JPS6311845A - Semiconductor ion sensor - Google Patents

Abstract

PURPOSE:To facilitate the work of building a sensor body, by providing a window adapted to bring an aqueous solution to be measured into contact with an ion sensitive film to induce an interface potential generated at the window to a gate area. CONSTITUTION:A sensor and a collation electrode are combined to be immersed into an electrolytic solution to be measured. When a Ta2O5 layer 8 gets in contact direct with the electrolytic solution through a window 10, an interface potential is generated in the layer 8 corresponding to the activity of ion to be measured in the solution. The interface potential is induced to an Si3N4 layer 6 through a ground metal film 7. As the portion of the layer 6 corresponding to a gate area 4 reaches a potential equivalent to the interface potential, the dielectric constant of the area 4 varies with the interface potential. So, a specified voltage is applied between a source and a drain to obtain a current value corresponding to the activity of ions. Therefore, the setting of an appropriate size of the window 10 produces I>=SD current almost corresponding to the ion activity while the arrangement of the window 10 at a desired position facilitates manufacturing work with a lower dimensional accuracy.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a semiconductor ion sensor.

[Conventional technology]

Conventionally, semiconductor ion sensors that integrate an ion-sensitive membrane and a field-effect transistor functioning as a preamplifier have been put into practical use. This semiconductor ion sensor is, for example, P
A drain diffusion region and a source diffusion region are formed on a shaped silicon substrate, a gate insulating film is formed between these source and drain diffusion regions, and this gate insulating film is used as an ion-sensitive film to detect the electrolyte to be measured. It is configured to directly contact the solution and measure the ionic activity in the electrolyte solution based on the change in conductivity between the source and drain corresponding to the interfacial potential generated between the gate insulating film and the electrolyte solution. . Since this semiconductor ion sensor is used with the gate section immersed in the aqueous solution to be measured, it has the disadvantage that leakage current is likely to occur and measurement errors are likely to occur.

In a conventional semiconductor ion sensor, 1000 µm is deposited on the surface of a P-type silicon substrate in which a drain diffusion region and a source diffusion region are formed.
00 SiO□ layers are formed, and this 8102
A layer of Si3N, which acts as an ion-sensitive membrane, is formed on the surface of the layer. This 513N4 layer is 1 in the gate part.
The thickness is 000 A, and the thickness is 70 A in areas other than the gate part.
The film is said to have a thickness of 0.00 mm, and functions as an ion-sensitive membrane as well as a protective layer.

[Problem that the invention seeks to solve]

In the conventional semiconductor ion sensor described above, the ion-sensitive film is formed between the source region and the drain region, but since the distance between the source region and the gate region is several 10 μm, the dimensions of the ion-sensitive film and This has the drawback that the placement position must be formed with high precision, making the process of creating the sensor body troublesome.

In addition, since the Si3N layer has high hardness and poor viscoelasticity,
Cracks are likely to occur even with the slightest impact from the outside, and once cracks occur, leakage current increases and measurement errors become large.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor ion sensor which eliminates the above-mentioned drawbacks, allows an ion-sensitive membrane to be defined at any desired position, and therefore facilitates the production of a sensor body.

[Means for solving problems]

A semiconductor ion sensor according to the present invention has a gate region formed between a source region and a drain region formed on a semiconductor substrate, and a semiconductor ion sensor that measures ion activity in an aqueous solution based on an interfacial potential acting on this gate region. The sensor is characterized in that a window is provided for bringing the aqueous solution to be measured into contact with the ion-sensitive membrane, and the interfacial potential generated in the window is guided to the gate region via the conductor layer. be.

[For production]

The aqueous solution to be measured comes into contact with the ion-sensitive membrane through the window, and an interfacial potential is generated on the ion-sensitive membrane depending on the ion activity to be measured. This interfacial potential is induced into the gate region via the underlying conductor layer and the insulating layer consisting of 5102 layers. As a result, the conductivity of the gate region changes depending on the ion activity, and therefore the source-drain current changes depending on the ion activity. As a result,
The window portion that allows the aqueous solution to be measured to come into contact with the ion-sensitive membrane can be formed at any position, and high dimensional accuracy is not required in the sensor manufacturing process, making the manufacturing process easier.

〔Example〕

FIG. 1 shows the configuration of an embodiment of a semiconductor ion sensor according to the present invention, in which FIG. 1a is a plan view, FIG. Figure C is ■ in Figure 1 a.
It is a sectional view taken along the line -■. Two n+ regions 2 and 3 are formed by diffusing phosphorus, arsenic, etc. at a predetermined distance in a P-type semiconductor substrate l, one of which serves as an n'-region source region 2 and the other n'-region a drain region. 3 and source area 2
A gate region 4 is defined between the drain region 3 and the drain region 3 .

Lead portions are formed in these source regions 2 and drain regions 3, and then 5tO2@5 is formed to a thickness of 1000 on the outer peripheral surface except for lead contact portions 2a and 3a. Furthermore, a Si, N, layer 6 is formed on the S'i02 layer 5.

This Si, N, layer 6 has a thickness of 1000 mm in the portion corresponding to the gate region 4 and a thickness of 7 mm in the portion other than the gate region 4.
000 people. For example, on this Si, N4 layer 6,
.

A metal film layer 7 made of Au or the like is formed, and Ta2O acts as an ion-sensitive film on this metal film layer 7.

Form layer 8. Furthermore, a protective layer 9 made of adhesive is formed on the Ta205 layer 8 except for the window portion 1O and the contact holes 2b and 3b. The window portion 10 is provided to bring the electrolyte solution into direct contact with the Ta2O3 layer 8, which is an ion-sensitive membrane, when the sensor is immersed in the electrolyte solution to be measured. An interfacial potential is generated between the electrolyte solution and the membrane 8, and the ionic activity of the electrolyte solution is measured based on the generated interfacial potential. This window part 10
The position and size of can be arbitrary. The protective layer 9 functions to reduce or absorb external mechanical impact and prevent cracks from occurring in the inner layers.

That is, since each layer including the ion-sensitive film is composed of an extremely thin film, cracks are likely to occur due to mechanical impact from the outside, and once cracks occur, a large measurement error will occur.

For this reason, in this example, a protective layer 9 is formed on the ion-sensitive film 8 to alleviate external impact and effectively prevent the occurrence of cracks. Note that the adhesive constituting the protective layer 10 must have viscoelasticity capable of mitigating external impact, electrical insulation, and water resistance, such as phenol resin, epoxy resin, polyurethane resin, α-cyano gelatin, etc. Preferred are resins, vinyl chloride resins, cellulose resins, and silicone resins.

Next, the operation of this semiconductor ion sensor will be explained. This semiconductor ion sensor is combined with a reference electrode and immersed in the electrolyte solution to be measured.

When the Ta205 layer 8, which is an ion-sensitive membrane, comes into direct contact with the electrolyte solution through the window 10, an interfacial potential is generated in the Ta205 layer 8 according to the activity of the ions to be measured in the electrolyte solution. This interfacial potential is applied to the Si via the underlying metal film 7.
, is induced into the N4 layer 6. When the portion of the Si3N layer 6 corresponding to the gate region 4 reaches a potential corresponding to the interface potential, the conductivity of the gate region 4 changes depending on the interface potential, so a predetermined voltage (VS.) is applied between the source and drain. By applying the voltage, a current value corresponding to the ion activity can be obtained. That is, the interfacial potential generated in the ion-sensitive membrane through the window 10 is guided to the gate region through the metal film 7 and the 513N4 layer 6, and the Isn (source - drain current) can be obtained. Therefore, if the window portion 10 is appropriately large, an Iso current approximately corresponding to the ion activity can be obtained, and
Since the window portion 1O can be placed at any position, dimensional accuracy is low, manufacturing work is facilitated, and yield is improved.

FIG. 2 shows the structure of a modified example of the semiconductor ion sensor according to the present invention, in which FIG. 2a is a plan view, FIG. is a sectional view taken along the line ■-■. In this example, the protective layer 10 is organosilanol (
R-3+ (OH) 4-1, R is C113゜C6H6
etc.) is used. An organic glass material typified by organosilanol is suitable for the protective layer 9 because it has viscoelasticity that alleviates mechanical shock, electrical insulation, and water resistance. Further, in this example, the metal film 7 is formed only on the gate region 4, the window portion 10, and the portion connecting the gate region 4 and the window portion 10, and a 513N4 layer 20 that functions as an ion-sensitive film is formed on the metal film 7. Form. With this configuration, the interfacial potential generated at the interface between the electrolyte solution and Si3N, 420 passes through the window lO and passes through the metal film 7 to the gate section 4.
It is possible to measure the Iso current according to the ionic activity in the electrolyte solution to be measured. In this case, since the potential of the metal film 7 is directly induced to the gate portion, the structure of the sensor can be further simplified.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the above embodiment, a Ta206 layer and a 5t3N4 layer were used as the ion-sensitive membrane, but various ion-sensitive membranes can be used depending on the ions to be measured in the electrolyte solution. For example, S'i0□
,, A12'03, 1n20, etc. can be used.゛, -The material layer constituting the protective layer only needs to have viscoelasticity to alleviate mechanical shock, electrical insulation, and water resistance, and may include polyimide resin, polyvinyl chloride, polymethyl methacrylate, etc. , a layer of an insulating polymer such as polystyrene, or a layer of a photosensitive resin material such as a photosensitive polyimide resin.

〔Effect of the invention〕

As explained above, according to the present invention, the interfacial potential generated in the ion-sensitive membrane is guided to the gate part through the conductor film, so the window part that brings the ion-sensitive membrane into contact with the electrolyte solution can be set at any arbitrary position. It can be installed in any position, does not require high dimensional accuracy, and facilitates manufacturing work.

Further, since a protective layer is formed on the outermost layer at least in the portion excluding the window portion, mechanical impact is relaxed and absorbed by the protective layer, and measurement accuracy can be improved. In particular, since mechanical shock during mounting can be alleviated, yield can be improved and mounting work can also be facilitated.

[Brief explanation of the drawing]

1A to 1C are plan views and sectional views showing the configuration of an example of the semiconductor ion sensor according to the present invention, and FIGS. 2A to 2C are plan views and sectional views showing the configuration of a modified example of the semiconductor ion sensor according to the present invention. It is. l...Semiconductor base 2...Source region 3...
Drain region 4...Gate part 5-8iO□ layer
6...-3t3N, layer 7...metal film
8... Ta205 layer 9... Protective layer 10
...Window part 20...513N4 layer Patent applicant Olympus Optical Industry Co., Ltd. Figure 2 cm-~ method≦Kayao m-ν

Claims (1)

[Claims] 1. A semiconductor ion device in which a gate region is formed between a source region and a drain region formed on a semiconductor substrate, and the ion activity in an aqueous solution is measured based on the interfacial potential acting on this gate region. A semiconductor ion sensor, characterized in that a window is provided for bringing an aqueous solution to be measured into contact with an ion-sensitive membrane, and the interface potential generated in the window is guided to the gate region via a conductor layer. sensor. 2. The semiconductor ion sensor according to claim 1, wherein the window portion is defined by a protective layer deposited on an ion-sensitive film.