Solid semiconductor ion sensor

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

Technical Field

[0001] The present invention relates to a solid semiconductor ion sensor.

Background Art

[0002] Conventionally, a glass electrode type ion sensor has been used as an ion sensor for measuring the ion concentration in a solution. The glass electrode type ion sensor measures the ion concentration of a sample solution by detecting the difference between the glass membrane potential of the indicator electrode and the electromotive force of the reference electrode. However, since the glass membrane of the indicator electrode of the glass electrode type ion sensor is thin, it is easily broken and lacks durability. In addition, since silver-silver chloride electrodes are used for both the indicator electrode and the reference electrode of the glass electrode type ion sensor, there is a risk of deterioration due to reaction with the sample solution. Further, since the reference electrode of the glass electrode type ion sensor maintains conductivity with the indicator electrode through the sample as a salt bridge, the internal liquid always leaks out, and it is necessary to replace the internal liquid.

[0003] In recent years, as an ion sensor, an ion sensor using a solid semiconductor is known. Such an ion sensor using a solid semiconductor is also called an Ion Sensitive Field Effect Transistor (hereinafter referred to as ISFET) sensor. The ISFET sensor is composed of an ISFET formed by forming an ion-sensitive film on an insulating film, a reference electrode immersed in a sample solution, and a power supply circuit connecting the ISFET and the reference electrode. A gate voltage is applied with reference to the reference electrode, and the ion concentration is measured by the change in the potential of the ion-sensitive film. Such an ion sensor has the advantages of being more durable and easier to miniaturize compared to the above-mentioned glass electrode type ion sensor. However, in such an ISFET sensor, a silver-silver chloride electrode is often used as the reference electrode, similar to the above-mentioned glass electrode type ion sensor, and there is a risk that the reference electrode will deteriorate due to reaction with the sample solution. In addition, since the internal liquid of the reference electrode needs to be exchanged, long-term measurement is difficult, and improvement in 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 (for example, refer to Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even when palladium hydride is used as the reference electrode, there is a risk of corrosion depending on the sample solution, and further improvement in long-term stability is required.

[0006] The object of the present invention is to provide a solid semiconductor ion sensor that eliminates the deterioration of the reference electrode due to the reaction between the sample solution and the electrode and the replacement of the internal solution of the reference electrode, and exhibits excellent stability even during long-term use.

Means for Solving the Problems

[0007] (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 a specific ion in a sample solution, including an ion-sensitive film sensitive to the specific ion, 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 capable of conducting with the sample solution, the film being a gate potential detection film capable of detecting a gate potential, wherein the gate potential detection film includes a sheet member made of a carbon material. (2) In the solid semiconductor ion sensor according to another embodiment, preferably, both side surfaces in the thickness direction of the sheet member of the gate potential detection film may be coated with resin. (3) In the solid semiconductor ion sensor according to another embodiment, preferably, the carbon material may be carbon fiber. (4) The solid semiconductor ion sensor according to another embodiment preferably further includes a wire made of a conductive material connected to the ion-sensitive film and the insulating film and capable of conducting charges approaching the ion-sensitive film to the insulating film. (5) In the solid semiconductor ion sensor according to another embodiment, preferably, the specific ion may be a hydrogen ion.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a solid semiconductor ion sensor that eliminates the deterioration of the reference electrode due to the reaction between the sample solution and the electrode and the replacement of the internal solution of the reference electrode, and exhibits excellent stability even during long-term use.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below do not limit the invention according to the claims, and not all of the elements and combinations thereof described in the embodiments are essential for the solution means of the present invention.

[0011] FIG. 1 shows a schematic plan view of a solid-state semiconductor ion sensor according to an embodiment of the present invention. FIG. 2 shows a plan view of an ion concentration measurement unit of the solid-state semiconductor ion sensor according to an embodiment of the present invention. FIG. 3 shows a side view of the ion concentration measurement unit of the solid-state semiconductor ion sensor according to an embodiment of the present invention and an enlarged view of a part A thereof, respectively.

[0012] The 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 the sample solution. Further, 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 measurement unit 10, a power supply unit 30, a circuit board 34, and a display unit 36. The power supply unit 30 preferably includes DC power supplies 31 and 32 (see FIG. 4) 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 a field effect transistor 13 described later by the DC-DC converter and supplies the transformed DC voltage to the various devices. The circuit board 34 is preferably a board constituting an arithmetic processing unit such as a microcomputer. The display unit 36 is a device that displays various information such as ion concentration, for example, an LCD (Liquid Crystal Display).

[0013] The ion concentration measurement unit 10 includes an ion-sensitive film 12 that is sensitive to specific ions, a field effect transistor (hereinafter referred to as FET) 13 having a gate region 13G (see FIG. 4), and a surface of the gate region 13G is covered with an insulating film 15 (see FIG. 4) that can conduct charges approaching the ion-sensitive film 12, and a gate potential detection film 20 that is a film that can be in conduction with the sample solution and can detect the gate potential. Further, the ion concentration measurement unit 10 preferably further includes a wire 16 made of a conductive material that is connected to the ion-sensitive film 12 and the insulating film 15 and can conduct charges approaching the ion-sensitive film 12 to the insulating film 15.

[0014] (1) Ion-sensitive film In this embodiment, the ion-sensitive film 12 is a film that is sensitive to hydrogen ions (H + ) in the sample solution. As the ion-sensitive film 12, for example, a film that collects hydrogen ions such as tantalum oxide (Ta2O5), silicon oxide (SiO2), silicon nitride (Si3N4), and alumina (Al2O3) can be used. Among these, tantalum oxide is particularly suitable. The ion-sensitive film 12 is preferably formed by forming 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 silver-silver chloride paste, and then the non-sensitive part is molded with an epoxy resin. The film thickness of tantalum oxide in the ion-sensitive film 12 is preferably 20 to 110 nm, more preferably 25 to 45 nm. Note that the configuration of the ion-sensitive film 12 is not particularly limited as long as it is a film that is sensitive to at least the specific ions to be measured for concentration in the sample solution.

[0015] (2) Field effect transistor (FET) In this embodiment, FET13 is an nMOS transistor in which two n-type regions are formed separately from each other on a p-type silicon substrate. The two n-type regions function as a source region 13S (source electrode) and a drain region 13D (drain electrode), respectively (see FIG. 4). The region sandwiched between the source region 13S and the drain region 13D is a channel region 13C that functions as a channel when FET13 is operated. FET13 includes an insulating film 15 that covers the surface of FET13 including a gate region 13G on the channel region 13C. As the insulating film 15, for example, Ta2O5, SiO2, Si3N4, Al2O3, a mixture of two or more of these, or the like can be used. Among these, SiO2 is particularly suitable. The insulating film 15 is a site where 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 a drain lead wire 17. The source region 13S is electrically connected to at least the circuit board 34 via a source lead wire 19. The gate region 13G is electrically connected to at least the circuit board 34 via a gate lead wire 18. The operation of FET13 will be described later in detail with reference to FIG. 4.

[0016] (3) Wire Wire 16 is a wire made of a conductive material that connects the ion-sensitive film 12 and the insulating film 15. Wire 16 is a member that conducts the charges approaching the ion-sensitive film 12 to the insulating film 15. There are no particular restrictions on Wire 16 as long as it is composed of a material having conductivity, and for example, it may be composed of metal, carbon fiber, glass fiber, conductive ink, conductive rubber, or the like. Examples of the metal include silver, gold, copper, aluminum, a gold-palladium alloy, nickel, or their plated products. Among these, metal is preferable as the material of Wire 16, and in particular, silver is preferable. The length of Wire 16 is preferably 20 mm to 100 mm, and more preferably 40 to 60 mm. By including Wire 16, the solid-state semiconductor ion sensor 1 has a configuration in which the ion-sensitive film 12 and the FET 13 are separated. Thereby, since it is not necessary to immerse the FET 13 in the sample solution, corrosion of the FET 13 by the sample solution can be suppressed. Further, 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 by the sample solution.

[0017] (4) Gate potential detection film The gate potential detection film 20 is a film that can be in conduction with the sample solution and has conductivity capable of detecting the gate potential. The gate potential detection film 20 includes a sheet member 22 made of a carbon material (see the enlarged view of part A in FIG. 3). As the carbon material, for example, graphite, carbon fiber, glassy carbon, carbon paste, conductive diamond, etc. can be used. Among these, carbon fiber is preferable from the viewpoints of stability, responsiveness, reproducibility, etc. The thickness of the sheet member 22 is preferably 0.1 to 1 mm, and more preferably 0.2 to 0.8 mm. The gate potential detection film 20 is preferably formed by coating both side surfaces in the thickness direction of the sheet member 22 with a resin 24. As the resin 24, for example, polylactic acid resin, polyamide resin, polyester resin, acrylic resin, polyvinyl alcohol-based resin, polyolefin resin, polyurethane resin, polyvinyl chloride resin, silicon-based resin, fluorine-based resin, and copolymers and modified products thereof can be used. Among these, polyimide, which is a printed circuit board material, is particularly preferable in terms of insulation. In this embodiment, the gate potential detection film 20 is electrically connected to at least the circuit board 34 via a lead wire, similar to the drain region 13D, the source region 13S, and the gate region 13G. Note that the gate potential detection film 20 may not include the resin 24.

[0018] Next, the operation of the solid semiconductor ion sensor 1 will be described.

[0019] FIG. 4 shows a schematic circuit diagram for explaining the operation of the solid semiconductor ion sensor according to the embodiment of the present invention. FIG. 5 shows a schematic configuration diagram for explaining the operation of the solid semiconductor ion sensor according to the embodiment of the present invention. FIG. 6 shows a detailed circuit diagram of the solid semiconductor ion sensor according to the embodiment of the present invention.

[0020] 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 Vd (hereinafter also referred to as the drain voltage) between the drain region 13D (drain electrode) and the source region 13S (source electrode) to cause a current Id (dashed arrow in FIG. 4) (hereinafter also referred to as the drain current) to flow. When the ion-sensitive film 12 of the solid-state semiconductor ion sensor 1 contacts 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, so that the interfacial potential due to the charge changes, and the size of the channel region 13C changes according to the magnitude of 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). Then, the solid-state semiconductor ion sensor 1 is configured with a feedback circuit that adjusts the gate potential Vgs so that the magnitude of the drain current Id becomes constant while keeping the drain voltage Vd constant. At this time, the gate potential Vgs is adjusted to a potential lower by only the 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 referred to as the 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 gate potential Vgs is adjusted by the DC power supply 32.

[0021] The solid-state semiconductor ion sensor 1 includes a control unit 50 having at least a current value acquisition unit 52, a gate potential adjustment unit 54, and a concentration acquisition unit 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 above-described circuit are, for example, configured as shown in FIG. 6.

[0022] The solid-state semiconductor ion sensor 1 configured as described above includes a gate potential detection film 20 instead of the reference electrode used in conventional glass electrode type ion sensors and ISFET sensors. Since the gate potential detection film 20 does not include an internal solution, replacement of the internal solution like a reference electrode is not required, and long-term measurement becomes possible. Further, since the gate potential detection film 20 is made of a carbon material, it has excellent corrosion resistance and can suppress the risk of reacting with the sample solution 80 and deteriorating. 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, it is not necessary to immerse the FET 13 in the sample solution 80 when measuring the ion concentration, so that the situation where the FET 13 (especially the silicon substrate) is corroded by the sample solution 80 can be suppressed. Further, the molding of the FET 13 that has been conventionally performed to suppress the corrosion of the FET 13 becomes unnecessary. Therefore, the solid-state semiconductor ion sensor 1 has excellent long-term stability and can easily measure the ion concentration of various sample solutions.

[0023] <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.

[0024] 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 a sample solution. However, by changing the type of the ion-sensitive film 12, it can also be applied to other sensors for measuring ion concentrations. For example, instead of hydrogen ions, the solid-state semiconductor ion sensor 1 can be applied to sensors for measuring ion concentrations such as chloride ions (Cl - ; also referred to as chlorine ions), bicarbonate ions (HCO3 - ), carbonate ions (CO3 2- ), sulfide ions (S 2- ), fluoride ions (F - ), ammonium ions (NH4 + ), lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + ), magnesium ions (Mg 2+ ), calcium ions (Ca 2+ ), etc. 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 replaced with a film composed of a combination of silver halide and silver sulfide, or a film composed of a combination of silver chloride and silver sulfide incorporated in an epoxy resin. However, for example, when the ions to be measured for concentration, such as chloride ions (Cl - ), bicarbonate ions (HCO3 - ), carbonate ions (CO3 2- ), sulfide ions (S 2- ), fluoride ions (F - ), etc., are anions having a negative charge, the solid-state semiconductor ion sensor 1 may employ, as the FET 13, a pMOS transistor in which two p-type regions are formed separately from each other on an n-type silicon substrate.

[0025] Further, the solid-state semiconductor ion sensor 1 may not include the wire 16. In this case, the solid-state semiconductor ion sensor 1 only needs to be configured such that the ion-sensitive film 12 is laminated on the insulating film 15 and the charges approaching the ion-sensitive film 12 can be conducted to the insulating film 15.

[0026] Further, although the solid-state semiconductor ion sensor 1 has been obtaining the hydrogen ion concentration based on the gate potential, it may be configured to obtain the hydrogen ion concentration based on, for example, the current value of the drain current Id measured by the ammeter 40.

Example

[0027] Next, examples of the present invention will be described while comparing with comparative examples. Note that the present invention is not limited to the following examples.

[0028] <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, a tantalum oxide film with a film thickness of 32 nm was formed using an ECR sputtering apparatus (product number: EIS-200ER) manufactured by Ellionix. Next, the surface of the silicon wafer where the tantalum oxide film was not formed and the tip portion of the FPC substrate were connected using a silver / silver chloride paste (SILVER SILVER CHLORIDE, Code No: C2131016D1) manufactured by GWENT GROUP. 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. Then, the ion-sensitive film (tantalum oxide film) portion was insulated by covering it with an epoxy resin (INPEI BLACK) manufactured by Sunhayato. As the epoxy resin, a mixture of the main agent and the curing agent in a ratio of 25:2 was used. And, an FET (product number: 2SK208-Y) manufactured by Toshiba Semiconductor Co., Ltd. was soldered onto the FPC substrate. A gate potential detection film was fabricated using carbon fiber (product number: 71135) <http: / / www.abchobby.com / JP / page / parts / mateline.html> manufactured by ABC HOBBY Co., Ltd. Two types of carbon fiber with a film thickness of 0.5 mm and a film thickness of 0.2 mm were used to fabricate the gate potential detection film, respectively. A solid-state semiconductor ion sensor was fabricated by electrically connecting an FET and a gate potential detection film to a circuit board via lead wires. Two types of solid-state semiconductor ion sensors were fabricated: one using carbon fiber with a thickness of 0.5 mm and the other using carbon fiber with a thickness of 0.2 mm. (2) Gate voltage measurement Using the fabricated solid-state semiconductor ion sensor, gate voltage measurement was performed with a buffer solution. The specific measurement method is as follows. First, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water (hereinafter simply referred to as ultrapure water) generated by a Merck Millipore Direct-Q system, and the moisture was wiped off. The ion-sensitive film and the gate potential detection film were immersed in a borate pH standard solution (hereinafter also referred to as pH 9.18 standard solution) manufactured by Fujifilm Wako Pure Chemical Corporation, and the gate voltage (gate potential) was measured for about 30 minutes. Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water, and the moisture was wiped off. The ion-sensitive film and the gate potential detection film were immersed in a neutral phosphate pH standard solution (hereinafter also referred to as pH 6.86 standard solution) manufactured by Fujifilm Wako Pure Chemical Corporation, and the gate voltage was measured for about 30 minutes. Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water, and the moisture was wiped off. The ion-sensitive film and the gate potential detection film were immersed in a sulfate pH standard solution (hereinafter also referred to as pH 1.68 standard solution) manufactured by Fujifilm Wako Pure Chemical Corporation, and the gate voltage was measured for about 30 minutes. Again, the gate voltage was measured in the same manner in the order of pH 9.18 standard solution, pH 6.86 standard solution, and pH 1.68 standard solution, and the measurement was completed. Note that the gate voltage was measured for the two types of solid-state semiconductor ion sensors, one using carbon fiber with a thickness of 0.5 mm and the other using carbon fiber with a thickness of 0.2 mm, by the above method.

[0029] <Comparative Example> (Comparative Example 1) (1) Fabrication of Solid-State Semiconductor Ion Sensor A solid-state semiconductor ion sensor was fabricated in the same manner as in Example 1, except that a conductive glass electrode (product number of AS ONE Corporation: NPV-CFT2-7A) <https: / / axel.as-1.co.jp / asone / g / NCTB150019 / > was used instead of the gate potential detection film of Example 1. (2) Gate Voltage Measurement Using the fabricated solid-state semiconductor ion sensor, the gate voltage was measured with reference seawater. The specific measurement method is as follows. In this measurement, three types of certified reference seawater (CRM) with predetermined total carbonate content and alkalinity were used: Certified Reference Seawater 164 (pH 7.542), Certified Reference Seawater 171 (pH 7.849), and Certified Reference Seawater Kanso (pH 7.955). These certified reference seawaters were sampled and certified at the Scripps Institution of Oceanography, University of California, San Diego, USA, and are distributed as seawater standard samples. First, 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 the ion-sensitive membrane and the gate potential detection membrane were immersed in Certified Reference Seawater 164, 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 to wipe off moisture, and the ion-sensitive membrane and the gate potential detection membrane were immersed in Certified 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 to wipe off moisture, and the ion-sensitive membrane and the gate potential detection membrane were immersed in Certified Reference Seawater Kanso, and the gate voltage was measured for about 20 minutes. Again, the gate voltage was measured in the same manner for Certified Reference Seawater 164, Certified Reference Seawater 171, and Certified Reference Seawater Kanso in this order, and the measurement was completed. (Comparative Example 2) (1) Fabrication of Solid-State Semiconductor Ion Sensor A solid-state semiconductor ion sensor was fabricated in the same manner as in Example 1, except that a lanthanum fluoride electrode (product number: PGEC-0000C01110) manufactured by PRECISION MICRO-OPTICS Co., Ltd. <https: / / www.pmoptics.com / lanthanum_fluoride.html> was used instead of the gate potential detection film of Example 1. (2) Gate voltage measurement Using the fabricated solid-state semiconductor ion sensor, the gate voltage was measured with reference seawater in the same manner as in Comparative Example 1. (Comparative Example 3) (1) Fabrication of solid-state semiconductor ion sensor A solid-state semiconductor ion sensor was fabricated in the same manner as in Example 1, except that a tantalum oxide electrode was used instead of the gate potential detection film of Example 1. (2) Gate voltage measurement Using the fabricated solid-state semiconductor ion sensor, the gate voltage was measured with a buffer solution. The specific measurement method is as follows. First, the surface of the ion-sensitive film and the surface of the gate potential detection film were washed with ultrapure water and the moisture was wiped off. The ion-sensitive film and the gate potential detection film 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 film and the surface of the gate potential detection film were washed with ultrapure water and the moisture was wiped off. The ion-sensitive film and the gate potential detection film were immersed in a pH 6.86 standard solution, and the gate voltage was measured for about 30 minutes. Next, the surface of the ion-sensitive film and the surface of the gate potential detection film were washed with ultrapure water and the moisture was wiped off. The ion-sensitive film and the gate potential detection film were immersed in a phthalate pH standard solution (hereinafter also referred to as pH 4.01 standard solution) manufactured by Fujifilm Wako Pure Chemical Corporation, and the gate voltage was measured for about 30 minutes. Again, the gate voltage was measured in the same manner in the order of the pH 9.18 standard solution, the pH 6.86 standard solution, and the pH 4.01 standard solution, and the measurement was completed. (Comparative Example 4) (1) Fabrication of solid-state semiconductor ion sensor A solid-state semiconductor ion sensor was fabricated in the same manner as in Example 1, except that a gold electrode (product number: EE046) manufactured by CYPRESS SYSTEMS, Inc. was used instead of the gate potential detection film of Example 1. (2) Gate voltage measurement Using the fabricated solid-state semiconductor ion sensor, the gate voltage was measured with a buffer solution in the same manner as in Comparative Example 3. (Comparative Example 5) (1) Fabrication of solid-state semiconductor ion sensor A solid-state semiconductor ion sensor was fabricated in the same manner as in Example 1, except that a chloride ion electrode (product number: CL-200B) <https: / / www.toadkk.co.jp / product / spec / sci / electrode / mm_ion_electrode.html> manufactured by Toa DKK Corporation was used instead of the gate potential detection film of Example 1. (2) Gate voltage measurement The gate voltage was measured with a buffer solution using the fabricated solid-state semiconductor ion sensor. The specific measurement method is as follows. First, the gate voltage was measured with a buffer solution in the same manner as in Example 1. Next, the ion-sensitive membrane and the gate potential detection film were immersed in a pH 1.68 standard solution, and the gate voltage was measured for about two days. Then, the gate voltage was measured with a buffer solution in the same manner as in Example 1 (hereinafter also referred to as the measurement after the pH 1.68 test). Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water to wipe off moisture, and the ion-sensitive film and the gate potential detection film were immersed in natural seawater. After measuring the gate voltage for about two days, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water to wipe off moisture, and the ion-sensitive film and the gate potential detection film were immersed in a pH 9.18 standard solution, and the gate voltage was measured for about 30 minutes. Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water to wipe off moisture, and the ion-sensitive film and the gate potential detection film were immersed in a pH 6.86 standard solution, and the gate voltage was measured for about 30 minutes. Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water to wipe off moisture, and the ion-sensitive film and the gate potential detection film were immersed in a pH 4.01 standard solution, and the gate voltage was measured for about 30 minutes. Next, the surfaces of the ion-sensitive film and the gate potential detection film were washed with ultrapure water to wipe off moisture, and the ion-sensitive film and the gate potential detection film were immersed in a pH 1.68 standard solution, and the gate voltage was measured for about 30 minutes, and the test was completed (hereinafter also referred to as the measurement after seawater test).

[0030] <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 qualified (indicated as "○" in the table), and if the gate voltage corresponding to the pH value of the reference seawater or buffer solution is not output, it is evaluated as unqualified (indicated as "×" in the table). (2) Repeatability In the gate voltage measurement, if the same gate voltage value is output each time during continuous repeated measurements, it is evaluated as qualified (indicated as "○" in the table), and if different gate voltage values are output each time during continuous repeated measurements, it is evaluated as unqualified (indicated as "×" in the table). (3) Comprehensive evaluation When all of the evaluations of each characteristic value were evaluated as qualified, it was evaluated as qualified (indicated as "○" in the table). Also, when at least one of the evaluations of each characteristic value was evaluated as unqualified, it was evaluated as unqualified (indicated as "×" in the table).

[0031] <Results> Table 1 shows the manufacturing conditions and evaluation results of the examples and each comparative example. Further, FIG. 7 shows a graph of the measurement results of the example. FIG. 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.

[0032]

Table 1

[0033] Example 1 was independent of the film thickness of the carbon fiber, and had good stability and repeatability. Comparative Examples 1 to 3 did not output the gate voltage corresponding to the pH value of the reference seawater or buffer solution. Comparative Example 4 had good stability, but particularly the gate voltage value when immersed in the pH 4.01 standard solution decreased every time it was measured, and the repeatability was not good. Comparative Example 5 had good repeatability, but the stability was not good. Therefore, for Comparative Examples 1 to 5, at least one of the stability and repeatability was unqualified. On the other hand, for Example 1, all characteristics passed.

[0034] From the above results, the effect of using a gate potential detection film made of carbon fiber as the gate potential detection part of the solid semiconductor ion sensor was confirmed.

Industrial Applicability

[0035] The solid semiconductor ion sensor according to the present invention can be used for detecting substances having an electric polarity such as ions. In particular, the solid semiconductor ion sensor according to the present invention is suitable for pH measurement of a sample solution, detection of an antibody, detection of a specific gas, and the like.

Explanation of Symbols

[0036] 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

Claim 1 A solid-state semiconductor ion sensor capable of measuring the ion concentration of specific ions in a sample solution, an ion-sensitive film 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 charges approaching the ion-sensitive film, a film that can be electrically connected to the sample solution and is a gate potential detection film capable of detecting a gate potential, comprising: The solid-state semiconductor ion sensor, wherein the gate potential detection film includes a sheet member made of a carbon material. Claim 2 The solid-state semiconductor ion sensor according to claim 1, wherein the gate potential detection film has both side surfaces in the thickness direction of the sheet member covered with resin. Claim 3 The solid-state semiconductor ion sensor according to claim 1 or 2, wherein the carbon material is carbon fiber. Claim 4 The solid-state semiconductor ion sensor according to any one of claims 1 to 3, further comprising a wire made of a conductive material connected to the ion-sensitive film and the insulating film and capable of conducting charges approaching the ion-sensitive film to the insulating film. Claim 5 The solid-state semiconductor ion sensor according to any one of claims 1 to 4, wherein the specific ion is a hydrogen ion.

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