JP2014206514A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor capable of preventing degradation of sensor characteristic.SOLUTION: A pressure sensor 10 includes: a semiconductor substrate 22 having a diaphragm part 21; and piezoresistive elements P1, P2, P3, and P4 for detecting a pressure applied to the diaphragm part 21 as a resistance value change. The pressure sensor 10 also includes an insulator film 26 covering the surface 22a of the semiconductor substrate 22 including the surface 21a of the diaphragm part 21 and the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4. The pressure sensor 10 further includes a conductive thin film 25 covering at least the surface 26a of the insulator film 26 corresponding to the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4. The conductive thin film 25 covers only a part of the surface 26a of the insulator film 26 corresponding to the surface 21a of the diaphragm part 21.

Description

  The present invention relates to a pressure sensor.

2. Description of the Related Art Conventionally, a pressure sensor that includes a semiconductor substrate on which a diaphragm portion is formed and in which a bridge circuit is configured by a plurality of piezoresistive elements arranged on the surface of the diaphragm portion is known (see, for example, Patent Document 1).
By configuring such a bridge circuit, it is possible to detect the deflection generated in the diaphragm portion when pressure is applied as a change in the output voltage with respect to the applied bias of the bridge circuit accompanying a change in the resistance value of the piezoresistive element. I have to.

  By the way, in the pressure sensor configured as described above, a phenomenon may occur in which the offset voltage (the output voltage value of the bridge circuit when no pressure is applied to the sensor) fluctuates when power is supplied to the bridge circuit. . One possible cause of this phenomenon is that the movable ions present on the sensor surface move on the surface of the piezoresistive element after the power is turned on, thereby changing the resistance value of the piezoresistive element.

  Therefore, in Patent Document 1, a conductive thin film is formed on the surface of the piezoresistive element so that a change in the resistance value of the piezoresistive element due to movable ions can be suppressed.

JP 2011-102775 A

  However, in Patent Document 1, a conductive thin film is formed on the entire surface of the diaphragm portion that is easily bent and deformed. Therefore, when the temperature changes, the diaphragm portion may be bent due to a difference in linear expansion coefficient between the conductive thin film and the silicon or silicon oxide film on the diaphragm portion. As described above, if the diaphragm portion is bent due to a temperature change or the like, the bending may affect the sensor characteristics, and the sensor characteristics may be deteriorated.

  Then, an object of this invention is to obtain the pressure sensor which can suppress further that a sensor characteristic deteriorates.

  According to a first aspect of the present invention, there is provided a semiconductor substrate including a diaphragm portion, a piezoresistive element that detects a pressure applied to the diaphragm portion as a change in resistance value, and a semiconductor including the surface of the diaphragm portion and the surface of the piezoresistive element. An insulating film covering a substrate surface; and a conductive thin film covering at least a surface of the insulating film corresponding to the surface of the piezoresistive element, wherein the conductive thin film corresponds to a surface of the diaphragm portion of the insulating film. The gist is that only a part of the surface is covered.

  The second feature of the present invention is summarized as comprising a plurality of the piezoresistive elements.

  The gist of the third feature of the present invention is that the conductive thin film has a point-symmetric shape with respect to the center point of the diaphragm portion in plan view.

  According to a fourth aspect of the present invention, the conductive thin film is an element disposed on the piezoresistive element, and a surrounding part disposed so as to surround the diaphragm part outside the diaphragm part in a plan view. The element covering portion is connected to a portion located in the vicinity of the element covering portion of the surrounding portion.

  A fifth feature of the present invention is summarized in that the separate element covering portions are disposed on the plurality of piezoresistive elements.

  ADVANTAGE OF THE INVENTION According to this invention, the pressure sensor which can suppress further that a sensor characteristic deteriorates can be obtained.

It is sectional drawing of the pressure sensor concerning one Embodiment of this invention. It is sectional drawing which showed schematically the sensor chip concerning one Embodiment of this invention. 1 is a plan view schematically showing a sensor chip according to an embodiment of the present invention. 1 is a circuit diagram of a piezoresistive element according to an embodiment of the present invention. It is sectional drawing which showed roughly the sensor chip concerning the modification of one Embodiment of this invention. It is the top view which showed roughly the sensor chip concerning the modification of one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, a pressure sensor that measures the pressure by taking a fluid (water or the like) in the washing machine into the inside will be exemplified.

  As shown in FIG. 1, the pressure sensor 10 according to the present embodiment includes a sensor chip 20 in which a diaphragm portion 21 is formed. The sensor chip 20 is included in a container-like package 40 together with an integrated circuit chip 30. It is stored in. The package 40 includes a housing 41, and a plurality of terminal portions 42 that are arranged in parallel in the paper front and back direction are arranged on the bottom 41 a of the housing 41. Then, both end portions 42 a and 42 b of the terminal portion 42 are arranged so as to protrude from both sides of the housing 41 by a predetermined amount. In addition, the sensor chip 20 and the integrated circuit chip 30, and the chips 20 and 30 and the terminal portion 42 are electrically connected by bonding wires 50.

  The housing 41 is filled with a potting material 60 in a state in which the sensor chip 20, the integrated circuit chip 30 and the terminal portion 42 are accommodated, and the chips 20, 30 and terminals are cured by curing the potting material 60. The part 42 is fixed in the embedded state. As the potting material 60, for example, it is preferable to use JCR (Junction Coating Resin) having high adhesion to the silicon substrate.

  In particular, when a fluid (water or the like) in a washing machine is taken in and pressure is measured, the pressure sensor 10 is used in a high humidity environment. At this time, if the sensor chip 20 is exposed to a high humidity environment, the sensor chip 20 may be deteriorated by moisture. Therefore, when the pressure sensor is attached to a washing machine and used, it is preferable to apply JCR on at least the sensor chip 20 in order to protect the sensor chip 20 (suppress the deterioration of the sensor chip 20 due to moisture).

  Thus, if JCR is applied on the sensor chip 20 (the sensor chip 20 is fixed in an embedded state by JCR), the sensor chip 20 can be prevented from being exposed to a high humidity environment. The sensor chip 20 can be protected from moisture.

  The opening 41 b of the housing 41 is closed by a cover 43.

  In addition, a columnar boss portion 41c protruding toward the opposite side of the sensor chip 20 is provided at a substantially central portion of the bottom portion 41a of the housing 41, and the boss portion 41c penetrates in the axial direction. Thus, a pressure introduction hole 41d for applying fluid pressure (water pressure) to the sensor chip 20 is formed. In the present embodiment, the pressure introduction hole 41d is filled with oil, and fluid pressure (water pressure) is transmitted to the sensor chip 20 through this oil. The fluid pressure (water pressure) transmitted to the sensor chip 20 is applied to the diaphragm portion 21.

  The diaphragm portion 21 is bent and deformed by the applied fluid pressure (water pressure), but the magnitude of the fluid pressure (water pressure), that is, the height of the fluid from the reference surface (water level) can be detected by the amount of bending. It has become. Specifically, as shown in FIGS. 2 to 4, the amount of deflection of the diaphragm portion 21 is detected by four piezoresistive elements P1, P2, P3, and P4. The diaphragm portion 21 is formed in a substantially rectangular shape at the central portion of the semiconductor substrate 22 as shown in FIG.

  The package 40 is entirely covered with a case 70. In this embodiment, the case 70 includes a first case 71 and a second case 72 that are divided into the bottom 41 a side and the opening 41 b side of the housing 41. Then, the package 40 is disposed inside the bottom wall portion 71a of the first case 71, the second case 72 is disposed so as to sandwich the package 40, and the first and second cases 71 and 72 are fitted to each other. Thus, the pressure sensor 10 is formed.

  The bottom wall 71a of the first case 71 is provided with a shallow recess 71b that engages the package 40, and a deep recess 71c that fits the boss 41c is provided in an inner region of the shallow recess 71b. ing. Specifically, the bottom 41a side of the housing 41 is fixed to the shallow recess 71b while the boss 41c of the housing 41 is fixed to the deep recess 71c.

  When the package 40 is fitted into the shallow recess 71b, both end portions 42a and 42b of the terminal portion 42 protruding from the package 40 abut on the inner surface of the outer region of the shallow recess 71b of the bottom wall portion 71a. It becomes. Further, attachment holes 42 c are formed in both end portions 42 a and 42 b of the terminal portion 42, and caulking projections 71 d are projected from the inner surface of the bottom wall portion 71 a of the first case 71. The package 40 is fixed to the first case 71 by inserting the caulking protrusion 71d into the mounting hole 42c and caulking.

  In addition, the O-ring 80 is inserted into the inner periphery of the deep recess 71c with the boss 41c fitted to the deep recess 71c, and the O-ring 80 allows the boss 41c and the first case 71 to be inserted. The liquid-tightness between the two is maintained. In this embodiment, the O-ring 80 is secured by a washer 81, and the washer 81 is secured by a caulking portion 71f.

  Further, the one end portion 42a of the terminal portion 42 protrudes further outward than the caulking portion by the caulking projection 71d, and the case end portions 71e and 72a of the first and second cases 71 and 72 are also one end portion of the terminal portion 42. It protrudes so as to cover 42a from both sides. When the first and second cases 71 and 72 are joined, the case end portions 71e and 72a surround the one end portion 42a of the terminal portion 42 so that the male connector C is formed. . By connecting a female connector (not shown) to the male connector C, the electrical signals of the sensor chip 20 and the integrated circuit chip 30 input to the terminal portion 42 can be extracted to the outside.

  Further, on the opposite side of the bottom wall portion 71a of the first case 71 from the sensor chip 20, a cylindrical projecting portion 71g protrudes through the bottom portion of the deep recess 71c. A fluid passage S is formed in the protrusion 71g. When the boss portion 41c is fitted into the deep recess 71c, the pressure introducing hole 41d of the boss portion 41c communicates with the base end portion 71h of the fluid passage S (projecting portion 71g). ing. The pressure (water pressure) of the fluid taken into the fluid passage S of the projecting portion 71g is applied to the sensor chip 20 via the oil in the pressure introduction hole 41d.

  The protrusion 71g of the first case 71 is formed with a predetermined thickness, and the pressure sensor 10 is attached to the washing machine so that the protrusion 71g contacts the fluid (water, etc.) in the washing machine. . An inlet 71j for fluid (water, etc.) is provided at the tip 71i of the protrusion 71g, and fluid (water, etc.) in the washing machine is taken into the fluid passage S of the protrusion 71g from this inlet 71j. Thus, the pressure of the fluid (water etc.) in the washing machine is measured.

  Here, in the present embodiment, the semiconductor substrate 22 is made of single crystal silicon having a (100) surface 22a, and the semiconductor substrate 22 is formed so that the outline shape is rectangular in plan view. .

  Then, by performing anisotropic etching from the back surface 22 b side of the semiconductor substrate 22, a thin plate-like diaphragm portion 21 is formed in the central portion of the semiconductor substrate 22.

  Specifically, the diaphragm portion 21 is formed on the semiconductor substrate by silicon anisotropic etching using an alkaline wet anisotropic etching solution (for example, KOH (potassium hydroxide aqueous solution), TMAH (tetramethyl ammonium hydroxide aqueous solution), etc.). It is formed by removing a part of 22.

  Then, the piezoresistive elements P1, P2, P3, and P4 are arranged at predetermined portions of the diaphragm portion 21 as shown in FIG. In the present embodiment, the pair of piezoresistive elements P1 and P3 are respectively arranged at the substantially central part of the opposed sides of the diaphragm portion 21, and the remaining pair of piezoresistive elements P2 and P4 are connected to the piezoresistive elements P1 and P1. It arrange | positions at the approximate center part of the opposing side part extended in the direction (crossing direction) orthogonal to the opposing side part which has arrange | positioned P3, respectively.

  At this time, the piezoresistive elements P1, P2, P3, and P4 are arranged so as to be point-symmetric with respect to the center point O of the diaphragm portion 21 in plan view. Furthermore, in the present embodiment, the piezoresistive elements P1, P2, P3, and P4 are straight lines passing through the center point O of the diaphragm portion 21 (straight lines extending in the vertical direction in FIG. 3 or extending in the horizontal direction in FIG. 3). Are arranged symmetrically with respect to the straight line).

  Then, the amount of deflection of the diaphragm portion 21 is measured based on the change of the resistance values R1, R2, R3, R4 of the piezoresistive elements P1, P2, P3, and P4 that are caused by the deflection change of the diaphragm portion 21. I have to.

  Specifically, one end of the piezoresistive element P1 is connected to the voltage output terminal Vout− via the diffusion lead wire 23a and the thin film metal wiring 24a, and the other end is connected to the voltage output terminal Vout− via the diffusion lead wire 23b and the thin film metal wiring 24d. It is connected to a bias voltage application terminal Vdd.

  Further, one end of the piezoresistive element P2 is connected to the voltage output terminal Vout− through the diffusion lead wire 23c and the thin film metal wiring 24a, and the other end is connected to the ground terminal GND through the diffusion lead wire 23d and the thin film metal wiring 24b. Connected to.

  Further, one end of the piezoresistive element P3 is connected to the ground terminal GND via the diffusion lead wire 23e and the thin film metal wiring 24b, and the other end is connected to the voltage output terminal Vout + via the diffusion lead wire 23f and the thin film metal wiring 24c. Connected.

  Then, one end of the piezoresistive element P4 is connected to the bias voltage application terminal Vdd via the diffusion lead wire 23g and the thin film metal wiring 24d, and the other end is voltage output via the diffusion lead wire 23h and the thin film metal wiring 24c. It is connected to the terminal Vout +.

  By doing so, the piezoresistive elements P1, P2, P3, and P4 form a bridge circuit BC as shown in FIG. That is, the piezoresistive element P1, the piezoresistive element P3, the piezoresistive element P2, and the piezoresistive element P4 are arranged in pairs on the bridge circuit BC so as to face each other.

  When the pressure sensor 10 having such a configuration is used, when pressure is applied from one surface of the diaphragm portion 21, a differential pressure is generated between the front surface 21a and the back surface 21b of the diaphragm portion 21, thereby causing the diaphragm portion 21 to have a pressure difference. Deflection will occur. When the diaphragm portion 21 is bent, crystals constituting the piezoresistive elements P1, P2, P3, and P4 are distorted, and the resistance values R1, R2, R3, and R4 of the piezoresistive elements P1, P2, P3, and P4 are changed. To do. Then, changes in the resistance values R1, R2, R3, and R4 of the piezoresistive elements P1, P2, P3, and P4 change in voltage with respect to the bias voltage Bias applied to the bias voltage application terminal Vdd using the bridge circuit BC. As detected from the voltage output terminals Vout + and Vout−.

  Furthermore, in this embodiment, an insulating film 26 is formed on the surface 22 a of the semiconductor substrate 22 so as to cover the entire surface 22 a of the semiconductor substrate 22. The insulating film 26 can be formed, for example, by forming a silicon oxide film on the surface 22 a of the semiconductor substrate 22.

  A conductive thin film 25 is formed on the surface 26a of the insulating film 26 corresponding to the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4. Note that the potential of the conductive thin film 25 may be a fixed potential by being connected to another electrode, or may be an open potential without being connected to another electrode. With this configuration, the conductive thin film 25 has the movable ions existing on the surface 22a of the semiconductor substrate 22 when the power is turned on so that the resistance values R1, R2, R3 of the piezoresistive elements P1, P2, P3, and P4. It will function as a shield layer that suppresses changing R4. As a result, it is possible to suppress the offset voltage of the bridge circuit BC from changing when the power is introduced.

  The conductive thin film 25 is preferably formed of aluminum or polysilicon. When the conductive thin film 25 is formed of aluminum, the pressure sensor 10 can be formed at a low cost because aluminum is an electrode and wiring material generally used in a semiconductor process. In addition, when the conductive thin film 25 is formed of polysilicon, there is an advantage that the influence due to the difference in linear expansion coefficient can be reduced as compared with the case where aluminum is used.

  A nitride film may be formed on the surface of the conductive thin film 25 or between the insulating film 26 and the conductive thin film 25 in order to balance the stress with the insulating film 26.

  As described above, in the present embodiment, the sensor chip 20 includes a semiconductor substrate 22 including the diaphragm portion 21 and a plurality (four in the present embodiment) of piezoelectric elements that detect the pressure applied to the diaphragm portion 21 as a change in resistance value. Resistance elements P1, P2, P3, and P4 are provided.

  The sensor chip 20 includes an insulating film 26 that covers the surface 21a of the semiconductor substrate 22 including the surface 21a of the diaphragm portion 21 and the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4. . Further, the sensor chip 20 includes a conductive thin film 25 that covers at least the surface 26a corresponding to the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4 of the insulating film 26.

  Here, in the present embodiment, the conductive thin film 25 covers only a part of the surface 26 a corresponding to the surface 21 a of the diaphragm portion 21 of the insulating film 26.

  Specifically, the conductive thin film 25 is disposed on the surrounding portion 25a disposed so as to surround the diaphragm portion 21 outside the region of the diaphragm portion 21 and the piezoresistive elements P1, P2, P3, and P4 in a plan view. And an element covering portion 25b to be arranged.

  The element covering portion 25b is connected to a portion located in the vicinity of the element covering portion 25b of the surrounding portion 25a.

  In the present embodiment, separate element covering portions 25b are arranged on a plurality (four) of piezoresistive elements P1, P2, P3, and P4, and each element covering portion 25b is separately connected to the surrounding portion 25a. It is like that.

  Specifically, the element covering portion 25b disposed on the piezoresistive element P1 includes the surrounding portion so as to cover the piezoresistive element P1 and the line segment (region) connecting the piezoresistive element P1 and the surrounding portion 25a in the shortest distance. 25a. The element covering portion 25b disposed on the piezoresistive elements P2, P3, and P4 is also connected to the surrounding portion 25a in the same manner (see FIG. 3).

  Thus, in the present embodiment, the four element covering portions 25b separately cover the surface 26a corresponding to the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4 of the insulating film 26. Yes. The four element covering portions 25b are the shortest distance between the piezoresistive elements P1, P2, P3, P4 in which the respective element covering portions 25b are arranged, and the piezoresistive elements P1, P2, P3, P4 and the surrounding portion 25a. Are connected to the surrounding portion 25a so as to cover the line segment (region) connected by.

  Further, in the present embodiment, the conductive thin film 25 has a point-symmetric shape with respect to the center point O of the diaphragm portion 21 in plan view.

  As described above, since the piezoresistive elements P1, P2, P3, and P4 are arranged at positions that are point-symmetric with respect to the center point O of the diaphragm portion 21, in this embodiment, the piezoelectric elements that are arranged point-symmetrically. The conductive thin film 25 having a point-symmetric shape covers the resistance elements P1, P2, P3, and P4.

  In the present embodiment, the conductive thin film 25 is in a plan view with respect to a straight line passing through the center point O of the diaphragm portion 21 (a straight line extending in the vertical direction or a straight line extending in the left-right direction in FIG. 3). It also has a line-symmetric shape.

  With such a configuration, the conductive thin film 25 has only a part of the surface 26a corresponding to the surface 21a of the diaphragm portion 21 of the insulating film 26 (almost all the piezoresistive elements P1, P2, P3, and P4 are arranged). Only the part that has been made).

  As described above, in this embodiment, the conductive thin film 25 is formed on the surface 26a of the insulating film 26 corresponding to the surfaces P1a, P2a, P3a, and P4a of the piezoresistive elements P1, P2, P3, and P4. . The conductive thin film 25 covers only a part of the surface 26 a corresponding to the surface 21 a of the diaphragm portion 21 of the insulating film 26.

  In this way, by forming the conductive thin film 25 on the piezoresistive elements P1, P2, P3, and P4, the resistance values R1, R2, R3, and R4 of the piezoresistive elements P1, P2, P3, and P4 due to movable ions are reduced. Change can be suppressed. Note that JCR is thought to have many mobile ions that affect sensor characteristics. Accordingly, when JCR is used to protect the sensor chip 20 from moisture, the piezoresistive elements P1, P2 due to movable ions must be formed unless the conductive thin film 25 is formed on the piezoresistive elements P1, P2, P3, P4. , P3, P4 resistance values R1, R2, R3, R4 change more significantly. However, if the conductive thin film 25 is formed on the piezoresistive elements P1, P2, P3, P4, even if JCR is used, the resistance value R1 of the piezoresistive elements P1, P2, P3, P4 due to movable ions. , R2, R3, R4 can be suppressed.

  Further, by covering only a part of the surface 26a corresponding to the surface 21a of the diaphragm portion 21 of the insulating film 26, an extra region on the diaphragm portion 21 that is susceptible to stress (is easily deformed) is formed. The conductive thin film 25 can be prevented from being formed.

  Therefore, it is possible to suppress the deflection of the diaphragm portion 21 due to the difference in linear expansion coefficient while suppressing changes in the resistance values R1, R2, R3, and R4 of the piezoresistive elements P1, P2, P3, and P4 due to movable ions. Thus, it is possible to further suppress the deterioration of the sensor characteristics.

  Thus, according to this embodiment, it becomes possible to obtain the pressure sensor 10 that can further suppress the deterioration of the sensor characteristics.

  In the present embodiment, the conductive thin film 25 has a point-symmetric shape with respect to the center point O of the diaphragm portion 21 in plan view. Therefore, it is possible to suppress the stress balance of the surface 21a of the diaphragm portion 21 from becoming unstable as much as possible.

  Furthermore, in this embodiment, the piezoresistive elements P1, P2, P3, and P4 are also arranged so as to be point symmetric with respect to the center point O of the diaphragm portion 21. Therefore, the influence of movable ions on the offset voltage can be suppressed without destabilizing the stress balance of the surface 21a of the diaphragm portion 21.

  Further, in the present embodiment, the conductive thin film 25 includes the surrounding portion 25a disposed so as to surround the diaphragm portion 21 outside the region of the diaphragm portion 21 and the piezoresistive elements P1, P2, P3, and P4 in a plan view. And an element covering portion 25b disposed above. The element covering portion 25b is connected to a portion located in the vicinity of the element covering portion 25b of the surrounding portion 25a.

  With such a configuration, the area covered by the conductive thin film 25 on the surface 26a corresponding to the surface 21a of the diaphragm portion 21 of the insulating film 26 can be suppressed as much as possible with a simpler configuration. It becomes possible to further suppress the deterioration of the characteristics.

  In particular, in the present embodiment, the semiconductor substrate 22 is made of single crystal silicon having a (100) surface 22a, and the piezoresistive elements P1, P2, P3, and P4 are arranged at substantially the center of each side of the diaphragm portion 21. In plan view, they are arranged so as to be point-symmetric with respect to the center point O of the diaphragm portion 21. As a result, it is not necessary to form the conductive thin film 25 in the central portion (a more easily bent portion) of the diaphragm portion 21, so that deterioration of sensor characteristics can be suppressed more effectively.

  Separate element covering portions 25b, 25b, 25b and 25b are arranged on the piezoresistive elements P1, P2, P3 and P4, respectively. Therefore, the area covered with the conductive thin film 25 on the surface 26a corresponding to the surface 21a of the diaphragm portion 21 of the insulating film 26 can be further suppressed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made.

  For example, it is possible to use a sensor chip 20A in which the piezoresistive elements P1, P2, P3, and P4 and the conductive thin film 25 are configured as shown in FIGS.

  Specifically, in FIGS. 5 and 6, a single crystal silicon substrate having a (110) surface is used as the semiconductor substrate 22, and the diaphragm portion 21 is formed in the semiconductor substrate 22.

  The piezoresistive elements P1 and P3 are arranged at the center of two opposite sides of the diaphragm portion 21, and the piezoresistive elements P2 and P4 are arranged near the center of the diaphragm portion 21. Furthermore, the conductive thin film 25 is disposed so as to cover all of the piezoresistive elements P1, P2, P3, and P4 so that the conductive thin film 25 corresponds to the surface 21a of the diaphragm portion 21 of the insulating film 26. Only a part of 26a is covered.

  Even with such a configuration, substantially the same operations and effects as the above-described embodiment can be achieved.

  In the above embodiment, the sensor chip is attached to the case via the package. However, the sensor chip may be directly attached to the case without the package.

  Moreover, in the said embodiment, although the pressure sensor which measures the pressure of the fluid (water etc.) in a washing machine was illustrated, it is also possible to apply this invention to the pressure sensor of another use.

  For example, the present invention can be applied to a pressure sensor that measures the pressure of a fluid (water or hot water) stored in a bathtub or a pressure sensor that measures the pressure of a fluid (water or hot water) in a water heater.

  In addition, specifications (shape, size, layout, etc.) of the package, case, and other details can be changed as appropriate.

DESCRIPTION OF SYMBOLS 10 Pressure sensor 21 Diaphragm part 21a Surface 22 Semiconductor substrate 22a Surface 25 Conductive thin film 25a Surrounding part 25b Element covering part 26 Insulating film 26a Surface O Center point P1, P2, P3, P4 Piezoresistive element P1a, P2a, P3a, P4a Surface

Claims (5)

A semiconductor substrate having a diaphragm portion; a piezoresistive element that detects a pressure applied to the diaphragm portion as a change in resistance; an insulating film that covers the surface of the diaphragm portion and the semiconductor substrate including the piezoresistive element surface; A conductive thin film covering at least the surface of the insulating film corresponding to the surface of the piezoresistive element,
The pressure sensor, wherein the conductive thin film covers only a part of the surface of the insulating film corresponding to the surface of the diaphragm portion.   The pressure sensor according to claim 1, comprising a plurality of the piezoresistive elements.   3. The pressure sensor according to claim 1, wherein the conductive thin film has a point-symmetric shape with respect to a center point of the diaphragm portion in a plan view. The conductive thin film is composed of an enclosing portion disposed so as to surround the diaphragm portion outside the region of the diaphragm portion in plan view, and an element covering portion disposed on the piezoresistive element. ,
The pressure sensor according to any one of claims 1 to 3, wherein the element covering portion is connected to a portion located in the vicinity of the element covering portion of the surrounding portion.   The pressure sensor according to claim 4, wherein the element covering portions are arranged separately on the plurality of piezoresistive elements.

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