JPH0875571A - Capacitive pressure sensor and method for manufacturing it, and sphygmomanometer - Google Patents

Abstract

PURPOSE: To prevent fixing of a diaphragm and a glass substrate at the time of anode joining. CONSTITUTION: A silicon wafer is etched, a diaphragm 2 is formed on a frame 1, and a movable electrode 5 is formed on the lower face of the diaphragm 2. A fixed electrode 9 and an annular recess part 8 on the circumference thereof are formed in an area opposed to the diaphragm 2 in a glass-made cover 3. The diaphragm 2, the fixed electrode 9 and the recess part 8 are opposed to one another, the frame 1 and the cover 3 are overlapped, and an anode is joined thereto. Even if the diaphragm is deflected in the direction of the cover by electrostatic attracting force between the movable electrode and the fixed electrode at the time of anode joining, the diaphragm does not come into contact with and fix on the glass area of the circumference of the fixed electrode, because the recess part exists on the circumference of the fixed electrode.

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 method of manufacturing the same 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 and the like, a manufacturing method thereof, and a sphygmomanometer using the capacitance type pressure sensor.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional pressure sensor E.
FIG. In the pressure sensor E, a diaphragm 52 is supported at approximately the center of a frame 51 having a rectangular frame shape. The diaphragm 52 and the frame 51 are integrally formed by etching a silicon wafer, and a movable electrode is formed on the lower surface of the diaphragm 52. 53 is formed. A glass substrate 54 is overlaid on the lower surface of the frame 51, and its peripheral portion is anodically bonded to the frame 51. A diaphragm 55 is formed between the frame 51 and the glass substrate 54 so that the diaphragm 52 can be freely displaced in its thickness direction.
Are formed. Further, a fixed electrode 56 is formed on the inner surface of the glass substrate 54 so as to face the movable electrode 53 with a minute gap therebetween.

When a gas pressure (measurement pressure) to be measured is applied from the upper surface of the diaphragm 52, the diaphragm 52 bends in the thickness direction according to the introduced gas pressure. When the diaphragm 52 bends, the gap between the movable electrode 53 and the fixed electrode 56 becomes smaller and the magnitude of the electrostatic capacitance between both electrodes increases. Therefore, the magnitude of the applied gas pressure can be known by detecting the change in the electrostatic capacitance.

[0004]

In such a capacitance type pressure sensor, it is preferable to make the capacitance as large as possible from the viewpoint of the sensor characteristics, but in order to make the capacitance large, the electrode should be made large. The larger the area, the larger the pressure sensor. Therefore, in order to increase the capacitance without increasing the size of the pressure sensor, it is preferable to reduce the gap between the electrodes.

However, the fixed electrode 56 is the fixed electrode 5
6 to prevent a short circuit between the frame 5 and the movable electrode 5
It is formed to be smaller than 3. Therefore, if the gap between the electrodes is made small, the diaphragm 52 is bent due to the electrostatic attractive force generated by the high applied voltage (usually about several hundreds V) applied at the time of anodic bonding, and as shown by the broken line in FIG. There has been a problem that the peripheral edge portion of 52 is fixed to the inner surface (glass region) of the glass substrate 54 around the fixed electrode 56.

The present invention has been made in view of the drawbacks of the above conventional examples, and an object thereof is to prevent the movable electrode and the fixed electrode from being fixed to each other during anodic bonding.

[0007]

According to a first capacitance type pressure sensor of the present invention, a silicon substrate provided with a diaphragm whose bending amount is changed by a pressure change and a glass substrate provided with a fixed electrode are joined. In the capacitance type pressure sensor that detects the pressure from the electrostatic capacitance between the movable electrode and the fixed electrode formed on the diaphragm by making the diaphragm and the fixed electrode face each other, in the area of the glass substrate facing the diaphragm. The distance to the diaphragm in the region where the fixed electrode exists is smaller than the distance to the diaphragm in the region where the fixed electrode does not exist.

The second capacitance type pressure sensor of the present invention is
A silicon substrate provided with a diaphragm whose deflection changes with pressure change and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other, and the static electrode between the movable electrode and the fixed electrode formed on the diaphragm is fixed. In a capacitance type pressure sensor for detecting pressure from an electric capacity, of the glass substrate, in a region facing the diaphragm,
It is characterized in that the region where the fixed electrode does not exist is a recess.

The third capacitance type pressure sensor of the present invention is
A silicon substrate provided with a diaphragm whose deflection changes with pressure change and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other, and the static electrode between the movable electrode and the fixed electrode formed on the diaphragm is fixed. An electrostatic capacity type pressure sensor for detecting pressure from an electric capacity is characterized in that an annular recess is provided around the fixed electrode of the glass substrate.

A fourth capacitance type pressure sensor of the present invention is
A silicon substrate provided with a diaphragm whose deflection changes with pressure change and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other, and the static electrode between the movable electrode and the fixed electrode formed on the diaphragm is fixed. In the electrostatic capacitance type pressure sensor for detecting pressure from the capacitance, the glass substrate is provided with a convex portion projecting from the surroundings, and a fixed electrode is formed on the convex portion.

According to the method of manufacturing a capacitance type pressure sensor of the present invention, a silicon substrate having a diaphragm for pressure sensing and a glass substrate having a fixed electrode, the region where the fixed electrode exists is higher than the surrounding area. It is characterized in that anodic bonding is performed on the glass substrate which is formed so that the diaphragm and the fixed electrode face each other.

A sphygmomanometer of the present invention is characterized by including the electrostatic capacitance type pressure sensor of the present invention.

[0013]

In the first capacitance type pressure sensor of the present invention, in the region of the glass substrate facing the diaphragm,
Even if the diaphragm in the area where the fixed electrode exists is smaller than the distance in the area where the fixed electrode does not exist and the diaphragm bends toward the glass substrate due to electrostatic attraction during anodic bonding, Since the diaphragm does not come into contact with the glass region where the fixed electrode does not exist, it is possible to prevent the diaphragm and the glass substrate from sticking to each other.

The second, third, and fourth capacitance type pressure sensors of the present invention more specifically show the first capacitance type pressure sensor. A concave portion may be provided in a region where the fixed electrode does not exist as in the capacitance type pressure sensor. If the fixed electrode has a circular shape, the concave portion is provided around the fixed electrode as in the third capacitance type pressure sensor. An annular recess may be provided. Further, like the fourth capacitance type pressure sensor, a convex portion protruding from the surroundings may be provided on the glass substrate, and the fixed electrode may be provided on the convex portion.

Therefore, according to the capacitance type pressure sensor of the present invention, the yield at the time of manufacturing can be improved, and in particular, the capacitance type pressure sensor having a small distance between the diaphragm and the fixed electrode and good detection sensitivity. This is an effective method.

Further, dust or the like that has entered between the fixed electrode and the diaphragm can be dropped into a region where the fixed electrode having a large distance from the diaphragm is not formed, and the entered dust will hinder the operation of the pressure sensor. Can be prevented.

The capacitance type pressure sensor of the present invention is
It can be easily manufactured by the manufacturing method of the present invention.

The sphygmomanometer of the present invention has a high detection sensitivity and can reduce malfunctions due to dust and the like.

[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 substrate 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 glass substrate 3. Between the support substrate 4 and the glass substrate 3 or the glass substrate 3
The frame 1 and the frame 1 are joined by anodic bonding, 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. The diaphragm 2 is shown in FIG.
As shown in (c), anisotropic deep etching is performed by wet etching from one surface (the back surface side of the drawing) of the silicon wafer to form a rectangular thin film portion 13, and then the other surface ( RIE and LO from the drawing surface side)
Shallow etching is performed by dry etching such as COS to form the circular recess 12, so that the recess 12 is formed into a substantially circular shape. That is, a silicon wafer is deeply etched in a large area from one surface, and then a region opposite to the etching region is shallowly etched into a circular shape in 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 a movable electrode 5, and the movable electrode 5 is formed by crimping the connection wiring (not shown) on the inner surface of the frame 1 and the lead wiring 6 on the upper surface of the glass substrate 3. It is electrically connected to the electrode pad 7 on the upper surface of the glass substrate 3.

The glass substrate 3 is manufactured as a thin plate by polishing the surface of the glass substrate 3 after anodic bonding on the support substrate 4. Further, on the upper surface of the glass substrate 3, an annular recess 8 is formed in the inner peripheral area of the area facing the diaphragm 2.
A fixed electrode 9 is formed on the upper surface of the glass substrate 3 which is surrounded by the concave portion 8 and has a convex shape with a small gap from the movable electrode 5, and is electrically connected to another electrode pad 10 on the upper surface of the glass substrate 3. ing.

A pressure introducing port 11 is opened in the support substrate 4 and the glass substrate 3, and a gas to be measured is directed toward the lower surface of the diaphragm 2 in a recess 12 (pressure chamber) formed in the inner surface of the frame 1. Pressure is introduced. When the gas pressure is introduced into the depression 12, the diaphragm 2 is proportional to the pressure difference between the introduced gas pressure and the pressure around the sensor (reference pressure).
Bends away from the glass substrate 3. When the diaphragm 2 bends, the gap amount between the movable electrode 5 and the fixed electrode 9 changes, and the magnitude of the electrostatic capacitance between both electrodes changes. Therefore, the change in the capacitance is changed to the electrode pads 7, 10
The magnitude of the introduced gas pressure can be known by detecting with a detection circuit (not shown) connected to the.

In this pressure sensor A, the fixed electrode 9
Further, the glass substrate 3 and the frame 1 are anodically bonded so that the recess 8 and the diaphragm 2 provided in the periphery thereof face each other. Therefore, even if the diaphragm 2 is attracted to the fixed electrode 9 by the electrostatic attraction at the time of anodic bonding, the peripheral portion of the diaphragm 2 does not adhere to the inner surface of the glass substrate 3 because of the recess 8. Therefore, the movable electrode 5
It is particularly effective when the gap amount between the fixed electrode 9 and the fixed electrode 9 is small, and a small pressure sensor A having a large capacitance can be manufactured. Further, since the recess 8 is provided, even if dust such as dust larger than the gap amount enters the gas introduced into the recess 12, the dust that has entered the recess 8 can be dropped. The effect that the flexure of the diaphragm 2 is not hindered is also obtained.

Further, in this pressure sensor A, since the supporting substrate 4 made of silicon is bonded to the lower surface of the thin glass substrate 3 to have a three-layer structure of silicon / glass / silicon, it is possible to heat the substrate during anodic bonding. Also, warpage and residual stress due to differences in physical properties such as linear thermal expansion coefficient and elastic modulus are small, and the pressure sensor A can be manufactured with high accuracy. 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 glass substrate 3 has a thin plate shape, the influence of the difference in the physical properties of silicon and glass is further small, and it is more effective.

Further, as in this embodiment, when the measuring pressure is introduced into the recess 12, the diaphragm 2 is bent so as to move away from the glass substrate 3. Therefore, even if the gap between the electrodes is made small, the diaphragm is made smaller. Since the deflection of 2 is not limited, it is convenient in that a large measurement pressure can be introduced.

It should be noted that an insulating material which is not anodically bonded to silicon other than glass may be embedded in the recess 8 provided in the peripheral portion of the fixed electrode 7. Although not shown in the figure, it is also possible to provide a convex portion projecting from the upper surface of the surrounding glass substrate 3 in the region where the fixed electrode 9 is formed, and form the fixed electrode 9 on the upper surface of this convex portion.

FIG. 3 is a sectional view of 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 glass substrate 3 are anodically bonded. The glass substrate 3 is provided with a pressure introduction port 11 so as to be located at the end of the recess 12, and the fixed electrode 9 provided on the inner surface of the glass substrate 3 is formed with an annular recess 8 on the outer periphery thereof. As described above, the present invention can be applied to the pressure sensor B having a two-layer structure in which the glass substrate 3 and the frame 1 are anodic-bonded, and the pressure sensor B can be manufactured without the diaphragm 2 sticking to the inner surface of the glass substrate 3.

Those shown in FIGS. 4 (a) and 4 (b) are, respectively,
It is an exploded perspective view and sectional view of pressure sensor C which is another example of the present invention. The pressure sensor C is the diaphragm 2
The glass substrate 23 is superposed on the upper surface of the frame 21 made of silicon supporting 2 and the peripheral portion thereof is anodically bonded. The diaphragm 22 is manufactured integrally with the frame 21 by deep etching a silicon wafer from either surface. A depression 24 is formed on the inner surface of the glass substrate 23 to form a pressure chamber 25,
A recess 26 is formed on the inner surface of the glass substrate 23 along the inner circumference of the pressure chamber 25. Further, a fixed electrode 28 is formed in the inner peripheral area of the recess 26 on the inner surface of the glass substrate 23 so as to face the movable electrode 27 formed on the upper surface of the diaphragm 22.
The fixed electrode 28 includes a connection wire 29 provided on the inner surface of the glass substrate 23 and a lead wire 30 provided on the upper surface of the frame 21.
Are pressed and electrically connected to the electrode pads 31 on the upper surface of the frame 21. Further, a pressure introducing port 32 is provided from the side surface of the glass substrate 23 to the pressure chamber 25,
A reference pressure can be introduced into the pressure chamber 25. Then, when the measurement pressure is introduced toward the lower surface of the diaphragm 22, the diaphragm 22 bends in accordance with the introduced measurement pressure (differential pressure from the reference pressure), and the distance between the movable electrode 27 and the fixed electrode 28 is increased. The magnitude of the capacitance changes. 3
Reference numeral 3 is another electrode pad electrically connected to the movable electrode 28.

Even in this pressure sensor C, the fixed electrode 28
Since the concave portion 26 is provided at the peripheral edge of the frame 22, the frame 21 and the glass substrate 23 can be anodically bonded without the peripheral edge of the diaphragm 22 being fixed to the glass substrate 23.

The pressure sensor of the present invention can be used in a blood pressure monitor or the like. FIG. 5 is a schematic configuration diagram of the sphygmomanometer according to the present invention. The sphygmomanometer D is composed of the electrostatic capacitance type pressure sensor 41, the cuff 42, the pump 43, the control unit 44 including a CPU, and the like. A pressure guiding tube 45 is connected between the cuff 42 and the pressure sensor 41.
A pump 43 is connected to the pump 43, and air can be sent from the pump 43 to the cuff 42. When measuring blood pressure with the sphygmomanometer D, first, the cuff 42 is wrapped around the upper arm of the measurement subject, and the age, sex, etc. of the measurement subject are input from the input unit 46 such as a keyboard, if necessary. Start total D. Upon receiving the start signal from the input unit 46, the control unit 44 closes the control valve 48, activates the pump 43, sends air to the cuff 42 until a predetermined pressure is reached, and tightens the upper arm portion. The pressure applied to the cuff 42 is always detected by the pressure sensor 41, and when the pressure reaches a certain level, the control unit 44 stops the pump 43. Next, the control unit 44
Opens the control valve 48 to gradually remove the air in the cuff 42 to reduce the pressure. At this time, the pressure sensor 4 is passed through the pressure guiding tube 45.
The pressure applied to No. 1 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 41 via the pressure guiding tube 45 by the control unit 44. When the minimum blood pressure is obtained, the control unit 44 fully opens the control valve 48 and discharges the air in the cuff 42 to the atmospheric pressure. The output unit 4 including a display displays the calculated maximum blood pressure and minimum blood pressure.
Displayed in 7 or referring to the entered age etc.,
It is possible to call attention such as an abnormal value if necessary.

[0030]

According to the present invention, the silicon substrate having the diaphragm and the glass substrate having the fixed electrode can be anodically bonded to each other without the diaphragm being fixed to the glass substrate, and the capacitance type pressure sensor with good yield can be obtained. Can be produced. Further, even if dust enters in the gap between the movable electrode and the fixed electrode, the invaded dust can be dropped into a region where the distance from the diaphragm is increased, so that the operation of the pressure sensor is not hindered. Therefore, by using the pressure sensor according to the present invention, it is possible to inexpensively provide a sphygmomanometer with high detection sensitivity and no malfunction.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a capacitance type pressure sensor which is 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. 4A is an exploded perspective view showing a capacitance type pressure sensor according to another embodiment of the present invention, and FIG. 4B is a sectional view thereof.

FIG. 5 is a schematic configuration diagram showing a sphygmomanometer according to the present invention.

FIG. 6 is a sectional view showing a capacitance type pressure sensor of a conventional example.

[Explanation of symbols]

 1 Silicon Frame 2 Diaphragm 3 Glass Substrate 4 Silicon Support Substrate 8 Recess 9 Fixed Electrode 11 Pressure Inlet 12 Cavity (Pressure Chamber)

Claims (6)

[Claims] 1. A silicon substrate provided with a diaphragm, the amount of flexing of which changes according to a pressure change, and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other, and a movable electrode formed on the diaphragm. In a capacitance-type pressure sensor that detects pressure from a capacitance between fixed electrodes, a distance between the glass substrate and a diaphragm in a region where the fixed electrode exists in a region facing the diaphragm is such that the fixed electrode does not exist. A capacitance type pressure sensor characterized in that the distance is smaller than the distance from the diaphragm in the region. 2. A movable substrate formed on the diaphragm, wherein a silicon substrate provided with a diaphragm, the amount of bending of which changes with pressure change, and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other. In a capacitance type pressure sensor for detecting pressure from a capacitance between fixed electrodes, a capacitance is characterized in that a region where the fixed electrode does not exist in a region of the glass substrate facing the diaphragm is a recess. Type pressure sensor. 3. A movable substrate formed on the diaphragm and a movable electrode formed on the diaphragm, wherein a silicon substrate provided with a diaphragm, the amount of flexing of which changes according to a pressure change, and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other. An electrostatic capacity type pressure sensor for detecting pressure from an electrostatic capacity between fixed electrodes, wherein an annular concave portion is provided around the fixed electrode of the glass substrate. 4. A movable substrate formed on the diaphragm, wherein a silicon substrate provided with a diaphragm, the amount of bending of which changes with pressure change, and a glass substrate provided with a fixed electrode are bonded to each other so that the diaphragm and the fixed electrode face each other. In a capacitance type pressure sensor for detecting pressure from a capacitance between fixed electrodes, a convex portion protruding from the surrounding is provided on the glass substrate, and a fixed electrode is formed on the convex portion. Capacitive pressure sensor. 5. A diaphragm and a fixed electrode, wherein a silicon substrate having a diaphragm for pressure sensing and a glass substrate having a fixed electrode in which a region where the fixed electrode exists is higher than its surroundings are provided. And a method of manufacturing an electrostatic capacity type pressure sensor, characterized in that anodic bonding is performed so as to face each other. 6. A sphygmomanometer comprising the capacitance type pressure sensor according to claim 1, 2, 3, or 4.