JPH10170376A - Capacitive pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive pressure sensor which can suppress the parasitic capacitance generated by a conductor approaching the outer periphery of the sensor and has excellent linearity in its input-output characteristic and the output of which does not fluctuate much even when the sensor is affected by an external conductor. SOLUTION: A sensor chip 30 and a signal processing circuit 71 are housed in cases 41 and 43 formed by molding a resin material and the cases 41 and 43 are used as guards. The capacitance generated between a conductor on the outside of the cases 41 and 43 and the internal wiring of the cases 41 and 43. In other words, a stable input-output characteristic having excellent linearity is obtained by reducing a parasitic capacitance which exists in parallel with the capacitance of the sensor chip 30.

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 between opposed electrode surfaces.

[0002]

2. Description of the Related Art A pressure sensor shown in FIGS. 4 and 5 is generally known as this type of capacitance type pressure sensor.
FIG. 4 is a cross-sectional view of the pressure sensor, and FIG. 5 is an external perspective view of the pressure sensor without the upper sealing housing 43.

The silicon substrate 10 has a diaphragm 11 that is deformed in response to pressure, and the glass substrate 20 has a fixed electrode 21 formed thereon. As shown, the silicon substrate 10 and the glass substrate 20 are joined at a part thereof, and a cavity 12 is formed below the diaphragm 11.

The silicon substrate 10 and the glass substrate 2
0 constitutes the sensor chip 30, and the sensor chip 30 is adhered to the lower sealing housing 41 as a case by the glass substrate 20. In addition, the sensor chip 30
A passage 42 for introducing atmospheric pressure or for introducing a pressure to be compared with a measured pressure is formed in the lower sealing housing 41 in which the glass substrate 20 and the sensor chip 30 are arranged. Bonding pads 51, 52, and 53 formed together during molding are arranged in the lower sealing housing 41. The fixed electrode 21 is provided on the upper surface of the glass substrate 20.
And a bonding pad 22 from which the movable electrode 13 formed on the diaphragm portion 11 is drawn.

The bonding pads 22 and 23 are respectively formed on the bonding pads 24 and 23 formed on the signal processing circuit 71.
25 is connected by lead wires 61 and 62.

The signal processing circuit 71 has input / output pads 26, 27, 28 formed thereon, and these bonding pads 26, 27, 28 are connected to the lead terminals 51 implanted in the lower sealing housing 41. , 52, 53 to lead wire 8
3, 84, 85.

[0007] The lower sealed housing 41 and the upper sealed housing 43 provided with an introduction path (hole) 44 for introducing a measured pressure are sealed by ultrasonic welding or the like.

In the illustrated conventional capacitance type pressure sensor, when pressure is applied to the diaphragm 11, the diaphragm 11 is deformed according to the magnitude of the pressure. The deformation of the diaphragm 11 causes the movable electrode 13 and the fixed electrode 21
Will change. Here, c = ξ (A / d) between the movable electrode 13 and the fixed electrode 21.
There is a relationship. Here, c: capacitance, Δ: 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 since there is a certain correlation between the pressure and the gap between the electrodes, the pressure is detected by detecting the capacitance. You can know.

[0010]

By the way, in the conventional capacitance type pressure sensor, as shown in an equivalent circuit of FIG.
The capacitance C of the sensor chip that changes according to the detected pressure
s is as small as 1 or 2 pF, and the sensor chip 30 and the signal processing circuit 71 are arranged in a sealed housing, and the sensor chip 3
0 to the signal processing circuit 71.
Bonding pads 24 and 25 with lead wires 61 and 6
Connect by two.

However, the bonding pads 22,
When an external conductor 91 approaches the wiring patterns 23, 24, 25, the lead wires 61, 62 and the signal processing circuit 71, the capacitance C formed via the conductor 91 is reduced.
It becomes a parasitic capacitance existing in parallel with d1, Cd2, and the capacitance Cs of the sensor chip, and has a drawback that the linearity is reduced when the reciprocal characteristic of the capacitance of the sensor chip is used.

Further, when the approach distance of the peripheral external conductor changes, the parasitic capacitance changes and the sensor output becomes unstable.

Therefore, the technical problem (object) of the present invention is as follows.
An object of the present invention is to provide a capacitance-type pressure sensor which suppresses a parasitic capacitance formed by a conductor approaching an outer periphery of a sensor, has good linearity of input / output characteristics, and has small output fluctuation due to the influence of the external conductor.

[0014]

According to the present invention, a sealed housing, a first substrate housed in the sealed housing on which an electrode portion is formed, and a diaphragm portion deformable in response to pressure are formed. And a bonding pad connected to the sensor chip via a bonding wire. The sensor chip includes a second substrate, and the diaphragm portion and the electrode portion are opposed to each other to form a gap. A pressure sensor comprising a signal processing circuit for processing the deformation of the diaphragm as an electric signal, and an input / output lead terminal implanted in the sealed housing and connected to the signal processing circuit. As the sealed housing, a capacitance type pressure sensor using a conductive resin material is obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a capacitance type pressure sensor according to an embodiment of the present invention, a case accommodating a sensor chip and a signal processing circuit is molded from a conductive resin material and guards the case. Used as That is, the capacitance generated between the conductor outside the case and the wiring inside the case is suppressed.

A capacitance type pressure sensor according to an embodiment of the present invention will be described in the following examples with reference to the drawings.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A capacitance type pressure sensor according to the present invention comprises a silicon substrate 10 on lower and upper sealed housings 41 and 43 as cases.
And a glass substrate 20. Silicon substrate 1
At 0, a diaphragm portion 11 that is deformed in response to pressure is formed, and a fixed electrode 21 is formed on a glass substrate 20. As shown, a silicon substrate 10 and a glass substrate 2
0 is joined at a part thereof, so that the cavity portion 12
Is formed.

These silicon substrate 10 and glass substrate 2
0 constitutes the sensor chip 30, and the sensor chip 30 is adhered on the lower sealing housing 41 by the glass substrate 20. Further, a passage 42 for introducing atmospheric pressure or for introducing a pressure to be compared with a measured pressure is formed in the glass substrate 20 constituting the sensor chip 30 and the lower sealing housing 41 in which the sensor chip 30 is disposed. I have. The lower sealing housing 41 includes an insulator portion 45 formed together during molding, and lead terminals 51, 52, and 53 are implanted and 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.

Each of the bonding pads 22 and 23 is connected to a bonding pad 24 formed on the signal processing circuit 71.
25 are connected by lead wires (bonding wires) 61 and 62.

The signal processing circuit 71 has input / output bonding pads 26, 27, and 28 formed thereon.
These input / output pads 26, 27, 28 are connected to the lead terminals 51,
52, 53 are connected via input / output lead wires 83, 84, 85.

Then, the lower sealed casing 41 and the upper sealed casing 43 provided with an introduction path (hole) 44 for introducing a measured pressure are sealed by ultrasonic welding or the like.

The sealing casings 41 and 43 are molded products made of a conductive resin material, and are connected to the GND of the circuit or to a stable potential of the circuit to thereby form the sealing casings 41 and 4.
3 is a guard for suppressing the capacitance generated between the conductor 91 approaching the outer periphery and the wiring inside the case.

That is, by reducing the parasitic capacitance existing in parallel with the capacitance of the sensor chip, stable input / output characteristics with good linearity can be obtained.

Accordingly, as shown in the equivalent circuit of FIG. 3, the capacitance Cs of the sensor chip which varies with the pressure to be detected.
In parallel with the bonding pads 22, 23, 24, 25
Further, the capacitance Cd generated around the wiring patterns of the lead wires 61 and 62 and the signal processing circuit 71 can be suppressed to be small.

[0025]

As described above, according to the capacitance type pressure sensor of the present invention, the sensor chip and the signal processing circuit are housed in a case molded of a conductive resin material, and the case is guarded. As a result, the capacitance generated between the conductor outside the case and the wiring inside the case can be suppressed.

As a result, good linearity and stable input / output characteristics for reducing the parasitic capacitance existing in parallel with the capacitance of the sensor chip can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a capacitance type pressure sensor of the present invention.

FIG. 2 is an upper sealed housing 4 of the capacitance type pressure sensor of FIG.
It is an external appearance perspective view except 3.

FIG. 3 is an equivalent circuit of the capacitance type pressure sensor of the present invention.

FIG. 4 is a sectional view of a conventional capacitance type pressure sensor.

5 is an external view of the conventional capacitance type sensor of FIG. 4 excluding an upper sealing case 43. FIG.

6 is an equivalent circuit of the conventional capacitance type pressure sensor of FIGS. 4 and 5. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Silicon substrate 11 Diaphragm part 12 Cavity part 13 Movable electrode 20 Glass substrate 21 Fixed electrode 22, 23, 24, 25, 26, 27, 28 Bonding pad 30 Sensor chip 41 Lower sealed housing 42 Passage 43 Upper sealed housing Body 44 Introducing path (hole) 45 Insulator part 51, 52, 53 Lead terminal 61, 62 Lead wire (bonding wire) 71 Signal processing circuit 83, 84, 85 I / O lead wire

Claims (2)

[Claims] A first substrate which is housed in the sealed housing, on which an electrode portion is formed, and a second substrate on which a diaphragm portion which is deformed in response to pressure is formed;
A sensor chip configured such that the diaphragm portion and the electrode portion face each other to form a gap,
A bonding pad connected to the sensor chip via a bonding wire is formed, a signal processing circuit for processing the deformation of the diaphragm portion as an electric signal, and a signal processing circuit implanted in the sealing housing and connected to the signal processing circuit. Pressure sensor with input and output lead terminals for
A capacitance type pressure sensor, wherein the sealing housing is made of a conductive resin material. 2. The capacitance type pressure sensor according to claim 1, wherein the sealing housing includes an insulator portion, and the input / output lead terminal is implanted in the insulator portion. Capacitance type pressure sensor.