Device, and concentration measuring apparatus including same and concentration measuring method using same

Abstract

[Problem] To provide a device usable for a concentration measuring apparatus and a concentration measuring method that make it possible to detect a threshold voltage Vth with high sensitivity and quickly measure the concentration of a substance of interest in a sample liquid even if the amount of the substance of interest in the sample liquid is extremely small. [Solution] A device comprising an insulating substrate, at least one insulating composite layer, and a liquid storage part capable of holding a sample liquid, wherein the insulating composite layer has a pair of electrodes and a semiconductor layer in contact with the pair of electrodes, and the liquid storage part has a reference electrode that makes contact with the sample liquid. The semiconductor layer is composed of an oxide containing an indium (In) element, a zinc (Zn) element, and an additive element (X), wherein the additive element (X) is at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb). A sensitive membrane selective for the substance of interest in the sample liquid is provided between the insulating composite layer and the liquid storage part.

Description

Device, concentration measuring apparatus including the same, and concentration measuring method using the same

[0001] The present invention is based on a threshold voltage V , which is the voltage value of the reference electrode at which current flows between a pair of electrodes depending on the concentration of the analyte in the sample solution. th More specifically, for devices where the threshold voltage V th The present invention relates to a concentration measurement device and a concentration measurement method for measuring the concentration of an analyte in a sample liquid based on a change in concentration.

[0002] Society 5.0, the coming super-smart society, aims to achieve both economic development and the resolution of social issues, and the IoT that will support this will require sensors to collect data.

[0003] Electrochemical sensors using semiconductors have been known as a method for detecting the presence or absence and concentration of a target substance in a sample liquid. For example, Patent Documents 1 and 2 disclose sensors with a field effect transistor (FET) structure.

[0004] 8, in a sensor 100 having such an FET structure, a gate electrode 102 is formed on a substrate 101, and an insulating film 103 is formed so as to cover this gate electrode 102. Furthermore, a semiconductor layer 104 is formed on the insulating film 103, and a drain electrode 105 and a source electrode 106 are formed so as to be in contact with the semiconductor layer 104.

[0005] 8, the sensitive film 107 may be provided alone to cover the gate electrode 102, or the insulating film 103 may be used as the sensitive film. The sensitive film 107 can selectively detect the target substance in the sample liquid. The threshold voltage V of the gate voltage is set according to the amount of the target substance adsorbed on the sensitive film 107. th Since the threshold voltage V of the gate voltage changes when the sample liquid is in contact with the sensitive film 107, th By measuring the concentration of the target substance in the sample liquid, it is possible to measure the concentration of the target substance in the sample liquid.

[0006] Such sensors using semiconductors are highly sensitive and compact, making them capable of detecting minute amounts and enabling them to be used as portable detection devices. Furthermore, because they use semiconductors, the detection results are output as electrical signals, making them highly compatible with communication devices and allowing them to be used for remote measurements.

[0007] JP 2011-043420 A JP 2012-122749 A

[0008] In Patent Documents 1 and 2, an oxide semiconductor containing gallium (Ga), aluminum (Al), iron (Fe), etc. in an oxide containing indium (In) and zinc (Zn), particularly an oxide semiconductor containing In, Ga, and Zn (hereinafter referred to as "InGaZnO"), is used as the semiconductor layer 104. Conventionally, crystalline silicon (Si) has often been used as the semiconductor layer 104.

[0009] However, when crystalline Si is used, it is not transparent to visible light and cannot be bent, which limits its applications. th When the leakage current from the drain electrode to the source electrode is less than 1.0 × 10 -12 A / μm~1.0×10 -7 Since it is relatively large at A / μm, it has the drawback that it is affected as noise during measurement and that it is difficult to detect trace amounts.

[0010] On the other hand, InGaZnO is transparent to visible light and flexible, so its applications are not limited. -16 Since it is smaller than crystalline Si, at A / μm to 1.0×10 −11 A / μm, it has little effect as noise during measurement.

[0011] However, InGaZnO has an electron mobility of approximately 10 cm 2 / Vs, the drain-source voltage V DS If the threshold voltage V th It is difficult to accurately detect changes in

[0012] In view of the current situation, the present invention aims to provide a method for detecting a detection target with high sensitivity, even if the amount of the target substance in the sample liquid is very small. th The present invention aims to provide a device that can be used in a concentration measurement apparatus and a concentration measurement method that can detect a target substance and quickly measure the concentration of the target substance in a sample liquid.

[0013] The present invention has been invented to solve the problems in the prior art as described above, and the device of the present invention, a concentration measuring apparatus equipped with the same, and a concentration measuring method using the same include those configured as follows.

[0014] [1] A device having an insulating substrate, at least one insulating composite layer, and a liquid storage section capable of holding a sample liquid, wherein the insulating composite layer has a pair of electrodes and a semiconductor layer in contact with the pair of electrodes, the liquid storage section has a reference electrode in contact with the sample liquid, the semiconductor layer is composed of an oxide containing indium (In), zinc (Zn), and an additive element (X), and the additive element (X) contains at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb), and the device has a sensitive membrane between the insulating composite layer and the liquid storage section that is selective for the target substance to be detected in the sample liquid.

[0015] [2] The device according to [1], wherein the sensitive membrane is an ionophore.

[0016] [3] The device according to [1], wherein the sensitive membrane is a nucleic acid probe.

[0017] [4] The field effect mobility of the semiconductor layer is 20 cm 2 The device according to any one of [1] to [3], wherein the Vs is 0.1V or more.

[0018] [5] An OFF current between the pair of electrodes of the semiconductor layer is 1×10 -12 The device according to any one of [1] to [4], wherein the device is A or less.

[0019] [6] A device according to any one of [1] to [5], and a control device, wherein the control device comprises: a voltage application means for varying a voltage applied between the electrode into which a current flows out of the pair of electrodes and the reference electrode; a current measurement means for measuring a current flowing between the pair of electrodes; and a threshold voltage V, which is a voltage value of the reference electrode when it is determined whether or not a current flows between the pair of electrodes, based on the voltage value applied by the voltage application means and the current value measured by the current measurement means. th a threshold voltage detection means for detecting a threshold voltage V th and a concentration calculation means for calculating the concentration of the target substance in the sample based on the above.

[0020] [7] A concentration measurement method for detecting the concentration of an analyte in a sample liquid using the device according to any one of [1] to [5], wherein a threshold voltage V is a voltage value of the reference electrode when a current flows between the pair of electrodes. th and detects the threshold voltage V th and measuring the concentration of an analyte in the sample liquid based on the above formula.

[0021] According to the present invention, by employing an oxide containing indium (In), zinc (Zn) and an additive element (X) as the semiconductor layer, where the additive element (X) is at least one element selected from tantalum (Ta), strontium (Sr) and niobium (Nb), it is possible to reduce the OFF current and increase the electron mobility compared to when a conventional oxide semiconductor is used. Therefore, even if the amount of the target substance to be detected in the sample solution is small, the threshold voltage V th The device may be capable of detecting

[0022] Furthermore, by using such a device, it is possible to provide a concentration measurement apparatus and a concentration measurement method that can quickly measure the concentration of the target substance in a sample liquid, even if the target substance is present in a trace amount in the sample liquid.

[0023] FIG. 1 is a schematic diagram illustrating the configuration of a concentration measurement device according to this embodiment. FIG. 2 is a schematic diagram illustrating the configuration of a device used in the concentration measurement device of FIG. 1. FIG. 3 is a graph illustrating the relationship between the concentration of the analyte (LiCl) and the threshold voltage Vth when the concentration of the analyte in the sample liquid L (aqueous LiCl solution) is measured using the concentration measurement device of FIG. 1. FIG. 4 is a graph illustrating the relationship between the concentration of the analyte (LiCl) and the threshold voltage Vth when the concentration of the analyte in the sample liquid L (aqueous LiCl solution) is measured using the concentration measurement device of FIG. 1. FIG. 5 is a graph illustrating the relationship between the concentration of the analyte in the sample liquid L and the threshold voltage Vth when crystalline Si is used as the semiconductor layer of the concentration measurement device. FIG. 6 is a graph illustrating the relationship between the concentration of the analyte in another sample liquid L (aqueous NH4Cl solution) and the threshold voltage Vth when the concentration measurement device of FIG. 1 is used to measure the concentration of the analyte. Fig. 7 is a graph showing the relationship between the concentration of the analyte (NH4Cl) and the threshold voltage Vth when the concentration of the analyte in another sample liquid L (aqueous NH4Cl solution) was measured using the concentration measuring device of Fig. 1. Fig. 8 is a schematic diagram for explaining the configuration of a conventional sensor with a FET structure.

[0024]

[0023] The present invention will be described in more detail below with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram illustrating the configuration of a concentration measuring apparatus according to the present embodiment; and Fig. 2 is a schematic diagram illustrating the configuration of a device used in the concentration measuring apparatus of Fig. 1.

[0025] As shown in FIG. 1, the concentration measuring device 50 of this embodiment includes a device 10 having an insulating substrate 12, at least one insulating composite layer 14, and a liquid storage section 16 capable of holding a sample liquid, and a control device 60.

[0026] The device 10 configured as shown in FIG. 2 may also be a semiconductor element such as a field effect transistor (FET) or a metal oxide semiconductor field effect transistor (MOSFET).

[0027] The insulating substrate 12 is a substrate made of an insulating material such as glass or ceramics.

[0028] The insulating composite layer 14 has a pair of electrodes (a first electrode 141 and a second electrode 142 ) and a semiconductor layer 144 in contact with the pair of electrodes 141 and 142 .

[0029] The reservoir 16 is not particularly limited as long as it has a configuration capable of holding the specimen liquid L, but in this embodiment, it is configured by a partition 16a provided to surround the sensitive membrane 18 in order to hold the specimen liquid L so that the specimen liquid L comes into contact with the sensitive membrane 18 described below. A reference electrode 161 is provided in the reservoir 16 so as to come into contact with the specimen liquid L.

[0030] A sensitive membrane 18 is provided between the insulating composite layer 14 and the liquid storage section 16. The sensitive membrane 18 has selectivity for the target substance to be detected in the sample liquid L. Specifically, the sensitive membrane 18 has the property of selectively allowing ions of the target substance to pass through and selectively capturing components of the target substance (e.g., nucleic acid). For example, an ionophore such as a lithium ionophore, a potassium ionophore, a sodium ionophore, a calcium ionophore, an ammonium ionophore, an ionophore for chloride ions, or a magnesium ionophore can be used as the sensitive membrane 18, or a nucleic acid probe can be used.

[0031] The method for producing such a sensitive film 18 is not particularly limited, but for example, when an ionophore is used, the sensitive film 18 can be produced by the following steps. First, polyvinyl chloride is weighed into a beaker. Here, it is preferable to use polyvinyl chloride with a degree of polymerization of approximately 1050 from the viewpoints of easy handling and smooth application to the insulating composite layer 14.

[0032] Next, tetrahydrofuran is added as a solvent to the beaker, and the mixture is stirred with a stirrer until the polyvinyl chloride is dissolved.

[0033] Once the polyvinyl chloride is dissolved, the plasticizer, ionophore, and anion scavenger are added, followed by further stirring with a stirrer.

[0034] Examples of the plasticizer that can be used include 2-nitrophenyl octyl ether (NPOE) and bis(2-ethylhexyl) sebacate. Examples of the anion scavenger that can be used include potassium tetrakis(4-chlorophenyl)borate.

[0035] The ionophore can be appropriately selected depending on the ion to be detected. For example, lithium ion (Li + ), dibenzyl-14-crown-4, TTD-14-crown-4, potassium ion (K + ), bis(benzo-15-crown-5), sodium ion (Na + ), bis(12-crown-4), calcium ions (Ca 2+ ) to detect HDOPP-Ca, ammonium ion (NH4 + ), nonactin, chloride ions (Cl - ), Bisthiourea-1, magnesium ions (Mg 2+ When it is desired to detect C14-K22B5, K22B1B5, or K22B9, C14-K22B5, K22B1B5, or K22B9 can be used.

[0036] The solution thus prepared is then spread on a glass petri dish and air-dried to form the sensitive film 18. From the viewpoint of increasing the response speed (establishment of ion diffusion equilibrium), it is effective to make the sensitive film 18 thinner, and in this case, it is preferable to form the sensitive film 18 by spin coating.

[0037] The thus prepared sensitive film 18 is cut to an appropriate size and attached to the insulating composite layer 14 without trapping air therein, and the liquid storage section 16 is then bonded onto the attached sensitive film 18 using, for example, epoxy resin, thereby completing the device 10.

[0038] The insulating composite layer 14 includes an insulating film 146 at least at a location in contact with the sensitive film 18. The insulating film 146 also serves as a protective layer to protect the semiconductor layer 144 from the sample liquid L. By providing the insulating film 146, corrosion of the semiconductor layer 144 can be prevented, and the durability and reliability of the semiconductor layer 144 can be improved. Any known insulating material can be used for the insulating film 146, and corrosion-resistant materials are preferred. Examples of insulating materials include Ta2O5, Si3N4, and SiO2, and the thickness is preferably 0.01 μm to 0.5 μm, and more preferably 0.03 μm to 0.2 μm.

[0039] The semiconductor layer 144 has a field effect mobility of 20 cm 2 / Vs or more, and particularly 60 cm 2 It is more preferable that the voltage is equal to or higher than / Vs.

[0040] In the device 10 having the above-described configuration, the semiconductor layer 144 is configured such that the voltage applied to the reference electrode 161 is a threshold voltage V th When the OFF current, which is the current flowing from the first electrode 141 to the second electrode 142 or the current flowing from the second electrode 142 to the first electrode 141, is 1×10 -12 A or less is preferable, and 1 × 10 -14 A or less. Such a small OFF current allows the threshold voltage V th When detecting the threshold voltage V, it is possible to detect the threshold voltage V with higher accuracy even if the voltage applied between the first electrode 141 and the second electrode 142 is small. th can be detected.

[0041] Such a semiconductor layer 144 is composed of an oxide containing indium (In), zinc (Zn), and an additional element (X), and the additional element (X) is at least one element selected from tantalum (Ta), strontium (Sr), and niobium (Nb).

[0042] Specifically, it is preferable that the atomic ratio of In and X satisfy the following formula (1) (X in the formula is the sum of the content ratios of the additive elements. The same applies to formulas (2) and (3) below): 0.4≦(In+X) / (In+Zn+X)≦0.8 (1) It is preferable that the atomic ratio of Zn satisfy the following formula (2): 0.2≦Zn / (In+Zn+X)≦0.6 (2) It is preferable that the atomic ratio of X satisfy the following formula (3): 0.001≦X / (In+Zn+X)≦0.015 (3)

[0043] When the atomic ratio of In, Zn, and X satisfies the formulas (1) to (3), the semiconductor layer 144 exhibits the field effect mobility and OFF current described above.

[0044] In order for the semiconductor layer 144 to exhibit higher field-effect mobility and lower OFF current, it is more preferable that the atomic ratios of In, Zn, and X satisfy the following formulas (1-2), (2-2), and (3-2): 0.43≦(In+X) / (In+Zn+X)≦0.79 (1-2) 0.21≦Zn / (In+Zn+X)≦0.57 (2-2) 0.0015≦X / (In+Zn+X)≦0.013 (3-2)

[0045] It is more preferable that the atomic ratios of In, Zn and X satisfy the following formulas (1-3), (2-3) and (3-3): 0.48≦(In+X) / (In+Zn+X)≦0.78 (1-3), 0.22≦Zn / (In+Zn+X)≦0.52 (2-3), and 0.002<X / (In+Zn+X)≦0.012 (3-3).

[0046] It is more preferable that the atomic ratios of In, Zn and X satisfy the following formulas (1-4), (2-4) and (3-4): 0.53≦(In+X) / (In+Zn+X)≦0.75 (1-4) 0.25≦Zn / (In+Zn+X)≦0.47 (2-4) 0.0025≦X / (In+Zn+X)≦0.010 (3-4)

[0047] It is more preferable that the atomic ratios of In, Zn and X satisfy the formulas (1-5), (2-5) and (3-5): 0.58≦(In+X) / (In+Zn+X)≦0.70 (1-5), 0.30≦Zn / (In+Zn+X)≦0.42 (2-5), and 0.003≦X / (In+Zn+X)≦0.009 (3-5).

[0048] As described above, the additive element (X) is one or more elements selected from Ta, Sr, and Nb. These elements can be used alone or in combination of two or more elements. The additive element (X) may contain elements other than Ta, Sr, and Nb, but preferably contains only these elements.

[0049] Furthermore, the thinner the thickness of the semiconductor layer 144, the greater the change in the conductivity of the surface layer, and therefore the greater the change in the moving charge, as described below, and the improved measurement accuracy. The thickness of such a semiconductor layer 144 is preferably 0.5 μm or less, more preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. There is no particular lower limit for the thickness of the semiconductor layer 144, but it is generally 0.005 μm or more.

[0050] Furthermore, it is preferable that the surface 144a of the semiconductor layer 144 on the sensitive film 18 side is as smooth as possible. If the surface 144a of the semiconductor layer 144 is not smooth, for example, gaps may occur between the insulating film 146 or the insulating film 146 may be formed discontinuously, reducing the adhesion between the insulating film 146 and the sensitive film 18 and making it impossible to accurately detect potential changes from the sensitive film 18. This reduces measurement accuracy and makes operation unstable.

[0051] Specifically, the maximum height Sz of the surface 144a of the semiconductor layer 144 is preferably 0.05 μm or less, more preferably 0.01 μm or less, and most preferably 0.003 μm or less. There is no particular restriction on the lower limit of this maximum height Sz, but it is generally 0.0005 μm or more. Furthermore, the arithmetic mean height Sa of the surface 144a of the semiconductor layer 144 on the sensitive film 18 side is preferably 0.03 μm or less, more preferably 0.005 μm or less, and most preferably 0.002 μm or less. There is no particular restriction on the lower limit of this arithmetic mean height Sa, but it is generally 0.0002 μm or more.

[0052] Here, the maximum height Sz and the arithmetic mean height Sa are parameters of surface roughness defined in ISO 25178, and such parameters can be measured, for example, by a 3D surface roughness profiler (NexView, manufactured by Zygo Corporation). In this case, the measurement conditions are preferably as follows:

[0053] Measurements are made in accordance with ISO 25178 using a 50x objective lens, a 20x zoom lens, and a measurement range of 89 μm × 87 μm. A roughness curve of a range of 3 μm × 3 μm is extracted from the obtained three-dimensional surface shape, and the roughness curve is corrected using the analysis program "Mx" attached to the 3D surface roughness profile measuring instrument under the following correction conditions to calculate the maximum height Sz and arithmetic mean height Sa.

[0054] <Correction conditions> -Remove: Form Remove -Filter Type: Spline -Filter: Low Pass -Type: Gaussian Spline Auto

[0055] When the device 10 described above is formed as a FET structure, it can be formed using a method similar to that used for conventionally known FETs, MOSFETs, etc. For example, a conductive metal thin film is formed on the insulating substrate 12 as the first electrode 141 and the second electrode 142 using a sputtering apparatus, and then an oxide thin film having the above-described configuration is formed as the semiconductor layer 144 using a sputtering apparatus. A shadow mask can be used for patterning when forming the first electrode 141 and the second electrode 142 and the semiconductor layer 144.

[0056] The conductive metal used as the first electrode 141 and the second electrode 142 is not particularly limited, but may be, for example, molybdenum (Mo) or tungsten (W), or an alloy of these metals with cerium oxide (CeO), copper (Cu), silver (Ag), or the like.

[0057] Next, a ceramic thin film can be deposited thereon to form the insulating film 146. Specifically, for example, a plasma CVD apparatus such as Samco Corporation's PD-2202L can be used to deposit a SiOx thin film under the following conditions: film formation gas: SiH4 / N2O / N2 mixed gas, film formation pressure: 110 Pa, and substrate temperature: 250°C to 400°C, to form the insulating film 146.

[0058] In addition, the control device 60 of the concentration measuring device 50 of this embodiment is equipped with a variable voltage source 32 for applying a voltage between the first electrode 141 and the second electrode 142, a variable voltage source 34 (voltage application means) for applying a voltage between the first electrode 141 and the reference electrode 161, an ammeter 36 (current measurement means) for measuring the current value between the first electrode 141 and the second electrode 142, and a voltmeter 38 (voltage measurement means) for measuring the voltage value between the first electrode 141 and the reference electrode 161.

[0059] The control device 60 has a computer equipped with an arithmetic means, a memory means, an input / output means, etc., and is configured to control the applied voltage of the variable voltage source 32 and the variable voltage source 34, measure the current value using the ammeter 36, and measure the voltage value using the voltmeter 38 based on a program stored in the memory means.

[0060] The control device 60 further includes a threshold voltage detection means 62. The threshold voltage detection means 62 is configured to control the voltages applied by the variable voltage sources 32 and 34, and to receive the current and voltage values ​​measured by the ammeter 36 and voltmeter 38 as electrical signals. Such threshold voltage detection means 62 can be realized by a computer incorporated in the control device 60, or the like.

[0061] The threshold voltage detection means 62 detects a predetermined voltage V between the first electrode 141 and the second electrode 142 by the variable voltage source 32. ds In this state, the voltage V applied between the first electrode 141 and the reference electrode 161 by the variable voltage source 34 is g Then, the threshold voltage detection means 62 measures the current I flowing between the first electrode 141 and the second electrode 142 using the ammeter 36. d The change in the voltage V between the first electrode 141 and the reference electrode 161 is detected by the voltmeter 38. g By detecting the change in the threshold voltage V th Measure.

[0062] In the device 10 configured as described above, the threshold voltage V th It is known that the threshold voltage V changes depending on the amount of the object to be detected present on the surface of the sensitive film 18 or inside the sensitive film 18. th By measuring the concentration of the target substance contained in the sample liquid L, it is possible to detect the concentration of the target substance contained in the sample liquid L.

[0063] The threshold voltage V th The method for measuring the current I is not particularly limited. For example, the current I d The voltage V when g may be detected, or the current I d When the voltage V g Gradually decrease the current I d The voltage V when the current stops flowing g Alternatively, the voltage V g By changing the current I dis a predetermined value (for example, 1×10 -9 V when A) is reached ds The value of this is the threshold voltage V th However, from the viewpoint of more accurate measurement, it is possible to use a conventionally known method such as ds is kept constant, and the voltage V g is applied within a predetermined range, and the current I d Measure V in a predetermined range g √I for d The approximate line is calculated using the least squares method, and the √I of the approximate line is calculated. d V when = 0 g is the threshold voltage V th It is preferable to set the following.

[0064] FIG. 3 shows the relationship between the concentration of the target substance and the threshold voltage V when the concentration of the target substance in the sample liquid L is measured using the concentration measuring device 50 of this embodiment. th In this measurement (Example 1), the sample liquid L was an aqueous solution of lithium chloride (LiCl), the object to be detected was lithium chloride (LiCl), the sensitive film 18 was a lithium ionophore, and the voltage V ds to 5V, voltage V g The predetermined range for changing is −3V to 3V, √I d A linear approximation of the above was performed in the range of 2V to 3V.

[0065] As shown in FIG. 3, the higher the LiCl concentration, the lower the threshold voltage V th Therefore, for example, the concentration of the object to be detected and the threshold voltage V th By creating a calibration curve showing the relationship between the threshold voltage V th Based on this, the concentration of LiCl, which is the detection target, can be determined.

[0066] Alternatively, the concentration of the object to be detected and the threshold voltage V th By performing machine learning by associating the threshold voltage V measured using the concentration measuring device 50 with the threshold voltage V th It is also possible to determine the concentration of the target substance based on the above.

[0067] The control device 60 of this embodiment further includes a concentration calculation means 64, which calculates the threshold voltage V detected by the threshold voltage detection means 62. th The concentration calculation means 64 can be realized by a computer incorporated in the control device 60, as described above.

[0068] FIG. 4 shows the relationship between the concentration of the target substance and the threshold voltage V when the concentration of the target substance in the sample liquid L is measured using the concentration measuring device 50 of this embodiment. th In this measurement, an aqueous solution of lithium chloride (LiCl) was used as the sample liquid L, lithium chloride (LiCl) was used as the detection target, and lithium ionophore was used as the sensitive membrane 18. ds is set to 1V or 5V, and √I d The linear approximation was performed in the range of 2 V to 3 V or 1.5 V to 2.5 V. Specific combinations of conditions are shown in Table 1.

[0069]

[0070] As shown in FIG. g Even if the threshold voltage V th Even if the predetermined range used to calculate th There is a correlation between

[0071] As a comparative example (Comparative Example 1), a concentration measuring device having a configuration similar to that of the concentration measuring device 50 described above, in which a sensitive film 18 and a liquid storage section 16 are provided on an ISFET electrode (for pH measurement: Code No. 001314) manufactured by BAS Co., Ltd., was used to measure the LiCl concentration and the threshold voltage V th The graph showing the relationship between the temperature and the pressure is shown in FIG.

[0072] In this measurement, the sample liquid L is an aqueous solution of lithium chloride (LiCl), the object to be detected is lithium chloride (LiCl), the sensitive membrane 18 is a lithium ionophore, and the voltage V ds to 5V, voltage V g The predetermined range for changing is −3V to 3V, √Id A linear approximation of the voltage was performed in the range of 1.5V to 2.5V.

[0073] As shown in FIG. 5A, when crystalline Si is used as the semiconductor layer 144, the LiCl concentration and the threshold voltage V th There is no correlation between the threshold voltage V th It is difficult to measure the LiCl concentration from

[0074] As another comparative example (Comparative Example 2), the concentration measuring device used in Comparative Example 1 was used, and a voltage V ds LiCl concentration and threshold voltage V when th The graph showing the relationship between the voltage V ds Even if the LiCl concentration and threshold voltage V are changed, similar to the results shown in FIG. th There is no correlation between the threshold voltage V th It is difficult to measure the LiCl concentration from

[0075] 6 and 7 show the relationship between the concentration of the target substance and the threshold voltage V when the concentration of the target substance in another sample liquid L is measured using the concentration measuring device 50 of this embodiment. th In this measurement (Examples 6 and 7), the sample liquid L was an aqueous solution of ammonium chloride (NH4Cl), the object to be detected was ammonium chloride (NH4Cl), the sensitive film 18 was an ammonium ionophore, the voltage Vds was 5 V, the range of voltage Vg was changed from -3 V to 3 V, and √I d A linear approximation of the voltage Vcc was performed in the range of 2 V to 3 V (FIG. 6) or 1.3 V to 1.5 V (FIG. 7).

[0076] As shown in FIGS. 6 and 7, the higher the NH4Cl concentration, the lower the threshold voltage V th That is, the relationship between the NH4Cl concentration and the threshold voltage V th The relationship between the LiCl concentration and the threshold voltage V th Therefore, the threshold voltage V measured using the concentration measuring device 50 of this embodiment has a similar tendency to the relationship between th Based on this, the concentration of NH4Cl, which is the detection target, can be determined.

[0077] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications are possible within the scope of the object of the present invention.

[0078] 10 Device 12 Insulating substrate 14 Insulating composite layer 141 First electrode 142 Second electrode 144 Semiconductor layer 144a Surface 146 Insulating film 16 Liquid storage section 16a Partition section 161 Reference electrode 18 Sensitive film 32 Variable voltage source 34 Variable voltage source 36 Ammeter 38 Voltmeter 50 Concentration measuring device 60 Control device 62 Threshold voltage detecting means 64 Concentration calculating means 100 Sensor 101 Substrate 102 Gate electrode 103 Insulating film 104 Semiconductor layer 105 Drain electrode 106 Source electrode 107 Ion sensitive film

Claims

1. A device having an insulating substrate, at least one insulating composite layer, and a liquid storage section capable of holding a sample liquid, wherein the insulating composite layer has a pair of electrodes and a semiconductor layer in contact with the pair of electrodes, the liquid storage section has a reference electrode in contact with the sample liquid, the semiconductor layer is composed of an oxide containing indium (In), zinc (Zn) and an additive element (X), the additive element (X) containing at least one element selected from tantalum (Ta), strontium (Sr) and niobium (Nb), and a sensitive membrane selective for the target substance in the sample liquid is provided between the insulating composite layer and the liquid storage section.

2. The device of claim 1, wherein the sensitive membrane is an ionophore.

3. The device of claim 1, wherein the sensitive membrane is a nucleic acid probe.

4. The field effect mobility of the semiconductor layer is 20 cm 2 The device of claim 1 , wherein Vs is greater than or equal to Vs.

5. The OFF current between the pair of electrodes of the semiconductor layer is 1×10 -12 The device of claim 1 , wherein the .lambda.

6. A device according to any one of claims 1 to 5, comprising: a control device; and a voltage application means for varying a voltage applied between the reference electrode and the electrode into which a current flows out of the pair of electrodes; a current measurement means for measuring a current flowing between the pair of electrodes; and a threshold voltage V, which is a voltage value of the reference electrode at which a current flows between the pair of electrodes and is determined based on a voltage value applied by the voltage application means and a current value measured by the current measurement means. th a threshold voltage detection means for detecting a threshold voltage V th and a concentration calculation means for calculating the concentration of the target substance in the sample liquid based on the result.

7. A method for measuring a concentration of a target substance in a sample liquid using a device according to any one of claims 1 to 5, comprising: determining a threshold voltage V, which is a voltage value of the reference electrode when a current flows between the pair of electrodes and does not flow; th Detect the threshold voltage V th and measuring the concentration of an analyte in the sample liquid based on the above.

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