JP2002181650A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent pressure sensor solving a problem that measurement is impossible in a micro pressure region in a conventional touch mode pressure sensor. SOLUTION: This pressure sensor 10 has an electrode 4 provided on a base body 2, a dielectric film 5 provided covering the electrode; a diaphragm 3 at least the surface of which is conductive, provided on the dielectric film with a clearance 8 and opposedly to the electrode. The change of contact area of the diaphragm receiving pressure to come in contact with the dielectric film is detected, and the pressure is measured. The pressure sensor further includes a DC voltage applying means 20 for applying DC voltage between the diaphragm and the electrode to generate electrostatic attraction between the diaphragm and the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute pressure gauge or a gauge pressure sensor capable of responding to a minute pressure range in a pressure sensor for measuring a barometric pressure and a water pressure of a tire, an engine, a boiler, a pump and the like.

[0002]

2. Description of the Related Art A silicon pressure sensor measures the pressure difference between the inside and outside of a diaphragm made of thin silicon by changing the resistance of an electric circuit formed on the surface of the diaphragm or other electrodes arranged close to the diaphragm from the deflection of the diaphragm. Is detected as a change in capacitance during the period. The silicon pressure sensor is suitable for mass production at a low cost because a large number of sensor elements can be simultaneously manufactured on a wafer at one time and cut in each element in the final step to manufacture the sensor. However, individual devices cut out from the wafer can measure pressure only when they are connected to a peripheral circuit that performs amplification and conversion of output signals from the devices. Such a pressure sensor is disclosed, for example, in U.S. Pat. No. 5,528,452. In this pressure sensor, a silicon structure provided with a diaphragm having a thickness of several μm is bonded to a glass substrate, and an appropriate gap is provided between the diaphragm and the glass.
This gap is isolated from the outside and is often kept in a vacuum. An electrode made of a metal thin film is formed on a part of the glass surface inside the gap, and this electrode is electrically insulated from the silicon structure to be joined by being covered with a dielectric film. Therefore, the entire silicon structure is 1
If it is considered as one electrode, this structure and the metal film electrode form a capacitor, and the capacitance changes due to the deflection of the diaphragm due to the fluctuation of the atmospheric pressure. The diaphragm is produced by etching a region slightly smaller than the gap from the direction opposite to the joint surface. By forming the metal film electrode on the glass surface only in a region facing the diaphragm, the stray capacitance is minimized and the pressure change can be detected most efficiently.

The pressure sensor disclosed in the above-mentioned US Pat. No. 5,528,452 detects a change in the contact area as a change in capacitance by contacting a dielectric film on a substrate-side electrode by bending a diaphragm. In this publication, this is referred to as “touch mode”. The touch mode pressure sensor is superior in many points, such as higher sensitivity, higher pressure resistance, and a linear relationship between pressure and capacitance than other capacitance type pressure sensors.

FIGS. 3 and 4 show a contact surface 1 in which a diaphragm contacts a dielectric film on an electrode in this pressure sensor.
FIG. 5 is a diagram schematically showing a state of spreading 1 from its cross section (FIGS. 3A to 3C) and a diaphragm surface (FIG. 4). As shown in these figures, when pressure is applied to the diaphragm, the center of the diaphragm initially has a straight region 11.
At -1, it comes into contact with the dielectric film on the electrode. As the pressure increases, the contact area increases as the line width increases.

FIG. 5 is a graph showing the pressure dependency of the capacitance in the pressure sensor. Due to the characteristics of the touch mode, the sensitivity is almost zero in a low-pressure region (non-contact region) before the diaphragm contacts the dielectric film on the electrode. After the diaphragm comes into contact with the dielectric film on the electrode as the pressure increases, the capacitance of the sensor increases almost linearly within a certain range with respect to the pressure (linear region). At high pressures beyond the linear region, the sensitivity of the sensor gradually decreases and the capacitance approaches a saturation value (saturation region).

[0006]

As described above,
In conventional touch mode pressure sensors, the capacitance hardly changes until a constant pressure is applied and the diaphragm and the opposing substrate come into contact, so it is difficult to measure in a minute pressure region below the contact start pressure. there were. The contact start pressure can be shifted to the lower pressure side by reducing the diaphragm thickness or the distance between the diaphragm and the substrate, but the lower limit is about 0.1 atm because it is limited by the processing accuracy and the breaking strength of the diaphragm. Met. Furthermore, measurement from zero pressure was extremely difficult with the structure of the present sensor.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an excellent pressure sensor which can solve the problem that measurement in a minute pressure region in a conventional touch mode pressure sensor is impossible. The present inventors have conducted intensive studies in order to lower the lower limit pressure of measurement of the touch mode pressure sensor, and as a result, applied a DC voltage (DC bias) between the diaphragm and the electrode to generate an electrostatic attractive force between the two. By this action of the electrostatic attraction, the contact starting pressure between the diaphragm and the dielectric film on the electrode can be reduced, and the touch mode is realized even when the pressure is zero (the pressure difference between the inside and outside of the diaphragm is zero). They have found that they can do this and have completed the present invention.

According to the present invention, an electrode (4) provided on a base (2) and a dielectric film (5) provided over the electrode (4) are provided.
And a conductive diaphragm (3) having at least a surface opposed to the electrode and provided on the dielectric film with a gap (8) therebetween, the diaphragm being subjected to pressure and having a dielectric film and In a pressure sensor for detecting a change in the contact area of the contact and measuring the pressure, a DC voltage applying means (20) for applying a DC voltage between the diaphragm and the electrode to generate an electrostatic attraction between the diaphragm and the electrode. A pressure sensor (10) is provided. In the pressure sensor of the present invention, an AC voltage is applied between the diaphragm and the electrode, a resonance frequency or a change in impedance is detected, a pressure applied to the diaphragm is measured, and a DC voltage is superimposed on the AC voltage at the same time. It may be configured to generate an electrostatic attraction between the electrodes. In the pressure sensor of the present invention, the touch mode may be configured by electrostatic attraction even when the diaphragm does not receive external pressure.

[0009]

1 and 2 show an embodiment of a pressure sensor according to the present invention. FIG. 1A is a plan view of the pressure sensor.
FIG. 2B is a side sectional view, FIG. 2C is a bottom view showing an electrode shape, and FIG. 2 is a perspective view of a pressure sensor. This pressure sensor 10 comprises a structure 1 provided with a conductive diaphragm 3 having a thickness of about several μm, and a base 2 provided with an electrode 4 made of a metal thin film and a dielectric film 5 covering the electrode 4. 3 and the electrode 4 are opposed to each other and are joined in a state where a small gap 8 of, for example, about several μm is provided between the diaphragm 3 and the dielectric film 5. A DC voltage is applied between the diaphragm 3 and the electrode 4. A DC voltage applying means 20 for generating electrostatic attraction between the diaphragm 3 and the electrode 4 is provided.

The diaphragm 3 of the structure 1 is formed by etching a wafer made of, for example, single-crystal silicon to make it concave. In order to form the diaphragm 3 on a wafer made of silicon, for example, a layer in which an impurity is added at a high concentration by a desired thickness (of the diaphragm) is formed on the silicon surface, and a high concentration doping of an impurity such as boron is performed. Using an etch stop technique. The thickness of the diaphragm and the depth of the depression on the lower side of the diaphragm (joint surface side with the base 2) defining the height of the gap 8 between the diaphragm 3 and the dielectric film 5 are:
It can be set appropriately so that the linear region of the sensor matches the load pressure range of the measurement target.

The constituent material of the base 2 is not particularly limited as long as the base 2 can secure an electrical insulation state with the electrode 4.
For example, a glass plate, a ceramic plate, a hard plastic plate, a metal provided with a glass layer on the surface, or the like may be used, and a glass plate is particularly preferably used. The electrodes 4 formed on the substrate 2 are made of Al, Cr, Au, Ag, Cu, T
Various metals generally used as electrode materials such as i are deposited on the surface of the substrate 2 by vapor deposition, sputtering, CVD,
It is manufactured using a thin film forming method such as an electroless plating method. The shape of the electrode 4 may be a method of covering the non-electrode film-forming portion on the surface of the substrate 2 with a mask and forming a metal film only on the electrode forming portion, or a method of forming a metal film uniformly on one surface of the substrate 2 followed by photolithography. The pattern can be formed by a method of etching into a desired shape using a technique.
As shown in (C), the film is formed in a rectangular shape having the same dimensions as the diaphragm 3. The base 2 is covered so as to cover the electrode 4.
The dielectric film 5 formed thereon is made of glass (quartz glass),
It is formed by forming a film of a known material such as ceramics using a thin film forming means such as a sputtering method or a CVD method. The thickness of the dielectric film 5 is appropriately set according to the required sensitivity of the pressure sensor 10,
Usually, it is about 0.1 to several μm.

The base 2 is provided with a terminal 7 connected to the electrode 4 and extending to the periphery of the base 2 and a terminal 6 provided on the dielectric film 5 and electrically connected to the structure 1. Have been. Reference numeral 23 denotes an opening in which the dielectric film 5 for connecting the terminal 7 is not formed. These terminal portions 6 and 7 can be formed using the same metal material as the electrode 4 and the same type of thin film forming means.

The gap 8 formed between the dielectric film 5 of the substrate 2 and the diaphragm 3 has a rectangular shape slightly larger than the electrode 4 and the diaphragm 3 as shown by reference numeral 22 in FIG. The structure 1 is formed by recessing the lower surface. The height of this gap, that is, the dimension between the dielectric film 5 and the diaphragm 3 is determined by the dimension (length, width and thickness) of the diaphragm 3.
Is appropriately selected according to the conditions. In this example, the inside of the gap 8 is evacuated so that the diaphragm 3 can easily contact the dielectric film 5 side according to the pressure.

A DC voltage applying means 20 for applying a DC voltage between the diaphragm 3 and the electrode 4 comprises a diaphragm 3
Suitable electrostatic attraction between the electrode 4 and the diaphragm 3, for example.
Any voltage can be applied as long as a constant DC voltage (hereinafter referred to as DC bias) necessary for generating electrostatic attraction to be in a touch mode due to electrostatic attraction can be applied even when no external pressure is applied. Means can also be used. For example, DC voltage applying means 20
May be provided separately from a measuring device for applying an AC voltage between the diaphragm 3 and the electrode 4 to measure the pressure applied to the diaphragm by detecting a change in the resonance frequency or impedance, or the pressure may be measured from one measuring device. AC voltage and DC bias may be superimposed and applied. The DC bias is applied from the DC voltage applying means 20 to the base 2.
The voltage is appropriately set according to the thickness of the diaphragm 3, the contact start pressure of the diaphragm 3, and the like.

In the pressure sensor 10, to measure the pressure applied to the diaphragm 3, an AC voltage is applied between the diaphragm 3 and the electrode 4, and the resonance frequency or impedance change is detected to measure the pressure applied to the diaphragm 3. At the same time, a DC bias is superimposed on the AC voltage to generate an electrostatic attraction between the diaphragm 3 and the electrode 4. When a constant DC bias is applied, an electrostatic attractive force is generated between the diaphragm 3 and the electrode 4, and the diaphragm 3 is bent toward the electrode 4 by the action of the attractive force, and contacts the dielectric film 5 on the electrode 4. It is easy to do. Therefore, even if the pressure applied to the diaphragm 3 is small, the diaphragm 3 contacts the dielectric film 5 on the electrode 4. Further, when the diaphragm 3 comes into contact with the dielectric film 5 by the electrostatic attraction even when the diaphragm 3 is not subjected to pressure from the outside, that is, when the electrostatic attraction to be in the touch mode is generated, the capacitance and the pressure shown in FIG. In the graph showing the relationship, it is possible to realize a measurement state in which a non-contact area is significantly reduced or eliminated, and a linear area in which the capacitance increases in proportion to an increase in pressure is started. This makes it possible to measure a minute pressure that cannot be measured by a conventional sensor.

FIG. 6 is a diagram showing another embodiment of the pressure sensor according to the present invention. The pressure sensor for measuring a differential pressure or a gauge pressure according to the present embodiment includes substantially the same components as the absolute pressure type pressure sensor 10 shown in FIGS. 1 and 2, and is a reference for allowing the base 2 to communicate the gap 8 with the outside. The pressure introducing hole 31 is provided. The pressure sensor for measuring the differential pressure or the gauge pressure measures the difference between the pressures (atmospheric pressure or water pressure) of two different spaces, so that the upper side of the diaphragm 3 communicates with one space and the lower side of the diaphragm 3 By communicating with the other space through the reference pressure introducing hole 31 and measuring the pressure applied to the diaphragm 3, it is used for measuring the pressure difference between these spaces.

The pressure sensor 32 for measuring a differential pressure or a gauge pressure has, as shown in FIG. 7, for example, a pressure introducing hole 36 communicating with one space and a pressure introducing hole 37 communicating with the other space. In addition, it is used by being mounted on a package provided with an extended portion for disposing a sensor. In the example of this package, the pressure sensor 32 is placed in the opening of the pressure introducing hole 37 communicating with the other space, and is fixed with the adhesive 38, and the terminal portions 6, 7 of the pressure sensor 32 are attached to the expanded portion. A hermetic seal 35 is used to connect a lead pin 34 partially inserted with a wire bond 33 to enable voltage application and signal extraction. The pressure introduction hole 36 communicates with the upper side of the diaphragm of the pressure sensor 32, and the pressure introduction hole 37
Communicates with the lower side of the diaphragm through the reference pressure introducing hole 31.

In order to measure the differential pressure between one pressure introducing hole 36 and the other pressure introducing hole 37 using the pressure sensor 32 for measuring the differential pressure or the gauge pressure, the pressure sensor 1 described above is used.
As in the case of 0, an AC voltage is applied between the diaphragm 3 and the electrode 4 to detect a resonance frequency or a change in impedance to measure a differential pressure applied to the diaphragm. At the same time, a DC bias is superimposed on the AC voltage. An electrostatic attraction is generated between the diaphragm 3 and the electrode 4. When a constant DC bias is applied, an electrostatic attraction is generated between the diaphragm 3 and the electrode 4, and the diaphragm 3 is bent by the action of the attraction toward the electrode 4 and comes into contact with the dielectric film 5 on the electrode 4. It is easy to do. Therefore, even if the differential pressure applied to the diaphragm 3 is small, the diaphragm 3 contacts the dielectric film 5 on the electrode 4. In addition, diaphragm 3
When the contact with the dielectric film 5 by the electrostatic attraction even when no pressure difference is applied, that is, when the electrostatic attraction that is in the touch mode is generated, the graph of FIG. 5 shows the relationship between the capacitance and the pressure. , The non-contact area is greatly reduced,
Alternatively, it is possible to realize a measurement state in which a linear region in which the capacitance increases in proportion to the increase in the pressure and the capacitance increases increases. This makes it possible to measure a small differential pressure that cannot be measured with a conventional sensor. Hereinafter, the effects of the present invention will be clarified by examples.

[0019]

[Example] (Comparative example: conventional pressure sensor) 0.4 mm ×
A capacitance type pressure sensor having a 1.5 mm rectangular diaphragm was manufactured. This sensor has a structure in which a structure made of single-crystal silicon and a base made of a glass plate are joined (see US Pat. No. 5,528,452), and a diaphragm is used as a first electrode and an electrode formed on the base is made of an electrode. As the second electrode, a change in capacitance between the electrodes is measured. Here, according to the description in the above-mentioned US Patent Publication, by making the dimensions of the diaphragm into a rectangle having a long side and a short side ratio of 3: 1 or more,
A linear dependence of the capacitance on the pressure in the touch mode can be obtained. A rectangular electrode having the same size (0.4 mm × 1.5 mm) as the diaphragm was formed on a substrate made of a glass plate at a position facing the diaphragm. After forming a film on the entire surface by using a sputtering method using Cr as a material of the electrode, a pattern was formed by etching into a rectangular shape using a photolithography method. After forming the electrode, a 0.4 μm glass film was formed on the electrode by a sputtering method to obtain a dielectric film. However, only the terminal portions of the electrodes were removed of the dielectric film as signal extraction ports. On the dielectric film, a terminal portion for signal extraction on the structure side was formed. A step was provided so that the distance from the diaphragm was 3 μm, and a structure having a thickness of the diaphragm of 3 μm was joined to a substrate in a vacuum to produce a touch-mode capacitive pressure sensor element. The fabricated sensor is put in a pressurized container, and the diaphragm for the applied pressure-(on the substrate)
The result of examining the change in the capacitance between the electrodes is shown in the graph A of FIG.
Shown in Capacitance is 100kHz using LCR meter
And a voltage of 0.1V. The measurement results were almost the same even when the measurement frequency was changed between 100 Hz and 10 MHz and the measurement voltage (effective value) was changed between 1 mV and 2 V. In this measurement, the contact start pressure was 1.3 atm, and between 1.5 and 2.5 atm, the capacitance of the sensor increased almost linearly with the applied pressure. And showed good characteristics.
However, the capacitance of the sensor hardly changed in a small pressure region of less than 1.3 atm, and it was not possible to accurately measure a pressure change between the atmospheric pressure and 1.3 atm.

(Embodiment 1) The relationship between the applied pressure and the capacitance when a DC bias is applied between the electrodes of the sensor manufactured in the conventional example is shown in graphs B, C and D of FIG. When the DC bias was 35 V (Graph D), the contact start pressure was 1 atm or less, and sufficient sensitivity could be obtained from atmospheric pressure to 3 atm.

Example 2 A sensor element of the prior art has the same structure as that of the conventional sensor element except for the points described later. The distance between the diaphragm and the electrode on the glass plate is 1 μm, the thickness of the diaphragm is 2 μm, The sensor shown in FIG. 6 in which a pressure introducing hole was formed in the portion was manufactured. This sensor was mounted on the package shown in FIG. 7 to produce a sensor for measuring differential pressure or gauge pressure. With reference to the pressure connected to the pressure introducing hole 37 communicating with the inside of the sensor (the lower side of the diaphragm), the pressure connected to the pressure introducing hole 36 outside the sensor element was measured. FIG. 9 shows the result. When no DC bias was applied, it was difficult to measure a differential pressure of 0.1 atm or less as shown by a curve A in FIG. Even when there is no pressure, the diaphragm is brought into contact with the dielectric film on the electrode, and measurement in a minute pressure range of 0 to 0.1 atm is possible. The present sensor can be similarly applied to a gauge pressure sensor using atmospheric pressure as a reference pressure.

[0022]

As described above, according to the present invention,
DC voltage is applied between the diaphragm and the electrode to generate an electrostatic attractive force between the diaphragm and the electrode. Mode operation is realized, and highly sensitive pressure measurement can be performed. Therefore, according to the present invention, it is possible to provide an excellent pressure sensor capable of measuring in a minute pressure region, which is impossible with a conventional touch mode pressure sensor.

[Brief description of the drawings]

FIG. 1 shows an example of a pressure sensor according to the present invention, in which (A) is a plan view of the pressure sensor, (B) is a side view, and (C) is a bottom view showing the shape of an electrode.

FIG. 2 is a perspective view of the same pressure sensor.

FIG. 3 shows an operation state of a conventional pressure sensor, and (A)
3 is a side view showing a state before the diaphragm is in contact, FIG. 3B is a side view showing a contact state, and FIG. 3C is a side view showing a state in which the contact area is further increased.

FIG. 4 is a schematic view schematically showing a state where a contact area of a diaphragm increases with an increase in pressure in a conventional pressure sensor.

FIG. 5 is a graph showing the relationship between pressure and capacitance in a conventional pressure sensor.

FIG. 6 is a side sectional view showing another embodiment of the pressure sensor of the present invention.

FIG. 7 is a schematic sectional view showing a state where the pressure sensor of FIG. 6 is mounted on a package.

FIG. 8 is a graph showing the results of the example and showing the relationship between the pressure and the capacitance of the prototype pressure sensor when no DC bias was applied and when a DC bias of 20 V to 35 V was applied.

FIG. 9 is a graph showing the results of the example, and showing the relationship between the pressure and the capacitance of the pressure sensor prototyped in the example 2 when no DC bias was applied and when a DC bias of 10 V was applied.

[Explanation of symbols]

1 ... structure, 2 ... substrate, 3 ... diaphragm, 4 ...
... electrodes, 5 ... dielectric film, 10 ... pressure sensor, 20 ...
... DC voltage applying means, 32 ... Pressure sensor.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoshi Yamamoto 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Office (72) Inventor Hitoshi Nishimura 1440, Misaki, Sakura City, Chiba Prefecture Inside Fujikura Sakura Office F Terms (reference) 2F055 AA40 BB03 BB05 CC02 DD05 DD19 EE25 FF07 FF11 GG01 GG12 HH05 4M112 AA01 BA07 CA12 CA15 FA01 FA03

Claims (3)

[Claims] 1. An electrode (4) provided on a substrate (2)
A dielectric film (5) provided to cover the electrode, and a diaphragm (3) opposed to the electrode and provided on the dielectric film with at least a surface provided with a gap (8). A pressure sensor that detects a change in a contact area where the diaphragm comes into contact with the dielectric film under pressure and measures the pressure, wherein a DC voltage is applied between the diaphragm and the electrode, A pressure sensor (10), including a DC voltage applying means (20) for generating an electrostatic attraction therebetween. 2. An AC voltage is applied between the diaphragm and the electrode to detect a change in the resonance frequency or impedance of the diaphragm to measure a pressure applied to the diaphragm. At the same time, a DC voltage is superimposed on the AC voltage to apply a voltage between the diaphragm and the electrode. 2. The pressure sensor according to claim 1, wherein the pressure sensor generates an electrostatic attraction. 3. The pressure sensor according to claim 1, wherein the touch sensor is configured to be in a touch mode by electrostatic attraction even when the diaphragm does not receive external pressure.