JPH02206754A - Ion sensor and production thereof - Google Patents

Abstract

PURPOSE:To facilitate miniaturization by forming a laminate film consisting of silver halide and hydrophobic film on the surface of the gate insulating film of a conductive base body or MOSFET and forming the laminate film by a neutral beam sputtering method. CONSTITUTION:After p type silicon layers 12 are etched and formed to island shapes on the regions of a substrate 11 where reference electrode parts 1 and sensor parts 2 are desired to be formed, source regions 13 and drain regions 14 are formed. Silicon oxide films 15 of 1,000Angstrom film thickness as the gate insulating film are thereafter formed by thermal oxidation in the respective gate parts of the electrode parts 1 and the sensor parts 2. Silicon nitride films 16 of 2,000Angstrom film thickness are formed in succession thereto and further, silver layers are formed on the gate parts of the electrode parts 1. The laminate films 18 having about 300 to 500Angstrom film thickness are formed in the electrode parts 1 formed with the silver layers 17 by using a neutral beam sputtering device. The thicknesses of the respective layers of the silver chloride layers and polytetrafluoroethylene resin layers in the films 18 are respectively specified to 30 to 50Angstrom . The production of the integral type sensor formed with the ion sensors on the same chip is facilitated in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion sensor and a method for manufacturing the same, and particularly to an ion sensor and a method for manufacturing the same.
OS (Metal Oxide Sem1cond
The present invention relates to an ion sensor using an uctorl field effect transistor and a method for manufacturing the same.

[Prior art] In recent years, MO5 field effect transistors (hereinafter referred to as ÷MO5
There have been many reports on the development of ion sensors using FETs (FETs), but in the past, small silver (Ag)/silver chloride (AgCQ) electrodes were generally used as reference electrodes for these sensors.

However, although this reference electrode is small, it has been difficult to miniaturize because it has a structure including a silver/silver chloride reference electrode portion, a reference liquid, a reference liquid chamber, and a liquid junction. Furthermore, it was not easy to integrate it with the ion electrode section. In order to overcome these drawbacks, a reference electrode has been disclosed in which a polystyrene film is deposited on the gate portion of a MOSFET using a plasma polymerization method (Japanese Unexamined Patent Application Publication No. 1983-1989).
No. 103658, No. 5B-34352).

On the other hand, conventionally, as an ion sensor, an insulating layer (for example, 5
iJ4. A carbon layer formed on a conductive carbon material (Aj2zOs, Ta1ls) or a redox functional film (for example, l-pyrenamine) formed on a conductive carbon material by electrolytic polymerization.

There are sensors in which a polymer film layer of 2,6-dimethylphenol, 4,4'-biphenol, etc. is formed, or an ion-sensitive film is further formed on the redox functional film. In order to miniaturize the
A structure consisting of a carbon layer, a redox functional membrane, and an ion-sensitive membrane,
A method in which the gate insulating film or the extended gate electrode surface of a MOSFET is coated has been disclosed (Japanese Patent Laid-Open No. 6
3-131056, 62-276452).

[Problem to be solved by the invention] However, using the above-mentioned plasma polymerization method, MOSFET
The reference electrode formed on ET does not have sufficient potential stability due to the permeation of ionic active substances mainly due to swelling of the polystyrene membrane and the influence of active residues or functional groups generated during electrolytic polymerization. There was a problem.

In addition, in the case of an ion sensor formed on a MOSFET, the carbon layer formed on the insulating layer has weak adhesion and mechanical strength, and also has a significantly different expansion coefficient and lattice constant from the redox functional film. There was a problem in that the redox functional film was likely to peel off from the insulating layer together with the carbon layer during or after the electrolytic reaction.

In addition, the carbon layer can be made thinner, for example, less than 1000% (then,
Although the adhesive strength increases, the electrical resistance becomes too large (
(more than 100KΩ/mouth) Electrolytic reaction was difficult. Also,
When using the coating method or dipping method, chemically polymerized materials do not function well and stable potential cannot be obtained, so it is necessary to use a redox functional film prepared by electrolytic polymerization method. However, there was a problem that it was poorly soluble and there was no suitable solvent.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a reference electrode that can be miniaturized and provide a stable potential, and a method for manufacturing the same.

Another object of the present invention is to provide an ion sensor that can be miniaturized and has stable functionality without the risk of the redox functional film peeling off from the base, and a method for manufacturing the same.

[Means for Solving the Problems] In order to solve the above problems, the reference electrode according to the present invention has the following features:
A conductive substrate, silver halide layers alternately formed on the substrate by neutral beam sputtering or vapor deposition, and a hydrophobic resin layer formed on the silver halide layer by neutral beam sputtering. and a laminate film consisting of a gate insulating film of a field effect transistor, a silver halide layer formed by a neutral beam sputtering method on the surface of the insulating film, and the halogenated film. The present invention is characterized by comprising a laminate film having a hydrophobic resin layer formed on a silver layer by a neutral beam sputtering method.

Here, after forming a thin silver layer on the surface of the gate insulating film of the field effect transistor, a laminate film may be formed on this thin silver layer.
Alternatively, an insulator with a silver layer formed on its surface may be used.

Further, the silver halide is preferably one of silver chloride, silver bromide, silver iodide, and silver fluoride, and further,
As the hydrophobic resin film, fluororesin and polytetrafluoroethylene (registered trademark: Teflon) are used, and the film thickness is in the range of monomolecular layer thickness (about 2.0 to 10 μm) to 10 μm, Preferably it is 10 to 1000 people.

Furthermore, the method for manufacturing a reference electrode according to the present invention includes a step of forming targets of silver halide and a hydrophobic resin on the surface of a predetermined substrate by electrolytic polymerization, and a step of forming targets of silver halide and hydrophobic resin alternately. The method is characterized in that it includes a step of sputtering the target by irradiating it with a chemical beam to form a laminate film consisting of a silver halide layer and a hydrophobic resin layer on the surface of the substrate.

Further, an ion sensor according to the present invention includes a conductive substrate;
It is characterized by comprising a redox functional film formed on the surface of the conductive substrate by a neutral beam sputtering method, and an ion sensitive film covering the redox functional film, and M
A gate insulating film of an OS type field effect transistor, a redox functional film formed on the surface of the gate insulating film by a neutral beam sputtering method, and an ion sensitive film covering the redox functional film. shall be.

The redox functional film includes, for example, poly(4°4'-biphenol), poly(2,6-dimethylphenol),
Poly(1,2-diaminobenzene), poly(1-birenamine), polyaniline, etc. are used.

In addition, ion-sensitive membranes include, for example, borosilicate glass, liquid membranes such as hydrogen ion carrier membranes, Na ion carrier membranes,
A K0 ion carrier membrane is used, and ion carrier substances such as tri-n dodecylamine, bis(1
2-Crown-4) etc. are used.

Further, the method for manufacturing an ion sensor according to the present invention includes a step of forming a target of a redox functional material on the surface of a predetermined substrate by electrolytic polymerization, and a step of sputtering the target by irradiating the redox functional material with a neutral beam. The method is characterized in that it includes a step of forming a redox functional film on the surface of a substrate, and a step of forming an ion-sensitive film on the surface of the redox functional film.

[Function] With the above configuration, the reference electrode of the present invention is a solid state in which a laminate film of a silver halide layer and a hydrophobic resin layer is formed on a conductive substrate or a gate insulating film of a field effect transistor. Since it is a type electrode, an internal liquid chamber and a liquid junction, which are necessary in conventional electrodes, are not required, and miniaturization becomes possible. When this reference electrode is immersed in an aqueous solution, the hydrophobic resin film swells, but since the film is very thin (~lOLLm), water permeates inside the laminate film and dissociates the silver halide. let In other words, the laminate film itself plays the role of a pseudo internal liquid.

Furthermore, although the hydrophobic resin membrane allows ions to pass through, it does so only to a very small extent, and furthermore, since it has a laminated structure, it also prevents ions from flowing out of the membrane. In other words, the stiff hydrophobic resin film plays the role of a pseudo liquid junction, and therefore the reference electrode according to the present invention exhibits a stable potential like a conventional reference electrode with an internal liquid chamber. The silver halide layer of the body membrane is produced by neutral beam sputtering or vapor deposition, and the hydrophobic resin layer is produced by neutral beam sputtering. etc., on the same chip, making it easy to manufacture an integrated membrane sensor.

In addition, in the ion sensor according to the present invention, when forming a redox functional film on a conductive substrate or a gate insulating film of an MO5 field effect transistor, a redox film is prepared in advance on a predetermined electrode surface by an electrolytic polymerization method. By forming a film of a functional material, etc., and using the neutral beam sputtering method using this redox functional material as a target,
A film having the same composition as the electrolytically polymerized film formed in advance can be formed on the surface of a conductive substrate or the like. Therefore, unlike in the past, there is no need to connect lead wires to the electrodes or insulate unnecessary parts for electrolytic reactions, making it possible to form easily adjusted films and oxidation-reduction There is no fear that the functional film will peel off. In addition, since a redox functional membrane that has been electrolytically polymerized in advance can be used as a target, membranes with clear characteristics can be used, and as a result, an ion sensor with uniform characteristics and stable functions can be manufactured. be able to. Furthermore, since a neutral atomic beam is used, there is no charge-induced charging or discharge breakdown, and therefore MO
It is possible to form a film even on a weak part such as the gate part of a type 3 field effect transistor, and miniaturization becomes easy.

In addition to the MO3 type field effect transistor, the ion sensor according to the present invention can also use a junction type or Schottky gate type field effect transistor.

[Embodiment J] An embodiment of the present invention will be specifically described below with reference to one drawing. First, the neutral beam sputtering method applied to the present invention will be explained.

This neutral beam sputtering method introduces a rare gas with a high sputtering rate into the reaction chamber, ionizes it with a cold cathode, etc.
After accelerating in a high voltage electric field, the target is irradiated with high-speed neutral particles (neutral beam) that are neutralized by passing through an electron atmosphere, and the sputtering phenomenon is used to deposit a thin film on the target substrate. This is a method of forming. This sputtering method directly converts the kinetic energy of rare gases into the kinetic energy of target atoms and molecules, whereas vacuum evaporation methods and ion implantation methods use energy transfer. Even with alloys, dense thin films can be formed.

As a neutral beam, it is preferable to use a beam that contains almost no ions (usually less than 1%).Those containing ions are preferable because they can cause charge-up, discharge, and decomposition of insulating or organic materials due to ions. do not have.

In particular, since the neutral atom beam sputtering method contains almost no ion particles, the formation of pinholes and compositional changes during thin film formation are small, and the reproducibility of the thin film is good.

(Example 1) Figure 1 shows a MOS using a reference electrode according to an example of the present invention.
FIG. 2 is a plan view showing an I5FET (ion-sensitive field effect transistor) sensor having a FET structure, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. FIG. This rSFET sensor is composed of a reference electrode part 1 and a sensor part 2. This 15FET sensor was manufactured by the following method. i.e. 2X5X0.5mm (7) SOS
After etching and forming a P-type silicon layer 12 in the form of an island in the regions where the reference electrode part 1 and the sensor part 2 are to be formed on the substrate 1) (Silicon on Sapphire), impurities are diffused according to the manufacturing process of an n-channel MO5FET. Thus, a source region 13 and a drain region 14 were formed. Thereafter, a silicon oxide (Si) film with a thickness of 1000 nm is used as an insulating film on each gate part of the reference electrode part l and the sensor part 2.
O□) film 15 is formed by thermal oxidation, followed by a film with a thickness of 200 mm.
For example, the silicon nitride (313N4) film 16 of
D (Chemical Vapor!2ep
position.

It was formed by a chemical vapor deposition (chemical vapor deposition) method. Further, a silver layer 17 was formed on the gate portion of the reference electrode portion 1 by vacuum evaporation.

Next, the neutral beam sputtering device 2 shown in FIG.
A laminate film 18 was formed to cover the reference electrode portion l on which the silver layer 17 was formed using 0. That is, the sensor base 2
5 on the sample stage 26, apply an argon atomic beam (argon gas to 7 KV in the high-speed atomic beam gun 21).
A high-speed atomic beam that is ionized and accelerated, then neutralized again by an electron shower, and an argon gas flow rate of 0.55.
CCM (current value 1.15 to 1.2 mA) 22 is irradiated onto the silver chloride target and the polytetrafluoroethylene resin target 23 placed on the target stand 27 for 6 hours alternately for 30 minutes each, and the target pops out. depositing the particles 24 on the surface of the reference electrode portion l in the sensor base 25;
A laminate film 18 having a thickness of about 300 to 500 layers was formed. The thickness of each layer of the silver chloride layer and the polytetrafluoroethylene resin layer in this laminate film 18 is 30 to 50 mm.
It was a person. In FIG. 4, 21a is a high voltage power supply for the high-speed atomic beam gun 21, 26a and 27a are drive motors for rotating the sample stage 26 and target stage 27, respectively, 28 is an exhaust chamber, and 29 is an exhaust pump, respectively. It shows.

After connecting the 15FET sensor 30 produced in Example 1 to the measuring device 31 shown in FIG. 5, it was immersed in an electrolyte salt aqueous solution 32, and its response characteristics were measured. Measuring device 31
sets the source-drain voltage VOS of the reference electrode section 1 and the sensor section 2 to 4V, drives the source current at a constant current of 50 μA, and outputs the source potential at the comparator 31a. Then, the difference V out between the source potentials of the reference electrode section 1 and the sensor section 2 is outputted from the output terminal of the comparator 31b. Note that the common electrode 31c is immersed in the aqueous solution at the same time to ensure electrical neutrality of the circuit.

The measurement results are shown in FIG.

In the figure, the ○ mark is in a solution that does not contain NaCε, and the opening is 0.2
The results are shown in a solution containing NaCQ of M.

As a result, although the output potential is abnormally low, the Cl2-
A constant potential (-171
3 mV), indicating that it has characteristics as a reference electrode.

(Example 2) A 15FET sensor having a MO5FET structure as shown in FIG. 3 was manufactured. That is, according to the manufacturing process of the n-channel MO3FET, impurities are diffused into the regions where the reference electrode part l and the sensor part 2 of the n-type silicon substrate 41 are to be formed, respectively, to form the p-type well region 42, and then the source region 43 and the drain region 44. formed. after that,
A silicon oxide film 45 with a thickness of 1,000 thick and a silicon nitride film 46 with a thickness of 1,500 thick were formed over the entire surface. Thereafter, in the same manner as in Example 1, a silver layer 17 was formed on the reference electrode portion l, followed by a laminate film 18.

The response characteristics of the 15FET sensor manufactured in Example 2 are shown in the fifth example.
The measurement was performed using the measuring device 31 shown in the figure. That is, the potential of the 15FET sensor when the pH of the solution was set to 6.8.8.0 was measured using the reference 15FET as a reference. The results are shown in FIG.

As a result, a response characteristic with a slope of about -45.9 mV/pH was observed.

In the above example, a pH sensor was used as an ion sensor combined with a reference electrode, but it is of course possible to combine it with any other sensor that detects by electric potential, such as other ion sensors, enzyme sensors, biosensors, and gas sensors. It is.

(Example 3) As shown in FIG. 8, a MO5FET 51 is formed on the surface of an SO8 substrate 50 using a normal semiconductor manufacturing process, and then a graphite layer with a thickness of 1000 nm is formed by CVD as a gate electrode film of the MO3FET 51. 52 was formed. At this time, a thickness of 20t is required for patterning the gate electrode.
A Lm metal mask (molybdenum plate) was used.

Next, a redox functional film 53 having a thickness of about 1000 layers was formed on the graphite layer 52 by the following method.

That is, first, as shown in FIG. 10, a diameter of 15 mm,
Using an isotropic graphite substrate 60 with a length of 5 mm, electrolysis was performed under the following conditions to form a film with a thickness of 150 μm as a target.
A poly(4,4'-biphenol) film 61 of m was formed on the surface of the substrate. The electrolyte was a mixture of 0.1M 4.4'-biphenol, 0.5M NaCff04, and acetonitrile (temperature 20°C) 62, and the graphite substrate 60 was immersed in it, and a saturated calomel electrode (SCE) 63 was used.
3 regressions at 0 to 1.5V (sweep speed 50mV/
After S), a constant potential electrolytic reaction was performed using an electrolytic device 64 at 1.5 V for 20 minutes.

The graphite substrate 60 coated with the electrolytically polymerized film thus obtained was taken out and fixed on the target stage 27 of the neutral beam sputtering apparatus 20 shown in FIG. 4 with the electrolytically polymerized film facing upward. A MOSFET having a gate formed with a graphite film was fixed to the sample stage 26. At this time, a metal mask with a pattern of approximately 50 μm was attached so that the entire surface of the graphite in the gate portion could be covered with a sputtered film. The sputtering device 20 is 10-
The high-speed atomic beam gun 21 is operated under a reduced pressure of '~l O-' Torr to generate an argon atomic beam (initial velocity + 3X
IO'c+++/sec or more) is generated and the target (
Here, the surface of the electropolymerized membrane) is irradiated, and the sputtered particles are irradiated with M for 6 hours.
It is deposited on the surface of OS FET to increase the film thickness.
A human redox functional film 53 was formed. Thereafter, it was annealed under vacuum at room temperature for one day and night, and then stored under nitrogen gas.

Approximately 10 μβ of the ion-sensitive membrane forming solution having the composition shown in Table 1 was dropped onto the surface of the gate film of the MOSFET thus prepared using a microdispenser several times.
Thereafter, the solvent was dried to form an ion-sensitive membrane (ion-selective membrane) 54 having a thickness of 10 to 20 μm.

After forming the gate film in this manner, the surrounding area was electrically insulated with an insulating adhesive film 55.

Table 1 All solvents used were Tl(F (tetrahydrofuran)).

The abbreviations for carrier materials are:

Bis-B15-12-Cro: Bis[(12-crown-4)methyl J dodecyl 70nate (manufactured by Doguchi Kagaku Co., Ltd.) TPSnCL: ) Liphenyl tin chloride (manufactured by Aldrich Co., Ltd.) Ca fDOPO) *:
Calcium bis[9-(n-octylphenyl)sulphate (manufactured by Dojin Kagaku Co., Ltd.) oopo: Di(n-octylphenyl) sulphate (manufactured by Dojin Kagaku Co., Ltd.) DHDMBA:
N,N'-dihectyl-N,N'-dimethyl-1,4-7thanocyamide (manufactured by FluKa) In addition, KTpCIPB as a carrier composition is potassium tetrakis(p-chlorophenyl)borate, PvC
represents polyvinyl chloride, and 00s represents dioctyl sebacate.

1) Connect the potassium ion FET sensor 70 prepared in Example 3 to the measuring device 71 shown in Figure 1), and use a saturated sodium chloride saturated calomel electrode (SSCE) as a reference electrode.
The sample was immersed in a cell together with 72, and the potassium ion concentration in the solution was varied to measure the change in output voltage. As shown in Fig. 12, the output voltage V out shows a good linear relationship with the logarithm of the potassium ion concentration, and the slope of the straight line is 60.5 mV/Qog ([K ''] /M) (
(37°C) The linear range was 10-4 to 5XIO-'M. It was also found that the response time was extremely fast, 95% of the time being within 1 second. Furthermore, it was found that the output voltage was not easily affected by changes in light illuminance and by the partial pressure of oxygen gas.

Note that the driving conditions of the FET were typically a source-drain voltage Vos = 4V, and a source current l5 = 50 μA. Further, although the results of Experimental Examples 4 to 7 are not shown, sufficient characteristics as an ion sensor were obtained.

(Example 4) As shown in Fig. 9, a P-type silicon substrate (10-20Ω
cm) 80 using normal semiconductor manufacturing process technology, and then a film thickness of approximately 1 cm is formed on the gate part.
A gate insulating film 8 consisting of a silicon oxide (Si02) film of 1,000 yen and a silicon nitride fsixN41 film of 1,500 yen.
1 was formed. Furthermore, using the CVD method, a graphite layer with a film thickness of 1) 00 to 1200 was added to the gate area.
After forming at ℃, the resist was spin-coated and patterned. Thereafter, the exposed graphite layer was etched in hydrogen plasma and the resist was removed so that the graphite layer 82 remained only in the gate area.Next, the redox functional film 83 was formed in the same manner as in Example 3. After forming a poly(4,4-biphenol) film with a thickness of approximately 1000 nm using a neutral atom beam sputtering device, Table 1
An ion-sensitive membrane layer 84 with a thickness of 10 μm and having the composition shown in FIG. After forming the gate film in this manner, the surrounding area was electrically insulated with an insulating adhesive layer 85.

(Example 5) After forming a silver layer by vacuum evaporation on the gate part of the reference electrode part of a twin-type 15FET manufactured in the same manner as in Example 1, a silver layer was formed using a vacuum evaporation apparatus (EB heating method) to a film thickness of approximately 100%. A silver chloride layer was formed.

Next, about 20 to 30 polytetrafluoroethylene (PTFE) thin films were formed using the above-mentioned neutral beam sputtering apparatus 20 under the same conditions as in Example 1, and then a silver chloride layer 20 was formed using the vacuum evaporation apparatus described above. ~50 people formed. By repeating these film formations 5 to 10 times, 400 to 8
A polytetrafluoroethylene-silver chloride laminated film was formed.

The response characteristics were determined in the same manner as in Experimental Examples 3 to 7, except that in Experimental Examples 3 to 7, an 15FET sensor having the structure shown in Figure 9 was used instead of the 15FET sensor shown in Figure 8. was measured. As a result, the same results as in Experimental Examples 3 to 7 were obtained.

Branch J1 As a result of measuring the 15FET sensor produced in Example 5 using the measuring device shown in FIG. 5, the same results as in Experimental Example 1 were obtained.

[Effects of the Invention] As detailed above, the reference electrode of the present invention has a structure in which the surface of a conductive substrate or a gate insulating film of a MOSFET is coated with a laminate film of silver halide and a hydrophobic film, and Since this laminated film is formed by a neutral beam sputtering method, it exhibits a stable potential and can be easily miniaturized, making it possible to fabricate an integrated sensor in which other ion sensors are formed on the same chip. It becomes easier.

In addition, in the ion sensor according to the present invention, when forming a redox functional film on a conductive substrate or a gate insulating film of an MO3 type field effect transistor, a redox film is prepared in advance on a predetermined substrate surface by an electrolytic polymerization method. By forming a functional film and using the neutral beam sputtering method using this redox functional film as a target, it is possible to form a film with the same composition as the pre-formed electropolymerized film on the surface of a conductive substrate, etc. . Therefore, the quality of the redox functional membrane can be easily adjusted, and an ion sensor having uniform characteristics and stable functions can be manufactured. Furthermore, since a neutral atomic beam is used, there is no electrostatic charge caused by charging.
No discharge breakdown occurs, therefore MOSFET
It is possible to form a film even on weak parts such as the gate part of
This has the effect of facilitating miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an integrated I5FET sensor according to Example 1 of the present invention, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is a plan view of an I5FET sensor according to Example 2. , FIG. 4 is a schematic configuration diagram of the neutral beam sputtering device, FIG. 5 is a circuit configuration diagram of the measuring device used in Experimental Example 2, FIG. 6 is a response characteristic diagram of the 15FET sensor created in Example 1, and FIG. Figure 7 is a response characteristic diagram of the 15FET sensor manufactured in Example 2, Figure 8 is a cross-sectional view of the ion sensor according to Example 3, Figure 9 is a cross-sectional view of the ion sensor according to Example 4, and Figure 10 is an experimental example. Figure 1) is a configuration diagram of the electrolytic device used in Examples 3 to 7, and Figure 1) is a measurement circuit configuration diagram as well, and Figure 12 is a characteristic diagram showing the results of Experimental Example 3 of the potassium ion sensor manufactured in Example 3. ■...Reference electrode part, 2...Sensor part 1).
50...-8O8 substrate, 12... P-type silicon layer 17
...Silver layer, 18.--Laminated film 20.
... Neutral beam sputtering device 21 ... High speed atom beam gun 23 ... Target, 31 ... Measuring device, 52 ... Graphite layer, 54 ... Ion sensitive membrane, 25 ... Electrode base 51 ...・・MOS FET 53−・Redox functional membrane 64・・Electrolyzer

Claims (6)

[Claims] (1) A conductive substrate, a silver halide layer formed on the substrate by neutral beam sputtering or vapor deposition, and a hydrophobic resin layer formed on the silver halide layer by neutral beam sputtering. A reference electrode comprising a laminate film comprising: (2) A gate insulating film of a field effect transistor, a silver halide layer formed on the surface of the insulating film by a neutral beam sputtering method, and a hydrophobic layer formed on the silver halide layer by a neutral beam sputtering method. 1. A reference electrode comprising: a laminate film having a synthetic resin layer; (3) Forming targets of silver halide and hydrophobic resin on the surface of a predetermined substrate, and sputtering the target by alternately irradiating the silver halide and hydrophobic resin with a neutral beam, A method for producing a reference electrode, comprising the step of forming a laminate film comprising a silver halide layer and a hydrophobic resin layer on the surface of the reference electrode. (4) An ion characterized by comprising an electrically conductive base, a redox functional film formed on the surface of the base by a neutral beam sputtering method, and an ion sensitive film covering the redox functional film. sensor. (5) A gate insulating film of a MOS field effect transistor, a redox functional film formed on the surface of the gate insulating film by a neutral beam sputtering method, and an ion sensitive film covering the redox functional film. An ion sensor characterized by: (6) Forming a target of a redox functional substance on the surface of a predetermined substrate, and sputtering the target by irradiating the redox functional substance with a neutral beam to form a redox functional film on the surface of the substrate. A method for manufacturing an ion sensor, comprising the steps of: forming an ion-sensitive film on the surface of the redox functional film.