JPS635232A - Pressure detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detector, and particularly to a pressure detector suitable for accurately measuring high pressure in a high temperature atmosphere such as a combustion chamber of an internal combustion engine.

[Prior Art] As a general structure of a pressure sensor, one in which a pressure receiving diaphragm is held in a housing and a strain gauge is attached to this is often used. Conventionally, metal strain gauges have been used as strain gauges, but in recent years, semiconductor strain gauges have been attracting attention because they can provide linear and highly sensitive output and can be extremely miniaturized.

As such a semiconductor strain gauge, it is well known that the surface of a silicon (Si) single crystal substrate is doped with impurities such as boron (B) or phosphorus (P) to form a strain gauge element and used as a pressure detection element. There is.

[Problems to be Solved by the Invention] By the way, although the semiconductor pressure sensing element described above has the above-mentioned advantages over conventional metal strain gauges,
Due to the N-junction structure, the leakage current that occurs as the temperature rises means that the operating temperature is relatively low (approximately 150°C).
temperature (below ℃).

On the other hand, U.S. Patent No. 3,858.150 discloses a method in which a polycrystalline silicon layer is formed on a single crystal silicon substrate with an insulating film interposed therebetween, and the silicon layer is doped with impurities to form a strain gauge element. A pressure detector is disclosed, which does not have a PN junction, and therefore can measure pressure in a higher temperature range.

However, the pressure sensor disclosed herein has a structure in which the central part of the single crystal silicon substrate is thinned by etching to form a pressure receiving diaphragm, and the pressure sensor is relatively low pressure (30K).
There was a problem in that it could only be used for measuring g/cd).

To measure the combustion pressure of an internal combustion engine, a high temperature atmosphere (approximately 500
℃) and high pressure (for example, in the case of a diesel engine, it is necessary to measure the maximum pressure of 100 J/d), and the present invention provides a pressure detector that can accurately measure high pressure at such high temperatures. The purpose is to provide.

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIGS. 1 and 2. A cylindrical housing 3 has a sensing body 2 held at its tip opening, and the sensing body 2 is The pressure receiving diaphragm 21 is made thinner. The pressure detection element 1 is bonded to the surface of the diaphragm 21 opposite to the pressure receiving surface. The sensing body 2 is made of a material with high strength and a small coefficient of thermal expansion, and the pressure detecting element 1 is formed by doping a polycrystalline silicon layer 13 formed on a silicon substrate 11 with an insulating layer 12 interposed therebetween. The strain gauge is made up of a semiconductor strain gauge element.

Then, the silicon substrate is bonded to the opposite surface of the pressure receiving surface of the pressure receiving diaphragm by eutectic bonding.

[Operations and Effects] When pressure is applied, the pressure receiving diaphragm 21 deforms accordingly, and the pressure sensing element 1 integrally joined to the diaphragm 21 emits an output signal corresponding to the deformation strain.

According to the present invention, since the semiconductor strain gauge element on the pressure sensing element 1 does not have a PN junction structure, it can be used in a high temperature atmosphere. Since the pressure receiving diaphragm 21 made of a small material is eutectic bonded with sufficient bonding strength, high pressure can be measured satisfactorily.

[Example] FIG. 4 shows the overall structure of a pressure detector. The pressure sensor has a cylindrical housing 4. A mounting thread 4a is formed on the outer periphery of the lower half of the housing 4, which has a small diameter, and the outer periphery of the upper half of the housing 4 has a hexagonal surface.

A metal cylindrical sensing head 3 is welded and fixed to the tip opening of the housing 4.
A sensing body 2 in the form of a thick plate is fitted and fixed in the opening at the tip. The details are shown in FIG.

In the figure, the sensing body 2 has a thinner wall in stages toward the center, and the smallest thinner wall serves as a pressure-receiving diaphragm 21, to which the pressure detecting element 1 is bonded directly above. The sensing body 2 is made of Fe-Ni- whose thermal expansion coefficient is as small as that of 3i (about 2 to 5X10-6i°C).
It is made of a Go-based alloy (for example, Mitsubishi Metals Co., Ltd., trade name "Kovar"), and a projecting wall 2a provided on the outer peripheral edge of the lower surface is welded and fixed to the opening edge of the sensing head 3.

The structure of the pressure detection element is shown in FIGS. 2 and 3.

The substrate 11 is a silicon single crystal plate with a thickness of 100 to 300 μm, and the entire upper surface of the substrate 11 is coated with 0.3
An 8102 layer 12 with a thickness of ~1.0 μm is formed, and a polycrystalline silicon layer 13 with a thickness of about 1 μm is formed thereon by low pressure CVD.

The polycrystalline silicon layer 13 contains boron (B) or phosphorus (
P) is doped by thermal diffusion and patterned by dry etching to form semiconductor strain gauge elements 13a, 1.
3. b, 13c, and 13d are formed.

Electrode patterns 14 made of Pt are formed on the polycrystalline silicon layer 13, and pad portions 14 of each electrode pattern 14 are formed.
Passivation film 1 of Si3N4 etc. is used for all except 1.
It is covered by 5. Each of the strain gauge elements 13a to 13d is located directly above the peripheral edge of the pressure receiving diaphragm 21, and forms a full bridge circuit.

The pressure sensing element 1 having such a structure is bonded and fixed to the sensing body 2 via the bonding layer 5 (FIG. 1). The bonding layer 5 is formed by plating Act on the top surface of the sensing body 2.
This is formed by eutecticizing this with Si of the silicon substrate 11. 3i and AQ are expressed as (
, 3i content of 14.5% and a eutectic point at a temperature of 830° C., and can be held at around this temperature for a certain period of time and then cooled to perform eutectic bonding.

An alumina ring plate 61 is provided around the pressure detection element 1.
are arranged, and a plurality of electrodes (flash) formed on the ring plate 61 and each of the pad portions 141 on the pressure detection element 1 are arranged.
are connected by a wire line 62 such as an AU line. The ring plate 61 is fixed to the sensing body 2 by brazing or the like. The lower ends of lead pins 63 are fixed to each of the electrodes of the ring plate 61 by brazing, and each lead pin 63 passes through the housing 4 (Fig. 4) and is soldered to a terminal plate 64 disposed within the upper end thereof. is fixed.

A ceramic substrate 65 on which a signal processing circuit for signal processing and temperature compensation is formed is disposed above the terminal plate 64.
The board 65 is connected to the terminal plate 6 by lead pins 67.
4 and is electrically connected thereto. The upper end opening of the housing 4 is covered with a cover body 41, and the tip of a lead wire 66 passed through the center thereof is connected to the substrate 6.
It is connected to the signal processing circuit on 5.

When the pressure detector having the above structure is fixed to the combustion chamber wall with the threaded part 4a, the tapered part 31 of the sensing head 3 (Fig. 1)
touches the chamber wall. When combustion pressure is applied to the pressure-receiving diaphragm 21 in this state, it deforms, and the resistance values of the semiconductor strain gauge elements 13a and 13d change in accordance with the deformation strain, so that a signal corresponding to the degree of output is obtained.

At this time, high combustion pressure is applied to the diaphragm 21, but the diaphragm 21 made of an Fe-Ni-Co alloy has sufficient strength and heat resistance, and the diaphragm 21 is eutectic bonded to Since the detection element 1 is firmly bonded, a highly sensitive output signal corresponding to the deformation of the diaphragm 21 can be obtained.

Furthermore, the heat received by the sensing body 2 is dissipated to the combustion chamber wall through the tapered portion 31 of the sensing head 3, thereby suppressing the temperature rise of the sensing body 2. Since the polycrystalline silicon layer 13 doped with impurities is provided on the layer 12 to form a semiconductor strain gauge element, highly accurate measurement is possible even in a high temperature atmosphere of about 500°C.

Sensing body 2 contains Ag2O3 or Ag2O
A ceramic of Si3N4 containing 3 can be used and is shown in FIG. The outer periphery of the upper surface of the sensing body 2 is joined to the stepped portion of the sensing head 3, and as shown in FIG.
This is done by laminating a metallized layer 71, an Nr plating layer 72, and a brazing layer 73 of A (J paste). Wrap the part tightly and hold it.

In this case, the pressure sensing element 1 and the sensing body 2 are bonded by forming a metallized layer 51 of Mo or W on the surface of the sensing body, and forming an AQ layer 52 on top of this, as shown in FIG.
is plated and eutectic bonded to the silicon substrate.

With such a structure, the same effects as in the above embodiment can be obtained.

Note that Pt can also be used instead of ACI in each of the above embodiments.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention, in which FIG. 1 is an enlarged sectional view of the tip of the pressure detector, FIG. 2 is a cross-sectional view of the pressure detection element, and FIG. ■ Line sectional view, Fig. 3 is a plan view of the pressure sensing element, Fig. 4 is an overall sectional view of the pressure detector, Fig. 5 is a state diagram of Ag-3i, and Figs. 6 to 8 are a diagram of the present invention. Another embodiment is shown in which FIG. 6 is an enlarged sectional view of the tip of the pressure detector, and FIGS. 7 and 8 are sectional views of the main parts, and are respectively an enlarged sectional view of section A and an enlarged sectional view of section B in FIG. 6. It is. 1...Pressure detection element 11...Silicon substrate 12...Insulating layer 13...Polycrystalline silicon layer 13a, 13b, 13c113CJ...Semiconductor Strain gauge element 2... Sensing pod 21... Pressure receiving diaphragm 3... Sensing head 4... Housing 5... Eutectic bonding layer @1 Figure 3 Figure 2 Figure 40 Figure 5 Ag Sit shoulder 4' (QiOm '10)
S! @Figure 6 Figure 8 Figure 7

Claims (3)

[Claims] (1) A sensing body is held in the tip opening of a cylindrical housing protruding into a pressure chamber, a part of the sensing body is made thin to form a pressure receiving diaphragm, and a pressure detecting element is bonded to the opposite surface of the pressure receiving surface of the diaphragm. The sensing body is made of a material with high strength and low coefficient of thermal expansion, and the pressure sensing element is made of a semiconductor by doping impurities into a polycrystalline silicon layer formed on a silicon substrate with an insulating layer interposed therebetween. 1. A pressure sensor comprising a strain gauge element, wherein the silicon substrate is bonded to the pressure receiving diaphragm by eutectic bonding. (2) The sensing body is made of a Fe-Ni-Co alloy, a plated layer of Ag or Pt is formed on the opposite side of the pressure-receiving surface of the diaphragm, and the plated layer is eutectic bonded to the silicon substrate. A pressure sensor according to claim 1. (3) The sensing body is made of Al_2O_3 or Si_3N_4 ceramic containing Al_2O_3, and the surface opposite to the pressure receiving surface of the diaphragm is made of Mo or W.
After forming a metallized layer, Ag
2. The pressure sensor according to claim 1, wherein a plating layer of Pt or Pt is formed and the plating layer is eutectic bonded to the silicon substrate.