Ion sensor and method for manufacturing the same

Abstract

To provide an ion sensor that can effectively improve the sensitivity, and a method for manufacturing the ion sensor.SOLUTION: An ion sensor 1 includes: a substrate 100; and a plurality of detectors 5. Each detector 5 includes: an ID part 21; an ICG electrode 22; a TG electrode 32; an SG electrode 51; an electrode pad 52; and an ion-sensitive film 13. The SG electrode 51 is arranged between the ICG electrode 22 and the TG electrode 32 on a main surface 100a. The electrode pad 52 is electrically connected to the SG electrode 51 and is arranged on the opposite side of the substrate 100 across the SG electrode 51. The ion-sensitive film 13 is provided in a surface 52a of the electrode pad 52 and the potential is changed according to the change of the ionic concentration of an aqueous solution 3 in contact with the ion-sensitive film 13. The width of the ion-sensitive film 13 in a facing direction D2 in which the ICG electrode 22 and the TG electrode 32 face each other is larger than the separation width between the ICG electrode 22 and the TG electrode 32.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an ion sensor and a method for manufacturing an ion sensor. [Background technology]

[0002] Non-Patent Document 1 discloses an ion sensor sensitive to odors. This ion sensor employs an apertured pixel structure (hereinafter referred to as an "apertured structure"). Specifically, in each pixel, an aperture is provided between a first electrode (ICG electrode) and a second electrode (TG electrode) on a semiconductor substrate, and an ion-sensitive film (Si3N4) is disposed at the bottom of the aperture. A polyaniline sensitive film is formed on this ion-sensitive film as a medium containing a substance to be detected (e.g., an odor substance). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Niina, N., Iwata, T., Hashizume, K., Kuroki, S., and Sawada, K. (2017). Gas distribution imaging using a charge-transfer sensor array with a polyaniline sensitive film. The 64th Spring Meeting of the Japan Society of Applied Physics, 16p-416-6. Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned ion sensor, in order to obtain sufficient sensitivity, it is necessary to secure a sufficient contact area between the ion-sensitive film and the medium. On the other hand, in the aperture-type structure described in Non-Patent Document 1, a part of the medium is inserted into the aperture, so the contact area between the medium and the ion-sensitive film depends on the aperture size. In addition, there is a limit to increasing the aperture size due to requirements such as pixel size and pixel pitch. For this reason, in the above-mentioned aperture-type structure, it was sometimes difficult to secure a sufficient contact area.

[0005] An object of one aspect of the present disclosure is to provide an ion sensor capable of effectively improving sensitivity and a method for manufacturing the ion sensor. [Means for solving the problem]

[0006] An ion sensor according to one aspect of the present disclosure includes a substrate and a plurality of pixels provided on a first surface of the substrate, each pixel having a charge accumulation portion, a first electrode, a second electrode, a third electrode, a fourth electrode, and an ion-sensitive membrane, the charge accumulation portion is formed in a region along the first surface of the substrate and accumulates charges to be injected into a potential well formed in a portion of the substrate that overlaps with the third electrode when viewed in a thickness direction of the substrate, the first electrode is disposed on the first surface and is configured to control the amount of charge injection from the charge accumulation portion into the potential well, and the second electrode is disposed on the first surface. and configured to control the transfer of charge from the potential well to the outside, the third electrode is disposed on the first surface between the first electrode and the second electrode, the fourth electrode is electrically connected to the third electrode and disposed on the opposite side of the substrate with the third electrode in between, the ion-sensitive membrane is provided on the surface of the fourth electrode opposite the substrate side, and changes the electric potential in response to changes in the ion concentration of a medium in contact with the ion-sensitive membrane, and the width of the ion-sensitive membrane in the opposing direction in which the first electrode and the second electrode face each other is greater than the separation width between the first electrode and the second electrode.

[0007] In the ion sensor, a third electrode is disposed between the first electrode and the second electrode on the first surface of the substrate. The third electrode is electrically connected to a fourth electrode on which an ion-sensitive membrane is provided. This realizes the function of an ion sensor. Specifically, the change in the potential of the ion-sensitive membrane can be transmitted to the substrate via the fourth electrode and the third electrode. This makes it possible to change the depth of the potential well according to the change in the potential of the ion-sensitive membrane. As a result, it becomes possible to detect the ion concentration of a test object that is brought into contact with a medium that is in contact with the ion-sensitive membrane, based on the amount of charge (i.e., the amount according to the depth of the potential well) extracted to the outside by controlling the first electrode and the second electrode.

[0008] Here, if a configuration in which an opening is provided between the first electrode and the second electrode and an ion-sensitive membrane is provided at the bottom of the opening (a so-called opening type structure) is adopted, the width of the ion-sensitive membrane is limited by the size of the opening, and the width of the ion-sensitive membrane cannot be made larger than the separation width between the first electrode and the second electrode. On the other hand, the above ion sensor adopts a configuration in which the potential change of the ion-sensitive membrane is transmitted to the substrate via the third electrode and the fourth electrode, thereby realizing a configuration in which the width of the ion-sensitive membrane is made larger than the separation width between the first electrode and the second electrode. This makes it possible to ensure a sufficient contact area between the ion-sensitive membrane and the medium, and effectively improve the sensitivity of the ion sensor.

[0009] The surface of the fourth electrode opposite to the substrate may be flat, and the ion-sensitive membrane may be formed flat along the opposite surface. According to the above configuration, the medium placed on the ion-sensitive membrane and the ion-sensitive membrane can be sufficiently tightly attached to each other, compared to the case where the above-mentioned open-type structure is adopted. This makes it possible to more effectively improve the sensitivity of the ion sensor.

[0010] The first electrode and the third electrode may be spaced apart from each other, and a first distance between the first electrode and the third electrode may be set within a range in which no potential barrier is generated that inhibits the injection of charges from the charge accumulation section to the potential well. With the above configuration, sufficient charge transfer efficiency from the charge accumulation section to the potential well is ensured.

[0011] The second electrode and the third electrode may be spaced apart from each other, and a second distance between the second electrode and the third electrode may be set within a range that does not create a potential barrier that inhibits the transfer of charges from the potential well to the outside. With the above configuration, sufficient charge transfer efficiency from the potential well to the outside is ensured.

[0012] The width of the third electrode in the opposing direction may be 80% or more of the separation width between the first electrode and the second electrode. According to the above configuration, it is possible to suitably prevent the occurrence of the above-mentioned potential barrier.

[0013] When viewed in the thickness direction, a part of the first electrode may overlap with the third electrode. According to the above configuration, it is possible to reduce the variation in the amount of charge stored in the potential well.

[0014] A portion of the first electrode may be disposed on the opposite side of the substrate with the third electrode interposed therebetween. With the above configuration, it is possible to reduce the voltage value required to form a potential well in the region of the substrate overlapping with the third electrode, compared to the case where a portion of the first electrode is disposed between the substrate and the third electrode.

[0015] The width of the first portion of the first electrode that overlaps with the third electrode in the opposing direction may be smaller than the width of the second portion of the first electrode that does not overlap with the third electrode in the opposing direction. With the above configuration, it is possible to suppress unintended leakage of charges from the potential well to the charge accumulation section.

[0016] The width of the first portion may be 25% or less of the width of the second portion.With the above configuration, unintended leakage of charges from the potential well to the charge accumulation portion can be suitably suppressed.

[0017] When viewed in the thickness direction, a part of the second electrode may overlap with the third electrode. According to the above configuration, it is possible to improve the efficiency of charge transfer from the potential well to the outside.

[0018] A portion of the second electrode may be disposed on the opposite side of the substrate with the third electrode interposed therebetween. With the above configuration, it is possible to reduce the voltage value required to form a potential well in the region of the substrate overlapping with the third electrode, compared to a case in which a portion of the second electrode is disposed between the substrate and the third electrode.

[0019] The width of the third portion of the second electrode that overlaps with the third electrode in the opposing direction may be smaller than the width of the fourth portion of the second electrode that does not overlap with the third electrode in the opposing direction. With the above configuration, it is possible to suppress unintended leakage of charges from the potential well to the outside.

[0020] The width of the third portion may be 25% or less of the width of the fourth portion.With the above configuration, unintended leakage of charges from the potential well to the outside can be suitably suppressed.

[0021] A single pixel may include a plurality of ion-sensitive films that react to different ions, a plurality of fourth electrodes may be provided corresponding to each of the plurality of ion-sensitive films, and a plurality of third electrodes may be provided corresponding to each of the plurality of fourth electrodes. According to the above configuration, it is possible to increase the amount of information obtained from a single pixel. In other words, it is possible to detect the concentrations of a plurality of types of ions using a single pixel.

[0022] A method for manufacturing an ion sensor according to another aspect of the present disclosure is a method for manufacturing an ion sensor having a substrate and a first electrode, a second electrode, and a third electrode formed on the substrate, the method including the steps of: forming a first insulating film on the substrate; forming, on the first insulating film, the first electrode, a second electrode arranged so as to be spaced apart from the first electrode, and a third electrode arranged between the first electrode and the second electrode so as to be spaced apart from both the first electrode and the second electrode; forming a second insulating film on the substrate to cover the first electrode, the second electrode, and the third electrode; and forming an opening in the second insulating film so as to expose a portion of the third electrode. The method includes the steps of forming an opening, and forming metal wiring in the opening that is electrically connected to the third electrode, forming a fourth electrode along the surface of the second insulating film opposite to the substrate side, the fourth electrode being electrically connected to the metal wiring, and forming an ion-sensitive membrane on the surface of the fourth electrode opposite to the substrate side, the ion-sensitive membrane changing its potential in response to a change in the ion concentration of a medium with which it comes into contact, wherein in the step of forming the ion-sensitive membrane, the width of the ion-sensitive membrane in the opposing direction in which the first electrode and the second electrode face each other is formed to be larger than the separation width between the first electrode and the second electrode. According to the above-mentioned method of manufacturing an ion sensor, it is possible to obtain an ion sensor having the above-mentioned effects.

[0023] A manufacturing method of an ion sensor according to still another aspect of the present disclosure is a manufacturing method of an ion sensor having a substrate and a first electrode, a second electrode, and a third electrode formed on the substrate, the method including the steps of: forming a first insulating film on the substrate; forming a third electrode on the first insulating film; forming a second insulating film covering a surface of the third electrode; forming the first electrode such that a portion of the first electrode overlaps with the third electrode via the second insulating film when viewed from the thickness direction of the substrate, and forming the second electrode such that a portion of the second electrode overlaps with the third electrode via the second insulating film when viewed from the thickness direction of the substrate; forming an insulating film, forming an opening in the third insulating film so as to expose a part of the third electrode and forming metal wiring in the opening electrically connected to the third electrode, forming a fourth electrode along the surface of the third insulating film opposite to the substrate side and electrically connected to the metal wiring, and forming an ion-sensitive film on the surface of the fourth electrode opposite to the substrate side, the ion-sensitive film changing its electric potential in response to a change in the ion concentration of a medium with which it comes into contact, wherein in the step of forming the ion-sensitive film, the ion-sensitive film is formed so that the width of the ion-sensitive film in the opposing direction in which the first electrode and the second electrode oppose each other is larger than the separation width between the first electrode and the second electrode. According to the above-mentioned method for manufacturing an ion sensor, it is possible to obtain an ion sensor having the above-mentioned effects. Effect of the Invention

[0024] According to one aspect of the present disclosure, it is possible to provide an ion sensor capable of effectively improving sensitivity and a method for manufacturing the ion sensor. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic plan view of an ion sensor according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a cross-sectional configuration of a detection unit (pixel). [Diagram 3] 11A and 11B are diagrams illustrating an example of the operation of a detection unit using an ID drive method. [Figure 4] FIG. 13 is a diagram showing an example of the operation of a detection unit using an ICG driving method. [Diagram 5] FIG. 2 is a diagram showing an example of a potential barrier between an ICG electrode and an SG electrode and between a TG electrode and an SG electrode. [Figure 6] FIG. 2 is a diagram showing the layout dimensions of the ICG electrodes, the TG electrodes, and the SG electrodes. [Figure 7] 3A to 3C are diagrams illustrating a manufacturing process of the ion sensor according to the first embodiment. [Figure 8] 10 is a diagram illustrating a cross-sectional configuration of a detection unit of an ion sensor according to a second embodiment. FIG. [Figure 9] 13A to 13C are diagrams illustrating an example of the operation of a detection unit of the ion sensor according to the second embodiment. [Figure 10] 6A to 6C are diagrams illustrating a manufacturing process of the ion sensor according to the second embodiment. [Figure 11] FIG. 13 is a diagram illustrating a cross-sectional configuration of a detection section of an ion sensor according to a third embodiment. [Figure 12] FIG. 13 is a diagram showing a first modified example of the ion sensor. [Figure 13] FIG. 13 is a diagram showing a second modified example of the ion sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0027] [First embodiment] FIG. 1 is a schematic plan view of an ion sensor 1 of a first embodiment. The right part of FIG. 1 typically shows an example of a layout common to each detection unit 5. FIG. 2 typically shows a cross-sectional configuration of the detection unit 5 taken along line II-II in FIG. 1. As shown in FIG. 2, the ion sensor 1 is a sensor device configured to be capable of detecting the ion concentration of a test object (not shown) that is brought into contact with an aqueous solution 3 (medium) by immersing the aqueous solution 3 on the surface of the ion sensor 1. The test object may be in a solid, liquid, or gaseous state.

[0028] The ion sensor 1 is a sensor in which a plurality of detection units 5 arranged two-dimensionally are formed on a substrate 100. The ion sensor 1 is a so-called charge transfer type CMOS image sensor. The plurality of detection units 5 are arranged two-dimensionally in M ​​rows and N columns (e.g., 256 rows and 256 columns) in a pixel formation region R (in this embodiment, a rectangular region provided in the center of the chip) provided on the chip of the ion sensor 1, thereby constituting a pixel array. M and N are integers of 2 or more. One detection unit 5 corresponds to one detection unit (pixel). The size (pixel size) of one detection unit 5 is, for example, 15 μm×15 μm.

[0029] The aqueous solution 3 is dropped onto the surfaces of the multiple detection units 5 included in the pixel formation region R during measurement. As a result, as shown in FIG. 2, the surface of each detection unit 5 is covered with the aqueous solution 3 during measurement. The aqueous solution 3 is, for example, an SSC solution, a pH standard solution, a cell culture solution, or the like. Furthermore, during measurement, a reference voltage Vref is applied to the aqueous solution 3 by an electrode (not shown). The electrode used to apply the reference voltage Vref may be, for example, an external electrode such as a glass electrode, or an electrode built into the ion sensor 1 (for example, an electrode embedded in the passivation layer 120 and electrically connected to the aqueous solution 3 through an opening provided in the passivation layer 120). The electrode may be made of a material that can contact the aqueous solution 3 and apply a voltage thereto.

[0030] As shown in FIG. 1 and FIG. 2, each detection unit 5 is formed on one main surface 100a (first surface) side of the substrate 100. The substrate 100 is a semiconductor substrate of a first conductivity type (for example, p-type) formed of, for example, silicon. In each detection unit 5, an input diode section 21 (hereinafter, "ID section 21") (charge storage section), a floating diffusion section 31 (hereinafter, "FD section 31"), and a reset drain section 41 (hereinafter, "RD section 41"), which are second conductivity type regions, are formed in a region along the main surface 100a of the substrate 100. A diffusion layer 11 of a first conductivity type (for example, p-type) is formed between the ID section 21 and the FD section 31 of the substrate 100. A first conductivity type region 12 doped to the first conductivity type is formed on the surface of the diffusion layer 11.

[0031] An input control gate electrode 22 (hereinafter, "ICG electrode 22") (first electrode), a transfer gate electrode 32 (hereinafter, "TG electrode 32") (second electrode), a reset gate electrode 42 (hereinafter, "RG electrode 42"), and a sensing gate electrode 51 (hereinafter, "SG electrode 51") (third electrode) are formed (arranged) on the main surface 100a of the substrate 100 via an insulating protective film 110. The protective film 110 is a so-called gate insulating film (gate oxide film). For example, SiO2 or the like can be used as the protective film 110. The protective film 110 is a thin film having a thickness of, for example, about 10 nm. In addition, an amplifier (signal amplifier) ​​33 that amplifies an out signal according to the amount of charge accumulated in the FD section 31, and an output circuit 34 that is a source follower circuit that outputs the out signal amplified by the amplifier 33 are provided on the main surface 100a of the substrate 100.

[0032] The SG electrode 51 is disposed between the ICG electrode 22 and the TG electrode 32 on the main surface 100a so as to overlap with the first conductivity type region 12 when viewed from the thickness direction D1 (see FIG. 2) of the substrate 100. An insulating passivation layer 120 is formed on the main surface 100a so as to cover each electrode (ICG electrode 22, TG electrode 32, RG electrode 42, SG electrode 51, etc.) provided on the main surface 100a. For example, SiO2 may be used as the passivation layer 120. Alternatively, Si3N4 may be used as the passivation layer 120.

[0033] A flat electrode pad 52 (fourth electrode) is provided on the surface 120a of the passivation layer 120 opposite to the substrate 100 side. That is, the electrode pad 52 is disposed on the opposite side of the substrate 100 with the SG electrode 51 interposed therebetween. The electrode pad 52 is electrically connected to the SG electrode 51. In this embodiment, the electrode pad 52 is electrically connected to the SG electrode 51 via a metal wiring 53 embedded in an opening (contact hole) formed in the passivation layer 120. In the example of FIG. 2, the electrode pad 52 is embedded in the passivation layer 120, and the surface 52a of the electrode pad 52 opposite to the substrate 100 side and the surface 120a of the passivation layer 120 are flush with each other. However, the electrode pad 52 may be disposed on the passivation layer 120. In this case, the height position of the surface 52a of the electrode pad 52 is a position that is farther from the substrate 100 than the height position of the surface 120a of the passivation layer 120 by the thickness of the electrode pad 52.

[0034] A thin-film ion-sensitive membrane 13 is provided on the surface 52a of the electrode pad 52. The ion-sensitive membrane 13 has a property of changing the electric potential (membrane potential) according to the change in the ion concentration of a medium (in this embodiment, the aqueous solution 3 immersed in the surface of the ion sensor 1) that contacts the ion-sensitive membrane 13. For example, Si3N4 or the like can be used as the ion-sensitive membrane 13. The thickness of the ion-sensitive membrane 13 is, for example, about 100 nm. The width of the ion-sensitive membrane 13 in the facing direction D2 in which the ICG electrode 22 and the TG electrode 32 face each other is larger than the separation width between the ICG electrode 22 and the TG electrode 32. The surface 52a of the electrode pad 52 is a flat surface, and the ion-sensitive membrane 13 is formed flat along the surface 52a of the electrode pad 52. The "flat surface" here means a surface that is formed so as to be substantially flat when viewed macroscopically without openings or the like in the opening-type structure described later. Therefore, for example, the surface 52a on which a fine uneven structure (for example, an uneven structure having a height sufficiently smaller than the thickness of the medium (aqueous solution 3) to be measured) is provided in order to increase the contact area and improve adhesion between the surface 52a of the electrode pad 52 and the ion-sensitive membrane 13 also corresponds to the above-mentioned "flat surface". As shown in FIG. 2, the ion-sensitive membrane 13 is disposed outside the electrode pad 52. That is, the ion-sensitive membrane 13 has a portion that protrudes outside the electrode pad 52 when viewed from the thickness direction D1. The portion of the ion-sensitive membrane 13 that protrudes outside the electrode pad 52 does not contribute to the sensitivity of the ion sensor 1, but plays a role in preventing the surface 52a of the electrode pad 52 from being exposed to the outside. This makes it possible to preferably suppress, for example, the aqueous solution 3 from penetrating the surface 52a of the electrode pad 52.

[0035] Next, there will be described a functional configuration and an operation principle of the detection unit 5. The detection unit 5 includes a sensing unit 10, a supply unit 20, a migration / accumulation unit 30, and a removal unit 40. In this embodiment, the charges are electrons.

[0036] The sensing section 10 is a region of the substrate 100 facing the SG electrode 51. More specifically, the sensing section 10 is a region between the ICG electrode 22 and the TG electrode 32, where the SG electrode 51 faces the first conductive type region 12 via the protective film 110. That is, the sensing section 10 is a sensing region configured by laminating the above-mentioned diffusion layer 11, the first conductive type region 12, the protective film 110, and the SG electrode 51. When a stimulus is applied to the aqueous solution 3 or the test object itself in order to perform an inspection (ion concentration measurement) of the test object, the ion concentration of the aqueous solution 3 changes depending on the state of the test object. The above stimulus includes, for example, simply bringing the test object into contact with the aqueous solution 3, or giving a physical, chemical, or medicinal stimulus to the aqueous solution 3 or the test object while the test object is in contact with the aqueous solution 3. Then, a potential change occurs in the ion-sensitive membrane 13 according to the change in the ion concentration of the aqueous solution 3. This change in potential of the ion-sensitive film 13 is transmitted to the first conductivity type region 12 via the electrode pad 52, the metal wiring 53, and the SG electrode 51. As a result, the depth of the potential well 14 formed in the portion (sensing portion 10) of the substrate 100 that overlaps with the SG electrode 51 when viewed from the thickness direction D1 changes.

[0037] The supply unit 20 is composed of the above-mentioned ID unit 21 and ICG electrode 22. The ID unit 21 is a unit that accumulates charge to be injected into the potential well 14. The ICG electrode 22 is a unit that controls the amount of charge injected from the ID unit 21 to the potential well 14.

[0038] The transfer and accumulation section 30 is composed of a TG electrode 32 and an FD section 31. The TG electrode 32 is a section that performs control for transferring charges from the potential well 14 to the FD section 31 (external). The FD section 31 is a section that accumulates the charges transferred from the potential well 14. Specifically, by changing the voltage of the TG electrode 32, the electric potential of a region (hereinafter, "TG region") facing the TG electrode 32 in the substrate 100 can be changed, and the charges filled in the potential well 14 can be transferred to and accumulated in the FD section 31.

[0039] The removal unit 40 is composed of an RG electrode 42 and an RD unit 41. The removal unit 40 is a section for resetting (removing) the charge accumulated in the FD unit 31. Specifically, by changing the voltage of the RG electrode 42, the potential of the region (hereinafter referred to as the "RG region") facing the RG electrode 42 in the substrate 100 can be changed, and the charge accumulated in the FD unit 31 can be discharged to the RD unit 41 (VDD).

[0040] Next, an operation example of the detection unit 5 will be described. Fig. 3 shows an operation example of a method (hereinafter, "ID driving method") in which charge is injected from the ID unit 21 into the potential well 14 by changing the potential of the ID unit 21 while the potential of the ICG electrode 22 is kept constant. Fig. 4 shows an operation example of a method (hereinafter, "ICG driving method") in which charge is injected from the ID unit 21 into the potential well by changing the potential of the ICG electrode 22 while the potential of the ID unit 21 is kept constant.

[0041] (ID drive system) The ID driving method will be described with reference to Fig. 3. First, when the above-mentioned stimulus is applied to the aqueous solution 3 or the test object to cause a change in the ion concentration of the aqueous solution 3, a potential change occurs in the ion-sensitive membrane 13 in contact with the aqueous solution 3, and the potential change in the ion-sensitive membrane 13 is transmitted to the diffusion layer 11 (first conductivity type region 12) via the electrode pad 52, the metal wiring 53, and the SG electrode 51. As a result, the depth of the potential well 14 changes in response to the potential change in the ion-sensitive membrane 13, as shown in Fig. 3(A).

[0042] 3B, the potential of the ID section 21 is lowered, causing charges to accumulate in the ID section 21. The charges accumulated in the ID section 21 are injected into the potential well 14, passing over a region of the substrate 100 facing the ICG electrode 22 (hereinafter, "ICG region"). At this time, the potential of the TG region is controlled to be lower than the potential of the ID section 21. Therefore, the charges injected into the potential well 14 do not reach the FD section 31 beyond the TG region.

[0043] 3C, the potential of ID section 21 is returned (raised) to its original level, thereby extracting charge from ID section 21. As a result, charge that has been leveled off at the preset potential height of the ICG region remains in potential well 14. The amount of charge left in potential well 14 corresponds to the depth of potential well 14.

[0044] Next, as shown in FIG. 3D, the voltage of the TG electrode 32 is increased, and the charge remaining in the potential well 14 is transferred to the FD section 31. After that, the voltage of the TG electrode 32 is returned to the original state, resulting in the state shown in FIG. 3E. In this state, an out signal corresponding to the amount of charge accumulated in the FD section 31 is output to a measurement section (not shown) via the amplifier 33 and the output circuit 34. As a result, the ion concentration of the test object is detected in the measurement section based on the amount of change from the reference potential of the out signal. Next, as shown in FIG. 3F, the voltage of the RG electrode 42 is increased, and the charge accumulated in the FD section 31 is discharged to the RD section 41. The RD section 41 is connected to a VDD power supply. As a result, the negatively charged charge is sucked up in the RD section 41.

[0045] The above-mentioned operations (B) to (E) in Fig. 3 may be repeated multiple times. This increases the amount of charge stored in the FD section 31, and amplifies the out signal by the number of repetitions. Also, by amplifying the out signal through such repeated operations, the amplifier 33 may be omitted. By performing repeated operations (accumulation operations) of (B) to (E) in Fig. 3, it is possible to improve the resolution.

[0046] (ICG drive system) Next, the ICG driving method will be described with reference to FIG. 4. In the ICG driving method, the operations of (A) to (C) in FIG. 3 are replaced with the operations of (A) to (C) in FIG. 4. First, as shown in (A) in FIG. 4, the potential of the ID section 21 is set to a constant value that is lower than the potential of the potential well 14 and higher than the potential of the TG region. On the other hand, the potential of the ICG region is made lower than the potential of the ID section 21. Next, as shown in (B) in FIG. 4, the potential of the ICG region is made higher than the potential of the potential well 14, so that charge is supplied from the ID section 21 to the potential well 14. Next, as shown in (C) in FIG. 4, the potential of the ICG region is made lower than the potential of the ID section 21 again, so that charge up to the preset potential height of the ID section 21 remains in the potential well 14. As a result, charge of a potential equivalent to that of the ID section 21 is accumulated in the potential well 14. Subsequent operations in the ICG driving method are similar to the operations of (D) to (F) in FIG. 3.

[0047] Next, the arrangement (positional relationship) of the ICG electrode 22, the TG electrode 32, and the SG electrode 51 will be described with reference to Fig. 5 and Fig. 6. The ICG electrode 22, the TG electrode 32, and the SG electrode 51 need to be insulated from one another. For this reason, as shown in Fig. 5, the ICG electrode 22 and the SG electrode 51 are arranged to be spaced apart from one another. Similarly, the TG electrode 32 and the SG electrode 51 are arranged to be spaced apart from one another.

[0048] (A) to (C) of Fig. 5 correspond to (A) to (C) of Fig. 4 (ICG driving method). Here, when the separation width between the ICG electrode 22 and the SG electrode 51 is greater than a certain value, a potential barrier 61 that inhibits the injection of charges from the ID section 21 to the potential well 14 may be generated. That is, even if the voltage of the ICG electrode 22 is controlled so that the potential of the ICG region is higher than the potential of the potential well 14, a potential barrier 61 that maintains a potential lower than the potential of the potential well 14 may be generated in the region between the ICG electrode 22 and the SG electrode 51, as shown in (B) of Fig. 5. When the potential barrier 61 is generated, the injection of charges from the ID section 21 to the potential well 14 is blocked by the potential barrier 61, and the efficiency of charge transfer from the ID section 21 to the potential well 14 deteriorates.

[0049] Similarly, when the separation width between the TG electrode 32 and the SG electrode 51 is greater than a certain value, a potential barrier 62 that inhibits the transfer of charges from the potential well 14 to the FD section 31 may be generated. That is, even if the voltage of the TG electrode 32 is controlled so that the potential of the TG region is higher than the potential of the potential well 14 as shown in (D) of Fig. 3, a potential barrier 62 that maintains a potential lower than the potential of the potential well 14 may be generated in the region between the TG electrode 32 and the SG electrode 51. When the potential barrier 62 is generated, the injection of charges from the potential well 14 to the FD section 31 is blocked by the potential barrier 62, and the efficiency of charge transfer from the potential well 14 to the FD section 31 deteriorates.

[0050] Therefore, in the ion sensor 1, the separation width d2 (first separation width) (see FIG. 6) between the ICG electrode 22 and the SG electrode 51 is set so that the potential barrier 61 is not generated. Here, the condition (upper limit value) of the separation width d2 for not generating a potential barrier 61 that inhibits the injection of charges from the ID section 21 to the potential well 14 depends on the magnitude of the voltage applied to the ICG electrode 22, the thickness of the protective film 110, the impurity concentration of the first conductivity type region 12, and the like. More specifically, the higher the voltage applied to the ICG electrode 22, the higher the upper limit value of the separation width d2. Also, the thicker the protective film 110, the higher the upper limit value of the separation width d2. However, in this case, it is necessary to increase the voltage applied to the ICG electrode 22 by the amount of the increase in the thickness of the protective film 110. Also, the higher (higher) the impurity concentration of the first conductivity type region 12, the smaller the upper limit value of the separation width d2. The upper limit of the separation width d2 is calculated by performing experiments and simulations using, for example, the voltage applied to the ICG electrode 22, the thickness of the protective film 110, and the impurity concentration of the first conductivity type region 12 as parameters. In the ion sensor 1, the upper limit of the separation width d2 for preventing the generation of the potential barrier 61 is calculated based on the voltage applied to the ICG electrode 22, the thickness of the protective film 110, and the impurity concentration of the first conductivity type region 12, and the separation width d2 is set within a range not exceeding the calculated upper limit. This ensures sufficient charge transfer efficiency from the ID portion 21 to the potential well 14.

[0051] Similarly, the separation width d3 (second separation width) (see FIG. 6) between the TG electrode 32 and the SG electrode 51 is set so that the potential barrier 62 is not generated. Here, the condition (upper limit) of the separation width d3 for not generating the potential barrier 62 that inhibits the transfer of charges from the potential well 14 to the FD section 31 depends on the magnitude of the voltage applied to the TG electrode 32, the thickness of the protective film 110, the impurity concentration of the first conductivity type region 12, and the like. More specifically, the higher the voltage applied to the TG electrode 32, the higher the upper limit of the separation width d2. Also, the thicker the protective film 110, the higher the upper limit of the separation width d3. However, in this case, it is necessary to increase the voltage applied to the TG electrode 32 by the amount of the increase in the thickness of the protective film 110. Also, the higher (higher) the impurity concentration of the first conductivity type region 12, the smaller the upper limit of the separation width d3. The upper limit of the separation width d2 is calculated by performing experiments and simulations using, for example, the voltage applied to the TG electrode 32, the thickness of the protective film 110, and the impurity concentration of the first conductivity type region 12 as parameters. In the ion sensor 1, the upper limit of the separation width d3 for preventing the generation of the potential barrier 62 is calculated based on the voltage applied to the TG electrode 32, the thickness of the protective film 110, and the impurity concentration of the first conductivity type region 12, and the separation width d3 is set within a range not exceeding the calculated upper limit. This ensures sufficient charge transfer efficiency from the potential well 14 to the FD section 31.

[0052] As an example, the width w of the SG electrode 51 in the facing direction D2 (see FIG. 6) is 80% or more of the separation width d1 (see FIG. 6) between the ICG electrode 22 and the TG electrode 32. That is, the separation width d2 between the ICG electrode 22 and the SG electrode 51 and the separation width d3 between the TG electrode 32 and the SG electrode 51 are each set to about 10% or less of the separation width d1 between the ICG electrode 22 and the TG electrode 32. By setting the arrangement and dimensions of the ICG electrode 22, the TG electrode 32, and the SG electrode 51 in this manner, it is possible to suitably suppress the occurrence of the above-mentioned potential barriers 61 and 62 under general conditions related to the above-mentioned applied voltage to the ICG electrode 22 and the TG electrode 32, the thickness of the protective film 110, the impurity concentration of the first conductivity type region 12, and the like.

[0053] Next, an example of a manufacturing method for the ion sensor 1 will be described with reference to Fig. 7. Here, the description will focus on the manufacturing process of the parts related to the ICG electrode 22, the TG electrode 32, and the SG electrode 51 in each pixel (each detection unit 5).

[0054] 7A, a substrate 100 is prepared, and a protective film 110 (first insulating film) serving as a gate oxide film is formed on a main surface 100a of the substrate 100. The protective film 110 is formed between the ID section 21 and the FD section 31 in a region where at least the ICG electrode 22, the TG electrode 32, and the SG electrode 51 are to be disposed.

[0055] 7B, the ICG electrode 22, the TG electrode 32, and the SG electrode 51 are formed on the protective film 110. The ICG electrode 22, the TG electrode 32, and the SG electrode 51 are formed of, for example, polysilicon. The TG electrode 32 is disposed so as to be spaced apart from the ICG electrode 22. In addition, the SG electrode 51 is disposed between the ICG electrode 22 and the TG electrode 32 so as to be spaced apart from both the ICG electrode 22 and the TG electrode 32.

[0056] 7C, a passivation layer 120 (second insulating film) covering the ICG electrode 22, the TG electrode 32, and the SG electrode 51 is formed on the main surface 100a of the substrate 100. Then, as shown in FIG 7D, an opening (contact hole) is formed in the passivation layer 120 so as to expose a part of the SG electrode 51, and a metal wiring 53 electrically connected to the SG electrode 51 is formed (embedded) in the opening.

[0057] Next, as shown in FIG. 7E, the electrode pad 52 electrically connected to the metal wiring 53 is formed in a flat shape along the surface 120a of the passivation layer 120. Next, as shown in FIG. 7F, the ion-sensitive film 13 is formed on the surface 52a of the electrode pad 52. Here, the ion-sensitive film 13 is formed so that the width of the ion-sensitive film 13 in the facing direction D2 is larger than the separation width between the ICG electrode 22 and the TG electrode 32. In this manner, the pixel structure (detection unit 5) described above is obtained. Note that in FIG. 7F, only a part of the detection unit 5 is illustrated, so that the width of the ion-sensitive film 13 is the same as the width of the electrode pad 52, but the ion-sensitive film 13 may be formed to the outside of the electrode pad 52. More specifically, in the above manufacturing method, when the electrode pad 52 is formed on the passivation layer 120, the surface 52a and the side surface of the electrode pad 52 are exposed to the outside. Therefore, the ion-sensitive film 13 may be formed so as to cover the surface 52a and side surfaces of the electrode pad 52, and the portion of the passivation layer 120 outside the electrode pad 52. The ion-sensitive film 13 formed in this manner can prevent the surface 52a and side surfaces of the electrode pad 52 from being exposed to the outside, and can suitably suppress the infiltration of the aqueous solution 3 into the surface 52a of the electrode pad 52.

[0058] In the ion sensor 1 described above, the SG electrode 51 is disposed between the ICG electrode 22 and the TG electrode 32 on the main surface 100a of the substrate 100. The SG electrode 51 is electrically connected to the electrode pad 52 on which the ion-sensitive membrane 13 is provided. This realizes the function of the ion sensor 1. Specifically, the change in the potential of the ion-sensitive membrane 13 can be transmitted to the substrate 100 (specifically, the region overlapping with the SG electrode 51 when viewed from the thickness direction D1 among the regions along the main surface 100a of the substrate 100) via the electrode pad 52 and the SG electrode 51. This makes it possible to change the depth of the potential well 14 according to the change in the potential of the ion-sensitive membrane 13. As a result, it becomes possible to detect the ion concentration of the test object brought into contact with a medium (aqueous solution 3 in this embodiment) in contact with the ion-sensitive membrane 13 based on the amount of charge (i.e., the amount according to the depth of the potential well 14) extracted to the outside (FD section 31) by controlling (controlling the voltage) the ICG electrode 22 and the TG electrode 32.

[0059] Here, if an opening (a recess where no passivation layer is formed) is provided between the ICG electrode 22 and the TG electrode 32 and an ion-sensitive membrane is provided at the bottom of the opening (opening structure), the width of the ion-sensitive membrane is limited by the size of the opening, and the width of the ion-sensitive membrane cannot be made larger than the separation width between the ICG electrode 22 and the TG electrode 32. On the other hand, the ion sensor 1 adopts a configuration in which the potential change of the ion-sensitive membrane 13 is transmitted to the substrate 100 via the above-mentioned SG electrode 51 and electrode pad 52, thereby realizing a configuration in which the width of the ion-sensitive membrane 13 is made larger than the separation width between the ICG electrode 22 and the TG electrode 32. This makes it possible to ensure a sufficient contact area between the ion-sensitive membrane 13 and the aqueous solution 3, and effectively improve the sensitivity of the ion sensor 1.

[0060] In the ion sensor 1, the SG electrode 51 is disposed directly on the substrate 100 via only an extremely thin (10 nm in this embodiment) protective film 110, thereby realizing a structure in which an electric field is easily transmitted from the bottom surface (the surface on the protective film 110 side) of the SG electrode 51 to the substrate 100 (a structure in which a channel is easily formed). This makes it possible to eliminate the need for depression injection (i.e., formation of the first-conductivity type region 12) for facilitating the formation of a channel in the substrate 100, which was required in the above-mentioned open-type structure. That is, in the ion sensor 1, the first-conductivity type region 12 may be omitted. Accordingly, it is also possible to eliminate the need for a negative voltage required for depression injection (i.e., a negative voltage for turning off the channels in the regions directly below the ICG electrode 22, the TG electrode 32, and the RG electrode 42 in the substrate 100).

[0061] Moreover, the surface 52a of the electrode pad 52 is a flat surface, and the ion-sensitive membrane 13 is formed in a flat shape along the surface 52a. According to the above configuration, the medium (aqueous solution 3) placed on the ion-sensitive membrane 13 can be sufficiently tightly attached to the ion-sensitive membrane 13, compared to the case where the above-mentioned open-type structure is adopted. This makes it possible to more effectively improve the sensitivity of the ion sensor 1.

[0062] [Second embodiment] 8 is a diagram showing a schematic cross-sectional configuration of a detection unit 5A of an ion sensor 1A of a second embodiment. The ion sensor 1A differs from the ion sensor 1 in that it has a detection unit 5A instead of the detection unit 5 (see FIG. 2) as a pixel structure, and other configurations of the ion sensor 1A are similar to those of the ion sensor 1. The detection unit 5A differs from the detection unit 5 mainly in that it has an ICG electrode 22A and a TG electrode 32A instead of the ICG electrode 22 and the TG electrode 32.

[0063] As shown in FIG. 8, when viewed in the thickness direction D1, a part of the ICG electrode 22A overlaps with the SG electrode 51. In the present embodiment, in order to insulate the ICG electrode 22A and the SG electrode 51, a protective film 130 is formed to cover the upper surface (the surface opposite to the protective film 110 side) and the side surface of the SG electrode 51. That is, a part of the ICG electrode 22A is in contact with the SG electrode 51 via the protective film 130. The protective film 130 can be formed of, for example, the same material (e.g., SiO2) as the protective film 110. The thickness of the protective film 130 is, for example, about 50 nm.

[0064] The width w11 in the facing direction D2 of the overlapping portion (the first portion) of the ICG electrode 22A with the SG electrode 51 is smaller than the width w12 in the facing direction D2 of the non-overlapping portion (the second portion) of the ICG electrode 22A with the SG electrode 51. This is due to the following reasons. That is, when the width w12 of the second portion is not sufficient, the ICG region does not function sufficiently as a gate region for controlling the flow of charges between the ID portion 21 and the potential well 14, and leakage of charges from the potential well 14 to the ID portion 21 may occur. For this reason, the ICG electrode 22A overlaps with the SG electrode 51 such that "w11 < w12". More preferably, the ICG electrode 22A overlaps with the SG electrode 51 such that the width w11 of the first portion is 25% or less of the width w12 of the second portion (that is, "w11 < 0.25 × w12" is satisfied). According to the above configuration, unintentional leakage of charges from the potential well 14 to the ID portion 21 can be preferably suppressed.

[0065] Also, when viewed in the thickness direction D1, a part of the TG electrode 32A overlaps with the SG electrode 51. In the present embodiment, a part of the TG electrode 32A is in contact with the SG electrode 51 via the above-described protective film 130. The width w21 in the facing direction D2 of the portion (third portion) of the TG electrode 32A that overlaps with the SG electrode 51 is smaller than the width w22 in the facing direction D2 of the portion (fourth portion) of the TG electrode 32A that does not overlap with the SG electrode 51. This is due to the following reason. That is, when the width w22 of the fourth portion is not sufficient, the TG region does not function sufficiently as a gate region that controls the flow of charges between the potential well 14 and the FD portion 31, and charge leakage from the potential well 14 to the FD portion 31 may occur. For this reason, the TG electrode 32A overlaps with the SG electrode 51 such that "w21 < w22". More preferably, the TG electrode 32A overlaps with the SG electrode 51 such that the width w21 of the third portion is 25% or less of the width w22 of the fourth portion (that is, "w21 < 0.25 × w22" is satisfied). According to the above configuration, unintended charge leakage from the potential well 14 to the FD portion 31 can be preferably suppressed.

[0066] With reference to FIG. 9, the effect achieved by the pixel structure (detection unit 5A) of the ion sensor 1A will be further described. (A) to (F) of FIG. 9 show each step of the operation of the detection unit 5A in the ICG driving method. As described above, in the detection unit 5A, a portion is formed where the ICG electrode 22A and the SG electrode 51 overlap. As a result, a region 63 having a potential between the potential of the ICG region and the potential of the potential well 14 is formed in the portion of the substrate 100 where the ICG electrode 22A and the SG electrode 51 overlap. The formation of such a region 63 achieves the following effect. If the region 63 is not formed (i.e., when the potential of the ICG region is flat), when the potential of the ICG region is made lower than the potential of the ID section 21 (i.e., when transitioning from the state of FIG. 9B to the state of FIG. 9C), it is uncertain whether the charge of the ICG region moves to the ID section 21 or the potential well 14 side. For this reason, variation (noise) may occur in the amount of charge that moves to the potential well 14 side of the charge in the ICG region (i.e., the amount of charge accumulated in potential well 14). On the other hand, when region 63 is formed, when the potential of the ICG region is made lower than the potential of the ID section 21, it is possible to generate a stepped (approximately slope-shaped) potential difference from the ID section 21 to the potential well 14, so that the charge in the ICG region can be smoothly moved to the potential well 14 side. This makes it possible to reduce variation in the amount of charge accumulated in potential well 14.

[0067] Also, a part (first part) of the ICG electrode 22A is disposed on the opposite side of the substrate 100 with the SG electrode 51 interposed therebetween. That is, an edge of the SG electrode 51 is disposed between the ICG electrode 22A and the substrate 100. According to the above configuration, compared with a case where a part of the ICG electrode 22A is disposed between the substrate 100 and the SG electrode 51 (ion sensor 1B of a third embodiment described later), it is possible to reduce the voltage value required to form a potential well 14 in a region of the substrate 100 overlapping with the SG electrode 51. Specifically, in the ion sensor 1B (see FIG. 11) described later, a protective film 110 and a protective film 130 are formed between the SG electrode 151 and the substrate 100, whereas in the ion sensor 1A, only the protective film 110 is formed between the SG electrode 51 and the substrate 100. That is, in the ion sensor 1A, the distance between the SG electrode 51 and the substrate 100 is smaller by the thickness of the protective film 130 than in the ion sensor 1B. This achieves the above-mentioned effect (reduction in the required voltage value).

[0068] Furthermore, in the detection unit 5A, a portion is formed where the TG electrode 32A and the SG electrode 51 overlap. As a result, a region 64 having a potential between the potential of the TG region and the potential of the potential well 14 is formed in the portion of the substrate 100 where the TG electrode 32A and the SG electrode 51 overlap. The formation of such a region 64 can improve the charge transfer efficiency when charge is transferred from the potential well 14 to the FD section 31 (see FIG. 9(D)). That is, the region 64 can generate a stepwise (approximately slope-shaped) potential difference from the potential well 14 to the FD section 31, so that charge can be transferred smoothly from the potential well 14 to the FD section 31.

[0069] Furthermore, a portion (third portion) of the TG electrode 32A is disposed on the opposite side of the substrate 100 with the SG electrode 51 interposed therebetween. That is, an edge portion of the SG electrode 51 is disposed between the TG electrode 32A and the substrate 100. According to the above configuration, for the same reason as described above, it is possible to reduce the voltage value required to form a potential well 14 in the region of the substrate 100 that overlaps with the SG electrode 51, compared to the case where a portion of the TG electrode 32A is disposed between the substrate 100 and the SG electrode 51 (ion sensor 1B of the third embodiment described later).

[0070] Next, an example of a manufacturing method for the ion sensor 1A will be described with reference to Fig. 10. Here, the description will focus on the manufacturing process of the parts related to the ICG electrode 22A, the TG electrode 32A, and the SG electrode 51 in each pixel (each detection unit 5A).

[0071] 10A, a substrate 100 is prepared, and a protective film 110 (first insulating film) serving as a gate oxide film is formed on a main surface 100a of the substrate 100. The protective film 110 is formed in a region between the ID section 21 and the FD section 31 where at least the ICG electrode 22A, the TG electrode 32A, and the SG electrode 51 are to be disposed. Then, the SG electrode 51 is formed on the protective film 110.

[0072] 10B, a protective film 130 (second insulating film) is formed to cover the surface of the SG electrode 51 (at least the surface of the portion in contact with the ICG electrode 22A and the TG electrode 32A). Then, as shown in FIG. 10C, the ICG electrode 22A is formed so that a portion of the ICG electrode 22A overlaps with the SG electrode 51 via the protective film 130 when viewed from the thickness direction D1. Also, the TG electrode 32A is formed so that a portion of the TG electrode 32A overlaps with the SG electrode 51 via the protective film 130 when viewed from the thickness direction D1.

[0073] Next, the same steps as in the manufacturing method of the ion sensor 1 described above (steps corresponding to (C) to (F) in FIG. 7) are performed. That is, a passivation layer 120 (third insulating film) is formed on the main surface 100a of the substrate 100 to cover the ICG electrode 22A, the TG electrode 32A, and the SG electrode 51. Next, an opening (contact hole) is formed in the passivation layer 120 so that a part of the SG electrode 51 is exposed, and a metal wiring 53 electrically connected to the SG electrode 51 is formed in the opening. In this embodiment, since the protective film 130 is formed so as to cover the entire upper surface of the SG electrode 51, an opening is also formed in the protective film 130 in the above-mentioned step of providing an opening in the passivation layer 120 (see FIG. 8). Next, an electrode pad 52 electrically connected to the metal wiring 53 is formed in a flat shape along the surface 120a of the passivation layer 120. Next, an ion-sensitive film 13 is formed on the surface 52a of the electrode pad 52. Here, the ion-sensitive membrane 13 is formed so that the width of the ion-sensitive membrane 13 in the facing direction D2 is larger than the separation width between the ICG electrode 22A and the TG electrode 32A. In this manner, the above-mentioned pixel structure (detection unit 5A) is obtained.

[0074] According to the ion sensor 1A described above, it is possible to reliably prevent the occurrence of potential barriers 61, 62 that may occur when the ICG electrode and the TG electrode are arranged at a distance from the SG electrode, and as described above, it is possible to improve the efficiency of charge transfer from the ID section 21 to the potential well 14 and the efficiency of charge transfer from the potential well 14 to the FD section 31.

[0075] [Third embodiment] 11 is a diagram showing a schematic cross-sectional configuration of a detection unit 5B of an ion sensor 1B of a third embodiment. The ion sensor 1B differs from the ion sensor 1 in that it has a detection unit 5B instead of the detection unit 5 (see FIG. 2) as a pixel structure, and other configurations of the ion sensor 1B are similar to those of the ion sensor 1. The detection unit 5B differs from the detection unit 5 mainly in that it has an SG electrode 151 instead of the SG electrode 51.

[0076] The detection unit 5B has a similar feature to the detection unit 5A in that, when viewed from the thickness direction D1, a part of the ICG electrode 22 overlaps with the SG electrode 151 and a part of the TG electrode 32 overlaps with the SG electrode 151. However, while in the detection unit 5A, a part of the ICG electrode 22A and a part of the TG electrode 32A are located above the SG electrode 51 (the opposite side of the substrate 100 with respect to the SG electrode 51), in the detection unit 5B, a part of the ICG electrode 22 and a part of the TG electrode 32 are located below the SG electrode 151 (the substrate 100 side with respect to the SG electrode 51).

[0077] The detection unit 5B can be manufactured, for example, as follows. First, the ICG electrode 22 and the TG electrode 32 are formed on the protective film 110. Next, a protective film 130 is formed to cover at least the surfaces (upper surface and inner (TG electrode 32 side) side) of the ICG electrode 22 and the surfaces (upper surface and inner (ICG electrode 22 side) side) of the TG electrode 32. Next, the SG electrode 151 is formed on the protective film 130 such that, when viewed from the thickness direction D1, a part of the SG electrode 151 overlaps a part of the ICG electrode 22 via the protective film 130 and another part of the SG electrode 151 overlaps a part of the TG electrode 32 via the protective film 130.

[0078] The above-described ion sensor 1B can also reliably prevent the generation of the potential barriers 61 and 62, similarly to the above-described ion sensor 1A.

[0079] [Variations] Although the preferred embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments. For example, in the ion sensors 1, 1A, and 1B, the multiple detection units 5, 5A, and 5B may be arranged in a one-dimensional manner. The substrate 100 does not necessarily have to be a semiconductor substrate, and may be, for example, a non-semiconductor substrate having a semiconductor region (e.g., a semiconductor film or the like) formed on the surface. The protective film 110 formed between each electrode member and the substrate 100 may be formed continuously. That is, the protective film 110 may be formed on the entire main surface 100a of the substrate 100.

[0080] The medium arranged on the ion-sensitive film 13 may be a substance other than the aqueous solution 3 (for example, a substance adsorption film having a property of changing electrical characteristics when an odorant is adsorbed). Here, the odorant is a chemical substance that causes an odor (for example, a specific molecular unit or molecular group aggregated at a predetermined concentration). An example of the substance adsorption film is a polyaniline-sensitive film that is sensitive to ammonia, etc. In this case, the ion sensor 1 functions as an odor sensor that detects odors. Even when a solid substance adsorption film that is not limited to one that adsorbs odorants is provided as the medium, it is preferable to form the ion-sensitive film 13 outside the electrode pad 52, as shown in FIG. 2. In this case, in the process of forming the substance adsorption film on the ion-sensitive film 13, the solvent used for film formation can be suitably prevented from penetrating into the surface 52a of the electrode pad 52.

[0081] Furthermore, in the second and third embodiments described above, the SG electrode may be disposed so as to overlap only one of the ICG electrode and the TG electrode, and to be spaced apart from the other of the ICG electrode and the TG electrode.

[0082] Also, as shown in FIG. 12, one detection unit 5, 5A, 5B (pixel) may include a plurality of (four here as an example) ion-sensitive membranes 13A, 13B, 13C, 13D that react to different ions. Also, a plurality of electrode pads 52 may be provided corresponding to each of the plurality of ion-sensitive membranes 13A, 13B, 13C, 13D. That is, the electrode pad 52 provided with the ion-sensitive membrane 13A, the electrode pad 52 provided with the ion-sensitive membrane 13B, the electrode pad 52 provided with the ion-sensitive membrane 13C, and the electrode pad 52 provided with the ion-sensitive membrane 13D may be provided independently (separately) from each other. And, a plurality of SG electrodes 51A, 51B, 51C, 51D may be provided independently (separately) from each other so as to correspond to each of the plurality of electrode pads 52 as described above. According to the above configuration, the amount of information obtained from one pixel can be increased. That is, it is possible to detect the concentration of a plurality of types of ions by one pixel. Specifically, it becomes possible to detect the total concentration of a plurality of kinds of ions with one pixel. For example, consider a case where the ion-sensitive films 13A-13D are formed of a material having a property of changing the electric potential according to the ion concentrations of the first to fourth ions, respectively. With the above configuration, for example, in a water quality test, when the first to fourth ions are not contained, it is judged as OK (i.e., when at least one of the first to fourth ions is contained, it is judged as NG), and the above judgment can be made only with information obtained from one pixel.

[0083] In the above embodiment, the ICG electrode 22 and the TG electrode 32 are formed in rectangular shapes of approximately the same size when viewed from the thickness direction D1, and the SG electrode 51 disposed between them is formed in a rectangular shape, as shown in Fig. 1, but the shape and size of each electrode are not limited to these. For example, in order to improve the charge transfer efficiency from the ID section 21 to the FD section 31, the ICG electrode 22 may be formed in a rectangular shape smaller than the TG electrode 32 when viewed from the thickness direction D1, as shown in Fig. 13, and the SG electrode 51 may be formed in a trapezoidal shape that becomes wider from the ICG electrode 22 side toward the TG electrode 32 side. [Explanation of symbols]

[0084] 1, 1A, 1B... ion sensor, 3... aqueous solution (medium), 5, 5A, 5B... detection section (pixel), 13... ion-sensitive membrane, 14... potential well, 21... ID section (charge storage section), 22, 22A... ICG electrode (first electrode), 31... FD section (external), 32, 32A... TG electrode (second electrode), 51, 51A, 51B, 51C, 51D, 151... SG electrode (third electrode), 52... electrode pad (fourth electrode), 53... metal wiring, 61, 62... potential barrier, 100... substrate, 100a... main surface (first surface), 110... protective film (first insulating film), 120... passivation layer (second insulating film, third insulating film), 130... protective film (second insulating film).

Claims

1. A substrate; a plurality of pixels disposed on a first surface of the substrate; Each of the pixels has a charge storage portion, a first electrode, a second electrode, a third electrode, a fourth electrode, and an ion-sensitive membrane, the charge accumulation portion is formed in a region along the first surface of the substrate, and accumulates charges to be injected into a potential well formed in a portion of the substrate that overlaps with the third electrode when viewed in a thickness direction of the substrate; the first electrode is disposed on the first surface and configured to control an amount of charge injection from the charge accumulation portion to the potential well; the second electrode is disposed on the first surface and configured to control a transfer of charge from the potential well to an outside; the third electrode is disposed on the first surface between the first electrode and the second electrode, the fourth electrode is electrically connected to the third electrode and is disposed on the opposite side of the substrate with the third electrode interposed therebetween; the ion-sensitive membrane is provided on a surface of the fourth electrode opposite to the substrate, and changes a potential in response to a change in an ion concentration of a medium in contact with the ion-sensitive membrane; a width of the ion-sensitive membrane in a direction in which the first electrode and the second electrode face each other is greater than a distance between the first electrode and the second electrode; When viewed from the thickness direction, a portion of the first electrode overlaps with the third electrode.

2. The ion sensor according to claim 1 , wherein the portion of the first electrode is disposed on an opposite side of the substrate with the third electrode interposed therebetween.

3. 3. The ion sensor according to claim 1, wherein a width in the opposing direction of a first portion of the first electrode that overlaps with the third electrode is smaller than a width in the opposing direction of a second portion of the first electrode that does not overlap with the third electrode.

4. The ion sensor of claim 3 , wherein the width of the first portion is less than or equal to 25% of the width of the second portion.

5. the second electrode and the third electrode are spaced apart from each other, 5. The ion sensor according to claim 1, wherein a second separation width between the second electrode and the third electrode is set within a range in which a potential barrier that inhibits transfer of charge from the potential well to an outside is not generated.

6. A substrate; a plurality of pixels disposed on a first surface of the substrate; Each of the pixels has a charge storage portion, a first electrode, a second electrode, a third electrode, a fourth electrode, and an ion-sensitive membrane, the charge accumulation portion is formed in a region along the first surface of the substrate, and accumulates charges to be injected into a potential well formed in a portion of the substrate that overlaps with the third electrode when viewed in a thickness direction of the substrate; the first electrode is disposed on the first surface and configured to control an amount of charge injection from the charge accumulation portion to the potential well; the second electrode is disposed on the first surface and configured to control a transfer of charge from the potential well to an outside; the third electrode is disposed on the first surface between the first electrode and the second electrode, the fourth electrode is electrically connected to the third electrode and is disposed on the opposite side of the substrate with the third electrode interposed therebetween; the ion-sensitive membrane is provided on a surface of the fourth electrode opposite to the substrate, and changes a potential in response to a change in an ion concentration of a medium in contact with the ion-sensitive membrane; a width of the ion-sensitive membrane in a direction in which the first electrode and the second electrode face each other is greater than a distance between the first electrode and the second electrode; When viewed from the thickness direction, a portion of the second electrode overlaps with the third electrode.

7. The ion sensor according to claim 6 , wherein the portion of the second electrode is disposed on an opposite side of the substrate with the third electrode interposed therebetween.

8. 8. The ion sensor according to claim 6, wherein a width in the opposing direction of a third portion of the second electrode that overlaps with the third electrode is smaller than a width in the opposing direction of a fourth portion of the second electrode that does not overlap with the third electrode.

9. The ion sensor of claim 8 , wherein the width of the third portion is less than or equal to 25% of the width of the fourth portion.

10. the first electrode and the third electrode are spaced apart from each other; 10. The ion sensor according to claim 6, wherein a first separation width between the first electrode and the third electrode is set within a range in which a potential barrier that inhibits injection of charge from the charge accumulation portion into the potential well is not generated.

11. the fourth electrode has a flat surface on a side opposite to the substrate; 11. The ion sensor according to claim 1, wherein the ion-sensitive film is formed flat along the opposite surface.

12. One pixel includes a plurality of the ion sensitive films that react to different ions, a plurality of the fourth electrodes are provided corresponding to the plurality of the ion-sensitive films, 12. The ion sensor according to claim 1, further comprising a plurality of the third electrodes provided in correspondence with the plurality of the fourth electrodes, respectively.

13. A method for manufacturing an ion sensor having a substrate and a first electrode, a second electrode, and a third electrode formed on the substrate, comprising the steps of: forming a first insulating film on the substrate; forming, on the first insulating film, the first electrode, the second electrode arranged to be spaced apart from the first electrode, and the third electrode arranged between the first electrode and the second electrode, such that at least one of the first electrode and the second electrode partially overlaps with the third electrode via the second insulating film; forming a third insulating film on the substrate to cover the first electrode, the second electrode, and the third electrode; forming an opening in the third insulating film so as to expose a portion of the third electrode, and forming a metal wiring in the opening that is electrically connected to the third electrode; forming a fourth electrode electrically connected to the metal wiring along a surface of the third insulating film opposite to the substrate; forming an ion-sensitive film on a surface of the fourth electrode opposite to the substrate, the ion-sensitive film changing an electric potential in response to a change in an ion concentration of a medium in contact with the fourth electrode; A method for manufacturing an ion sensor, wherein in the step of forming the ion-sensitive membrane, the ion-sensitive membrane is formed so that a width of the ion-sensitive membrane in a direction in which the first electrode and the second electrode face each other is larger than a separation width between the first electrode and the second electrode.

14. A method for manufacturing an ion sensor having a substrate and a first electrode, a second electrode, and a third electrode formed on the substrate, comprising the steps of: forming a first insulating film on the substrate; forming the third electrode on the first insulating film; forming a second insulating film covering a surface of the third electrode; forming the first electrode such that a portion of the first electrode overlaps with the third electrode via the second insulating film when viewed from a thickness direction of the substrate, and forming the second electrode such that a portion of the second electrode overlaps with the third electrode via the second insulating film when viewed from a thickness direction of the substrate; forming a third insulating film on the substrate to cover the first electrode, the second electrode, and the third electrode; forming an opening in the third insulating film so as to expose a portion of the third electrode, and forming a metal wiring in the opening that is electrically connected to the third electrode; forming a fourth electrode electrically connected to the metal wiring along a surface of the third insulating film opposite to the substrate; forming an ion-sensitive film on a surface of the fourth electrode opposite to the substrate, the ion-sensitive film changing an electric potential in response to a change in an ion concentration of a medium in contact with the fourth electrode; A method for manufacturing an ion sensor, wherein in the step of forming the ion-sensitive membrane, the ion-sensitive membrane is formed so that a width of the ion-sensitive membrane in a direction in which the first electrode and the second electrode face each other is larger than a separation width between the first electrode and the second electrode.

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