JP4059306B2 - Servo capacitive vacuum sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo-type capacitive vacuum sensor, and more particularly to an improvement of a vacuum sensor that measures an absolute pressure value based on a change in capacitance.
[0002]
[Prior art]
In recent years, a sensor for pressure measurement having a small size and a wide measuring range has been developed by a semiconductor manufacturing process technology. For example, the servo type presented in TRANSDUCER 97 held at IEEE Electron Device Society, 1997 International Conference on Solid-State Sensor and Actuators Chicago, June 16-19, 1997 Proceedings Volume 2, p.1457-p.1460 There is a capacitance type vacuum sensor (hereinafter referred to as “vacuum sensor”). The structure of this vacuum sensor is shown in FIG. In FIG. 6, the thickness is exaggerated as compared with the actual structure of the vacuum sensor.
[0003]
In FIG. 6, the vacuum sensor includes a silicon substrate 131 and pyrex substrates 132 and 133 bonded to both sides of the silicon substrate 131. A diaphragm-like electrode portion 134 is formed on the intermediate silicon substrate 131. An internal space 139 is formed between the electrode portion 134 and the upper Pyrex substrate 132, and an internal space 140 is formed between the electrode portion 134 and the lower Pyrex substrate 133. A gas as a measurement target (hereinafter referred to as “measurement gas”) is introduced into the internal space 139 from the outside through the inlet 141. The internal space 140 communicates with the getter chamber 153 in which the getter material 154 is accommodated, and the internal space 140 and the getter chamber 153 are exhausted by the getter material 154 and kept in a high vacuum state. The electrode part 134 receives the pressure of the gas to be measured introduced into the internal space 139. The electrode part 134 has a thick part 135 below the center part, and has a thin part 136 around the thick part 135. The thick part 135 is convex downward. The electrode part 134 is a movable electrode in which the entire thick part 135 and thin part 136 are displaced. When the electrode portion 134 receives the pressure of the gas to be measured, the lower internal space 140 is maintained in a high vacuum state, so that the thin portion 136 is deformed downward, and the central thick portion 135 is downward. Displace.
[0004]
The electrode part 134 having the above structure is formed by etching both surfaces of a silicon substrate 131 having a certain thickness by applying a semiconductor manufacturing process technique. The Pyrex substrates 132 and 133 are made of Pyrex glass and have insulating properties and high rigidity. A servo electrode 137 is provided on the surface of the Pyrex substrate 132 on the inner space 139 side. The servo electrode 137 is formed of a p ++ silicon layer. The servo electrode 137 faces the electrode portion 134. A fixed electrode 138 is provided on the surface of the Pyrex substrate 133 on the inner space 140 side. The fixed electrode 138 faces the thick portion 135. The thick part 135 functions as an electrode for the fixed electrode 138, and the capacitance according to the interval is determined between the thick part 135 and the fixed electrode 138.
[0005]
The upper Pyrex substrate 132 is formed with three through holes for forming conductive terminals. The first through hole is provided with an Al (aluminum) electrode 142 and filled with a conductive epoxy resin 143 connected to the servo electrode 137. The second through hole is provided with an Al electrode 144 and filled with a conductive epoxy resin 146 connected to the electrode part 134 via the silicon part 145. The third through hole is provided with an Al electrode 147 and filled with a conductive epoxy resin 149 connected to the fixed electrode 138 through the silicon portion 148. Lead wires 150, 151, and 152 are electrically connected to the epoxy resins 143, 146, and 149, respectively. Lead wires 150, 151, and 152 are connected to external circuits (not shown). Specifically, the lead wire 150 is connected to a servo voltage output unit in the external circuit, the lead wire 151 is connected to a reference potential unit in the external circuit, and the lead wire 152 is connected to a detection unit in the external circuit. A servo voltage is applied to the servo electrode 137 through the lead wire 150.
[0006]
In the above configuration, when the gas to be measured is introduced into the internal space 139 through the inlet 141, the electrode portion 134 receives the pressure of the gas to be measured, and the thin portion 136 is deformed downward as described above, so that the thick portion 135 is obtained. Is displaced toward the inner space 140 side. As a result, the interval between the thick part 135 of the electrode part 134 and the fixed electrode 138 changes, and the capacitance between the thick part 135 and the fixed electrode 138 changes. This change in capacitance is detected by, for example, a detection unit including an AC bridge circuit. A servo voltage is applied to the servo electrode 137 of the Pyrex substrate 132 so as to balance the pressure applied to the electrode unit 134 based on the detection action of the detection unit. In the electrode part 134, a balance arises between the electrostatic attraction by the servo voltage and the pressure by the gas to be measured, and the electrode part 134 is kept at the center position. Since there is a proportional relationship between the square of the applied servo voltage and the pressure, the pressure of the gas to be measured applied to the vacuum sensor is measured by measuring the servo voltage applied to the servo electrode 137. be able to.
[0007]
[Problems to be solved by the invention]
The conventional vacuum sensor described above has the following problems.
[0008]
In order to make it possible to measure a minute pressure with high accuracy using a vacuum sensor that detects a change in capacitance by displacing the electrode part 134, the thickness part 135 of the electrode part 134 and the fixed electrode 138 It is required to increase the capacitance between them. In order to increase the capacitance, it is necessary to increase the area of the opposing portion of the thick portion 135 in the electrode portion 134 or to narrow the gap between the thick portion 135 and the fixed electrode 138. However, when the capacitance is increased with the conventional vacuum sensor, it is necessary to provide a thick portion 135 having a large mass at the center of the electrode portion 134 due to the structure. For this reason, the thick portion 135 of the electrode portion 134 is weighted. This causes a problem that it tends to be sensitive to vibration from the outside and adversely affects measurement sensitivity and measurement accuracy.
[0009]
Furthermore, in the conventional vacuum sensor, when measuring the pressure of the gas to be measured, the capacitance between the thick portion 135 and the fixed electrode 138 is the same as the capacitance when the pressure of the gas to be measured is not applied. In addition, a servo voltage is applied to the servo electrode 137. The electrostatic capacitance when no pressure is applied varies depending on the interval between the thick portion 135 of the electrode portion 134 and the fixed electrode 138 for each vacuum sensor, and the electrostatic capacitance caused by this interval varies. Capacitance variation depends on vacuum sensor manufacturing variation and thermal expansion that varies with temperature. For this reason, according to the conventional vacuum sensor, there is a problem that the capacitance between the thick portion 135 and the fixed electrode 138 must be measured for each vacuum sensor in a state where no pressure is applied to the vacuum sensor. It was.
[0010]
The object of the present invention is to solve the above-mentioned problems, structurally suppressing the sensitivity to vibration, reducing the dependence on thermal expansion due to manufacturing variations and temperature, and measuring the capacitance of each vacuum sensor. An object of the present invention is to provide a servo-type capacitive vacuum sensor that is unnecessary, increases the measurement accuracy of minute pressure, is small, has high sensitivity, and can perform pressure measurement over a wide range.
[0011]
[Means and Actions for Solving the Problems]
The servo capacitive vacuum sensor according to the present invention is configured as follows to achieve the above object.
The vacuum sensor has a three-layer structure in which a silicon substrate is disposed between a first glass substrate and a second glass substrate, and the silicon substrate and the first glass substrate, and the silicon substrate and the second glass substrate are bonded to each other. The silicon substrate includes an electrode portion, and a first internal space that communicates with the outside through, for example, a gas inlet formed in the first glass substrate is formed between the electrode portion and the first glass substrate, and the electrode portion and the second glass substrate are formed. A second internal space that is maintained in a high vacuum state is formed between the two. The electrode portion receives the pressure of the gas introduced into the first internal space from the gas inlet. The electrode portion includes a movable electrode that is displaced by receiving a gas pressure, and a surrounding electrode that is formed to support the movable electrode around the movable electrode and is not displaced even when the gas pressure is received. The surface on the second internal space side of the movable electrode and the surface on the second internal space side of the surrounding electrode are formed as the same surface. A fixed electrode facing the movable electrode and a reference electrode facing the surrounding electrode are provided on the surface of the second glass substrate on the second internal space side. A convex servo electrode facing the movable electrode is provided on the surface of the first glass substrate on the first internal space side.
In the vacuum sensor, more preferably, when the pressure of the gas to be measured is not applied to the same surface formed by the surface on the second internal space side of the movable electrode and the surface on the second internal space side of the surrounding electrode, The second glass substrate provided with the reference electrode is parallel to the surface on the second internal space side.
In the electrode part of the vacuum sensor, a thin movable electrode that is displaced by the pressure of the gas to be measured is provided in the center, and a thick surrounding electrode that is not displaced by the pressure of the gas to be measured is provided around the movable electrode. I tried to support it. Here, the gas to be measured is, for example, a gas having a viscous flow, a molecular flow, or a flow characteristic in an intermediate region thereof. The pressure range measurable by the vacuum sensor is a range having the above displacement characteristics with respect to the movable electrode and the surrounding electrode. A first internal space that communicates with the outside through a gas inlet is formed on one side of the electrode portion, and a second internal space that is maintained in a high vacuum state is formed on the other side. The surface of the movable electrode and the surrounding electrode on the second internal space side is the same surface. When no pressure is applied to the movable electrode, a fixed electrode is provided for the movable electrode and parallel to the same surface and at the same interval, and a reference electrode is provided for the surrounding electrode. When the pressure of the gas to be measured is applied to the movable electrode, the movable electrode is displaced to the second internal space side, and the interval between the movable electrode and the fixed electrode is narrowed, but the thick surrounding electrode is not displaced, The distance between the reference electrodes is kept constant. In the above vacuum sensor, there is no thick part having a weighting action at the center of the electrode part, so even when vibration or impact is applied to the vacuum sensor, unnecessary vibrations that cause noise are generated in the electrode part. Therefore, the conventional problems concerning the sensitivity and accuracy of measurement are solved. In particular, the measurement accuracy of minute pressure can be improved. Further, by applying a necessary servo voltage to the servo electrode, the pressure of the gas to be measured applied to the movable electrode is balanced with the electrostatic attraction by the servo voltage. According to the vacuum sensor described above, in determining the value of the servo voltage, the first capacitance (C1) determined between the movable electrode and the fixed electrode, and the second capacitance determined between the surrounding electrode and the fixed electrode ( Cs) can be used to eliminate manufacturing variations for each vacuum sensor and eliminate temperature dependence.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
[0013]
A representative embodiment of a servo capacitive vacuum sensor according to the present invention will be described with reference to FIGS. The cross-sectional view of FIG. 1 exaggerates the thickness as compared with the actual structure of the vacuum sensor for convenience of explanation. 2 shows a cross section taken along line AA in FIG. 1, FIG. 3 shows a cross section taken along line BB in FIG. 1, and FIG. 4 shows a cross section taken along line CC in FIG. FIG. 5 is a block diagram showing the relationship between the vacuum sensor and the external circuit.
[0014]
As shown in FIG. 1, the vacuum sensor 11 has a three-layer structure. The layer located in the center is the silicon substrate 12. Pyrex substrates 13 and 14 are provided on the upper and lower sides of the silicon substrate 12. The Pyrex substrates 13 and 14 are plate-shaped members made of Pyrex glass, have insulating properties and high rigidity. The Pyrex substrates 13 and 14 are anodically bonded to the silicon substrate 12. An electrode portion 20 is provided on the silicon substrate 12. The electrode portion 20 is formed in a space (shown in FIG. 3) sandwiched between the Pyrex substrates 13 and 14 and surrounded by the support wall portion 38 around the silicon substrate 12.
[0015]
The electrode part 20 is formed using a silicon substrate. The electrode portion 20 is composed of a thin movable electrode 21 formed substantially at the center and a thick peripheral electrode 22 formed so as to be positioned around and support the movable electrode 21. The movable electrode 21 is a silicon thin film having a thickness of about 5 μm, for example. As will be described later, the movable electrode 21 is deformed and displaced when the electrode portion 20 receives the pressure of the gas to be measured. The planar shape of the movable electrode 21 is, for example, a square as shown in FIG. As shown in FIG. 1, the movable electrode 21 is opposed to a lower fixed electrode 24 and an upper servo electrode 16 described later, and is held at a reference potential such as a ground potential, and between the fixed electrode 24 and the movable electrode 21. An electrostatic capacity is generated or an electrostatic attractive force is generated between the servo electrode 16 and the electrostatic capacity. On the other hand, the peripheral electrode 22 is a silicon thick film having a thickness of less than 400 μm, for example. The planar shape of the peripheral electrode 22 is, for example, a substantially rectangular shape as shown in FIG. The movable electrode 21 is formed in the approximate center of the surrounding electrode 22. Further, as shown in FIG. 1, the peripheral electrode 22 faces a lower reference electrode 25 described later, and generates a capacitance with the reference electrode 25. The electrode part 20 is a single unit as a whole, and the movable electrode 21 and the peripheral electrode 22 are integrally formed. When the electrode unit 20 receives the pressure of the gas to be measured and the movable electrode 21 is displaced, the surrounding electrode 22 is not displaced and supports the movable electrode 21.
[0016]
The electrode unit 20 having the above-described structure is manufactured by preparing a silicon substrate having a thickness of 400 μm, for example, and applying a semiconductor manufacturing process such as etching on both sides of the silicon substrate. In the electrode part 20 shown in FIG. 1, the silicon layer 23 is formed by remaining as an etching stop layer during etching. A part of the silicon layer 23 becomes the movable electrode 21. In FIG. 1, the movable electrode 21 is shown in a different manner of drawing the cross section because the action is different with respect to other portions of the silicon layer 23. The other part of the silicon layer 23 other than the movable electrode 21 overlaps with the peripheral electrode 22 and acts in the same manner as the peripheral electrode. The electrode portion 20 made by applying a semiconductor manufacturing process is formed so that the lower surface of the movable electrode 21 and the lower surface of the peripheral electrode 22 are flush with each other. This is apparent from the fact that the movable electrode 21 itself and the lower surface portion of the peripheral electrode 22 are made of the silicon layer 23. Since the electrode portion 20 is formed in the above shape by etching, a recess 22 a is formed above the movable electrode 21.
[0017]
Pyrex substrates 13 and 14 are anodically bonded to both sides of the silicon substrate 12 on which the electrode portion 20 is formed. The electrode portion 20 is anodically bonded to the lower Pyrex substrate 14 at the edge of the thick surrounding electrode 22 in the manufacturing process. An internal space S <b> 1 is formed between the electrode unit 20 and the Pyrex substrate 13. The internal space S1 communicates with the outside of the vacuum sensor 11 through an inlet 15 formed in the Pyrex substrate 13, for example, and a gas to be measured is introduced from the outside. The movable electrode 21 is exposed to the internal space S1 through the recess 22a. Note that the inlet for introducing the gas to be measured into the internal space S <b> 1 can be formed at a place other than the Pyrex substrate 13. Further, an internal space S <b> 2 that is maintained in a high vacuum state is formed between the electrode unit 20 and the Pyrex substrate 14. The internal space S2 is a sealed space.
[0018]
The introduction port 15 formed in the upper Pyrex substrate 13 communicates the outside and the internal space S1, and the gas to be measured is introduced from the outside into the internal space S1 through the introduction port 15. Here, the gas to be measured by the vacuum sensor 11 is, for example, a gas having a viscous flow, a molecular flow, or a flow characteristic in an intermediate region thereof. The pressure range that is a measurement target of the vacuum sensor 11 is a range in which the movable electrode 21 is displaced and the surrounding electrode 22 is not displaced. If it is a target included in such a pressure range, a general fluid other than the above gas is also included in the measurement target of the vacuum sensor 11. On the surface of the Pyrex substrate 13 on the inner space S1 side, a convex servo electrode 16 that protrudes so as to face the movable electrode 21 is formed in a substantially central portion. The servo electrode 16 is formed by applying a semiconductor manufacturing process technique to a separately prepared silicon substrate to form a p-type (or n-type) silicon layer 17 and performing etching. The convex portion of the servo electrode 16 protrudes downward from the Pyrex substrate 13. The shape of the convex portion of the servo electrode 16 substantially matches the shape of the recess 22 a of the electrode portion 20. A servo voltage is applied to the servo electrode 16 from the outside through the silicon layer 17 and the Al electrode 18. The Al electrode 18 is formed by a method such as vapor deposition, and the end of the silicon layer 17 is connected to the Al electrode 18. The servo electrode 16 is connected to an external circuit 50 (for example, an AC bridge circuit or a circuit including arithmetic processing means constituted by a microcomputer) via the Al electrode 18 and applied with a servo voltage.
[0019]
As shown in FIG. 2, the tip surface of the convex portion of the servo electrode 16 has a square shape, for example, and the end portion of the silicon layer 17 is connected to the Al electrode 18. Moreover, the inlet 15 is formed in four places, for example. When FIG. 1 is compared with FIG. 2, for example, the positions and the number of the introduction ports 15 are not exactly the same, but are illustrated for easy understanding.
[0020]
A capacitance detecting fixed electrode 24 (hereinafter simply referred to as “fixed electrode 24”) and a reference electrode 25 are provided on the surface of the lower Pyrex substrate 14 on the inner space S2 side. The reference electrode 25 is provided around the fixed electrode 24 in an electrically insulated state. The fixed electrode 24 is provided to face the movable electrode 21, and the reference electrode 25 is provided to face the surrounding electrode 22. When the pressure of the gas to be measured is not applied to the electrode unit 20, the lower surfaces of the movable electrode 21 and the surrounding electrode 22 are the same surface and are parallel to the surface on which the fixed electrode 24 and the reference electrode 25 are provided. It has become. At this time, the distance between the movable electrode 21 and the fixed electrode 24 and the distance between the surrounding electrode 22 and the reference electrode 25 are substantially equal. The fixed electrode 24 and the reference electrode 25 are formed of, for example, a silicon layer. Based on the above structure, the capacitance is detected by each of the movable electrode 21 and the fixed electrode 24, the surrounding electrode 22, and the reference electrode 25. The reference electrode 25 is an electrode that creates a capacitance for obtaining a specific value based on a calculation formula described later, and performs zero point compensation that eliminates manufacturing variations and temperature compensation that eliminates temperature dependence. It is an electrode provided.
[0021]
As described above, the internal spaces S1 and S2 are formed on both sides of the movable electrode 21 of the electrode unit 20. When the gas to be measured is introduced from the outside into the internal space S1 through the introduction port 15, the pressure of the gas to be measured is applied to the movable electrode 21, and the internal space S2 is kept at a high vacuum. It is displaced toward the space S2. Since the surrounding electrode 22 supporting the periphery of the movable electrode 21 is formed as a thick film, it is not displaced.
[0022]
On the other hand, the lower Pyrex substrate 14 is provided with electrode pins 31, 32, 33, and 34. Each of the electrode pins 31 to 34 has a conductive epoxy resin 35 as an adhesive agent in an electrode portion through hole, a fixed electrode through hole, a reference electrode through hole, and a servo electrode through hole formed in the Pyrex substrate 14. It is fixed with. The electrode pin 31 is connected to the electrode portion 20, the electrode pin 32 is connected to the fixed electrode 24, and the electrode pin 33 is connected to the reference electrode 25. As shown in FIG. 4, the reference electrode 25 is preferably arranged around the fixed electrode 24 so as to surround it. An Al electrode 36 is provided on each of the electrode pins 31 to 24. Further, the electrode pin 34 is connected to the Al electrode 18 and the silicon layer 17 described above via a connection portion 37 made of silicon, and further connected to the servo electrode 16.
[0023]
In FIG. 1 to FIG. 3, reference numeral 38 denotes a supporting wall portion formed of silicon, in FIG. 1, 39 denotes a silicon layer, 40 denotes a deep depression, and 41 denotes a getter material. As shown in FIGS. 2 and 3, the support wall portion 38 is formed on the entire circumference so as to surround the periphery of the electrode portion 20. In the internal space S2, the gas generated from the member is adsorbed by the getter material 41 accommodated in the recess 40, and is maintained at a high vacuum as described above. Also, comparing FIG. 1 and FIG. 4, for example, the installation positions of the four electrode pins are not exactly the same, but in FIG. 1, the cross-section is partially changed so that the installation relationship of the four electrode pins is clear. Are shown.
[0024]
In the structure shown in FIG. 1, the silicon substrate 12 has a laminated structure in which Pyrex substrates 13 and 14 having insulating properties and high rigidity are bonded to both sides thereof. However, it is also possible to use a material having the same or very similar thermal expansion coefficient as that of the silicon substrate, for example, SD glass (borosilicate glass; manufactured by Hoya Co., Ltd.). .
[0025]
The silicon substrate 12 is wet-etched with an etching solution such as EPW (ethylenediamine pyrocatechol aqueous solution) or TMAH (tetramethylammonium hydroxide), and at least a part of the bottom is formed into a flat recess on one side thereof. The silicon layer 23 is formed on the surface of the recess by a semiconductor diffusion technique. A recess 40 for accommodating the getter material 41 is formed at the end of the recess.
[0026]
The silicon substrate 12 and the Pyrex substrate 14 are joined in a vacuum after the getter material 41 is accommodated in the recess 40 to form an internal space S2. Thereafter, the silicon substrate 12 is selectively etched with the above etching solution to form the electrode portion 20 including the movable electrode 21 and the peripheral electrode 22 and the support wall portion 38.
[0027]
When the pressure of the gas to be measured is not applied to the electrode unit 20, the distance between the surface formed by the lower surfaces of the movable electrode 21 and the surrounding electrode 22, and the surface on which the fixed electrode 24 and the reference electrode 25 are provided is, for example, about 10 μm. is there. The area of each of the movable electrode 21 and the fixed electrode 24 is, for example, □ 4 mm (a square with a side of 4 mm). The reference electrode 25 is formed so as to have the same area or a fixed area relative to the area of the fixed electrode 24. The movable electrode 21 and the fixed electrode 24 constitute a capacitor having a capacitance C1, and the peripheral electrode 22 and the reference electrode 25 constitute a capacitor having a capacitance Cs.
[0028]
The convex servo electrode 16 is disposed so as not to contact the peripheral electrode 22 of the electrode portion 20. The interval between the servo electrode 16 and the movable electrode 21 is set to be about 10 μm, for example. Since the thickness of the peripheral electrode 22 positioned around the movable electrode 21 is about 400 μm as described above, in the actual structure, the convex portion of the servo electrode 16 is arranged in a state of entering the inside of the recess 22a.
[0029]
FIG. 5 shows the relationship between the vacuum sensor 11 and the external circuit 50. The fixed electrode 24 is connected to the external circuit 50 through the Al electrode 36, the conductive epoxy resin 35, and the electrode pin 32 in the corresponding through hole of the Pyrex board 14, and the reference electrode 25 is Al in the corresponding through hole of the Pyrex board 14. The electrode 36, the conductive epoxy resin 35, and the electrode pin 33 are connected to the external circuit 50. On the other hand, the electrode portion 20 is connected to the external circuit 50 through the Al electrode 36, the conductive epoxy resin 35, and the electrode pin 31 in the through hole corresponding to the silicon layer 23. The electrode unit 20 is held at a reference potential such as a ground potential. Further, the servo electrode 16 is connected to the external circuit 50 via the silicon layer 17, the Al electrode 18, the connection portion 37, the silicon layer 39, the Al electrode 36 and the conductive epoxy resin 35 and the electrode pins 34 in the corresponding through holes of the Pyrex substrate 14. It is connected to the. In the external circuit 50, the capacitance C1 and the capacitance Cs are input based on the connection relationship with the electrode pins 31, 32, 33, and a specific value is calculated based on the following formula prepared in advance. . Then, a servo voltage to be applied to the electrode pin 34 is determined so that this value becomes almost zero, and the servo voltage is applied to the servo electrode 16 through the electrode pin 34. When the electrostatic attractive force due to the applied servo voltage and the pressure of the gas to be measured are balanced, the displacement at the movable electrode 21 becomes zero, and the specific value becomes zero.
[0030]
In the vacuum sensor 11, when the gas to be measured enters the internal space S <b> 1 from the introduction port 15, a pressure for displacing the movable electrode 21 toward the internal space S <b> 2 is applied. At this time, the surrounding electrode 22 is not displaced toward the internal space S2 due to the pressure of the gas to be measured. The servo electrode 16 has a calculation formula “C1−Cs × (area of the fixed electrode 24) / (area of the reference electrode 25)” created using the capacitance C1 and the capacitance Cs as 0. Thus, the servo voltage is applied by the external circuit 50. An electrostatic attractive force equal to the pressure applied to the movable electrode 21 is applied in the opposite direction to the movable electrode 21 by the servo voltage. Thereby, the movable electrode 21 is always kept in a state without displacement. Since the electrostatic attraction force and the square of the servo voltage are in a proportional relationship, the pressure applied by the gas to be measured can be obtained by detecting the applied servo voltage. Therefore, the external circuit 50 includes a calculation unit that calculates a pressure value based on the relationship, and the pressure value calculated by the calculation unit is output as a measurement value.
[0031]
In the vacuum sensor 11, the gap formed between the movable electrode 21 and the fixed electrode 24 is set as narrow as 10 μm, and the vacuum sensor 11 also has manufacturing variations for each vacuum sensor and has temperature dependence. However, according to the vacuum sensor 11 of the present embodiment, because of the structure, the distance between the movable electrode 21 and the fixed electrode 24 and the distance between the surrounding electrode 22 and the reference electrode 25 are equal when no pressure is applied to each vacuum sensor. In the circuit design, the value of the above calculation formula “C1−Cs × (area of the fixed electrode 24) / (area of the reference electrode 25)” when the pressure is not applied is 0 regardless of manufacturing variation and temperature dependency. Become. Further, when the gas to be measured enters from the inlet 15 and detects its pressure, “C1−Cs × (the area of the fixed electrode 24) / (the area of the reference electrode 25)” becomes 0, that is, electrostatic attractive force. Thus, the servo voltage can be applied to the servo electrode 16 so that the position of the movable electrode 21 can be maintained without any displacement. Therefore, the pressure detection by the vacuum sensor 11 is not affected by the manufacturing variation and temperature dependency of each vacuum sensor with respect to the gap interval between the electrodes in terms of structure and control circuit configuration.
[0032]
In the vacuum sensor 11 according to the present embodiment, the thin movable electrode 21 that is displaced by receiving pressure is formed in the approximate center of the electrode portion 20, and the thick peripheral electrode 22 that is not displaced around is formed. Since the movable electrode 21 has a small mass and the electrode portion 20 is formed by integrating the surrounding electrodes 22, the positional relationship of the electrodes hardly changes due to vibration and impact, and the operation of the vacuum sensor can be stabilized.
[0033]
【The invention's effect】
As is apparent from the above description, the present invention has the following effects.
[0034]
A movable electrode that is displaced by the pressure of the gas to be measured is formed almost at the center of the electrode, and a thick surrounding electrode is formed around it, so there is no weight in the center compared to conventional vacuum sensors, and vibration occurs. Further, it is possible to realize a vacuum sensor that can eliminate the influence of an impact and perform stable operation. Furthermore, the detection operation is strong and stable against the influence of vibration and the like, and the interval between the movable electrode and the fixed electrode and the interval between the surrounding electrode and the reference electrode are reduced to, for example, about 10 μm so that the capacitance determined by each interval is increased. Therefore, high measurement sensitivity can be achieved not only for measurement of high pressure but also for measurement of minute pressure.
[0035]
In addition, since the lower surface of the movable electrode and the surrounding electrode are the same surface with no pressure applied to the electrode portion, the distance between the movable electrode and the fixed electrode and the distance between the surrounding electrode and the reference electrode are equal. The movable electrode, the surrounding electrode, the fixed electrode, and the reference electrode can be made with good reproducibility and yield according to the design purpose. The capacitance between the movable electrode and the fixed electrode without pressure, the surrounding electrode The ratio of the capacitance between the reference electrode and the reference electrode can be realized as designed with good yield. Further, it is possible to compensate for manufacturing variations in the gap interval between the electrodes for each vacuum sensor.
[0036]
Even when pressure is applied to the electrode, the capacitance between the surrounding electrode and the reference electrode is multiplied by the value obtained by dividing the fixed electrode area by the reference electrode area, and this value is the value of the capacitance between the movable electrode and the fixed electrode. Since the operation of subtracting is performed by arithmetic processing, the servo voltage is applied so that the subtracted value is substantially zero, and the displacement of the movable electrode is maintained at zero, so that the gap between the electrodes for each vacuum sensor is The manufacturing variation of the gap interval can be eliminated, and a correct pressure indication value independent of temperature can be obtained.
[0037]
In addition, by adopting a servo structure, the thin movable electrode is not mechanically strained, so the vacuum sensor is not subject to mechanical fatigue, and the life of the vacuum sensor can be extended, providing long-term reliability. Measurements can be made.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an essential part showing a representative embodiment of a servo capacitive vacuum sensor according to the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
3 is a cross-sectional view taken along line BB in FIG.
4 is a cross-sectional view taken along line CC in FIG. 1. FIG.
FIG. 5 is a configuration diagram showing a relationship between a vacuum sensor and an external circuit.
FIG. 6 is a longitudinal sectional view of a main part of a conventional servo-type capacitive vacuum sensor.
[Explanation of symbols]
11 Servo-type capacitive vacuum sensor
12 Silicon substrate
13,14 Pyrex board
15 introduction port
16 Servo electrodes
20 electrodes
21 Movable electrode
22 Ambient electrode
24 Fixed electrode for capacitance detection
25 Reference electrode
31-34 Electrode pins
35 Epoxy resin

Claims (2)

A silicon substrate is disposed between the first glass substrate and the second glass substrate, the silicon substrate and the first glass substrate, and the silicon substrate and the second glass substrate are joined to form a three-layer structure,
The silicon substrate includes an electrode portion, a first internal space communicating with the outside through a gas inlet is formed between the electrode portion and the first glass substrate, and between the electrode portion and the second glass substrate. A second internal space that is maintained in a high vacuum state is formed, and the electrode portion receives the pressure of the gas introduced into the first internal space from the gas inlet,
The electrode portion includes a movable electrode that is displaced by receiving the pressure of the gas, and a peripheral electrode that is formed to support the movable electrode around the movable electrode and that is not displaced even by receiving the pressure of the gas. The surface of the movable electrode on the second internal space side and the surface of the peripheral electrode on the second internal space side are formed as the same surface,
On the surface of the second glass substrate on the second internal space side, a fixed electrode facing the movable electrode and a reference electrode facing the surrounding electrode are provided,
Provided on the surface of the first glass substrate on the first internal space side is a convex servo electrode that is close to and opposed to the movable electrode,
A servo-type capacitive vacuum sensor. The same surface formed by the surface of the movable electrode on the second internal space side and the surface of the peripheral electrode on the second internal space side is configured so that the fixed electrode and the reference electrode are arranged when the gas pressure is not applied. The servo capacitive vacuum sensor according to claim 1, wherein the servo glass vacuum sensor is parallel to a surface of the second glass substrate provided on the second internal space side.

Images