JPH08184517A - Capacitance type pressure sensor - Google Patents

Abstract

PURPOSE: To detect pressure accurately by isolating the output terminals of a circuit board mounting a sensor chip through grooves and arranging a shielding material in the groove thereby eliminating the effect of parasitic capacitance of the circuit board. CONSTITUTION: Grooves 9, 10 are made between a sensor output terminal fixing hole (common) 1, a sensor output terminal fixing hole (pressure-sensitive) 2, and a sensor output terminal fixing hole (reference) 3. Shielding materials 11, 12 are then arranged between them and connected with a GND pattern 7 for shielding the sensor. Subsequently, a molded sensor chip is mounted on a detection circuit board 8 and a sensor output terminal (common) 35 is connected with the sensor output terminal fixing hole (common) 1, a sensor output terminal (pressure-sensitive) 36 is connected with the sensor output terminal fixing hole (pressure-sensitive) 2, and a sensor output terminal (reference) 37 is connected with the sensor output terminal fixing hole (reference) 3. Sensor output terminals (GND) 38, 39, 40 are then connected with sensor output terminal fixing holes (GND) 38, 39, 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic capacitance type pressure sensor which detects pressure by changing electrostatic capacitance between opposed electrodes.

[0002]

2. Description of the Related Art Generally, a pressure sensor shown in FIG. 2 is known as a capacitance type pressure sensor of this type. FIG. 2 is a structural cross-sectional view of the sensor chip of the capacitance type pressure sensor. A diaphragm portion 23 that deforms in response to pressure is formed on the silicon substrate 21, and fixed electrodes 26 and 27 are formed on the glass substrate 22. The silicon substrate 21 and the glass substrate 22 are joined at a part thereof,
As a result, the cavity portion 24 is formed below the diaphragm portion 23. The silicon substrate 21 and the glass substrate 22 form a sensor chip 25.

Fixed electrode 2 formed on glass substrate 22
6 and the silicon substrate 21 are arranged to face each other with a predetermined gap therebetween to form a pressure-sensitive capacitor 41. In addition, the fixed electrode 27 formed on the glass substrate 22 and the silicon substrate 21
And the reference capacitor 42 with a predetermined interval and facing each other.
And As shown in the circuit diagram of FIG. 5, these capacitors are pressure-sensitive capacitors (Cs) whose capacitance changes according to pressure as pressure-sensitive capacitors of the sensor detection circuit.
41 and a reference capacitor (Cr) 42 having a predetermined electrostatic capacity as a reference capacitor.

As shown in the external perspective view of FIG. 3, the sensor chip 25 is molded and packaged, and the sensor output terminal (common) 35 is attached to the sensor output terminal mounting hole (common) on the detection circuit board 8 shown in FIG. ) 1, the sensor output terminal (pressure sensitive) 36 in the sensor output terminal mounting hole (pressure sensitive) 2, the sensor output terminal (reference) 37 in the sensor output terminal mounting hole (reference) 3, the sensor output terminal (GND) 38, 39, 40
Is connected to the sensor output terminal mounting holes (GND) 4, 5 and 6 for mounting.

Here, the sensor detection circuit of FIG. 5 will be described. The capacitance type pressure sensor has a predetermined capacitance connected between the operational amplifier 31 having the non-inverting input terminal connected to the reference potential, the pulse generation circuit 33, and the inverting input terminal of the operational amplifier 31. Reference capacitor (Cr)
42, a pressure-sensitive capacitor (Cs) 41 connected between the inverting input and the output terminal of the operational amplifier 31 and having a capacitance that changes according to the pressure applied from the outside, and the operational amplifier 31.
The switch 34 is connected between the inverting input terminal and the external output terminal 32 and is turned on / off by the signal Vp of the pulse generation circuit 33. The portion surrounded by the dashed line is the sensor chip.

The output pulse Vo of the sensor detection circuit is expressed by the following equation.

Vo = Vp * (Cr + Crp) / (Cs + Csp) (1)

Here, Csp 43 is a pressure-sensitive capacitor 4
Parasitic capacitance of the circuit board that comes in parallel to 1, Crp.4
Reference numeral 4 is a parasitic capacitance of the circuit board that enters the reference capacitor 42 in parallel, and is shown by a dotted line in FIG.

[0009]

In the conventional capacitance type pressure sensor, the capacitance that changes depending on the pressure to be detected is as small as 1,2 pF. Therefore, when mounting on a circuit board,
Since it is easily affected by the parasitic capacitance of the circuit board, as shown in FIG. 6, the linearity with respect to the detected pressure of the output pulse V ₀ is deteriorated, and the characteristics are greatly affected by the temperature change, and the accurate pressure is detected. There is a problem that it becomes impossible.

A technical object of the present invention is to provide an electrostatic capacitance type pressure sensor which is less susceptible to the influence of the parasitic capacitance of the circuit board and which can perform accurate pressure detection.

[0011]

The capacitance type pressure sensor of the present invention comprises a first substrate having an electrode portion formed thereon and a second substrate having a diaphragm portion which is deformable in response to pressure. And a structure in which the first and second substrates are joined so that the diaphragm portion and the electrode portion face each other with a gap in between, depending on the pressure applied to the diaphragm portion. Is a capacitance type pressure sensor configured to detect the pressure by changing the gap width and changing the capacitance between the diaphragm portion and the electrode portion. On the circuit board to be mounted, the sensor output terminals are separated from each other by a groove, and a shield material is arranged in the groove to prevent the influence of parasitic capacitance and to enable accurate pressure detection. Electrostatic It is the amount pressure sensor.

[0012]

Function: The sensor output terminals of the circuit board on which the sensor chip of the capacitance type pressure sensor is mounted are separated from each other by the groove, and the shield material is arranged in the groove. By doing so, the influence of the parasitic capacitance of the circuit board is eliminated, and accurate pressure detection can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a capacitance type pressure sensor according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a detection circuit board according to the present invention. Here, the same components as those of the conventional one are denoted by the same reference numerals as those in FIG. Sensor output terminal mounting hole (common)
1, sensor output terminal mounting hole (pressure sensitive) 2, sensor output terminal mounting hole (reference) 3 between the sensor mounting holes 9, 1
0 is provided, the shield materials 11 and 12 are arranged between them, and they are connected to the sensor shield GND pattern 7. A sensor chip 25 that is molded and packaged as shown in FIG.
The sensor output terminal (common) 3 on the detection circuit board of FIG.
5 for the sensor output terminal mounting hole (common) 1 and the sensor output terminal (pressure sensitive) 36 for the sensor output terminal mounting hole (pressure sensitive) 2
The sensor output terminal (reference) 37 in the sensor output terminal mounting hole (reference) 3 and the sensor output terminals (GND) 38, 3
9 and 40 are sensor output terminal mounting holes (GND) 4, 5 and 6
Connect to and install.

By doing so, in the sensor detection circuit shown in FIG. 5, the parallel circuit board parasitic capacitance (Csp) 43 of the pressure-sensitive capacitor and the parallel circuit board parasitic capacitance (Csp) of the reference capacitor (enclosed by the dotted line) are shown. Crp) 44 disappears, and the output pulse Vo of the sensor detection circuit is represented by the following equation instead of the above equation (1).

Vo = Vp * Cr / Cs (2)

[0017]

As described above, according to the present invention, the circuit board on which the capacitance type pressure sensor is mounted is separated from the sensor terminals by the groove, and the shield material is arranged in the groove.

As described above, the circuit board in which the sensor terminals are separated by the groove and the shield material is arranged in the groove is not affected by the parasitic capacitance of the circuit board, and accurate pressure detection can be performed. A capacitance type pressure sensor can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory view of a substrate on which a capacitance type pressure sensor of the present invention is mounted.

FIG. 2 is a cross-sectional view of a sensor chip portion of a capacitance type pressure sensor.

FIG. 3 is an external perspective view of a capacitance type pressure sensor.

FIG. 4 is an explanatory diagram of a substrate on which a conventional capacitance type pressure sensor is mounted.

FIG. 5 is a circuit diagram of a detection circuit of the capacitance type pressure sensor.

FIG. 6 is a graph of a detection circuit output of the capacitance type pressure sensor.

[Explanation of symbols]

 1 (Sensor output terminal) mounting hole (common) 2 (Sensor output terminal) mounting hole (pressure sensitive) 3 (Sensor output terminal) mounting hole (reference) 4, 5, 6 Sensor output terminal mounting hole (GND) 7 Sensor shield GND pattern 8 Circuit board 9, 10 Groove 11, 12 Shield material 21 Silicon substrate 22 Glass substrate 23 Diaphragm section 24 Cavity section 25 Sensor chip 26, 27 Fixed electrode 31 Op-amp 32 External output terminal 33 Pulse generation circuit 34 Switch 35 Sensor Output terminal (common) 36 Sensor output terminal (pressure sensitive) 37 Sensor output terminal (reference) 38, 39, 40 Sensor output terminal (GND) 41 Pressure sensitive capacitor 42 Reference capacitor 43 Parallel circuit board parasitic capacitance of pressure sensitive capacitor 44 Reference Parallel circuit board parasitic capacitance of capacitor

Claims (2)

[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 a pressure is formed, and a gap is formed between the electrode portion and the diaphragm portion. In the structure in which the first and second substrates are joined so as to face each other, the gap width changes according to the pressure applied to the diaphragm part, and the gap between the diaphragm part and the electrode part is changed. A capacitance type pressure sensor configured to detect the pressure by changing a capacitance, characterized in that a groove is provided between sensor output terminals of a circuit board on which a sensor chip of the pressure sensor is mounted. Capacitance type pressure sensor. 2. The capacitance type pressure sensor according to claim 1, wherein a shield material is arranged in a groove that separates the sensor output terminals.