JP2877822B2 - Multi-gas identification gas detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas detection device that discriminates and detects the presence of one or more types of gases in an atmosphere.

(Prior art)

Gas detection devices include a semiconductor detection type using a metal oxide and a catalytic combustion type using a catalyst. In any case, it is necessary to heat a gas-sensitive element using a heater. Power consumption is large and there is a problem in responsiveness. For this reason, a gas detector using a micro heater (Japanese Patent Publication No. 62-2438) formed by fine processing has been proposed (Japanese Patent Application Laid-Open No. 61-191953). Although the power consumption and responsiveness have been greatly improved by the use of the micro heater, it is necessary to add a filter or the like in order to have gas selectivity, which leaves a problem in terms of cost and the like. In addition, the filter detects only a target gas except for miscellaneous gases, and it is impossible to identify various types of gases with one gas detection device.

〔Purpose〕

An object of the present invention is to provide a gas detection device capable of discriminating various kinds of gases with one gas detection device without requiring an additional filter or the like.

〔Constitution〕

The present invention relates to a substrate, an overhang portion made of an electrically insulating material provided overhanging the substrate over the air, a metal oxide semiconductor layer for gas detection provided over the overhang portion, and the metal oxide semiconductor layer. In a gas detection device having a contact electrode lead and a heater lead provided substantially juxtaposed to the electrode lead, the metal oxide semiconductor layer, two or more overhangs provided with the electrode lead and the heater lead are present, And the material of the metal oxide semiconductor layer and the electrode lead on each overhang or overhangs of some of them, respectively,
The response pattern of each detection element (electrode material and metal oxide semiconductor layer) is shown in Table 1 below, and further, when the temperature of the gas detection section at the overhang is set as shown in Table 1. Is characterized by identifying the corresponding gas type shown in the table when it becomes as shown in the table.

Hereinafter, the device of the present invention will be described in more detail with reference to the accompanying drawings. In short, the present invention has a plurality of micro heaters and a gas detecting element in a gas detecting device, By changing the material of the oxide semiconductor layer and the material of the electrode lead in contact with the oxide semiconductor layer, a single gas detection device attempts to identify various types of gases.

1 and 2 show examples of a gas detector according to the present invention in which a cross-linking structure is employed. Here, four overhang portions 2, 3, 4, and 5 made of an electrically insulating material are provided on a substantially square-shaped substrate 1 as a nice bridge structure floating in the air. Accordingly, the number of overhang portions may be any number as long as it is two or more.

FIG. 3 shows an example of a gas detection device according to the present invention in which a cantilever structure is employed. Here, any number of overhanging portions may be used as long as the number is two or more. FIG. 4 is a sectional view taken along the line (IV)-(IV ') of FIG.

The substrate 1 is made of a material that can be easily subjected to undercut etching and does not deform even at a high temperature, for example, Si, Al, Cu, Ni, Cr, or the like, and is preferably made of Si (100). The reason for using the (100) plane is to use a known anisotropic etchant when performing undercut etching. The external dimensions of the substrate 1 are about 1 to 4 mm square, and the thickness is suitably 0.1 to 1 mm.

Heater leads 6,7,8,9 and metal oxide semiconductor layers 10,11,12,13 are provided on four overhangs 2,3,4,5 formed by undercut etching of the substrate 1, respectively. And the electrode leads 14, 15, 16, 17, connected to the metal oxide semiconductor layer
18, 19, 20, and 21 are formed.

As one specific example of the device of the present invention, the overhang portions 2, 3, 4
3 and 5 will be described with reference to the case where the upper metal oxide semiconductor layers 10, 11, 12 are made of TiO ₂ and the metal oxide semiconductor layer 13 on the overhang portion 5 is made of SnO ₂ . I will do it. 5 (a), (b), (c), and (d) are (X ₂ ) − of the gas detectors of the overhanging parts 2, 3, 4 and 5 in FIG.
(X ₂ ′), (X ₃ ) − (X ₃ ′), (X ₄ ) − (X ₄ ′) and (X ₅ ) − (X ₅ ′).

The gas detectors of the overhanging parts 2 to 4 are Pd / TiO ₂ or A
It has a u / TiO ₂ diode configuration. The thicknesses of Pd and Au, which are the electrode leads 15, 17, and 19 on TiO ₂ , are desirably about 200 mm. The electrode leads 14, 16, and 18 under TiO ₂ are preferably made of In for making ohmic contact. Metal oxide semiconductor layer,
There are various methods for forming the electrode, such as a vapor deposition method, a sputtering method, and a method using a “thin film deposition apparatus” (JP-A-59-89763) invented by one of the present inventors, Ota. May be.

The IV characteristic of the Pd / TiO ₂ diode when the heater lead is energized and the gas detection unit is heated to about 70 ° C. is shown in FIG. In the figure, (a) shows the characteristics when the atmosphere does not contain CO, and (b) shows the characteristics when the atmosphere contains about 3500 ppm of CO. If a constant voltage is applied in the forward direction,
The presence of CO gas can be detected by a change in the current value. The type of detection gas can be selected by changing the material of the electrode and the temperature of the gas detection unit.

SnO _{2 in the} overhanging portion 5 detects gas by a change in the resistance value of SnO ₂ itself. In this case, the electrode materials are Pt, Au, Pd
Any material having heat resistance such as described above may be used.

For convenience, in FIG. 5, 10, 11, and 12 are TiO ₂ , 1
3 is SnO ₂ , 14, 16 and 18 are In, 15 and 19 are Pd, 17 is Au, 20
And 21 use Pt.

Table 1 shows the gases that can be responded to by the gas detection elements at each overhang.

When the temperature of the gas detectors of the overhang portions 2 and 3 is set to normal temperature, the temperature of the gas detector of the overhang portion 4 is 70 ° C., and the temperature of the gas detector of the overhang portion 5 is 35 ° C., SiH ₄ , H ₂ , C
For gas of O, C ₂ H ₅ OH, each gas detection element
The response of the pattern shown in FIG. 2 is shown, and the gas type can be identified.
In Table 2, −２ means that there was a response, and × means that there was no response.

In the above description, the oxides of tin and titanium have been given as examples of the metal oxide semiconductor, but oxides such as zinc, indium, nickel, iron, tungsten, cadmium, and dynadium may also be used. .

The gas detection device of the present invention changes the material of the metal oxide semiconductor layer and the electrodes (upper and lower electrode leads) in various ways.
By changing the temperature of the gas detector, it is possible to identify more other gases.

〔effect〕

According to the gas detection device of the present invention, various types of gases can be easily identified without using a filter or the like.

[Brief description of the drawings]

FIG. 1 is a plan view of an example of a gas detection device according to the present invention, and FIG. 2 is a sectional view taken along the line (II)-(II ') of FIG. FIG. 3 is a plan view of another example of the gas detector according to the present invention, and FIG. 4 is a sectional view taken along the line (IV)-(IV ') of FIG. 5 (a) (ii) (c) and (d) of FIG. 3, respectively _{(X 2) - (X 2} ') line, (X ₃₎ - (X _3') lines, (X ₄₎ -
(X ₄ ') line and the _{(X 5) - (X 5} ' is a cross-sectional view of) lines. FIG. 6 is a graph showing IV characteristics of a Pd / TiO ₂ diode. 1 ... substrate, 2,3,4,5 ... overhang 6,7,8,9 ... heater lead 10,11,12,13 ... metal oxide semiconductor layer 14,15,16,17,18 , 19,20,21 …… Electrode lead 22 …… Insulating film, O …… Cavity

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/12

Claims (1)

(57) [Claims] 1. A substrate, an overhanging portion made of an electrically insulating material provided overhanging the substrate over the air, a metal oxide semiconductor layer for gas detection provided over the overhanging portion,
In a gas detection device having an electrode lead in contact with the metal oxide semiconductor layer and a heater lead substantially juxtaposed to the electrode lead, an overhang portion provided with the metal oxide semiconductor layer, the electrode lead and the heater lead And two or more, and the material of the metal oxide semiconductor layer and the electrode lead on each overhanging portion or overhanging some of them, and the temperature of the gas detecting portion of the overhanging portion are as follows, respectively. When the response pattern of each detection element is as shown in Table 1, the corresponding gas type shown in the table is identified. Gas detector.