JP2008032451A - Variable capacitance pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable capacitance pressure sensor which can maintain satisfactory sensitivity, even if the thermal environment is changed, and can be prevented from easily breaking. <P>SOLUTION: The pressure sensor comprises a substrate 32; a detecting element 41 including a deformation area 42 formed with reduced thickness so as to deform according to the received pressure and a support part 43 with a large thickness, the support part being formed integrally with the deformation area so as to surround the circumference of the deformed region area, and fixed to the substrate; a first electrode 44, formed on the substrate side of opposing faces of the deforming surface of the deformed region of the detecting element and the substrate; a second electrode 46, formed on the deformation surface side of the opposing faces, with a predetermined distance from the first electrode; a dielectric film 22, formed on the surface side of the first electrode so as to be interposed between the first electrode and the second electrode; and bottomed grooves 54 and 55, formed in the support part so as to surround the deformation area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of a capacitance change type pressure sensor having a detection body (diaphragm) formed to be thin so as to be deformed in accordance with a received pressure.

Capacitance-change pressure sensors, which are widely used as medical instruments such as blood pressure monitors and industrial instruments such as automobile tire pressure monitoring systems, are less sensitive than other methods, that is, piezoresistive pressure sensors. It has many advantages such as high sensitivity in measurement and low power consumption during measurement.
In such a capacitance change type pressure sensor, a dielectric film is interposed with a certain gap between a diaphragm on which one electrode is formed and deformed according to pressure, and a base on which the other electrode is formed. It has an opposing structure. And a pressure is detected from the change of the electrostatic capacitance between the diaphragm side and base | substrate side by deformation | transformation.

Specifically, a conventional capacitance change type pressure sensor (touch type pressure sensor) (hereinafter referred to as “pressure sensor”) is configured as shown in FIG. 6, for example (Patent Document 1, FIG. )reference).
FIG. 6 is a schematic cross-sectional view of the pressure sensor. In the figure, the pressure sensor 1 supports a diaphragm 2 having conductivity as a deformation region and a diaphragm 2 which is a thin deformation region around the periphery thereof. And a silicon structure having a supporting portion 3 to be supported.
The silicon structure is bonded to a base 6 on which an electrode 4 and a dielectric film 5 covering the electrode 4 are formed, with a gap 7 provided.

The pressure sensor 1 is configured as described above, and is energized through an extraction electrode (not shown), so that the gap 7 that is an airtight space and the deformation region 2 that is opposed to each other through the dielectric film 5 are provided. The pressure applied to the deformation region 2 can be detected based on the change in the capacitance value.
That is, when pressure is applied to the deformation region 2, the deformation region 2 is deformed so as to protrude downward. Then, the lower surface of the deformation region 2 is pressed against and contacts the dielectric film 5.

  In this structure, when the applied pressure is large, the contact area between the deformation region 2 and the dielectric film 5 becomes large, and when the applied pressure is smaller than that, the contact area becomes small. Since the capacitance increases as the contact area increases, the size of the pressure can be measured by measuring the capacitance value when the pressure is applied.

JP2002-214058

However, the conventional pressure sensor 1 has the following disadvantages.
FIG. 7 shows the pressure sensor 1 of FIG. 6 in a simplified manner. As shown in FIG. 7A, the silicon support portion 3 and the base 6 are made of, for example, heat fusion or an inorganic adhesive. Etc. are joined.
Here, the silicon constituting the support portion 3 and the glass or hard plastic constituting the base 6 have different expansion coefficients upon thermal expansion.

For example, when the environmental temperature is high, when the expansion coefficient on the base 6 side is large, the base 6 is warped as shown in FIG. 7B. For this reason, in the deformation region 2 of the silicon structure. Tensile stress is applied, the elasticity is changed, the deformation region 2 is hardened, and the stress sensitivity is deteriorated.
Further, there is a problem that tensile stress acts on the deformation region 2 of the silicon structure, the pressure resistance is reduced, and the silicon structure is easily damaged.
That is, since the deformation of the deformation region 2 when the pressure is applied becomes small, the capacitance change becomes dull, and the sensitivity to the stress change is lowered as shown in FIG.
In addition, since the stress due to the warp of the base 6 is transmitted to the deformation region 2, there is a disadvantage that the pressure resistance capability is reduced due to the stress and is easily damaged.

  The present invention has been made to solve the above problems, and has an object to provide a capacitance change type pressure sensor capable of maintaining good sensitivity even when the thermal environment changes and preventing the sensor from being easily damaged. To do.

  In the first invention, the first object is to form a base body made of a dielectric material, a deformation area formed so as to be deformed according to the pressure received, and a deformation area formed integrally with the deformation area. A detection body including a support portion having a large thickness that is surrounded by the base body and fixed to the base; a deformation surface of the deformation area of the detection body; and a facing surface where the base faces each other. A first electrode formed on the substrate side; a second electrode formed on the deformed surface side of the opposing surface at a predetermined interval from the first electrode; the first electrode and the second electrode; A dielectric film formed on the surface side of the first electrode so as to be interposed between the electrodes, and a bottomed bottom formed on the support portion so as to surround the deformation region This is achieved by a capacitive change pressure sensor with a groove.

According to the configuration of the first invention, when the deformation region of the detection body receives pressure, the deformation region is deformed so as to protrude downward, and the deformation surface comes into contact with the upper surface of the base. In accordance with the contact area, a base body as an insulator is interposed between the first electrode and the second electrode, and the opposing area of the first electrode and the second electrode is increased by that area. For this reason, the capacitance value C increases, and the pressure applied to the deformation region can be detected by detecting this capacitance value change.
In this case, the ambient temperature environment changes, and the substrate is warped due to the difference in thermal expansion coefficient due to the difference in material between the substrate and the support, and the support fixed to the substrate is pulled. However, since the bottomed groove is formed in the support portion so as to surround the deformation region, the deformation due to the warpage of the base is absorbed by the deformation of the groove portion. The stress transmitted to is extremely reduced. Accordingly, the elasticity of the deformation region hardly changes due to stress, and good sensitivity can be maintained without lowering the sensitivity to pressure.
In addition, stress due to the warp of the substrate is hardly transmitted to the deformation region, and the pressure resistance capability is not reduced due to such stress, so that it is not easily damaged.

According to a second invention, in the configuration of the first invention, the bottomed groove is provided on a front surface and / or a back surface of the support portion.
According to the configuration of the second invention, if the bottomed grooves are respectively provided on the front and back sides of the support part, one groove part is expanded due to deformation on the base side, and the distance between the other groove parts is increased. Since it can be appropriately deformed by acting so as to be narrow, the stress from the substrate side is more reliably absorbed by the groove.

According to a third invention, in the configuration of the second invention, the inner edge position and the outer edge position of each groove on the front and back sides are formed close to each other.
According to the structure of 3rd invention, the material thickness between grooves becomes small and it becomes easy to deform | transform.

According to a fourth aspect of the invention, in the configuration of the third aspect of the invention, the detection body is formed of quartz and is formed at a location where the inner edge position and the outer edge position of each groove on the front and back sides substantially coincide. And
According to the configuration of the fourth aspect of the invention, when the front and back grooves are formed by wet etching, the etching from the front side and the back side does not overlap due to the etching anisotropy of quartz, and an appropriate material thickness can be realized.

According to a fifth invention, in the configuration of any one of the first to fourth inventions, a depth dimension of the bottomed groove is more than half of a thickness dimension of the support portion.
According to the configuration of the fifth aspect of the present invention, the structure can be sufficiently deformed by receiving the stress on the substrate side, so that a structure that does not transmit stress to the deformation region can be obtained.

FIG. 1 is a schematic cross-sectional view of a capacitance change type pressure sensor according to an embodiment of the present invention.
In the figure, a capacitance change type pressure sensor (hereinafter referred to as “pressure sensor”) 30 has a structure in which a detection body 41 is joined on a plate-like base 32 having a relatively large thickness.
In the illustrated structure, the detection body 41 is exposed on the base 32. However, the detection body 41 may be housed in a hermetically sealed package or the like as a hollow housing container (not shown).
2 is a diagram showing the detection body 41, FIG. 2 (a) is a schematic plan view, FIG. 2 (b) is a schematic cross-sectional view along the line BB of FIG. 2 (a), and FIG. 3 is a schematic bottom view, FIG. 3 is a diagram showing the base 32, FIG. 3 (a) is a schematic plan view, FIG. 3 (b) is a schematic cross-sectional view taken along the line CC of FIG. 3 (a), and FIG. FIG. 6 is a bottom view of the base 32.
The configuration of the pressure sensor 30 will be described with reference to these drawings as appropriate.

The substrate 32 is made of a dielectric material, and can be formed of, for example, glass, a ceramic plate, hard plastic, silicon, or the like. When glass or silicon is used, the substrate 32 can be formed from a process of processing those wafers.
Alternatively, when the substrate 32 is formed of ceramic, for example, an aluminum oxide ceramic green sheet can be formed into the shape shown in the figure. The thickness dimension of the base 32 is, for example, about 200 μm.
The detector 41 is preferably selected from those that can be processed with a wafer material, and can be formed of, for example, silicon or a quartz material. In the present embodiment, a case where quartz is used will be particularly described.

That is, the detection body 41 is made of, for example, quartz, and is obtained by processing a square or rectangular quartz plate as a whole, as can be understood from FIG.
Specifically, the detection body 41 uses a quartz wafer made of an AT-cut quartz plate having a thickness shear vibration mode or a thickness longitudinal vibration mode, and a substantially central portion of the quartz plate is, for example, as shown in FIG. It is formed into a rectangular thin plate. That is, for example, the center region is half-etched into a rectangle from the front surface and the back surface of the crystal plate, thereby forming the deformation region 42 shown in FIG. A lower surface of the deformation region 42 is a deformation surface 49. The deformation area 42 is an area that is deformed by receiving pressure as described later.

In this case, for example, wet etching using a hydrofluoric acid solution can be used as the etching. Moreover, the etching amount (depth) of the front surface can be set to, for example, about 84 μm, and the etching amount (depth) of the back surface can be set to, for example, about 6 μm.
Simultaneously with the formation of the deformation region 42, a support portion 43 is formed so as to surround the deformation region 42. The support portion 43 is a region formed by leaving the quartz material in a state where the material thickness is large without being etched in the etching step. The support portion 43 is used for bonding to the base body 32.

At the same time, a through hole 45 is formed at a location shifted laterally from the deformation region 42. The through holes 45 can be formed by etching from the front and the back simultaneously with half-etching of the deformation region 42 and continuing the etching only at the positions of the through holes 45 after the deformation region is completed.
And the detection body 41 is joined to the base | substrate 32, for example in atmospheric pressure so that the airtight space shown with code | symbol S1 in FIG. 1 may be formed. This bonding may be performed while the material of the base body 32 and the material of the detection body 41 are in a wafer state. The thickness of the detection body 41 is, for example, about 100 μm.

A bottomed groove (hereinafter referred to as a “groove”) for absorbing stress transmitted to the detection body 41 due to warping of the base body 32 is formed in the support portion 43 positioned around the deformation region 42. Has been. The groove is formed so as to surround the deformation region.
In this embodiment, two grooves are provided. The first groove 54 provided from the front surface side of the detection body 41 in FIG. 1 and the second groove provided from the back surface of the detection body 41 inside the first groove 54. For example, these grooves have a groove width that is reduced along the thickness direction.
Further, the first groove 54 and the second groove 55 are formed using the above-described etching process. The first groove 54 and the second groove 55 are preferably close to each other as long as they are not too close to each other.
In this embodiment, the inner edge position 54a of the first groove 54 and the outer edge position 55b of the second groove 55 are formed so as to coincide with each other on the position P in FIG.
Since the etching speed in a predetermined direction is delayed due to the etching anisotropy of the quartz crystal positioned in this way during the manufacturing, the first groove 54 and the second groove 55 do not communicate with each other and are appropriately approached. Formed.
The function of these grooves will be described in detail later.

In this embodiment, for example, as shown in FIG. 3, the first electrode 44 is formed on the upper surface of the base 32 that is the surface facing the deformation surface 49 of the detection body 41. As shown in FIG. 2, the second electrode 46 is formed on the deformation surface 49.
As shown in FIGS. 1 and 2, the first electrode 44 is formed on a base layer 48 provided on the upper surface of the substrate 32. The film thickness of the first electrode 44 is, for example, about 1500 angstroms. The film thickness of the second electrode 46 is, for example, about 2000 angstroms.
That is, for example, when the base 32 is made of quartz and the first electrode 44 is made of, for example, gold (Au), the base layer 48 is preferably formed on the surface of the base 32, thereby It is possible to improve the adhesion or to form a gold film by plating.
Further, when the first electrode 44 is aluminum (Al) or an alloy thereof, the first electrode 44 can be formed directly on the surface of the base 32 by sputtering, vapor deposition, or the like, so that the base layer 48 is unnecessary. It is.

The configuration of the electrode will be further described.
As shown in FIG. 2C, a conductive portion 37 is formed at the edge along the outer periphery of the back surface 51 of the detection body 41. The conductive portion 37 serves to join the base body 32 and the detection body 41.
That is, the detection body 41 and the base body 32 are joined by anodic bonding between the metal of the conductive portion 37 and the glass of the base body 32.
Further, as shown in FIG. 1, the conductive portion 37 is connected to a lead electrode 44 a (underlying electrode) that extends integrally from the first electrode 44 that is a fixed electrode, and is electrically connected to the first electrode 44. ing. Although not shown in FIG. 2A, the conductive portion 37 is connected to a bonding wire W2 that is led to the surface 52 side of the detection body 41 and supplies a driving voltage.

As shown in FIGS. 1 and 2C, the through-hole 45 is filled with a conductive material to form a conductive through hole, and the extraction electrode 46a extends from the second electrode 46 that is a movable electrode. Further, the conductive material is connected to an electrode pad 46b formed around the hole on the surface side of the through hole 45 as shown in FIG. A bonding wire W1 for supplying a driving voltage is connected to the electrode pad 46b.
Further, as shown in FIGS. 2A and 2C, electrode pads 48 a and 46 b are formed on opposing edges of the detection body 41, and these electrode pads 48 a and 46 b are formed on the detection body 41. It can be used as a mounting terminal that can detect a change in capacitance due to the deformation.

The pressure sensor 30 of the present embodiment is configured as described above, and can operate as follows.
For example, the pressure sensor 30 is disposed in the atmosphere. In this state, since the atmospheric pressure in the airtight space S1 is atmospheric pressure, it is balanced with the external atmospheric pressure, and the deformation region 42 of the detection body 41 is not deformed.
Here, when there is a pressure change, when the deformation region 42 receives the pressure change, the capacitance value between the first electrode 44 and the second electrode 46 changes, and the pressure changes based on the capacitance change. Can be detected.

That is, when the deformation region 42 is deformed so as to protrude downward according to the pressure received by the deformation region 42, and the deformation surface 49 comes into contact with the upper surface of the base 32, the first electrode 44 according to the contact area. A base 32 as an insulator is interposed between the first electrode 44 and the second electrode 46, and the opposing area of the first electrode 44 and the second electrode 46 is increased by the area. When the opposing area between the first electrode 44 and the second electrode 46 increases, the capacitance value C increases.
By detecting this change in capacitance value, the pressure applied to the deformation region 42 can be detected.

Furthermore, the operation principle of this embodiment will be described with reference to FIG.
FIG. 4A is a schematic diagram showing the state of the base 32 of the acceleration sensor and the base 43 of the detection body 41 bonded thereto.
From this state, the ambient temperature environment changes, and as shown in FIG. 4B, the peripheral portion of the base 32 is slightly changed due to the difference in thermal expansion coefficient due to the difference in the materials of the base 32 and the support portion 43. It will be in a state of warping upward.
For this reason, the support part 43 fixed to the base body 32 is pulled. That is, the stress due to deformation is transmitted to the support portion 43.
However, since the first groove 54 and the second groove 55 are formed in the support portion 43 so as to surround the deformation region 42, as shown in FIG. 4C, the groove is deformed. The stress due to the warp of the substrate is absorbed.

That is, in FIG. 4C, the second groove 55 opened on the back surface in response to deformation on the base 32 side functions so that the groove width is expanded, and the second groove 55 which is the other groove portion opened on the front surface. Since it can be appropriately deformed by acting so that the groove width becomes small, that is, the interval becomes narrow, the stress from the substrate side is more reliably absorbed by these groove portions.
For this reason, even if a temperature environment changes, the stress transmitted to the deformation | transformation area | region 42 of the detection body 41 is reduced extremely. Therefore, the elasticity of the deformation region 42 hardly changes due to stress, and good sensitivity can be maintained without lowering the sensitivity to pressure.
Further, since the stress due to the warp of the base body 32 is hardly transmitted to the deformation region 42 and the pressure resistance capability is not reduced due to such stress, there is a conventional problem that the detection body 41 is easily damaged. Absent.
FIG. 5 is a diagram showing a pressure-capacitance value characteristic of the pressure sensor 30 of the present embodiment with respect to pressure.
As can be seen in contrast to FIG. 8 described above, the pressure-stress sensitivity is significantly improved.

The present invention is not limited to the above-described embodiment. The configurations of the embodiment and the modified examples can be combined or omitted as appropriate, and can be combined with other configurations not shown.
In the above-described embodiment, the detection body 41 is described as being rectangular, but it may be square or circular. Moreover, although the deformation | transformation surface 49 is demonstrated as a rectangular thing, this is good also as a round shape or a square.
The substrate constituting the base 32 is described as a single layer, but a plurality of layers may be provided.

The schematic sectional drawing of the embodiment of the capacity change type pressure sensor of the present invention. The figure of the detection body of the pressure sensor of FIG. The figure of the base | substrate of the pressure sensor of FIG. Explanatory drawing for demonstrating the effect | action principle of the pressure sensor of FIG. The figure which shows the pressure-capacitance value characteristic of the pressure sensor of FIG. The schematic sectional drawing which shows the conventional capacity | capacitance change type pressure sensor. Explanatory drawing which shows the bad influence by the environmental temperature change of the pressure sensor of FIG. The figure which shows the pressure-capacitance value characteristic of the pressure sensor of FIG.

Explanation of symbols

  22 ... Dielectric film, 30 ... (Capacitance change type) pressure sensor, 32 ... Base, 41 ... Detector, 42 ... Deformation region, 44 ... First electrode, 46 ... Second electrode, 54 ... First groove, 55 ... Second groove

Claims (5)

A substrate made of a dielectric material;
A deformation region formed by reducing the thickness so as to be deformed according to the pressure received, and a thick support portion which is integrally formed with the deformation region and surrounds the periphery thereof and is fixed to the base body. A detection object;
A first electrode formed on the base side of a facing surface where the deformation surface of the deformation area of the detection body and the base face each other;
A second electrode formed on the deformation surface side of the facing surface at a predetermined interval from the first electrode;
A dielectric film formed on the surface side of the first electrode so as to be interposed between the first electrode and the second electrode,
A capacitance change pressure sensor comprising a bottomed groove formed in the support portion so as to surround the deformation region.   The capacitance change pressure sensor according to claim 1, wherein the bottomed groove is provided on a front surface and / or a back surface of the support portion.   The capacity change pressure sensor according to claim 2, wherein an inner edge position and an outer edge position of each groove on the front and back sides are formed close to each other.   The capacitance change pressure sensor according to claim 3, wherein the detection body is made of quartz and is formed at a location where an inner edge position and an outer edge position of each groove on the front and back sides substantially coincide with each other. 5. The capacitance change type pressure sensor according to claim 1, wherein a depth dimension of the bottomed groove is more than half of a thickness dimension of the support portion. 6.

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