JPH10170367A - Semiconductor pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the effect of thermal hysteresis stably by bonding a foundation for securing a sensor chip to a resin base through a resin adhesive of specified thickness thereby relaxing the effect of thermal strain from the foundation. SOLUTION: A sensor chip 1 comprises a silicon substrate on which a diaphragm 1a is formed and a diffusion gauge 2 for detecting displacement of the diaphragm 1a is formed on the surface thereof. A vacuum chamber 4 is defined by the sensor chip 1 and a glass foundation 3 and the diaphragm 1a is displaced depending on the difference between the pressure being applied to the surface thereof and the pressure in the vacuum chamber 4. The glass foundation 3 is bonded through an adhesive 6 to a base, i.e., a package material 5. The package material 5 is composed of epoxy resin and a silicon based adhesive is used as the adhesive 6. The adhesive 6 is thicker than 40μm and mixed with microbeads of divinylbenzene in order to ensure that thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor, and can be used, for example, as an intake pressure sensor for automobiles.

[0002]

2. Description of the Related Art A semiconductor type pressure sensor of this type has a sensor chip having a diaphragm which is displaced by receiving pressure, and a glass or silicon pedestal for fixing the sensor chip. Then, the strain of the diaphragm caused by the pressure is detected by a piezo resistor (strain gauge). The pedestal is soldered on a base such as a metal stem.

Here, if distortion occurs in the diaphragm due to factors other than the pressure to be measured, it becomes an error factor in sensor characteristics. For example, when the base is distorted due to a temperature change, the distortion is transmitted to the diaphragm and causes an error. For this reason, a Kovar, 42 alloy, or ceramic substrate having a thermal expansion coefficient close to that of silicon or a glass pedestal is used as a base, and thermal distortion from the base is minimized.

[0004]

In contrast to the above-mentioned conventional structure, it is conceivable that the base is made of a resin material and the pedestal is adhered to the base with an adhesive from the viewpoint of cost. In this case, the resin material has a larger coefficient of thermal expansion and a larger amount of distortion than Kovar, 42 alloy, or ceramic, so that the thermal distortion from the base greatly affects the sensor characteristics.

Japanese Patent Application Laid-Open No. 55-19864 discloses that the influence of thermal strain from a base on sensor characteristics is reduced by sufficiently increasing the height of a pedestal for fixing a sensor chip. If the height of the pedestal is increased, even if the base is made of a resin material, the influence of the thermal strain on the sensor characteristics can be reduced. However, increasing the height of the pedestal has the disadvantage of increasing the height of the sensing section and increasing the size of the assembly.

Further, the influence of the thermal strain on the temperature change as described above can be corrected by the temperature correction circuit of the signal processing circuit together with the temperature characteristics of the sensor itself. However, a factor that does not correspond to a temperature change cannot be corrected by the temperature correction circuit. Factors that do not correspond to the temperature change include those due to the creep characteristics of the adhesive or the resin material.
In this case, when the adhesive or the resin material is once returned to the original state by raising the temperature, the adhesive and the resin material do not return to the original state immediately, but gradually return over time (this is caused by heat). Hysteresis). It is difficult to correct such a change that does not correspond to the temperature change of the sensor by the signal processing circuit.

The present invention has been made in view of the above problems, and has as its object to reduce the influence of thermal strain from a base and stably reduce the influence of thermal hysteresis without increasing the height of a pedestal. And

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a pedestal for fixing a sensor chip is adhered to a base made of a resin material with a resin adhesive. It is characterized in that the thickness of the agent is 40 μm or more. As described above, by setting the thickness of the resin adhesive to 40 μm or more, the influence of thermal strain from the base is reduced, and the amount of thermal hysteresis is stably reduced as shown in the measurement results of FIG. can do.

Incidentally, as the resin adhesive, a silicon adhesive can be used as in the second aspect of the present invention. In this case, it is preferable that the silicon-based adhesive has an elastic force of 1 MPa or less, as in the third aspect of the present invention. Further, if the means for securing the thickness is mixed with the resin adhesive as in the invention according to claim 4, the thickness of the resin adhesive can be easily reduced by 40%.
μm or more. In this case, as means for securing the thickness, as in the invention described in claim 5,
Beads can be used.

[0010]

FIG. 1 shows the structure of a semiconductor pressure sensor according to an embodiment of the present invention. The semiconductor pressure sensor according to the present embodiment is used as an intake pressure sensor for an automobile. The sensor chip 1 is formed of a silicon substrate, has a diaphragm 1a formed thereon, and a diffusion gauge (strain gauge) 2 for detecting a displacement of the diaphragm 1a is formed on the surface thereof. The sensor chip 1 is anodically bonded to an alumina silicate glass base 3 having a height of 0.7 mm. Then, a vacuum chamber 4 is formed between the sensor chip 1 and the glass pedestal 3, and the diaphragm 1 a is displaced according to a pressure difference between the pressure applied to the surface and the pressure of the vacuum chamber 4.

The glass pedestal 3 is adhered to a package material 5 as a base with an adhesive 6. The package material 5 is made of an epoxy resin, and has a coefficient of thermal expansion of 14 ppm / ° C. As the adhesive 6, a silicon-based adhesive having an elasticity of 0.6 MPa is used. Further, since the adhesive 6 has a low elasticity and it is difficult to obtain a desired thickness with the adhesive 6 alone, the adhesive 6 has micro beads 7 made of divinylbenzene in order to secure the thickness. Is mixed in.

The diffusion gauge 2 is electrically connected to an external signal processing circuit (not shown) by a wiring pattern and a bonding wire of an Al thin film (not shown) formed on the sensor chip 1. The diffusion gauges 2 are formed at four locations on the surface of the sensor chip 1, and the four diffusion gauges 2 form a bridge circuit shown in FIG. In this case, the resistance value of each diffusion gauge 2 increases and decreases in the direction of the arrow in response to a change in pressure applied to the diaphragm 1a, and a potential difference corresponding to the pressure applied to the diaphragm 1a is generated between the output terminals B and C. Let it. The potential difference between the B and C terminals is amplified by a signal processing circuit to obtain a sensor output.

FIG. 3 shows the measurement results of the thermal hysteresis when the thickness of the adhesive 6 is changed. The amount of thermal hysteresis measures the initial value of the sensor output at room temperature (25 ° C),
It is determined from the difference from the initial value when the sensor output is left at a high temperature (120 ° C.) for 2 hours, then returned to room temperature (25 ° C.) over 2 hours and the sensor output is measured again. In this case, A in FIG.
A current of 0.74 mA flows from the terminal, and the above-mentioned sensor output is obtained by amplifying the potential difference between the B and C terminals about 220 times by a signal processing circuit. In this measurement, the pressure P applied to the diaphragm 1a is 750.
mmHg is constant.

From the results shown in FIG. 3, when the thickness of the adhesive 6 is set to 40 μm or more, the amount of thermal hysteresis can be stably reduced. The black circles in the figure indicate those without microbeads 7 mixed therein, and the white circles indicate those with microbeads 7 of various sizes mixed therein. In this case, in order to secure the thickness of the adhesive 6 to 40 μm or more, a diameter of 50 μm is used.
m or more microbeads 7 are mixed.

By setting the thickness of the adhesive 6 to 40 μm or more, the influence of thermal distortion from the package material 5 to the pedestal 3 can be extremely reduced. For this reason, the influence of thermal distortion can be reduced without increasing the height of the glass pedestal 3. Actually, it has been confirmed that the same result as described above is obtained even when the height of the pedestal 3 is changed from 0.7 mm to 0.5 mm.

The upper limit of the thickness of the adhesive 6 does not cause any particular problem as long as the thickness is within a range where there is no problem in use. The silicone adhesive 6 has an elastic force of 0.6.
Although a material of MPa was used, it is considered that the above-described effect can be obtained if the material is 1 Mpa or less.

Furthermore, the present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope described in the claims. For example, as a pressure sensor,
The type which introduces the pressure of the measurement medium into the diaphragm 1a through the pedestal 3 may be used. The pedestal 3 is not limited to the glass pedestal, but may be a silicon pedestal.
It is also possible to use a material other than the above embodiment for the resin material and the resin adhesive 6 described above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a semiconductor pressure sensor according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a bridge circuit using a diffusion gauge 2.

FIG. 3 is a diagram showing the relationship between the thickness of an adhesive 6 and the amount of thermal hysteresis.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sensor chip, 1a ... Diaphragm, 2 ... Diffusion gauge, 3 ... Glass pedestal, 5 ... Package material, 6 ... Adhesive,
7 Micro beads.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasutoshi Suzuki 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation

Claims (5)

[Claims] A diaphragm (1) that is displaced under pressure.
a) formed with a sensor chip (1) having a strain gauge (2) for detecting displacement of the diaphragm; and a pedestal (3) for fixing the sensor chip, wherein the pedestal is made of a resin material. A semiconductor pressure sensor which is adhered to a base (5) with a resin adhesive (6), wherein the thickness of the resin adhesive is set to 40 μm or more. 2. The semiconductor pressure sensor according to claim 1, wherein the resin adhesive is a silicon-based adhesive. 3. The silicone-based adhesive has an elastic force of 1
3. The semiconductor pressure sensor according to claim 2, wherein the pressure is equal to or less than MPa. 4. The resin adhesive according to claim 1, further comprising means for ensuring the thickness thereof.
4. The semiconductor pressure sensor according to any one of claims 1 to 3. 5. The semiconductor pressure sensor according to claim 4, wherein the means for securing the thickness is a bead (7).