Patent Publication Number: US-2019195718-A1

Title: Pressure Sensor

Description:
TECHNICAL FIELD 
     The present invention relates to a pressure sensor. In particular, the invention relates to a pressure sensor using a pressure detection element using a piezoresistance effect for example. 
     BACKGROUND ART 
     Conventionally, as a pressure sensor for detecting a fluid pressure, a pressure sensor such as a semiconductor pressure sensor chip using a piezoresistance effect has been known as disclosed in Patent Literature 1 for example. 
     A piezo resistance-type pressure detection element is structured to include a diaphragm consisting of material having the piezoresistance effect (e.g., monocrystalline silicon) and a bridge circuit that forms a plurality of semiconductor strain gauges on the diaphragm and that connects these semiconductor strain gauges in a bridge connection manner. A change of the gauge resistance of the semiconductor strain gauges depending on the deformation of the diaphragms can be taken out of the bridge circuit as an electric signal to thereby detect a fluid pressure. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent No. 5044896 
     [PTL 2] Japanese Patent No. 3987386 
     SUMMARY OF INVENTION 
     Technical Problem 
     The pressure sensor using the pressure detection element as described above is configured so that the pressure detection element is fixed by adhesive agent to a support member such as a column or a housing made by metal material such as Fe⋅Ni-base alloy or stainless for example. When the ambient temperature changes, a thermal stress is caused by a difference in the linear expansion coefficient among the pressure detection element, the column member, and the adhesive agent. Specifically, when the ambient temperature declines for example, then the adhesive agent contracts compared with the pressure detection element. When the ambient temperature increases, then the adhesive agent expands compared with the pressure detection element. This thermal stress causes a disadvantage that the pressure detection element has a strain to change the output characteristic of the pressure detection element, which causes a lower sensor output accuracy. Another disadvantage is that, when the thermal stress changes, the viscoelasticity of the adhesive agent requires a long time for the stress to have an equilibrium state, which causes a deteriorated temperature response. 
     Therefore, it is an objective of the present invention to provide a pressure sensor using a pressure detection element using a piezoresistance effect for example by which the strain of the pressure detection element due to a temperature change can be reduced, the accuracy can be improved, and the temperature response can be improved. 
     Solution to Problem 
     In order to solve the above disadvantages, the pressure sensor of the present invention includes: a pressure detection element for detecting a fluid pressure, a support member for supporting the pressure detection element; and an adhesive agent layer formed by coating adhesive agent, for adhesively fixing the pressure detection element and the support member. The adhesive agent layer is composed of two layers of an initial hardening layer and a chip mount hardening layer. 
     The initial hardening layer may be formed in a flat manner on the entire surface of the support member. 
     The initial hardening layer also may be formed to have a shape having a projection portion at the center of the surface of the support member. 
     The support member may have a linear expansion coefficient in a range from 2 to 22 [10 −6  /degrees C.]. 
     The support member may have a linear expansion coefficient in a range from 2.6 to 8.5 [10 −6  /degrees C.]. 
     The adhesive agent layer including the initial hardening layer and the chip mount hardening layer may have a thickness of 5 μm or more. 
     Advantageous Effects of Invention 
     The pressure sensor of the present invention can reduce the strain of the pressure detection element due to a temperature change in the pressure sensor using the pressure detection element using the piezoresistance effect for example, thus providing an improved accuracy and an improved temperature response. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view illustrating the attaching structure of the pressure detection element of the pressure sensor of the present invention; 
         FIG. 2  is a longitudinal sectional view illustrating the entirety of a liquid sealing pressure sensor as an example of the pressure sensor of the present invention; 
         FIG. 3  is a longitudinal sectional view illustrating the attaching structure of the pressure detection element of a conventional pressure sensor; 
         FIG. 4A  illustrates the output characteristic of the pressure detection element when there is no temperature response delay; 
         FIG. 4B  illustrates the output characteristic of the pressure detection element when there is a temperature response delay; 
         FIG. 5A  illustrates the comparison of the output accuracy of the pressure detection element depending on the existence or nonexistence of an adhesive agent layer; 
         FIG. 5B  illustrates the displacement due to a load; 
         FIG. 6  illustrates the correlation between the thickness of the adhesive agent layer and the temperature response; and 
         FIG. 7  is a longitudinal sectional view illustrating another example of the attaching structure of the pressure detection element of the pressure sensor of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following section will describe an embodiment of the present invention with reference to the drawings. 
       FIG. 1  is a longitudinal sectional view illustrating the attaching structure of a pressure detection element  126  of a pressure sensor  100  of the present invention. 
     In  FIG. 1 , the pressure detection element  126  is attached to a support member such as a column  125  via an adhesive agent layer  125 A formed by coated adhesive agent. Thereafter, a lead terminal (not shown) of the pressure detection element  126  and a plurality of lead pins  128  are connected by a wire bonding step by a bonding wire  126   a  made of gold or aluminium. 
     The pressure detection element  126  is a semiconductor pressure sensor chip using a piezoresistance effect for example. The pressure detection element  126  using the piezoresistance effect is mainly composed of a semiconductor substrate unit having a diaphragm consisting of material having a piezoresistance effect (e.g., monocrystalline silicon) and a base unit consisting of glass for example. The semiconductor substrate unit and the base unit are joined by an anodic bonding method for example. A space between the diaphragm of the semiconductor substrate unit and the base unit functions as a reference pressure chamber. The diaphragm of the semiconductor substrate unit includes a plurality of semiconductor strain gauges. These semiconductor strain gauges are bridge-connected to configure a bridge circuit. This bridge circuit allows the deformation of the diaphragm caused by a pressure difference between an outside pressure and the reference pressure chamber to be extracted as an electric signal showing a change of the gauge resistance of the semiconductor strain gauge, thereby detecting the fluid pressure. 
     The column  125  has been described as being formed by Fe⋅Ni-base alloy. However, the invention is not limited to this. The column  125  also may be formed by other metal materials such as stainless. Alternatively, the column  125  may be omitted to achieve the direct fixation on a flat face forming a concave unit of a hermetic glass  124 . 
     The adhesive agent layer  125 A may be silicone-base adhesive agent. For example, the adhesive agent layer  125 A may preferably be the flexible one having an addition type-one component system but also may be gel-like adhesive agent. Silicone-base adhesive agent may be adhesive agent having a low molecular siloxane bond for example. 
     The silicone-base adhesive agent may be, for example, the one in which the substitutional group on a silicon atom of polysiloxane of a base polymer is a fluorinated hydrocarbon group such as a methyl group, a phenyl group, or a trifluoropropyl group. Alternatively, the silicone-base adhesive agent also may be condensation silicone rubber having the following structural formula as a main component. 
     
       
         
         
             
             
         
       
     
     The silicone-base adhesive agent also may be the one including addition type silicone rubber having the following structural formula for example as a main component. 
     
       
         
         
             
             
         
       
     
     The silicone-base adhesive agent may be the one having a two-component system or the condensation or UV-curing one. The silicone-base adhesive agent may be substituted with urethane-base adhesive agent having a two-component system. Fluorine-based adhesive agent also may be used. The fluorine-based adhesive agent may be liquid fluorine elastomer having self adhesiveness or may be a gel-like adhesive agent. 
     The fluorine-based adhesive agent may be substituted, for example, with elastomer having the following structural formula as filling material including fluorinated polyether skeleton and a silicone crosslinking reaction group at an end. 
     
       
         
         
             
             
         
       
     
     The fluorine-based adhesive agent also may be substituted, for example, with perfluoro elastomer having the following structural formula. 
     
       
         
         
             
             
         
       
     
     The fluorine-based adhesive agent also may be substituted, for example, with fluorine rubber having the following structural formula. 
     
       
         
         
             
             
         
       
     
     As shown in  FIG. 1 , the pressure sensor  100  of the present invention is configured so that the adhesive agent layer  125 A is composed of two layers of an initial hardening layer  125 A 1  and a chip mount hardening layer  125 A 2 . In order to maintain the adhesive agent layer  125 A having a predetermined thickness, the initial hardening layer  125 A 1  is prepared, prior to the adhesion of the pressure detection element  126 , by being coated and cured in advance. The initial hardening layer  125 A 1  is entirely formed to have a flat shape. After the initial hardening layer  125 A 1  is coated and cured, the chip mount hardening layer  125 A 2  is coated when the pressure detection element  126  is actually mounted. The initial hardening layer  125 A 1  and the chip mount hardening layer  125 A 2  are made of one material among the above-described materials of the adhesive agent layer  125 A. However, the initial hardening layer  125 A 1  and the chip mount hardening layer  125 A 2  also may be made of different materials that are compatible. As described above, the adhesive agent layer  125 A composed of the two layers of the initial hardening layer  125 A 1  and the chip mount hardening layer  125 A 2  allows the adhesive agent layer  125 A to maintain a predetermined thickness as described later. This can reduce the strain of the pressure detection element  126  due to a temperature change, thus providing an improved accuracy and an improved temperature response. 
     The following section will describe the entire structure of the liquid sealing-type pressure sensor  100  as an example of the pressure sensor of the present invention having the attaching structure of the pressure detection element  126  as described above. 
       FIG. 2  is a longitudinal sectional view illustrating the entirety of the liquid sealing pressure sensor  100  as an example of the pressure sensor of the present invention. 
     In  FIG. 2 , the liquid sealing-type pressure sensor  100  includes a fluid introduction unit  110  that introduces pressure-detected fluid to a pressure room  112 A (which will be described later), a pressure detection unit  120  that detects the pressure of the fluid of the pressure room  112 A, a signal sending unit  130  that sends a pressure signal detected by the pressure detection unit  120  to the exterior, and a cover member  140  that covers the fluid introduction unit  110 , the pressure detection unit  120 , and the signal sending unit  130 . 
     The fluid introduction unit  110  includes a metal-made joint member  111  that is connected to a piping through which pressure-detected fluid is guided and a bowl-like shaped metal base plate  112  that is connected by welding for example to an end connected to the piping of the joint member  111  and another end. 
     The joint member  111  includes a female screw  111   a  screwed in a male screw at the connection of the piping and a port  111   b  to guide, to the pressure room  112 A, the fluid introduced through the piping. The port  111   b  has an opening end connected by welding for example to an opening provided at the center of the base plate  112 . Although the joint member  111  includes the female screw  111   a  in this example, the joint member  111  also may include a male screw. The joint member  111  also may be substituted with a copper-made connection pipe. The base plate  112  has a bowl-like shape expanding to the side opposed to the joint member  111  to form the pressure room  112 A between the base plate  112  and a diaphragm  122  (which will be described later). 
     The pressure detection unit  120  includes a housing  121  having a penetration hole, the diaphragm  122  that isolates the above-described pressure room  112 A from a liquid-sealing room  124 A (which will be described later), a diaphragm protection cover  123  provided at the pressure room  112 A side of the diaphragm  122 , hermetic glass  124  fitted to the interior of the penetration hole of the housing  121 , a liquid-sealing room  124 A in which pressure transmission medium such as silicone oil or fluorine-based inert liquid is filled between the concave unit at the pressure room  112 A side of the hermetic glass  124  and the diaphragm  122 , a column  125  provided in a penetration hole at the center of the hermetic glass  124 , a pressure detection element  126  that is fixed to the column  125  and that is provided in the liquid-sealing room  124 A, a potential adjustment member  127  provided to surround the liquid-sealing room  124 A, a plurality of lead pins  128  fixed to the hermetic glass  124 , and an oil filling pipe  129  fixed to the hermetic glass  124 . 
     The housing  121  is formed by metal material such as Fe⋅Ni-base alloy or stainless for example. The diaphragm  122  and the diaphragm protection cover  123  are both formed by metal material and are both welded at the peripheral edge part of the penetration hole at the pressure room  112 A side of the housing  121 . The diaphragm protection cover  123  is provided in the pressure room  112 A in order to protect the diaphragm  122  and includes a plurality of communication holes  123   a  through which fluid introduced from the fluid introduction unit  110  passes. After the pressure detection unit  120  is assembled, the housing  121  is connected by welding for example at the peripheral edge part of the base plate  112  of the fluid introduction unit  110 . 
     The column  125  is obtained by allowing the pressure detection element  126  to adhere to the liquid-sealing room  124 A side by the adhesive agent layer  125 A. As described above, the pressure sensor  100  of the present invention is configured so that the adhesive agent layer  125 A is composed of the two layers of the initial hardening layer  125 A 1  and the chip mount hardening layer  125 A 2 . The pressure detection element  126  detects the pressure of fluid introduced from the fluid introduction unit  110  to the pressure room  112 A via the diaphragm  122  as the pressure fluctuation of silicone oil for example in the liquid-sealing room  124 A. 
     As disclosed in Patent Literature 2, the potential adjustment member  127  is provided in order to provide the pressure detection element  126  in a zero potential so that a circuit in a chip for example is prevented from being subjected to the adverse influence by a potential generated between a frame ground and a secondary power source. The potential adjustment member  127  is provided between the pressure detection element  126  in the liquid-sealing room  124 A and the diaphragm  122 , is formed by conductive material such as metal, and is connected to a terminal connected to the zero potential of the pressure detection element  126 . 
     The hermetic glass  124  has the plurality of lead pins  128  and the oil filling pipe  129  that are fixed by a hermetic treatment while penetrating therethrough. In this embodiment, the total of eight lead pins  128  are provided as the lead pins  128 . Specifically, three lead pins  128  are used for external input/output (Vout), driving voltage supply (Vcc), and grounding (GND) applications and five lead pins  128  are used as terminals for the adjustment of the pressure detection element  126 . In  FIG. 2 , four lead pins  128  are shown among the eight lead pins  128 . The plurality of lead pins  128  are connected to the pressure detection element  126  by the bonding wire  126   a  made of gold or aluminium for example to constitute the external input/output terminal of the pressure detection element  126 . 
     The oil filling pipe  129  is provided to inject silicone oil or fluorine-based inert liquid for example used as pressure transmission medium in the liquid-sealing room  124 A. After the oil injection, one end of the oil filling pipe  129  is crushed and sealed as shown by the dotted line of  FIG. 2 . 
     The signal sending unit  130  is provided at a side opposed to the pressure room  112 A of the pressure detection unit  120  and includes a terminal base  131  on which the plurality of lead pins  128  are arranged, a plurality of connection terminals  132  that are fixed to the terminal base  131  by adhesive agent  132   a  and that are connected to the plurality of lead pins  128 , a plurality of electric wires  133  electrically connected to outer ends of the plurality of connection terminals  132 , and a static electricity protection layer  134  formed by silicone-base adhesive agent between an upper end of the housing  121  and the terminal base  131 . The static electricity protection layer  134  also may be adhesive agent such as epoxy resin. 
     The terminal base  131  has a substantially circular cylinder-like shape and is provided, at a middle of the circular cylinder, to have a shape having a guide wall to guide the above-described plurality of lead pins  128  and is formed by resin material such as polybutylene terephthalate (PBT). The terminal base  131  is fixed to the upper part of the housing  121  of the pressure detection unit  120  by the adhesive agent used for the static electricity protection layer  134  for example. 
     The connection terminal  132  is formed by metal material and is fixed by the adhesive agent  132   a  in a direction vertical to a side wall of the circular cylinder at the upper side of the above-described fixation wall of the terminal base  131 . In this embodiment, three connection terminals  132  are provided for external input/output (Vout), driving voltage supply (Vcc), and grounding (GND) applications. The three connection terminals  132  have inner ends electrically connected to the corresponding lead pins  128 , respectively. The invention is not limited to this connection method and other connection methods may be used. 
     In this embodiment, three electric wires  133  are provided for the connection to the three connection terminals  132 . The electric wire  133  is obtained by presoldering a core wire  133   a  obtained by peeling the coating of the electric wire  133  formed by polyvinyl chloride (PVC) for example in advance to prepare a bundle of the twisted wire which is electrically-connected to the above-described connection terminal  132  by soldering or welding for example. However, the invention is not limited to this connection method and other connection methods also may be used. The three electric wires  133  are pulled out from the cover member  140  covering the periphery of the pressure sensor  100  and are prepared as a bundle covered by a protection tube (not shown) formed by polyvinyl chloride (PVC) for example. 
     The static electricity protection layer  134  is provided in order to allow the pressure detection unit  120  to have an improved static electricity proof stress without being influenced by the existence or nonexistence of an ESD protection circuit. The static electricity protection layer  134  is mainly coated on an upper end face of the housing  121  so as to cover the upper end face of the hermetic glass  124 . The static electricity protection layer  134  is composed of an annular adhesion layer  134   a  formed by silicone-base adhesive agent and having a predetermined thickness and a coating layer  134   b  that is coated on the entire upper end face of the hermetic glass  124  from which the plurality of lead pins  128  are protruded and that consists of silicone-base adhesive agent. An inner circumferential face is provided that forms a hollow portion of the terminal base  131  and that faces the upper end face of the hermetic glass  124 . This inner circumferential face includes an annular projection  131   a  protruding to the hermetic glass  124 . The annular projection  131   a  has a protrusion length set depending on the viscosity of the coating layer  134   b  for example. The existence of the annular projection  131   a  formed in the manner as described above allows the coated coating layer  134   b  to be partially to be strained and maintained by a surface tension within a small space between the annular projection  131   a  and a part of the inner circumferential face forming the hollow portion of the terminal base  131  that is substantially orthogonal to the upper end face of the hermetic glass  124 . This allows the coating layer  134   b  to be coated without being excessively coated on any one side of the interior of the hollow portion of the terminal base  131 . The coating layer  134   b  is formed on the upper end face of the hermetic glass  124  to have a predetermined thickness. However, the coating layer  134   b  also may be formed, as shown by a part  134   c  of  FIG. 2 , so as to further cover a part of the plurality of lead pins  128  protruding from the upper end face of the hermetic glass  124 . 
     The cover member  140  includes a waterproof case  141  having a substantially-cylindrical shape and covering the periphery of the pressure detection unit  120  and the signal sending unit  130 , a terminal base cap  142  covering the upper part of the terminal base  131 , and an encapsulant  143  to fill the space between the inner circumferential face of the waterproof case  141  and the outer peripheral face of the housing  121  and the outer peripheral face of the terminal base  131 . 
     The terminal base cap  142  is formed by resin material for example. In this embodiment, the terminal base cap  142  is formed to have a shape to seal the upper part of the above-described terminal base  131  having a circular cylinder and is used to cover the upper part of the terminal base  131  prior to the injection of the encapsulant  143  such as urethane-base resin. However, the terminal base cap  142  is not limited to this shape. The terminal base cap  142  may have any shape that is formed to seal the upper part of the terminal base  131  and the upper part of the waterproof case  141  in an integrated manner to be covered after the injection of the encapsulant  143 . Alternatively, another configuration may be used in which another cover member is provided in addition to the terminal base cap  142  so that the upper part of the waterproof case  141  is covered by the cover member after the terminal base cap  142  and the encapsulant  143  are placed. 
     The waterproof case  141  is formed to have a substantially-cylindrical shape by resin material such as polybutylene terephthalate (PBT). The cylindrical shape has a lower end having a flange unit provided in an inward direction. This flange unit is abutted to the signal sending unit  130  inserted through the opening of the upper part of the waterproof case  141  and the outer periphery of the base plate  112  of the fluid introduction unit  110  connected to the pressure detection unit  120 . In this status, the encapsulant  143  is injected to thereby fix interior components such as the pressure detection unit  120 . 
     In this embodiment, the pressure sensor  100  will be described as an example of the pressure sensor of the present invention. However, the invention is not limited to this. The present invention can be applied to all pressure sensors using a pressure detection element using a piezoresistance effect for example. 
     Next, the following section will describe the attaching structure of a conventional pressure detection element. 
       FIG. 3  is a longitudinal sectional view illustrating the attaching structure of a pressure detection element  326  of a conventional pressure sensor  300 . 
     In  FIG. 3 , the pressure detection element  326  of the conventional pressure sensor  300  is attached to a column  325  via an adhesive agent layer  325 A formed by coated adhesive agent. Thereafter, a lead terminal (not shown) of the pressure detection element  326  and the plurality of lead pins  128  are connected by the bonding wire  126   a  made of gold or aluminium by a wire bonding step. The conventional pressure sensor  300  is configured so that the adhesive agent layer  325 A is composed of not two layers but one layer. 
     In the attaching structure of the pressure detection element  326  of the conventional pressure sensor  300  shown in  FIG. 3 , the strain of the pressure detection element  326  is caused by a difference in the linear expansion coefficient among the pressure detection element  326 , the column  325 , and the adhesive agent layer  325 A, which causes a disadvantage of deteriorated measurement accuracy and temperature response. Specifically, when the ambient temperature decreases for example, the adhesive agent layer  325 A contracts compared with the pressure detection element  326 . When the ambient temperature increases, the adhesive agent layer  325 A expands compared with the pressure detection element  326 . Thus, a thermal stress is caused by the difference in the linear expansion coefficient among the pressure detection element  326 , the column  325 , and the adhesive agent layer  325 A. This thermal stress causes the strain of the pressure detection element  326  to cause a change in the output characteristic of the pressure detection element, which causes a change in the output accuracy of the pressure detection element  326 . Furthermore, a change of the thermal stress requires, due to the viscoelasticity of the adhesive agent layer  325 A, the stress to have an equilibrium state for a certain time, which causes a deteriorated temperature response. The following section will describe this. 
       FIG. 4A  illustrates the output characteristic of the pressure detection element  326  when there is no temperature response delay.  FIG. 4B  illustrates the output characteristic of the pressure detection element  326  when there is a temperature response delay. 
     Graphs shown in  FIG. 4A  and  FIG. 4B  both show the output accuracy of the pressure detection element  326  under such temperature cycle conditions that causes a change from a high temperature status at a predetermined time to a low temperature status at a predetermined time. It can be seen that the graphs shown in  FIG. 4A  and  FIG. 4B  both show that the pressure detection element  326  has deteriorated output accuracy in the high temperature status. In addition, it can be seen that the graph shown in  FIG. 4B  shows that the pressure detection element  326  has a further-deteriorated output accuracy in a part including a deteriorated temperature response delay. 
     Generally, the high temperature (or the low temperature) status shown in  FIG. 4A  and  FIG. 4B  has an output accuracy of the pressure detection element  326  that linearly changes. Thus, the correction can be performed by the interior of the pressure detection element  326  or an external circuit. On the other hand, there is a disadvantage that a deteriorated output accuracy of the pressure detection element  326  caused by the temperature response delay is difficult to be corrected because the deteriorated output accuracy changes nonlinearly. Thus, the following section will describe what causes the temperature response delay. 
       FIG. 5A  shows the comparison of the output accuracy of the pressure detection element  326  depending on the existence or nonexistence of the adhesive agent layer  325 A.  FIG. 5B  illustrates the displacement due to a load. 
     The graph shown in  FIG. 5A  shows the output accuracy of the pressure detection element  326  when the temperature changes from a high temperature to a low temperature. As described above, the pressure detection element  326  is attached to the column  325  via the adhesive agent layer  325 A. The graph shows the comparison between a case where the adhesive agent layer  325 A is attached during the measurement and a case where the adhesive agent layer  325 A is not attached. It can be seen that, when the adhesive agent layer  325 A is not attached, no temperature response delay is caused in the output accuracy of the pressure sensor  300 . 
     The graph shown in  FIG. 5B  shows, from the upper side, the displacement of the elasticity, viscosity, and plasticity when a load is applied. Among the elasticity, viscosity, and plasticity, the first displacement of the elasticity is followed by the return to the original value without a response delay. On the other hand, the displacement of the plasticity is followed by no change without a response delay. On the other hand, the displacement of the viscosity is caused together with a response delay and is followed by no return to the original value. Specifically, the temperature response delay is caused by the adhesive agent layer  325 A having viscoelasticity. The following section will describe how to cope with this. 
       FIG. 6  shows the correlation between the thickness and the temperature response of the adhesive agent layer  325 A. 
     In  FIG. 6 , the vertical axis shows the output accuracy of the pressure detection element  326  after the temperature change from a high temperature to a low temperature and the horizontal axis shows the thickness of the adhesive agent layer  325 A. The measurement was performed by forming projections at a plurality of positions in the column  325  by laser irradiation to adjust the thickness of the adhesive agent layer  325 A. The result showed that the adhesive agent layer  325 A having a thickness larger than 5 μm caused the pressure detection element  326  to resolve the deterioration of output accuracy due to a temperature response delay. This is presumably due to that the adhesive agent layer  325 A having a thickness smaller than a predetermined thickness causes the pressure detection element  326  to have strain due to a thermal stress due to a difference in the linear expansion coefficient among the pressure detection element  326 , the column  325 , and the adhesive agent layer  325 A to thereby cause the pressure detection element  326  to have a deteriorated output accuracy and the adhesive agent layer  325 A having a thickness larger than a predetermined thickness provides the absorption of the thermal stress due to a difference in the linear expansion coefficient due to the elasticity of the adhesive agent layer  325 A to thereby suppress the strain of the pressure detection element  326 . 
     Regarding the linear expansion coefficients at a normal temperature of the respective members used in the pressure sensor  100  of the present invention, glass used as a base unit of the pressure detection element  126  has a linear expansion coefficient of 9.0 [10 −6  /degrees C.] and the adhesive agent layer  125 A has a linear expansion coefficient of about 300 [10 −6  /degrees C.]. Regarding the linear expansion coefficient of materials of the column  125  at a normal temperature, Fe⋅Ni-base alloy has a linear expansion coefficient of 5.0 [10 −6 /degrees C.], stainless steel has a linear expansion coefficient of 17.3 [10 −6  /degrees C.], brass has a linear expansion coefficient of 20.8 [10 −6  /degrees C.], and silicon has a linear expansion coefficient of 2.6 [10 −6  /degrees C.]. Thus, the column  125  has a linear expansion coefficient of 2-22 [10 −6  /degrees C.] and preferably has a linear expansion coefficient of 2.6-8.5 [10 −6  /degrees C.]. The reason is that the hermetic glass  124  has a linear expansion coefficient of 8.5(8-10) [10 −6  /degrees C.] and the column  125  desirably has a linear expansion coefficient lower than this. 
     Next, the following section will describe another embodiment of the attaching structure of the pressure sensor of the present invention. 
       FIG. 7  is a longitudinal sectional view illustrating another example  700  of the attaching structure of a pressure detection element  726  of the pressure sensor of the present invention. 
     In  FIG. 7 , as in the pressure sensor  100  shown in  FIG. 1 , the pressure detection element  726  is attached to a column  725  via an adhesive agent layer  725 A formed by coated adhesive agent. Thereafter, a lead terminal (not shown) of the pressure detection element  726  and the plurality of lead pins  128  are connected in a wire bonding step by the bonding wire  126   a  made of gold or aluminium. Similar members will be denoted with similar reference numerals and will not be further described. 
     A pressure sensor  700  is different from the pressure sensor  100  shown in  FIG. 1  in that the adhesive agent layer  725 A composed of two layers of an initial hardening layer  725 A 1  and a chip mount hardening layer  725 A 2  is configured so that the initial hardening layer  725 A 1  is formed to have a projection portion at the center. By allowing the initial hardening layer  725 A 1  to have a shape having a projection portion at the center as described above, the adhesive agent layer  725 A can have a thickness maintained at a predetermined thickness and the strain of the pressure detection element  726  due to a temperature change can be reduced and the accuracy and the temperature response can be improved. 
     The adhesive agent layers  125 A and  725 A each of which is composed of two layers have been described with reference to  FIG. 1  and  FIG. 7 . The shapes of the initial hardening layers  125 A 1  and  725 A 1  are not limited to the above-described shapes and other shapes also may be used. 
     As described above, the pressure sensor of the present invention can reduce the strain of the pressure detection element due to a temperature change in the pressure sensor using the pressure detection element using the piezoresistance effect for example, thus providing an improved accuracy and an improved temperature response. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  300 ,  700  Pressure sensor 
           110  Fluid introduction unit 
           111  Joint member 
           111   a  Female screw 
           111   b  Port 
           112  Base plate 
           112 A Pressure room 
           120  Pressure detection unit 
           121  Housing 
           122  Diaphragm 
           123  Diaphragm protection cover 
           123   a  Communication hole 
           124  Hermetic glass 
           124 A Liquid-sealing room 
           125 ,  325 ,  725  Column 
           125 A,  325 A,  725 A Adhesive agent layer 
           125 A 1 ,  725 A 1  Initial hardening layer 
           125 A 2 ,  725 A 2  Chip mount hardening layer 
           126 ,  326 ,  726  Pressure detection element 
           126   a  Bonding wire 
           127  Potential adjustment member 
           128  Lead pin 
           129  Oil filling pipe 
           130  Signal sending unit 
           131  Terminal base 
           132  Connection terminal 
           132   a  Adhesive agent 
           133  Electric wire 
           133   a  Core wire 
           134  Static electricity protection layer 
           134   a  Adhesion layer 
           134   b  Coating layer 
           134   c  Part 
           140  Cover member 
           141  Waterproof case 
           142  Terminal base cap 
           143  Encapsulant