JP2007278716A - Variable capacitance pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable capacitance pressure sensor capable of stably operating by preventing peeling a dielectric film to cause leakage of electrodes. <P>SOLUTION: The pressure sensor comprises a substrate 32 made of dielectric material, a detecting body 41 that is overlaid on and fixed to the substrate and has small thickness so that the detecting body deforms in response to the received pressure, a first electrode 44 formed on the substrate side of the facing surface where a deforming surface 42 of the detecting body 41 faces the substrate, a second electrode 46 formed on the deforming surface side of the facing surface at a predetermined distance from the first electrode, a dielectric film 22 formed on the front surface side of the first electrode so as to be interposed between the first electrode and second electrode, and an adhesive auxiliary layer 21 between the first electrode and the dielectric film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an improvement of a capacity change type pressure sensor having a detection body (diaphragm) formed to be thin so as to be deformed according to 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 pressure sensor (touch pressure sensor) (hereinafter referred to as “pressure sensor”) is configured as shown in FIG. 4 (see Patent Document 1 and FIG. 1).
4A is a schematic cross-sectional view of the pressure sensor, and FIG. 4B is a cross-sectional view taken along line AA in FIG. 4A.
The illustrated pressure sensor is accommodated in a package 2 that is a container.
The package 2 has a box-like shape including a base body 4 and a frame-shaped side wall portion 5 provided integrally therewith. The detection body 10 is accommodated inside and sealed by a lid body 6. Here, the substrate 4 can be made of glass, ceramic plate, hard plastic, silicon wafer or the like.

A lower electrode 7 is formed on the surface of the substrate 4, and a dielectric film 8 as an insulating film is formed thereon.
Is formed, and the detection body 10 is bonded thereon.
The detection body 10 is a plate body made of silicon, crystal, or the like, and has a thin diaphragm portion 12 in the center and a frame portion 11 with a thick plate so as to surround the periphery. An upper electrode 13 is formed on the lower surface of the diaphragm portion 12, and a gap or an airtight space S is formed between the upper electrode 13 and the dielectric film 8.
As shown in FIG. 4B, the upper electrode 13 and the lower electrode 7 are provided with extraction electrodes 13 a and 7 a so as to be routed outside the package 2.

The pressure sensor 1 is configured as described above. When the pressure sensor 1 is energized through the extraction electrodes 13a and 7a, the upper electrode 13 and the lower electrode 7 that are opposed to each other through the airtight space S and the dielectric film 8 are provided. The pressure applied to the diaphragm unit 12 can be detected based on the change in the capacitance value between the two.
That is, as shown in FIG. 4, when pressure is applied to the diaphragm portion 12, the diaphragm portion 12 is deformed so as to protrude downward. Then, the upper electrode 13 formed on the lower surface of the diaphragm portion 12 is pressed against and contacts the dielectric film 8.

In this structure, when the applied pressure is large, the contact area between the upper electrode 13 and the dielectric film 8 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 magnitude of the pressure can be measured by measuring the capacitance value when the pressure is applied.

WO 2005/003711

However, the conventional pressure sensor 1 has the following disadvantages.
In FIG. 4A, for example, a dielectric film 8 as an insulating film is formed of SiO ₂ on the surface side of the lower electrode 7 formed of gold Au or the like, but under high temperature conditions or high humidity conditions. The very thin dielectric film 8 may be peeled off from the lower electrode 7 in some cases.
For this reason, if pressure is applied to the diaphragm portion 12 and the diaphragm portion 12 is deformed so as to protrude downward, the peeled portion of the dielectric film 8 of the lower electrode 7 may come into contact with the upper electrode 13 and may leak. There is a problem that it does not operate as a sensor.

The present invention has been made to solve the above problems, and provides a capacitance change type pressure sensor that can stably operate by preventing the peeling of a dielectric film that causes leakage between electrodes. Objective.

The first object is that in the first invention, the base is made of a dielectric material, and is fixed to be overlapped with the base, and the thickness is reduced so as to be deformed according to the pressure received. A detection object;
A first surface formed on the base side of a facing surface where the deformation surface of the detection body and the base face each other.
The second electrode formed on the deformed surface side of the opposing surface at a predetermined distance from the first electrode, and the first electrode and the second electrode. And a dielectric film formed on the surface side of the first electrode, and a capacitance change type pressure sensor in which an adhesion auxiliary layer is provided between the first electrode and the dielectric film. Achieved.

According to the configuration of the first invention, an adhesion auxiliary layer is formed between the first electrode formed on the surface of the substrate and the dielectric film, that is, on the surface of the first electrode. . As a result, the adhesive strength between the first electrode and the dielectric film is enhanced. For this reason, for example, due to environmental changes such as high temperature and high humidity, external impact, etc. The dielectric film covering the electrodes is not easily peeled off.
Accordingly, it is possible to provide a capacitance change type pressure sensor that can prevent the peeling of the dielectric film that causes leakage between the electrodes and can operate stably.

According to a second invention, in the configuration of the first invention, the adhesion auxiliary layer is formed of a metal layer of chromium (Cr), nickel (Ni), titanium (Ti) or an alloy layer of each metal. It is characterized by being.
According to the configuration of the second invention, the metal layer of chromium (Cr), nickel (Ni), or titanium (Ti) or the alloy of each metal adheres to the substrate made of a dielectric material such as quartz. It is easy to do, and a dielectric film such as SiO ₂ can be firmly adhered.

A third invention is characterized in that, in the structure of either the first or second invention, the adhesion auxiliary layer is formed larger than the first electrode.
According to the structure of 3rd invention, since the said adhesion auxiliary layer can cover the said 1st electrode completely, peeling, damage, etc. of this 1st electrode can be prevented reliably.

A fourth invention is characterized in that, in the structure of any one of the first to third inventions, an underlayer is formed between the base and the first electrode.
According to the configuration of the fourth invention, when the first electrode is formed of “gold” having an extremely low electric resistance and high efficiency, the first electrode is formed by forming the base layer. It is preferable because the metal layer to be formed can be easily attached, and in some cases, it can be formed by plating, and peeling can be prevented.

A fifth invention is characterized in that, in the structure of the fourth invention, the first electrode is made of aluminum (Al) or an alloy thereof, so that the base layer is omitted.
According to the configuration of the fifth aspect of the invention, when forming an electrode made of aluminum, it can be formed, for example, by vapor deposition or sputtering on a base made of quartz without using the base layer.

A sixth invention is characterized in that, in the configuration of any one of the first to fifth inventions, the thickness of the adhesion auxiliary layer is several tens to 500 angstroms (Å).
According to the structure of 6th invention, when the said adhesion auxiliary | assistant layer is less than several tens of angstroms, there exists a bad effect that adhesive force falls. In addition, when the thickness exceeds 500 angstroms, the adhesion assisting layer functions as an electrode, so that the electrode area changes.

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.
You may make it accommodate airtightly in the package as a non-hollow accommodation container.
FIG. 2 is a view showing the detection body 41, FIG. 2 (a) is a schematic plan view, and FIG. 2 (b) is FIG.
FIG. 2C is a schematic bottom view, FIG. 3 is a diagram showing the base 32, FIG. 3A is a schematic plan view, and FIG. 3B is a diagram. Fig. 3 (c) is a schematic sectional view taken along line CC of Fig. 3 (a).
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 base 32 is made of a dielectric material, for example, glass, ceramic plate, hard plastic,
It can be formed of silicon or the like, and when glass or silicon is used, it can be made 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 this embodiment, 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 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 rectangular as shown in FIG. It is formed into a 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.

At the same time, a through hole 45 is formed on the side of the deformation area 42 in the vicinity thereof. 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. 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.
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.

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 a base layer 48 provided on the upper surface of the substrate 32.
Is formed on top. 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 plays a role of joining the base body 32 and the detection body 41, and at the same time, as shown in FIG. 1, is connected to a lead electrode 44a extending integrally from the first electrode 44 which is a fixed electrode. The electrode 44 is electrically connected. 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 2 (c), the through hole 45 is filled with a conductive material, etc.
A lead-out electrode 4 which is a conductive through hole and extends from the second electrode 46 which 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.

Further, as can be understood with reference to FIGS. 1 and 3, an adhesion assisting layer 21 is formed between the first electrode 44 and the dielectric film 22 formed on the surface side thereof. .
The dielectric film 22 is an insulating film provided to prevent a short circuit between the first electrode 44 and the second electrode 46, and is formed of SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ or the like. I'm going.
Preferably, in this case, the film thickness of the dielectric film is 5000 angstroms or less, and by setting the film thickness to less than 1000 angstroms, the tensile stress of the film is limited, and adverse effects due to the tensile stress of the film are suppressed.

The adhesion auxiliary layer 21 is made of, for example, chromium (Cr), nickel (Ni), titanium (Ti
), Or an alloy layer of each metal. These metals can be formed on the surface of the substrate 32 by a technique such as vapor deposition or sputtering. These metal layers of chromium (Cr), nickel (Ni), titanium (Ti) or alloys of the respective metals are easily attached to a dielectric material such as a crystal base, such as SiO ₂ . The dielectric film 22 can be firmly bonded.

Here, as shown in FIGS. 1 and 3B, the adhesion auxiliary layer 21 is formed larger than the first electrode 44. For this reason, since the auxiliary adhesion layer 21 can completely cover the first electrode 44, peeling and damage of the first electrode 44 can be reliably prevented.
In particular, as shown in FIG. 3A, the width dimension DW is 50 to 100 from the outer edge of the first electrode 44.
It is preferable to form the adhesion assisting layer 21 larger than the first electrode 44 so as to be about μm. Thereby, the protective effect of the adhesion assistance layer 21 can be exhibited reliably.

Furthermore, it is preferable that the thickness of the adhesion auxiliary layer 21 be several tens to 200 angstroms (Å).
That is, when the adhesion auxiliary layer is less than several tens of angstroms, there is a problem that the adhesive force is reduced.
Moreover, since the adhesion auxiliary layer functions as an electrode when exceeding 500 angstroms,
There is an adverse effect that the electrode area changes. In this embodiment, it is about 100 angstroms.

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 4 depends on the contact area.
The base 32 as an insulator is interposed between the fourth electrode 46 and the second electrode 46, and the opposing area of the first electrode 44 and the second electrode 46 is increased by that 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.

In the present embodiment, the first electrode 44 and the dielectric film 22 formed on the surface of the substrate 32.
In other words, the adhesion auxiliary layer 21 is formed on the surface of the first electrode 44. As a result, the adhesive strength between the first electrode 44 and the dielectric film 22 is increased. For this reason, for example, due to environmental changes such as high temperature and high humidity, external impact, etc. Electrode 44
The dielectric film 22 covering the film is not easily peeled off.
For this reason, it is possible to provide the capacitance change type pressure sensor 30 that can prevent the peeling of the dielectric film 22 that causes leakage between the electrodes and can operate stably.

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 object of the pressure sensor of FIG. The figure of the base | substrate of the pressure sensor of FIG. The schematic sectional drawing which shows the conventional capacity | capacitance change type pressure sensor.

Explanation of symbols

21 ... Adhesion auxiliary layer, 22 ... Dielectric film, 30 ... (Capacitance change type) pressure sensor,
32 ... Substrate, 41 ... Detector, 42 ... Deformation region, 44 ... First electrode, 46
... Second electrode

Claims (6)

A substrate made of a dielectric material;
A detection body that is fixed to the substrate in an overlapping manner, and is formed with a reduced thickness so as to be deformed according to the pressure received;
A first electrode formed on the substrate side of a facing surface where the deformation surface of the detection body and the substrate 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, wherein an adhesion auxiliary layer is provided between the first electrode and the dielectric film. 2. The capacitance change according to claim 1, wherein the adhesion auxiliary layer is formed of a metal layer of chromium (Cr), nickel (Ni), or titanium (Ti) or an alloy layer of each metal. Mold pressure sensor. The capacitance change pressure sensor according to claim 1, wherein the adhesion auxiliary layer is formed larger than the first electrode. The capacitance change pressure sensor according to claim 1, wherein a base layer is formed between the base and the first electrode. The capacitance change pressure sensor according to claim 4, wherein the first layer is made of aluminum (Al) or an alloy thereof to omit the base layer. 6. The capacitance change pressure sensor according to claim 1, wherein a thickness of the adhesion auxiliary layer is set to several tens to 500 angstroms (Å).

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