JPH05249063A - Pressure gage integrating gas sensor - Google Patents

Abstract

PURPOSE:To obtain a gas sensor enabling simultaneous measurement of the concentration and pressure of a gas to be inspected. CONSTITUTION:Projecting parts 3 formed of an electrically insulative material are provided on an Si substrate 2, a gas-sensitive element and a heater lead 10 are provided and thereby the concentration of a gas is measured. Besides, a diaphragm 5 is provided on the same Si substrate 2, piezo-resistance elements 20 are provided and thereby the pressure of the gas is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor, and more particularly to a pressure sensor integrated gas sensor having both the function of measuring the concentration of a test gas and the function of measuring the pressure of a gas containing the test gas.

[0002]

2. Description of the Related Art Conventionally, in order to measure the concentration of a test gas and the pressure of a gas containing the test gas, a concentration sensor for measuring the concentration of the test gas and a pressure of the gas containing the test gas are measured. It was necessary to separately use the pressure sensors that operate.

[0003]

In the conventional gas sensor, an installation space for two gas sensors is required to simultaneously measure the concentration of the test gas and the pressure of the gas containing the test gas, and the gas sensor 2 is used. The cost for the unit is required.

The present invention is intended to solve the above problems, and an object thereof is to provide a pressure sensor integrated type gas sensor capable of simultaneously measuring the concentration of a test gas and the pressure of the gas containing the test gas with one chip. Is.

[0005]

According to the present invention, an overhang portion made of an electrically insulating material is provided on a Si substrate of a gas sensor, and a gas sensitive element (for example, a metal oxide semiconductor layer) is placed on the overhang portion. The concentration of the gas in the gas containing the test gas is measured by the change in the resistance value of the gas sensitive element. Further, in the present invention, a part of the same Si substrate is thinned to provide a diaphragm and a piezoresistive element is installed on the diaphragm, and the pressure of the gas containing the test gas is changed by changing the resistance value of the piezoresistive element. taking measurement.

That is, according to the present invention, in a pressure sensor integrated gas sensor comprising a Si substrate, a gas sensing element, a heater lead and a piezoresistive element, an overhanging portion made of an electrically insulating material is provided on the Si substrate in the air. The gas sensitive element and the heater lead are installed on the projecting portion, and a diaphragm is provided by thinning a part of the Si substrate and the piezoresistive element is installed on the diaphragm.

[0007]

As described above, in the pressure sensor-integrated gas sensor according to the present invention, the gas sensitive element and the piezo element are provided on the same chip so that the concentration of the test gas can be measured by the gas sensitive element and the piezo element can be used. Can measure the pressure of the gas in the gas containing the test gas.

[0008]

The present invention will be described in more detail with reference to the examples shown in the drawings. FIG. 1 is a schematic explanatory view showing the overall configuration of a pressure gauge integrated gas sensor according to the present invention. However, the electrode wiring, the heater lead, and the gas sensitive element are not shown. A substrate 2 is anodically bonded on a glass base 1 in the figure. Here, a case of using a Si substrate, which is convenient for performing anisotropic etching as the substrate 2, will be described as an example. In particular, in order to form the p-type piezoresistive element 20, it is preferable to use the n-type Si (100) surface as the substrate 2. The Si substrate 2 is anisotropically etched with an etching solution (eg, potassium hydroxide aqueous solution),
The protruding portion 3, the concave portion 4 and the diaphragm 5 are formed. If necessary, the glass base 1 is provided with a reference pressure introduction port 1a for introducing a reference pressure on the back surface side of the diaphragm 5.

First, the sensor for measuring the concentration of the test gas according to the present invention will be described. FIG. 2 shows an enlarged view of the vicinity of the overhanging portion 3, and FIG. 3 shows a sectional view taken along line XX ′ in FIG. Here, a cantilever structure is adopted as an example of the projecting portion 3, but a bridge structure or the like may be used. Further, the number of the overhanging portions 3 may be any number as needed. A heater lead 10 and a metal oxide semiconductor layer 11 as a gas-sensitive element are provided on the projecting portion 3. Since the resistance value of the metal oxide semiconductor layer 11 changes when the test gas is detected, this change is detected by the detection lead 12. When the Si (100) surface is used for the substrate 2, the lengthwise direction of the overhanging portion 3 is set to (11
When the direction inclined by 45 degrees from the 0) direction is selected, the projecting portion 3 can be easily manufactured. Silica is preferable as the material of the overhang portion 3, and platinum is preferable as the material of the heater lead 10 and the detection lead 12. Metal oxide semiconductor layer 11
Examples of the material include oxides of tin, zinc, indium, titanium, iron and the like, and among them, the use of tin oxide is most preferable.

Next, FIG. 4 shows an embodiment in which an oxidation catalyst layer carrying platinum or palladium is used as a gas sensing element. FIG. 5 shows a YY ′ cross section in FIG. The heater lead 10 and the oxidation catalyst layer 13 are formed on the projecting portion 3. The oxidation catalyst layer 13 is formed on or near the heater lead 10. This is for facilitating transmission of the temperature change of the oxidation catalyst layer 13 due to combustion of the test gas to the heater lead 10. As the material of the oxidation catalyst layer 13, for example, a material containing platinum or palladium as a catalyst on a carrier containing alumina or silica as a main component is used. When the oxidation catalyst layer 13 is exposed to the test gas, the test gas burns near the oxidation catalyst layer 13 and a temperature change occurs in the oxidation catalyst layer 13. The oxidation catalyst layer 13
The temperature change appears in the heater lead 10 as a resistance value change, and the concentration of the test gas is detected by measuring the resistance value change.

Further, the sensor for measuring the gas pressure to be measured according to the present invention will be described. FIG. 6 shows an enlarged view around the diaphragm, and FIG. 7 shows a ZZ ′ cross section in FIG. The piezoresistive element 20 is formed by diffusing impurities or ion-implanting boron into the n-type Si (100) surface, for example. In this case, it is preferable that the piezoresistive element 20 is arranged in the peripheral portion of the diaphragm as shown in the figure in order to improve sensitivity, and the longitudinal direction thereof is the (100) direction. A wiring 21 is connected to the piezoresistive element 20. Aluminum is generally used as the material, but using platinum simplifies the manufacturing process. Although not shown, wire bonding is performed so that these piezoresistive elements 20 form a bridge circuit.

Finally, an example of the manufacturing process of the pressure sensor integrated gas sensor according to the present invention will be briefly described with reference to FIG. The figure shown here is slightly different from the actual sectional view for the sake of clarity. The case where the gas-sensitive element is a metal oxide semiconductor layer will be described. The pressure gauge integrated gas sensor according to the present invention is manufactured in the order of (a) to (g) of FIG. The contents are as follows. (A) The n-type Si (100) substrate 2 is thermally oxidized to obtain the Si
Silica layers are formed on both upper and lower surfaces of the substrate 2. (B) The silica layer in the portion where the piezoresistive element 20 is formed is etched. (C) After depositing boron, drive in in an oxidizing atmosphere to form a piezoresistive element 20. (D) A contact hole is formed at a predetermined position on the piezoresistive element 20. At this time, a resist is also applied to the lower surface of the Si substrate 2 to protect the silica layer. (E) Platinum is vapor-deposited on the Si substrate 2 by sputtering to form the wiring 21 of the piezoresistive element 20, the heater lead 10, and the detection lead pattern. (F) After patterning the tin oxide film by sputtering,
A metal oxide semiconductor layer (gas sensitive element) 11 is formed. (G) Silica between the two metal oxide semiconductor layers (gas sensitive element) 11 is anisotropically etched with an aqueous solution of potassium hydroxide, and overhangs 3 made of an insulating material on the Si substrate.
Then, the recess 4 and the diaphragm 5 provided between the Si substrate and the overhanging portion 3 are formed.

[0013]

As described above, according to the present invention, 1
A pressure sensor integrated gas sensor capable of simultaneously measuring the concentration of a test gas and the pressure of a gas containing the gas can be realized with a chip.
Moreover, since the gas concentration sensor and the pressure sensor can be formed on the same substrate, the gas sensor can be downsized. Further, since only one type of gas sensor needs to be produced, the gas sensor can be mass-produced and the production cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing the overall configuration of a pressure gauge-integrated gas sensor according to the present invention.

FIG. 2 is an enlarged view of a projecting portion in FIG.

3 is a cross-sectional view taken along the line X-X 'in FIG.

FIG. 4 is an explanatory diagram showing a case where an oxidation catalyst layer is used as a gas sensing element.

5 is a cross-sectional view taken along the line Y-Y ′ in FIG.

FIG. 6 is an enlarged view of the vicinity of the diaphragm portion in FIG.

7 is a sectional view taken along the line Z-Z 'in FIG.

FIG. 8 is an explanatory view showing a manufacturing process of the gas sensor integrated gas sensor of the present invention.

[Explanation of symbols]

 1a Reference pressure introduction port 1 Glass base 2 Substrate (Si substrate) 3 Overhanging part 4 Recessed part 5 Diaphragm 10 Heater lead 11 Metal oxide semiconductor layer 12 Detection lead 13 Oxidation catalyst layer 20 Piezoresistive element 21 Wiring

Claims (1)

[Claims] 1. A pressure sensor integrated gas sensor comprising a Si substrate, a gas sensing element, a heater lead and a piezoresistive element, wherein an overhanging portion made of an electrically insulating material is used for the S
The gas sensing element and the heater lead are installed on the i substrate in the air, and the gas sensing element and the heater lead are installed on the overhanging portion. A part of the Si substrate is thinned to provide a diaphragm, and the piezoresistive element is provided on the diaphragm. A gas sensor integrated with a pressure gauge, which is characterized by being installed.