JP2023037900A - Solid semiconductor ion sensor - Google Patents

Abstract

To provide a solid semiconductor ion sensor that eliminates deterioration of a reference electrode due to reaction between a sample solution and an electrode and the necessity of replacing internal liquid of the reference electrode, and exhibits excellent stability even for a long-term service.SOLUTION: A solid semiconductor ion sensor 1 capable of measuring ion concentration of specific ion in sample solution comprises: an ion sensitive film 12 sensitive to a specific ion; a field effect transistor 13 including a gate area 13G a surface of which is coated with an insulator film 15 capable of conducting electric charges approaching the ion sensitive film 12; and a gate potential detection film 20 electrically conducting with a sample solution 80, capable of detecting a gate potential. The gate potential detection film 20 comprises a sheet member 22 including carbon materials.SELECTED DRAWING: Figure 1

Description

There is an application for exception to loss of novelty

The present invention relates to solid state semiconductor ion sensors.

Conventionally, a glass electrode type ion sensor has been used as an ion sensor for measuring the ion concentration in a solution. A glass electrode ion sensor measures the ion concentration of a sample solution by detecting the difference between the glass membrane potential of an indicator electrode and the electromotive force of a reference electrode. However, the glass electrode type ion sensor is fragile and poor in durability because the glass film of the indicator electrode is thin. In addition, since the glass electrode type ion sensor uses silver-silver chloride electrodes for both the indicator electrode and the reference electrode, there is a risk of deterioration due to reaction with the sample solution. In addition, the reference electrode of the glass electrode type ion sensor maintains conductivity with the indicator electrode through the sample as a salt bridge, so the internal solution is constantly leaking out, and it is necessary to replace the internal solution.

In recent years, ion sensors using solid semiconductors have been known as ion sensors. An ion sensor using such a solid semiconductor is also called an ion sensitive field effect transistor (hereinafter referred to as ISFET) sensor. An ISFET sensor is composed of an ISFET having an ion-sensitive film formed on an insulating film, a reference electrode immersed in a sample solution, and a power supply circuit connecting the ISFET and the reference electrode. It is an ion sensor that measures the ion concentration by applying a gate voltage and by changing the potential of the ion sensitive membrane. Such an ion sensor has the advantage of being more durable and easier to miniaturize than the glass electrode type ion sensor described above. However, such an ISFET sensor often uses a silver-silver chloride electrode as a reference electrode in the same manner as the glass electrode type ion sensor described above, and there is a risk that the reference electrode will react with the sample solution and deteriorate. there were. In addition, since it is necessary to replace the internal liquid of the reference electrode, long-term measurement is difficult, and improvement of long-term stability is required. As a method for improving long-term stability, an ISFET sensor using a solid reference electrode made of palladium hydride is known (see Patent Document 1, for example).

JP-A-6-249824

However, even when palladium hydride is used as a reference electrode, corrosion may occur depending on the sample solution, and further improvement in long-term stability is required.

An object of the present invention is to provide a solid-state semiconductor ion sensor that eliminates the need for deterioration of the reference electrode and replacement of the internal solution of the reference electrode due to the reaction between the sample solution and the electrode, and exhibits excellent stability even in long-term use. and

(1) A solid semiconductor ion sensor according to one embodiment for achieving the above object is a solid semiconductor ion sensor capable of measuring the ion concentration of specific ions in a sample solution, wherein a film, a field effect transistor having a gate region, the surface of the gate region being covered with an insulating film capable of conducting charges approaching the ion sensitive film, and a film conductive to the sample solution, the film comprising a gate. a gate potential detection film capable of detecting potential, wherein the gate potential detection film includes a sheet member made of a carbon material.
(2) In the solid-state semiconductor ion sensor according to another embodiment, preferably, the gate potential detection film may be formed by coating both side surfaces in the thickness direction of the sheet member with a resin.
(3) In the solid-state semiconductor ion sensor according to another embodiment, preferably, the carbon material may be carbon fiber.
(4) The solid-state semiconductor ion sensor according to another embodiment is preferably connected to the ion sensitive film and the insulating film, and charges approaching the ion sensitive film from a conductive material capable of conducting to the insulating film. A wire may be further provided.
(5) In the solid-state semiconductor ion sensor according to another embodiment, preferably, the specific ions may be hydrogen ions.

According to the present invention, it is possible to provide a solid semiconductor ion sensor that does not require deterioration of the reference electrode due to reaction between the sample solution and the electrode and exchange of the internal solution of the reference electrode, and exhibits excellent stability even in long-term use.

FIG. 1 shows a schematic plan view of a solid state semiconductor ion sensor according to an embodiment of the invention. FIG. 2 shows a plan view of the ion concentration measurement part of the solid-state semiconductor ion sensor according to the embodiment of the present invention. FIG. 3 shows a side view of the ion concentration measuring part of the solid-state semiconductor ion sensor according to the embodiment of the present invention and an enlarged view of a part A thereof, respectively. FIG. 4 shows a schematic circuit diagram for explaining the operation of a solid-state semiconductor ion sensor according to an embodiment of the invention. FIG. 5 shows a schematic configuration diagram for explaining the operation of the solid-state semiconductor ion sensor according to the embodiment of the present invention. FIG. 6 shows a detailed circuit diagram of a solid state semiconductor ion sensor according to an embodiment of the invention. FIG. 7 shows a graph of the measurement results of the example. 8 shows a graph of the measurement results of Comparative Example 1. FIG. 9 shows a graph of the measurement results of Comparative Example 2. FIG. 10 shows a graph of the measurement results of Comparative Example 3. FIG. 11 shows a graph of the measurement results of Comparative Example 4. FIG. 12 shows a graph of the measurement results of Comparative Example 5. FIG.

Next, embodiments of the present invention will be described with reference to the drawings. In addition, the embodiments described below do not limit the invention according to the claims, and all of the elements described in the embodiments and their combinations are essential to the solution of the present invention. not necessarily.

FIG. 1 shows a schematic plan view of a solid state semiconductor ion sensor according to an embodiment of the invention. FIG. 2 shows a plan view of the ion concentration measurement part of the solid-state semiconductor ion sensor according to the embodiment of the present invention. FIG. 3 shows a side view of the ion concentration measuring part of the solid-state semiconductor ion sensor according to the embodiment of the present invention and an enlarged view of a part A thereof, respectively.

A solid-state semiconductor ion sensor 1 according to this embodiment is an ion sensor capable of measuring the ion concentration of specific ions in a sample solution. In this embodiment, the solid-state semiconductor ion sensor 1 is a pH sensor capable of measuring the ion concentration of hydrogen ions (H ⁺ ) in a sample solution. Moreover, in this embodiment, the solid-state semiconductor ion sensor 1 is an ISFET sensor using an ISFET. More specifically, the solid-state semiconductor ion sensor 1 preferably includes at least an ion concentration measuring section 10, a power supply unit 30, a circuit board 34, and a display section . The power supply unit 30 preferably includes DC power supplies 31 and 32 (see FIG. 4), which will be described later, and a DC-DC converter. The power supply unit 30 preferably transforms the DC voltage of the battery into a DC voltage suitable for various devices such as the field effect transistor 13 described later by a DC-DC converter, and supplies the transformed DC voltage to the various devices. The circuit board 34 is preferably a board that constitutes an arithmetic processing unit such as a microcomputer. The display unit 36 is, for example, a device such as an LCD (Liquid Crystal Display) that displays various information such as ion concentration.

The ion concentration measurement unit 10 has an ion sensitive film 12 that is sensitive to specific ions, and a gate region 13G (see FIG. 4). ) covering the surface of the gate region 13G with a field effect transistor (hereinafter referred to as FET) 13, and a gate potential detection film which is conductive to the sample solution and capable of detecting the gate potential. 20 and. Moreover, the ion concentration measuring unit 10 preferably further includes a wire 16 connected to the ion sensitive film 12 and the insulating film 15 and made of a conductive material capable of conducting charges approaching the ion sensitive film 12 to the insulating film 15 . .

(1) Ion Sensitive Membrane In this embodiment, the ion sensitive membrane 12 is a membrane sensitive to hydrogen ions (H ⁺ ) in the sample solution. For the ion sensitive film 12, for example, a film that collects hydrogen ions such _as tantalum oxide ( _Ta2O5 ), silicon oxide ( _SiO2 ) _, silicon nitride ( _Si3N4 ), alumina ( _Al2O3 ), etc. may be used _. can be done. Among these, tantalum oxide is particularly suitable. The ion sensitive film 12 is preferably formed by depositing tantalum oxide on a silicon wafer. The ion sensitive film 12 is preferably fixed on a flexible printed circuit board (hereinafter also referred to as an FPC board) 11 using a silver-silver chloride paste, and then molded with epoxy resin except for the sensitive portion. The film thickness of tantalum oxide in the ion sensitive film 12 is preferably 20-110 nm, more preferably 25-45 nm. The configuration of the ion sensitive film 12 is not particularly limited as long as it is a film sensitive to at least specific ions whose concentration is to be measured in the sample solution.

(2) Field effect transistor (FET)
In this embodiment, FET 13 is an nMOS transistor in which two n-type regions are formed on a p-type silicon substrate with a space therebetween. The two n-type regions function as a source region 13S (source electrode) and a drain region 13D (drain electrode), respectively (see FIG. 4). A region sandwiched between the source region 13S and the drain region 13D is a channel region 13C that functions as a channel when the FET 13 is operated. The FET 13 has an insulating film 15 covering the surface of the FET 13 including the gate region 13G on the channel region 13C. For example, Ta ₂ O ₅ , SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , a mixture of two or more of these, or the like can be used for the insulating film 15 . Among these, _SiO2 is particularly suitable. The insulating film 15 is a portion through which charges approaching the ion sensitive film 12 are conducted via the wire 16 . The drain region 13D is electrically connected to at least the circuit board 34 via the lead wire 17 for drain. The source region 13S is electrically connected to at least the circuit board 34 via the lead wire 19 for source. The gate region 13G is electrically connected to at least the circuit board 34 via the lead wire 18 for gate. Details of the operation of the FET 13 will be described later with reference to FIG.

(3) Wire The wire 16 is a wire made of a conductive material that connects the ion sensitive film 12 and the insulating film 15 . The wire 16 is a member that conducts charges approaching the ion sensitive film 12 to the insulating film 15 . The wire 16 is not particularly limited as long as it is made of a conductive material. For example, the wire 16 may be made of metal, carbon fiber, glass fiber, conductive ink, conductive rubber, or the like. Examples of metals include silver, gold, copper, aluminum, gold-palladium alloys, nickel, and plated products thereof. Among these, metal is suitable as the material of the wire 16, and silver is particularly suitable. The wire 16 preferably has a length of 20 mm to 100 mm, more preferably 40 mm to 60 mm. The solid-state semiconductor ion sensor 1 has a configuration in which the ion sensitive film 12 and the FET 13 are separated from each other by providing the wire 16 . Thereby, since the solid-state semiconductor ion sensor 1 does not need to immerse the FET 13 in the sample solution, it is possible to suppress corrosion of the FET 13 due to the sample solution. Moreover, in the manufacturing process of the solid-state semiconductor ion sensor 1, the step of molding the FET 13 can be omitted in order to suppress corrosion due to the sample solution.

(4) Gate Potential Detection Film The gate potential detection film 20 is a film that can be electrically connected to the sample solution and has conductivity that allows the gate potential to be detected. The gate potential detection film 20 includes a sheet member 22 made of a carbon material (see enlarged view of part A of FIG. 3). Examples of carbon materials that can be used include graphite, carbon fiber, glassy carbon, carbon paste, and conductive diamond. Among these, carbon fiber is preferable from the viewpoint of stability, responsiveness, reproducibility, and the like. The thickness of the sheet member 22 is preferably 0.1-1 mm, more preferably 0.2-0.8 mm. The gate potential detection film 20 is preferably formed by coating both side surfaces in the thickness direction of a sheet member 22 with a resin 24 . The resin 24 is, for example, polylactic acid resin, polyamide resin, polyester resin, acrylic resin, polyvinyl alcohol resin, polyolefin resin, polyurethane resin, polyvinyl chloride resin, silicone resin, fluorine resin, and copolymers thereof. Modified products and the like can be used. Among these, polyimide, which is a material for printed circuit boards, is particularly suitable for its insulating properties. In this embodiment, the gate potential detection film 20 is electrically connected to at least the circuit board 34 via lead wires, like the drain region 13D, the source region 13S, and the gate region 13G. Note that the gate potential detection film 20 does not have to include the resin 24 .

Next, operation of the solid-state semiconductor ion sensor 1 will be described.

FIG. 4 shows a schematic circuit diagram for explaining the operation of a solid-state semiconductor ion sensor according to an embodiment of the invention. FIG. 5 shows a schematic configuration diagram for explaining the operation of the solid-state semiconductor ion sensor according to the embodiment of the present invention. FIG. 6 shows a detailed circuit diagram of a solid state semiconductor ion sensor according to an embodiment of the invention.

The solid-state semiconductor ion sensor 1 measures the pH of the sample solution 80 by immersing the ion sensitive film 12 and the gate potential detection film 20 in the sample solution 80 containing hydrogen ions. The solid-state semiconductor ion sensor 1 includes a DC power supply 31 connected to the drain region 13D and the source region 13S. The DC power supply 31 applies a voltage (hereinafter also referred to as drain voltage) Vd between the drain region 13D (drain electrode) and the source region 13S (source electrode) to generate current (hereinafter also referred to as drain current). ) Id (dashed arrow in FIG. 4). In the solid-state semiconductor ion sensor 1, when the ion sensitive film 12 comes into contact with the sample solution 80, the charge generated on the surface of the ion sensitive film 12 by the hydrogen ions in the sample solution 80 is conducted to the insulating film 15 via the wire 16. , the interfacial potential changes due to the charge, and the size of the channel region 13C changes according to the hydrogen ion concentration (pH). Therefore, the magnitude of the drain current Id flowing between the drain region 13D and the source region 13S changes according to the magnitude of the hydrogen ion concentration (pH). The solid-state semiconductor ion sensor 1 is configured with a feedback circuit that adjusts the magnitude of the drain current Id to be constant while keeping the drain voltage Vd constant, thereby adjusting the gate potential Vgs. At this time, the gate potential Vgs is adjusted to a potential lower by a potential corresponding to the hydrogen ion concentration in the sample solution 80 . The gate potential Vgs is the potential difference (voltage) between the gate region 13G and the source electrode (source region 13S), that is, the potential difference (voltage) between the gate potential detection film 20 and the source electrode, and is also called gate voltage. . The solid-state semiconductor ion sensor 1 includes a DC power supply 32 connected to the source region 13S (source electrode) and the gate potential detection film 20, and the DC power supply 32 adjusts the gate potential Vgs.

The solid-state semiconductor ion sensor 1 includes a control section 50 having at least a current value acquisition section 52, a gate potential adjustment section 54, and a concentration acquisition section 56 (see FIG. 5). The current value acquisition unit 52 acquires the current value of the drain current Id measured by the ammeter 40 . The gate potential adjustment unit 54 adjusts the gate potential (gate voltage) Vgs so that the current value of the drain current Id acquired by the current value acquisition unit 52 becomes a predetermined value specified in advance. The concentration acquisition unit 56 acquires the gate potential Vgs from a voltmeter (not shown) capable of measuring the gate potential Vgs, and acquires the hydrogen ion concentration (pH) based on the gate potential Vgs. The details of the circuit described above are, for example, the configuration shown in FIG.

The solid-state semiconductor ion sensor 1 configured in this manner includes a gate potential detection film 20 in place of the reference electrode used in conventional glass electrode ion sensors and ISFET sensors. Since the gate potential detection film 20 does not contain an internal liquid, it is not necessary to replace the internal liquid unlike the reference electrode, and long-term measurement is possible. In addition, since the gate potential detection film 20 is made of a carbon material, it is excellent in corrosion resistance, and can suppress the risk of deterioration due to reaction with the sample solution 80 . Further, in the solid-state semiconductor ion sensor 1, since the ion sensitive film 12 and the FET 13 are connected by the wire 16, there is no need to immerse the FET 13 in the sample solution 80 when measuring the ion concentration. can be suppressed from being corroded by the sample solution 80 . In addition, molding of the FET 13, which has been conventionally performed to suppress corrosion of the FET 13, becomes unnecessary. Therefore, the solid-state semiconductor ion sensor 1 is excellent in long-term stability and can easily measure the ion concentration of various sample solutions.

<Other embodiments>
As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these and can be implemented in various modifications.

In the above-described embodiment, the solid-state semiconductor ion sensor 1 was a sensor capable of measuring the ion concentration (pH) of hydrogen ions in the sample solution. It is also applicable to sensors for For example, the solid-state semiconductor ion sensor 1 uses chloride ions (Cl ⁻ ; also referred to as chloride ions), hydrogen carbonate ions (HCO ₃ ⁻ ), carbonate ions (CO ₃ ²⁻ ), sulfide ions instead of hydrogen ions. (S ^2- ), fluorine ion (F ⁻ ), ammonium ion (NH ₄ ⁺ ), lithium ion (Li ⁺ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), magnesium ion (Mg ²⁺ ), calcium ion It can also be applied to sensors for measuring ion concentrations such as (Ca ²⁺ ). For example, when measuring the ion concentration of chloride ions, the ion-sensitive film 12 of the solid-state semiconductor ion sensor 1 may be a film made of a combination of silver halide and silver sulfide, or silver chloride and silver sulfide incorporated in an epoxy resin. may be replaced with a film composed of a combination of However, for example, chloride ion (Cl ^- ), hydrogen carbonate ion (HCO ₃ ^- ), carbonate ion (CO ₃ ^2- ), sulfide ion (S ^2- ), fluoride ion (F ^- ), etc. ions are negatively charged anions, the solid-state semiconductor ion sensor 1 may employ a pMOS transistor as the FET 13, in which two p-type regions are formed on an n-type silicon substrate with a space therebetween.

Moreover, the solid-state semiconductor ion sensor 1 does not have to include the wire 16 . In this case, the solid-state semiconductor ion sensor 1 may be configured such that the ion sensitive film 12 is laminated on the insulating film 15 so that charges approaching the ion sensitive film 12 can be conducted to the insulating film 15 .

Further, the solid-state semiconductor ion sensor 1 acquires the hydrogen ion concentration based on the gate potential. Also good.

Next, examples of the present invention will be described in comparison with comparative examples. In addition, the present invention is not limited to the following examples.

<Example>
(Example 1)
(1) Manufacture of solid-state semiconductor ion sensor On the surface or end face of a silicon wafer cut into 5 mm squares using a dicing saw, an ECR sputtering device manufactured by Elionix (product number: EIS-200ER) is used to oxidize the film thickness to 32 nm. A tantalum film was formed. Next, the surface of the silicon wafer on which the tantalum oxide film is not formed and the tip of the FPC substrate are connected using a silver/silver chloride paste (SILVER SILVER CHLORIDE, Code No: C2131016D1) manufactured by GWENT GROUP. bottom. At this time, heat treatment was performed at 150° C. for 30 minutes using a constant temperature bath (DESK-TOP Hi-TEMP, CHAMBER ST-110) manufactured by ESPSC. Thereafter, an epoxy resin (INPEI BLACK) manufactured by Sunhayato Co., Ltd. was used to cover the ion-sensitive film (tantalum oxide film) portion for insulation. The epoxy resin used was obtained by mixing a main agent and a curing agent at a ratio of 25:2. Then, a FET (part number: 2SK208-Y) manufactured by Toshiba Semiconductor Corp. was soldered onto the FPC board.
Carbon fiber manufactured by ABC HOBBY Co., Ltd. (product number: 71135) <http://www. abchobby. com/JP/page/parts/mateline. html> was used to prepare a gate potential detection film. Two types of carbon fibers, one with a thickness of 0.5 mm and the other with a thickness of 0.2 mm, were used to prepare gate potential detection films.
A solid semiconductor ion sensor was fabricated by electrically connecting the FET and the gate potential detection film to a circuit board through a lead wire. Two types of solid semiconductor ion sensors were produced: a solid semiconductor ion sensor using carbon fibers with a film thickness of 0.5 mm and a solid semiconductor ion sensor using carbon fibers with a film thickness of 0.2 mm.
(2) Gate voltage measurement Gate voltage measurement with a buffer solution was performed using the produced solid semiconductor ion sensor. A specific measuring method is as follows.
First, the surface of the ion-sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water (hereinafter simply referred to as ultrapure water) generated by a Direct-Q system manufactured by Merck Millipore, and wiped off. The ion-sensitive membrane and the gate potential detection membrane were immersed in a borate pH standard solution (hereinafter also referred to as pH 9.18 standard solution) manufactured by Yaku Co., Ltd., and the gate voltage (gate potential) was measured for about 30 minutes.
Next, the surface of the ion-sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, and a neutral phosphate pH standard solution (hereinafter referred to as pH 6.86 standard solution) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. The ion-sensitive membrane and the gate potential detection membrane were immersed in a solution, and the gate voltage was measured for about 30 minutes.
Next, the surface of the ion-sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water, wiped off moisture, and treated with an oxalate pH standard solution (hereinafter also referred to as pH 1.68 standard solution) manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. ), and the gate voltage was measured for about 30 minutes.
Again, the gate voltage was measured in the same order for the pH9.18 standard solution, the pH6.86 standard solution, and the pH1.68 standard solution, and the measurement was completed.
Two types of solid semiconductor ion sensors, a solid semiconductor ion sensor using carbon fiber with a film thickness of 0.5 mm and a solid semiconductor ion sensor using carbon fiber with a film thickness of 0.2 mm, were measured by the above method. Each gate voltage was measured.

<Comparative example>
(Comparative example 1)
(1) Manufacture of solid semiconductor ion sensor Instead of the gate potential detection film of Example 1, a conductive glass electrode (AS ONE Co., Ltd. product number: NPV-CFT2-7A) <https://axel. as-1. co. A solid semiconductor ion sensor was produced in the same manner as in Example 1, except that jp/asone/g/NCTB150019/> was used.
(2) Gate voltage measurement Gate voltage measurement with reference seawater was performed using the fabricated solid-state semiconductor ion sensor. A specific measuring method is as follows.
In this measurement, reference seawater 164 (pH 7.542), reference seawater 171 (pH 7.849), reference seawater Kanso (pH 7.955) were used. These pricing reference seawaters were sampled and rated at the Scripps Institute of Oceanography, University of California, San Diego, USA, and distributed as seawater standards.
First, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water and wiped dry, then the ion sensitive membrane and the gate potential detection membrane were immersed in the reference seawater 164, and the gate voltage was measured for about 20 minutes.
Next, the surfaces of the ion sensitive membrane and the gate potential detection membrane were washed with ultrapure water and wiped dry, and the ion sensitive membrane and the gate potential detection membrane were immersed in the reference seawater 171, and the gate voltage was measured for about 20 minutes.
Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water and wiped dry, and the ion sensitive membrane and the gate potential detection membrane were immersed in reference seawater Kanso, and the gate voltage was measured for about 20 minutes.
Again, the gate voltage was similarly measured in the order of the reference seawater 164, the reference seawater 171, and the reference seawater Kanso.
(Comparative example 2)
(1) Manufacture of solid semiconductor ion sensor Instead of the gate potential detection film of Example 1, a lanthanum fluoride electrode manufactured by PRECISION MICRO-OPTICS Co., Ltd. (product number: PGEC-0000C01110) <https://www. pmoptics. com/lanthanum_fluoride. A solid semiconductor ion sensor was fabricated in the same manner as in Example 1, except that html> was used.
(2) Gate voltage measurement Gate voltage measurement with reference seawater was performed in the same manner as in Comparative Example 1 using the prepared solid-state semiconductor ion sensor.
(Comparative Example 3)
(1) Production of solid semiconductor ion sensor A solid semiconductor ion sensor was produced in the same manner as in Example 1, except that the gate potential detection film in Example 1 was replaced with a tantalum oxide electrode.
(2) Gate voltage measurement Gate voltage measurement with a buffer solution was performed using the produced solid semiconductor ion sensor. A specific measuring method is as follows.
First, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water and wiped off, and the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 9.18 standard solution, and the gate voltage was measured for about 30 minutes. .
Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 6.86 standard solution, and the gate voltage was measured for about 30 minutes. bottom.
Next, the surface of the ion-sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water, wiped off moisture, and treated with a phthalate pH standard solution (hereinafter also referred to as pH 4.01 standard solution) manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. ), and the gate voltage was measured for about 30 minutes.
Again, the gate voltage was measured in the same order for the pH 9.18 standard solution, the pH 6.86 standard solution, and the pH 4.01 standard solution.
(Comparative Example 4)
(1) Manufacture of solid semiconductor ion sensor A solid semiconductor ion sensor was manufactured in the same manner as in Example 1, except that a gold electrode (product number: EE046) manufactured by CYPRESS SYSTEMS Co., Ltd. was used instead of the gate potential detection film of Example 1. made.
(2) Gate voltage measurement Gate voltage measurement with a buffer solution was performed in the same manner as in Comparative Example 3 using the prepared solid semiconductor ion sensor.
(Comparative Example 5)
(1) Manufacture of solid semiconductor ion sensor In place of the gate potential detection film of Example 1, a chloride ion electrode (part number: CL-200B) manufactured by Toa DKK Co., Ltd. <https://www. toadkk. co. jp/product/spec/sci/electrode/mm_ion_electrode. A solid semiconductor ion sensor was fabricated in the same manner as in Example 1, except that html> was used.
(2) Gate voltage measurement Gate voltage measurement with a buffer solution was performed using the produced solid semiconductor ion sensor. A specific measuring method is as follows.
First, in the same manner as in Example 1, gate voltage was measured using a buffer solution.
Next, the ion sensitive membrane and the gate voltage detection membrane were immersed in a pH 1.68 standard solution, and the gate voltage was measured for about 2 days. Hereinafter, it is also referred to as measurement after pH 1.68 test).
Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, the ion sensitive membrane and the gate potential detection membrane were immersed in natural seawater, and the gate voltage was measured for about two days. The surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water and wiped off, and the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 9.18 standard solution, and the gate voltage was measured for about 30 minutes. Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 6.86 standard solution, and the gate voltage was measured for about 30 minutes. bottom. Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 4.01 standard solution, and the gate voltage was measured for about 30 minutes. bottom. Next, the surface of the ion sensitive membrane and the surface of the gate potential detection membrane were washed with ultrapure water to wipe off moisture, the ion sensitive membrane and the gate potential detection membrane were immersed in a pH 1.68 standard solution, and the gate voltage was measured for about 30 minutes. and finished (hereinafter also referred to as post-seawater test measurement).

<Evaluation method>
(1) Stability In the gate voltage measurement, if the gate voltage value corresponding to the pH value of the reference seawater or buffer solution is output, it is evaluated as passing (“○” in the table), and the pH value of the reference seawater or buffer solution When the gate voltage corresponding to was not output, it was evaluated as fail ("x" in the table).
(2) Repeatability In the gate voltage measurement, if the same gate voltage value is output each time during continuous repeated measurement, it is evaluated as passing ("○" in the table), and it is different for each time during continuous repeated measurement. When the gate voltage value was output, it was evaluated as fail (“x” in the table).
(3) Comprehensive Evaluation A pass (“○” in the table) was evaluated when all of the characteristic value evaluations were evaluated as pass. Also, when at least one of the characteristic value evaluations was evaluated as unacceptable, it was evaluated as unacceptable (“x” in the table).

<Results>
Table 1 shows the production conditions and evaluation results of Examples and Comparative Examples. Moreover, FIG. 7 shows the graph of the measurement result of an Example. 8 shows a graph of the measurement results of Comparative Example 1. FIG. 9 shows a graph of the measurement results of Comparative Example 2. FIG. 10 shows a graph of the measurement results of Comparative Example 3. FIG. 11 shows a graph of the measurement results of Comparative Example 4. FIG. 12 shows a graph of the measurement results of Comparative Example 5. FIG.

Example 1 was good in stability and repeatability independent of the film thickness of the carbon fiber. Comparative Examples 1-3 did not output a gate voltage according to the pH value of the reference seawater or buffer solution. In Comparative Example 4, the stability was good, but especially the gate voltage value when immersed in the pH 4.01 standard solution decreased each time it was measured, and the repeatability was not good. Comparative Example 5 had good repeatability, but not good stability. Therefore, at least one of stability and repeatability failed for Comparative Examples 1-5. On the other hand, in Example 1, all the properties were passed.

From the above results, the effect of using the gate potential detection film made of carbon fiber as the gate potential detection part of the solid semiconductor ion sensor was confirmed.

The solid-state semiconductor ion sensor according to the present invention can be used to detect substances having electrical polarity such as ions. In particular, the solid-state semiconductor ion sensor according to the present invention is suitable for pH measurement of sample solutions, detection of antibodies, detection of specific gases, and the like.

REFERENCE SIGNS LIST 1 solid semiconductor ion sensor, 12 ion sensitive film, 13 field effect transistor (FET), 13G gate region, 15 insulating film, 16 wire, 20. Gate potential detection film 22 Sheet member 24 Resin 80 Sample solution.

Claims (5)

A solid semiconductor ion sensor capable of measuring the ion concentration of specific ions in a sample solution,
an ion sensitive membrane sensitive to the specific ions;
a field effect transistor having a gate region, the surface of the gate region being covered with an insulating film capable of conducting electric charges approaching the ion sensitive film;
a gate potential detection film that is conductive to the sample solution and capable of detecting a gate potential;
with
A solid-state semiconductor ion sensor, wherein the gate potential detection film includes a sheet member made of a carbon material. 2. The solid-state semiconductor ion sensor according to claim 1, wherein the gate potential detection film is formed by coating both side surfaces in the thickness direction of the sheet member with a resin. 3. The solid-state semiconductor ion sensor according to claim 1, wherein said carbon material is carbon fiber. 4. The wire according to claim 1, further comprising a wire connected to said ion sensitive film and said insulating film and made of a conductive material capable of conducting electric charges approaching said ion sensitive film to said insulating film. 2. The solid semiconductor ion sensor according to item 1. 5. The solid-state semiconductor ion sensor according to claim 1, wherein said specific ions are hydrogen ions.

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