JPH0749310A - Gas detector - Google Patents

Abstract

PURPOSE:To provide a gas detector with even higher sensitivity and selectivity of a detection gas. CONSTITUTION:This element includes a semiconductor substrate 1 with one main surface thereof made porous 1a finely, a light emitting element 5 comprising an electrode 2 arranged in a mesh or in a lattice on the surface made porous 1a and an opposed electrode layer 3 arranged on the rear of the substrate 1 and a detector 6 to detect the intensity of light emitted from the light emitting element 5 varying with a gas contacting the surface made porous 1a or a variation of the wavelength of the light.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a gas sensing element.

[0002]

2. Description of the Related Art As is well known, since an oxide semiconductor gas sensing element (gas sensor) has been used in the industrial world as a gas alarm for safety and disaster prevention, it has been widely used in the consumer field such as household appliances. is there. Here, the oxide semiconductor type gas detection is a gas in which an n-type oxide semiconductor is used as a main body and is heated by a heater such as Ni, while a catalyst such as Pt is added to have a sensitizing action on a gas to be detected. It is configured as a sensing element. Then, this gas detection element is incorporated into a required detection circuit, and gas detection is performed by utilizing the change in electrical conductivity when the test gas comes into contact.

By the way, in recent years, against the background of the global environment and energy problems, environmental pollutant gases such as NO _x , SO _x , and CO ₂ have become a problem. For detecting (detecting) this kind of environmental pollutant gas. In addition, the development of high-sensitivity gas sensors is in progress. For example, in the oxide semiconductor type, various investigations have been made on the composition of the n-type oxide semiconductor including additives or the structure of a thin film type element to which various film forming methods are applied in order to increase the sensitivity of the gas detection element. Although it has been tried, a gas detection element having sufficient characteristics has not been developed.

[0004]

As described above, in an n-type oxide semiconductor gas detecting element, in order to improve its sensitivity, the material / composition surface of the gas sensor main body or the structure / shape of the gas sensor main body. Considered from the aspect. However, since the properties of the oxide semiconductor thin film forming the main body, such as porosity or porosity, are limited and it is difficult to control the structure of the gas adsorption site, it is the current situation that sufficient sensitivity characteristics are not obtained. is there. In other words, it is desired to develop a gas detection element having a large surface area (gas adsorption area), capable of controlling the structure of gas adsorption sites, and exhibiting high sensitivity and selectivity of detection gas. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas detection element having higher sensitivity and selectivity of detection gas.

[0005]

A gas detecting element according to the present invention is a semiconductor substrate having one main surface made fine and porous, electrodes arranged in a mesh or lattice on the porous surface, and the substrate. A light emitting element formed of a counter electrode layer disposed on the back surface of the light emitting element and the light emitted from the light emitting element, and the amount of change in the emission intensity or the emission wavelength of the light emitting element changed by the gas contacting the porous surface is detected And a detector.

In the present invention, the porous region of the semiconductor substrate or the metal substrate not only has the function of emitting light, but also sensitively reflects the characteristics of gas, and the emission intensity and emission wavelength change due to gas adsorption. It was achieved by focusing on the first thing that can be surely captured.

[0007]

In the gas detecting element according to the present invention, the surface having an increased surface area due to the fine porosity is used as the gas sensitive portion, so that the adsorption of the test gas is dramatically increased and the sensitivity is greatly improved. To do. Further, since the gas to be detected is detected as the light emission intensity and the light emission wavelength change of the light emitting element, it becomes possible to sensitively reflect the characteristics of the detection gas, and accordingly, the selectivity of the test gas is excellent. Furthermore, since the pores forming the adsorption site can be easily controlled, the selectivity of the test gas is further improved, and the selective adsorption of the test gas is sensitively reflected in the emission intensity and the emission wavelength change, It will function as a highly sensitive gas detection element.

[0008]

Embodiments of the present invention will be described below with reference to FIGS.

Example 1 FIG. 1 is a sectional view showing an example of the structure of a gas detecting element (gas sensor) according to the present invention.
1a is a semiconductor substrate, 2 is a porous 1a of the semiconductor substrate 1
The mesh-like or lattice-like electrodes integrally arranged on the conversion surface, 3 is a counter electrode layer arranged on the back surface of the semiconductor substrate 1, and 4 is a light emitting element 5 in a frame connected to the counter electrode layer 3. Is formed. Reference numeral 6 denotes a detector for receiving the light emitted from the light emitting element 5 and detecting the emission intensity and the emission wavelength change of the light emitting element 5 due to the gas contacting the porous surface 1a. here. The detector 6 is, for example, an n-Si layer 7
a, i-Si layer 7b, p-Si layer 7c forming the light receiving surface, SiO
_A first electrode layer 7e installed via _two layers 7d, said p-S
The antireflection film 7f arranged on the surface of the i layer 7c, and the n-S
The silicon photodiode 7 composed of the second electrode layer 7g integrally disposed on the back surface of the i layer 7a is used as a main body, and the electrode layer 7g integrally disposed on the back surface side of the n-Si layer 7a of the silicon photodiode 7 is used. The frame 6 and the detector 6 connected to
Is formed. Further, in this embodiment, the light emitting surface of the light emitting element 5 (the porous 1a surface) and the p-Si layer 7c forming the light receiving surface of the detector 6 are arranged facing each other with an interval of about 0.3 to 9 mm. The composition is adopted.

Next, the fine porous layer 1a of the semiconductor substrate 1
In other words, the light emitting surface of the light emitting element 5 or the gas sensitive portion can be formed by, for example, anodization of a Si substrate. That is, it can be formed by forming an ohmic electrode (back surface electrode) which forms an anode on the back surface of the Si substrate, and etching while conducting electricity in hydrofluoric acid using a Pt electrode or the like as a counter electrode. Here, the porosity and the porous structure (state) of the porous 1a region depend on the conditions of the anodization, such as the type of Si substrate, the current density, the presence or absence of light irradiation during the anodization, the anodization time, and the anodization solution. It can be controlled arbitrarily depending on the type and concentration, but chemical etching treatment after anodization is also effective. That is, when the anodized Si substrate is immersed in a solution of hydrofluoric acid, nitric acid or the like for several tens of seconds to several hours and subjected to etching treatment, the formation of the porous layer 1a can be performed more effectively.

In this etching process, by irradiating light to limit the wavelength of the irradiating light with a cut filter or the like, the size of the pores corresponding to the detection gas can be arbitrarily controlled, and the porous 1a region can be controlled. It is also possible to control the emission wavelength of.

The conditions for the anodization and the chemical etching treatment are selected and set according to the material (type) of the substrate forming the porous 1a region and the detection gas. It is preferable to carry out in a hydrofluoric acid of about 49% at a current density of 0.5 to 100 mA / cm ^{2 for} a time of about 20 seconds to 100 minutes. Forming with electricity is also effective. On the other hand, the etching treatment is preferably performed in a hydrofluoric acid solution of about 49% or less in the dark or while irradiating with light.

Incidentally, the S containing the porous 1a region of the embodiment is formed.
In the case of the i substrate 1, first, the n-type Si substrate is subjected to anodization treatment while irradiating light to form the porous 1a region forming the gas sensitive portion or the light emitting portion, and then the concentration of 1 to 49%. Chemical etching was performed in hydrofluoric acid. Furthermore, in order to enhance the gas selectivity, and at the same time to promote the adsorption and desorption of gas, P
The t catalyst was supported. That is, the n-type Si substrate that has been subjected to the anodizing treatment and the chemical etching treatment is immersed in an aqueous solution of chloroplatinic acid to impregnate the porous 1a region under reduced pressure, then pulled up and subjected to heat treatment at 500 ° C. Supported a Pt catalyst.

Further, Au is vapor-deposited in a mesh shape (lattice shape or grid shape) on the surface of the porous 1a region supporting the Pt catalyst of the n-type Si substrate 1 by an ion plating method to form the electrode 2. On the other hand, a part of the conductive frame 4 (forming the counter electrode 3) was attached to the back surface to form the light emitting element 5. FIG. 2 shows the main body of the light emitting device 5, that is, the porous type of the n-type Si substrate 1 carrying the catalyst.
Mesh shape (lattice or grid) on 1a area surface
The configuration when the electrode 2 is formed is shown in a perspective view. The electrode 2 is patterned to have a pattern width of several μm to several tens of μm. It is set to 10 to 30 nm. That is, the test gas can easily reach the porous region 1a forming the gas sensitive portion and can secure a sufficient gas adsorption surface.

Next, an example in which the gas detection element having the structure shown in FIG. 1 is used as a hydrogen gas sensor will be described. First, after aging the gas sensing element in the atmosphere with a required potential applied, when hydrogen gas was injected into the atmosphere at a concentration of 20000 ppm, the light emitting element 5
The change in the emission intensity and the change in the emission wavelength of was detected by the detector 6, and this was electrically output to detect hydrogen gas.
The electric output change shown in FIG. 3 was observed. As can be seen from FIG. 3, in the atmosphere, the light output of the porous 1a region forming the light emitting part or the gas sensitive part of the light emitting element 5 decreases, and the output reaches a stable level within about 30 minutes. In addition, the increase in light output with the injection of hydrogen gas, that is, the 80% response time was within 3 minutes. Furthermore, even when the gas detection element was removed from the measurement system (exhausted), it was confirmed that the gas level was restored to the atmospheric level within a few minutes. Since the emission wavelength also changes individually depending on the concentration of hydrogen gas, hydrogen gas can be detected by detecting the amount of change in emission wavelength instead of emission intensity.

In the structure of the light emitting device 5, B is formed on the surface of the n-type Si substrate 9 as shown in a sectional view in FIG.
(Boron) is doped to about 10 ¹⁹ / cm ³ to make it p-type, and anodization is performed in a hydrofluoric acid solution to make the p-type region and the n-type region porous, thereby forming a pn junction with porous Si. After forming the porous regions 10a and 10b that form the chemical emission part or the gas sensitive part, a thickness of 10 to 30n is formed on the surface of the porous region 10a.
When the light emitting element 12 in which the electrodes 11 made of Au film are formed in a grid shape with m and a pattern width of several μm to several tens of μm is used, pn
Since the porous regions 10a and 10b are formed by the joining and the surface area in the vicinity of the pn junction is increased, the sensitivity is further improved.

Embodiment 2 This embodiment is a structural example in which a plurality of gas detecting elements having different characteristics are combined and integrated to further enhance the sensitivity.

That is, one main surface of the Si substrate 13 is anisotropically etched to form a plurality of recesses of 1 × 1 mm apart from each other, and P is ion-implanted into these recessed regions to have different resistivities. Area is provided. Next, after selectively forming each of the doped recessed surface regions by a hydrofluoric acid solution to make them porous (13a), Au is sputtered on the porous 13a-formed surface through a required mask, A transparent grid electrode 14 was formed to prepare a light emitting device having a plurality of light emitting devices 15a on the main surface of one Si substrate 13.

On the other hand, a detector corresponding to this light emitting device was prepared. That is, the detection element 17 having a plurality of pin photodiodes 16a forming a detector main body is provided corresponding to the light emitting element 15 having a plurality of light emitting elements 15a on the main surface of the one Si substrate 13. The light-emitting element 15 was produced according to the production method.

In this way, the prepared light emitting element 15 having a plurality of light emitting elements 15a on the main surface of the Si substrate 13 and the plurality of pin photodiodes 16a on the main surface of the Si substrate 18 are prepared. As shown in the cross-sectional view of FIG. 5, the detection element 17 provided with a plurality of gas detection elements is combined by opposing and opposing the light emitting element 15a and the pin photodiode 16a to each other, and adhering them together. An integrated gas sensing element was constructed. In addition, in this configuration, the test gas can flow into each gas detection element unit,
An inflow path for the test gas is appropriately formed on the bonding surfaces of the Si substrate 13 and the Si substrate 18.

In the case of such a constitution including a plurality of gas detecting element portions having different characteristics, the statistical output is used to detect the electrical output of the photodiode functioning as the light receiving element of each photodetector portion. The pattern recognition of the gas significantly improves the gas identification capability, in other words, the gas selectivity. In other words, it is not only versatile for the test gas, but on the other hand
Since the relationship between the configuration and the response to the test gas is clarified, there is an advantage that the corresponding gas detection element can be easily selected.

In the above description, the Si semiconductor substrate is exemplified as the substrate provided with the porous layer forming the light emitting element body, but the present invention is not limited to this, and other semiconductor substrates may be used. A substrate provided with a porous layer such as SiC may be used as well. Furthermore, the light receiver main body is not limited to the Si photodiode illustrated above, but may be, for example, an (In.Ga) As photodiode.

On the other hand, the positional relationship between the light emitting element and the detector is
The arrangement is not limited to the above-described opposing arrangement, and for example, a detector may be arranged side by side with respect to the light emitting element, and light emitted from the side or reflected light may be received.

[0024]

As described above, the gas detecting element according to the present invention can improve the selectivity with respect to the detection gas, and is further improved in sensitivity and stability in sensitivity characteristics. In other words, various gas detection, including the case of minute concentration which is a problem due to environmental pollution, can be performed with good reproducibility.
Further, since it can be performed with high reliability, it can be said that the practicality of this kind of gas detection element can be further enhanced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a main part of a gas detection element according to the present invention.

FIG. 2 is a perspective view showing a configuration example of a main part of a light emitting element body included in the gas detection element according to the present invention.

FIG. 3 is a curve diagram showing a characteristic example of a gas detection element according to the present invention.

FIG. 4 is a perspective view showing another structural example of a main part of a light emitting element body included in the gas detection element according to the present invention.

FIG. 5 is a cross-sectional view showing another structural example of the main part of the gas detection element according to the present invention.

[Explanation of symbols]

1, 9 ... Semiconductor substrate 1a, 13a ... Porous 2, 14 ...
Grid-shaped electrode 3 ... Counter electrode layer 4 ... Light emitting element side frame 5, 12, 15 ... Light emitting element 6 ... Detector
7, 16 ... Photodiode 7a ... n-Si 7b ... i-
Si 7c ... p-Si 7d ... SiO ₂ layer 7e ... first electrode layer 7f ... antireflection film 7g ... first electrode layer 8 ... detector side frame 10a ... p type porous Si 10b ... n type porous Si 13, 18 ... Si substrate 15a ... Light emitting element section 17 ... Detection element

Claims (1)

[Claims] 1. A light emitting device comprising a semiconductor substrate whose one main surface is finely porous, electrodes arranged in a mesh or grid pattern on the porous surface, and a counter electrode layer arranged on the back surface of the substrate. And a detector for receiving the emitted light of the light emitting element and detecting the amount of change in the emission intensity or the emission wavelength of the light emitting element changed by the gas contacting the porous surface. Gas detection element.