JP2004212388A - Electrostatic capacity pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic capacity pressure sensor, which has a replacable element, suppresses changes in the electrostatic capacity due the manner of mounting, and moreover, even if the environmental temperature is changing system, suppresses output variations due to the temperature change, so as to carry out a reliable pressure measurement. <P>SOLUTION: A substrate in which a diaphragm electrode is formed is inserted between a substrate, in which a fixed electrode is formed and a substrate in which a pressure-introducing hole is formed. The pressure sensor is constituted that the electrostatic capacity type pressure sensor element is fixed on a retaining member in replaceable manner via a sealing member so that the electrodes overlap in a space. In the substrate, having the pressure introducing hole, an extended area is added, in comparison with those of other substrates, and this extended area is press-contacted with the retaining member via the sealing member by using a holding plate. Further, a shock absorber is mounted in between the holding plate and the substrate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a capacitive pressure sensor, and more particularly, to a pressure sensor excellent in measurement accuracy in which a capacitive pressure sensor element having a laminated structure is detachably fixed.

  In recent years, various product developments have been promoted using manufacturing techniques for semiconductor devices and the like. This is called micromachine technology, and has started to be used in many technical fields such as actuators and sensors for the purpose of miniaturization and weight reduction. One of them is a capacitive pressure sensor.

  As a conventional capacitive pressure sensor, a pressure sensor element produced by joining a silicon substrate on which a diaphragm electrode is formed and a glass substrate on which a fixed electrode is formed so as to form an airtight chamber between both electrodes, In general, a structure in which a pressure introducing portion is fixed to a holding member provided with a pressure introducing portion has been used. The pressure sensor of this structure has a problem that it is extremely uneconomical because the holding member must be replaced when the sensor element is replaced due to its life. Therefore, the present inventor has studied a pressure sensor in which only the sensor element can be replaced by holding the sensor element on the holding member via a sealing member such as an O-ring. This will be described in detail with reference to FIGS. 8 and 9 are a schematic cross-sectional view and a perspective view, respectively, showing a conventional electrostatic pressure sensor.

  The pressure sensor element 1 has a structure in which, for example, a glass substrate 10 on which a fixed electrode 13 is formed, a silicon substrate 11 on which a diaphragm electrode 15 is formed, and a glass substrate 12 on which a pressure introduction hole 18 is formed are bonded. Yes. The fixed electrode 13 and the diaphragm electrode 15 are connected to a measuring instrument (not shown) via lead wires 14 and 14 ', respectively.

  An airtight chamber 16 is formed between the glass substrate 10 and the silicon substrate 11, and the inside thereof is always kept at a high vacuum by a non-evaporable getter 17 that adsorbs residual gas. The thickness of the diaphragm 15 of the silicon substrate 11 is usually several μm to several tens of μm, and the thickness and size of the diaphragm are determined according to the pressure range to be measured. The diaphragm is deformed by the pressure difference between the two sides, and the capacitance between the fixed electrode 13 and the diaphragm electrode 15 changes according to the magnitude of the deformation. From the relationship between the capacitance and the pressure, the pressure of the measured space 4 can be obtained.

  As shown in the figure, the sensor element 1 is placed on the holding member 3 via an O-ring 30, and the entire sensor element 1 is pressed by a pressing plate 2, and a plurality of screws (not shown) are used. Fixed. In this state, it is attached to a vacuum device or the like and, for example, after zero point adjustment is performed by an adjustment trimmer for a display power supply, it is used for actual pressure measurement.

By adopting such a configuration, when the sensor element 1 is damaged or deteriorated, the holding member 3 can be used as it is, and the function as the pressure sensor can be restored by replacing only the sensor element 1. The cost can be reduced as a whole.
JP-A-8-35899 JP 2001-201417 A

  However, in the pressure sensor having the configuration shown in FIGS. 8 and 9, it was found that the pressure indication value changes depending on how the sensor element 1 is attached, and the measurement accuracy is lowered. That is, in order to securely perform the vacuum seal, it is necessary to hold down the sensor element 1 with a force that causes the O-ring 30 to be crushed by the holding plate 2, but this is related to the degree of tightening of the holding plate 2 and its uniformity. As a result, the measured value changed.

  As a result of examining the cause, as described above, since the diaphragm 15 is thin and easily deformed, the diaphragm itself is distorted by the mounting method of the sensor element 1 and the pressing force, and the capacitance value is designed. It was found that this greatly deviated from the value, and this was a pressure measurement error. Therefore, in order to perform an accurate measurement within a predetermined pressure range, it is necessary to adjust the screw tightening so that the deviation from the design value of the capacitance is within a range that can be corrected by an electric circuit. There were problems such as being extremely complicated and requiring skill.

  Accordingly, the present inventor has studied various sensor structures and mounting methods in which the diaphragm is less likely to be distorted based on the above knowledge, and as a result, has completed the pressure sensor of the present invention capable of accurate pressure measurement. It is a thing. That is, the present invention provides a pressure sensor to which a capacitance type sensor element can be attached and detached, and provides a pressure sensor that suppresses fluctuations and variations in capacitance depending on how it is attached. Even so, an object of the present invention is to provide a pressure sensor capable of suppressing pressure fluctuations due to temperature changes and performing reliable pressure measurement.

In order to achieve the above object, the capacitive pressure sensor of the present invention is configured as follows.
That is, the capacitance type pressure sensor of the present invention includes a substrate on which a diaphragm electrode is formed between a substrate on which a fixed electrode is formed and a substrate on which a pressure introduction hole is formed, and the fixed electrode, the diaphragm, and the like. A capacitive sensor in which an electrode and the pressure introduction hole are joined so as to overlap with each other through a space, and is detachably fixed to a holding member via a seal member, the pressure introduction port A region extending outward from the substrate on which the diaphragm electrode is formed is provided on the formed substrate, and a seal surface that contacts the seal member is provided in the region, and the seal surface is interposed via the seal member. It is configured to be pressed against the holding member.
Here, the structure which presses the area | region extended outward of the board | substrate in which the said pressure introduction port was formed from the surface on the opposite side to the said seal surface with a pressing plate is preferable.

  As described above, since the sensor element is sandwiched and fixed by applying force only to the substrate on which the pressure introducing hole is formed without applying force to the entire sensor element, the distortion of the diaphragm accompanying the mounting is suppressed. It becomes. This makes it possible to obtain a capacitance as designed, and to stably perform pressure measurement with high measurement accuracy in a desired pressure region.

  In the present invention, since the anodic bonding method is preferably used for bonding each substrate, an insulating substrate and a diaphragm electrode are formed on the substrate on which the fixed electrode is formed and the substrate on which the pressure introduction hole is formed. A conductive substrate is preferably used as the substrate. As a material of the insulating substrate and the conductive substrate, a combination of Pyrex (registered trademark) glass (manufactured by Corning) and a silicon substrate or an Fe—Ni alloy having a similar thermal expansion coefficient is preferably used. The thickness and size of the diaphragm are appropriately selected according to the measurement pressure range, and the size of the substrate on which the diaphragm electrode is formed is determined accordingly. Further, the substrate on which the pressure introducing hole is formed is preferably larger by 3 mm or more on one side than the substrate on which the diaphragm electrode is normally formed in order to form the sealing surface of the sealing member. The thickness of the substrate on which the pressure introducing hole is formed is 1 to 5 mm.

  In addition, it is preferable to arrange a guide member for preventing the distance between the pressing plate and the holding member from becoming a predetermined distance or less. As a result, the substrate can be prevented from being damaged due to excessive tightening of screws or the like, and the sensor mounting operation can be performed more easily and safely.

Furthermore, it is preferable to arrange a buffer between the pressing plate and the region. In particular, a configuration in which an O-ring used as a seal member is arranged at symmetrical positions on the upper and lower sides of the substrate is preferable. By arranging such a buffer, the difference in thermal expansion is absorbed by the buffer and the distortion of the substrate is alleviated. As a result, the temperature characteristics of the capacitance are improved and more accurate pressure measurement is possible. It becomes.
In the present invention, the buffer means a material that alleviates the distortion of the substrate formed with the pressure introducing hole due to the difference in thermal expansion between the holding plate and the substrate formed with the pressure introducing hole, such as rubber. In addition to the elastic body, a material having a low friction coefficient can be used even if it is a rigid body.

According to the present invention, that is, the substrate on which the pressure introduction hole is formed is made larger than the substrate on which the fixed electrode is formed or the substrate on which the diaphragm electrode is formed, and its peripheral portion protrudes from the other substrate, and the protruding portion Applying a seal member (O-ring, etc.) to the holding member and vacuum-sealing it, and adopting an attachment method that holds only the O-ring seal part makes it unintentional to the silicon substrate that is the key to pressure measurement An accurate pressure can be measured without generating a measurement error due to a large stress.
Furthermore, by disposing the buffer body between the press plate and the glass substrate, distortion due to temperature fluctuation is alleviated, and as a result, a sensor capable of measuring pressure with high reliability even in a system with temperature fluctuation can be provided. It becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the configuration and the arrangement relation are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, each configuration (material), numerical conditions, and the like are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and can be applied to various forms based on the description of the scope of claims.

FIG. 1 is a schematic cross-sectional view for explaining a configuration example of a capacitive pressure sensor of the present invention, and FIG. 2 is an exploded perspective view.
As shown in the drawing, the pressure sensor element 1 of the present embodiment includes a glass substrate 10 on which a fixed electrode 13 is formed, and a silicon substrate on which a diaphragm (electrode) 15 having a thickness of several μm to several tens of μm is formed ( For example, a structure in which a boron-doped silicon) 11 and a glass substrate 12 in which a pressure introducing hole 18 is formed is joined is formed. The glass substrate 12 is larger than the glass substrate 10 and the silicon substrate 11, and has a structure in which the peripheral edge protrudes from other substrates.

  The electric signal of the fixed electrode 13 is taken out through the lead wire 14 penetrating the glass substrate 10, and the electric signal of the diaphragm electrode 15 is taken out through the lead wire 14 ′ connected to the silicon substrate 11. .

An airtight (vacuum) chamber 16 is formed between the glass substrate 10 and the silicon substrate 11, and the inside is always kept at a high vacuum by a non-evaporable getter 17 or the like that adsorbs residual gas. When there is a pressure difference between the measured space 4 and the hermetic chamber 16, the diaphragm 15 is deformed according to the pressure difference, and as a result, the capacitance between the capacitive electrode 13 and the diaphragm electrode 15 changes. Therefore, by obtaining this capacitance, the pressure in the measured space 4 can be obtained from the relationship between the pressure and the capacitance.
In addition, the formation method of a diaphragm and the joining method of each board | substrate can use the well-known method described in Unexamined-Japanese-Patent No. 2002-43585, for example.

Next, a method for mounting the sensor element 1 to the holding member 3 will be described below.
The holding member is formed with, for example, a square groove 31 for mounting an O-ring, and the size of the groove is such that the O-ring 30 to be loaded is a peripheral portion of the glass substrate 12, that is, the glass substrate 10. In addition, the size is in contact with the portion protruding from the silicon substrate 11. The sensor pressing plate 2 has a window 21 formed at the center thereof so that the glass substrate 10 and the silicon substrate 11 can be accommodated in the window 21 when the sensor element 1 is pressed from above.

  With such a configuration, even if the sensor element 1 is pressed with a strong force in order to obtain a reliable vacuum seal, or even if there is a variation in the tightening condition of the screw, the force is applied only to the glass substrate 12. In addition, no force is applied to the silicon substrate 11. That is, the sensor element 1 can be securely attached to the holding member 3 without causing distortion in the diaphragm 15. As a result, the designed capacitance is ensured and accurate pressure measurement is possible.

Here, the result of analyzing how the sensor element shown in FIG. 1 and FIG. 8 is distorted by receiving stress due to the O-ring will be described below. In this analysis, the amount of displacement when a pressure of 24 N was applied to the contact surface so that the O-ring was crushed by 20% was obtained using structural analysis software of COSMOS WORKS.
Here, the glass substrate 10 on which the fixed electrode is formed and the substrate 11 on which the diaphragm electrode is formed are each 11.6 × 11.6 mm, and the thicknesses are 0.4 mm and 0.8 mm, respectively. The diaphragm was 4.2 × 4.2 mm and the thickness was 7 μm. Further, the substrate 12 on which the pressure introducing hole is formed is 20 × 20 × 2.0 mm in the case of the sensor of FIG. 1 and 11.6 × 11.6 × 2.0 mm in FIG. Furthermore, as a sensor material, a substrate on which a fixed electrode is formed and a substrate on which a pressure introduction hole is formed are Pyrex (registered trademark) glass (Corning 7740), and a substrate on which a diaphragm electrode is formed is a p-type Si substrate. The values shown in Table 1 were used for each material characteristic.

The analysis results for the sensors of FIGS. 1 and 8 are shown in FIGS. 3 and 4, respectively. In the figure, black (darkest color) and white (most light color) indicates a region where displacement is respectively ^{7x10 -13} m or more, and 3.5 × 10 ^-13 m or less. Further, the intermediate color is a region where the amount of displacement is between them, and indicates that the amount of displacement increases as it becomes darker.

  As can be seen from FIGS. 3 and 4, in the conventional sensor structure (FIG. 8), the diaphragm receives a force and greatly distorts, whereas the sensor element 1 of the present embodiment receives the force by the O-ring 30 and the glass substrate. It can be seen that 12 is only the contacted portion, and the other portions are not subjected to any force. That is, even if the sensor pressing plate 2 presses the sensor element 1 with a considerably strong force in order to secure the vacuum seal of the sensor element 1 with the O-ring 30, the diaphragm 15 of the silicon substrate 11 is distorted thereby. It can be seen that it is possible to perform stable and accurate pressure measurement.

Next, a second embodiment of the pressure sensor of the present invention is shown in FIG.
FIG. 5 shows a guide member 32 arranged around the sensor element 1 of FIG. By adopting such a structure, it is possible to prevent an unnecessary force from being applied to the glass plate 12 and to avoid breakage, etc., so that the mounting operation becomes safer and easier.

  As described above, the pressure sensors of Examples 1 and 2 can suppress the distortion of the sensor element due to the mounting method, and can greatly reduce the variation and variation in the obtained capacitance. On the other hand, although the sensors of Examples 1 and 2 were smaller than the conventional sensors, it became clear that the output fluctuated depending on the environmental temperature. In the process of investigating and examining the cause of this output fluctuation, it was found that this temperature change increases as the deviation from the design value of the capacitance increases.

  The reason is considered as follows, for example. That is, since the holding plate and the holding member are usually made of stainless steel, the coefficient of thermal expansion thereof is larger than that of silicon or Pyrex (registered trademark) glass. It is considered that distortion occurs between the two due to the difference in the expansion coefficient, thereby changing the capacitance. Furthermore, when the strain at the time of attachment is large, it is considered that the strain is promoted by the temperature change and shows a larger temperature change.

In view of this, various sensor structures have been studied to further reduce the distortion when the sensor element is fixed, and a pressure sensor with extremely small output fluctuation with respect to temperature has been devised. This is shown in FIG.
The pressure sensor of this embodiment shown in FIG. 6 has the same structure as the pressure sensor of Embodiment 1 except that an O-ring (buffer body) is disposed between the glass substrate 12 and the pressing plate 2.
The pressure sensor of the present example and the pressure sensor of Example 1 were repeatedly attached to the vacuum vessel, and the average value of the capacitance temperature characteristics measured for each was shown in FIG. In FIG. 7, the vertical axis represents the amount of change in capacitance of the pressure sensor when measuring a constant pressure.
As can be seen from the figure, the amount of variation in capacitance can be greatly reduced by employing the sensor structure of this embodiment. Although not shown in the figure, the sensor of the first embodiment increases and varies depending on the temperature as 10 to 30 fF / ° C. depending on how the screw is tightened, whereas the sensor of the first embodiment has 1 to 2 fF. / ℃ and fluctuation amount decreased, and no variation was observed.

  In the present embodiment, the same O-ring as the sealing member 30 is used as the buffer 33, but it is not necessary to be limited to this, and it is attributed to the difference in thermal expansion between the pressing plate and the substrate on which the pressure introducing hole is formed. Any material and shape may be used as long as they alleviate the distortion of the substrate on which the pressure introducing hole is formed. For example, in addition to an elastic body such as rubber, a material having a small friction coefficient such as a fluororesin may be used even if it is a rigid body. Moreover, the shape is good also as a structure arrange | positioned partially between a glass substrate and a pressing board. However, it is preferable to arrange the same material and the same shape as the sealing member at positions symmetrical to the glass substrate, and a pressure sensor with smaller distortion and smaller output fluctuation with respect to temperature becomes possible. In addition, you may provide an O-ring groove | channel similarly to a holding member in a pressing plate.

1 is a schematic cross-sectional view showing a capacitive pressure sensor of Example 1. FIG. It is a disassembled perspective view of the pressure sensor of FIG. It is a schematic diagram which shows distribution of the stress added to the diaphragm etc. of the pressure sensor shown in FIG. It is a schematic diagram which shows distribution of the stress added to the diaphragm etc. of the pressure sensor shown in FIG. 6 is a schematic cross-sectional view showing a capacitance type pressure sensor of Example 2. FIG. 6 is a schematic cross-sectional view showing a capacitive pressure sensor of Example 3. FIG. It is a graph which shows the relationship between the electrostatic capacitance of a pressure sensor, and temperature. It is typical sectional drawing which shows an example of the electrostatic pressure sensor which has a conventional sensor element which can be attached or detached. It is a typical perspective view which shows an example of the conventional electrostatic pressure sensor which has a sensor element which can be attached or detached.

Explanation of symbols

1 pressure sensor element,
2 holding plate,
3 holding member,
4 Measurement space,
10 glass substrate,
11 Silicon substrate,
12 glass substrate,
13 Fixed electrode,
14, 14 'lead wire,
15 Diaphragm electrode,
16 Airtight (vacuum) chamber,
17 Non-evaporable getter,
18 pressure introducing hole,
21 windows,
30 O-ring,
31 grooves,
32 guide members,
33 Buffer.

Claims (6)

  A substrate on which a diaphragm electrode is formed is interposed between a substrate on which a fixed electrode is formed and a substrate on which a pressure introduction hole is formed, and the fixed electrode, the diaphragm electrode, and the pressure introduction hole overlap with each other through a space. A pressure sensor in which a capacitive pressure sensor element joined in this manner is detachably fixed to a holding member via a seal member, and the diaphragm electrode is formed on a substrate on which the pressure introduction port is formed A region extending outward from the substrate is provided, a seal surface that contacts the seal member is provided in the region, and the seal surface is configured to be pressed against the holding member via the seal member. Capacitance type pressure sensor.   2. The capacitance according to claim 1, wherein a region extending outward of the substrate in which the pressure introduction hole is formed is configured to be pressed by a pressing plate from a surface opposite to the sealing surface. Mold pressure sensor.   The capacitive pressure sensor according to claim 2, further comprising a guide member that prevents a distance between the pressing plate and the holding member from being a predetermined distance or less.   4. The capacitive pressure sensor according to claim 2, wherein a buffer is disposed between the pressing plate and the substrate on which the pressure introducing hole is formed.   The capacitive pressure sensor according to claim 4, wherein the buffer body and the seal member are O-rings.   The region where the buffer body is pressed against the outwardly extending region and the region where the seal member is pressed are symmetrical vertically with respect to the substrate on which the pressure introducing hole is formed. Item 6. The capacitive pressure sensor according to Item 4 or 5.