JPH0617892B2 - Amorphous semiconductor ion sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an amorphous semiconductor ion sensor. More specifically, it relates to an ion sensor including a field effect transistor using an amorphous semiconductor as an active region.

[Problems to be Solved by the Related Art and Invention] Conventionally, as a sensor for detecting the ion concentration in an electrolytic solution, a so-called semiconductor field effect ion sensor in which a field effect transistor and an ion sensitive film are combined ( ISFE
(Also called T). Its structure is almost the same as that of the insulated gate field effect transistor, but the gate of the transistor has an electric insulating film instead of metal and an ion sensitive film formed thereon.

In such an ISFET, a potential that is determined by the ion concentration and activity in the electrolytic solution is generated between the electric insulating film on the gate and the electrolytic solution, which changes the conductivity of the semiconductor surface under the gate insulating film. As a result, the current value between the source electrode and the drain electrode changes, so that the ion concentration in the electrolytic solution is detected.

As such an ISFET, there is conventionally a crystalline silicon semiconductor ion sensor having a structure in which a bulk silicon wafer is used as a semiconductor layer and is covered with an ion sensitive film such as tantalum oxide. However, when manufacturing such an ion sensor, in order to insulate the part of the ion sensor that is not covered with the ion-sensitive film from the electrolytic solution that is the solution to be measured, this part needs to be covered with an electrically insulating film. is there. However, the production of the crystalline silicon semiconductor ion sensor with such a coating has a problem that the process is complicated.

In order to eliminate such defects, a method of forming an island-shaped silicon layer on a sapphire substrate as described in Jun Kimura, Mie Kawana, Toshihide Kuriyama: Electronic Materials, Vol 23, No. 12, 1984. Invented. In the ISFET manufactured by such a method, sapphire is a good insulator, so that there is an advantage that insulation of the substrate region is easily achieved, but since sapphire is expensive, the manufacturing cost of such ISFET is low. There is the problem of becoming expensive.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an amorphous semiconductor ion sensor that does not require a complicated manufacturing process and can be manufactured easily and inexpensively.

[Means for Solving Problems] An amorphous semiconductor ion sensor according to the present invention has a source electrode and a drain electrode made of metal on an insulating substrate, and an active layer made of an amorphous semiconductor layer covering both electrodes. Have an area,
The active region is covered with an electrically insulating film and / or an ion sensitive film.

Example An amorphous semiconductor ion sensor according to the present invention will be described below with reference to the drawings showing an example. 1 to 4 are views showing an embodiment of an amorphous semiconductor ion sensor according to the present invention.

FIG. 1 is a plan view of an amorphous semiconductor ion sensor which is an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA in FIG. 1, and FIG. 3 is a sectional view taken along the line BB in FIG. FIG. 4 is a sectional view taken along line CC in FIG. 1. In the figure, (1) is an insulating substrate made of glass having a rectangular vertical cross section and a rectangular horizontal cross section. On the surface of the insulating substrate (1), the left end portion shown in FIG. 1 (hereinafter, upper, lower, left, right are
What is shown in each figure of FIG. 4 is shown. Further, when the upper, lower, left and right sides in FIGS. 2 to 4 are shown, they are described as shown in the left side of FIG. ) And an upper end portion, a source electrode (2) made of L-shaped chromium is fixedly formed along these ends by a vacuum deposition method. The lower left end of the source electrode (2) is formed so as to extend from the upper end of the insulating substrate (1) in the width direction to almost the center of the width.

A drain electrode (3) made of substantially inverted L-shaped chromium is formed on the left and lower ends of the surface of the insulating substrate (1) in the same manner as the source electrode (2). There is. The upper left end of the drain electrode (3) is formed so as to extend from the lower end in the width direction of the insulating substrate (1) to almost the center of its width. And the lower left corner of the source electrode (2) and the drain electrode (3)
A gap with a constant interval of 15 μm is formed between the upper left corner and the upper left corner. An amorphous semiconductor layer (4) made of amorphous silicon is formed so as to cover the gap, the lower left end of the source electrode (2) and the upper left end of the drain electrode (3). The amorphous semiconductor layer (4) is formed by glow discharge decomposition of a mixed gas of silane gas and phosphine gas diluted with hydrogen gas at a high frequency of 13.56 MHz.
The right end portion of each of the source electrode (2) and the drain electrode (3) is formed to be a little wider than the other portions thereof, and the other portion excluding the right end portion and the amorphous semiconductor layer.
An electric insulating film (5) made of silicon oxide is formed so as to completely cover (4) and cover almost the entire surface of the insulating substrate (1) except for the right end portion. This electrical insulation film (5)
A mixed gas of silane gas and laughing gas (N ₂ O gas) 1
It is formed by glow discharge decomposition at a high frequency of 3.56MHz. And as shown in FIGS. 1 and 2,
The amorphous semiconductor layer (4) on the upper surface of the electric insulating film (5)
Within the range corresponding to the range in which the source electrode (2)
The gap between the drain electrode (3) and the source electrode (2)
An ion sensitive film (6) having a slightly smaller area than the amorphous semiconductor layer (4) is formed so as to cover the lower left lower end and the upper left end of the drain electrode (3). The ion sensitive film (6) is made of silicon nitride. The ion-sensitive film (6) is formed by glow discharge decomposition of a mixture of silane and ammonia at 13.56 MHz.

Next, the operation of the amorphous semiconductor ion sensor of the present embodiment having the above structure will be described with reference to FIG.

FIG. 5 shows an ion concentration measuring circuit by the source follower method. Vds (domain source voltage) in this circuit
Is kept constant and Id (domain current) is kept constant so that a constant current circuit is used. Here, Vds is set to about several volts.

Although the conductivity of the semiconductor surface under the gate insulating film changes depending on the ion concentration and activity of the solution to be measured (electrolyte), since Id is kept constant, the interface potential between the gate insulating film and the solution to be measured is changed. Is detected as a change in source potential (Vout).

The insulating substrate (1) and the source electrode in the above examples
The materials of (2), the drain electrode (3), the amorphous semiconductor layer (4), the electric insulating film (5) and the ion sensitive film (6) are not limited to those in the above-mentioned embodiment, and the material to be measured Appropriate other materials can be used depending on the type of liquid and the usage conditions of the ion sensor. Further, the method of forming the source electrode (2), the drain electrode (3), the amorphous semiconductor layer (4), the electric insulating film (5) and the ion sensitive film (6) is not limited to those in the above-mentioned embodiments. Alternatively, another method may be used.

EFFECTS OF THE INVENTION Since the amorphous semiconductor ion sensor of the present invention is configured as described above, the amorphous semiconductor layer can be easily and safely formed by forming an electric insulating film by a glow discharge decomposition method. The desired part of the ion sensor of the present invention such as can be insulated and separated from the solution to be measured, and further, it uses an insulating substrate having a long length and after completing the wiring connection between the source electrode and the drain electrode and the external circuit. This can be easily performed by coating the desired portion with an electric insulating film.

Further, in the present invention, the formation of the amorphous semiconductor layer or the electrically insulating film on the insulating substrate can be easily performed at a low temperature by decomposing a gas such as a silane gas by glow discharge. As sapphire, an inexpensive amorphous semiconductor ion sensor can be manufactured because glass, plastic, or metal whose surface is oxidized and coated with resin to insulate it can be used.

[Brief description of drawings]

FIG. 1 is a plan view of an amorphous semiconductor ion sensor which is an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA in FIG.
FIG. 3 is a sectional view taken along the line BB in FIG. 1, FIG. 4 is a sectional view taken along the line CC in FIG. 1, and FIG. 5 shows an ion concentration measuring circuit by the source follower method. (Main symbols in the drawing) (1): Insulating substrate (2): Source electrode (3): Drain electrode (4): Amorphous semiconductor layer (5): Electrical insulating film (6): Ion-sensitive film

Claims (3)

[Claims] 1. An insulating substrate having a source electrode and a drain electrode made of metal, and having an active region made of an amorphous semiconductor layer covering both electrodes, the active region being an electrically insulating film and / or An amorphous semiconductor ion sensor characterized by being covered with an ion sensitive film. 2. The amorphous semiconductor ion sensor according to claim 1, wherein the amorphous semiconductor layer contains an element of Group 4 of the periodic table as a main component. 3. The amorphous semiconductor ion sensor according to claim 2, wherein the amorphous semiconductor layer contains silicon as a main component.