JPH07253364A - Stress detector - Google Patents

Abstract

PURPOSE:To provide a stress detector which can detect a load without compressive stress concentrated on a pressure sensitive element surface. CONSTITUTION:A stress detector includes a pressure sensitive element having a bridge circuit comprising gage resistors 25a to 25d for outputting a signal according to an applied load and a load transmitting member 2 for transmitting the load to the pressure sensitive element, wherein the load transmitting member 2 is placed on the pressure sensitive element. Electrically insulating adhesive agent 22 comprising a cushioning layer for buffering concentration of a stress on the pressure sensitive element surface and a cushioning member 23 are interposed between the load transmitting member 2 and the pressure sensitive element, wherein the load transmitting member 2 is attached to a pressing face for pressing at least the bridge circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stress detecting device utilizing the piezoresistive effect of a semiconductor which outputs a signal according to an applied load.

[0002]

2. Description of the Related Art As a stress detecting device of this type, the applicant of the present invention discloses a device for detecting and outputting a pressure, for example, as shown in FIG. 24 in Nippon Denso Koho Giho (reference number 92-220). . In FIG. 24, a cup 65 having a metal diaphragm portion 64 is provided at the front end side opening of a housing 63 (case) having a screw portion 62. Further, a support base 67 for hermetically sealing and holding the lead 66 is provided inside the support base 67, and a pressure sensitive element 68 having a gauge resistance (not shown) is provided on the support base 67. A rod 69 having a spherical upper surface is provided for the load transmission. Further, a heat dissipation agent 70 is provided below the support table 67.

As described above, the space between the rod 69 and the pressure-sensitive element 68, and the space between the pressure-sensitive element 68 and the support 67 are formed by the insulating adhesive 71 or the frictional force due to the assembling under pressure. Adhesive fixed. Further, the pressure sensitive element 68 and the lead 66 are electrically connected by a bonding wire 72.

According to the stress detecting device having this structure, the load applied to the diaphragm portion 64 is guided to the pressure sensitive element 68 via the rod 69, and the stress is caused by the piezoresistive effect generated in the gauge resistance on the pressure sensitive element 68. Will be detected.

[0005]

In the above-mentioned conventional stress detecting device, the rod 69 made of a sufficiently hard material is necessary to efficiently transmit the load, and therefore the rod 69 is used.
Is made of a hard material such as metal or ceramic. However, the pressure sensitive element 68 is caused by the frictional force caused by assembling such a hard rod 69 in the adhesive 71 or under pressure.
When adhesively fixed to the upper portion, the stress generated on the pressure sensitive element 68 is concentrated immediately below the outer peripheral portion of the rod 69.

Normally, such a state is such that peaks of the generated compressive stress are concentrated immediately below the outer peripheral portion of the rod, as shown in FIG. 18 (a). Therefore, since the compressive stress concentrates on the negative part on the pressure sensitive element 68 in this way, Si
Since the strength of the substrate is lowered and the substrate is easily broken, it is difficult to use the device in a place where the load is relatively large, so that the use range is limited.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a stress detecting device capable of detecting a load without the concentration of compressive stress on the surface of the pressure sensitive element.

[0008]

In order to achieve the above object, the present invention provides, according to claim 1, a pressure-sensitive element that outputs a signal according to an applied load, and a load to the pressure-sensitive element. A stress detecting device comprising a load transmitting member for transmitting the load, wherein the load transmitting member is arranged on the pressure-sensitive element, wherein the pressure-sensitive element surface is provided between the load transmitting member and the pressure-sensitive element. The technical means of providing a buffer layer for relaxing stress concentration is provided.

According to a second aspect of the present invention, there is provided a pressure sensitive element which is provided with a bridge circuit composed of a gauge resistance and which outputs a signal according to an applied load, and a load transmission member which transmits the load to the pressure sensitive element. A stress detecting device in which the load transmitting member is arranged on the pressure sensitive element, wherein a buffer layer for relaxing stress concentration on the pressure sensitive element surface is sandwiched between the load transmitting member and the pressure sensitive element. The load transmission member is attached to at least a pressing surface that presses the bridge circuit.

According to a third aspect of the present invention, the area of the surface of the buffer layer that contacts the pressure sensitive element is the same as or larger than the pressing surface that presses the pressure sensitive element by the load transmitting member. Further, in claim 4 or 5, the buffer layer is an electrically insulating adhesive containing an electrically insulating buffer member, and the elastic modulus of the buffer member and the electrically insulating adhesive is the elastic modulus of the load transmitting member. Smaller, and then
The buffer member is a film made of either resin or glass.

Further, in claim 6, the buffer layer may be an electrically insulating adhesive to which a filler made of any one of glass, ceramic and resin is added.

[0012]

According to claims 1 to 6 of the present invention,
When a load is applied to the load transfer rod, the load is transferred to the pressure sensitive element via the load transfer member. Then, stress due to the transmitted load is generated on the pressure sensitive element, and the pressure sensitive element outputs a signal according to this stress. At this time, since the buffer layer is provided between the load transmitting member and the pressure sensitive element,
The concentration of compressive stress on the surface of the pressure-sensitive element directly below the load transmitting member is avoided and relieved.

Therefore, there is an excellent effect that the stress can be detected without stress concentration.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall schematic cross-sectional view showing an example of a stress detecting device of the present invention, which is, for example, a device attached to an engine block (not shown) of an internal combustion engine to detect and output pressure.

The stress detector shown in FIG. 1 has a housing 7 made of a cylindrical stainless steel (hereinafter abbreviated as SUS) having open ends, and a screw portion 8 is provided on the outer peripheral surface of the housing 7.
And a screw hole (not shown) formed through a cylinder head (not shown) of the engine block.
The housing 7 and the engine block are electrically connected with each other by screwing, and a heat radiation effect is obtained in which heat is released to the outside through contact with the screw portion 8. At this time, a gasket 12 as a sealing ring is pressed against the outer surface of the cylinder head between the hexagonal portion 9 of the housing and the engine block to perform gas sealing.

Further, an O-ring 13 is provided at a predetermined position of the case 14 for waterproofing against the outside, and a spacer 11 for ensuring insulation between the lead 6 and the housing 7 is provided inside the housing 7. While holding the spacer 11 in the housing 7, the case 14 is crimped by the crimping portion 10 of the housing 7, and at the same time, the O-ring 13 is fixed.

The opening on the front end side (combustion chamber side) of the housing 7 has a structure as shown in FIG. 2 in which an essential part is enlarged, and a thin cup 1 is pushed therein. The outer periphery of the bottom portion of the cup 1 (corresponding to the portion A in the drawing) is the housing 7
Is welded to the tip of the to seal the opening from the combustion chamber. In this way, electrical connection is established between the cup 1 and the housing 7. At this time, the disc-shaped bottom portion of the cup 1 serves as a pressure receiving portion, and the pressure received here is transmitted to the load transmission rod 2 as a load transmission member. That is, since this pressure receiving portion functions as a diaphragm, it is hereinafter referred to as a diaphragm portion 1a. It is desirable that the cup 1 having such a diaphragm portion 1a is made of a material having excellent spring properties, corrosion resistance, heat resistance, etc., such as high temperature resistant SUS.

In the central portion of the pressure receiving surface of the diaphragm portion 1a which directly receives the combustion gas, in order to reduce the heat output at the time of combustion, the central portion in the radial direction is depressed toward the semiconductor element 3 in the axial direction. Compared to the outer peripheral portion of the diaphragm portion 1a, the concave portion 1b has a concave shape that is located on the side opposite to the combustion chamber.
Is provided. A cup-shaped eyelet 4 is provided in the opening of the cup 1 on the opposite side of the diaphragm portion 1a.
The stem 4 in which a and the lead 6 are fixed by an insulating member 4b made of glass or the like is inserted, and is welded to the cup 1 at a portion B in the drawing. In this way, electrical connection is established between the diaphragm portion 1a and the stem 4. Therefore, the stem 4 is electrically connected to the engine block by the welding of the portions A and B, and serves as a body ground.

The plane of the stem 4 (the surface viewed from the X direction in FIG. 2) is constructed as shown in the enlarged view of the main part shown in FIG. The stem 4 is provided with a plurality of small holes 15 penetrating in the axial direction, and the small holes 15 are made of metal electrode rods as a predetermined number (here, three are shown) of signal transmission media. The leads 6A, 6B, 6C are fitted and hermetically sealed by the insulating member 4b.
As a result, as shown in FIG.
As a result, the closed space S is formed. At a substantially central portion of the stem 4 facing the closed space S, a semiconductor element 3 as a pressure sensitive element integrated with a processing circuit is adhered and fixed by an electrically insulating adhesive 22 described later. This electrically insulating adhesive 22
Has a function of relaxing thermal stress. Further, the semiconductor element 3 and the ends of the leads 6A, 6B, and 6C are connected to the Al electrode pad 18a via the bonding wire 16,
18b and 18c are electrically connected to each other, and the other end is connected to the connector lead 17 in the case 14.
As described above, it is possible to exchange electric signals between the outside and the semiconductor element 3.

The bottom of the stem 4 is filled with an electrically insulating heat-dissipating agent 5 such as Si gel in order to efficiently dissipate the heat transferred from the load transfer rod 2 to the semiconductor element 3 through the housing 7 to the engine block. ing. Note that the semiconductor element 3 is formed with a gauge resistance and an aluminum electrode. When pressure transmitted from the load transmission rod 2 is applied to this gauge resistance, the resistance value changes due to the piezoresistive effect. It is output as a voltage change, which will be described later.

On the surface of the semiconductor element 3, as shown in FIG.
One Al electrode pad 18a, 18b, 18c and a piezoresistive element as a gauge resistance whose resistance value changes in response to compressive strain are bridge-configured, and the load transmission rod 2 serves as a pressing surface for transmitting pressure to this piezoresistive element. Gauge section 1
9 and an amplifier circuit 20 described later that amplifies the bridge output. In the amplifier section 20, transistors, diodes, capacitors, resistors, etc. are usually integrated and formed and arranged. Three Al electrode pads 18a, 18
Reference numerals b and 18c are, for example, an electrode pad for a power supply of 5 V or the like, an electrode pad for grounding (hereinafter referred to as GND), and an electrode pad for output.

On the other hand, the rear surface of the semiconductor element 3 is electrically insulated, such as a Si-N film, as shown in a portion C in FIG. 2, that is, a partially enlarged view showing a joined state of the semiconductor element 3 and the stem 4. The semiconductor element 3 is adhesively fixed to the stem 4 by the electrically insulating adhesive 22 while being covered with the film 21 to ensure contact insulation with the stem 4. Here, in this embodiment, since the pre-curing viscosity of the electrically insulating adhesive 22 is lowered during the adhesive fixing as described above, the semiconductor element 3 is similarly shown as in the partially enlarged view of the portion D in FIG. The lower end face of the semiconductor element 3 at the joining end face between the stem 4 and the stem 4 is surely caused by the rising of the electrically insulating adhesive 22.
It is covered with 2 to prevent leakage current at the junction interface. The eyelet 4a is effective to use a metal such as kovar for matching the thermal expansion coefficient with Si.

When the load transmitting rod 2 and the semiconductor element 3 are joined, the load transmitting rod 2 is arranged immediately above the gauge portion 19 as shown in a partially enlarged view of an E portion in FIG. Thus, the load insulating rod 23 and the semiconductor element 3 are bonded and fixed by sandwiching the electrically insulating film 23 as a buffer member and forming a buffer layer using the electrically insulating adhesive 22. Here, the load transmission rod 2 is made of metal, ceramic or the like having a large elastic modulus (Young's modulus) in order to increase the load transmission efficiency, and has a function of transmitting the pressure transmitted from the diaphragm portion 1a to the semiconductor element 3. When the measured atmosphere has a high temperature, ceramic is more effective as the material selected for the load transmission rod 2. This is because the thermal conductivity of ceramics is smaller than that of other metals, and therefore the effect of blocking the heat flowing into the semiconductor element 3 from the diaphragm portion 1a and lowering the temperature of the semiconductor element 3 is great.

The tip portion 24 of the load transmitting rod 2 is formed into a spherical shape as shown in FIG. 2, and point contact is made at the center of the convex surface of the recessed portion 1b of the diaphragm portion 1a, that is, at the center of the bottom portion, as shown in F portion in the figure. However, the force transmitted from the combustion chamber side via the diaphragm portion 1a always acts on the axial center of the load transmission rod 2. The point contact of the spherical shape as described above prevents an eccentric load on the gauge portion 19 of the semiconductor element 3 when the load transmission rod 2 is assembled in an inclined manner,
This is because both the effect of constantly transmitting uniform compressive stress to the gauge portion 19 and the effect of insulating the semiconductor element 3 from the diaphragm portion 1a having increased thermal resistance and receiving combustion heat are obtained.

The film 23 is made of resin, glass, or the like, which has a smaller elastic modulus than the load transmission rod 2 and a low thermal conductivity, and is used to equalize the compressive stress on the gauge portion 19 of the semiconductor element 3. , To prevent temperature rise. However, if the effects of stress concentration relaxation and temperature rise prevention can be obtained, it is not always necessary to use the film 23, and for example, an adhesive containing a filler described below is also effective.

Next, the semiconductor device 3 will be described with reference to FIGS. 7 to 10. First, the semiconductor element 3 is manufactured through known manufacturing steps as shown in FIG. That is, a gauge is formed on the surface of the Si wafer in the step of FIG. Next, in the step of FIG. 2B, the back surface of the wafer is polished, and an electrically insulating film such as a SiN film or SiO ₂ film is formed on the back surface in the step of FIG. Then, in the last step of FIG. 6D, the semiconductor element 3 is taken out by cutting into the gauge chips.

The plane of the semiconductor element 3 produced through the above manufacturing process is configured as shown in the enlarged view of FIG. In FIG. 8, (110) is used as the plane orientation of the Si substrate, and four piezoresistive elements 25a, 25b, 25 are used.
A bridge circuit is configured by c and 25d. Of these, the pair of piezoresistive elements 25a and 25b are <110>
It is arranged so that a current flows in the direction, and the resistance value increases with respect to the compressive stress due to the piezoresistance effect. The remaining pair of piezoresistive elements 25c and 25d are arranged in the <100> direction, and their resistance values do not change with respect to compressive stress. This principle is
This is due to the crystal anisotropy of Si. Generally, P-type Si (11
It is well known that the amount of change in resistance value with respect to the compressive stress in the (0) plane is as shown in FIG. 10 for each direction.

These bridge resistors 25a to 25d are arranged in the gauge portion 19 so as to be sufficiently contained within the range of the lower end of the load transmitting rod 2, and even if the load transmitting rod 2 is displaced during the assembly. The load transmission rod 2 is arranged to be small enough so as to be surely fitted within the range of the lower end of the load transmission rod 2. The bridge resistors 25a to 25d are connected to the Al wiring 27 outside the load transmission rod 2 and guide the output generated by the piezoresistance effect to the amplifier circuit 20. Thereby, the sensitivity can be increased and the variation in the sensitivity can be reduced. Further, since the bridge resistance can take an arbitrary line width and length within a range of being contained within the lower end of the load transmission rod 2, the degree of freedom in selecting the resistance value is increased.

Similarly, the temperature compensating resistor 2 of the bridge is used.
Since 6a and 26b are also arranged within the range of the lower end of the load transmission rod 2, the temperature becomes substantially the same as that of the bridge resistors 25a to 25d, and the accuracy is improved as compared with the case where they are arranged at other positions. These resistances are connected to the low sheet resistance layer 29 while avoiding the seal film 28 made of a seal member as an Al shield region, and the gauge portion 1 at the lower end of the load transmission rod 2 is connected.
The wiring is wired from the area where 9 is provided to another area by the Al wiring 27.

Next, the cross-sectional structure of the semiconductor element 3 including the joined state of the load transmission rod 2 and the stem 4 will be described with reference to FIG. FIG. 9 shows a cross section taken along the line AA in FIG.
FIG. 7 is an enlarged view of a main part showing a joint state between the load transmission rod 2 and the stem 4. In FIG. 9, a seal film 28 is formed on the piezoresistive element 25b formed in the gauge portion 19 with an insulating film 30b interposed therebetween. The sealing film 28 is connected to the GND electrode 18a shown in FIG. 8 and blocks high-frequency noise (10 MHz to 10 GHz, hereinafter abbreviated as noise) from the load transmission rod 2. continue,
An insulating film 30a is formed on the seal film 28, and the load transmission rod 2 is bonded and fixed by an electrically insulating adhesive 22 via a film 23.

On the other hand, an N-type resistance island 31 is formed below the piezoresistive element 25b, and a power supply potential is applied thereto. Further below that, the GND potential is applied by the P-type Si substrate 32. Then, an electric insulating film 21 is formed on the back surface side, and the semiconductor element 3 is adhered and fixed to the stem 4 with an electric insulating adhesive 22. Such a semiconductor device 3
The output terminals I and J (shown in FIG. 20 to be described later) of the bridge have resistance values of R _25a = R _25b <R _25c =
R _25d and bridge outputs V _I and V _J are V _I > V
It is set to be _J. In this state, in this embodiment, when the stem 4 and the cup 1 are welded at the portion B in FIG. 2, a preset load is applied to the semiconductor element 3 to increase R _25a and R _25b. 1 is a load value such that V _I = V _{J, which} is to be assembled for each product. In this way, variations in the bridge outputs V _I and V _J are adjusted during assembly. This eliminates the need to separately adjust the offset or use an AC coupling circuit (not shown). R _25a ,
R _25b , R _25c , and R _25d are piezoresistive elements 26a.
Each resistance of ~ 26d.

Further, as a method of manufacturing the piezoresistive elements 25a to 25d, for example, other transistors formed by a manufacturing technique described in Japanese Patent Application Laid-Open No. 4-257272 filed by the present applicant, Since the resistors and the like are created by a well-known bipolar manufacturing process, details of each are omitted here. In the stress detecting device of the present invention having the above-described configuration, the concave portion 1b having a concave shape is provided in the pressure receiving central portion of the diaphragm portion 1a formed on the disc-shaped bottom portion of the cup 1. The function and effect of the recessed portion 1b will be further described below.

Since the recessed portion 1b is recessed toward the semiconductor element 3 side as shown in FIG. 2, the temperature difference between the surface α of the diaphragm portion 1a (measured pressure acting surface) α and the surface β on the opposite side thereof. Increases and the surface α tends to extend relative to the surface β. As a result, even if the radial center portion of the diaphragm portion 1a tries to swell toward the combustion chamber side in the axial direction, the slope of the recessed portion 1b extends in the opposite direction, so the diaphragm portion 1a does not move toward the surface α side in the axial direction. It'll be easy.

This mechanism is further described with reference to FIG.
This will be specifically described. FIG. 11 shows the diaphragm of this embodiment.
FIG. 3 is an enlarged cross-sectional view of a main portion of the ram portion 1a, showing its function and effect.
Exaggerate the area around the dent 1b so that you can understand it
There is. Further, 1c is the maximum on the surface A side of the diaphragm portion 1a.
The flat end portion 1d is the bottom on the surface A side of the recessed portion 1b.
Flat part, 1e is the front end of the recessed part 1b on the surface A side
The tape is held so as to hold the flat end portion 1c and the flat bottom portion 1d.
Shows the slope formed in the shape of a pad, the thickness of the most advanced flat portion 1c
Only t₁And the thickness t of the bottom flat portion 1d₂And the thickness of slope 1e
t₃Is t₃≤t ₁And t₃≤t₂Has a relationship
It

Here, when the temperature difference between the surfaces α and β increases and the surface α of the diaphragm portion 1a tries to extend relatively to the surface β, the diaphragm portion 1a has the following action. . That is, the tipmost flat portion 1b tries to expand so as to bulge in the direction of the solid arrow X (upward direction in the drawing). Similarly, the bottom flat portion 1d also tries to expand so as to bulge in the direction of the dashed arrow Y (upward direction in the drawing), but the extension Z in the longitudinal direction of the slope portion 1e (shown in the solid arrow Z) is the bottom flat portion 1d.
Of the bottom flat portion 1d, there is almost no displacement (expansion toward the combustion chamber side in the axial direction) in the vicinity of the radial center of the flat portion 1d. This is at least the thickness t _{3 of the} slope 1e.
Is smaller than the thicknesses t ₁ and t ₂ of the flat portions 1c and 1d, so that the elongation Z is larger than the elongations X and Y. The diaphragm portion 1a in this state is displaced as shown by the broken line shape in FIG.

Therefore, in this embodiment, since the load transmission rod 2 is installed in the radial center portion of the diaphragm portion 1a, which is less displaced due to the temperature difference between the surfaces α and β, the combustion cycle, the rotational speed, and the engine load. Even if the temperature difference between the surfaces α and β changes due to the degree of adhesion of soot to the surface α and the surface α, the load transmission rod 2 is hardly affected by this change.
Since the pressure is transmitted to the pressure sensitive element 3 via the load transmission rod 2, the measurement accuracy is improved.

Incidentally, in order to fully exert the effects of the diaphragm portion 1a described above, the recessed portion 1 of this embodiment is used.
b is formed so as to be symmetrical with respect to the central axis of the diaphragm portion 1a. Further, as an example, the planar shape of the diaphragm portion 1a is circular as shown in FIG. 12, but if the recessed portion 1b is symmetrical with respect to the central axis of the diaphragm portion 1a, it is adhered to the circular shape. There is no need, and the same effect as that of the present embodiment can be obtained even if, for example, a square shape or a star shape is used. Note that FIG. 12 is a plan view seen from above in FIG. 11, and the hexagonal portion of the housing and the like are omitted.

Further, the load transmission rod 2 is located approximately at the center of the flat portion on the surface β side of the recessed portion 1b where the influence of the fluctuation is minimized.
If the tip shape is such that the tip 24 is point-contacted with the dented portion 1b so that the tip 24 is spherically processed and point-contacted as in FIG. It is possible to further suppress the influence of the variation in the temperature difference between the two surfaces α and β. That is, the shape of the tip portion 24 of the load transmission rod 2 does not need to be spherically adhered,
Any shape may be used as long as it has a shape in which it makes point contact with the approximate center of the flat portion on the surface β side of the recessed portion 1b and is capable of transmitting pressure to the pressure sensitive element 3.

On the other hand, another embodiment which makes it possible to reduce the variation in the amount of bending between the surfaces α and β without providing the dented portion 1b on the diaphragm portion 1a will be described with reference to FIG. explain. In this stress detecting device, the central portion in the radial direction of the diaphragm portion 1a itself is the semiconductor element 3 in the axial direction.
Although it is configured to have no so-called recessed portion 1b that is not recessed to the side, the surface α of the central portion in the radial direction of the diaphragm portion 33 is formed.
A column 34 having a small diameter is erected on the side, and a heat-shielding umbrella-shaped plate 35 made of a disc is arranged parallel to the diaphragm portion 33 on the top of the column 34. The pillar 34 and the heat-shielding umbrella plate 35 are formed as a body of the diaphragm portion 33.

In this way, the radiation heat energy radiated from the combustion gas is prevented from being received by the diaphragm portion 33. As a result, the change in the temperature of the surface α of the diaphragm portion 33 is reduced due to the change in the combustion gas temperature accompanying the change in various engine operating conditions. Due to the decrease in the temperature change, the variation in the deflection amount of the diaphragm portion 33 is reduced, and the output error of the semiconductor element 3 is reduced.

In addition to the above, another embodiment will be described with reference to FIG. Also in this stress detection device, the diaphragm portion 36 itself has a radial center portion recessed toward the semiconductor element 3 in the axial direction, like the diaphragm portion 1a shown in FIG. Here, in this embodiment, a small-diameter support 37 is further planted on the surface α side of the central portion in the radial direction of the diaphragm 36, and the top of the support 37 is parallel to the diaphragm 36 from the disk. A heat shield umbrella-shaped plate 38 is provided.

In this way, the effect of reducing deflection by the diaphragm portion 1a with the recessed portion 1b as shown in FIG.
A synergistic effect with the bending reduction effect by the heat shielding umbrella plate 35 as shown in FIG. 14 is obtained. In contrast to the above, another embodiment will be described with reference to FIG. Also in this stress detecting device, the diaphragm 39 itself has its radial center recessed toward the semiconductor element 3 in the axial direction, like the diaphragm 1a shown in FIG. Here, in the present embodiment, the SU
A shallow cup-shaped heat shield can 40 made of S is placed around the diaphragm portion 39. A combustion gas inlet / outlet 41 is opened on the peripheral wall of the thin heat shield can 40, and the combustion gas can act on the diaphragm portion 39. This heat shield can 40 is provided with the heat shield umbrella plates 35 and 38 shown in FIGS.
Similarly to the above, the radiant heat energy radiated from the combustion gas is prevented from being received by the surface α of the diaphragm portion 39.
4 and FIG. 15 have the same effect.

In addition to the above, another embodiment will be described with reference to FIG. In this stress detecting device, the diaphragm portion 42 itself has a radial center portion recessed toward the semiconductor element 3 in the axial direction, like the diaphragm portion 1a shown in FIG. Here, in this embodiment, the heat shield layer 43 is further adhered to the surface α of the diaphragm portion 42 by thermal spraying of a ceramic such as alumina.

This heat shield layer 43, like the heat shield umbrella plates 35 and 38 in FIGS. 14 and 15, and the heat shield can 40 in FIG. 16, emits radiant heat energy from the combustion gas to the diaphragm portion 42.
Heat is inhibited from being received at the surface α of the, and the same effect as in the case of adopting the configurations of FIGS. 14, 15, and 16 is obtained. Next, the bonding state between the semiconductor element 3 and the stem 4 described in FIG. 4 will be described in more detail.

Since the housing 7 screwed to the engine block is electrically connected to the stem 4 through the cup 1 which constitutes the diaphragm portion 1a, the stem 4 is electrically connected to the engine block. It has already been mentioned that it has a body ground. At this time, small irregularities are present on the surface of the stem 4 as shown in FIGS. 4 and 5, and there is a possibility that the stem 4 and the semiconductor element 3 are partially in contact with each other to be electrically connected. In this case, since the semiconductor element 3 is directly affected by the body ground and the sensor characteristics fluctuate, an insulating film is formed on the entire back surface of the semiconductor element 3 using the electrically insulating adhesive 22 to form the stem 4. Insulation from the semiconductor element 3 is performed.

However, even if an insulating film is formed on the entire back surface, it may not be completely insulated. That is, the electrically insulating adhesive 22 may not reach the side surface of the semiconductor element 3 at the lower end surface of the semiconductor element 3, so that an interface leak occurs on the side surface of the semiconductor element 3. Therefore, in the present invention, the viscosity of the electrically insulative adhesive 22 is reduced in advance by means such as heating in order to surely raise the electrically insulative adhesive 22 to the side surface of the semiconductor element 3. Thus, as shown in FIG. 5, the side surface of the semiconductor element 3 is covered by the rising of the electrically insulating adhesive 22 to completely prevent the interface leak.

By increasing the thickness of the insulating film to, for example, several tens of μm, it is possible to prevent the occurrence of interfacial leak without lowering the viscosity of the electrically insulating adhesive 22, but the heat dissipation is lowered. In consideration of the fact that the time required for film formation and the time required for film formation increase, it is obvious that it is preferable to take measures to reduce the viscosity of the electrically insulating adhesive 22. In addition, at least the surface of the stem 4 where the semiconductor element 3 is disposed is provided with an insulating coating (not shown), so that the stem 4 and the semiconductor element 3 can be formed without forming an insulating film over the entire back surface of the semiconductor element 3. It can also be insulated.

In this way, the stem 4 and the semiconductor element 3 are
Since and are completely non-insulated, it is possible to eliminate characteristic fluctuation due to leak current. Next, regarding the joining state between the load transmitting rod 2 and the semiconductor element 3 described in FIG. 6,
This will be described in detail with reference to FIGS. 18A, 18B, and 19. Normally, a hard semiconductor element 45 is attached to a hard load transmission rod 4
When 4 is directly applied, the stress generated on the semiconductor element 45 immediately below the hard load transmitting rod 44 is concentrated immediately below the outer peripheral portion of the load transmitting rod 44. In such a case, FIG.
As shown in (a), the strength of the semiconductor element 45 is reduced. Therefore, as shown in FIG.
By sandwiching the soft member 46 as a stress buffer layer between the semiconductor element 45 and the semiconductor element 45, stress concentration on the outer peripheral portion is eliminated.

However, interposing the soft member 46 in the pressure transmission path is nothing but causing a pressure transmission loss. Therefore, in order to prevent the variation in the sensitivity of the semiconductor element 45 due to this, the soft member 46 is prevented. It is necessary to manage the spring characteristics of. Therefore, it is necessary to manage the elastic modulus and thickness, which are factors that determine the spring characteristics of the soft member 46, to desired values. However, since the adhesive used for joining the semiconductor element 45 and the load transmission rod 44 is generally liquid or gel, it is very difficult to control the thickness of the adhesive.

Therefore, in the present embodiment, in order to control the thickness of the buffer layer, a film 23 such as resin or glass having a small elastic modulus and a low thermal conductivity is required, and the outer peripheral portion of the load transmitting rod 2 is required. The spring characteristics of the buffer layer are skillfully managed so that the stress concentration immediately below is relaxed and the compressive stress reaches a desired value. The area of the film 23 in contact with the pressure-sensitive element 3 is substantially the same as the area of the pressing surface (gauge portion 19) of the load transmission rod 2 against the pressure-sensitive element 3 or larger. It is possible to more reliably mitigate stress concentration immediately below the outer peripheral portion of the load transmission rod 2.

Therefore, the concentration of the compressive stress on the surface of the pressure sensitive element 3 directly below the load transmission rod 2 is avoided and alleviated.
Therefore, the stress can be detected without stress concentration. Further, since the compressive stress is relieved on the pressure sensitive element 3 in this manner, the strength of the Si substrate is not reduced, and the device can be used in a place where the load is relatively large, so that the range of use is expanded more than ever before. It will be.

By the way, the buffer layer formed by the electrically insulating adhesive 22 and the film 23 in this embodiment has a function of relaxing the concentration of stress generated by the load as described above. It is also possible to take That is, in FIG. 19, the electrically insulating adhesive 22 or the low melting point glass itself is used as the buffer layer without using the film 23. In order to secure the thickness of the buffer layer necessary in this case, this electrically insulating adhesive is used. Insulating filler 47 such as glass, ceramics, and resin is added to the agent 22.

In the present embodiment, the device for outputting a signal according to the pressure is shown as an example, but the means for generating the stress need not be limited to the application of the pressure as described above, and the load transmitting rod 2 is used. Even load means capable of transmitting stress to the pressure sensitive element 3, for example, load means transmitting stress to the load transmitting rod 2 by acceleration, magnetic force, electrostatic force or the like can be realized without departing from the gist of the present invention. Needless to say.

Next, the semiconductor element 3 described with reference to FIG.
First, the function and effect when the pressure from the load transmission rod 2 is transmitted will be described in detail. As the stress acting on the semiconductor element 3, that is, the stress acting on the bridge resistance arranged in the gauge portion 19 on the semiconductor element 3 just below the lower end of the load transmitting rod 2, only the stress in the pressing direction from the load transmitting rod 2 is used. Considering this, the piezoresistive effect in the (110) plane is

[0055]

[Equation 1]

It becomes like this. Where E <100>, E
<110> is an electric field, i <100>, i <110>
Is the component of the current density in each crystal axis direction, ρ is the resistivity, σ _ZZ is the stress component in the direction perpendicular to the semiconductor element surface (pressure direction from the rod), and π ₁₁ , π ₁₂ , π ₄₄ Is the piezoresistance coefficient with respect to the crystal principal axis.

Here, in the case of a normal P-type Si substrate,
Since π ₁₁ and π ₁₂ << π ₄₄ , the piezoresistive elements arranged in the <100> direction hardly generate a piezoresistive effect, and other piezoresistive elements arranged in the <110> direction do not. The maximum piezoresistive effect can be obtained for the piezoresistive element. That is, the resistance in the <110> direction increases due to the compressive stress in the ρ _ZZ direction. Therefore, in order to use such a piezoresistive effect most efficiently, <10
It is important to arrange piezoresistive elements in the <0> and <110> directions, respectively, and connect them in a bridge type.

[0058] Therefore, in the present invention, it uses a [pi _'13 gauge resistors that vary the resistance value with respect to the vertical compressive stress on the semiconductor element 3 surface as a piezoresistive element 25 a to 25 d, the contact of the output terminals The influence of the electrode width (not shown) is removed to improve the sensitivity. Furthermore, this π '
Piezoresistive element 25 composed of _13- gauge bridge
Since all of a and 25d are arranged in the gauge portion 19 of the semiconductor element 3 just below the lower end of the load transmission rod 2, variations in sensitivity can be reduced and variations in temperature characteristics can be reduced.

Regarding the sensitivity at this time, according to the effect of the FEM carried out by the present inventors, the bridge-connected gauge resistors 25a to 25d of the present embodiment are approximately 1.5 times the square gauge resistors (not shown). It was confirmed that the sensitivity of was obtained.
Therefore, irrespective of the electrode width of the pressure sensitive element 3, even if the acting surface of the compressive stress due to the load transmitting rod 2 is displaced, the sensitivity does not decrease, and accurate temperature characteristics can be obtained.

Further, the temperature compensating resistor 26 of the bridge
It has already been described in FIG. 8 above that a and 26b are also arranged within the range of the lower end of the load transmission rod 2. In this way, the gauge resistance and the temperature compensation resistance are arranged within the range of the lower end of the rod, and further, as shown in FIG.
The reason why it is arranged near the center is because this portion is selected as the portion having the smallest temperature gradient in the surface of the semiconductor element 3 at the joint surface with the load transmission rod 2. The temperature compensating resistors 26a and 26b are the gauge resistors 2
It is arranged in the crystal axis <100> direction similar to 5c and 25d. Therefore, the resistance values of the temperature compensating resistors 26a and 26b hardly change with respect to the stress, so that the change in the amplification factor due to the pressure caused by the resistance can be suppressed.

In this way, each of the resistors 25a to 25d,
FIG. 20 shows an equivalent circuit including a gauge section 19 in which 26a and 26b are arranged and an amplifier circuit 20. In FIG. 20, four piezoresistive elements 25a to 25d are bridge-connected and a change in resistance value due to a piezoresistive effect is detected as a voltage change. Then, when the output voltage is amplified by the operational amplifier (OP), the amplification factor of the operational amplifier (OP) is changed by the temperature compensation resistors 26a and 26b to compensate for the sensitivity change due to the temperature characteristics of the piezoresistive elements 25a to 25d. There is.

Here, generally, the temperature coefficient of the resistance value of the diffusion resistance and the temperature coefficient of the piezoresistive effect depend on the impurity concentration. Therefore, in order to perform the compensation as described above, each of the resistances 25a to 25d. , 26a, 26b, it is necessary to set the impurity concentration to an appropriate value. Therefore, in the present embodiment, as an example, the resistors 25a to 25d, 26a, and 26b have the same concentration, and the temperature compensation resistor 26 is used.
A resistors having a temperature coefficient of 0 are used for the resistors R1 and R2 that determine the amplification factor together with a and 26b.

The transistor Tr and the resistors R ₄ , R ₅ , and R ₆ in this circuit are virtual GNs of the operational amplifier (OP).
It is a constant voltage circuit for setting D, and the resistor R ₃ is a resistor for adjusting the operational amplifier offset. And the resistors R ₅ and R ₆
Is a thin film resistor laser trimmed on the wafer.
Further, by using a plurality of amplifiers (OP), a highly accurate amplifier circuit can be obtained.

Next, the function and effect of the semiconductor element 3 having the structure described in FIG. 9 will be described in detail. When ignition noise or noise from a transceiver or the like is mixed into the engine block, the load transmission rod 2 is electrically connected to the load transmission rod 2 if the load transmission rod 2 is made of metal, so that the noise is transmitted to the load transmission rod 2. At this time, as shown in FIG. 9, the sealing film 2 of GND potential is formed on the piezoresistive elements 25a to 25d.
8, the noise is absorbed by the parasitic capacitance formed between the load transmission rod 2 and the sealing film 28. As a result, the influence of noise on the piezoresistive elements 25a to 25d is removed. Similarly, although the noise is transmitted to the stem 4, since the potential of the P-type Si substrate 32 of the semiconductor element 3 is connected to the GND, the noise is absorbed by the parasitic capacitance formed between the stem and the GND. Therefore, similarly, the influence of noise on the piezoresistive elements 25a to 25d is eliminated. Therefore, it is possible to suppress the characteristic variation due to noise.

Therefore, the equivalent circuit shown in FIG. 20 is shown in FIG. 21 in consideration of the parasitic capacitance. In FIG. 21, C ₁ , C ₂ and C ₃ are signal lines 18a, 18b and 18 composed of leads 6A, 6B and 6C.
It is the parasitic capacitance formed by the insulating member 4b between the c and the stem 4. At this time, the respective leads 6A, 6
B and 6C are output terminals obtained by impedance-converting the gauge output by an operational amplifier (OP) or a transistor (Tr). Since the impedance of each signal line is 1Ω or less, it is not affected by noise. Also, an adjustment terminal (not shown) that does not affect the output signal is added, and further, although not shown, between the power supply-GND and the output-G.
Even if a capacitor is provided between the NDs, the influence of noise can be similarly prevented.

C ₄ is a parasitic capacitance formed by the electrically insulating adhesive 22 and the electrically insulating film 21 between the stem 4 and the P-type Si substrate 32. Since it is connected to the GND line, it is the piezoresistive element 25a. The effect of noise on ~ 25d is eliminated. Also, C _{6 to} C ₉ are piezoresistive elements 25a to 2
Parasitic capacitance formed between the 5d and the sealing film 28, C ₅ is the parasitic capacitance formed between the sealing membrane 28 and the load transmission rod 3, the seal film 28 is connected a low impedance of the signal line, namely the GND Piezoresistive element 2
The influence of noise on 5a to 25d is removed. In this embodiment, since the load transmission rod 2 is made of a conductive material, the insulating film 30 is formed on the gauge resistors 25a to 25d.
Although the Al seal film 28 is provided via a and 30b,
The use of the load transmission rod 2 made of an insulating member eliminates the need for the seal film 28.

Although not shown in the drawing, the insulating adhesive 22 on the gauge resistors 25a to 25d is thickened without using the seal film 28 as described above, and the bridge output terminal I-
Capacitors may be provided between GND and between the output terminals J-GND of the bridge. Next, the manufacturing method of this embodiment, which is assembled while adjusting the variations in the bridge outputs V _I and V _J , will be described in detail with reference to FIGS.

FIG. 22 is an overall schematic view of an assembling apparatus that sets a preset load for each product. In FIG. 22,
Semiconductor element 3, stem 4, and bonding wire 1
The sensor unit 48 consisting of 6 is set on a holding jig 49, and the leads 6A, 6B, 6C are inserted in a socket 50 for taking out signals. And lead 6
The product power line 51 is connected to A, and the product GN is connected to the lead 6B.
D line 52 is connected, and product output signal line 53 is connected to lead 6C.
Are connected, and each is connected to the control unit 54. The control unit 54 is provided with a comparator 57 which compares the voltage of the product driving power supply 55 with the reference voltage 56 and the input voltage from the product output signal line 53 and outputs a load adjustment signal 58. Load adjustment signal 5 from the control unit 54
When 8 is output, the load generator 59 receives this and generates a load, and transmits this load to the preset load applying jig 60. And the preset load applying jig 60 is a cup 1
Is set in the diaphragm portion 1a provided in the cup 1 and the cup 1 is set coaxially with the sensor unit 48 together with the load transmission rod 2. Thus, the preset load applying jig 60, the diaphragm portion 1a and the cup 1, the load transmitting rod 2, the sensor unit 48, the holding jig 49, and the socket 50 are all arranged coaxially.

According to the assembling apparatus having such a configuration, the resistance R ₃ is adjusted on the wafer of the semiconductor element 3 configured as shown in FIG. 20, and the offset voltage of the operational amplifier (OP) becomes 0V. Further, when the gauge output ΔV _G = 0V, the resistance R ₆ is adjusted so as to have a zero-point voltage (for example, 1.2V). At this time, the gauge offset voltage is set to a negative voltage (for example, -60 mV). The relationship between the gauge output ΔV _G and the preset load F in this state is as shown in FIG.

In FIG. 23, when the preset load applying jig 60 is set on the diaphragm portion 1a and the gauge output ΔV _G varies, for example, when the values show sample γ and sample δ, the sensor output is 0. A preset load γ ′ is applied to the sample γ so that the voltage becomes a point voltage, and a preset load δ ′ is applied to the sample δ so that the gauge output ΔV _G is 0V. Even if the gauge offset voltage varies in this way, the gauge offset voltage can always be set to 0 V, and thus is not affected by power supply noise.

In this way, by applying a load to the pressure sensitive element 3 so that the output of the bridge circuit becomes 0 V and maintaining this output, it is possible to prevent the zero-point voltage of the sensor output from varying. Therefore, the laser beam is shown in FIG. 2 while keeping the state where the load generator 59 applies a constant preset load F to the product and simultaneously rotating the respective members arranged coaxially with each other about the rotation shaft 61. Since the stem 4 and the cup 1 are welded all around by irradiating the portion B, it is possible to obtain a product in which variations in the bridge outputs V _I and V _J are adjusted.

Further, the control in the control unit 54 can be implemented by software using a personal computer or the like. Also, by adding laser control and rotation control to the function of the control unit 54, automatic automation can be achieved. It should be noted that the pressure detecting device of the present invention is devised in various ways at each location, but it goes without saying that various modifications can be made without departing from the spirit of the invention.

[Brief description of drawings]

FIG. 1 is an overall schematic cross-sectional view of a stress detection device of the present invention.

FIG. 2 is an enlarged view of a main part of a front end portion of a housing according to the present invention.

FIG. 3 is an enlarged view of a main part showing a stem plane of the present invention.

FIG. 4 is a partial enlarged view showing a bonded state of the semiconductor element of the present invention and a stem.

FIG. 5 is a partial enlarged view showing a joined state of the end faces of the semiconductor element of the present invention and the stem.

FIG. 6 is a partially enlarged view showing a joined state of the end faces of the load transmission rod and the semiconductor element of the present invention.

FIG. 7 is a diagram showing a manufacturing process of a semiconductor device of the present invention, in which (a) is surface gauge formation, (b) is back surface polishing,
(C) is an insulating film formation, (d) is a cut.

FIG. 8 is an enlarged plan view of a semiconductor device of the present invention.

9 is an enlarged view of an essential part showing a cross section taken along line AA in FIG. 8 of the present invention and showing a joint state with a load transmission rod and a stem.

FIG. 10 is a diagram showing the amount of change in resistance value with respect to the compressive stress in the P-type Si (110) plane for each direction.

FIG. 11 is an enlarged view of a main part of the diaphragm portion of the present invention.

FIG. 12 is a plan view of FIG.

FIG. 13 is an enlarged view of another main part of the diaphragm portion of the present embodiment.

FIG. 14 is a view showing another embodiment of the cup constituting the diaphragm portion of the present invention.

FIG. 15 is a view showing still another embodiment of the cup constituting the diaphragm portion of the present invention.

FIG. 16 is a view showing still another embodiment of the cup constituting the diaphragm portion of the present invention.

FIG. 17 is a view showing still another embodiment of the cup constituting the diaphragm portion of the present invention.

FIG. 18 is a diagram showing a state of compressive stress just below the outer peripheral portion of the rod, where (a) is a case without a buffer layer and (b) is a case with a buffer layer.

FIG. 19 is a diagram showing another example of the buffer layer of the present invention.

FIG. 20 is an equivalent circuit including a gauge unit and an amplifier circuit according to the present invention.

FIG. 21 is an equivalent circuit in the case where parasitic capacitance is taken into consideration in FIG.

FIG. 22 is an overall schematic view of an assembly device for setting a preset load according to the present invention.

FIG. 23 is a diagram showing the relationship between gauge output ΔV _G and applied load F.

FIG. 24 is an overall schematic sectional view of a conventional stress detecting device.

[Explanation of symbols]

1a, 33, 36, 39, 42 Diaphragm section 1b Dent section 2 Load transmission rod (load transmission member) 3 Semiconductor element (pressure sensitive element) 4 Stem 6A, 6B, 6C Lead (signal transmission medium) 7 Housing 11 Spacer 14 Case 18a, 18b, 18c Al electrode pad 19 Gauge section 20 Amplifier circuit 21 Electric insulating film 22 Electric insulating adhesive 23 Film (buffer member) 25a, 25b, 25b, 25d Piezoresistive element (gauge resistance) 26a, 26b For temperature compensation Resistance 28 Seal film (seal member) 48 Sensor unit 49 Holding jig 54 Control unit 59 Load generator 60 Preset load applying jig 61 Rotating shaft

Claims (6)

[Claims] 1. A pressure sensitive element for outputting a signal according to an applied load, and a load transmitting member for transmitting a load to the pressure sensitive element, wherein the load transmitting member is arranged on the pressure sensitive element. A stress detecting device, wherein a buffer layer is provided between the load transmitting member and the pressure sensitive element to reduce stress concentration on a surface of the pressure sensitive element. 2. A pressure sensitive element for outputting a signal according to an applied load, comprising a bridge circuit composed of a gauge resistance, and a load transmitting member for transmitting a load to the pressure sensitive element, wherein the load transmitting member is A stress detection device arranged on a pressure-sensitive element, wherein a buffer layer for relaxing stress concentration on the surface of the pressure-sensitive element is sandwiched between the load transmission member and the pressure-sensitive element, and at least the bridge circuit is pressed. The stress detecting device, wherein the load transmitting member is attached to the pressing surface. 3. The area of a surface of the buffer layer which is in contact with the pressure sensitive element is the same as or larger than the pressing surface which the load transmitting member presses the pressure sensitive element. Alternatively, the stress detection device described in 2. 4. The buffer layer is an electrically insulative adhesive containing an electrically insulative cushioning member, and the elastic modulus of the cushioning member and the electrically insulative adhesive is smaller than the elastic modulus of the load transmitting member. The stress detection device according to any one of claims 1 to 3, which is characterized in that. 5. The stress detecting device according to claim 4, wherein the buffer member is a film made of either resin or glass. 6. The stress detecting device according to claim 1, wherein the buffer layer is an electrically insulating adhesive to which a filler made of any one of glass, ceramic and resin is added.