JPH0875582A - Electrostatic capacitance type pressure sensor, pressure measurement method, and blood pressure meter - Google Patents

Abstract

PURPOSE: To expand the detection range of a pressure sensor by preventing the short-circuiting between a movable electrode and a fixed electrode. CONSTITUTION: Frames 1 made of silicon, where a support substrate 4 made of silicon, a cover 3 made of glass, and a thin-film diaphragm 2 are supported, are overlapped and they are subjected to anode joint. A pressure room 11 is provided between the frame 1 and the cover 3 and a gas pressure is introduced to the lower surface of the diaphragm 2 from a pressure introduction entrance 10 which is opened at the support substrate 4 and the cover 3. Even if a large gas pressure is introduced, the movable electrode does not contact the fixed electrode, thus preventing short-circuiting. Also, a gap can be reduced, thus increasing the electrostatic capacitance output and improving sensitivity.

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, a pressure measuring method and a sphygmomanometer. Specifically, the present invention relates to a capacitance-type pressure sensor for measuring the pressure of a fluid used in a sphygmomanometer, a gas meter, etc., a pressure measuring method using the capacitance-type pressure sensor, and a sphygmomanometer.

[0002]

2. Description of the Related Art FIGS. 7A and 7B are an exploded perspective view and a sectional view showing a pressure sensor D of a conventional example, respectively. The pressure sensor D includes a frame 51 having a rectangular frame shape and a diaphragm 5
2 is supported, the diaphragm 52 and the frame 5
1 is integrally formed by etching a silicon wafer. A movable electrode 53 is formed on the upper surface of the diaphragm 52, and is electrically connected to an electrode pad 54 on the upper surface of the frame 51. Also, the frame 51
A glass cover 55 is superposed on the upper surface of, and its peripheral portion is anodically bonded to the frame 51. A recess 56 is formed on the inner surface of the cover 55 so that the diaphragm 52 can be elastically deformed freely in the thickness direction, and a fixed electrode 57 is formed on the inner surface of the recess 56 with a small gap from the movable electrode 53. Has been done. The fixed electrode 57 is the frame 51
The connection wiring 58 provided on the inner surface of the cover 55 is joined to the lead wire 59 on the upper surface of the frame 51 by joining the cover 55 and the cover 55.
And is electrically connected to another electrode pad 60 on the upper surface of the frame 51.

A differential pressure hole 61 for opening the inside of the recess 56 to the outside of the sensor is opened in the cover 55.
The inside is open to the atmosphere. Then, when the gas pressure (measurement pressure) to be measured is introduced from the lower surface of the diaphragm 52, the differential pressure between the introduced gas pressure and the atmospheric pressure (reference pressure) as indicated by the broken line in FIG. 7B. Accordingly, the diaphragm 52 bends toward the inner surface of the recess 56. Diaphragm 5
When 2 bends, the gap between the movable electrode 53 and the fixed electrode 57 narrows, and the capacitance between both electrodes increases. Therefore,
The applied gas pressure (differential pressure from the reference pressure) can be known by detecting the increased amount of the electrostatic capacitance with a detection circuit (not shown) connected to the electrode pads 54 and 60.

[0004]

However, in this pressure sensor D, the diaphragm 52 bends toward the inner surface of the depression 56 when the measurement pressure is introduced, and therefore the diaphragm 52 is deformed when a large measurement pressure is introduced. There is a problem in that the movable electrode 53 and the fixed electrode 57 are largely bent and come into contact with each other to cause a short circuit. This short circuit can be prevented by increasing the gap between the movable electrode 53 and the fixed electrode 57. However, if the gap is increased, the electrostatic capacitance between the movable electrode 53 and the fixed electrode 57 is reduced, so that the sensitivity is reduced. Deteriorate. Further, it is preferable to increase the electrode area in order to maintain the sensitivity, but there is a problem that the entire pressure sensor becomes large if the electrode area is increased.

Further, since the pressure sensor D is made of materials such as silicon and glass having different linear thermal expansion coefficients and elastic moduli, the pressure sensor D is warped and residual stress is generated by heating at the time of anodic bonding, and electrostatic discharge by design. The temperature characteristics of the pressure sensor were adversely affected by the inability to obtain the capacity and poor linearity due to temperature change.

The present invention has been made in view of the drawbacks of the above conventional examples, and an object of the present invention is to solve the above-mentioned problems to provide a small-sized electrostatic capacitance having good sensitivity and temperature characteristics. Type pressure sensor.

[0007]

A capacitance type pressure sensor according to the present invention comprises a diaphragm whose amount of deflection changes due to pressure change, a movable electrode formed on the diaphragm, and a fixed electrode opposed to the movable electrode. In the electrostatic capacity type pressure sensor which detects pressure from the electrostatic capacity between the movable electrode and the fixed electrode, the detected pressure is introduced so as to bend the diaphragm in the direction in which the gap between the movable electrode and the fixed electrode widens. It is characterized by doing so. At this time, a pressure introducing chamber may be formed between the movable electrode and the fixed electrode.

Further, it is preferable that the gap amount between the movable electrode and the fixed electrode is smaller than the deflection amount of the diaphragm when the rated pressure is applied.

It is also possible to have a three-layer structure in which silicon substrates are bonded to both surfaces of a glass substrate, and the diaphragm is provided on one of the silicon substrates.

Further, a reference pressure higher than the detected pressure may be introduced between the movable electrode and the fixed electrode.

The pressure measuring method of the present invention is an electrostatic capacitance type pressure sensor having a diaphragm whose flexure amount changes according to pressure change, a movable electrode formed on the diaphragm, and a fixed electrode facing the movable electrode. Introducing a detection pressure so as to bend the diaphragm in a direction in which the gap between the movable electrode and the fixed electrode widens, and detecting the pressure based on a change in capacitance between the movable electrode and the fixed electrode. Is characterized by.

The sphygmomanometer of the present invention is characterized by using the capacitance type pressure sensor of the present invention.

[0013]

According to the capacitance type pressure sensor of the present invention, since the detection pressure is introduced so as to bend the diaphragm in the direction in which the gap between the movable electrode and the fixed electrode widens, a large detection pressure is generated. Even if introduced, the movable electrode and the fixed electrode are not short-circuited, so that the detection range of the pressure sensor can be widened.

At this time, even if the amount of the gap between the movable electrode and the fixed electrode is smaller than the amount of deflection of the diaphragm when the rated pressure is applied, the movable electrode and the fixed electrode do not come into contact with each other. The capacitance output is larger than that of the capacitance type pressure sensor, and the detection sensitivity can be increased. Further, since the gap amount is reduced, the pressure sensor can be downsized.

If a silicon substrate is bonded to both surfaces of a glass substrate to form a three-layer structure and one of the silicon substrates is provided with a diaphragm, warpage and residual stress are less likely to occur during anodic bonding. Further, the sensor is not warped or the diaphragm is distorted due to the temperature change, and the change in the capacitance output is small, so that the temperature characteristics can be improved. Further, even if the structure has a three-layer structure, the bending amount of the diaphragm is not limited. Further, since the pressure sensor does not warp or the like, even if the gap is made small, there is no possibility that the electrodes contact each other.

Further, by introducing a reference pressure such as an atmospheric pressure higher than the detected pressure between the movable electrode and the fixed electrode, even if the detected pressure is a negative pressure such as a reduced pressure state, the movable electrode and The diaphragm may be bent in a direction in which the gap between the fixed electrodes widens.

According to the pressure measuring method of the present invention, the detected pressure is introduced so that the gap between the movable electrode and the fixed electrode is widened as in the capacitance type pressure sensor of the present invention, so that a large pressure is applied. , The flexed diaphragm does not contact the fixed electrode. Therefore, the detection range of the pressure sensor can be widened.

According to the sphygmomanometer of the present invention, since the capacitance type pressure sensor of the present invention having good detection sensitivity is used, the detection sensitivity can be increased. In addition, it can be a small blood pressure monitor.

[0019]

1 is a partially broken exploded perspective view showing a pressure sensor A according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are a plan view and a sectional view thereof. Show. In the pressure sensor A, a glass cover 3 is stacked on a silicon support substrate 4, and a silicon frame 1 on which a silicon diaphragm 2 is supported is stacked on the cover 3. The support substrate 4 and the cover 3 and the cover 3 and the frame 1 are bonded by anodic bonding, respectively, and have a three-layer structure of silicon / glass / silicon. The diaphragm 2 is disposed in the substantially center of the frame 1, and is integrally formed with the frame 1 from a silicon wafer. As shown in FIG. 2C, the diaphragm 2 is anisotropically deep-etched by wet etching from one surface (back surface side in the drawing) of the silicon wafer to form a rectangular thin film portion 12. The other side (the surface side in the drawing) is subjected to shallow etching by dry etching such as RIE or LOCOS to form a circular recess 11 and is thus formed into a substantially circular shape. That is, a silicon wafer is deeply etched with a large area from one surface, and then a region facing the etching area is shallowly etched into a circular shape with a small area from the opposite side of the silicon wafer, whereby the silicon wafer is accurately positioned at a predetermined position. The circular diaphragm 2 can be formed. The inner surface of the diaphragm 2 thus formed serves as the movable electrode 5, and the movable electrode 5 is formed by crimping the connecting wiring (not shown) on the inner surface of the frame 1 and the lead wire 6 on the upper surface of the cover 3. It is electrically connected to the electrode pad 7 on the upper surface.

The glass cover 3 is formed into a thin plate by anodic bonding on the support substrate 4 and then polishing the surface. A fixed electrode 8 is formed on the upper surface of the cover 3 with a small gap from the movable electrode 5 and is electrically connected to another electrode pad 9 on the upper surface of the cover 3.

The support substrate 4 and the cover 3 have pressure inlets 1
0 is opened, and a gas pressure, which is a measurement pressure, is introduced toward the lower surface of the diaphragm 2 into a recess 11 (pressure chamber) formed between the frame 1 and the cover 3. . When the gas pressure is introduced into the depression 11, the diaphragm 2 bends in proportion to the magnitude of the introduced gas pressure so that the diaphragm 2 widens the gap between the movable electrode 5 and the fixed electrode 8. , The magnitude of the electrostatic capacitance between both electrodes 5, 8 changes. Therefore, the magnitude of the introduced gas pressure (differential pressure) can be known by detecting the change in the capacitance.

In the pressure sensor A, the gas pressure is introduced toward the lower surface of the diaphragm 2 so that the gap between the electrodes 5 and 8 is widened. Therefore,
Even if a large measurement pressure is introduced, pressure measurement can be performed without short-circuiting the movable electrode 5 and the fixed electrode 8. Further, the gap amount between both electrodes can be reduced, and for example, by setting the gap amount smaller than the deflection amount of the diaphragm 2 when the rated pressure is introduced, the rated pressure can be increased as compared with the conventional pressure sensor D. The capacitance output at the time of pressure increases, and the detection sensitivity of the pressure sensor A can be increased. Moreover, since the gap between the electrodes is small, the pressure sensor A can be downsized.

A supporting substrate 4 made of silicon is bonded to the lower surface of the thinner cover 3 to form a silicon / glass / silicon 3 layer.
Since it has a layered structure, warpage and residual stress due to differences in physical properties such as the coefficient of linear thermal expansion and elastic modulus are small even by heating during anodic bonding, and the pressure sensor A can be manufactured accurately. In addition, since warpage and stress due to temperature change can be suppressed, the pressure sensor A having good temperature characteristics can be obtained. In particular, in this embodiment, since the cover 3 is in the shape of a thin plate, the influence of the difference in the physical properties of silicon and glass is further reduced, and it is more effective.

FIG. 3 is a sectional view showing a pressure sensor B which is another embodiment of the present invention. In the pressure sensor B, a silicon frame 1 on which a diaphragm 2 manufactured in the same manner as in the above embodiment is supported and a thick plate-shaped glass cover 3 are anodically bonded. A movable electrode 5 is formed on the lower surface of the diaphragm 2, and a fixed electrode 8 is formed on the inner surface of the cover 3 so as to face the movable electrode 5 with a minute gap therebetween. The cover 3 is provided with the pressure introducing port 10 so as to be positioned at the end of the recess 11.
The gas pressure is introduced into the recess 11 provided between the frame 1 and the frame 1 so that the gap increases toward the lower surface of the diaphragm 2. In this way, the pressure sensor B having a two-layer structure of glass / silicon in which the frame 1 and the cover 3 are bonded together can be used.

Further, by using the conventional pressure sensor D, the pressure can be introduced by widening the gap between the movable electrode 53 and the fixed electrode 57. As shown in FIG. 4, the pressure sensor D is disposed in the pressure introducing pipe 15 for introducing the measured pressure, and the atmosphere is introduced into a region corresponding to the diaphragm 52 on the pipe wall of the pressure introducing pipe 15 on the lower surface of the diaphragm 52. The mouth 16 is open. When the gas pressure, which is the measurement pressure, is introduced into the pressure introducing pipe 15, the diaphragm 52 bends so that the gap between the movable electrode 53 and the fixed electrode 56 widens. in this way,
Even with the conventional pressure sensor D, a large pressure can be measured by changing the pressure introduction direction.

Further, in the case where the measured pressure is a negative pressure than the reference pressure such as the atmospheric pressure, which is the standard, such as the measurement of the degree of vacuum, as shown in FIG.
If a reference pressure higher than the measurement pressure is introduced into the recess 56 and the measurement pressure is introduced toward the lower surface of the diaphragm 52 as shown in, the gap between the movable electrode 53 and the fixed electrode 57 is widened. Thus, the diaphragm 52 can be bent. Of course, even in the pressure sensor A having the structure as in the first embodiment, the negative pressure can be measured by introducing the reference pressure higher than the measured pressure into the recess 11.

The pressure sensor of the present invention can be used in a blood pressure monitor or the like. FIG. 6 is a schematic configuration diagram of a sphygmomanometer according to the present invention. A sphygmomanometer C is composed of a capacitance type pressure sensor 21, a cuff 22, a pump 23, a control unit 24 including a CPU, and the like according to the present invention. A pressure guiding tube 25 is connected between the cuff 22 and the pressure sensor 21.
A pump 23 is connected to the pump 23, and air can be sent from the pump 23 to the cuff 22. When measuring the blood pressure, first, the cuff 22 is wrapped around the upper arm of the measurement subject, the age and sex of the measurement subject are input from the input unit 26 such as a keyboard as necessary, and the blood pressure monitor C is started. . Control unit 2
When receiving a start signal from the input section 26, the control valve 4 closes the control valve 28, activates the pump 23, sends air to the cuff 22 until a predetermined pressure is reached, and tightens the upper arm portion. The pressure applied to the cuff 22 is always detected by the pressure sensor 21, and when the pressure becomes constant, the control unit 24
Stops the pump 23. Next, the controller 24 controls the control valve 2
8, the air in the cuff 22 is gradually removed to reduce the pressure. At this time, the pressure applied to the pressure sensor 21 via the pressure guiding tube 25 becomes small while changing periodically with the pressure of the blood flow flowing through the upper arm. Therefore, the systolic blood pressure, the diastolic blood pressure, and the pulse rate can be obtained by detecting the change in the pressure applied to the pressure sensor 21 via the pressure guiding tube 25 by the control unit 24. When the minimum blood pressure is obtained, the control unit 24 fully opens the control valve 28 and discharges the air in the cuff 22 to the atmospheric pressure. The obtained systolic blood pressure and diastolic blood pressure are displayed on the output unit 27 including a display or the like, or by referring to the input age or the like, it is possible to call attention to an abnormal value or the like as necessary. In this sphygmomanometer, the detection sensitivity of the pressure sensor is high, and a small sphygmomanometer can be used.

[0028]

In the capacitance type pressure sensor of the present invention, the movable electrode and the fixed electrode are not short-circuited, and the detection range of the measured pressure can be widened. Also, the gap between the movable electrode and the fixed electrode can be reduced.

At this time, if the gap amount between the electrodes is made smaller than the deflection amount of the diaphragm when the rated pressure is applied, for example, the capacitance output is increased and the detection sensitivity can be increased. Further, since the gap amount is small, the pressure sensor can be downsized.

Further, the silicon / glass / silicon three-layer structure can reduce the occurrence of warpage and residual stress during anodic bonding. Further, since the warp does not occur due to the temperature change and the diaphragm does not distort, the temperature characteristic of the pressure sensor becomes good.
In addition, the amount of deflection of the diaphragm is not limited, and warpage or the like does not occur. Therefore, even if the gap between the electrodes is reduced, there is no possibility that the electrodes will come into contact with each other.

According to the pressure measuring method of the present invention, since the detected pressure is introduced so that the gap between the movable electrode and the fixed electrode is widened like the pressure sensor of the present invention, a large pressure is introduced. However, the bent diaphragm does not come into contact with the fixed electrode. Further, even if the negative pressure is large, the bent diaphragm does not come into contact with the fixed electrode. Therefore, the detection range of the pressure sensor can be widened.

Therefore, according to the present invention, it is possible to provide a small blood pressure monitor with high detection sensitivity.

[Brief description of drawings]

FIG. 1 is a partially broken exploded perspective view showing a capacitance type pressure sensor according to an embodiment of the present invention.

2A is a plan view showing the same electrostatic pressure sensor, FIG. 2B is a sectional view thereof, and FIG. 2C is a back view showing the frame of the same electrostatic pressure sensor.

FIG. 3 is a sectional view showing a capacitance type pressure sensor which is another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a pressure measuring method according to the present invention.

FIG. 5 is an explanatory view of another pressure measuring method according to the present invention.

FIG. 6 is a configuration diagram showing a sphygmomanometer of the present invention.

7A is an exploded perspective view showing a capacitance type pressure sensor as a conventional example, and FIG. 7B is a sectional view thereof.

[Explanation of symbols]

 1 Silicon Frame 2 Diaphragm 3 Glass Cover 4 Silicon Support Substrate 8 Fixed Electrode 10 Pressure Inlet 11 Cavity (Pressure Chamber)

Claims (7)

[Claims] 1. A diaphragm, the amount of flexure of which varies according to pressure change, a movable electrode formed on the diaphragm, and a fixed electrode opposed to the movable electrode, wherein pressure is applied from a capacitance between the movable electrode and the fixed electrode. A capacitance type pressure sensor for detecting, wherein a detection pressure is introduced so as to bend the diaphragm in a direction in which a gap between the movable electrode and the fixed electrode widens. . 2. The capacitance type pressure sensor according to claim 1, wherein a pressure introducing chamber is formed between the movable electrode and the fixed electrode. 3. The capacitance type pressure according to claim 1, wherein a gap amount between the movable electrode and the fixed electrode is smaller than a deflection amount of the diaphragm when a rated pressure is applied. Sensor. 4. The capacitive pressure according to claim 1, wherein a silicon substrate is bonded to both surfaces of a glass substrate to form a three-layer structure, and the diaphragm is provided on one of the silicon substrates. Sensor. 5. The capacitance type pressure sensor according to claim 1, wherein a reference pressure higher than a detected pressure is introduced between the movable electrode and the fixed electrode. 6. A capacitance type pressure sensor comprising a diaphragm, the amount of flexing of which changes according to a pressure change, a movable electrode formed on the diaphragm, and a fixed electrode facing the movable electrode. A pressure measuring method in which a detected pressure is introduced so as to bend the diaphragm in a direction in which the gap between the fixed electrodes widens, and the pressure is detected based on the electrostatic capacitance between the movable electrode and the fixed electrode. 7. A sphygmomanometer comprising the capacitance type pressure sensor according to claim 1, 2, 3, 4 or 5.