JPH07128278A - Ion detecting device - Google Patents

Abstract

PURPOSE:To regularly perform a comparatively precise measurement related to various ion concentrations and change thereof in a solution to be inspected by arranging a water repellent member around a sensor part and a comparing electrode, and arranging a hydrophilic member adjacent thereto. CONSTITUTION:This detecting device has a basically constituted FET, and an n-type source electrode 12 and a drain electrode 14 formed in a p-type silicon base 10 by thermal diffusing method. An ion sensitive gate film 20 (sensor part) is set in the gate part nipped by the electrodes 12, 14. The part other than the gate film 20 is covered with a hydrophilic member 22 such as SiO2 or SiNx. The circumference of the gate film 20 and a wiring 24 is further covered with a water repellent member 26. Thus, a solution to be inspected remaining in the comparing electrode 28 and the gate film 20 is repelled by the water repellent member arranged around them, and moved on the hydrophilic member 22 side. The unnecessary washed away of KC1 from the comparing electrode 28 by the remaining solution is suppressed, and the life of the device can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion detecting device which is sensitive to various ions in a liquid and detects the concentration of ions in a test liquid and the state of its change.

[0002]

2. Description of the Related Art Conventionally, when detecting the ion concentration in a solution or the state of its change, a reference electrode composed of KCl and Ag / AgCl electrodes, a glass electrode utilizing the characteristics of a relatively thin glass film, or The potential difference between the gate of the field effect transistor having the ion sensitive film as the gate film and the sensor unit such as the sensor unit is detected as voltage or current, or a change thereof. Here, as an example thereof, a conventional example of a pH detecting device having a field effect transistor as a basic configuration will be briefly described with reference to FIG.

The sensor portion of the pH detecting device has a field effect transistor portion manufactured by using semiconductor technology, and has an ion sensitive gate film 52, a source electrode 54, and a drain electrode 5.
6, a silicon substrate 57, an insulating film 58 and the like. The reference electrode 50 is provided in the vicinity of the sensor portion, and is installed on, for example, the polyimide resin on which the field effect transistor itself is installed. When the ion-sensitive gate film 52 made of SiNx and the reference electrode 50 come into contact with the test liquid 60 containing hydrogen ions, the pH value of the test liquid 60 is increased, and the ion-sensitive gate film 52 and the test liquid 60 are separated from each other. Interfacial potential is generated at The reference electrode 50 functions to apply this interface potential as a gate voltage to the gate portion 55 between the source electrode 54 and the drain electrode 56 of the pH detection device. Since the interfacial potential is determined by the pH value of the test solution 60, an appropriate voltage is applied between the source electrode 54 and the drain electrode 56, which are installed below the ion-sensitive gate film 52 via the insulating film 58 made of SiO _2. Is applied, the current and voltage corresponding to the pH value of the test liquid 60 are output from the field effect transistor.

During detection of the ion concentration of the test solution 60, while the reference electrode 50 and the ion-sensitive gate film 52 composed of KCl and Ag / AgCl electrodes are in contact with the test solution 60, The KCl contained in the reference electrode 50 flows out little by little, and if this KCl completely flows out into the test liquid, it will not function stably as a pH detection device.

[0005]

However, in the above-mentioned ion detector, KCl and Ag / AgCl are not used.
While the reference electrode 50 composed of electrodes is in contact with the test liquid 60, KCl flows out little by little. Therefore, in order to extend the life of the reference electrode 50 as much as possible, the comparison electrode 50 should be compared except during detection. It is necessary to prevent the electrode 50 from coming into contact with the test liquid 60.

However, even after completion of the detection, the test liquid 6 is left on the comparison electrode composed of the KCl and Ag / AgCl electrodes.
A part of 0 may remain, and in this case, KCl flows out from the reference electrode 50 into the residual test liquid even if the detection is unnecessary. As a result, not only the life of the comparison electrode 50 is shortened, but also the operating point fluctuates, causing an error in the measured value. Furthermore, a part of the solution may remain on the ion-sensitive gate film 20, in which case dust, dirt, and the like are likely to adhere to the ion-sensitive gate film 20, which also changes the operating point. It was the cause.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to always relatively accurately measure the types and concentrations of various ions in a test liquid and their changes. It is an object of the present invention to provide an ion detector having a long life.

[0008]

In order to achieve this object, an ion detector of the present invention comprises an ion-sensitive sensor section and a reference electrode, and determines the concentration of ions in a liquid and the state of change thereof. In the ion detecting device for detecting, a water repellent member is arranged around at least one of the sensor unit and the comparison electrode, and a hydrophilic member is arranged close to the water repellent member.

Further, it is preferable that the sensor section is made of a water repellent member, and the sensor section is made of an ion sensitive field effect transistor.

[0010]

According to the ion detector of the present invention having the above-described structure, the comparison is made in a state where the detection of the concentration of ions in the test liquid is completed and the ion detector is not immersed in the test liquid. The test liquid remaining in the electrodes and the sensor that is sensitive to ions is repelled by the water-repellent member that is arranged around the reference electrode and the sensor, and moves to the hydrophilic member that is installed in close proximity. The reference electrode and the sensor section are exposed in the atmosphere.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the pH detection device of this embodiment.

This pH detecting device has a field effect transistor as a basic structure. An n-type source electrode 12 and a drain electrode 14 are built in a p-type silicon substrate 10 by a thermal diffusion method. On the source electrode 12 and the drain electrode 14, wirings 16 for supplying power to the respective electrodes are installed, and the other portion of the silicon substrate 10 is covered with an insulating film 18 obtained by thermal oxidation. In this case, the wiring 16 for supplying power to each electrode is preferably made of Al or W, and the insulating film 18 is SiO ₂ . On the gate portion 13 sandwiched between the source electrode 12 and the drain electrode 14, an ion-sensitive gate film 20 made of Ta ₂ O ₅ , Al ₂ O ₃ or the like is provided as shown. This ion-sensitive gate film 2
Parts other than the installation position of 0 are covered with a hydrophilic member 22 made of SiO ₂ , SiNx, or the like.

Further, on the hydrophilic member 22, a wiring 24 formed of Al, W or the like is provided in the vicinity of the ion sensitive gate film 20, and the circumference of the ion sensitive gate film 20 and the wiring 24 is provided. It is covered with a water repellent member 26. In this case, the water-repellent member 26 is made of an inorganic material such as Al ₂ O ₃ or
Organic materials such as fluororesin and Si-containing perfluorooctyl polyethoxysilane are preferably used.
The water-repellent member 26 is installed so as to leave the outer portion of the hydrophilic member 22 of the base, and the hydrophilic member 22 of the outer portion is exposed. Further, on the wiring 24, Ag /
A reference electrode 28 in which Ag / AgCl is embedded in a jelly-like felt material impregnated with KCl is installed so that AgCl is connected.

The pH detecting device having the above-described structure is such that the substrate 3 made of a polyimide resin whose surface is hydrophilically treated.
It is installed on 0. The hydrophilic treatment of the base material 30 may be performed by thermal oxidation, ozone oxidation, discharge treatment, or the like, or a hydrophilic material such as SiO ₂ or SiNx may be placed on the surface.

The ion sensitive gate film 52, the source electrode 54, the drain electrode 56, the silicon substrate 57 and the insulating film 58 form a sensor section.

The manufacturing process of the pH detecting device of this embodiment is shown in FIG.
Shown in.

In the step shown in FIG. 2A, a field effect transistor which is a basic constituent part of the pH detecting device is manufactured. Here, P and As are contained in the p-type silicon substrate 10.
Is doped by thermal diffusion to form an n-type region, so that the source electrode 12 and the drain electrode 14 are built.
Then, the surface of the silicon substrate 10 is thermally oxidized to form the insulating film 18
Then, an opening is formed by a photolithography technique and an etching technique in order to install the power supply wiring 16 in a portion corresponding to the source electrode 12 and the drain electrode 14. in this case,
The insulating layer 18 is SiO ₂ .

By the way, as the etching technique,
There are a dry etching method performed by ion bombardment in a vacuum and a wet etching method performed using a solution of hydrochloric acid, sulfuric acid, hydrofluoric acid or the like. Further, a conductive material such as Al or W is vapor-deposited on the surface, and the vapor deposition film is patterned by using the photolithography technique so that power can be supplied individually to both electrodes formed in the silicon substrate 10, and the wiring 16 is formed. It

In the step shown in (B), the hydrophilic member 2
2 is installed while leaving the gate portion of the field effect transistor. In this case, on the element obtained in the step (A),
SiO can be formed by a known method such as a sputtering method, a vapor deposition method, or a CVD method.
₂ or SiNx is attached to about 0.5 μm. After that, an opening is provided in the portion of the hydrophilic member 22 corresponding to the gate portion 13 by using the photolithography technique and the etching technique described above.
The hydrophilic member 22 made of SiO ₂ or SiNx may be formed by a sol-gel method in which an organic solvent containing these components is hydrolyzed. Further, the opening of the hydrophilic member 22 is formed by covering and protecting the portion corresponding to the gate portion with a resist material in advance, and after forming the hydrophilic member 22, the resist material is peeled off to form the opening. May be used. Incidentally, SiO ₂ and SiNx used as the hydrophilic member 22 have a contact angle of water of about 15 degrees and 34 degrees, respectively, and have a property that water is very easily wetted.

In the step (C), the ion-sensitive gate film 20 selectively sensitive to H ⁺ ions is applied to the portion corresponding to the gate portion 13 of the device obtained in the step (B). Is installed. In this case, the sputtering method, the vapor deposition method, the
Ta ₂ O ₅ and Al ₂ O ₃ are formed by a known method such as the CVD method. Alternatively, the ion-sensitive gate film 20 may be formed by combining the photolithography technique and the etching technique.

In the step shown in (D), it is installed in the step (A) for supplying electric power to the reference electrode 28 in the vicinity of the ion-sensitive gate film 20 on the device obtained in the step (C). Different wiring 24 from the wiring 16 and the water repellent member 2
6 is installed. The wiring 24 is formed and installed by the same method as the wiring 16 installed in the step (A). The water repellent member 26 is formed by the lift-off method. After the ion sensitive gate film 20, another wiring 24 for supplying power to the reference electrode 28 and the hydrophilic member 22 located outside the element are covered and protected with a resist material, the entire surface of the element is covered with a water repellent member 26. To do. After that, the resist material is peeled off to be formed. As the water repellent member 26, Al ₂
When O ₃ is used, it is formed by a known method such as a sputtering method, a vapor deposition method, a CVD method or a sol-gel method.

When an organic material such as fluororesin or perfluorooctyl polyethoxysilane is used, a solvent as a raw material is applied by a method such as spin coating, roll coating, dipping or spraying, and this is applied at 100 ° C. To 200 ° C. in air and then molded by the lift-off method to obtain the water-repellent member 26 having a desired shape.

Al used as the water-repellent member 26
₂ O ₃ has a high water contact angle of about 125 degrees. Further, the fluororesin has a temperature of about 110 degrees, and the perfluorooctyl polyethoxysilane has a temperature of about 115 degrees, and all materials have a property that water is very difficult to wet.

In the step shown in (E), a reference electrode 28 is placed on another wiring 24 of the element obtained in the step (D), and the entire element is bonded onto a base material 30 made of polyimide.
Adhesion of the element to the base material 30 is performed by soldering, epoxy resin, silicon resin, or the like. The base material 30
Has its surface hydrophilically treated in advance. The pH detection device is manufactured by the above steps.

Next, the operation of this embodiment will be described.

This pH detecting device is a detecting device having a field effect transistor as a basic structure as described above. It has a structure without a gate metal, and the test liquid in contact with the ion-sensitive gate film 20 functions as a gate metal. When the ion-sensitive gate film 20 and the test solution come into contact with each other, p of the test solution
An interfacial potential is generated between the ion-sensitive gate film 20 and the test solution corresponding to the H value, but this alone induces an inversion layer in the gate portion of the field effect transistor and a signal corresponding to the pH value of the test solution. Information cannot be retrieved from the pH detector. Therefore, in the vicinity of the ion sensitive gate film 20,
A reference electrode 28 having a structure in which AgCl is immersed in a KCl solution is installed. The reference electrode 28 serves to apply the interfacial potential generated by the contact between the ion-sensitive gate film 20 and the test liquid to the gate portion 13 of the pH detection device as a gate voltage which is the function of a general field effect transistor. do.

On the other hand, the interfacial potential is determined by the ion activity in the test solution, that is, the pH value. Therefore, if an appropriate voltage is applied between the source electrode 12 and the drain electrode 14, the gate portion 13 in contact with the ion-sensitive gate film 20 is generated due to the interface potential that changes according to the pH value of the test liquid. The thickness of the inversion layer that is induced by the change is changed, and a current or voltage corresponding to the pH value of the test liquid is output.

Further, when the pH of the test liquid is not required to be detected and the pH detecting device is held in the atmosphere, the residual liquid of the test liquid adheres to the ion-sensitive gate film 20 and the reference electrode 28. Also, since the ion-sensitive gate film 20 and the reference electrode 28 are surrounded by the water-repellent member 26, and the hydrophilic member 22 is provided outside the water-repellent member 26, the residual liquid is quickly removed from the surface of each member. Hydrophilic member 2 due to difference in tension
Move to side 2. Since the field effect transistor itself is also installed on the hydrophilic substrate 30, this effect is promoted.

In this way, when it is not necessary to detect the pH of the test liquid, the ion-sensitive gate film 20 and the reference electrode 28 are always exposed to the atmosphere, so the reference electrode 2
There is no unnecessary outflow of KCl from 8 and the adhesion of dust and dirt to the ion-sensitive gate film 20 is suppressed.
The operating point of the H detector does not fluctuate, and the life of the H detector can be extended.

The present invention is not limited to the embodiments described in detail above, and various modifications can be made without departing from the spirit of the invention.

For example, the insulating film and the hydrophilic member may be made of the same material, and the insulating film and the hydrophilic member may be commonly used. The reference electrode and the field effect transistor section are separated, and the reference electrode is placed on the base material. You may. Further, in the present embodiment, the water repellent member is superposed on the hydrophilic member, but it may be provided on the same surface.

Further, in this embodiment, the field effect transistor portion has the surface opposite to the side on which the ion-sensitive gate film and the reference electrode are installed adhered to the base material. An opening may be provided in a portion corresponding to the film or the reference electrode, and the base material may be adhered to the side where the ion-sensitive gate film or the reference electrode is installed by aligning with the opening. Even in this case, it is effective that the surface of the base material in contact with the test liquid is subjected to hydrophilic treatment. Further, it is conceivable that the residual liquid of the reference electrode and the ion-sensitive gate film can be effectively removed by forming the sensor part itself composed of the ion-sensitive gate film or the like with a water-repellent member.

[0033]

As is apparent from the above description, according to the pH detecting device of the present invention, the test liquid remaining on the reference electrode and the sensor part is repelled by the water-repellent member arranged around it. Since it moves to the side of the hydrophilic member, unnecessary outflow of KCl from the reference electrode due to the remaining test liquid is suppressed, and dust and dirt are less likely to adhere to the sensor unit, so The fluctuation of the operating point of the detection device is small, and the life of the ion detection device can be extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a main part of a pH detection device of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the pH detector of the present invention.

FIG. 3 is a diagram showing a configuration of a main part of a conventional pH detection device.

[Explanation of symbols]

 10 Silicon Substrate 12 Source Electrode 13 Gate Part 14 Drain Electrode 16 Wiring 18 Insulating Film 20 Ion Sensitive Gate Film 22 Hydrophilic Member 24 Wiring 26 Water Repellent Member 28 Reference Electrode 30 Base Material

Claims (3)

[Claims] 1. An ion detection device comprising a sensor section sensitive to ions and a comparison electrode, for detecting the concentration of ions in a test liquid and the state of change thereof, at least one of the sensor section and the comparison electrode. An ion detecting device, wherein a water-repellent member is arranged around, and a hydrophilic member is arranged close to the water-repellent member. 2. The ion detecting device according to claim 1, wherein the sensor unit is made of a water repellent member. 3. The ion detection device according to claim 1, wherein the sensor unit is composed of an ion sensitive field effect transistor.