JP6130765B2 - Capacitive pressure sensor - Google Patents

Description

  The present invention relates to a capacitance type pressure sensor that detects a change in a diaphragm (diaphragm) that is deflected by the pressure of a fluid to be measured as a change in capacitance.

  2. Description of the Related Art Conventionally, a capacitance type pressure sensor that detects a change in a diaphragm that is bent under the pressure of a fluid to be measured as a change in capacitance has been widely known. For example, a capacitive pressure sensor is used to measure a vacuum pressure during a thin film formation process in a semiconductor manufacturing apparatus or the like, and a capacitive pressure sensor for measuring the vacuum pressure is used. This is called a diaphragm gauge.

  This diaphragm vacuum gauge is a sensor that detects a change in the capacitance of a housing that has an introduction portion of a fluid to be measured and that is deflected by the pressure of the fluid to be measured guided through the introduction portion of the housing as a change in capacitance. It has a chip and a sensor case that covers the main body of the housing that houses the sensor chip.

  In this diaphragm vacuum gauge, basically, the same material as the thin film to be processed and its by-products are deposited on the diaphragm. Hereinafter, this deposited substance is called a contaminant. When this pollutant accumulates on the diaphragm, the stress caused by them causes the diaphragm to bend, resulting in a shift (zero drift) in the output signal of the sensor. Further, since the diaphragm is apparently thick due to the accumulated contaminants, the diaphragm is difficult to bend, and the change width (span) of the output signal due to the pressure application is also smaller than the change width of the original output signal.

  Therefore, in the diaphragm vacuum gauge, there is a baffle between the introduction portion and the diaphragm that prevents the deposition of contaminants contained in the measured fluid on the diaphragm by making the plate surface perpendicular to the direction of passage of the measured fluid. Is provided. Further, by heating with a heater, the temperature in the sensor case is kept at a high temperature at which no contaminants are deposited (see, for example, Patent Document 1). In Patent Document 1, a heater is provided in the sensor case. However, for example, as shown in Patent Document 2, it is conceivable that the heater is wound around the outer peripheral wall of the sensor case.

JP 2007-155500 A Japanese Patent Laid-Open No. 5-281073 JP 2002-1111011 A

  However, for example, when a sheath type heater (sheath heater) is configured to be wound around the outer peripheral wall of the sensor case in a coil shape, the sheath heater itself generates thermal expansion due to heat generation, and the contact area of the sheath heater becomes insufficient.

  When the contact area of the sheath heater becomes insufficient, a large change occurs in the amount of heat transferred to the sensor case, and the temperature in the sensor case is the lower limit value (the lower limit temperature (for example, 300 ° C.)) at which no contaminant is deposited. There is a risk that contaminants will accumulate on the diaphragm. The sheath heater is an electric heater in which a spiral heating element is filled in the center of a metal pipe with a highly insulating powder having good heat conduction.

  On the other hand, it is conceivable to apply a tightening force to the sheath heater using a fastening member such as a bolt or nut. However, if the tightening force is excessive, the sheath heater temperature becomes excessive during the sheath heater heating control. (For example, when it becomes 350 degreeC or more) The deformation | transformation accompanying the thermal expansion of a sheath heater is suppressed with a clamping force, The heater itself may be damaged and a possibility that a heater lifetime may be shortened arises.

  The present invention has been made to solve such a problem. The object of the present invention is to suppress a decrease in contact area due to the thermal expansion of the heater and to perform thermal expansion when the temperature of the heater becomes excessive. It is an object of the present invention to provide a capacitance type pressure sensor that can absorb deformation accompanying the above.

In order to achieve such an object, the present invention relates to a change in the capacitance of a housing having an introduction portion for a fluid to be measured and a diaphragm that is bent by receiving the pressure of the fluid to be measured guided through the introduction portion. In a capacitive pressure sensor comprising: a sensor chip that detects the sensor chip; a sensor case that covers the body of the housing that houses the sensor chip; and a heater that is wound around the outer peripheral wall of the sensor case. A first metal block that covers one side of the outer surface of the heater with the outer surface of the one side being in contact with the inner peripheral surface thereof, and is opposed to the first metal block with the sensor case interposed therebetween, and the outer surface of the heater A second metal block that covers the other side of the first metal block and an outer surface of the other side in contact with the inner peripheral surface thereof, and a fastening member that fastens the first metal block and the second metal block. , The fastening member is a combination of a disc spring washer consisting of bolt and nut and the shape memory alloy or are a combination of a washer made of bolt and nut and bimetal, due to thermal expansion at a predetermined temperature or higher of the area of the heater It is characterized by having flexibility only against deformation.

  In this invention, a fastening member has flexibility only with respect to the deformation | transformation accompanying thermal expansion in the area | region more than predetermined temperature of a heater. That is, in the present invention, when the predetermined temperature is, for example, 350 ° C., the fastening member has flexibility only with respect to the deformation accompanying the thermal expansion of the heater in the region of 350 ° C. or higher, and is less than 350 ° C. It does not have flexibility with respect to the deformation accompanying the thermal expansion of the heater in the region. Thereby, in the region below 350 ° C., the decrease in contact area due to the thermal expansion of the heater is suppressed by the fastening force of the fastening member, while in the region above 350 ° C., the thermal expansion of the heater is caused by the flexibility of the fastening member. Accompanying deformation is absorbed.

  According to the present invention, one side of the outer surface of the heater is covered with the first metal block with the inner peripheral surface thereof in contact with the outer surface of the one side, and the other side of the outer surface of the heater is covered with the outer side of the other side. The inner peripheral surface is brought into contact with the surface and covered with the second metal block, and only the first metal block and the second metal block are deformed due to the thermal expansion of the heater in a region of a predetermined temperature or higher. Since fastening is performed with a flexible fastening member, in a region below a predetermined temperature, a reduction in contact area due to thermal expansion of the heater is suppressed by a fastening force of the fastening member, and in a region above a predetermined temperature, Due to the flexibility of the fastening member, the deformation due to the thermal expansion of the heater is absorbed, and if the heater temperature becomes excessive during the heating control of the heater, the heater life will be reduced so as not to damage the heater itself. To eliminate the risk of shortening It becomes ability.

It is a longitudinal cross-sectional view which shows the principal part of one Embodiment (diaphragm vacuum gauge) of the electrostatic capacitance type pressure sensor which concerns on this invention. It is a top view of the baffle used for this diaphragm vacuum gauge. It is a side view of this diaphragm vacuum gauge. It is a front view before attaching the 2nd metal block of this diaphragm vacuum gauge. It is a front view after attaching the 2nd metal block of this diaphragm vacuum gauge. It is the side view and sectional drawing which show the state which does not have flexibility, and the state which has flexibility of the disk spring washer made from shape memory alloy used for this diaphragm vacuum gauge.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a main part of an embodiment of a capacitive pressure sensor according to the present invention.

  This capacitive pressure sensor (diaphragm vacuum gauge) 1 includes a housing 10, a pedestal plate 20 accommodated in the housing 10, and a sensor chip 30 that is also accommodated in the housing 10 and joined to the pedestal plate 20. And an electrode lead portion 40 that is directly attached to the housing 10 and electrically connects the inside and outside of the housing 10.

  The pedestal plate 20 includes a first pedestal plate 21 and a second pedestal plate 22. The pedestal plate 20 is spaced from the housing 10 and is supported by the housing 10 only through the support diaphragm 50. .

  The housing 10 includes a lower housing 11, an upper housing 12, and a cover 13. The lower housing 11, the upper housing 12, and the cover 13 are made of Inconel, which is a corrosion-resistant metal, and are joined by welding.

  The lower edging 11 has a shape in which cylindrical bodies having different diameters are connected, the large diameter portion 11a has a joint portion with the support diaphragm 50, and the small diameter portion 11b forms an introduction portion 10A into which a fluid to be measured flows. Yes.

  The upper housing 12 has a substantially cylindrical shape, and forms an independent vacuum reference vacuum chamber 10 </ b> B in the housing 10 via the cover 13, the support diaphragm 50, the pedestal plate 20, and the sensor chip 30. The reference vacuum chamber 10B is provided with a gas adsorbing material called a getter (not shown) to maintain the degree of vacuum.

  Further, the cover 13 is made of a circular plate, and an electrode lead insertion hole 13a is formed at a predetermined position of the cover 13, and the electrode lead portion 40 is embedded through a hermetic seal 60, and the sealing performance of this portion is ensured. Has been.

  On the other hand, the support diaphragm 50 is made of an Inconel thin plate having an outer shape matched to the shape of the housing 10, and is sandwiched between the first pedestal plate 21 and the second pedestal plate 22 and its outer peripheral portion ( The peripheral edge) is sandwiched between the lower housing 11 and the upper housing 12 and joined by welding or the like.

  The thickness of the support diaphragm 50 is, for example, several tens of microns in the case of the present embodiment, and is sufficiently thinner than the pedestal plates 21 and 22. Further, a large-diameter hole 50 a that forms a slit-like space (cavity) 20 </ b> A is formed between the first pedestal plate 21 and the second pedestal plate 22 in the central portion of the support diaphragm 50.

  The first pedestal plate 21 and the second pedestal plate 22 are made of sapphire, which is a single crystal of aluminum oxide, and the first pedestal plate 21 is spaced from the inner surface of the housing 10 on the upper surface of the support diaphragm 50. The second pedestal plate 22 is bonded to the lower surface of the support diaphragm 50 while being separated from the inner surface of the housing 10.

  The first pedestal plate 21 is formed with an introduction hole 21a for a fluid to be measured that communicates with a slit-shaped space (cavity) 20A at the center thereof. The second pedestal plate 22 has a slit-like shape. A plurality of (four in this example) lead-out holes 22a are formed in the sensor chip 30 and communicated with the space (cavity) 20A.

  Each pedestal plate 21, 22 is sufficiently thick as described above with respect to the thickness of the support diaphragm 50, and has a structure in which the support diaphragm 50 is sandwiched between both pedestal plates 21, 22. ing. This prevents this portion from warping due to thermal stress generated by the difference in thermal expansion coefficient between the support diaphragm 50 and the base plate 20.

  A sensor chip 30 having a rectangular shape in a top view made of sapphire, which is a single crystal of aluminum oxide, is bonded to the second pedestal plate 22 via an aluminum oxide-based bonding material. In addition, since the joining method of this sensor chip 30 is described in detail in Patent Document 3, a description thereof is omitted here.

  The sensor chip 30 has a size of 1 cm square or less in a top view, a spacer 31 made of a rectangular thin plate, a sensor diaphragm 32 that is bonded to the spacer 31 and generates a strain in response to application of pressure, and a sensor diaphragm. The sensor pedestal 33 is formed so as to form a vacuum capacity chamber (reference chamber) 30A. The vacuum capacity chamber 30 </ b> A and the reference vacuum chamber 10 </ b> B maintain the same degree of vacuum through a communication hole (not shown) drilled at an appropriate position of the sensor base 32.

  The spacer 31, the sensor diaphragm 32, and the sensor pedestal 33 are joined together by so-called direct joining to constitute an integrated sensor chip 30. The sensor diaphragm 32 which is a component of the sensor chip 30 corresponds to the diaphragm referred to in the present invention.

  Further, in the capacity chamber 30A of the sensor chip 30, a fixed electrode (not shown) made of a conductor such as gold or platinum is formed on the inner surface of the sensor pedestal 33, and the inner surface of the sensor diaphragm 32 facing the fixed electrode. A movable electrode (not shown) made of a conductor such as gold or platinum is formed on the (back surface). Further, contact pads 35 and 36 made of gold or platinum are formed on the upper surface of the sensor chip 30, and the fixed electrode and the movable electrode in the capacity chamber 30A are connected to the contact pads 35 and 36 by wiring (not shown).

  On the other hand, the electrode lead portion 40 includes an electrode lead pin 41 and a metal shield 42. The electrode lead pin 41 is embedded in the metal shield 42 with a hermetic seal 43 made of an insulating material such as glass, An airtight state is maintained between both end portions of the lead pin 41. One end of the electrode lead pin 41 is exposed to the outside of the housing 10 so that the output of the diaphragm vacuum gauge 1 is transmitted to an external signal processing unit through a wiring (not shown). A hermetic seal 60 is interposed between the shield 42 and the cover 13 as described above. Further, conductive contact springs 45 and 46 are connected to the other end of the electrode lead pin 41.

  Even if the support diaphragm 50 is slightly changed due to a sudden pressure increase caused by a sudden flow of the fluid to be measured from the introduction portion 10A, the contact springs 45 and 46 have a biasing force of the contact springs 45 and 46 of the sensor chip 30. It is soft enough not to affect the measurement accuracy.

  In this diaphragm vacuum gauge 1, between the sensor diaphragm 32 of the sensor chip 30 and the introduction part 10A, the plate surface is orthogonal to the measurement fluid passage direction F at the outlet of the measurement fluid from the introduction part 10A. Thus, a baffle 70 made of Inconel is disposed. FIG. 2 shows a plan view of the baffle 70. The baffle 70 has tabs 70 a formed at predetermined angular intervals on the outer periphery thereof, and the fluid to be measured passes through the gap 70 b between the tabs 70 a and is sent to the sensor diaphragm 32.

  Further, in the diaphragm vacuum gauge 1, the housing 10 is provided inside the cylindrical sensor case 80 so that the introduction portion (pressure guiding tube) 10A of the fluid to be measured is drawn out (downward). The upper part of the sensor case 80 is closed with a lid 80a that forms a part of the sensor case 80, that is, the body of the housing 10 that houses the sensor chip 30 is covered with the sensor case 80, and this sensor Through the lead-out hole (not shown) provided in the lid 80a of the case 80, the wiring connected to the electrode lead pin 41 is guided to an external signal processing unit.

  In the diaphragm vacuum gauge 1, a sheath heater 90 is wound around the outer peripheral wall of the sensor case 80 in a coil shape. Further, with respect to the sheath heater 90, the inner peripheral surface thereof is brought into contact with the outer surface on one side of the sheath heater 90 so as to cover one side (the back side in FIG. 1) of the outer surface of the sheath heater 90. A cylindrical first metal block 100 is provided. The first metal block 100 has flange portions 100a and 100a on both sides thereof, and lower end surfaces thereof are fixed to the bottom surface of the sensor case 80 by bolts 201 and 201. Three through holes 100b are provided in the flange portions 100a and 100a.

  FIG. 3 shows a side view of the diaphragm vacuum gauge 1. The sheath heater 90 has a semi-cylindrical shape with its inner peripheral surface in contact with the outer surface on the other side of the sheath heater 90 so as to cover the other side of the outer surface of the sheath heater 90 (front side in FIG. 1). The second metal block 101 is provided. That is, the semi-cylindrical second metal block 101 is provided so as to face the first metal block 100 with the sensor case 80 interposed therebetween. Similar to the first metal block 100, the second metal block 101 also has flanges 101a and 101a on both sides thereof. The flanges 101a and 101a are also provided with three through holes 101b.

  The front view of the diaphragm vacuum gauge 1 before attaching the 2nd metal block 101 to FIG. 4 is shown. In the state before the second metal block 101 is attached, the other side (front side) of the outer surface of the sheath heater 90 is exposed as shown in FIG. From this state, the flanges 100a, 100a of the first metal block 100 and the flanges 101a, 101a of the second metal block 101 are aligned with each other on the other side (front side) of the outer surface of the sheath heater 90. It arrange | positions so that the 2 metal block 101 may be covered.

  Then, with the flanges 100a and 100a of the first metal block 100 and the flanges 101a and 101a of the second metal block 101 being combined, the bolt 301, the nut 302, and the disc spring washer 303 are used as fastening members. The first metal block 100 and the second metal block 101 are fastened.

  That is, the three through holes 100b of the flange portions 100a and 100a of the first metal block 100 and the three through holes 101b of the flange portions 101a and 101a of the second metal block 101 are combined and combined. The first metal block 100 and the second metal block 101 are inserted into a total of six through-holes 100b and 101b by inserting bolts 301 through plate spring washers 303 and tightening nuts 302 at the ends of the bolts 301. And conclude. The front view of the diaphragm vacuum gauge 1 after attaching the 2nd metal block 101 to FIG. 5 is shown.

  In the fastening member that fastens the first metal block 100 and the second metal block 101, that is, in the combination of the bolt 301, the nut 302, and the disc spring washer 303, the disc spring washer 303 has a predetermined temperature of the sheath heater 90. It has flexibility only against deformation caused by thermal expansion in the above region.

  In this embodiment, the Belleville spring washer 303 is a Belleville spring washer made of shape memory alloy, and has flexibility only against deformation caused by thermal expansion of the sheath heater 90 in a region of 350 ° C. or higher, and is less than 350 ° C. In this region, the sheath heater 90 is not flexible with respect to deformation caused by thermal expansion.

  A disc spring washer 202 made of a shape memory alloy similar to the disc spring washer 303 is also provided between the bolts 201 fixing the first metal block 100 to the sensor case 80.

  On the other hand, the diaphragm vacuum gauge 1 assumes that the lower limit value (lower limit temperature) of the temperature at which the contaminant does not precipitate is 300 ° C., so that the temperature in the sensor case 80 does not fall below 300 ° C. A heating control circuit 400 is provided for controlling the heating. The heating control circuit 400 inputs a measured value (measured temperature) Tpv of the temperature in the sensor case 80 and a predetermined lower limit temperature Tsp (Tsp = 300 ° C.), and the measured temperature Tpv does not fall below the lower limit temperature Tsp. Thus, the current to the sheath heater 90 is controlled.

  In this example, the sensor chip 30 is provided with a temperature sensor (not shown), and the temperature of the sensor portion detected by the temperature sensor is heated through the electrode lead portion 40 as the measured temperature Tpv in the sensor case 80. It is supposed to be sent to the control circuit 400.

  In this diaphragm vacuum gauge 1, the temperature in the sensor case 80 is controlled by the heating control circuit 400 so that it does not fall below 300 ° C. During this control, the temperature in the sensor case 80 moves up and down in the region of 300 ° C. or higher. If the temperature in the sensor case 80 and the temperature of the sheath heater 90 are substantially the same, the temperature of the sheath heater 90 also moves up and down in the region of 300 ° C. or higher.

  In this case, in the fastening member that fastens the first metal block 100 and the second metal block 101, that is, in the combination of the bolt 301, the nut 302, and the disc spring washer 303, the disc spring washer 303 is less than 350 ° C. It does not have flexibility with respect to deformation due to thermal expansion of the sheath heater 90 in the region.

  As a result, in the region below 350 ° C., the sheath heater 90 is pressed against the sensor case 80 by the tightening force of the fastening member, and the reduction of the contact area due to the thermal expansion of the sheath heater 90 is suppressed. There is no great change in the amount of heat transfer, and there is no possibility of the deposition of contaminants due to a decrease in temperature in the sensor case 80.

On the other hand, the disc spring washer 303 has flexibility with respect to deformation accompanying thermal expansion of the sheath heater 90 in a region of 350 ° C. or higher. That is, the disc spring washer 303 is not flexible (thickness is maintained ) as shown in the side view of FIG. 6A due to its shape memory effect, and the cross section of FIG. It changes to a state having flexibility (thickness can be reduced) as shown in the figure and the arrow .

  As a result, when the temperature of the sheath heater 90 is 350 ° C. or higher during the heating control of the sheath heater 90, the deformation due to the thermal expansion of the sheath heater 90 is absorbed by the flexibility of the fastening member. For this reason, it is possible to avoid shortening the heater life without damaging the heater itself.

  In this embodiment, it is assumed that the lower limit value (lower limit temperature) of the temperature at which the pollutant does not precipitate is 300 ° C., but this lower limit temperature varies depending on the pollutant, and becomes lower depending on the pollutant. Sometimes it gets higher. Even if the lower limit temperature is slightly different, it is possible to cope with the shape memory effect of one type of disc spring washer 303, but the temperature at which the disc spring washer 303 has flexibility according to the contaminant is set. It may be changed.

  In the above-described embodiment, the fastening member is a combination of the bolt 301, the nut 302, and the disc spring washer 303. However, the fastening member is not limited to the combination of the bolt 301, the nut 302, and the disc spring washer 303. Absent. For example, instead of the Belleville spring washer 303 made of shape memory alloy, a bimetallic washer may be used.

[Extension of the embodiment]
The present invention has been described above with reference to the embodiment. However, the present invention is not limited to the above embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Diaphragm gauge (capacitance type pressure sensor), 10 ... Housing, 10A ... Introduction part, 11 ... Lower housing, 12 ... Upper housing, 13 ... Cover, 20 ... Base plate, 21 ... 1st base plate, 22 ... second pedestal plate, 30 ... sensor chip, 31 ... sensor plate, 32 ... sensor diaphragm, 33 ... sensor pedestal, 50 ... support diaphragm, 70 ... baffle, 80 ... sensor case, 90 ... sheath heater, 100 ... first 101 ... second metal block, 100a, 101a ... collar, 100b, 101b ... through hole, 201 ... bolt, 202 ... disc spring washer, 301 ... bolt, 302 ... nut, 302 ... disc spring washer.

Claims (2)

A housing having an introduction section for a fluid to be measured;
A sensor chip that detects a change in the diaphragm that is deflected by receiving the pressure of the fluid to be measured guided through the introduction unit, as a change in capacitance;
A sensor case that covers the body of the housing that houses the sensor chip;
In a capacitive pressure sensor comprising a heater wound around the outer peripheral wall of the sensor case,
A first metal block fixed to the sensor case and covering one side of the outer surface of the heater with the outer surface of the one side being in contact with the inner peripheral surface;
A second metal block facing the first metal block across the sensor case and covering the other side of the outer surface of the heater with the outer surface of the other side in contact with the inner peripheral surface;
A fastening member for fastening the first metal block and the second metal block;
The fastening member is
It is a combination of a disc spring washer made of a bolt, nut and shape memory alloy or a washer made of a bolt, nut and bimetal,
A capacitance type pressure sensor characterized by having flexibility only with respect to deformation accompanying thermal expansion in a region of a predetermined temperature or higher of the heater. The capacitive pressure sensor according to claim 1,
A capacitance-type pressure sensor, comprising: a heating control unit configured to control the heating of the heater so that the temperature in the sensor case does not fall below a predetermined lower limit temperature.

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