JPS61149857A - Sensor for analyzing dissolved material - Google Patents

Abstract

PURPOSE:To detect the electrically neutral dissolved material in a soln. by forming a thin semiconductor layer as a photocatalyst on a gate insulating film of an FET. CONSTITUTION:The thin semiconductor layer 5 which acts photocatalytically is formed on the gate insulating film of the FET consisting of a gate 1, a source 2, a drain 3 and the gate insulating film 4, by which a sensor 6 for analyzing the dissolved material is constituted as a whole. The semiconductor which acts catalytically is exemplified by Si and Ge alone, metallic phosphide such as InP, GaP or Zn3O2, metallic arsenide such as AlAs or GaAs, metallic sulfide such as CdS, ZnS or Cu2S, metallic selenide such as CdSe ZnSe, metallic telluride such as CdTe or ZnTe, metallic oxide such as TiO2, ZnO or SrTiO3, and the ternary or quaternary mixed crystals consisting of semiconductors, for example, GaAlAs, InGaAs, CdSSe, ZnSSe, InGaAsP, GaAlAsP, CuInS2, CuInSe2, etc.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a sensor for analyzing dissolved substances suitable for quantitative analysis of dissolved substances in a solution. The present invention relates to a sensor for analyzing dissolved substances that is capable of quantitatively analyzing dissolved substances that do not have an electric charge.

[Technical background of the invention and its problems] In recent years, devices using field effect transistors (hereinafter referred to as FETs) have been attracting attention for quantitative analysis of dissolved substances in solutions. That is, an FET with a substance sensitive to a specific substance attached to the gate surface can function as a sensor sensitive to the specific substance. This FET sensor has a high impedance at the gate and a low impedance at the output side, so it has both a sensor function and an impedance converter function. For this reason, F
Measurements using ET sensors are less affected by noise from the environment, ensuring accuracy.

This can be miniaturized, and sensors with the same characteristics and shape can be manufactured in large quantities with little variation, which is a source of low prices.

When this FET sensor is immersed in a solution and used as an analyzer for measuring volume concentration, for example, even if the potential and capacitance between the gate and the liquid interface change slightly, the drain on the cutting edge side will be the first to change. This can be effectively reflected in the current. That is, electrochemical changes between the gate/liquid interface can be detected as changes in drain current.

By the way, as mentioned above, the FET sensor performs detection by changing the gate potential, so if the detection substance has a charge such as an ion, the detection substance directly changes the gate potential. No problem, but
There is a problem in that detection is impossible when the detection substance has no electric charge, such as a gas, that is, it is electrically neutral.

[Object of the Invention] The present invention solves the conventional problems and provides a sensor for analyzing dissolved substances using an FET.

The object of the present invention is to provide a sensor for analyzing dissolved substances that can detect electrically neutral dissolved substances in a solution.

[Summary of the Invention/1] As a result of extensive research to achieve the above object, the present inventors have developed a semiconductor that can function as a so-called photocatalyst, which functions as a catalyst that participates in redox reactions of substances when irradiated with light. Focusing on this, if such a semiconductor is added to an FET sensor and used, the photocatalytic action of the semiconductor will cause the neutral dissolved substances present there to be ionized by the redox action, so that the electrical behavior can be changed to an FET sensor. The present invention was completed by confirming that it is possible to detect electrically neutral dissolved substances by sensing.

That is, the sensor for dissolved gas analysis of the present invention is as follows.

A sensor for analyzing dissolved substances using the gate of a field effect transistor as a working electrode, characterized in that a semiconductor thin layer as a photocatalyst is formed on the gate insulating film of the field effect transistor.

FIG. 1 shows an example of the basic structure of a sensor 6 for analyzing dissolved substances according to the present invention. A thin semiconductor layer 5 which acts as a material is formed, and the sensor 6 for analyzing dissolved substances is constituted as a whole.

In the sensor for analyzing dissolved substances of the present invention, semiconductors that act photocatalytically include, but are not particularly limited to, simple substances such as Si and Ge; InP;

Metal phosphides such as GaP, Zn3P2; Al
l Metal arsenides such as As, GaAs; CdS,
Metal sulfides such as Zr+S and Cu2S; GdS
e, metal selenide such as Zn5e: CdTe, Zn
Metal telluride such as Te; TiO2, ZnO1Sr
Metal oxides such as Ti03; and ternary or quaternary mixed crystals made of these semiconductors, such as GaAJL A
s, rnGaAs, Cd5Se, ZnSSe,
InGaAgP, GaA! LAsP, Cu1nS
2, (:ulnSe2, etc.).

Semiconductors with a photocatalytic effect as described above have the function of causing a redox reaction of dissolved substances present at the interface simply by irradiation with light, so there is no need for any operation such as applying a bias from the outside. Therefore, the structure of the sensor for dissolved substance analysis is basically as described above.
A structure in which a thin film made of the above semiconductor is laminated on the gate insulating film of the ET is sufficient. At this time, the semiconductor thin film does not disturb the operating characteristics of the FET itself at all.
The sensor for analyzing dissolved substances of the present invention can be easily manufactured by applying a conventional method to manufacturing an FET, and then forming the above-mentioned semiconductor thin layer having a photocatalytic effect on the gate insulating film. . A vacuum evaporation method, a sputtering method, a CVD method, etc. can be applied to form the semiconductor thin layer. and.

The layer thickness is preferably about 500 to 10,000 A. On the other hand, some of the above-mentioned photocatalytic semiconductors are not stable in aqueous solutions, so when using such semiconductors, It is preferable to laminate a protective film to protect the semiconductor thin layer.

Such a protective film is therefore required to transport carriers generated by light to the surface of the semiconductor thin layer.

It is preferable to use a thin metal film, a conductive polymer film such as polypyrrole, etc. However, even an insulating material such as 5102 can be used as long as it is an ultra-thin film of about 100 layers.

Next, the principle of the photocatalytic action of such a semiconductor will be explained. FIG. 2 schematically shows the energy level of the semiconductor itself and the redox level of dissolved substances in the solution. First, the semiconductor 11 is exposed to light 17 in the wavelength range that the semiconductor can absorb in the solution 14. When irradiated, valence band 12
Holes are excited in the conduction band 13, and electrons are excited in the conduction band 13. At this time.

The conduction band 13 is at a position higher than the redox level 15 of the electron-accepting substance (acceptor) in the solution 14, and the valence band 12 is at a position higher than the redox level 15 of the electron-donating substance (donor) in the solution 14.
If the redox level is lower than 16, the electrons and holes generated by the light irradiation can reduce acceptors and oxidize donors, respectively.

In other words, the substance to be detected can be detected by appropriately selecting and using a semiconductor that can take on the valence band and conduction band levels as shown in Figure 2, relative to the redox level of the substance to be detected in the solution. It can be ionized.

In this case, in order to detect the electrically neutral 7 receptor (A), if a donor (D-) is present in the solution to promote the reaction, the redox level is 1 in Figure 2.
In 5, the reaction A→A- is also at the redox level 1B.
In this case, the reaction D−→D progresses, and the acceptor A is quickly ionized. On the other hand, when detecting an electrically neutral donor (D), on the other hand, an acceptor (A1) may be allowed to coexist.

The ionized substance to be detected changes the gate potential of the analytical sensor, and as a result, it is detected as a change in drain current.

However, if substances with similar redox levels coexist in the solution, the reaction may proceed competitively, and analysis of the target substance may be inhibited. In such a case, 1) the selectivity of the semiconductor itself as a catalyst is utilized, or 2) it has a selective catalytic effect on the dissolved substance to be further detected on the semiconductor thin layer.

By providing a catalyst layer (metal layer or organometallic complex modification layer) or by providing a selective substance permeable membrane on this metal layer, it becomes possible to substantially detect only the desired reaction. .

The above metal layer not only acts selectively on the dissolved substances to be detected, but is also extremely effective in increasing the sensitivity of senna by promoting the photocatalytic action for the desired reaction. be. Metals with such catalyst selectivity include Ir, Os, Pd, P
t, Rh, Ru, Re, Fe, Go.

Old or Raney nickel is preferred, and oxides of these metals can also be used.

As described above, the dissolved substance analysis sensor of the present invention makes it possible to measure a number of electrically neutral dissolved substances, such as 02a degrees or 002 concentration in blood.

During actual measurements, the sensor described above is immersed in a solution and then irradiated with light at the absorption wavelength of the semiconductor used to carry out the appropriate redox reaction in the solution.
It is sufficient to detect fluctuations in the drain current of the FET due to the generated ions.

[Embodiments of the invention] (1) Manufacture of sensors for dissolved substance analysis - As an example, a 02 gas analysis sensor was manufactured.

That is, as shown in FIG. 3, after manufacturing an FET consisting of a gate 21, a source 22, a drain 23, and a gate insulating film (Si02) 24 formed on a p-type silicon substrate by applying a conventional method, gate protection is performed. A Si3N4 film 27 with a thickness of about 1000 mm is formed as a film by the GVD method, and TiO2 is selected as a semiconductor that acts photocatalytically on the 02 gas, and a Si3N4 film 27 with a thickness of about 5000 mm is formed on the Si3N4 film 27. A thin layer 25 of the material was formed by sputtering to cover the surface other than the TiO2 surface, and a sensor 26 for 02 gas analysis was completed.

(2) Determination of dissolved substance concentration The 02 gas analysis sensor 2B manufactured as described above is immersed in the liquid to be measured having various dissolved 02 concentrations, and the surface of the TiO2 layer is irradiated with light 28 from a high-pressure mercury lamp while draining. We investigated changes in current. The results are shown in Figure 4. In other words, Figure 4 shows the relationship between 02 concentration and drain current,
This is shown by plotting OG[pp(02)] on the horizontal axis and current on the vertical axis, and as is clear from Figure 1, the drain current changed with a certain relationship depending on the dissolved 02 concentration. Therefore, it was confirmed that this 02 gas sensor functioned well.

[Effects of the Invention] As is clear from the above description, the sensor for analyzing dissolved substances of the present invention is obtained by adding a photocatalytic action to the FET function, which is impossible with conventional FET sensors. Quantitative analysis of electrically neutral substances has become possible. Namely.

It can be used as a highly sensitive sensor not only for gases such as 02 and 002, but also for all electrically neutral substances. Furthermore, the sensor for analyzing dissolved substances of the present invention, in principle, selectively detects substances using only the band position of the semiconductor used and, in some cases, the selective catalytic activity of the metal. Compared to other methods, such as selective detection methods that involve diffusion processes in selective substances, senna has the advantage of a very fast response speed.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram showing an example of the basic configuration of the senna for dissolved substance analysis of the present invention, Fig. 2 is a conceptual diagram showing the principle of the photocatalytic reaction of the present invention, and Fig. 3 is a conceptual diagram showing an example of the present invention. FIG. 4 is a diagram showing the relationship between the dissolved enzyme concentration and the drain current of the sensor. ■, 21......Gate, 5, 25...
...Semiconductor thin layer. 6.26......Dissolved substance analysis sensor, 1
2・・・・・・・・・Valence band, 13・・・・・・・
...Conduction band. Figure 1 Figure 3 1o9 [02+ppm +]

Claims (1)

[Claims] A sensor for analyzing dissolved substances that uses the gate of a field effect transistor as a working electrode, characterized in that a semiconductor thin layer as a photocatalyst is formed on the gate insulating film of the field effect transistor. Sensor for analysis.