Odor sensor element array

Abstract

To solve the problem that, in an odor detection element array including an odor-sensitive film made of a conductive polymer covering a potential detection unit, and a metal electrode which is in contact with the odor sensitive film and applies a reference potential, the potential detection unit is covered with the odor sensitive film, but in a structure where the metal electrode applied with the reference potential is formed on the odor-sensitive film, gas molecules of the incoming gas do not reach a place covered with the metal electrode, and therefore the detectable surface area decreases, along with the accuracy of the odor detection.SOLUTION: Provided is an odor sensor element array with sensitivity made excellent by suitably arranging an odor sensitive film and a metal electrode by using an extended gate CMOS type ion image sensor structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention aims to enhance the multifunctionality of an odor sensor element array, particularly improving the detection sensitivity of the odor sensor element array.

Background Art

[0002] A CMOS type ion image sensor (Non-Patent Document 1) is intended to detect changes in pH or hydrogen ion concentration. On the uppermost surface of the sensor, a Ta2O5 film that selectively binds to hydrogen ions is formed. The change in the depth of the potential well formed in the semiconductor due to the variation in the amount of positive charge caused by hydrogen ions enables the detection of fluctuations in pH or hydrogen ion concentration. That is, it serves as a mechanism for detecting potential changes in the Ta2O5 film. Therefore, an odor-sensitive film (which may be referred to as an "odor-sensitive film" in this specification) is provided on the sensor, in which a substance that reacts with odor molecules such as inorganic ions and organic acids is added to a conductive polymer material such as polyaniline. Furthermore, by forming an electrode for fixing the potential, changes in the electrical characteristics of the odor-sensitive film due to odor molecule adsorption are reflected in the depth of the potential well formed in the semiconductor (Patent Document 1).

[0003] Animals have about 400 types of olfactory receptors in humans and about 800 types in dogs, and odors are discriminated based on their adsorption patterns. An ion image sensor has a large number of sensor elements integrated. If a large number of odor-sensitive films can be formed in a minute area, an odor sensor capable of discriminating a large number of odors can be realized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] Patent Document 1 discloses that a gas can be detected by comprising a sensing unit, a first sensitive film covering the sensing unit, a second sensitive film made of a conductive polymer covering the measuring unit including the sensing unit (corresponding to the "odor sensitive film" in this specification), and a constant potential unit in contact with the second sensitive film (corresponding to the "reference potential" in this specification). Embodiments disclose a structure in which a measuring unit formed on a semiconductor substrate is covered with a polyaniline film, and a metal electrode that serves as the constant potential unit is arranged on the polyaniline film, and a structure in which a metal electrode that serves as the constant potential unit is arranged on the same plane as the measuring unit.

[0007] However, in a structure where metal electrodes are formed on a polyaniline film, gas molecules arriving at the area covered by the metal electrodes do not reach the polyaniline film, reducing the surface area on which gas molecules can be detected. Furthermore, in a structure where the metal electrodes, which form a constant potential zone, are placed on the same plane as the measurement unit, the metal electrodes and the measurement unit are placed on the same plane on the semiconductor substrate, and are subjected to disturbances from the semiconductor substrate with a high dielectric constant when detecting changes in the electrical properties of the polyaniline film.

[0008] Patent Document 2 discloses a sensing unit having a sensitive membrane that changes its potential according to the state of the object to be measured, a substance adsorption membrane (corresponding to the "odor-sensitive membrane" in this specification) disposed on the sensitive membrane and changing its state by adsorbing odor substances, and a reference electrode to which a reference voltage (corresponding to the "reference potential" in this specification) is applied, wherein the reference electrode is spaced apart from the sensitive membrane and is arranged so as not to overlap with the sensing unit.

[0009] The structure described in Patent Document 2 is characterized by the fact that a substance adsorption film can be formed in the final stage of the manufacturing process after the sensing unit and reference electrode have been formed. However, since the substance adsorption film is provided so as to cover the passivation layer, the thickness of the substance adsorption film must be determined considering the thickness of the passivation film. This presents a challenge in that there are limitations when adjusting the thickness of the substance adsorption film to improve detection sensitivity.

[0010] As disclosed in Patent Documents 1 and 2, a conductive polymer film or substance adsorption film with a thick film thickness is present on the sensing unit and metal electrode formed on the semiconductor substrate. On the other hand, it is desirable that the conductive polymer film or substance adsorption film be thin. Gas molecules are detected by generating an electric charge in the odor-sensitive film, and the detected potential change is the partial pressure of the capacitance of the potential detection unit itself and the capacitance of the odor-sensitive film itself. In other words, by making the odor-sensitive film thin and increasing the capacitance ratio, a large voltage change can be observed. [Means for solving the problem]

[0011] In view of the above circumstances, the inventors have invented an odor sensor element array with excellent detection sensitivity, which utilizes an expanded-gate CMOS type ion image sensor structure to suitably arrange an odor-sensitive film and metal electrodes, and allows for the setting of an optimal film thickness for the odor-sensitive film.

[0012] The first aspect of this invention is a sensing unit on a Si substrate that changes the depth of a potential well according to the surface potential, an interlayer insulating film formed on the sensing unit, first and second metal electrodes formed on the interlayer insulating film, and a third metal electrode formed within the interlayer insulating film, the first metal electrode being electrically connected to the sensing unit via a first through-hole provided within the interlayer insulating film, a first sensitive film made of a Ta2O5 film formed directly above the first metal electrode, and the second metal electrode being electrically connected via a second through-hole provided within the interlayer insulating film. In a potential detection unit electrically connected to a third metal electrode, a first sensitive film made of a Ta2O5 film is formed on the uppermost surface of the arrayed potential detection units, and a second sensitive film made of a conductive polymer is formed as an odor sensitive film directly above the second metal electrode. The first and second metal electrodes are arranged on the same plane, the first and second metal electrodes and the third metal electrode are arranged on different planes, and the second metal electrodes of each potential detection unit constituting the array are interconnected via the third metal electrode.

[0013] A second aspect of this invention is characterized in that, in the first aspect, the materials or film thicknesses of the first and second metal electrodes and the third metal electrode are different, and the resistance value of the third metal electrode is lower than that of the second metal electrode.

[0014] To suitably implement the first and second aspects, first and second metal electrodes are formed to become the uppermost metal electrodes of an extended-gate CMOS type potential detection unit. A first sensitive film is formed by covering the first metal electrode, and a second sensitive film, an odor-sensitive film, is formed by covering the first sensitive film and the second metal electrode. The first metal electrode is made into a thin film to form a thin odor-sensitive film. [Effects of the Invention]

[0015] According to the element structure shown above, the detection sensitivity of odor components can be improved. Furthermore, since the odor-sensitive film can be formed after the semiconductor element manufacturing process is completed, there is an advantage that there are no restrictions on the method of forming the odor-sensitive film. In the case of an odor sensor element, it is preferable to form the odor-sensitive film by an inkjet printing method after assembling the chip into a package or the like. Here, the inkjet printing method is a method of forming a three-dimensional object by injecting and depositing molten metal, resin, etc. only on the part having the model shape.

Brief Description of the Drawings

[0016] [Figure 1] It is a cross-sectional view of an odor sensor element showing the structure of this embodiment. [Figure 2] It is a cross-sectional view of an odor sensor element showing another structure of this embodiment. [Figure 3] It is an explanatory diagram showing the first to fourth steps in the stacking process of the odor sensor element array of the embodiment. [Figure 4] It is an explanatory diagram showing the fifth to seventh steps in the stacking process of the odor sensor element array of the embodiment. [Figure 5] It is an explanatory diagram showing the eighth to ninth steps in the stacking process of the odor sensor element array of the embodiment. [Figure 6] It is a cross-sectional view showing the configuration of the potential detection unit of this embodiment. [Figure 7] It is a potential distribution diagram explaining the operation of the potential detection unit according to this embodiment.

Modes for Carrying Out the Invention

[0017] (Embodiment) The structure of the odor sensor element array 100 according to this embodiment is shown in FIG. 1. The sensor element is composed of a CMOS extended gate type potential detection unit 1, an odor sensitive film 40, and a metal electrode 36 for applying a reference potential to the odor sensitive film 40. The potential detection unit 1 includes interlayer insulating films 30 and 33, a first metal electrode 35 and a second metal electrode 36 directly above the interlayer insulating films, and a first sensitive film 37 is formed in a shape covering the first metal electrode 35. The first metal electrode 35 is electrically connected to the sensing region defining electrode 13 of the potential detection unit 1 through through-holes 31A and 34A in the interlayer insulating films 30 and 33.

[0018] The odor sensor element array 100 includes a third metal electrode 38 in the interlayer insulating films 30 and 33 and is electrically connected to the second metal electrode 36 through a through-hole 34B. The second metal electrode 36 applies a reference potential to the odor sensitive film 40, and low wiring resistance is desirable for the wiring between the arrayed potential detection units. This is because when the wiring resistance is high, an RC delay occurs for a steep change, resulting in a delay in the sensor response. Here, the RC delay means that in a semiconductor element or the like, the time from input to drive is delayed due to the influence of the wiring resistance (R), the wiring capacitance or the interlayer capacitance (C). This causes an extra driving time to charge or discharge the parasitic capacitance of the capacitor.

[0019] The structure shown in FIG. 1 forms the interlayer insulating films 30 and 33 in two layers. After forming the first layer of the interlayer insulating film 30, a through-hole 31A is formed for the electrical connection between the sensing region defining electrode 13 of the potential detection unit 1 and the metal electrode 32 formed in the upper layer. A metal material such as tungsten is deposited over the entire surface, and planarized by the CMP (Chemical Mechanical Polishing) method and the metal film attached other than the through-hole is removed. Next, the metal film 32 is formed using photolithography, and the second layer of the interlayer insulating film 33 is formed. A through-hole 34A is formed for the electrical connection with the upper layer.

[0020] The stacking process for the odor sensor element array 100 of this embodiment will now be described. Figure 3 shows an explanatory diagram of the first to fourth steps in the stacking process for the odor sensor element array 100 of this embodiment. Figure 4 shows an explanatory diagram of the fifth to seventh steps in the stacking process for the odor sensor element array 100 of this embodiment. Figure 5 shows an explanatory diagram of the eighth and ninth steps in the stacking process for the odor sensor element array 100 of this embodiment.

[0021] In the first step of the lamination process for the odor sensor element array 100, the sensing unit 50 is already formed within the silicon substrate 2. Next, in the second step, an interlayer insulating film 30 is formed on the silicon substrate. A specific example of a method for forming the interlayer insulating film 30 is the P-CVD (Plasma Chemical Vapor Deposition) method.

[0022] Next, in the third step, through holes are formed in the region where the electrical connection part is to be formed. Specifically, through holes are formed on the sensing region defining electrode 13. One method for forming the through holes is to pattern by photolithography and then remove the unnecessary portion of the interlayer insulating film 30 by etching. Next, in the fourth step, a metal film 31 is formed while filling the through holes. Specific examples of methods for forming the metal film 31 include sputtering and vapor deposition. Next, in the fifth step, the metal film other than the through holes 31A is removed to form the electrical connection part. One method for removing the metal film 31 is the CMP method or the etch-back method.

[0023] Next, in the sixth step, a metal film that will form the basis of the third metal electrode 38 is formed. A specific example of a method for forming the metal film is the sputtering method. Another specific example of a formation method is a method in which the metal film is patterned by photolithography and then the unwanted parts are removed by etching.

[0024] As the seventh step, the procedures of steps 2 to 5 are repeated. In the eighth step, the first metal electrode 35 and the second metal electrode 36 are formed. A specific example of a method for forming the metal film is sputtering. As a method for forming the metal electrodes, a method is used in which the metal film is patterned by photolithography and then the unwanted parts are removed by etching. The first sensitive film 37 is formed directly on the first metal electrode 35. A sputtering method is used as a method for forming the first sensitive film 37. A specific example of a formation method is used in which the first sensitive film 37 is patterned by photolithography and then the unwanted parts are removed by the lift-off method. As the first sensitive film 37, a Ta2O5 film or a Si3N4 film can be used, but a Ta2O5 film, which can be formed at a relatively low temperature, is suitable.

[0025] As the ninth step, a second sensitive film 40 is formed. A specific example of a formation method is inkjet printing.

[0026] Here, we consider the formation of the conductive polymer film, which is the second sensitive film 40. It is desirable that the conductive polymer film be exposed to the gas as much as possible, and the structure of the present invention is suitable because it can expose the conductive polymer film over its entire surface. The potential change detected by the gas molecules is the partial pressure between the capacitance of the potential detection unit 1 itself and the capacitance of the conductive polymer film itself. In other words, in order to obtain a large voltage change, it is desirable to make the conductive polymer film a thin layer and increase the capacitance ratio.

[0027] Next, we consider the flatness of the surface of the interlayer insulating film 33. If the first metal electrode 35 and the second metal electrode 36 formed on the interlayer insulating film 33 are thick films, it becomes difficult to coat the metal electrodes with a thin conductive polymer film, which is undesirable. Therefore, it is desirable that the first metal electrode 35, the second metal electrode 36, and the first sensitive film 37 be thin. On the other hand, it is desirable that the metal electrode that applies a reference potential between the odor sensor elements has low resistance. Therefore, it is preferable to place a third metal electrode 38 in the interlayer insulating film and apply a reference potential to it. Even if the third metal electrode 38 is made thick, it will not have any effect when performing a planarization process such as CMP.

[0028] As described above, according to the present invention, the entire surface of the gas-responsive conductive polymer film is exposed to the atmosphere, the conductive polymer film can be made into a thin film, and a reference potential can be applied to the conductive polymer film by a low-resistance metal electrode, providing a structure suitable for an odor sensor element.

[0029] (Configuration and operation of the potential detection unit) Figure 6 shows the fundamental configuration of the CMOS extended gate type potential detection unit 1 that constitutes the odor sensor element of this embodiment. The potential detection unit 1 is configured on a silicon substrate 2, with the following areas partitioned in order from the first charge discharge (D1) area 4 in the direction of charge transfer: a sensing (Sen) area 6, a first floating diffusion (FD1) area 7, a charge transfer (TG) area 10, a second floating diffusion (FD2) area 8, a charge transfer control (AG) area 11, a charge storage (FD) area 9, a reset (RG) area 12, and a second charge discharge (D2) area 5.

[0030] The division of each region is defined by the difference in the conduction type of the silicon semiconductor on the surface of the silicon substrate 2. When electrons are used as the charge, the first charge discharge (D1) region 4, the first floating diffusion (FD1) region 7, the second floating diffusion (FD2) region 8, the charge accumulation (FD) region 9, and the second charge discharge (D2) region 5 are n+ type regions, while the sensing (Sen) region 6, the charge transfer (TG) region 10, the charge transfer control (AG) region 11, and the reset (RG) region 12 are p type regions.

[0031] A silicon oxide insulating film 3 is laminated on the surface of the silicon substrate 2. A sensing region defining electrode 13 is formed on the sensing (Sen) region 6. Furthermore, a silicon oxide layer 33 and a metal electrode 35 are laminated, and a tantalum pentoxide film is laminated on the surface of the metal electrode 35 as a first sensitive film 37. Potential changes on the surface of the first sensitive film 37 are transmitted to the sensing region defining electrode 13 via a conductive layer 34 embedded in the silicon oxide layer 33. A charge transfer electrode 14 is formed on the charge transfer (TG) region 10 via a silicon oxide insulating film 3, a charge transfer control electrode 15 is formed on the charge transfer control (AG) region 11 via a silicon oxide insulating film 3, and a reset electrode 16 is formed on the reset (RG) region 12 via a silicon oxide insulating film 3.

[0032] The first floating diffusion (FD1) region 7 is positioned in close proximity to the sensing (Sen) region 6 and accumulates a charge amount that reflects the potential of the sensing (Sen) region 6. The potential of the charge transfer (TG) region 10 is appropriately set to a sufficiently low voltage or sufficiently high voltage, such as the ground potential (GND) or the power supply voltage (VDD), and the charge transfer (TG) region 10 performs charge transfer between the first floating diffusion (FD1) region 7 and the second floating diffusion (FD2) region 8.

[0033] The charge transfer control (AG) region 11 is positioned in close proximity between the second floating diffusion (FD2) region 8 and the charge storage (FD) region 9, and a predetermined potential, either ground potential or between the power supply voltage and the potential of the sensing (Sen) region 6, is applied to it. The charge transfer control (AG) region 11 controls the amount of charge transferred from the second floating diffusion (FD2) region 8 to the charge storage (FD) region 9.

[0034] The reset (RG) region 12 is located in close proximity between the charge storage (FD) region 9 and the second charge discharge (D2) region 5, and is to which the ground potential or power supply voltage is applied. The reset (RG) region 12 controls the charge transfer from the charge storage (FD) region 9 to the second charge discharge (D2) region 5.

[0035] The operation of the potential detection unit 1 will be explained with reference to Figure 7. The operation of the potential detection unit 1 consists of four steps, as shown in Figures 7A to 7D. The potential height is indicated by the arrows, with lower arrows indicating higher potential. Here, we assume that the charge is an electron. In the following explanation, we will use electrons, which are negatively charged, as the charge.

[0036] The first charge discharge (D1) region 4 and the second charge discharge (D2) region 5 are subjected to a sufficiently high voltage throughout the entire step, such as the power supply voltage, to constantly discharge charge.

[0037] Figure 7A shows the initial state. When the potential of the reset (RG) region 12 is set to the power supply voltage, the potentials of the second charge discharge (D2) region 5 and the charge storage (FD) region 9 become equal, and the charge in the charge storage (FD) region 9 is discharged. However, an unspecified amount of charge remains in the first floating diffusion (FD1) region 7 and the second floating diffusion (FD2) region 8. At the end of this step, the potential of the reset (RG) region 12 must be set to ground potential, and charge movement between the charge storage (FD) region 9 and the second charge discharge (D2) region 5 must be blocked.

[0038] In Figure 7B, charge is injected into the second floating diffusion (FD2) region 8. The potentials of the charge transfer (TG) region 10 and the charge transfer control (AG) region 11 are temporarily set to ground potential, and charge is injected from the charge injection circuit 20. The minimum potential of the charge held in the second floating diffusion (FD2) region 8 is equal to ground potential. At the end of this step, charge injection from the charge injection circuit 20 is terminated.

[0039] In Figure 7C, the potential of the charge transfer (TG) region 10 is set as the power supply voltage, and a portion of the charge in the second floating diffusion (FD2) region 8 is transferred to the first charge discharge (D1) region 4 via the first floating diffusion (FD1) region 7. The minimum potential of the charge remaining in the second floating diffusion (FD2) region 8 is determined by the potential of the sensing (Sen) region 6.

[0040] In Figure 7D, the potential of the charge transfer (TG) region 10 is set to the ground potential, blocking the movement of charge between the first floating diffusion (FD1) region 7 and the second floating diffusion (FD2) region 8. In this step, the lowest potential of the charge held in the first floating diffusion (FD1) region 7 is the potential detected by the sensing (Sen) region 6, and the lowest potential of the charge held in the second floating diffusion (FD2) region 8 is held at the potential of the charge transfer control (AG) region 11. At this time, by making the potential of the charge transfer control (AG) region 11 higher than the potential of the sensing (Sen) region 6, an amount of charge corresponding to the potential difference is transferred to the charge storage (FD) region 9.

[0041] Since the amount of charge accumulated in the charge storage (FD) region 9 reflects the potential height in the sensing (Sen) region 6, the potential can be measured using a buffer circuit 21 or similar device with high input impedance.

[0042] Figure 2 shows a modified example of the structure shown in Figure 1, in which the interlayer insulating film is formed over five layers. The present invention is not limited by the number of layers of interlayer insulating film lamination. [Explanation of symbols]

[0043] 1. Potential detection unit 2. Silicon substrate 3. Insulating film (silicon oxide film) 4. First charge discharge (D1) region 5. Second charge discharge (D2) region 6. Sensing (Sen) area 7. First floating-diffusion (FD1) region 8. Second floating-diffusion (FD2) region 9 Charge storage (FD) region 10 Charge Transfer (TG) Region 11 Charge Transfer Control (AG) Region 12 Reset (RG) area 13 Sensing area defining electrode 14 Charge transfer electrodes 15 Charge transfer control electrodes 16 Reset electrode 20 Charge injection circuit 21 Output voltage detection circuit (buffer circuit) 30, 33 Interlayer insulating film (silicon oxide film) 31, 31A, 34A, 34B through hole 32, 32A metal film 35 First metal electrode 36. Second metal electrode 38. Third metal electrode 37. First sensitive film (tantalum pentoxide film) 40. Second sensitive film (conductive polymer film) 50 Sensing Unit 100 Odor Sensor Element Array

Claims

1. The device comprises a sensing unit on a Si substrate that changes the depth of a potential well according to the surface potential, an interlayer insulating film formed on the sensing unit, first and second metal electrodes formed on the interlayer insulating film, a third metal electrode formed within the interlayer insulating film, the first metal electrode electrically connected to the sensing unit via a first through-hole provided within the interlayer insulating film, the second metal electrode electrically connected to the third metal electrode via a second through-hole provided within the interlayer insulating film, and a first sensitive film formed directly above the first metal electrode, and the potential detection units are arranged in an array. A second sensitive film made of a conductive polymer is formed directly above the first sensitive film and the second metal electrode of the potential detection unit that constitutes the array. The first and second metal electrodes are arranged on the same plane, and the first and second metal electrodes and the third metal electrode are arranged on different planes. An odor sensor element array characterized in that the same potential (reference potential) is applied to the third metal electrode of each potential detection unit constituting the array.

2. The odor sensor element array according to claim 1, characterized in that the film thickness of the first and second metal electrodes is different from the film thickness of the third metal electrode, and the resistance value of the third metal electrode is lower than that of the second metal electrode.

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