JPS60127766A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To employ a back surface pressurizing groove and to obtain high reliability for high pressure by selectively forming a piezoelectric resistance element on one surface of a semiconductor crystal substrate, forming an annular with film, bonding the thick portion of the substrate to a base which is opened with a pressure applying hole, and communicating the hole with a thin portion. CONSTITUTION:When a pressure P is applied to a pressure applying hole 6, the pressure P is transmitted through the hole 6 and a pressure guiding slot 9 to a recess 8. Accordingly, a thin portion 3 is deformed, the resistance value of a piezoelectric element 7 is varied, thereby obtaining an electric output proportional to the pressure P. Since the center of a diaphragm 1 is secured to a base 5 to increase the rigidity of the diaphragm, the maximum stress sigmaa of the bonding surface is reduced as compared with a conventional thin central shape, and when a borosilicate glass which has substantially equal thermal expansion to the silicon is used for the base 5, the strength of the glass is weak, and it is particularly advantageous, thereby performing the increase in the pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensor used for detecting oil pressure of construction machinery, and more particularly to a semiconductor pressure sensor using a semiconductor as a diaphragm.

Conventionally, semiconductor pressure sensors have been provided in which a diaphragm made of a semiconductor is provided with a thin strain-generating portion, and a piezoresistive element is entirely formed on the strain-generating portion. In such a semiconductor pressure sensor, when the measurement range becomes several tens to 100 atmospheres, the strength of the valley becomes a problem as well as the output characteristics.

In particular, when a piezoresistive element formed on the surface of a diaphragm is placed in a fluid to be measured, a protective structure is required because the piezoresistive element may be deteriorated by acid, alkali, etc. in the fluid to be measured. Since the structure must have a high voltage resistance structure, there is a problem in that it is difficult to reduce costs.

Therefore, in order to solve this problem, we created a hole for pressure introduction in the base bonded to the back of the diaphragm.
An innate pressure sensor with a back-pressure structure has been developed in which the sound of the fluid to be measured is guided from this hole to the back surface of the piezoresistive element.

Figure 1 is a plan view showing an example of a conventional semiconductor pressure sensor employing such a bag surface pressure structure, Figure 2 (a) is a stress distribution diagram, and Figure 2 (b) is the semiconductor pressure shown in Figure 1. FIG. 3 is a cross-sectional view of the sensor. In these figures, a diaphragm 1 made of a flat silicon single crystal has a thin part 3 formed by providing a recess 2 with a circular planar shape on the back surface, and a diaphragm 1 formed around this thin part 3. It has a thick part 4. The lower surface of the thick part 4 of this diaphragm l is fixed to a base 5 whose coefficient of thermal expansion is approximately equal to that of silicon, and a pressure introduction hole 6 is bored in the center of this base 5 to lead the pressure t to the diaphragm l. has been done. Further, near the periphery of the thin wall portion 3 region of the main surface of the diaphragm l, there are two sets of piezoresistive elements 7 arranged in a radial direction and a tangential direction.
A total of 4 are formed by diffusion method or ion implantation method,
These piezoresistive elements 7 are bridge-connected.

In the semiconductor output sensor configured in this way, the second
When a measured pressure P is applied to the pressure introduction hole 6 of the base 5 as shown in FIG. By changing the value, an electrical output proportional to the applied pressure P can be obtained. Figure 2 (a) &! , which shows the state of stress distribution occurring at the joint surface between the diaphragm l and the base 5. As shown in this figure, the maximum stress σa occurs at the boundary between the thin wall portion 3 and the thick interior portion 4.

However, in the above-mentioned conventional semiconductor output sensor, when the applied pressure P becomes a sieve of several tens to 100 atmospheres, the maximum stress σa becomes significantly large, and a large tensile stress is generated in the base 5. This base 5 is made of borosilicate glass, which has a thermal expansion bond almost equal to that of silicon, but its strength is weak, so under high pressures of several tens to 100 atmospheres, the stress generated at the joint surface of the diaphragm 1 and the base 5 The drawback was that base 5 was often destroyed.

The object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a back-pressure sanding machine which is advantageous in terms of cost reduction.

The present invention also provides a highly reliable semiconductor pressure sensor for high pressure.

In order to achieve all of these objectives, the present invention selectively forms a piezoresistive element on one side of a substrate made of semiconductor crystal, and thickens the center and outer periphery on the other side of the substrate. It is possible to join the thick part of the board to the base which has been formed with a massive thin part and drilled with a loud output, and to communicate the pressure hole and the thin part. .

Embodiments of the present invention will be described below based on the drawings.

3 is a plan view showing an embodiment of the semiconductor pressure sensor according to the present invention, FIG. 4(a) is a stress distribution diagram, and FIG. 4(b) is a sectional view of the semiconductor pressure sensor shown in FIG. 3. 8 is a concave portion and 9 is a pressure introduction groove, as shown in FIGS. 1 and 2.
Parts corresponding to the figures are given the same reference numerals.

A diaphragm l made of a flat silicon single crystal is formed with, for example, an annular recess 8 on its back surface so that the central part and the outer periphery are the thick part 4. An annular thin wall portion 3 is formed. The shape of this diaphragm l is, for example, an internal plate thickness of 0.18 rom,
One side of the outer peripheral shape is 3nlnl angle. diaphragm l
Four piezoresistive elements 7 are diffused and formed on the main surface in the region where the thin wall portion 3 is formed, one set of which coincides in the tangential direction and the other set coincides with the radial direction. The eaves are arranged to look like this. Each of these piezoresistive elements 7 is assembled into a full bridge, and they are drawn out to the outside by an aluminum electrode (not shown) deposited on the surface of the diaphragm l.

The diaphragm 1 constitutes a strain-generating portion in the thin-walled portion 3 in the region where the concave portion 8 is formed. A pressure introduction groove 9 is formed from the center position of the central thick wall s4b to the recessed portion 8. The pressure introducing groove 9 and the concave portion 8 can be formed simultaneously, for example, by using an alkali etching method.

The base 5 is made of, for example, borosilicate glass, and a pressure hole 6 is bored in the center of the base 5.

The outer circumference thickness inside 4a and the central thickness g of the diaphragm l
4b is bonded to the main surface of the base 5 using an adhesive such as low melting point glass, and the pressure introduction hole 6 of the base 5 and the recessed part 8 of the diaphragm 1 are communicated via a pressure gauge groove 9. Ru.

In the semiconductor pressure sensor e configured in this manner, when pressure P is applied to the pressure introduction hole 6, this pressure P is transferred to the pressure hole 6 and the recessed portion 8 through the pressure hole 6 and the pressure hole 6.
, the thin wall portion 3 deforms, and the piezoresistive element 7
The resistance value changes, and a drowsiness output proportional to the pressure P can be obtained. FIG. 4(a) shows the stress distribution state r occurring at the joint surface between the diaphragm 1 and the base 5. Since the center part t is fixed to the base 5 to increase the rigidity of the diaphragm, it is different from the conventional thin center part. It can be seen that the maximum stress σa at the joint surface is reduced compared to cedar. This means that
It is particularly advantageous to use borosilicate glass, which has almost the same thermal expansion as silicon, for the base 5, since borosilicate glass has a weak strength, and this makes it possible to use borosilicate glass.

In addition, in this embodiment, the pressure is applied to the center of the 4-bar 6-t base 5! 7! Since the pressure introducing groove 9 and the concave portion 8 are integrally formed by an alkali etching method or the like, it is very advantageous in terms of cost reduction.

FIG. 5 is a plan view of another embodiment of the semiconductor pressure sensor according to the present invention, and parts corresponding to those in FIG. 3 are given the same reference numerals. The difference between this embodiment and the first embodiment is as follows.
This is possible because four pressure introducing grooves 9 are formed radially from the central position of the central thick portion 4b toward the direction of each piezoresistive element 7. In this way, the number r of 9 before pressure introduction increases.
The effects of the first embodiment are maintained as they are, and furthermore, the several pressure introduction grooves 9 completely prevent clogging due to foreign matter in the constant fluid.

FIG. 6 is a plan view showing still another embodiment of the semiconductor pressure sensor according to the present invention, and FIG. 7 is a sectional view, in which parts corresponding to FIGS. 3 and 4 are given the same reference numerals. The difference between this embodiment and the above-mentioned first and second embodiments is that the output is 6? r: 'Fit the position offset from the center of the base 5 (K valve membrane, this output inlet hole 6t diaphragm 1
The concave part 8VC is connected directly to the pressure introduction jg 9'
E is omitted.

In this way, it is possible to prevent clogging caused by @objects in the fluid to be measured, and furthermore, since the joint surface between the central thick part 4b and the ball surface of the base 5 becomes large, the diaphragm l Stiffness *-tm a can be reduced.

As explained above, according to the present invention, it is possible to adopt a back pressure structure that guides the d111 constant fluid from the pressure introduction hole of the base to the back surface of the piezoresistive collector, which is advantageous for cost reduction. Since the stress generated at the joint surface with the base can be completely reduced, a semiconductor pressure sensor for high pressure can be provided.

[Brief explanation of the drawing]

1 and 2 are configuration diagrams showing an example of a conventional semiconductor output sensor, in which FIG. 1 is a plan view, FIG. 2(a) is a stress distribution diagram, and FIG. 2(b) is a cross-sectional view. 3 and 4 are configuration diagrams showing the first embodiment of the semiconductor pressure sensor according to the present invention, in which FIG. 3 is a plan view, FIG. 4(a) is a stress distribution diagram, and FIG.
Figure (b) is a sectional view, Figure 5 is a plan view showing a second embodiment of the semiconductor pressure sensor according to the invention, and Figures 6 and 7 are a third embodiment of the semiconductor pressure sensor according to the invention. In the configuration diagrams, FIG. 6 is a plan view and FIG. 7 is a sectional view. l...Diaphragm, 3...Thin wall part,
4a...Thick wall at outer periphery @s, 4b...Thick wall at center, 5...Base, 6...Pressure base, 7. ...Piezoresistance element, 8...
... Concave portion, 9... Pressure introduction groove. Figure 1 7 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 7

Claims (1)

[Claims] A piezoresistive element on one side of a substrate made of semiconductor crystal?
! - selectively forming an annular thin part on the other surface of the substrate so that the central part and the outer peripheral part are thick parts, and attaching the thick part of the board to the base having a pressure introduction hole. At the same time, the pressure introduction hole and the thin wall portion are connected to each other. ]l Semiconductor pressure sensor with t% of connections.