JPS6015010B2 - pressure detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensor, and particularly to a pressure sensor that detects pressure using a semiconductor strain gauge that is resistance-diffused in a semiconductor single crystal.

This type of pressure detector is made by selectively diffusing a p-type resistor into a semiconductor single crystal such as n-type silicon, generating strain in the semiconductor single crystal by applying pressure, and creating a resistance in the p-type paper antibody due to the piezoresistance effect. The applied pressure is known by measuring the change. Figures 1a and 1b show the structure of the silicon diaphragm that is the pressure sensor of this pressure detector.
indicates the top surface, and b indicates the cross section. This sensor consists of a silicon diaphragm 1, a silicon pedestal 3, and a metal pedestal 4.
2, and gauge resistors 21, 22, 23, and 24 formed by diffusion of p-type impurities are diffused on the super strained portion 11, and each gauge resistor 21, 22, 23, and 24 is
There is an electrode 25 made of aluminum extending on the fixed part 12.
is provided. This silicon diaphragm 1 is supported by a fixing portion 12 on a silicon base 3 via an adhesive layer 5, and the silicon base 3 is further adhesively supported on a metal base 4 via an adhesive layer 6. In order to apply pressure to the silicon diaphragm of this pressure sensor, it is generally attached to a metal case (not shown) and a pressure difference is generated between the front and back sides of the strain generating part 11.

When the strain generating part 11 is distorted due to this pressure difference, the gauge resistors 21 and 23 in the center and the gauge resistors 22 and 24 in the peripheral part are arranged so that their resistance values increase and decrease in the opposite way to each other.
By assembling these gauge resistors 21, 22, 23 and 24 into a bridge and applying a voltage, an output signal approximately proportional to the pressure can be extracted. In pressure detectors, the expansion coefficient of the metal case is generally larger than that of silicon, so the silicon diaphragm 1
When attaching the silicon diaphragm 1 to a metal case, the silicon diaphragm 1 is airtightly bonded to a silicon base 3 with the same expansion coefficient using an adhesive layer 5, and then the silicon diaphragm 1 is airtightly bonded to a metal base 4 using an adhesive layer 6. The structure is welded to the case.

The metal base 4 is made of a material with an expansion coefficient between that of silicon and the case metal, such as fanico, tungsten, and molybdenum. may also be used. The adhesive layer 6 is made of gold silicon (Au-Sj
) Eutectic, gold-germanium (Au-W) eutectic alloy, organic adhesive, glass, etc. are used, but in all cases, those with a solidification temperature of 100 to several 100 qo are used. . However, in a pressure detector having such a structure, the expansion coefficient of the metal constituting the metal base 4 is larger than that of the silicon base 3, so when assembling the pressure sensor, the silicon base 3 is When the adhesive layer 6 of the silicone base 3 is returned to room temperature after adhesion, tensile stress is concentrated on the free outer end of the adhesive layer 6, and since silicone is weak against tensile stress, It had the disadvantage of increasing the probability of cracking, and the manufacturing process was slow.

The present invention makes it possible to provide a pressure sensor that can prevent cracking by reducing the tensile stress generated in a support base made of a semiconductor. a semiconductor diaphragm having a fixed part formed therein and a strain gauge resistor formed in the strain-generating part by selective diffusion; a disk-shaped support base made of the same type of semiconductor and having a hole in the center, which supports the semiconductor diaphragm in the fixed part;
In a pressure sensor having a pressure sensor formed by bonding the support base and a cylindrical metal base with a hole in the center to support the support base, the support base has a circumferential groove on the metal base side. and the inner diameter of the groove is equal to or smaller than the outer diameter of the metal base, and the outer diameter of the groove of the bracket is larger than the outer diameter of the metal base. .

Examples will be described below.

FIGS. 2a and 2b show a cross section and a bottom view of one embodiment, respectively, and the same parts as in FIGS. 1a and 1b are given the same reference numerals.

This device differs from the device shown in FIG. 1 in that it has a circumferential groove 31 on the metal base 4 side of the silicon base 3, as shown in FIG. The inner diameter of this circumferential groove 31 is smaller than the outer diameter of the metal base 4, and its outer diameter is larger than the outer diameter of the metal base 4. Figure 4 shows the distribution of stress that occurs when the silicon base 3 and metal base 4 are cooled after joining with this structure, and Figure 5 shows the stress distribution of the conventional structure for comparison. case silicon stand 3
This shows the stress distribution on the bottom surface.

That is, in FIG. 5, which shows the conventional structure without grooves, A shows the compressive stress distribution on the bottom surface of the silicon pedestal, and B shows the tensile stress distribution on the bottom surface of the silicon pedestal.
It can be seen that a large tensile stress is acting just outside the joint end of the silicon base 3 and metal base 4.

On the other hand, in FIG. 4, which shows the structure of an embodiment in which the groove 31 is formed, C indicates the compressive stress distribution on the lower surface of the silicon pedestal 3, and 0 indicates the tensile stress distribution on the side surface of the groove 31. In this case, it can be seen that the tensile stress on the lower surface of the silicon stand 3 is gone. However, on the other hand, a tensile stress D is generated on the side surface of the groove 31;
This can be reduced by increasing the depth to a certain extent. For example, if the inner diameter of the metal base 4 is 2 ribs and the outer diameter is 4 ribs, and the depth of the groove 31 is 1 rib or more, the stress generated will be approximately 1'2 compared to the case without grooves in Fig. 5. It can be done. In this way, when bonding the silicon base 3 with the metal base 4 by making the area of the adhesive surface smaller than the area of the metal base 4, the metal base 4
Even if the expansion coefficient of the silicon base is larger than that of the silicon base, the stress on the adhesive surface is only compressive stress, and since silicon is generally strong against compressive stress, cracks will not occur in the silicon base 3, and the walking performance can be improved.

In addition, in the example, a case was described in which the area of the adhesive surface between the silicon base and the metal base was made smaller than the area of the metal base, but the area of the bonded surface between the silicon base and the metal base is the area of the metal base. Almost the same effect can be obtained in equivalent cases.

As described above, the pressure detector of the present invention can prevent cracking by reducing the tensile stress generated in the support base made of semiconductor, and has a great industrial effect.

[Brief explanation of drawings]

Figures 1a and b are a top view and a sectional view of a subordinate pressure detector, respectively, Figures 2a and b are a sectional view and a bottom view of an embodiment of the pressure detector of the present invention, respectively, and Figure 3 is the same. FIG. 4 is a stress distribution diagram of the main part, and FIG. 5 is a stress distribution diagram of the main part of the conventional pressure detector of FIG. 1 shown for comparison. 1...Silicon diaphragm, 3...Silicon stand, 4.
...Metal stand, 6...Adhesive layer, 31...
·groove. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. A semiconductor diaphragm in which a diaphragm-like thin part is provided in a semiconductor single crystal to form a strain generating part and a fixing part, and a strain gauge resistor is formed in the strain generating part by selective diffusion, and the semiconductor diaphragm A disc-shaped support base made of the same type of semiconductor and having a hole in the center, which is supported by the fixing part, and a cylindrical metal base with a hole in the center, which supports the support base, are each concentrically bonded. In the pressure sensor having a pressure sensor, the support base has a circumferential groove on the metal base side, and the inner diameter of the groove is equal to or smaller than the outer diameter of the metal base, and A pressure detector comprising a support base in which the outer diameter of the groove is larger than the outer diameter of the metal base. 2. The pressure sensor according to claim 1, wherein the semiconductor is silicon.