Pressure sensor

A pressure sensor according to the present invention includes a diaphragm (3) including a first principal surface (3A) and a second principal surface (3B) that is opposite thereto, the first principal surface receiving a pressure of a fluid; a semiconductor chip (1) provided with resistors that constitute a strain gauge; and at least three support members (2a, 2b, 2c) made of an insulating material, each support member being fixed to the second principal surface at one end thereof and to the semiconductor chip at the other end thereof and extending perpendicularly to the second principal surface so as to support the semiconductor chip. One of the support members (2a) is provided at a center (30) of the diaphragm in plan view. At least two of the other support members (2b, 2c) are provided at positions point-symmetrical about the center of the diaphragm in plan view in a region in which the diaphragm is deformed when a pressure greater than a pressure applied to the second principal surface is applied to the first principal surface.

TECHNICAL FIELD

The present invention relates to pressure sensors, and more particularly to a sanitary pressure sensor.

BACKGROUND ART

In general, sanitary pressure sensors used in, for example, facilities for manufacturing food, medical supplies, etc., which require sanitary care, are expected to satisfy strict requirements regarding, for example, corrosion resistance, cleanliness, reliability, and versatility.

For example, to satisfy the requirements regarding corrosion resistance, a liquid contact portion of a sanitary pressure sensor that comes into contact with fluid (for example, liquid) to be subjected to pressure measurement needs to be made of a highly corrosion-resistant material, such as a stainless steel (SUS), a ceramic, or titanium. In addition, to satisfy the requirements regarding cleanliness, the sanitary pressure sensor needs to have a flush diaphragm structure that enables easy cleaning and to be highly thermal-shock resistant to withstand steam washing. In addition, to satisfy the requirements regarding reliability, the sanitary pressure sensor needs to have an encapsulant-free structure (oil-free structure) and a structure in which a diaphragm does not easily break (high rigidity barrier). In addition, to satisfy the requirements regarding versatility, a connecting portion of the sanitary pressure sensor to be connected to a pipe through which the fluid that serves as a measurement object flows needs to have the shape of a coupling.

As described above, the material and structure of the sanitary pressure sensor are more strictly limited than those of other pressure sensors, and therefore the sensitivity of the sanitary pressure sensor cannot be easily increased. For example, when the film thickness of the diaphragm is increased (aspect ratio of diameter to thickness of the diaphragm is reduced) to realize a structure in which the diaphragm does not easily break, the amount of deformation of the diaphragm is reduced, and the sensitivity of the sensor is reduced accordingly. Therefore, a technology for accurately detecting a small amount of deformation of the diaphragm in the sanitary pressure sensor is desired.

For example, PTL 1 and PTL 2 disclose load converting pressure sensors including a semiconductor chip (beam member) made of, for example, Si on which a strain gauge including diffused resistors is formed. To increase the sensitivity of the sensor, only a displacement of a central portion of a diaphragm is transmitted to the semiconductor chip, and changes in the resistances of the diffused resistors due to the piezoresistive effect based on deformation of the semiconductor chip are detected.

More specifically, in the load converting pressure sensors according to the related art disclosed in PTL 1 and PTL 2, a central portion of the semiconductor chip is supported at a central portion of the diaphragm, and both ends of the semiconductor chip are fixed to portions that do not substantially move. For example, according to PTL 1, a strip-shaped semiconductor chip is supported at the center thereof by a rod-shaped member called a pivot at the center of a diaphragm. Both ends of the semiconductor chip in a long-side direction are fixed to a thick portion formed at the outer rim of the diaphragm with insulating pedestals interposed therebetween. According to PTL 2, the center of a rectangular semiconductor chip is fixed to the center of a diaphragm, and both ends of the semiconductor chip in the long-side direction are fixed to a base that does not move.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the pressure sensors disclosed in PTL 1 and PTL 2, the central portion of the semiconductor chip is supported at the center of the diaphragm, and both ends of the semiconductor chip in the long-side direction are fixed to portions of the diaphragm that do not substantially move. Accordingly, when the diaphragm is bent, a large displacement of the central portion of the diaphragm can be efficiently transmitted to the semiconductor chip. Accordingly, the sensitivity of the pressure sensor can be increased.

However, the above-described pressure sensors have a problem that the semiconductor chip is large. For example, in the pressure sensor disclosed in PTL 1, the thick portion is formed at the outer rim of the diaphragm, which is circular, and both ends of the strip-shaped semiconductor chip are fixed to the thick portion. Therefore, when, for example, the diameter of the coupling of the pressure sensor connected to a pipe is increased, the diameter of the diaphragm is also increased, and the length of the semiconductor chip needs to be increased by increasing the chip size accordingly.

The present invention has been made in light of the above-described problem, and an object of the present invention is to provide a high-sensitivity pressure sensor including a small semiconductor chip on which a strain gauge is formed.

Solution to Problem

A pressure sensor according to the present invention includes a diaphragm including a first principal surface and a second principal surface, the first principal surface receiving a pressure of a fluid that serves as a measurement object, the second principal surface being opposite to the first principal surface; a semiconductor chip having a rectangular shape and provided with resistors that constitute a strain gauge; and at least three support members made of an insulating material, each support member being fixed to the second principal surface at one end thereof and to the semiconductor chip at the other end thereof and extending perpendicularly to the second principal surface so as to support the semiconductor chip. One of the support members is provided at a center of the diaphragm in plan view. At least two of the other support members are provided in a region in which the diaphragm is deformed when a pressure greater than a pressure applied to the second principal surface is applied to the first principal surface. The at least two of the other support members are provided at positions point-symmetrical about the center of the diaphragm in plan view.

Advantageous Effects of Invention

Thus, the present invention provides a high-sensitivity pressure sensor including a small semiconductor chip on which a strain gauge is formed.

DESCRIPTION OF EMBODIMENTS

First, the summary of a pressure sensor according to the present invention will be described.

A pressure sensor according to the present invention includes a diaphragm (3) including a first principal surface (3A) and a second principal surface (3B), the first principal surface receiving a pressure of a fluid that serves as a measurement object, the second principal surface being opposite to the first principal surface; a semiconductor chip (1) having a rectangular shape and provided with resistors (R1to R4) that constitute a strain gauge; and at least three support members (2a,2b,2c) made of an insulating material, each support member being fixed to the second principal surface at one end thereof and to the semiconductor chip at the other end thereof and extending perpendicularly to the second principal surface so as to support the semiconductor chip. One of the support members (2a) is provided at a center (30) of the diaphragm in plan view. At least two of the other support members (2b,2c) are provided in a region in which the diaphragm is deformed when a pressure greater than a pressure applied to the second principal surface is applied to the first principal surface. The at least two of the other support members are provided at positions point-symmetrical about the center of the diaphragm in plan view.

The above-described pressure sensor may further include a housing (4) having a tubular shape that contains the semiconductor chip, the support members, and the diaphragm. The diaphragm is fixed so as to cover an opening in one end portion (4A) of the housing, and the at least two of the other support members are provided at positions such that the least two of the other support members do not come into contact with an inner wall (4B) of the housing when the pressure greater than the pressure applied to the second principal surface is applied to the first principal surface.

In the above-described pressure sensor, the at least two of the other support members may be provided in a region (3D) in which an inclination of the second principal surface is greatest when the pressure greater than the pressure applied to the second principal surface is applied to the first principal surface and the diaphragm is deformed.

In the above-described pressure sensor, the resistors (R1to R4) may be formed on the semiconductor chip in a region in which a tensile stress is generated in the semiconductor chip due to the support members when the pressure greater than the pressure applied to the second principal surface is applied to the first principal surface and the diaphragm is deformed, and the resistors may be arranged in a direction orthogonal to a direction connecting the at least two of the other support members in plan view.

In the above-described pressure sensor, the resistors may be formed on the semiconductor chip in a region in which a tensile stress is generated in the semiconductor chip when the pressure greater than the pressure applied to the second principal surface is applied to the first principal surface and the diaphragm is deformed. Among the resistors, the resistors that oppose each other in the bridge circuit (resistors R1and R3and resistors R2and R4) may be formed at positions point-symmetrical about the center (11) of the semiconductor chip in plan view.

In the above description, components of the invention are given their corresponding reference numerals in the drawings in brackets for example.

Embodiments of the present invention will now be described with reference to the drawings. In the following description, components common to the embodiments are denoted by the same reference numerals, and redundant description of the components will be omitted.

<Overall Structure of Pressure Sensor>

FIGS. 1 to 3illustrate the structure of a pressure sensor according to an embodiment of the present invention.

FIG. 1is a sectional perspective view illustrating the structure of a pressure sensor100according to the present embodiment.FIG. 2is a plan view illustrating the structure of the pressure sensor100viewed in a Z direction inFIG. 1.FIG. 3is a sectional view illustrating the structure of the pressure sensor100taken along line A-A inFIG. 2.

The pressure sensor100illustrated inFIGS. 1 to 3is a device that detects a pressure of a fluid that serves as a measurement object by transmitting a displacement of a diaphragm that occurs when the diaphragm is bent by the pressure of the fluid to a semiconductor chip on which a strain gauge is formed. The pressure sensor100is structured so that the semiconductor chip is supported by at least three support members fixed to the diaphragm at positions at which the displacement occurs.

More specifically, the pressure sensor100includes a semiconductor chip1, support members2ato2c, a diaphragm3, and a housing4.FIGS. 1 to 3illustrate a mechanism for transmitting a deformation of the diaphragm3to the semiconductor chip1in the pressure sensor100. Other functional units, such as a circuit for processing a signal output from the semiconductor chip1, are omitted. The pressure sensor100may also include, for example, a display (for example, a liquid crystal display) for presenting various types of information, such as the detected pressure, to the user.

The semiconductor chip1, the support members2ato2c, and the diaphragm3are contained in a housing4made of a highly corrosion-resistant metal material. As illustrated inFIGS. 1 to 3, the housing4has a tubular shape. One end portion4A of the housing4has the shape of a coupling that enables connection to a pipe through which the fluid that serves as the measurement object flows. The inner space of the housing4is filled with, for example, air, and the pressure in the housing4at an inner wall4B is, for example, atmospheric pressure.

The semiconductor chip1is constituted by a semiconductor substrate made of, for example, Si. The semiconductor chip1has a strain gauge that detects a deformation caused by stress applied to the semiconductor chip1based on variations in resistances.

As illustrated inFIG. 4, the strain gauge is constituted by, for example, a bridge circuit10including four resistors (for example, diffused resistors) R1to R4formed on the semiconductor chip1. The positions at which the resistors R1to R4are formed on the semiconductor chip1will be described in detail below. The pressure sensor100is capable of measuring the pressure of the fluid that serves as the measurement object by detecting a change in voltage based on changes in the resistances of the resistors R1to R4caused by a stress generated in the semiconductor chip1while a constant current is applied to the bridge circuit10.

A span voltage Vo output from the bridge circuit10can be expressed as in Equation (1) given below by using resistances R1to R4. In Equation (1), VA and VB are voltages at nodes A and B inFIG. 4, and I is a current supplied from a constant current source.

The diaphragm3is a film that receives the pressure of the fluid that serves as the measurement object. The diaphragm3is made of a highly corrosion-resistant material, such as a stainless steel (SUS) a ceramic, or titanium, and is, for example, circular in plan view. The diaphragm3supports the semiconductor chip1and the support members2a,2b, and2c.

The diaphragm3is fixed to the end portion4A of the housing4and covers an opening in the end portion4A of the housing4. For example, the outer rim of the diaphragm3is joined to the inner wall4B of the end portion4A of the housing4without leaving a gap therebetween. More specifically, the diaphragm3includes a pressure receiving surface (liquid contact surface)3A that contacts the fluid that serves as the measurement object, and a support surface3B that is opposite to the pressure receiving surface3A and that supports the semiconductor chip1and the support members2a,2b, and2c. The diaphragm3is bent when a pressure greater than the pressure applied to the support surface3B (for example, atmospheric pressure) is applied to the pressure receiving surface3A by the fluid that serves as the measurement object.

The support members2a,2b, and2c(hereinafter may be referred to generically as “support members2”) are components that support the semiconductor chip1above the diaphragm3. The support members2have the shape of a column, such as a polygonal column (for example, a rectangular column). The support members2are made of an electrically insulating material. More preferably, the support members2are made of an electrically insulating material with low thermal conductivity. The material of the support members2may be, for example, glass (for example, borosilicate glass (Pyrex (registered trademark))).

Each of the support members2a,2b, and2cextends perpendicularly from the support surface3B and supports the semi conductor chip1. More specifically, each of the support members2a,2b, and2cis fixed to the support surface3B of the diaphragm3at one end thereof and is fixed to the semiconductor chip1at the other end thereof.

<Joining Structure of Support Members2>

The joining structure in which the diaphragm3, the support members2, and the semiconductor chip1are joined together will now bee described in detail.

FIG. 5is an enlarged view of a joining section in which the diaphragm3, the support members2, and the semi conductor chip1illustrated inFIG. 3are joined together.

As illustrated inFIGS. 2 and 5, one end portion of the support member2ais joined to a central portion of one principal surface of the semiconductor chip1. One end portion of the support member2bis joined to one side portion of the one principal surface of the semiconductor chip1. One end portion of the support member2cis joined to a side portion of the one principal surface of the semiconductor chip1that opposes the one side portion.

FIG. 5illustrates an example in which joining portions of the semiconductor chip1that are joined to the support members2are thicker than other portions of the semiconductor chip1in the Z direction. However, the joining portions may have the same thickness as that of the other portions.

The other end portion of each of the support members2ato2cis fixed to the support surface3B of the diaphragm3. More specifically, as illustrated inFIGS. 2 and 5, the support members2ato2care fixed to the support surface3B so that central axes20a,20b, and20cof the support members2ato2care substantially perpendicular to the support surface3B (X-Y plane) of the diaphragm3.

The support members2ato2care fixed to the support surface3B of the diaphragm3at positions described below.

The support member2ais provided on the support surface3B at a center30of the diaphragm3. More specifically, the support member2ais fixed to the support surface3B of the diaphragm3so that the center of the bottom surface of the support member2acoincides with the center30of the diaphragm3in plan view.

The center30of the diaphragm3is the point where the displacement of the diaphragm3in a Z-axis direction is greatest when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A. For example, when the diaphragm3is circular in plan view, the center30is the central point of the diaphragm3(circle).

As described above, the support member2ais preferably fisted to the support surface3B of the diaphragm3so that the center of the bottom surface of the support me caber2acoincides with the center30of the diaphragm3. However, the center of the bottom surface of the support member2amay be somewhat displaced from the center30of the diaphragm3as long as, for example, the center of the bottom surface of the support member2ais in a region3C within a circle centered on the point30.

The support members2band2care provided at positions point-symmetrical about the center30of the diaphragm3(support member2a) in plan view in a region in which the diaphragm3is deformed when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A.

In other words, the support members2band2care each fixed to the support surface3B at one end thereof at positions that are point-symmetrical about the center30of the diaphragm3in plan view and at which the support members2band2care tilted with respect to the Z-axis when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A.

Preferably, the support members3band2care provided at positions such that the support members2band2care tilted with respect to the Z-axis without coming into contact with the inner wall4B of the housing4when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A and the diaphragm3is deformed.

More preferably, the support members2band2care provided at positions at which the inclination (gradient) of the support surface3B of the diaphragm3is greatest when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A and the diaphragm3is deformed.

As illustrated inFIG. 7, the positions at which the inclination of the support surface3B of the diaphragm3is greatest are the positions (points31band31c) at which the inclination of the support surface3B of the diaphragm3is greatest when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A and the diaphragm3is bent.

As illustrated inFIG. 6, the points at which the inclination of the diaphragm3is greatest (for example, points31band31c) form a circle32centered on the center30of the diaphragm3. Accordingly, by fixing the support members2band2cso that the centers of the bottom surfaces thereof coincide with two points on the circle32that are point-symmetrical about the center30, the displacement of the diaphragm3can be most efficiently transmitted to the semiconductor chip1, and the sensitivity of the pressure sensor100can be maximized.

As described above, when the sensitivity of the sensor is to be maximized, the support members2band2care preferably provided at the points where the inclination of the diaphragm3is greatest. However, the support members2band2cmay each be fixed at one thereof at positions determined as appropriate in consideration of the desired sensitivity of the sensor and the chip size of the semiconductor chip1. For example, as illustrated inFIG. 6, the support members2band2cmay each be fixed at one end thereof at positions within a region3D including the circle32drawn by connecting the points at which the inclination of the diaphragm3is greatest (hereinafter referred to as “region in which the inclination of the diaphragm3is greatest”). Examples of such positions will now be described.

FIG. 8is a graph of displacement of the diaphragm and inclination of the support surface versus radial position on the diaphragm. InFIG. 8, the horizontal axis represents the relative distance from the center of the diaphragm3when the radius of the diaphragm3is “1”. The vertical axis represents the relative displacement of the diaphragm3when the maximum displacement is “1” and the relative inclination of the diaphragm3when the maximum inclination is “1”. InFIG. 8, reference numeral301denotes the displacement of the diaphragm3versus relative distance from the center of the diaphragm3, and reference numeral302denotes the inclination of the support surface3B of the diaphragm3versus relative distance from the center of the diaphragm3.

FIG. 8shows that the inclination of the diaphragm3is greatest at points31band31con the diaphragm3. The inclination is 80% of more of the maximum inclination when the relative distance from the center of the diaphragm3is in the range of “0.35 to 0.77”. Accordingly, the sensitivity of the sensor can be increased by, for example, defining this range as the region3D in which the inclination of the diaphragm3is greatest and fixing each of the support members2band2cat one end thereof so that the centers of the bottom surfaces of the support members2band2care within this region3D.

In particular, when the support members2band2care disposed in a region within the circle32in the region3D in which the inclination of the support surface3B of the diaphragm3is greatest (for example, in the region in which the relative distance is in the range of “0.35 to 0.50”), the size of the semiconductor chip1in the long-side direction can be further reduced.

Thus, by appropriately setting the positions at which the support members2band2care fixed in the region3D of the diaphragm3, the size of the semiconductor chip1can be further reduced without reducing the sensitivity of the sensor.

<Principle of Operation of Pressure Sensor100>

FIG. 9is a schematic diagram illustrating displacements of the support members2and the semiconductor chip1when the diaphragm3is deformed.

Referring toFIG. 9, the diaphragm3is bent when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A of the diaphragm3. Since one end of the support member2ais fixed to the diaphragm3at the center30, the other end of the support member2ais moved by a large amount in the Z-axis direction but is hardly moved in an X-axis direction and a Y-axis direction. In contrast, the support members2aand2bare fixed so as to extend substantially perpendicularly from the support surface3B of the diaphragm3at positions apart from the center30of the support surface3B, and are therefore tilted with respect to the Z-axis. In other words, the other ends of the support members2band2care moved not only in the Z-axis direction but also in the x-axis direction. More specifically, the support members2band2care tilted so that the other ends thereof move away from the center30of the diaphragm3(support member2a), that is, toward the inner walls4B of the housing4.

Accordingly, the semiconductor chip1is stretched, and a tensile stress is generated in the semiconductor chip1. More specifically, a tensile stress corresponding to the differences in displacements in the X-axis direction and the Y-axis direction between the support members2aand2bis generated in the semiconductor chip1. Accordingly, the pressure of the fluid that serves as the measurement object can be accurately detected by appropriately forming the resistors R1to R4that constitute the above-described strain gauge (bridge circuit) in the region where the above-described tensile stress is generated in the semiconductor chip1.

The arrangement of the resistors R1to R4formed on the semiconductor chip1will now be described.

FIG. 10is a diagram illustrating regions in which the resistors R1to R4are formed on the semiconductor chip1. A plan view of the semiconductor chip1is shown in the lower part ofFIG. 10. The graph shown in the upper part ofFIG. 10has a horizontal axis representing the distance in the X-axis direction corresponding to that in the plan view of the semiconductor chip1shown in the lower part ofFIG. 10, and a vertical axis representing the stress generated in the semiconductor chip1when the diaphragm3is bent.

Referring toFIG. 10, the resistors R1to R4are formed in regions in which a positive (+) stress is generated in the semiconductor chip1when the diaphragm3is bent by the pressure of the fluid, that is, in regions10aband10acin which a tensile stress is generated in the semiconductor chip1.

The locations, for example, of the resistors R1to R4in the regions10aband10acare not particularly limited. For example, the resistors R1to R4are preferably arranged as illustrated inFIGS. 11 and 12.

As illustrated inFIG. 11, the resistors R1to R4may be arranged in a direction (Y-axis direction) orthogonal to the direction connecting the two support members2band2cin plan view in the regions in which the tensile stress is generated in the semiconductor chip1due to the support members2when a pressure greater than the pressure applied to the support surface3B is applied to the pressure receiving surface3A and the diaphragm3is deformed. More specifically, the resistors R1to R4may be arranged in a short-side direction of the semiconductor chip in one of the regions10aband10acof the semiconductor chip1.

Alternatively, as illustrated inFIG. 12, among the resistors R1to R4, the resistors that oppose each other in the bridge circuit10may be formed at positions point-symmetrical about the center11of the semiconductor chip1in plan view. More specifically, the resistors R1and R3may be arranged point-symmetrically about the center11of the semiconductor chip1in plan view. Also, the resistors R2and R4may be arranged point-symmetrically about the center11of the semiconductor chip1in plan view.

FIG. 13shows the result of a simulation of variation in the span voltage of the bridge circuit versus displacement of the semiconductor chip1relative to the diaphragm3in the Y-axis direction in the case where the resistors R1to R4are arranged as illustrated inFIG. 11.

InFIG. 13, the horizontal axis represents the percentage of the displacement of the semiconductor chip1relative to the diameter of the diaphragm3, and the vertical axis represents the variation rate [% FS] of the span voltage of the bridge circuit including the resistors R1to R4.

As is clear fromFIG. 13, when the resistors R1to R4are arranged on the semiconductor chip1as illustrated inFIG. 11, the variation in the span voltage can be set to 1% FS or less by controlling the displacement of the semiconductor chip1in the short-side direction (Y-axis direction) relative to the diameter of the diaphragm3within the range of ±5%.

Therefore, by forming the resistors R1to R4on the semiconductor chip1as described above, the allowance for the displacement of the semiconductor chip1relative to the diaphragm3in the Y-axis direction can be increased. This effect can also be obtained when the resistors that oppose each other in the bridge circuit10are formed at positions point-symmetrical about the center12of the semiconductor chip1(seeFIG. 12).

When the resistors that oppose each other in the bridge circuit10are formed at positions point-symmetrical about the center11of the semiconductor chip1as illustrated inFIG. 12, the influence of displacement of the semiconductor chip1relative to the diaphragm3in the X-axis direction can be reduced.

FIG. 14is a graph of the variation rate of the span voltage of the bridge circuit versus displacement of the semiconductor chip in the Y-axis direction.FIG. 14illustrates the result of a simulation of the stress distribution in the semiconductor chip1generated when the pressure is applied to the semiconductor chip1on which the resistors R1to R4are arranged as illustrated inFIG. 12. InFIG. 14, the horizontal axis represents the position in the X-axis direction when the center30of the diaphragm3is at the origin, and the vertical axis represents the stress generated in the semiconductor chip1.

As is clear fromFIG. 14, assuming that the resistors that oppose each other in the bridge circuit10(resistors R1and R3and resistors R2and R4) are arranged point-symmetrically about the center11of the semiconductor chip1, the opposing resistors receive equal stress when the center11of the semiconductor chip1and the center30of the diaphragm3coincide with each other. When the center11of the semiconductor chip1is displaced from the center30of the diaphragm3in a positive or negative direction along the X-axis, the stress applied to one of the opposing resistors decreases, and the stress applied to the other resistor increases. For example, as illustrated inFIG. 14, when the semiconductor chip1is shifted in the positive direction along the X-axis, the stress applied to the resistor R1increases and the stress applied to the resistor R3decreases. Similarly, the stress applied to the resistor R4increases and the stress applied to the resistor R2decreases.

Thus, when the semiconductor chip1is displaced relative to the center30of the diaphragm3along the X-axis, the stresses applied to be opposing resistors change in opposite directions. Therefore, the changes in the resistances of the resistors R1to R4cancel each other in the above-described Equation (1) expressing the span voltage Vo.

Accordingly, when the resistors that oppose each other in the bridge circuit10, that is, the resistors R1and R3and the resistors R2and R4, are arranged point-symmetrically about the center11of the semiconductor chip1, the influence of the displacement of the semiconductor chip1relative to the diaphragm3in the X-axis direction on the span voltage Vo of the bridge circuit100can be reduced.

<Effects of Pressure Sensor100>

As described above, the pressure sensor according to the present invention is structured such that the semiconductor chip on which the strain gauge is formed is supported by the support member2aand the two support members2band2c. The support member2ais fixed to the support surface3B so as to extend substantially perpendicularly therefrom at the center30of the diaphragm3. The two support members2band2care fixed to the support surface3B so as to extend substantially perpendicularly therefrom at positions point-symmetrical about the center30of the diaphragm in the region in which the diaphragm3is deformed. With this structure, when the diaphragm3is bent, the support members2band2carranged on both sides of the support member2aare tilted outward so that the tensile stress corresponding to the displacement of the diaphragm3can be efficiently generated in the semiconductor chip1.

In the pressure sensor100, the support members2band2cthat support both end portions of the semiconductor chip are fixed in the region in which the diaphragm3is deformed. Therefore, the chip size of the semiconductor chip can be reduced from that in the case where the support members2band2care fixed at positions at which substantially no movement occurs, that is, at positions outside the region in which the diaphragm3is deformed, as in the load converting pressure sensors according to the related art.

As described above, according to the pressure sensor100of the present invention, the size of the semiconductor chip can be reduced and the sensitivity can be increased at the same time.

In the pressure sensor100, the support members2band2care fixed at positions such that the support members2band2care tilted with respect to the Z-axis without coming into contact with the inner wall4B of the housing4when the diaphragm3is bent by the pressure applied by the fluid. Thus, the tilting of the support members2band2cis not restricted by the inner wall4B of the housing4, and the detectable pressure range of the pressure sensor100can be increased accordingly.

When the support members2band2care fixed at the points31band31bwhere the inclination of the diaphragm3is greatest, the sensitivity of the sensor can be further increased as described above. When the support members2band2care fixed in the region3D in which the inclination of the diaphragm3is greatest, the size of the semiconductor chip can be further reduced while the sensitivity of the sensor can be maintained at a high level as described above.

As illustrated inFIG. 11, the resistors R1to R4that constitute the bridge circuit100may be arranged in the short-side direction of the semiconductor chip1in the region in which the tensile stress is generated in the semiconductor chip1. In such a case, as described above, the allowance for the displacement of the semiconductor chip1relative to the diaphragm3in the short-side direction can be increased. Accordingly, the sensitivity of the pressure sensor100can be increased.

The resistors that oppose each other in the bridge circuit10may be formed at positions point-symmetrical about the center11of the semiconductor chip1in the region in which the tensile stress is generated in the semiconductor chip1(seeFIG. 12). In such a case, as described above, not only can the allowance for the displacement of the semiconductor chip X relative to the diaphragm3in the Y-axis direction be increased, but the influence of the displacement of the semiconductor chip1relative to the diaphragm3in the X-axis direction can be reduced. Accordingly, the sensitivity of the pressure sensor100can be further increased.

Although the invention made by the present inventors is described in detail based on the embodiment, the present invention is not limited to this, and may, of course, be modified in various ways without departing from the gist thereof.

For example, in the above-described embodiment, the support members2have the shape of a polygonal column. However, the support members2may instead have the shape of, for example, a circular column.

INDUSTRIAL APPLICABILITY

The pressure sensor according to the present invention may be used as various types of sensors, such as a sanitary pressure sensor.

REFERENCE SIGNS LIST

100: pressure sensor,1semiconductor chip,2,2a,2b,2csupport member,3diaphragm,3A pressure receiving surface,3B support surface,3C central region,3D region in which inclination of diaphragm is greatest,30center of diaphragm,31b,31cpoint where inclination of diaphragm is greatest,32circle,4housing,4A end portion of housing,4B inner wall of housing,10bridge circuit, R1to R4resistor,10ab,10acregion.