranged and the signal processing circuit are housed in a resin case whose surface is metal-plated, and the metal plating is used as a guard, whereby the conductor outside the case and the wiring inside the case Capacitance generated between them can be suppressed.

That is, by reducing the parasitic capacitance existing in parallel with the electrostatic capacitance of the sensor chip, it is possible to obtain stable output characteristics with good linearity.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A capacitance type pressure sensor of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view and a cross-sectional view of a capacitance type pressure sensor of the present invention.

As shown in FIG. 1, a silicon substrate 10 is provided with a diaphragm portion 11 which is deformable in response to pressure.
A fixed electrode 21 is formed on the glass substrate 20.

Further, the silicon substrate 10 and the glass substrate 20 are joined at a part thereof, whereby
The cavity 12 is formed below the diaphragm 11.

A sensor chip 30 is constituted by the silicon substrate 10 and the glass substrate 20, and the sensor chip 30 is bonded onto the lower sealed casing 41 by the glass substrate 20.

In order to introduce a pressure for introducing atmospheric pressure, or for introducing a pressure to be compared with the measured pressure, into the glass substrate 20 constituting the sensor chip 30 and the lower sealed casing 41 in which the sensor chip 30 is arranged. A through hole 42, which is a passage of, is formed.

In the lower sealed casing 41, lead terminals 51 and 52, which are produced together at the time of molding, are arranged. On the upper surface of the glass substrate 20, a bonding pad 23 from which the fixed electrode 21 is drawn and a bonding pad 22 from which the movable electrode 13 formed on the diaphragm 11 is drawn are formed.

The lead terminal 52 and the bonding pad 23 are electrically connected by a lead wire 61, and the lead terminal 51 and the bonding pad 22 are connected by a lead wire 62.

The lower sealed casing 41 and the upper sealed casing 43 provided with a pressure introducing passage 44 for introducing the measured pressure are sealed by ultrasonic welding.

The lead terminal 5 is provided on the signal processing circuit board 81 for converting the electrostatic capacity of the sensor chip into a voltage output.
1, 52 are connected.

A resin case 71 whose surface is metal-plated with the sealed casings 41 and 43 and the signal processing circuit board 81.
And the metal plating 72 is connected to GND or a stable potential on the circuit, so that electrostatic generated between the conductor 91 approaching the outer periphery of the case 71 and the wiring inside the case 71. Use as a guard to suppress the capacity.

Therefore, as shown in the equivalent circuit of FIG. 2, the capacitance Cs of the sensor chip, which changes depending on the pressure to be detected.
The conductor 9 that approaches the outer periphery of the case 71 in parallel with
It is possible to suppress the parasitic capacitance, which is an electrostatic capacitance generated between the wiring 1 and the wiring inside the case 71, to be small.

[0031]

As described above, according to the present invention, the parasitic capacitance formed by the conductor close to the outer periphery of the sensor is suppressed, the linearity of the output characteristic is good, and the influence of the outer conductor is exerted. It was possible to provide a capacitance type pressure sensor with small output fluctuation.

[Brief description of drawings]

FIG. 1 is a perspective view and a cross-sectional view showing an embodiment of a capacitance type pressure sensor of the present invention. 1A is a perspective view, FIG.
(B) is a sectional view.

FIG. 2 is an equivalent circuit diagram of the capacitance type pressure sensor of the present invention.

3A and 3B are a perspective view and a cross-sectional view showing a structural example of a conventional capacitance type pressure sensor. 3A is a perspective view and FIG. 3B is a sectional view.

FIG. 4 is an equivalent circuit diagram of a conventional capacitive pressure sensor.

[Explanation of symbols]

10 Silicon Substrate 11 Diaphragm Section 12 Cavity Section 13 Movable Electrode 20 Glass Substrate 21 Fixed Electrodes 22, 23 Bonding Pad 30 Sensor Chip 41 (Lower) Sealing Housing 42 Through Hole 43 (Upper) Sealing Housing 44 Pressure Introducing Path 51,52 Lead terminal 61,62 Lead wire 71,73 (resin) case 72 Metal plating 81 Signal processing circuit board 91 Conductor Cs Capacitance of sensor chip Cd1, Cd2 Capacitance V via external conductor V _OVT output voltage

Claims (1)

[Claims] 1. A first substrate on which an electrode portion is formed, and a second substrate on which a diaphragm portion that deforms in response to pressure is formed, wherein the diaphragm portion and the electrode portion have a gap. The first so that they have a relationship of facing each other.
And a second substrate to form a sensor chip, the width of the gap is changed according to the pressure applied to the diaphragm, and the diaphragm and the electrode are changed in accordance with the change of the width of the gap. Is configured to detect the pressure by a change in capacitance between the sensor chip, the sensor chip is arranged in a sealed housing having a lead terminal for connecting the electrode output terminal of the sensor chip, the lead terminal In a pressure sensor connected to a signal processing circuit and housing the sealed housing in a resin case, the sealed housing and the signal processing circuit are housed in a resin case whose surface is metal-plated. Characteristic capacitance type pressure sensor.