JP2000055761A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a capacitance type sensor with small output fluctuation even when an ambient temperature is changed by providing a reference-pressure chamber for applying a reference pressure to a sensor chip, and a second diaphragm for transferring an outside air pressure to the reference-pressure chamber. SOLUTION: When pressure is applied to a pressure introduction hole 44, a diaphragm 91 is deformed, and a diaphragm 11 is deformed according to the difference between the pressure of a pressure chamber 93 to be measured and that of a reference- pressure chamber 94. Due to the deformation of the diaphragm 11, the gap between a movable electrode 13 and a fixed electrode 21 is changed. According to change in the gap between the electrodes, capacitance is changed. Furthermore, fixed correlation exists between pressure and the gap between the electrodes, thus determining the pressure by detecting the capacitance. Also, although the internal pressure of the pressure chamber 93 to be measured is changed when the ambient temperature is changed, the internal pressure of the reference-pressure chamber 94 is similarly changed, thus performing treatment so that the pressure change of the pressure chamber 93 to be measured and the pressure change of the reference-pressure chamber 94 cancel differentially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor, and more particularly, to a capacitance type pressure sensor for detecting a capacitance of an opposed electrode surface.

[0002]

2. Description of the Related Art As this kind of capacitance type pressure sensor,
Generally, a pressure sensor shown in FIG. 2 is known. In the pressure sensor, a diaphragm 11 that is deformed in response to pressure is formed on a silicon substrate 10, and a movable electrode 13 is held on the diaphragm 11. On the other hand, a fixed electrode 21 is formed on the glass substrate 20. The silicon substrate 10 and the glass substrate 20 are joined only at a part thereof, so that the diaphragm 11
The cavity part 12 is formed below. An external pressure (atmospheric pressure) is introduced into the cavity 12 through a reference pressure introducing hole 14 formed in the lower sealed housing 41.

[0003] The silicon substrate 10 and the glass substrate 20 constitute a sensor chip 30. The sensor chip 30 is adhered on the lower sealing housing 41 by the glass substrate 20.

Further, bonding pads 51, 5 formed together during molding are formed on the lower sealing housing 41.
2, 53 are arranged. On the upper surface of the glass substrate 20, a bonding pad 23 from which the fixed electrode 21 is drawn,
A bonding pad 22 from which the movable electrode 13 formed on the diaphragm 11 is drawn is formed. The bonding pads 22 and 23 are connected to the bonding pads 24 and 25 formed on the signal processing circuit 71, respectively.
62.

The signal processing circuit 71 has input / output pads 26,
27 and 28 are formed. These pads 26, 2
7, 28 are bonding pads 51, 52, 53 attached to the lower sealing housing 41 and lead wires 83, 84,
85.

Further, an upper sealing case 43 provided with a pressure introducing hole 44 for introducing a measured pressure is fitted to the lower sealing case 41 and sealed by ultrasonic welding or the like. Thus, the measured pressure chamber 93 is formed. A diaphragm 91 is provided at a boundary between the pressure introducing hole 44 and the measured pressure chamber 93.

In the capacitance type pressure sensor shown in FIG. 2, when pressure is applied to the pressure introducing hole 44, the diaphragm 91 is deformed.
The pressure in the measured pressure chamber 93 increases, and the diaphragm 1
1 is applied, and the diaphragm portion 11 is deformed according to the difference between the pressure in the measured pressure chamber 93 and the atmospheric 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. 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 furthermore, since there is a certain correlation between the pressure and the gap between the electrodes, the capacitance is detected. The pressure.

[0009]

As described above, the conventional capacitance type pressure sensor detects the capacitance of the sensor chip which changes according to the difference between the measured pressure chamber and the atmospheric pressure. However, when the ambient temperature changes, the internal pressure of the pressure chamber to be measured changes, so that the sensor output fluctuates.

[0010] Therefore, an object of the present invention is to provide a capacitance type pressure sensor whose output fluctuation is small even when the ambient temperature changes.

[0011]

According to the present invention, a measured pressure chamber to which a measured pressure is transmitted via a first diaphragm, and a pressure of the measured pressure chamber are measured based on a reference pressure. A pressure sensor including a sensor chip for converting the pressure into a capacity, a reference pressure chamber for applying the reference pressure to the sensor chip, and a second diaphragm for transmitting an outside air pressure to the reference pressure chamber. A characteristic pressure sensor is obtained.

The sensor chip holds a fixed electrode, a movable electrode facing the fixed electrode, and the movable electrode.
Preferably, a pressure-displacement conversion mechanism for displacing the movable electrode with respect to the fixed electrode in accordance with a pressure difference between the measured pressure chamber and the reference pressure chamber is preferable.

Further, according to the present invention, the second substrate having the movable electrode held therein so as to face the first substrate on which the fixed electrode is formed and the fixed electrode with a gap, and having a diaphragm portion deformed in response to pressure is formed. A sensor chip having a substrate, a measured pressure chamber provided with a pressure introducing hole for applying a measured pressure to the sensor chip, and a reference pressure applied to the sensor chip in contact with the measured pressure chamber with the diaphragm as a boundary surface. Pressure chamber, a first diaphragm provided at an interface between the measured pressure chamber and the outside, and a second diaphragm provided at an interface between the reference pressure chamber and the outside. Is obtained.

It is preferable that the volume of the measured pressure chamber and the volume of the reference pressure chamber are substantially equal to each other.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A capacitance type pressure sensor according to an embodiment of the present invention will be described with reference to FIG.

In the pressure sensor shown in FIG. 1, a diaphragm 11 which is deformed in response to pressure is formed on a silicon substrate 10, and a movable electrode 13 is held on the diaphragm 11. On the other hand, the movable electrode 13 is provided on the glass substrate 20.
A fixed electrode 21 is formed with a gap therebetween. The silicon substrate 10 and the glass substrate 20 are joined only at a part thereof, whereby a cavity 12 is formed below the diaphragm 11. A reference pressure described later is introduced into the cavity portion 12 through a reference pressure introduction hole 14 formed in the lower sealing housing 41.

The silicon substrate 10 and the glass substrate 20 constitute a sensor chip 30. The sensor chip 30 is adhered on the lower sealing housing 41 by the glass substrate 20.

The lower sealing housing 41 has bonding pads 51, 5 and 5 formed together during molding.
2, 53 are arranged. On the upper surface of the glass substrate 20, a bonding pad 23 from which the fixed electrode 21 is drawn,
A bonding pad 22 from which the movable electrode 13 formed on the diaphragm 11 is drawn is formed. The bonding pads 22 and 23 are connected to the bonding pads 24 and 25 formed on the signal processing circuit 71, respectively.
62.

The signal processing circuit 71 has input / output pads 26,
27 and 28 are formed. These pads 26, 2
7, 28 are bonding pads 51, 52, 53 attached to the lower sealing housing 41 and lead wires 83, 84,
85.

Further, an upper sealing case 43 provided with a pressure introducing hole 44 for introducing a measured pressure is fitted into the lower sealing case 41 and sealed by ultrasonic welding or the like. Thus, the measured pressure chamber 93 is formed. A diaphragm 91 is provided at a boundary between the pressure introducing hole 44 and the measured pressure chamber 93. This diaphragm 91 constitutes a first diaphragm.

An additional housing 42 is provided below the lower sealed housing 41. The additional case 42 is fitted into the lower sealed case 41 and sealed by ultrasonic welding or the like. Thus, the reference pressure chamber 94 is formed by the lower sealing housing 41 and the additional housing 42. Further, a diaphragm 92 is provided at a boundary between the external pressure introducing hole 15 formed in the additional housing 42 and a reference pressure chamber 94 for introducing an external atmospheric pressure (atmospheric pressure). Thus, the reference pressure is generated by the reference pressure chamber 94. Note that the diaphragm 92 forms a second diaphragm.

Here, the volume of the measured pressure chamber 93 and the reference pressure chamber 9
4 are almost equal to each other, and they are filled with dry air or nitrogen.

In the capacitance type pressure sensor shown in FIG. 1, when pressure is applied to the pressure introducing hole 44, the diaphragm 91 is deformed,
The pressure in the measured pressure chamber 93 increases, and the diaphragm 1
1, the pressure in the pressure chamber 93 to be measured and the reference pressure chamber 9
The diaphragm portion 11 is deformed in accordance with the difference from the fourth. The gap between the movable electrode 13 and the fixed electrode 21 changes due to the deformation of the diaphragm portion 11. 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, it is necessary to know the pressure by detecting the capacitance. Can be. That is, the sensor chip 30 converts the pressure in the measured pressure chamber 93 into a capacitance based on the reference pressure.

When the ambient temperature changes, the internal pressure of the measured pressure chamber 93 changes, but the internal pressure of the reference pressure chamber 94 also changes. The processing is performed so that the pressure change in the reference pressure chamber 94 is canceled out differentially. Therefore, a change in the accuracy of the pressure measurement can be suppressed, and an output less affected by the ambient temperature can be obtained.

[0025]

As described above, according to the pressure sensor of the present invention, the pressure change due to the ambient temperature change between the pressure chamber to be measured and the reference pressure chamber is canceled out differentially, so that the change in pressure measurement accuracy can be reduced. Can be suppressed. That is, it is possible to obtain a sensor output that is less affected by the ambient temperature.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing a structural example of a conventional capacitance type pressure sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Silicon substrate 11 Diaphragm part 12 Cavity part 13 Movable electrode 14 Reference pressure introducing hole 15 External pressure introducing hole 20 Glass substrate 21 Fixed electrode 22, 23, 24, 25, 26, 27, 28 Bonding pad 30 Sensor chip 41 Lower sealing Case 42 Sealed case 43 Upper sealed case 44 Pressure introduction hole 91, 92 Diaphragm 93 Pressure chamber to be measured 94 Reference pressure chamber 51, 52, 53 Lead terminal 61, 62, 83, 84, 85 Lead wire 71 Signal Processing circuit

Claims (4)

[Claims] 1. A pressure that includes a measured pressure chamber to which a measured pressure is transmitted via a first diaphragm, and a sensor chip that converts the pressure of the measured pressure chamber into a capacitance based on a reference pressure. A pressure sensor, comprising: a reference pressure chamber for applying the reference pressure to the sensor chip; and a second diaphragm for transmitting an outside air pressure to the reference pressure chamber. 2. The sensor chip holds a fixed electrode, a movable electrode opposed to the fixed electrode, and the movable electrode, and the movable electrode according to a differential pressure between the measured pressure chamber and the reference pressure chamber. The pressure sensor according to claim 1, further comprising: a pressure-displacement conversion mechanism for displacing the fixed electrode relative to the fixed electrode. 3. A sensor comprising: a first substrate on which a fixed electrode is formed; and a second substrate on which a diaphragm is formed to hold a movable electrode so as to face the fixed electrode with a gap and to deform in response to pressure. A chip, a measured pressure chamber provided with a pressure introduction hole for applying a measured pressure to the sensor chip, and a reference pressure applied to the sensor chip in contact with the measured pressure chamber with the diaphragm portion as a boundary surface. A reference pressure chamber, a first pressure chamber provided at an interface between the pressure chamber to be measured and the outside.
And a second diaphragm provided at a boundary surface between the reference pressure chamber and the outside. 4. The pressure sensor according to claim 1, wherein the volume of the measured pressure chamber and the volume of the reference pressure chamber are substantially equal to each other.