JPH04302479A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To get a sensor, which outputs a static pressure signal and an excessive pressure signal and is capable of miniaturization with simple structure, by junctioning a second silicon plate and a third silicon plate, respectively, so that each region and oxide film may oppose to each other, to both sides of a first silicon plate thereby providing an overpressure protective mechanism in itself. CONSTITUTION:A second silicon plate 34 and a third silicon plate 38 are junctioned, so that each region and oxide film 33, 35, 39, and 42 may oppose to each other, to both sides of a first silicon plate 31. The first silicon plate 31 bends according to the difference of the pressure introduced into the pressure introduction holes 36, 40, and 41 of the silicon plates 34 and 38 at both sides. And the pressure on one side becomes large, it is pushed against the wall of the opposed silicon plate, and it is protected from the breakdown by excessive pressure. And the pressure difference is detected by a first pressure detection element 32, and static pressure and the excessive pressure are detected by the second pressure detection element 37.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor pressure sensors, and more particularly to improving overpressure protection mechanisms and detecting overpressure and static pressure in differential pressure transmitters.

0002

2. Description of the Related Art FIG. 4 is a block diagram of an example of a conventional pressure sensor. In the figure, 1 is a body, on one side of which a first seal diaphragm 2 made of metal is provided, on which the measured pressure PL on the low pressure side acts, and on the other side, the measured pressure PH on the high pressure side acts. A second seal diaphragm 3 made of metal is provided, and an overpressure protection diaphragm 4 made of metal is provided inside.

[0003] In the above configuration, the seal diaphragm 2
If excessive pressure is applied to sensor 3 or 3, overpressure protection diaphragm 4 seats on the opposing body as shown by the dashed line to prevent pressure above a certain level from being applied to the sensor.

0004

[Problems to be Solved by the Invention] However, with such a conventional configuration, since the metal expands and contracts,
Output hysteresis occurs before and after overpressure, leading to deterioration of accuracy.

[0005] It becomes large in size and is difficult to downsize. There are other problems.

[0006]Although there are devices that output static pressure signals,
Nothing that outputs an overpressure signal has been put into practical use.

The present invention has been made in view of these problems, and its purpose is to provide an overpressure protection mechanism in itself and to have a simple structure capable of outputting a static pressure signal and an overpressure signal. An object of the present invention is to provide a semiconductor pressure sensor that can be miniaturized.

[0008]

[Means for Solving the Problems] The present invention, which solves these problems, includes a first silicon plate on which a first pressure sensing element is formed on one surface, and a first silicon plate on which a first pressure sensing element is formed, and on one surface excluding two areas. In this way, an oxide film is formed, and a hole for introducing pressure is formed in the center of the first region, and a second pressure sensing element is formed in the other surface of the second region. It is composed of a silicon plate and a third silicon plate on which an oxide film is formed on one surface except for two regions, and a hole for introducing pressure is formed in the center of each region, and A second silicon plate and a third silicon plate are respectively bonded to both surfaces of the first silicon plate so that the respective regions and oxide films face each other.

[0009]

[Operation] The first silicon plate bends in response to the difference in pressure introduced into the pressure introduction holes of the silicon plates on both sides. When the pressure on one side becomes large, it is pressed against the wall of the opposing silicon plate and is protected from damage due to excessive pressure.

[0010]The differential pressure is detected by the first pressure detection element, and the static pressure and excessive pressure are detected by the second pressure detection element.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall structural diagram of a differential pressure measuring device using a semiconductor pressure sensor according to the present invention. In the figure, 1
0 is a body, which is composed of an upper body 11 and a lower body 12. A support base 20 that supports a semiconductor pressure sensor 30 is fixed inside the upper body 11 . The semiconductor pressure sensor 30 is bonded to the support base 20 using low melting point glass. A hermetic terminal 21 for connecting the signal line of the semiconductor pressure sensor 30 to an external signal lead line 22 is formed in a part of the support base 20 . The joint between the upper body 11 and the support base 20 and the joint between the upper body 11 and the lower body 12 are fixed by welding.

FIG. 2 is an assembly process diagram of the semiconductor pressure sensor 30. (Step A) For example, a piezoresistive element 32 is formed on one surface of the first silicon plate 31 as a first pressure detection element. Note that the piezoresistive element 32 is inside.
Diffusion leads connected to are formed, but are not shown in the figure. An oxide film 33 is formed on the surface on which the piezoresistive element 32 is formed, excluding two regions.

An oxide film 35 is formed on one surface of the second silicon plate 34 except for two regions, and a hole 36 for introducing pressure is formed in the center of the first region. For example, a piezoresistive element 37 is formed as a second pressure detection element on the other surface of the area No. 2.

An oxide film 39 is formed on one surface of the third silicon plate 38 except for two regions, and holes 40 and 41 for introducing pressure are formed in the center of each region. .

Note that each silicon plate 31, 34, 3
The shape of the region where the oxide films 33, 35, and 39 of No. 8 are not formed may be circular or rectangular. (Step B) The surface of the first silicon plate 31 on which the piezoresistive element 32 is formed and the oxide film 33 is formed is overlapped with the surface on which the oxide film 35 of the second silicon plate 34 is formed, and heated at 800°C to 1000°C. Heat to ℃ and thermocompress. The resulting bonding strength is comparable to that of single-crystal silicon. (Step C) After polishing the back surface of the first silicon plate 31 to make it thinner, an oxide film 4 is formed by removing two areas.
form 2. (Step D) The surface of the third silicon plate 38 on which the oxide film 39 is formed is superimposed on the oxide film 42 formed in the step C, and heated to 800° C. to 1000° C. to bond them by thermocompression. (Step E) Connect the lead wires of each piezoresistive element 32 and 37 to the hermetic terminal 21.

[0017] As a result, each silicon plate 31, 3
In the two regions where the oxide films 33, 35, 39 and 42 are not formed, the maximum displacement is the oxide films 33, 35, 39 and 42.
Two silicon diaphragms A and B whose film thicknesses are determined by 39 and 42 are constructed.

In such a configuration, the normal differential pressure ΔP
(=PH-PL) is measured by detecting the stress on the silicon diaphragm A due to the differential pressure ΔP using the piezoresistive element 32 and outputting it as an electrical signal. In this case, measurements can be made even under large static pressures.

[0019] Then, if the excessive pressure becomes PH as shown in FIG.
When acting on the side, the first silicon plate 31
It is seated on the third silicon plate 38 on the side and is prevented from breaking. On the other hand, when excessive pressure acts on the PL side, the first silicon plate 31 is seated on the second silicon plate 34 on the PH side, and destruction is prevented.

[0020] With this configuration, a diaphragm for overpressure protection as in the conventional case is not required, so the overall structure can be simplified and made smaller.

The thickness of the first silicon plate 31, the thickness of the oxide films 33, 35, 39 and 42, and the dimensions of each region forming the diaphragm are determined depending on the differential pressure range and the magnitude of excessive pressure. Select appropriately.

Furthermore, in detecting the deflection of the diaphragm, it is possible to form an electrode on the diaphragm portion and detect it as a change in capacitance, or to form a beam on the diaphragm portion and detect it as a change in vibration of the beam. Good too.

On the other hand, the magnitude of the static pressure is detected by a piezoresistive element 37 formed on the surface of the second silicon plate 35 corresponding to the region of the diaphragm B. Also,
The piezoresistive element 37 can also detect the deformation stress of the diaphragm B caused by excessive pressure from the PH side or the PL side.
The magnitude of overpressure can also be measured. Since the magnitude of static pressure and excessive pressure can be detected in this way, the amount of process information increases, and more accurate process processing becomes possible than conventional control and maintenance based only on differential pressure information.

Furthermore, by forming an arithmetic circuit on the surface of the second silicon plate 34, an integrated pressure sensor can be constructed.

Furthermore, a protective film such as a nitride film may be formed on the contact portions of the silicon plates 31, 34, and 38 that are seated when excessive pressure is applied.

[0026]

As described above in detail, according to the present invention, the following effects can be obtained.

(2) The semiconductor pressure sensor of the present invention has a structure in which an overpressure protection mechanism is provided by microfabrication of silicon, and the entire structure of the differential pressure system can be simplified and made smaller.

(2) Since the overpressure protection mechanism is composed of silicon and its oxide film, the hysteresis is smaller than that of an overpressure protection mechanism using a metal diaphragm.

[0029] Semiconductor pressure sensors are suitable for mass production, similar to the manufacturing process of integrated circuits, and together with miniaturization of mechanical parts, low-cost differential pressure gauges can be realized.

(2) Since the magnitude of static pressure and excessive pressure can also be detected, highly accurate process processing becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an overall structural diagram of a differential pressure measuring device using a semiconductor pressure sensor according to the present invention.

FIG. 2 is an explanatory diagram of a process for manufacturing an embodiment of a semiconductor pressure sensor according to the present invention.

FIG. 3 is an explanatory diagram of the operation of the semiconductor pressure sensor according to the present invention.

FIG. 4 is a configuration diagram of an example of a conventional overpressure protection mechanism.

[Explanation of symbols]

30 Semiconductor pressure sensor 31 First silicon plate 32, 37 Piezoresistance element 33, 35, 39, 42 Oxide film (SiO2) 3
4 Second silicon plate 36, 40, 41 Pressure introduction hole 38 Third silicon plate

Claims (1)

[Claims] Claims: 1. A first silicon plate on which a first pressure sensing element is formed on one surface; an oxide film is formed on one surface except for two regions; A hole for introducing pressure is formed in the part, a second silicon plate in which a second pressure detection element is formed is formed on the other surface of the second region, and two regions are excluded on one surface. and a third silicon plate in which a hole for introducing pressure is formed in the center of each region, and each region and the oxide film are opposite to each other on both sides of the first silicon plate. A semiconductor pressure sensor characterized in that a second silicon plate and a third silicon plate are respectively bonded to each other in such a manner.