JP2007132907A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly sensitive pressure sensor of high pressure-proofness capable of securing an operation area from a contact start-up to a saturation area, over a wide area ranging up to high pressure. <P>SOLUTION: This pressure sensor has a base body 30, and a detecting piece 20 comprising a flexible thin wall part 22 and a thick wall part 24 formed in the periphery of the thin wall part 22, wherein the thick wall part 24 is joined to the base body 30 to form a sealed space between the base body 30 and the thin wall part 22, and is constituted to form an upper electrode film 26 in the thin wall part 22 on an under face of the detecting piece 20, to form a lower electrode film 32 in a portion opposed to the upper electrode film 26 on an upper face of the base body 30 and to coat the lower electrode film 32 with a dielectric film 34. The thin wall part 22 is constituted of a flat part 22a, and an inclined part 22b formed integrally with the flat part 22a and having a wall thickness thickened gradually toward the thick wall part 24, and the upper electrode film 26 is arranged in the inclined part 22b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pressure sensor, and more particularly, to a touch mode type absolute pressure sensor that measures a change in capacitance between electrodes using a diaphragm as a detection piece.

  It is known that there are two types of absolute pressure sensors. That is, a piezoresistive type and a capacitance change type. The piezoresistive sensor has a strain gauge disposed in the pressure detection unit, and converts pressure detected by the pressure detection unit into pressure to obtain pressure information. On the other hand, a capacitance change type sensor obtains pressure information by converting a change in capacitance between electrodes pressed by a load pressure and asymptotically via a dielectric film into pressure.

  The capacitance change type sensors are further classified into a gap type and a touch mode type, and the touch mode type sensor has a characteristic that it is superior in sensitivity and pressure resistance as compared with the gap type sensor. As a touch mode type absolute pressure sensor having such characteristics, there is one disclosed in Patent Document 1.

  As shown in FIG. 5, the absolute pressure sensor disclosed in Patent Document 1 has a basic configuration including a diaphragm 2, a base 3 to which the diaphragm 2 is bonded, and a lower electrode film 5 disposed on the base 3. It is said. More specifically, the diaphragm 2 is made of silicon, and the diaphragm 2 is energized so that the thin portion 2a acts as an upper electrode. The substrate 3 may be made of an insulating member such as glass (soda lime glass), and the lower electrode film 5 is formed on the upper surface of the substrate 3 at a position facing the thin portion 2a. A dielectric film 4 is formed on the upper surface of the lower electrode film 5 so as to cover the lower electrode film 5.

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特開２００２−２１４０５８号公報 In the absolute pressure sensor 1 having such a configuration, when a pressure is applied to the thin portion 2a of the diaphragm 2 which is a detection piece, the thin portion 2a is bent and pressed against the dielectric film 4. When the load pressure increases, the amount of deflection of the thin portion 2a increases, and the contact area of the thin portion 2a with the dielectric film 4 increases. According to such an action, the lower electrode film 5 and the thin portion 2a serve as a capacitor that causes charging between the electrodes via the dielectric film 4. For this reason, pressure data can be obtained by converting the change in capacitance between the lower electrode film 5 and the thin portion 2a into pressure. Here, the capacitance C between the electrodes is

It can be expressed as. Here, ε is the dielectric constant of the dielectric film 4, S is the area of the electrode film facing through the dielectric film 4, and d is the film thickness of the dielectric film 4, so that the amount of deflection of the thin portion 2 a is changed. That is, it can be seen that the capacitance changes due to the change in the contact area between the thin portion 2a and the lower electrode film 5 through the dielectric film 4.
Japanese Patent Laid-Open No. 2002-214058

  The absolute pressure sensor configured as described above is excellent in sensitivity and pressure resistance, but has a drawback that the rate of increase in capacitance with respect to increase in pressure is high, and the operating region from the start of contact to the saturation region is narrow. is there. That is, the linearity in pressure-capacity characteristics is poor.

  Therefore, in the present invention, the linearity of the pressure-capacitance characteristics is improved, and the operation region from the start of contact to the saturation region can be secured in a wide region up to a high pressure, and the pressure is high in sensitivity and high withstand voltage. An object is to provide a sensor.

  In order to achieve the above object, a pressure sensor according to the present invention comprises a base made of an insulating material, a flexible thin-walled portion, and a thick-walled portion formed around the thin-walled portion. A detection piece that is bonded to the base to form a sealed space between the base and the thin portion, and an upper electrode film is formed on the thin portion on a lower surface of the detection piece, A pressure sensor having a structure in which a lower electrode film is formed at a portion facing the upper electrode film and the lower electrode film is covered with a dielectric film, wherein the thin portion is formed integrally with the flat portion and the flat portion, It is comprised by the inclination part which thickened gradually toward the said thick part, and the said upper electrode film has been arrange | positioned to the said inclination part, It is characterized by the above-mentioned. With such a configuration, the upper electrode film does not come into contact with the dielectric film covering the lower electrode film in the initial contact where the flat portion contacts the upper surface of the substrate, and the upper electrode film is gently brought into contact with the pressurization. The contact area between the dielectric film and the dielectric film increases. For this reason, the characteristic indicated by the capacitance and the pressure can be shown by extending the operation region to the high pressure region, and the linearity thereof is also improved. Further, as described above, the pressure sensor having the above-described configuration has the characteristics of a gap mode type pressure sensor, and the configuration itself is a touch mode type pressure sensor. It also has the characteristics of sensitivity and high breakdown voltage.

  In the pressure sensor configured as described above, the sealed space may be formed by a recess formed on the lower surface of the detection piece and / or the upper surface of the substrate. The sealed space provided between the detection piece and the base is a minute gap that can contact both of the thin pieces of the detection piece by bending. This gap is the lower surface of the detection piece or the base. Or a recess on the lower surface of the detection piece and the upper surface of the substrate. Further, by forming a gap by forming a recess in at least one member in this way, the degree of freedom in design can be increased.

  In the pressure sensor configured as described above, it is preferable that the detection piece is formed of an AT-cut quartz plate. The AT-cut quartz plate has a characteristic of causing a thickness difference in the thin part by forming the thin part by wet etching according to the characteristics of the crystal orientation. Moreover, since the AT-cut quartz plate excites thickness shear vibration, the thickness can be measured by measuring the resonance frequency. For this reason, it is possible to perform the thickness processing with high accuracy by finely adjusting the thickness based on the resonance frequency. Moreover, a yield can be improved by adjusting thickness using this effect | action. Further, since quartz is a material that is materially stable compared to a member such as silicon, there is little change over time.

  Further, in the pressure sensor configured as described above, the detection piece may have a through-hole for guiding a part of the upper electrode film to the upper surface side of the detection piece on a joint surface with the base. good. Since the joint surface is hermetically sealed to ensure a sealed space, the airtightness of the gap portion can be maintained even when the through hole is formed.

  Further, in the pressure sensor configured as described above, the base may have a through hole for guiding a part of the upper electrode film to the lower surface side of the base on the joint surface with the detection piece. . Since the joint surface is hermetically sealed, the airtightness of the gap can be maintained even when the through hole is formed.

  Moreover, it is desirable that the base and the detection piece are joined by anodic bonding. In anodic bonding, since substances are bonded together by electrostatic attraction, the bonding strength is high, and it is advantageous for maintaining the airtightness of the gap for a long period of time.

  Hereinafter, embodiments of the pressure sensor of the present invention will be described with reference to the drawings. The following embodiments are some embodiments according to the present invention, and the technical scope of the present invention is not limited only to the embodiments described below.

  First, a first embodiment according to the pressure sensor (absolute pressure sensor) of the present invention will be described with reference to FIGS. 1 and 2. Here, FIG. 1 shows a cross-sectional view of the sensor portion of the pressure sensor of the present embodiment, and FIG. 2 shows the overall configuration of the pressure sensor. 2A is a diagram showing an upper surface and a right side surface of a detection piece, which will be described later, and FIG. 2B is a diagram showing a lower surface and a left side surface of the detection piece, and FIG. C) is a diagram showing an upper surface of a substrate described later.

  The pressure sensor 10 of this embodiment includes a detection piece 20, a base 30, electrode films 26 and 32 formed on both the detection piece 20 and the base 30, and an electrode film 32 formed on the base 30 side. And a dielectric film 34 covering the substrate.

  First, the detection piece 20 will be described. As shown in FIG. 1, the detection piece 20 forms a so-called diaphragm having a thin portion 22 at a detection position and a thick portion 24 formed integrally with the thin portion around the thin portion 22. is doing. The detection piece 20 of the present embodiment employs a configuration in which the concave portions 23 and 25 are formed at opposite positions on both plate surfaces of the substrate that is the base material of the detection piece 20, and the thin portion 22 is formed. Regarding the formation of the recesses 23 and 25, the amount of excavation from one surface (upper surface) is increased and the amount of excavation from the other surface (lower surface) is decreased. The thin-walled portion 22 is thinner than the other thin-walled portions 22, and is formed flat with a flat portion 22 a that is formed flat, and is gradually formed toward the thick-walled portion 24. And an inclined portion 22b for increasing the thickness.

  Examples of the constituent material of the detection piece 20 include silicon and quartz. Examples of the processing method include etching (dry etching, wet etching), a processing method using plasma CVM, and the like. For example, when the constituent material is silicon, the flat portion 22a and the inclined portion 22b described above can be arbitrarily formed by forming the thin portion 22 using plasma CVM.

  On the other hand, when the constituent material is quartz, a processing method using plasma CVM can be adopted as in the case of silicon, but etching (wet) is devised by devising a cut angle for cutting out a quartz substrate as a base material. Etching) can form the thin portion 22 having the flat portion 22a and the inclined portion 22b as described above. That is, the difference in etching rate based on the anisotropy of the crystal structure is used. Further, by processing the quartz substrate by etching, batch processing becomes possible and productivity can be increased. A quartz substrate most suitable for such a processing method by etching is an AT-cut quartz plate.

  In the AT-cut quartz plate, when the direction of the Z ′ axis is set to the direction shown in FIG. 1 (rotation Y cut), the recess 23 on the upper surface side of the detection piece gradually forms an inclined portion as the amount of moat increases, The ratio of the flat portion 22a is reduced. On the other hand, the concave portion 25 on the lower surface side has an extremely small amount of digging compared to the concave portion 23 on the upper surface side, so that a flat structure is maintained.

  The quartz crystal substrate used as the constituent material may be selected from those that excite thickness-slip vibration, such as an AT-cut quartz plate, and those that can excite thickness longitudinal vibration. In such a quartz substrate, the resonance frequency can be adjusted by the thickness of the substrate. Therefore, the thickness of the thin portion 22 can be adjusted with high accuracy by performing the etching process based on the resonance frequency. For example, when processing is performed by etching with the detection piece base material being silicon as in the case of a conventional pressure sensor, the processing target thickness is 10 μm, but the actual thickness is about 8 to 12 μm. It was. On the other hand, when the base material of the detection piece 20 is quartz as in the present embodiment and the plate thickness is adjusted based on the resonance frequency, the plate thickness targeted for processing is 10 μm. It is possible to finish with high accuracy of about 03 μm. In addition, since quartz is a material that is materially stable compared to a member such as silicon, it is possible to provide a high-quality pressure sensor with little secular change. Therefore, in this embodiment, the case where an AT cut quartz plate is adopted as the base material of the detection piece 20 will be described as an example in the following description.

  The detection piece 20 as described above has a through hole 28 formed in the thick portion 24 as can be seen by referring to the entire configuration shown in FIGS. 2 (A) and 2 (B). The through hole 28 is a through hole that draws out an electrode film (hereinafter referred to as an upper electrode film) 26, which will be described later in detail, formed on the lower surface side of the detection piece 20 to the upper surface side of the detection piece 20.

  The upper electrode film 26 is formed on the thin portion 22 on the lower surface of the detection piece 20. Specifically, the thin portion 22 is disposed on the inclined portion 22b. The thin portion 22 serves as a detection portion of the pressure sensor 10 and bends to the lower surface side according to the pressure applied from the upper surface side of the detection piece 20 and comes into contact with the upper surface of the base body 30 described later. In this contact with the upper surface of the base body 30, the thinnest flat portion 22a comes into initial contact, and then the load pressure increases and the inclined portion 22b gradually comes into contact. That is, the inclined portion 22b changes the contact area with the conductor film 34 over a wide region from a low pressure region to a high pressure region. Therefore, the detection piece 20 in the pressure sensor 10 of the present embodiment employs a structure in which the arrangement position of the upper electrode film 26 is shifted from the initial contact position toward the inclined portion 22b where the thickness increases, and pressure in a wide region The configuration allows detection.

  An extraction electrode 26 a is formed on the upper electrode film 26 arranged as described above, and the extraction electrode 26 a is led to the periphery of the above-described through hole (through hole) 28. The through hole (through hole) 28 is subjected to conduction treatment (through hole plating), and a metal as an external terminal 26b for mounting is provided around the through hole (through hole) 28 on the upper surface side of the detection piece 20. A pattern is formed.

  2B, a metal pattern 32b is formed on the lower surface of the detection piece 20 so as to surround the thick portion 24 in addition to the upper electrode film 26 and the extraction electrode 26a. It is arranged. Further, a part of the metal pattern 32b extends on the side surface of the detection piece 20 and forms a body as the external terminal 32c.

  Next, the base body 30 will be described. The base body 30 in this embodiment is an insulating substrate having the same outer shape as the detection piece 20 described above, that is, a rectangular shape, as shown in FIGS. 1 and 2C. The shape of the substrate 30 is not particularly limited as long as a sealed space is ensured between the detection piece 20 formed by the above-described recess 25 and the substrate 30 and can be kept airtight. Not. Examples of the constituent material of the base body 30 include glass, crystal, and ceramic. In the present embodiment, a case where glass, specifically, soda lime glass is employed as the material of the substrate 30 will be described as an example. A suitable condition for selecting the constituent material is that the thermal expansion coefficient is close to that of the constituent material of the detection piece 20 described above.

  As will be described later, the base 30 is joined to the detection piece 20 described above. An electrode film (hereinafter referred to as a lower electrode film) 32 is formed on the upper surface of the substrate 30 at a position facing the upper electrode film 26 disposed on the lower surface of the detection piece 20 when bonded to the detection piece 20. Yes. An extraction electrode 32a is formed on the lower electrode film 32 arranged in this manner. When the base 30 and the detection piece 20 are joined, the extraction electrode 32a contacts the metal pattern 32b disposed around the thick portion 24, and contacts the upper electrode film 26 and the extraction electrode 26a. It is routed to a position that does not. The lower electrode film 32 is covered with a dielectric film 34. The dielectric film 34 can prevent the lower electrode film 32 and the upper electrode film 26 from coming into direct contact and short-circuiting.

  The pressure sensor 10 of the present embodiment is configured by joining the detection piece 20 having the above configuration and the base body 30. The detection piece 20 and the substrate 30 are joined by anodic bonding through the electrode pattern 32b. When the detection piece 20 and the base body 30 are joined, it is desirable that the gap (sealed space) formed by the recess 25 formed on the lower surface side of the thin portion 22 is a vacuum. This is because the outside air temperature or the like does not affect the detected pressure. Therefore, bonding is performed in a vacuum region such as a vacuum chamber, and anodic bonding is performed in the following process. First, a member to be bonded, that is, the detection piece 20 and the base 30 are overlapped, and both are heated to soften the glass that is a constituent material of the base 30. In the case of the present embodiment, the detection piece 20 (metal pattern 32b formed on the detection piece 20) made of quartz is set as an anode, and a high voltage is applied between both members. As a result, an electric double layer is generated on the joint surfaces of the two members, a strong joint is realized by electrostatic attraction, and the space formed by the recess 25 is hermetically sealed. Although a through hole (through hole) 28 is formed in the detection piece 20, the detection piece 20 and the base body 30 are firmly bonded by anodic bonding, so that the through hole (through hole) 28 is interposed. Thus, the airtightness of the space is not hindered.

  Detection of pressure by the pressure sensor 10 configured as described above is as follows. First, when pressure is applied to the thin portion 22 of the detection piece 20, the thin portion 22 is elastically bent toward the lower surface and comes into contact with the upper surface of the substrate 30. The contact of the thin-walled portion 22 with the upper surface of the base 30 is brought into contact with the flat portion 22a that is thin and easily bent as an initial contact. Here, in the pressure sensor 10 of the present embodiment in which the sealed space is evacuated, initial contact by the flat portion 22a occurs by exposing the pressure sensor 10 to the external space (in the atmosphere) (see the two-dot chain line in FIG. 1). . In this state, when the load pressure on the thin portion 22 increases, the inclined portion 22b on which the upper electrode film 26 is disposed gradually comes into contact with the upper surface of the substrate 30. Here, as described above, the inclined portion 22b of the thin portion 22 has a structure in which the thickness gradually increases from the flat portion 22a to the thick portion 24. The change is more gradual than the conventional diaphragm having a thin wall portion having a constant thickness. In addition, since the flat portion 22a and the inclined portion 22b have different degrees of bending with respect to pressure, the configuration in which the upper electrode film 26 is disposed on the inclined portion 22b stabilizes the change in capacitance with respect to the load pressure. Become.

  As described above, in the pressure sensor 10 of the present embodiment, the upper electrode film 26 is disposed at a position shifted from the flat portion 22a serving as the initial installation position toward the inclined portion 22b in the thin portion 22 of the detection piece 20. The lower electrode film 32 is disposed on the upper surface of the substrate 30 at a position facing the upper electrode film 26, and is covered with a dielectric film 34 to prevent direct contact between the electrode films 26 and 32. The touch mode type pressure sensor converts a change in capacitance in a capacitor formed by a contact surface between the upper electrode film and the lower electrode film into a pressure value. Therefore, in the pressure sensor 10 of the present embodiment, the change in the inclined portion 22b where the upper electrode film 26 is disposed becomes gentle with respect to the load pressure, so that the electrostatic capacitance of the capacitor formed by both the electrode films 26 and 32 is increased. The capacity can shift the saturation region to the high pressure side as compared with the conventional pressure sensor. That is, the linearity of the pressure-capacitance characteristic is improved, and the operating region indicated by this characteristic can be expanded. FIG. 3 shows the pressure-capacitance characteristics of the pressure sensor 10 of the present embodiment and the pressure-capacitance characteristics of a conventional touch mode type pressure sensor. Thus, it can be read from FIG. 3 that the pressure-capacitance characteristic of the pressure sensor 10 according to the present embodiment extends to a high-pressure range as compared with the related art.

  In the pressure sensor 10 as described above, the following effects can be obtained in addition to the effects peculiar to the touch mode type sensor, that is, high sensitivity and high pressure resistance compared to the gap mode type sensor and the like. Can do. First, the linearity in the operation region is improved in the graph showing the pressure-capacitance characteristics as compared with the conventional touch mode type sensor. In addition, the operating range can be expanded to a high pressure range as compared with a conventional touch mode type sensor. Further, when the detection piece 20 is made of quartz, variation in thickness of the thin portion 22 can be reduced by a thickness control technique unique to quartz. Thereby, the variation in the detected pressure can be suppressed, and a highly accurate pressure sensor can be obtained.

  In the present embodiment, a through hole (through hole) 28 is formed in the detection piece 20 and the upper electrode film 26 is electrically connected to the upper surface of the detection piece 20. However, the through hole is formed in the base body 30. The lower electrode film 32 may be electrically connected to the lower surface of the substrate 30. Naturally, two through holes may be formed in either the detection piece 20 or the base 30 and the respective electrodes of the upper electrode film 26 and the lower electrode film 32 may be electrically connected to an external terminal.

  Next, a second embodiment according to the pressure sensor of the present invention will be described with reference to FIG. Note that the basic configuration of the pressure sensor in this embodiment is the same as that of the pressure sensor shown in the first embodiment. That is, it is basically composed of a detection piece, a base, an electrode film formed on both the detection piece and the base, and a dielectric film covering the electrode film formed on the base. Accordingly, parts having the same function are denoted by reference numerals obtained by adding 100 to the reference numerals shown in FIG. 1, and detailed description thereof will be omitted.

  The difference between the pressure sensor 110 of the present embodiment and the pressure sensor 10 described in the first embodiment is the shape of the detection piece and the shape of the gas. More specifically, the detection piece 120 of this embodiment has a flat shape on the lower surface side of the base material, and a recess 135 for securing the space formed by the recess 25 is formed in the base body 30. Even with the pressure sensor 110 having such a configuration, an effect equivalent to that of the pressure sensor 10 described in the first embodiment can be obtained. When manufacturing the pressure sensor 110 shown in the present embodiment, the processing of the recess 123 in the detection piece 120 is performed by a combination of blast processing, etching, plasma CVM, and the like, so that the processing time can be shortened. Become. This is because cracks during blasting can be suppressed by flattening the lower surface of the detection piece 120 of the present embodiment.

  In the said embodiment, when joining the detection pieces 20 and 120 and the base | substrates 30 and 130, it described that anodic bonding was used. However, as long as it is a bonding method that can maintain the airtightness of the gap (space) provided between the upper electrode films 26 and 126 and the lower electrode films 32 and 132, it is a matter of course that other bonding methods can be used. It can be regarded as an embodiment of the invention.

It is a figure which shows the structure of the sensor part of the pressure sensor which concerns on 1st Embodiment. It is a figure which shows a mode that the detection piece and base | substrate which comprise a pressure sensor were decomposed | disassembled. It is a figure which shows the pressure-capacitance characteristic of the conventional touch mode type pressure sensor and the pressure sensor which concerns on this invention. It is a figure which shows the structure of the sensor part of the pressure sensor which concerns on 2nd Embodiment. It is a figure which shows the structure of the conventional touch mode type pressure sensor.

Explanation of symbols

  10 ......... Pressure sensor, 20 ... Detection piece, 22 ......... Thin portion, 22a ......... Flat portion, 22b ......... Inclined portion, 23 ......... Recess, 24 ......... Thick portion, 25 ............ Recess, 26... Upper electrode film, 28... Through hole, 30... Base, 32 ....... Lower electrode film, 34.

Claims (6)

A base made of an insulating material, a flexible thin-walled portion, and a thick-walled portion formed around the thin-walled portion, and the thick-walled portion is joined to the base and the base and the thin-walled portion A detection piece that forms a sealed space in between, an upper electrode film is formed on the thin portion on the lower surface of the detection piece, and a lower electrode film is formed on a portion of the upper surface of the substrate facing the upper electrode film And a pressure sensor configured to cover the lower electrode film with a dielectric film,
The thin portion is formed by a flat portion and an inclined portion that is formed integrally with the flat portion and gradually increases in thickness toward the thick portion,
The upper electrode film is disposed on the inclined portion,
A pressure sensor characterized by that.   2. The pressure sensor according to claim 1, wherein the sealed space is configured by a recess formed on a lower surface of the detection piece and / or an upper surface of the base.   The pressure sensor according to claim 1, wherein the detection piece is configured by an AT-cut quartz plate.   4. The detection piece according to claim 1, wherein the detection piece has a through hole for guiding a part of the upper electrode film to the upper surface side of the detection piece on a joint surface with the base. The described pressure sensor.   The said base | substrate has a through-hole for guide | inducing a part of said upper electrode film to the lower surface side of the said base | substrate at the joint surface with the said detection piece. Pressure sensor.   6. The pressure sensor according to claim 1, wherein the base and the detection piece are bonded by anodic bonding.

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