JP2008185460A - Pressure sensor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To join a metal stem to a sensor chip without the use of low-melting glass, and to constitute the metal stem using a material other than Kovar (R). <P>SOLUTION: The back surface of a sensor chip 30 is jointed directly to the front surface of a diaphragm 21. Thus, sensor chip 30 does not need to be jointed to the diaphragm 21 by using the low-melting glass, and the metal stem 20 does not need to be constituted with Kovar, or the like, differently from the conventional structure employing the low-melting glass. Thus, the metal stem 20 can be constituted with SUS, or the like, that is inexpensive and is processed more easily than Kovar, or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pressure sensor including a sensor chip in which a strain gauge is formed on a stem in which a metal diaphragm is formed, and a manufacturing method thereof.

Conventionally, as a pressure sensor, for example, in Patent Document 1, a sensor chip made of a silicon chip in which a strain gauge is formed on a metal stem on which a diaphragm is formed is joined with low-melting glass so that the pressure sensor can be detected. There is. In this pressure sensor, a high pressure resistance is realized by configuring the diaphragm with metal.
Japanese Patent Publication No.7-111461

  However, in the pressure sensor, it is necessary to use a material such as Kovar having a thermal expansion coefficient close to that of the silicon chip used for the sensor chip in order to suppress thermal stress. Such a material such as Kovar is poor in workability and expensive compared with general SUS and the like. Further, since the metal stem is made of a different material from the metal constituting the housing in which the metal stem is accommodated, the metal stem cannot be joined to the housing by welding.

  Further, during the sintering in the joining process for joining the sensor chip to the diaphragm, the molten low melting point glass flows, so that the sensor chip mounted thereon moves. For this reason, in order to ensure the accuracy of pressure detection, the diameter of the diaphragm must be increased, and there is a problem that the metal stem is prevented from being miniaturized.

  In view of the above points, the first object of the present invention is to enable a metal stem and a sensor chip to be joined without using low-melting glass, and to allow the metal stem to be made of a material other than Kovar. A second object is to allow the metal stem to be made of the same material as the housing.

  In order to achieve the above object, the present invention is characterized in that the surface of the diaphragm in the metal stem and the back surface of the sensor chip are directly joined.

  Thus, the back surface of the sensor chip is directly joined to the surface of the diaphragm. For this reason, it is not necessary to bond the sensor chip to the diaphragm using the low melting point glass, and there is no need to configure the metal stem with Kovar or the like as in the conventional structure using the low melting point glass. For this reason, it is easy to process compared to Kovar or the like, and it is possible to configure the metal stem with an inexpensive material such as SUS.

  For example, it becomes possible to directly bond the surface of the diaphragm and the back surface of the sensor chip by activating them.

  In this case, it is preferable that the thickness (L1) of the diaphragm in the metal stem and the thickness (L2) of the sensor chip are the same. When a sensor chip or diaphragm undergoes thermal expansion or contraction during manufacturing or when pressure is applied, one of these will be subject to compressive stress and the other will be subject to tensile stress. The sensor chip thickness is the thickness of the diaphragm. If the Si Young's modulus and the Young's modulus of the material constituting the metal stem are substantially equal, these boundary portions become stress neutral points. Therefore, the stress applied to the boundary between the sensor chip and the diaphragm can be reduced, and the durability and reliability of the joint surface between the sensor chip and the diaphragm can be improved.

  The sensor chip can be constituted by an SOI substrate (36) in which a silicon layer (36a) and a support substrate (36b) are bonded together via an insulating film (36c), and a strain gauge formed on the silicon layer. By configuring the sensing unit at (32) and activating the back surface of the support substrate, it is possible to directly bond to the surface of the diaphragm. In this case, the SOI substrate constituting the sensor chip may have a mesa structure in which a strain gauge is surrounded by an insulating film (36d) and a portion of the silicon layer excluding the strain gauge is removed.

  The material constituting the support substrate is preferably a material whose thermal expansion coefficient is located between the thermal expansion coefficient of the material constituting the metal stem and the thermal expansion coefficient of silicon.

  As described above, when the thermal expansion coefficient of the support substrate is between the thermal expansion coefficient of Si and the material of the metal stem, the stress generated by the support substrate is bonded to the diaphragm and the support substrate. It is dispersed stepwise between the surfaces and between the support substrate and the Si layer. Therefore, it is possible to further improve the durability and reliability of the joint surface between the sensor chip and the diaphragm.

  Further, if the support substrate is made of an insulator, an electrostatic potential can be generated between the back surface of the sensor chip and the surface of the diaphragm by generating a potential difference between the sensor chip and the metal stem. In addition to activation, bonding using electrostatic attraction can be achieved. Therefore, the stability (yield) at the time of joining of the joint surfaces of the sensor chip and the diaphragm can be further improved.

  Moreover, it is preferable to make the corner | angular part of the back surface of a sensor chip into a taper obtuse angle. With such a shape, it is possible to disperse stress that tends to concentrate at the corners on the back surface of the sensor chip. Therefore, the durability and reliability of the joint surface between the sensor chip and the diaphragm can be improved.

  When the sensor chip is composed of single crystal silicon (31), insulating films (24, 37) can be disposed between the back surface of the single crystal silicon and the surface of the diaphragm. In this case as well, by generating a potential difference between the sensor chip and the metal stem, an electrostatic attractive force can be generated between the back surface of the sensor chip and the surface of the diaphragm. Can be joined using attractive force. Therefore, the stability (yield) at the time of joining of the joint surfaces of the sensor chip and the diaphragm can be further improved.

  In addition, although the case where this invention was grasped | ascertained as a product invention was shown here, this invention can also be grasped | ascertained as a method invention.

  Moreover, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a diagram showing an overall cross-sectional configuration of a pressure sensor 100 according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a circled portion A in FIG. 1, specifically, the metal stem 20 and the sensor chip 30.

  The pressure sensor 100 is attached to, for example, a fuel pipe (not shown) in a fuel injection system (for example, a common rail) of an automobile, and is used to detect the pressure of fuel as a pressure medium in the fuel pipe.

  As shown in FIG. 1, the pressure sensor 100 includes a housing 10. The housing 10 is directly attached to the fuel pipe, and an attachment screw 11 is formed on the outer peripheral surface thereof. A pressure introduction passage 12 is formed in the housing 10. The pressure introduction passage 12 communicates with the inside of the fuel pipe in a state where the housing 10 is attached to the fuel pipe, and a pressure medium to be detected is introduced from one end side (lower side in FIG. 1). ing.

  Here, as a material of the housing 10, SUS (for example, SUS430, SUS304, SUS630, etc.) having corrosion resistance can be adopted. In addition, carbon steel (for example, S15C, etc.) having both corrosion resistance and high strength that has been subjected to Zn plating for improving corrosion resistance, XM7 having corrosion resistance, or the like can also be used as the material of the housing 10.

  A metal stem 20 having a hollow stepped cylindrical shape is disposed in the pressure introduction passage 12 of the housing 10. The metal stem 20 has a thin-walled pressure detecting diaphragm (detecting portion in the present invention) 21 at one end side, and an opening 22 for guiding pressure to the diaphragm 21 at the other end side. Yes. Further, a stepped portion 23 having a diameter increased in a taper shape is formed at an intermediate portion in the axial direction on the outer peripheral surface of the metal stem 20.

  On the other hand, the pressure introduction passage 12 of the housing 10 is configured as a stepped inner hole having a shape corresponding to the outer shape of the metal stem 20, and has an inner diameter on the other end side than an inner diameter on one end side (pressure introduction side). Is reduced. Thereby, a tapered seat surface 13 corresponding to the step portion 23 of the metal stem 20 is formed on the inner surface of the pressure introduction passage 12.

  Further, the pressure introduction passage 12 has a diameter equivalent to the outer diameter of the metal stem 20 on the pressure introduction side of the seating surface 13 and a diameter smaller than the inner diameter of the pressure introduction passage 12 on the pressure introduction side. An arrangement unit 14 is configured. The end portion 14a on the pressure introduction side in the stem placement portion 14 is flush with the end portion on the opening portion 22 side in the metal stem 20, and the end portion 14a of the stem placement portion 14 and the end portion of the metal stem 20 are all over. The metal stem 20 is fixed to the stem placement portion 14 by being the welded welded portion 15. Since the metal stem 20 is welded in a state in which the step portion 23 is pressed against the seat surface 13 side, a force that presses the step portion 23 against the seat surface 13 side acts even after welding.

  In this way, the seal portion K is formed by the stepped portion 23 and the seating surface 13 that are in close contact with each other, and specifically between the metal stem 20 and the housing 10, specifically, the outer peripheral surface of the metal stem 20 and the inner surface of the pressure introduction passage 12. The space between them is sealed. This sealing is performed by pressing the step portion 23 of the metal stem 20 against the seat surface 13 in the pressure introduction passage 12 in the housing 10 from the other end side to the one end side of the metal stem 20. ing. For this reason, the direction of the force that presses the outer peripheral surface of the metal stem 20 against the housing 10, that is, the direction of the force that presses the step 23 against the seat surface 13, and the pressure applied to the metal stem 20 when the pressure is introduced into the pressure introduction passage 12. The direction is the same. For this reason, the pressing force is increased by the applied pressure.

  Accordingly, the surface pressure of the seal portion K formed by abutting and pressing the outer peripheral surface (step portion 23) of the metal stem 20 against the housing 10 (seat surface 13) rises at the time of pressure detection. A decrease in the surface pressure of K can be prevented. And the higher the pressure to be detected, the higher the surface pressure of the seal part K and the better effect of improving the sealing performance.

  A sensor chip 30 made of single crystal Si (silicon) is bonded to the surface of the diaphragm 21 of the metal stem 20 by direct bonding. Thus, since the sensor chip 30 mainly made of Si is bonded to the metal stem 20, the material of the metal stem 20 is selected in consideration of the Young's modulus close to that of Si. Further, the material of the metal stem 20 is considered to be high strength because it receives an ultra-high pressure, easy to process, and the same material as the housing 10 so that the housing 10 can be welded. There is also a need. For this reason, in this embodiment, the same SUS as the material of the housing 10 is used as the material of the metal stem 20.

  The sensor chip 30 functions as a strain gauge that guides the pressure introduced into the metal stem 20 from the opening 22 to the diaphragm 21 and detects strain generated when the diaphragm 21 is deformed by the pressure.

  As shown in FIG. 2, the sensor chip 30 includes a single crystal Si 31, a strain gauge 32, an insulating film 33, a wiring part 34, and a protective film 35 that covers the wiring part 34. The strain gauge 32 constitutes a sensing portion, and is formed in a surface layer portion of the single crystal Si 31 and is constituted by, for example, an impurity layer arranged in a Wheatstone bridge shape. The insulating film 33 covers the single crystal Si 31 and exposes a desired position of the strain gauge 32 through the contact hole 33a. The wiring part 34 is electrically connected to a desired position of the strain gauge 32. The protective film 35 covers the wiring part 34 and exposes the wiring part 34 in a region to be a pad part. The sensor chip 30 configured as described above is bonded to the diaphragm 21 on the back side thereof, that is, on the side opposite to the surface on which the strain gauge 32 and the like are formed.

  Further, a diaphragm 21 of the metal stem 20 protrudes from the other end side of the pressure introduction passage 12 in the housing 10, and a ceramic substrate 50 is disposed on the housing 10 by bonding or the like on the outer periphery of the diaphragm 21. . An IC chip 52 such as an amplifier IC chip that amplifies the output of the sensor chip 30 or a characteristic adjustment IC chip is fixed to the substrate 50 with an adhesive.

  These IC chips 52 are connected to conductors (wiring portions) of the ceramic substrate 50 by aluminum thin wires 54 formed by wire bonding. Further, pins 56 for electrical connection to the connector terminal 60 are joined to the conductor of the ceramic substrate 50 by silver solder.

  The connector terminal 60 is an assembly in which a terminal 62 is formed by insert molding on a resin 64. The terminal 62 and the ceramic substrate 50 are joined to the pin 56 by laser welding. Further, the connector terminal 60 is fixedly held between the connector case 70 and the housing 10, and the terminal 62 can be electrically connected to an ECU or the like of the automobile via a wiring member.

  The connector case 70 constitutes the outer shape of the connector terminal 60, and is integrated with the housing 10 assembled via the O-ring 80 to form a package. The sensor chip 30 in the package, various ICs, electrical connection The part is protected from moisture and mechanical external force. As the material of the connector case 70, highly hydrolyzable PPS (polyphenylene sulfide) or the like can be adopted.

  A method for assembling the pressure sensor 100 having such a configuration will be described with reference to FIGS. FIG. 3 is a diagram showing a disassembled state of each part before assembly in a cross section corresponding to FIG. 1 above. Basically, each part is assembled along the one-dot chain line in FIG. It has become. FIG. 4 is a view showing a state in which the sensor chip 30 is directly joined to the metal stem 20.

  First, the sensor chip 30 is directly bonded to the metal stem 20. Specifically, as shown in FIG. 4, the back surface of the sensor chip 30 and the surface of the diaphragm 21 of the metal stem 20 are cleaned as necessary, and then the sensor chip 30 is held by the clamping device 102 in the vacuum chamber 101. Hold it. Then, after vacuuming with the vacuum pump 103, the beam irradiator 104 irradiates the back surface of the sensor chip 30 and the surface of the diaphragm 21 of the metal stem 20 with an argon high-speed beam. Thereby, the back surface of the sensor chip 30 and the surface of the diaphragm 21 are activated, and a bond that easily reacts with other atoms is exposed. Thereafter, the clamping device 102 is moved, and the back surface of the sensor chip 30 is joined to the surface of the diaphragm 21.

  Normally, even if the surface is activated, the back surface of the sensor chip 30 and the surface of the diaphragm 21 are covered with an oxide film, water molecules, and the like. Therefore, even if an attempt is made to join the back surface of the sensor chip 30 and the surface of the diaphragm 21, High bond strength cannot be expected. However, in the vacuum chamber 101, when the surface is activated, there is no molecule that covers the back surface of the sensor chip 30 or the surface of the diaphragm 21, so that the surface is activated so that it can easily react with other atoms. The state where the hand is exposed can be maintained, and when the back surface of the sensor chip 30 is joined to the surface of the diaphragm 21, a chemical reaction between atoms can be promoted to exhibit a high bonding force. Such direct bonding is called normal temperature (low temperature) direct bonding, and does not require a heating step. For example, the sensor chip 30 can be bonded to the diaphragm 21 at room temperature.

Although the case where an argon high-speed beam is used has been described here, it is only necessary to remove the surface layer portion of the back surface of the sensor chip 30 and the surface of the diaphragm 21, and an ion beam different from argon, and also plasma (O ₂ plasma or N ₂ Sputter etching using plasma or the like can be used.

  Thus, the metal stem 20 to which the sensor chip 30 is coupled is inserted from one end side (diaphragm 21 side) into one end side (pressure introduction side) of the pressure introduction passage 12 of the housing 10. When the metal stem 20 is inserted up to the stem placement portion 14 in the pressure introduction passage 12, the pressure introduction side end 14 a and the metal stem 20 of the stem placement portion 14 are pressed while the stepped portion 23 is pressed against the seat surface 13 side. Welding is performed by irradiating a laser along the boundary portion to form a welded portion 15. Thereby, the step part 23 of the metal stem 20 and the seating surface 13 of the housing 10 are tightly sealed, and the sealing performance of the communication part between the opening 22 of the metal stem 20 and the pressure introduction passage 12 of the housing 10 is ensured. At the same time, the metal stem 20 is fixed at the weld 15 as shown in FIG.

  Next, the ceramic substrate 50 on which the chip 52 and the pin 56 are mounted is fixed to a portion on the other end side of the pressure introducing passage 12 in the housing 10 with an adhesive or the like. Then, by performing wire bonding, the sensor chip 30 and the conductor (wiring portion) of the ceramic substrate 50 are electrically connected by the thin wire 54.

  Next, the connector terminal 60 and the pin 56 are joined by laser welding (YAG laser welding or the like). Next, the connector case 70 and the housing 10 are fixed by assembling the connector case 70 to the housing 10 via the O-ring 80 and caulking the end of the housing 10. Thus, the pressure sensor 100 shown in FIG. 1 is completed.

  The pressure sensor 100 is connected and fixed to the fuel pipe by directly coupling and attaching the screw 11 of the housing 10 to a screw portion formed in the fuel pipe (not shown). When the fuel pressure (pressure medium) in the fuel pipe is introduced from one end side of the pressure introduction passage 12 and guided from the opening 22 of the metal stem 20 to the inside (hollow portion) of the metal stem 20, The diaphragm 21 is deformed by the pressure.

  The deformation of the diaphragm 21 is converted into an electrical signal by the sensor chip 30, and this signal is processed by the ceramic substrate 50 or the like constituting the sensor processing circuit to perform pressure detection. Then, based on the detected pressure (fuel pressure), the fuel injection control is performed by the ECU or the like. Although the processing circuit is built in the ceramic substrate 50, it may be integrated into the sensor chip 30 without providing the ceramic substrate 50 separately. When the processing circuit is integrated in the sensor chip in this way, the above parts can be eliminated, and the number of parts can be reduced and the apparatus can be downsized.

  In the pressure sensor 100 of the present embodiment described above, the back surface of the sensor chip 30 is directly bonded to the surface of the diaphragm 21. For this reason, it is not necessary to join the sensor chip 30 to the diaphragm 21 using the low melting point glass, and there is no need to configure the metal stem 20 with Kovar or the like as in the conventional structure using the low melting point glass. For this reason, the metal stem 20 can be configured by SUS or the like which is easy to process and inexpensive compared to Kovar or the like.

  Further, if the metal stem 20 can be made of a material different from Kovar or the like in this way, the metal stem 20 can be made of the same material as that of the housing 10. Thereby, the metal stem 20 and the housing 10, specifically, the stem placement portion 14 can be fixed by the welded portion 15.

(Second Embodiment)
A second embodiment of the present invention will be described. The pressure sensor 100 of this embodiment is obtained by changing the thickness of the sensor chip 30 with respect to the first embodiment, and the other parts are the same as those of the first embodiment, and therefore only different parts will be described.

  FIG. 5 is an enlarged cross-sectional view showing the relationship between the metal stem 20 and the sensor chip 30 in the pressure sensor 100 of the present embodiment. As shown in FIG. 5, in this embodiment, when the thickness of the diaphragm 21 is L1, the thickness L2 of the sensor chip 30 is also the same as the thickness L1 of the diaphragm 21. Specifically, a strain gauge 32, an insulating film 33, and the like are formed in the single crystal Si 31 constituting the sensor chip 30, and then the back surface of the single crystal Si 31 is ground and polished, so that the thickness L2 of the sensor chip 30 is reduced to a diaphragm. It is the same as the thickness L1 of 21.

  With such a configuration, the following effects can be obtained. That is, when the sensor chip 30 or the diaphragm 21 is thermally expanded or contracted during manufacturing or when pressure is applied, one of them is subjected to compressive stress and the other is subjected to tensile stress. When L2 is equal to the thickness L1 of the diaphragm 21, the Young's modulus of Si is approximately 170 GPa and the Young's modulus of SUS is approximately equal to 190 GPa, so these boundary portions become stress neutral points. Therefore, the stress applied to the boundary portion between the sensor chip 30 and the diaphragm 21 can be reduced, and the durability and reliability of the joint surface between the sensor chip 30 and the diaphragm 21 can be improved.

(Third embodiment)
A third embodiment of the present invention will be described. In the first and second embodiments, the sensor chip 30 is configured using the single crystal Si31. However, in the present embodiment, the sensor chip 30 is configured using the SOI substrate. Others are the same as in the first embodiment.

  FIG. 6 is a cross-sectional view of the sensor chip 30 of the pressure sensor 100 of the present embodiment. As shown in this figure, a strain gauge 32, an insulating film 33, a wiring portion 34 and a protective film 35 are formed on an SOI substrate 36. The SOI substrate 36 is configured by bonding an Si layer 36a and a support substrate 36b via an insulating film 36c. After bonding the silicon substrate to the support substrate 36b, the silicon substrate is ground and polished. It is formed by a method of forming the Si layer 36a or a method of forming a Si layer 36a by depositing a silicon thin film on the support substrate 36b or by solid-phase growth and then crystallizing it by laser annealing or the like. The strain gauges 32 are formed in the Si layer 36a, and the strain gauges 32 are insulated from each other by surrounding the strain gauges 32 with an insulating film 36d.

  By using such an SOI substrate 36, a high-temperature operation of the sensing unit constituted by the strain gauge 32 built in the sensor chip 30 becomes possible. As a result, the pressure sensor 100 can be applied to engine combustion pressure measurement or the like in the engine combustion chamber.

(Modification 1 of 3rd Embodiment)
FIG. 7 is a view showing a modified example of the sensor chip 30 shown in the third embodiment. The sensor chip 30 is configured by using the SOI substrate 36, but other than the strain gauge 32 in the Si layer 36 a. By removing the portion, the strain gauge 32 has a mesa structure. Thus, when the strain gauge 32 is insulated by being surrounded by the insulating film 36d, the strain gauge 32 may have a mesa structure.

(Modification 2 of 3rd Embodiment)
Although various commonly used substrates can be applied to the support substrate 36b of the SOI substrate 36 shown in the third embodiment, the thermal expansion coefficient thereof is that of Si (~ 33 × 10 ⁻⁷ / ° C.) to a material having a thermal expansion coefficient of the material of the metal stem 20 (for example, a material having a thermal expansion coefficient (˜170 × 10 ⁻⁷ / ° C.) when the metal stem 20 is made of SUS304). It is preferable that the support substrate 36b is constructed.

  Since the back surface of the sensor chip 30, that is, when the support substrate 36 b is bonded to the surface of the diaphragm 21, since it is performed by direct bonding, it is possible to bond these at room temperature, and between the support substrate 36 b and the diaphragm 21 at the time of bonding. The stress generated on the joint surface can be made zero. However, due to a temperature change during use of the pressure sensor 100, a stress is generated on the joint surface between the support substrate 36b and the diaphragm 21 along with the temperature change.

  At this time, when the single crystal Si 31 is directly bonded to the surface of the diaphragm 21 without using the support substrate 36b as in the first embodiment, a stress corresponding to the difference between these thermal expansion coefficients is generated. However, in the third embodiment, the support substrate 36b is sandwiched between them. Therefore, if the thermal expansion coefficient of the support substrate 36b is between the thermal expansion coefficient of Si and the thermal expansion coefficient of the material of the metal stem 20, in the structure of the first embodiment, between the single crystal Si 31 and the diaphragm 21. On the other hand, a large stress is generated in the substrate, but by the support substrate 36b, the stress generated between the bonding surface of the diaphragm 21 and the support substrate 36b and between the support substrate 36b and the Si layer 36a is stepped. Can be dispersed. Therefore, the durability and reliability of the joint surface between the sensor chip 30 and the diaphragm 21 can be further improved.

As a material in which the thermal expansion coefficient of the support substrate 36b is between the thermal expansion coefficient of Si and the thermal expansion coefficient of the material of the metal stem 20 as described above, for example, 7059 glass (used as a photomask or TFT substrate). Corning glass can be applied to thermal expansion coefficient α = ˜46 × 10 ⁻⁷ / ° C.) or alumina (thermal expansion coefficient α = ˜70 × 10 ⁻⁷ / ° C.).

(Fourth embodiment)
A fourth embodiment of the present invention will be described. The pressure sensor 100 of the present embodiment is obtained by changing the shape of the corner on the back surface side of the sensor chip 30 with respect to the first embodiment, and is otherwise the same as the first embodiment. Only explained.

  FIG. 8 is an enlarged cross-sectional view showing the metal stem 20 and the sensor chip 30 in the pressure sensor 100 of the present embodiment. As shown in FIG. 8, in this embodiment, the corner of the back surface of the sensor chip 30 (the back surface of the single crystal Si 31) is removed, and the corner of the contact surface of the sensor chip 30 with respect to the surface of the diaphragm 21 is tapered. An obtuse angle is set.

  Thus, when the corners on the back surface of the sensor chip 30 are tapered, the following effects can be obtained. Specifically, when the sensor chip 30 or the diaphragm 21 undergoes thermal expansion / contraction, and stress is generated on these contact surfaces, the end of the contact surface between the sensor chip 30 and the diaphragm 21, that is, the back surface of the sensor chip 30. Stress tends to concentrate on the corners. The concentrated stress can be relaxed so that it can be dispersed at the corners on the back surface of the sensor chip 30. For this reason, it becomes possible to disperse the stress as the angle of the corner of the back surface of the sensor chip 30 increases. Therefore, the durability and reliability of the joint surface between the sensor chip 30 and the diaphragm 21 can be improved by tapering the corners on the back surface of the sensor chip 30 as in the present embodiment.

(Fifth embodiment)
A fifth embodiment of the present invention will be described. The pressure sensor 100 of the present embodiment is obtained by changing the shape of the corner on the back surface side of the sensor chip 30 with respect to the first embodiment, and is otherwise the same as the first embodiment. Only explained.

  FIG. 9 is an enlarged cross-sectional view showing the metal stem 20 and the sensor chip 30 in the pressure sensor 100 of the present embodiment. As shown in FIG. 9, in this embodiment, an insulating film 37 is disposed on the back surface of the sensor chip 30 (the back surface of the single crystal Si 31).

  As described above, when the insulating film 37 on the back surface of the sensor chip 30 is disposed, the surface of the insulating film 37 and the surface of the diaphragm 21 are directly bonded. The surface of the insulating film 37 and the surface of the diaphragm 21 can be directly joined while applying an electric voltage to generate an electrostatic attractive force based on a potential difference between the single crystal Si 31 and the metal stem 20. Thereby, in addition to surface activation of a joint surface, joining using electrostatic attraction can be performed, and it becomes possible to improve a joining yield more.

  In the third embodiment, even when the support substrate 36b of the SOI substrate 36 is made of an insulator, an electrostatic attraction is generated by generating a potential difference between the Si layer 36a and the metal stem 20. be able to. Therefore, also in this case, it is possible to improve the junction yield using electrostatic attraction.

(Sixth embodiment)
A sixth embodiment of the present invention will be described. In the fifth embodiment, the insulating film 37 is arranged on the sensor chip 30, but in this embodiment, the pressure sensor 100 of the insulating film on the diaphragm 21 side is closer to the back surface side of the sensor chip 30 than the first embodiment. Since the shape of the corner portion is changed and the other portions are the same as those in the first embodiment, only different portions will be described.

  FIG. 10 is an enlarged cross-sectional view showing the metal stem 20 and the sensor chip 30 in the pressure sensor 100 of the present embodiment. As shown in FIG. 10, in this embodiment, an insulating film 24 is disposed on the surface of the diaphragm 21.

  As described above, even when the insulating film 24 on the surface of the diaphragm 21 is arranged, as in the fifth embodiment, a voltage is applied to the single crystal Si 31 through, for example, the wiring portion 34 at the time of direct bonding, so that the single crystal Si 31 and the metal stem 20 are applied. The surface of the insulating film 24 and the back surface of the sensor chip 30 can be directly bonded to each other while generating an electrostatic attractive force based on a potential difference therebetween. Thereby, in addition to surface activation of a joint surface, joining using electrostatic attraction can be performed, and it becomes possible to improve a joining yield more.

(Other embodiments)
In the above embodiment, the case of surface activation is taken as an example of direct bonding, but direct bonding by other methods may be used.

  In addition, the present invention can be applied to various pressure sensors other than the one that detects the fuel pressure of the fuel injection system of the automobile.

1 is an overall cross-sectional view of a pressure sensor according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a metal stem and a sensor chip corresponding to part A surrounded by a circle in FIG. 1. It is a figure which shows the decomposition | disassembly state of the pressure sensor shown in FIG. It is the figure which showed a mode that a sensor chip was directly joined to a metal stem. It is the expanded sectional view which showed the relationship between the metal stem and sensor chip of the pressure sensor concerning 2nd Embodiment of this invention. It is sectional drawing of the sensor chip of the pressure sensor concerning 3rd Embodiment of this invention. It is sectional drawing of the sensor chip concerning the modification of 3rd Embodiment. It is sectional drawing of the sensor chip of the pressure sensor concerning 4th Embodiment of this invention. It is sectional drawing of the sensor chip of the pressure sensor concerning 5th Embodiment of this invention. It is sectional drawing of the sensor chip of the pressure sensor concerning 6th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Housing, 12 ... Pressure introduction path, 13 ... Seat surface, 14 ... Stem arrangement part, 15 ... Welding part, 20 ... Metal stem, 21 ... Diaphragm, 22 ... Opening part, 23 ... Step part, 24 ... Insulating film, DESCRIPTION OF SYMBOLS 30 ... Sensor chip, 31 ... Single crystal Si, 32 ... Strain gauge, 33 ... Insulating film, 34 ... Wiring layer, 35 ... Protective film, 36 ... SOI substrate, 36a ... Si layer, 36b ... Support substrate, 37 ... Insulating film , 60 ... Connector terminal, 70 ... Connector case, 100 ... Pressure sensor.

Claims (9)

A housing (10) having a pressure introduction passage (12) whose one end side is a pressure introduction side into which a pressure measurement medium is introduced;
A sensor chip having a pressure detecting diaphragm (21) on one end side, an opening (22) for guiding the pressure to the diaphragm on the other end side, and a sensing part formed on the surface of the diaphragm A metal stem (20) in which (30) is disposed,
The metal stem is arranged in the pressure introduction passage so that the other end side of the metal stem is located on the pressure introduction side of the pressure introduction passage,
The pressure sensor, wherein a surface of the diaphragm in the metal stem and a back surface of the sensor chip are directly joined. The pressure sensor according to claim 1, wherein the front surface of the diaphragm and the back surface of the sensor chip are directly joined by being activated. The sensor chip includes an SOI substrate (36) in which a silicon layer (36a) and a support substrate (36b) are bonded together via an insulating film (36c), and a strain gauge formed on the silicon layer. The pressure sensor according to claim 1 or 2, wherein the sensing unit is configured in (32), and the back surface of the support substrate is activated to be directly bonded to the surface of the diaphragm. . The SOI substrate constituting the sensor chip has a mesa structure in which the strain gauge is surrounded by an insulating film (36d) and a portion of the silicon layer excluding the strain gauge is removed. The pressure sensor according to claim 3. 5. The material constituting the support substrate is a material whose thermal expansion coefficient is located between the thermal expansion coefficient of the material constituting the metal stem and the thermal expansion coefficient of silicon. The pressure sensor described in 1. 6. The pressure sensor according to claim 1, wherein a corner of the back surface of the sensor chip has a tapered obtuse angle. The sensor chip is composed of single crystal silicon (31), and an insulating film (24, 37) is disposed between the back surface of the single crystal silicon and the surface of the diaphragm. The pressure sensor according to claim 1 or 2. A housing (10) having a pressure introduction passage (12) whose one end side is a pressure introduction side into which a pressure measurement medium is introduced;
A sensor chip having a pressure detecting diaphragm (21) on one end side, an opening (22) for guiding the pressure to the diaphragm on the other end side, and a sensing part formed on the surface of the diaphragm A metal stem (20) in which (30) is disposed,
The metal stem is a method of manufacturing a pressure sensor in which the other end side of the metal stem is positioned on the pressure introduction side of the pressure introduction passage in the pressure introduction passage,
The pressure in which the surface of the diaphragm and the back surface of the sensor chip in the metal stem are bonded together in a surface activated state, and the surface of the diaphragm and the back surface of the sensor chip are directly joined by electrostatic attraction. Sensor manufacturing method. 9. The method of manufacturing a pressure sensor according to claim 8, wherein the sensor chip (30) is a chip integrated with a processing circuit, and the back surface of the chip is bonded to the surface of the diaphragm in a surface activated state. .

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