JP2007071770A - Capacitance type pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance type pressure sensor which prevents any leakage from occurring in an airtight cavity and also prevents any sensing body and substrate from being broken. <P>SOLUTION: The capacitance type pressure sensor comprises: the substrate 32 made of a dielectric material; the sensing body 41 which is fixed so as to be stacked on the substrate and whose thickness is made thin so as to deform in response to a pressure applied thereto; a fist electrode 44 having a radial electrode finger 44 which is formed on any one plane of opposite planes defined by the substrate and the deforming plane 49 of the sensing body being opposite to each other; and a second electrode 36 which is formed on the other plane and positioned at a prescribed spacing from the first electrode 44 so as not to overlap each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

Capacitive pressure sensors, which are widely used as medical instruments such as blood pressure monitors and industrial instruments such as tire pressure monitoring systems for automobiles, are less sensitive than other methods, that is, piezoresistive pressure sensors. The measurement also has many advantages such as high sensitivity and low power consumption during measurement.
In such a capacitive pressure sensor, a dielectric film is interposed with a certain gap between a diaphragm on which one electrode deformed according to pressure is formed and a base on which the other electrode is formed. It has the structure which was made to oppose. 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 capacitive 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 is formed thereon. The detection body 10 is joined on it.
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. 5, when the pressure P 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.

When the pressure P is large, the contact area M1 is large as shown in FIG. 6A, and when the pressure P is smaller than this, the contact area M2 is small as shown in FIG. 6B. Since the capacitance increases as the contact area increases, the magnitude of the pressure P can be measured by measuring the capacitance value when the pressure P is applied.
In addition, almost the same structure is described in other literatures, and as shown in FIG. 7, it is clarified that the capacitance value corresponds to the magnitude of the pressure (Patent Document 2, FIG. 1). FIG. 4).

WO 2005/003711 JP2002-214058

However, the conventional pressure sensor 1 has the following disadvantages.
That is, as a first problem, the dielectric film 8 is formed to be thick to some extent in order to prevent a short circuit between the diaphragm portion 12 side and the lower electrode 7, and usually has a thickness of 0.1 μm to several μm.
Then, the base 4 is warped by the film stress of the dielectric film 8, and it is difficult to uniformly bond the base 4 and the detection body 10, and a leak in the airtight space S may occur.

Further, by forming the base 4 from a glass wafer or the like and the diaphragm portion 12 from a silicon wafer or the like, it is possible to manufacture a large number of pressure sensors 1 at a time.
In this case, it is conceivable that the wafers are bonded to each other after the respective outer shapes are formed. However, when the dielectric film 8 is formed on the wafer on the base 4 side, if the wafer is warped, the warp is large. In the case where a large number of wafers are damaged at a time due to damage to the wafer, or even when individual product units can be processed, defective products are generated due to the leakage of the airtight space S described above. Is significantly reduced.

  Further, as a second problem, as shown in FIG. 7, in the region G where the correlation between the capacitance and the pressure is linearly changed, the pressure sensor is excellent in sensitivity. Although it can be used, particularly in the high pressure region, as indicated by the range of Z, there is a disadvantage that the capacitance change with respect to the pressure change becomes small and the sensitivity becomes poor.

The present invention has been made to solve the above-described problems. It is a first object of the present invention to provide a capacitance-type pressure sensor that can prevent leakage in an airtight space and destruction of a detection body and a substrate. 1 purpose.
Furthermore, preferably, in addition to the first object, a second object is to provide a capacitive pressure sensor having excellent sensitivity in a high pressure region.

  In the first invention, the first object is to form a base made of a dielectric material and a thickness that is fixed so as to overlap with the base and deform according to the pressure received. A first electrode having a radial electrode finger formed on any one of a detection body, a deformation surface of the detection body, and a facing surface of the base body facing each other; and formed on the other surface; This is achieved by a capacitive pressure sensor comprising a second electrode formed at a position that does not overlap the first electrode at a predetermined interval.

According to the configuration of the first invention, there is a first electrode having radial electrode fingers on one of the opposing surfaces of the substrate and the detection body, and a second electrode is formed on the other surface. Has been. These electrodes are spaced apart from each other by a predetermined distance.
In other words, in the conventional configuration, the electrodes are in an overlapping position, but a dielectric film is formed between the electrodes, and a predetermined capacity is obtained by avoiding a short circuit. is there.
However, in the present invention, since this dielectric film, which has been used in the past, is not used, the substrate and the detection body are deformed by the film stress, which has been regarded as a problem in the past, and a leak in the airtight space is generated, or the substrate and the detection are performed. It is effectively prevented that the body is destroyed.

Here, even if the detection body is deformed by receiving a predetermined pressure and the opposing surfaces come into contact with each other, the first electrode and the second electrode are in positions that do not overlap, so the dielectric film is used. There is no short circuit even if it is not. In this contact state, the base is always interposed between the first electrode and the second electrode.
That is, in the present invention, the role of the dielectric film between the conventional electrodes is played by the substrate formed of the dielectric material. In addition, when the contact area that contacts the base when the detection body is deformed according to the magnitude of the pressure increases due to an increase in the pressure, the amount of contact of the radial first electrode with the base increases, so the capacity is increased. growing. As described above, the pressure value can be detected in relation to the change in capacitance without using a dielectric film.

A second invention is characterized in that, in the configuration of the first invention, the radial center position of the first electrode is arranged at a position where the thickness of the detection body is thinned.
According to the configuration of the second aspect of the invention, the central portion of the first electrode is arranged corresponding to the most easily deformable portion of the detection body, so that the correlation between the change in pressure and the capacitance is further improved. Become linear.

A third invention is characterized in that, in the configuration of either the first or second invention, the electrode fingers of the first electrode are formed widely in the vicinity of the radial outer edge.
According to the configuration of the third invention, the second object is achieved. That is, when the detection body is deformed by receiving pressure, the contact area of the electrode with respect to the deformation of the detection body is increased by increasing the width of the electrode finger as it goes to the peripheral region where deformation is difficult. The sensitivity in the high pressure region is improved.

According to a fourth invention, in the configuration of any one of the first to third inventions, a dielectric film is less than 1000 angstroms (0.1 μm) on either or both of the first electrode and the second electrode. It is characterized by forming with the film thickness.
According to the configuration of the fourth invention, a short circuit can be prevented more reliably by forming the dielectric film on the electrode. In this case, by setting the thickness of the dielectric film 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.

A fifth invention is characterized in that, in the configuration of the fourth invention, the dielectric film is formed only on one of the first electrode and the second electrode formed on the substrate surface. To do.
According to the configuration of the fifth aspect of the invention, if the dielectric film is formed only on the substrate side while avoiding the deformation region of the detection body that is formed to be thin, the adverse effect due to the tensile stress of the dielectric film. Is more reliably suppressed.

FIG. 1 is a schematic plan view of a capacitive pressure sensor according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view taken along line BB in FIG.
In these drawings, a capacitive pressure sensor (hereinafter referred to as “pressure sensor”) 30 accommodates a detection body 41 in a package 31 as a hollow housing container as shown in FIG. This is a sealed configuration.

The package 31 is formed in a rectangular box shape, for example, as shown in FIG. Specifically, the package 31 includes a base 32 serving as a first substrate and a frame-shaped second substrate 33 disposed on the base 32.
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 base 32 is formed of ceramic, the base 32 as the first substrate and the second substrate 33, for example, an aluminum oxide-based ceramic green sheet are respectively formed, and each substrate is illustrated. After forming, it can be formed by stacking and sintering.

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.
By combining the detection body 41 with the base body 32, the detection body 41 can be used as a pressure detection means (sensor) as a single unit without necessarily being housed in the package 31 or the like.

In this embodiment, the detection body 41 is made of quartz and is processed from a square or rectangular quartz plate as a whole as understood from FIG. Specifically, an AT-cut quartz plate having a thickness shear vibration mode or a thickness longitudinal vibration mode is used, and the central portion of the quartz plate is formed as thin as possible into a thin plate. That is, for example, the center region is half-etched circularly from the front surface and the back surface of the quartz plate to form a circular 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.
And the detection body 41 is joined to the base | substrate 32, for example in atmospheric pressure so that the airtight space shown by code | symbol S1 in FIG. 2 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.

In this embodiment, for example, as shown in FIG. 2, the first electrode 44 is formed on the upper surface of the base body 32, which is the facing surface of the deformation surface 49 of the detection body 41 facing the upper surface of the base body 32. Is formed. A second electrode 36 is formed on the deformed surface 49.
In FIG. 1, the first electrode 44 is represented by a dotted line, and the second electrode 36 is represented by a solid line. The first electrode 44 may be formed on the detection body 41 side, and the second electrode 36 may be formed on the base body 32 side.

  As shown in FIGS. 1 and 2, the first electrode 44 is a radial electrode having a center that substantially coincides with the center of the substantially circular deformation surface 49. The spoke width of each of the radial first electrodes 44, that is, the outer edge of the electrode finger 48 or the vicinity of the outer end 48 a is enlarged in electrode width. Preferably, the electrode fingers 48 are preferably configured such that the electrode width gradually increases toward the outer edge.

Further, it is preferable that the center of the first electrode 44 is determined by selecting the position where the material thickness is the thinnest when forming the deformation region 42 of the detection body 41 and determining the position. Further, when the deformation region 42 of the detection body 41 is formed by wet etching, a portion where the material thickness is the thinnest is selected based on the etching anisotropy, not the circular central portion, and the first region is selected. More preferably, the center of the electrode 44 is used.
As shown in FIG. 1, the first electrode 44 is routed to one side of the package 31 through a ring portion 44 a that is routed in a ring shape outside the radial portion, thereby forming a lead electrode 45. Has been. The extraction electrode 45 wraps around the outer edge of the base 32, is drawn to the bottom surface, and is electrically connected to the mounting terminal 46. The ring portion 44a is a sealing electrode for sealing the sealed space S1 by anodic bonding.

As shown in FIG. 1, the second electrode is positioned so as not to overlap each other as shown in FIG. 1, that is, at a position facing each electrode or at a projection position as shown in FIG. 36 is formed. The second electrode 36 is indicated by a solid line in FIG. In other words, the first electrode 44 and the second electrode 36 are assumed to be such that the deformation surface 49 of the deformation region 42 comes into contact with the upper surface of the base 32 due to the deformation of the deformation region 42 of the detection body 41 and the electrodes approach each other. Also, a predetermined interval which is a slight interval as shown by a solid line and a dotted line in the figure is separated.
As shown in FIG. 1, the second electrode 36 has a plurality of triangular or fan-shaped portions of the same size divided by forming gaps 36 c so as to avoid the spoke-shaped electrode fingers 48 of the first electrode 44. And a portion of the bus bar 36a that integrally connects the outsides of these portions. In the portion indicated by the reference numeral 36b, electrode formation is omitted, and unnecessary electrodes are prevented from being formed as much as possible near the outer edge of the deformation region 42 where no deformation occurs.

The second electrode 36 is routed from the surface of the substrate 32 to the front side of the detection body 41 by a conductive through hole (not shown) and connected to the terminal 37 on the upper surface of the detection body 41.
On the other hand, an electrode part (leading electrode) 38 is formed on the upper surface of the base 32 of the package 31, and the electrode part 38 wraps around the outer edge of the base 32, is drawn to the bottom, and is electrically connected to the mounting terminal 39. ing.
The terminal 37 on the upper surface of the detection body 41 and the electrode portion 38 of the package 31 are electrically connected by wire bonding with a wire 47.
The lid 34 is made of, for example, glass, ceramics, or metal, and seals the package 31 and has a vent hole 51 formed as a through hole near the center.

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, the air enters the package 31 through the vent hole 51 of the lid 34. Since the air pressure in the airtight space S1 is atmospheric pressure, it is balanced with the air pressure in the package 31, 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 36 changes, and the pressure is changed based on the capacitance change. Can be detected.

  That is, similar to the principle described with reference to FIG. 6, the deformation region 42 is deformed so as to protrude downward according to the pressure received by the deformation region 42, and when the deformation surface 49 comes into contact with the upper surface of the base body 32, Depending on the area, the base 32 as an insulator is interposed between the first electrode 44 and the second electrode 36, and the opposing area of the first electrode 44 and the second electrode 36 is increased by that area. To do. Then, as the facing area between the first electrode 44 and the second electrode 36 increases, the capacitance value C increases, so the correlation shown in FIG. 3 is recognized.

  That is, the basic relationship between the capacitance on the vertical axis and the pressure on the horizontal axis is the same as that of a conventional pressure sensor, and pressure can be detected based on the same principle. In the above-described embodiment, since the dielectric film that has been used conventionally is not used, the base and the diaphragm are deformed by the film stress that has been considered as a problem in the past, and the leak of the airtight space S1 occurs. And the destruction of the diaphragm is effectively prevented.

Further, as described above, the electrode finger 48 of the first electrode 44 has the electrode width of the outer edge or the vicinity of the outer end portion 48a enlarged.
For this reason, in the deformation region 42 of the detection body 41, the width of the electrode finger 48 of the first electrode 44 is increased toward the peripheral region that is difficult to be deformed when being deformed by receiving pressure. become. As a result, the contact area of the electrode increases even if the deformation amount is small, and as shown in FIG. 3, the sensitivity in the high pressure region can be improved and the pressure can be detected even in a part of the conventional saturation region. it can.

Further, a dielectric film may be formed with a film thickness of less than 1000 angstroms (0.1 μm) on both or either of the first electrode 44 and the second electrode 36 (not shown). .
Thereby, the short circuit of the 1st electrode 44 and the 2nd electrode 36 can be prevented more reliably. In this case, by setting the thickness of the dielectric film 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.
Here, the dielectric film can be formed of SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ or the like.

In addition, preferably, the dielectric film is formed only on the electrode formed on the surface of the substrate 32 of the first electrode 44 and the second electrode 36.
Thus, if the dielectric film is formed only on the base 32 side while avoiding the deformation region 42 of the detection body 41 that is formed to be thin, the adverse effect due to the tensile stress of the dielectric film is more reliably ensured. It is suppressed.

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 having a square shape, but may be rectangular or circular. Moreover, although the deformation | transformation surface 49 is demonstrated as a circular thing, this is good also as a rectangle or a square.
Although the number of the radial electrode fingers of the first electrode 44 is eight, the number may be less than that or more than eight.
The substrate constituting the base 32 is described as a single layer, but a plurality of layers may be provided.

1 is a schematic plan view of an embodiment of a capacitive pressure sensor of the present invention. BB schematic sectional drawing of FIG. The figure which shows the electrostatic capacitance of the pressure sensor of embodiment, and the relationship of detected pressure. The figure which shows the conventional electrostatic capacitance type pressure sensor. The figure explaining operation | movement of the pressure sensor of FIG. The figure explaining operation | movement of the pressure sensor of FIG. The figure which shows the electrostatic capacitance of the conventional pressure sensor, and the relationship of detected pressure.

Explanation of symbols

  30 ... (electrostatic capacity type) pressure sensor, 31 ... package, 32 ... base, 41 ... detection body, 42 ... deformation region, 44 ... first electrode, 36 ... ..Second electrode

Claims (5)

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 having radial electrode fingers formed on any one of the opposing surfaces of the deformed surface of the detection body and the substrate facing each other;
A capacitance type pressure sensor comprising: a second electrode formed on the other surface and formed at a position that does not overlap the first electrode with a predetermined interval.   2. The capacitive pressure sensor according to claim 1, wherein a radial center position of the first electrode is disposed at a position where the thickness of the detection body is thinnest.   3. The capacitive pressure sensor according to claim 1, wherein the electrode fingers of the first electrode are formed widely in the vicinity of the radial outer edge.   4. The dielectric film according to claim 1, wherein a dielectric film is formed with a film thickness of less than 1000 angstroms (0.1 .mu.m) on both or either of the first electrode and the second electrode. Capacitance type pressure sensor described in 1.   5. The capacitance type pressure sensor according to claim 4, wherein the dielectric film is formed only on an electrode formed on the surface of the base body among the first electrode and the second electrode. 6.

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