JPH0668481B2 - Ion-selective FET sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ion-selective FET sensor, and more specifically, an ion-selective FET (hereinafter, ISFET) for measuring an ion concentration in a solution by an electrode potential response. Say) sensor.

[Prior Art and its Problems] Conventionally, many ISFET sensors using MOSFETs are known, but all the ion-selective FET sensors have a common drawback that the potential drift is generally large.

It is known that the potential drift can be reduced by using a structure in which a polymer layer containing no ion-sensitive substance is interposed between the gate insulating layer and the ion-selective layer in order to enhance the adhesion therebetween. (JP-A-59-164952)
issue). However, the ISFET sensor having this structure has a drawback in that the intervening polymer layer has a poor electron conductivity, resulting in a high film impedance and being susceptible to interference such as measurement noise.

It is also known that a structure in which a metal layer is interposed between the gate insulating layer and the ion selective layer improves the adhesion of the ion selective layer, and an ISFET sensor having excellent durability can be obtained ( JP-A-57-63444, JP-A-60
-73351). However, there is a problem in stability that the gate portion is easily affected by oxygen and the like.

Therefore, it has been desired to provide an ISFET sensor having good adhesion between the ion-selective layer and the gate insulating layer, excellent durability, and less likely to be affected by interfering ions, and excellent in stability.

[Problems to be Solved by the Invention] The present invention eliminates the above-mentioned conventional drawbacks, provides an ion selective FET sensor having excellent durability and stability, and also having excellent sensor characteristics.

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventor provided a conductor layer on the surface of a gate insulating layer, and did not directly deposit an ion selective layer on the conductor layer. In addition, a redox functional layer having a redox function, in particular, an electrolytic solution containing 2,6-xylenol (2,6-dimethylphenol) is electrolytically oxidatively polymerized to form a layer deposited on the surface of the conductor layer. It has been found that an ion-selective FET sensor having excellent durability and stability, and also excellent sensor characteristics can be obtained by applying the same.

The ion selective FET sensor of the present invention is a MOSFET
And a conductor layer deposited on the surface of the gate insulating layer of the MOSFET and an electrolytic solution containing 2,6-xylenol (2,6-dimethylphenol) by electrolytic oxidation polymerization to form a surface of the conductor layer. A redox functional layer having a redox function, and an ion selective layer having ion selectivity deposited on the surface of the redox functional layer.

[Operation] In such a configuration, the gate insulating layer of the MOSFET and the ion-selective layer sensitive to predetermined ions are separated by 2,6-
By inserting an oxidation-reduction functional layer having an oxidation-reduction function, which is obtained by electrolytically oxidatively polymerizing an electrolytic solution containing xylenol (2,6-dimethylphenol), the durability and stability are improved, and excellent sensor characteristics are shown. A conductor layer is inserted between the gate insulating layer and the redox functional layer to improve adhesion and durability.

[Embodiment] As the MOSFET used in this embodiment, any MOSFET can be used as long as it is used in a known ISFET and a gate insulating layer (hereinafter sometimes referred to as a gate insulating film) can be used. [Matsuo, Esashi “Electrochemistry and Industrial Physical Chemistry” 50, 64 (1982)], for example, a FET having an Si—SiO ₂ gate insulating layer formed on a silicon or sapphire substrate and further separated. A gate type is preferably used.
The one using a silicon substrate is versatile because it is relatively inexpensive, and the one using a sapphire substrate is superior in terms of functionality, such as easy multi-processing, easy insulation, and easy miniaturization. .

The MOSFET can be manufactured by utilizing the conventional planar technology, ion implantation technology, or the like.

In order to form a conductor layer on the gate insulating layer of the MOSFET thus manufactured, a conductor is deposited on the surface of the gate insulating layer by a vapor deposition method, a sputtering method, an ion plating method, a CVD method, an ion beam sputtering method. It is possible to use a method of depositing using the above. The film thickness is preferably a thickness at which light is not substantially transmitted, for example, 100 Å or more. As the conductor, conductive carbon is most preferable, but any compound having good adhesion to the gate insulating layer and the redox film can be used without particular limitation. Further, the conductor layer may have not only one layer but also a multilayer structure. In the case of a multi-layered structure, a preferable result is obtained by covering the gate insulating layer with a thin film of a metal such as Ni or Cr and further providing another conductor layer.

The redox film deposited on the surface of the conductor layer has a property that the electrode formed by depositing it on the surface of the conductive substrate can generate a constant potential on the conductor substrate by a reversible redox reaction. In the present invention, it is preferable that the potential does not fluctuate due to the partial pressure of oxygen gas. Examples of such a redox film include an organic compound film or a polymer film capable of performing a quinone-hydroquinone type redox reaction, an organic compound film or a polymer film capable of performing an amine-quinoid type redox reaction. Preferable examples include conductive substances such as poly (pyrrole) and poly (thienylene). Here, the quinone-hydroquinone type redox reaction means, for example, in the case of a polymer, a reaction represented by the following reaction formula.

(In the formula, R ₁ and R ₂ represent, for example, a compound having an aromatic-containing structure.) The amine-quinoid type redox reaction means, for example, in the case of a polymer similar to the above, for example, the following reaction formula Means the one represented by.

(In the formula, R ₃ and R ₄ represent, for example, a compound having an aromatic-containing structure) Examples of the compound capable of forming the redox functional layer having the redox function include the following (a) to (d) Compounds of

(A) (Wherein Ar ₁ is an aromatic nucleus, each R ₅ is a substituent, m 2 is an effective valence number of ₁ to Ar ₁ , and n 2 is 0 to an effective valence number of Ar ₁ −1) Family compounds.

The aromatic nucleus of Ar ₁ may be monocyclic such as a benzene nucleus, or polycyclic such as an anthracene nucleus, pyrene nucleus, chrysene nucleus, perylene nucleus, coronene nucleus, Further, not only benzene skeleton but also heterocyclic skeleton may be used. Examples of the substituent R ₅ include an alkyl group such as a methyl group, an aryl group such as a phenyl group, and a halogen atom. Specifically, for example, dimethylphenol, hydroxypyridine, o- or m
-Benzyl alcohol, o-, m- or p-hydroxybenzaldehyde, o- or m-hydroxyacetophenone, o-, m- or p-hydroxypropiophenone, o-, m- or p-hydroxybenzophenone , O-, m- or p-carboxyphenol, diphenylphenol, 2-methyl-8-hydroxyquinoline, 5-hydroxy-1,4-naphthoquinone, 4- (p
-Hydroxyphenyl) 2-butanone, 1,5-dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-dihydroxyanthraquinone, Examples thereof include 5-hydroxy-1,4-naphthoquinone.

(B) The following formula (In the formula, Ar ₂ is an aromatic nucleus, each R ₆ is a substituent, m 3 is an effective valence number of 1 to Ar ₂ , n 3 is 0 to an effective valence number of AR ₂ −1) Family compounds.

As the aromatic nucleus and the substituent R ₆ of Ar ₂ , the same ones as Ar ₁ and the substituent R ₅ in the compound (a) are used. Specific examples of the amino aromatic compound include aniline, 1,2-diaminobenzene, aminopyrene, diaminopyrene, aminochrysene, diaminochrysene, 1-aminophenanthrene, 9-aminophenanthrene, 9,
10-diaminophenanthrene, 1-aminoanthraquinone, p-phenoxyaniline, o-phenylenediamine, p-chloroaniline, 3,5-dichloroaniline,
2,4,6-trichloroaniline, N-methylaniline, N-phenyl-p-phenylenediamine and the like.

(C) Quinones such as 1,6-pyrenequinone, 1,2,5,8-tetrahydroxynalizarin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone and anthralphine Kind.

Of these compounds, especially 2,6-xylenol, 1
-Aminopyrene is preferred.

(D) Pyrrole and its derivatives (for example, N-methylpyrrole), thiophene and its derivatives (for example, methylthiophene) and the like.

Further, as the compound capable of forming the redox layer according to the present invention, poly (N-methylaniline) [Onuki, Matsuda, Koyama, Journal of Chemical Society of Japan, 1801-1809 (1984)] poly (2,6-
Dimethyl-1,4-phenylene ether), poly (o-
(Phenylenediamine), poly (phenol), polyxylenol; polymers of pyrazoloquinone vinyl monomers,
(A) to (c) such as a quinone-based vinyl polymer polycondensation compound such as a polymer of an isoalloxazine-based vinyl monomer
An organic compound containing a compound of (a) to (c), a low-polymerization polymer compound (oligomer) of compounds (a) to (c), or (a) to (c) is immobilized on a polymer compound such as a polyvinyl compound or a polyamide compound. Examples thereof include those having the redox reactivity. In the present specification, the term polymer includes both homopolymers and interpolymers such as copolymers.

In this example, in order to deposit the compound capable of forming the above redox functional layer on the surface of the conductor layer, an amino aromatic compound, a hydroxy aromatic compound or the like is electrolytically oxidized or polymerized or electrolytically deposited. Polymer synthesized on conductive substrate such as conductive carbon or noble metal by the method or electron beam irradiation, light,
A method in which a polymer synthesized by applying heat or the like is dissolved in a solvent and applied to the surface of a conductor layer by coating or dipping, or by reacting in the gas phase under vacuum and directly depositing on the FET gate insulating film. It is possible to employ a method of depositing, a method of electrolytic oxidation polymerization or a method of directly depositing on the surface of the conductor layer by irradiation with light, heat, radiation or the like. Among these methods, the method of directly depositing by the electrolytic oxidative polymerization method is particularly preferable.

The electrolytic oxidative polymerization method is carried out by electrolytically oxidatively polymerizing an aminoaromatic compound, a hydroxyaromatic compound and the like in a solvent in the presence of a suitable supporting electrolyte to coat the surface of a conductor with a polymer layer. As the solvent, for example, acetonitrile, water, dimethylformamide, dimethylsulfoxide, propylene carbonate and the like, and as the supporting electrolyte, for example, sodium perchlorate, sulfuric acid, disodium sulfate, phosphoric acid, boric acid, potassium tetrafluorophosphate, Suitable examples include quaternary ammonium salts.

The thickness of the redox functional layer is preferably 0.01 μm to 0.5 mm, and particularly preferably 0.1 to 10 μm. 0.
When the thickness is less than 01 μm, the effect of the present invention is not sufficiently exhibited, and when the thickness is more than 0.5 mm, it is not preferable for downsizing the sensor.

Further, the redox functional layer used in this example can be used by impregnating it with an electrolyte. Examples of the electrolyte include phosphoric acid, dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. In order to impregnate the redox functional layer with the electrolyte, it is convenient to coat the redox functional layer on the surface of the conductor layer and then immerse the surface in the electrolyte solution.

As described above, as the ion-selective layer that is overlaid on the surface of the redox functional layer that is coated on the conductor layer, the ion carrier substance of the test ion and, if necessary, the electrolyte salt may be supported on the polymer compound. Layer (Neutrarkyariya layer) is used. As the ion carrier substance, for example, the following substances are used according to the ions to be detected.

(I) Potassium ion valinomycin; nonactin, monactin; crown ether compounds such as dicyclohexyl-18-crown-6, naphth-15-crown-5, bis (15-crown-5) and the like, among which valinomycin, Bis (15-crown-5) is preferred.

(Ii) Sodium ion aromatic amides or diamides, aliphatic amides or diamides, crown compounds such as bis [(1
2-crown-4) methyl] dodecyl malonate, N,
N, N, N-tetrapropyl-3,6-dioxanate diamide, N, N, N ', N'-tetrabenzyl-
1,2-ethyleneoxydiacetamide, N, N'-dibenzyl-N, N'-diphenyl-1,2-phenylenediacetamide, N, N ', N "-triheptyl-N,
N ', N "-trimethyl-4,4', 4" -propyridine tris (3-oxabutyramide), 3-methoxy-
N, N, N, N-tetrapropyl-1,2-phenylenedioxydiacetamide, (-)-(R, R) -4,5
-Dimethyl-N, N, N, N-tetrapropyl-3,6
-Dioxaoctane diamide, 4-methyl-N, N,
N, N-tetrapropyl-3,6-dioxaoctane
Diamide, N, N, N, N-tetrapropyl-1,2-
Phenylenedioxy diacetamide, N, N, N, N-
Tetrapropyl, 2,3-naphthalenedioxydiacetamide, 4-t-butyl-N, N, N, N-tetrapropyl-1,2-cyclohyexanedioxy-diacetamide, cis-N, N, N, N-tetrapropyl-1,2
-Cyclohexanedioxyacetamide, trans-
N, N, N, N-tetrapropyl-1,2-cyclohexanedioicidiacetamide and the like can be mentioned. Among them, bis [(12-crown-4) methyl] dodecyl malonate is preferably used.

(Iii) Chloride ion (In the formula, R ₇ , R ₈ and R ₉ are the same or different and each represents an alkyl group having 8 to 18 carbon atoms, and R ₁₀ represents hydrogen or an alkyl group having 1 to 8 carbon atoms). Salt of And triphenyl tin chloride represented by the following.

(IV) Calcium ion Calcium bis [di- (n-octylphenyl) phosphate], (-)-(R, R) -N, N'-bis [(11-ethoxycarbonyl) undecyl] -N,
Preferred examples include N ', 4,5-tetramethyl-3,6-dioxaoctane-diamide and calcium bis [di (n-decyl) phosphate].

(V) Hydrogen carbonate ion (In the formula, R ₁₁ , R ₁₂ , and R ₁₃ are the same or different and each represent an alkyl group having 8 to 18 carbon atoms, R ₁₄ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ⁻ represents C ⁻ , Br ⁻
Or OH ⁻ ); (In the formula, R ₁₅ represents a phenyl group, a hydrogen atom or a methyl group, R ₁₆ represents a hydrogen atom or a methyl group, and R ₁₇ represents a hydrogen atom, a methyl group or an octadecyl group). The following formula And the like.

Examples of the electrolyte salt include sodium tetrakis (p-
Chlorophenyl) borate, potassium tetrakis (p-
Chlorophenyl) borate, and the following formula R ₁₈ NBF ₄ (in the formula, R ₁₈ is an alkyl group, preferably having 2 to 6 carbon atoms).
Which represents an alkyl group of).

Further, as the polymer compound, for example, vinyl chloride resin,
Examples thereof include organic polymer compounds such as vinyl chloride-ethylene copolymer, polyester, polyacrylamide and polyurethane, and inorganic polymer compounds such as silicone resin, and those in which the plasticizer is difficult to elute are used.
Examples of such a plasticizer include dioctyl stearate, dioctyl adipate, dioctyl maleate, di-n-octylphenyl phosphonate and the like.

In order to coat the surface of the redox functional layer of the gate portion of the MOSFET with the ion-selective layer having such a composition, for example, 5 parts of a plasticizer is added to 100 parts by weight of a polymer compound as a carrier.
0 to 500 parts by weight, ion carrier substance 0.1 to 5
A solution of 0 parts by weight and an electrolyte salt in a solvent (for example, tetrahydrofuran) is formed on the gate insulating film to a thickness of 0.1 μm.
It is possible to use a method in which it is placed at a thickness of m to 10 mm and dried at room temperature or under heating, or a method in which the gate insulating film is immersed in the solution and then dried in the same manner. The thickness of the ion-selective layer thus coated is 1 μm to 10 mm.
Is preferred. Example 1 A conductive carbon film is formed on the surface of a gate insulating layer of a MOSFET by the following method, an oxidation-reduction functional layer is formed on the film, and a hydrogen ion selective layer is further formed on the conductive carbon film to form an ISF for pH measurement.
An ET sensor was produced. The schematic diagram is shown in FIG. 1 and FIG. FIG. 2 is a sectional view taken along line AA in FIG.

(1) MOSFET As a MOSFET, an FE having a structure in which a p-type Si-SiO ₂ gate insulating film is stacked on a p-type silicon wafer.
T (so-called insulated FET) was used. This is p
It is manufactured by using a general planer technique using a Holorolin graphi on a mold type silicon wafer, and further coated with an insulating film 14 made of silicon nitride by using a sputtering method.

(2) Conductor Layer A conductive carbon film (film thickness: 2000Å) was formed as a conductive layer 15 on the surface of the gate insulating film 14 of the MOSFET thus manufactured by the ion beam sputtering method.

(3) Redox functional layer Next, one end of the carbon coating film 15 is electrically contacted with a gold contactor, and electrolytic oxidation is performed under the following conditions in an electrolytic solution having the following composition. I was wearing In the electrolysis, a platinum mesh is used as a counter electrode, and a saturated sodium chloride saturated calomel electrode (SS) is used as a reference electrode.
CE) was used.

(Electrolyte solution) 0.5M 2,6-Dimethylphenol 0.2M Sodium perchlorate Solvent: Acetonitrile (Electrolysis conditions) 3 sweeps from 0V to 1.5V vs SSCE (50 mV /
Second), and then 1.5 V vs. SSCE for 10 minutes at constant potential electrolysis (−20 ° C.). Thus, as a redox functional layer, a polymer film (thickness: about 1 μm) for performing a quinone-hydroquinone type redox reaction.
m) was formed.

(4) Hydrogen ion selective layer Further, a hydrogen ion carrier film (film thickness: 0.4 mm) was coated on the electrode coated with the redox functional layer 16 by applying and drying a hydrogen ion carrier composition having the following composition. .

(Hydrogen ion carrier composition) Tridodecylamine 2.0 mg / ml Potassium tetrakis (p-chlorophenyl) borate 1.2 mg / ml (KT _p CPB, Dojindo) Polyvinyl chloride (PVC, average degree of polymerization P _n = 1050 65.6) mg / ml Di (2-ethylhexyl) sebacate (DOS) 131.2mg
/ ml Solvent: Tetrahydrofuran (THF) Example 2 An ISFET for pH measurement was produced in the same manner as in Example 1 except that a sapphire substrate was used as the substrate of the MOSFET. A schematic sectional view of the gate portion is shown in FIG.

Example 3 In Example 1, as a MOSFET, FIG. 4 and FIG.
An ISFET for pH measurement was produced in the same manner as in Example 1 except that a so-called separated gate type having the structure shown in the figure was used.

Example 4 In Example 1, a potassium ion carrier composition having the following composition was used in place of the hydrogen ion carrier composition, and a potassium ion selective layer (film thickness:
An ISFET sensor for measuring potassium ion concentration was prepared in the same manner as in Example 1 except that the ISFET sensor was coated with 0.4 mm).

(Potassium Ion Carrier Composition) Valinomycin 3.2 mg / ml PVC 65.6 mg / ml DOS 131.2 mg / ml Solvent: THF Test Example 1 The characteristics of the ISFET sensor for pH measurement prepared in Example 1 are shown in FIG. Using the measurement circuit and equipment, SSCE
It was investigated by measuring the source voltage (VOUT) of the sensor for. For the measurement of Vout, a digital voltmeter (TR6841, manufactured by Advantest) was used. A 50 mM phosphate buffer solution was used as the test solution. The measurement was carried out in the atmosphere with constant light illuminance while stirring the test liquid in the range of pH 5 to 9 (37 ° C.).

The response characteristic to pH shows a linear relationship according to the Nernst equation represented by E = E ^o −S · pH (E is an electromotive force, E ^o is a constant potential, and S is a slope), and S = 61 mV / pH (3
7 ° C.), and a value close to the theoretical value was obtained. Also, 99
% Response is within 5 seconds, extremely quick response, and Vou even if the light illuminance is changed in the range of 0 to 10000 lux.
Since t is constant within the experimental error (± 1 mV),
It became clear that it was not easily affected by light.

Furthermore, the temporal stability of this pH sensor was examined by repeating the same measurement as above for 40 days. The result is No. 7
It is shown in FIGS. As the comparative product, a gate insulating layer directly coated with a hydrogen ion carrier film was used.

As shown in FIGS. 7 and 8, the sensor of this embodiment is
The sensor characteristics were stable for more than a month and were stable, while the comparative product was extremely unstable.

Test Example 2 When the ISFETs obtained in Examples 2 and 3 were measured in the same manner as in Test Example 1, the same results as in Test Example 1 were obtained.

Test Example 3 ISF for measuring potassium ion concentration obtained in Example 4
The response characteristics of ET were examined in the same manner as in Test Example 1.

The logarithmic value of Vout and potassium ion concentration is 10 ^{−4 to} 5
A very good linear relationship was shown in the range of × 10 ^-1 M, and the inclination of the straight line was 60 mV / og [K ⁺ ]. In addition, it was found that the response speed was 95%, that is, the response was extremely fast within 1 second, it was difficult to receive the change of the light illuminance, and the characteristics were stable for 1 month or more.

Examples 5 to 10 In Example 1, the ion carrier composition shown in Table 1 was used in place of the hydrogen ion carrier composition, and an ion selective layer (film thickness: 0.3 mm) was coated on the redox functional layer. Except for the above, in the same manner as in Example 1, the ISFET for ion concentration measurement shown in Table 1 was produced.

Bis-12-Crown-4: Bis [(12--crown-4) methyl] dodecyl malonate (manufactured by Dojindo Co., Ltd.) TPSnCl: triphenyl tin chloride (manufactured by Aldrich) TDDA-Cl: tridodecyl ammonium chloride Ca (DOPO) ) ₂ : Calcium bis [di- (n-octylphenyl) phosphate] (manufactured by Dojindo) DOPO: Di- (n-octylphenyl) phosphate (manufactured by Dojindo) DHDMBA: N, N′-diheptyl- N, N′-dimethyl 1,4-butanediamide (manufactured by FluKa) Example 11 In Example 1, except that a conductive iridium oxide coating (film thickness: 2000Å) was formed as the conductive layer 15 instead of the conductive carbon coating. In the same manner as in Example 1, an ISFET sensor for pH measurement was manufactured.

Example 12 An ISFET for pH measurement was prepared in the same manner as in Example 11 except that a sapphire substrate was used as the MOSFET substrate. A schematic sectional view of the gate portion is shown in FIG.

Example 13 ISFE for pH measurement was performed in the same manner as in Example 11 except that a MOSFET of the so-called separated gate type having the structure shown in FIGS. 6 and 7 was used as the MOSFET.
Created T.

Example 14 In Example 11, a potassium ion carrier composition having the following composition was used in place of the hydrogen ion carrier composition,
A potassium ion selective layer (film thickness: 0.
An ISFET sensor for measuring kalim ion concentration was produced in the same manner as in Example 11 except that the ISFET sensor was coated with 4 mm).

(Potassium ion carrier composition) Valinomycin 3.2 mg / ml PVC 65.6 mg / ml DOS 131.2 mg / ml Solvent: THF Test Example 11 The characteristics of the ISFET sensor for pH measurement prepared in Example 11 are shown in FIG. Using circuits and devices, SSCE
It was investigated by measuring the source voltage (Vout) of the sensor for. For the measurement of Vout, a digital voltmeter (TR6841, manufactured by Advance Test Co.) was used. A 50 mM phosphate buffer solution was used as the test solution. The measurement was carried out in the atmosphere with constant light illuminance while stirring the test liquid in the range of pH 5 to 9 (37 ° C.).

As shown in FIG. 9, the response characteristic to pH is E = E ^o
-S · pH (E is an electromotive force, E ^o is a constant potential, S is a slope) shows a linear relationship according to the Nernst equation, S
= 61 mV / pH (37 ° C), which was close to the theoretical value. In addition, the 99% response is within 5 seconds, the response is extremely fast, and Vout is constant within the experimental error (± 1 mV) even when the light illuminance is changed in the range of 0 to 10000 lux, so the influence of light It became clear that it was hard to receive.

Furthermore, the time stability of this pH sensor was examined by repeating the same measurement as above for 40 days. As a result, the sensor of this example was stable for one month or more without any change in the sensor characteristics.

Test Example 12 With respect to the ISFETs obtained in Examples 12 and 13, the same measurement as that of Test Example 11 was performed. When the same measurement as that of the above Test Example was performed, the same result as that of the above Test Example 11 was obtained. It was

Test Example 13 IS for measuring potassium ion concentration obtained in Example 14
The response characteristics of the FET were examined in the same manner as in Test Example 11.

As shown in FIG. 10, the logarithmic value of Vout and potassium ion concentration shows a very good linear relationship in the range of 10 ^{−4 to} 5 × 10 ⁻¹ M, and the slope of the straight line is 60 mV / o.
It was g [K ⁺ ]. The response speed is 95% and the response is 1
It was found that it was extremely fast within seconds, was not easily affected by changes in light illuminance, and had stable characteristics for 1 month or longer.

Examples 15-18 and Test Examples 15-18 For measuring pH in the same manner as in Example 11 except that platinum, palladium, indium oxide, and silver were used as the conductor layer instead of iridium oxide. ISF
When ET was prepared and the same measurement as in Test Example 11 was performed, the same result as in Test Example 11 was obtained.

[Advantages of the Invention] In the ion-selective FET sensor of the present invention, a conductor layer is provided on the surface of a gate insulating layer of a MOSFET, and an ion-selective layer is formed thereon with 2,6-xylenol (2,6-dimethylphenol). Since the electrolyte is coated with a redox functional layer that is electro-oxidatively polymerized, the adhesion and durability of these layers are good and they are not easily affected by light. Is excellent.

Further, since the MOSFET has a high input impedance, the ion-selective FET sensor of the present invention operates stably even if it is coated with a high-resistivity ion-selective layer, and since its amplifying action can be utilized, it can be made compact. Nevertheless, it has a fast response speed and can be practically used advantageously.

[Brief description of drawings]

FIG. 1 is a schematic view of an ISFET sensor for pH measurement produced in Example 1, FIG. 2 is a sectional view taken along the line AA of the ISFET sensor of FIG. 1, and FIG. 3 is Example 2 and Example. 12 is a sectional view of the gate portion of the pH-measurement ISFET sensor manufactured in 12, FIG. 4 is a schematic view of the pH-measurement ISFET sensor manufactured in Examples 3 and 13, and FIG. 5 is a graph of FIG. 6 is a sectional view taken along line CC of the ISFET sensor, and FIG. 6 shows a source voltage (Vou) for a cell and a reference electrode for measuring pH by the ISFET sensor of this embodiment.
7 is a schematic explanatory view showing a circuit for measuring t), and FIGS. 7 and 8 are views showing changes with time of Vout and the slope S of the Nernst plot of the ISFET sensor of this embodiment and the comparative product, respectively. The figure shows the ISFET for pH measurement manufactured in Example 11.
FIG. 10 is a diagram showing the results of Test Example 11 of the sensor, and FIG. 10 is a diagram showing the results of Test Example 13 of the ISFET sensor for measuring potassium ions prepared in Example 14. In the figure, 10 ... Gate, 11 ... Drain, 12 ... Source, 13 ... Oxide film, 14 ... Insulating film, 15 ... Conductive layer, 16 ... Redox functional layer, 17 ... Ion reaction film ,
18 ... Silicon substrate, 19 ... SOS substrate, 20 ...
p-type silicone, 21 ... Insulator, 22 ... ISFE
T, 23 ... Reference electrode, 24 ... Stirrer, 25 ... Vo
ut.

Continuation of the front page (56) Reference JP-A-59-176662 (JP, A) JP-A-60-202347 (JP, A) JP-A-60-14159 (JP, A) JP-A-52-142584 (JP , A) Journal of the Chemical Society of Japan, 1984, NO. 11, P. 1801-1808

Claims (2)

[Claims] 1. A MOSFET, a conductor layer deposited on a surface of a gate insulating layer of the MOSFET, and 2,6-xylenol (2,6-dimethylphenol).
And a redox functional layer having a redox function, which is deposited on the surface of the conductor layer by electrolytically oxidatively polymerizing an electrolytic solution containing a, and an ion selectivity deposited on the surface of the redox functional layer. An ion-selective FET sensor comprising an ion-selective layer. 2. The ion-selective FET sensor according to claim 1, wherein the ion-selective layer is a polymer film supporting an ion carrier substance.