CN106449861B - Optical sensor components and photoelectric conversion device - Google Patents

Optical sensor components and photoelectric conversion device Download PDF

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Publication number
CN106449861B
CN106449861B CN201610621913.4A CN201610621913A CN106449861B CN 106449861 B CN106449861 B CN 106449861B CN 201610621913 A CN201610621913 A CN 201610621913A CN 106449861 B CN106449861 B CN 106449861B
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oxide semiconductor
voltage
film
gate electrode
light
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CN106449861A (en
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竹知和重
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Tianma Microelectronics Co Ltd
Tianma Japan Ltd
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NLT Technologeies Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/112—Devices sensitive to infrared, visible or ultraviolet radiation characterised by field-effect operation, e.g. junction field-effect phototransistor
    • H01L31/113—Devices sensitive to infrared, visible or ultraviolet radiation characterised by field-effect operation, e.g. junction field-effect phototransistor being of the conductor-insulator-semiconductor type, e.g. metal-insulator-semiconductor field-effect transistor
    • H01L31/1136—Devices sensitive to infrared, visible or ultraviolet radiation characterised by field-effect operation, e.g. junction field-effect phototransistor being of the conductor-insulator-semiconductor type, e.g. metal-insulator-semiconductor field-effect transistor the device being a metal-insulator-semiconductor field-effect transistor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H01L27/14612—Pixel-elements with integrated switching, control, storage or amplification elements involving a transistor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14689—MOS based technologies
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
    • H01L29/7869—Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312

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Abstract

The present invention relates to optical sensor components and photoelectric conversion device.The upper side and lower side of oxide semiconductor active layer is arranged in two gate electrodes across insulating film respectively.In addition, the left and right side in oxide semiconductor active layer is equipped with the first read-out electrode and the second read-out electrode.In optical sensor components, in the case where applying voltage to each gate electrode, potential difference is generated between the first read-out electrode and the second read-out electrode, and the intensity of irradiation light is detected based on the electric current flowed through between read-out electrode.

Description

Photosensor element and photoelectric conversion device
Technical Field
The present invention relates to a photosensor element using an oxide semiconductor thin film element formed on a substrate, and more particularly to a photosensor element using a double-gate type oxide semiconductor thin film element including gate electrodes on both upper and lower sides of an oxide semiconductor thin film, and a photoelectric conversion device.
Background
A photoelectric conversion device combining a Thin Film Transistor (TFT) and a PIN diode (PIN-type diode) is being developed. As a PIN diode used as a photosensor, a PIN diode in which three layers of P-type amorphous silicon doped with boron (element symbol: B) as an impurity, high-resistance amorphous silicon not doped with an impurity, and N-type amorphous silicon doped with phosphorus (element symbol: P) as an impurity are stacked is used. The band gap energy of amorphous silicon constituting the PIN diode is about 1.6eV, which is sufficiently smaller than the light energy in the visible light region (wavelength: 400nm (3.2eV) to 700nm (1.8 eV)). Therefore, the photosensor using the PIN diode almost completely absorbs a light beam of a wavelength in the visible light region, and generates carriers. Therefore, the photosensor functions as an efficient photoelectric conversion element.
In recent years, high-performance photoelectric conversion devices in which an oxide semiconductor TFT having high electric field effect mobility and a PIN diode are combined have been actively developed. When an oxide semiconductor TFT is used as a switch or an amplification circuit, a light intensity distribution can be extracted after being converted into an electric signal with excellent reproducibility, and an occupied area of the amplification circuit can be reduced.
As described above, various techniques related to a photoelectric conversion apparatus that combines a switch using an oxide semiconductor TFT and a photosensor including a PIN diode or an amorphous silicon TFT are disclosed.
For example, WO2011/135920 (hereinafter, referred to as patent document 1) discloses a photoelectric conversion device in which a switch composed of a top gate oxide semiconductor TFT having a large on/off ratio and a photosensor composed of a bottom gate amorphous silicon TFT having a large light sensitivity are combined. In the technique disclosed in patent document 1, the gate lines and the drain lines can be connected without forming contact holes due to the combination of the top gate type and the bottom gate type, and thus the photolithography process can be reduced.
Further, japanese patent application laid-open No. 2010-153834 (hereinafter, referred to as patent document 2) discloses a high-performance photoelectric conversion device in which an oxide semiconductor TFT (constituting a switch and an amplifier circuit) having a large electric field effect mobility is combined with a PIN diode. In the technique disclosed in patent document 2, an oxide semiconductor TFT is used, whereby the light intensity distribution can be extracted after being converted into an electric signal having excellent reproducibility. In addition, the occupied area of the amplifier circuit can be reduced.
In addition, Japanese patent application laid-open No.2006 165530 (hereinafter, referred to as patent document 3) discloses the following technique: in order to impart visible light sensitivity to an oxide semiconductor, the oxide semiconductor is made to adsorb a pigment, and the oxide semiconductor is used in a photosensor or an X-ray sensor of a photodiode as a two-terminal element.
Further, japanese patent application laid-open No. h 5-235398 (hereinafter, referred to as patent document 4) discloses a structure in which a top gate electrode made of a transparent material is added to a photosensor made of an amorphous silicon TFT. In the technique disclosed in patent document 4, the dark current when the gate voltage is 0V is reduced by fixing the potential of the top gate electrode to a potential lower than the potential of the source electrode and moving the threshold voltage in the positive direction. Thereby achieving a large bright-dark current ratio.
In addition, in Seung-eon Ahn and "Oxide based Photosenor Thin film transistor for Interactive Display" of seven other people (The Proceedings of AM-FPD 2013, The Japan society of Applied Physics, 7 months 2013, pages 67 to 70) (hereinafter, referred to as non-patent document 1), a technology using an Oxide semiconductor TFT in both a switch and a Photosensor is disclosed. In non-patent document 1, a light shielding portion for shielding light is provided above the oxide semiconductor TFT for switching, but a light shielding portion is not provided above the oxide semiconductor TFT for photosensor. In the technique disclosed in non-patent document 1, in the case of irradiating a light beam of green to blue-violet colors having a wavelength equal to or less than 550nm, light sensing is performed using a phenomenon in which an off-current in an oxide semiconductor TFT for a light sensor is increased.
However, in the technique disclosed in patent document 1 or patent document 2, the switching TFT is an oxide semiconductor, and the photosensor is formed of an amorphous silicon TFT or a PIN diode, and thus a separate formation process is required. Therefore, there is a problem of high cost or reduction in yield. In addition, in particular, the electrical characteristics of silicon vary according to the ambient temperature, and therefore there is a problem that the performance of the photoelectric conversion device varies according to the ambient temperature. Even in the technique disclosed in patent document 4, since an amorphous silicon TFT is used, it is difficult to avoid a problem that the performance varies depending on the ambient temperature due to the physical properties of a specific material whose conductivity of silicon has a large temperature dependence.
In addition, in the technique disclosed in patent document 3, both the switch cell and the photosensor cell are formed using an oxide semiconductor. However, in order to impart visible light sensitivity to the oxide semiconductor of the sensor cell, it is made to adsorb a pigment, thereby imparting a light sensitivity function. When the organic material as described above is mixed, the organic material becomes a source of contamination in the oxide semiconductor TFT of the switching cell which originally does not require a pigment, and thus there is a problem that reliability or yield is lowered.
In the technique disclosed in non-patent document 1, the photosensor using the oxide semiconductor TFT has no sensitivity for red light having a wavelength equal to or greater than 600nm, and thus the photosensor cannot function as a photosensor that functions in the entire visible light region. In addition, the light sensitivity with respect to the light beam from blue to green is uniquely determined according to the characteristics of the oxide semiconductor TFT, and thus has a problem of being difficult to control from the outside.
Disclosure of Invention
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a photosensor element in which a light sensitivity function can be controlled by controlling voltages applied to an oxide semiconductor active layer via two gate electrodes, and which has light sensitivity in the entire visible light region, and a photoelectric conversion apparatus.
A light sensor element according to an aspect of the present invention includes: gate electrodes respectively disposed on the upper and lower sides of the oxide semiconductor active layer with an insulating film interposed therebetween; and a voltage applying unit that applies a first voltage to one gate electrode and a second voltage to the other gate electrode.
According to an aspect of the present invention, in a photosensor element formed using an oxide semiconductor, a light sensitivity function can be controlled, and light sensitivity can be realized in the entire visible light region.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.
Drawings
Fig. 1 is a cross-sectional view of a light sensor according to a first embodiment;
fig. 2 is a cross-sectional view of a photosensor according to example 1 of the first embodiment;
fig. 3A and 3B are diagrams showing a photosensor according to a second embodiment;
fig. 4A and 4B are diagrams showing a photosensor according to a third embodiment;
fig. 5A is a cross-sectional view of a photosensor according to example 4 of a third embodiment;
fig. 5B is a sectional view of a photosensor according to a modification of example 4 of the third embodiment;
fig. 5C is a sectional view of a photosensor according to a modification of example 4 of the third embodiment;
fig. 6 is a cross-sectional view of a photosensor according to example 5 of a third embodiment;
fig. 7A and 7B are sectional views of a photosensor according to example 6 of the third embodiment;
fig. 8 is a diagram showing a photoelectric conversion apparatus according to a fourth embodiment;
fig. 9 is a diagram showing a photoelectric conversion apparatus according to a fourth embodiment;
fig. 10 is a diagram showing a photoelectric conversion device of example 7 of a fourth embodiment;
fig. 11A to 11C are diagrams showing light sensing characteristics of a photosensor element used in a photoelectric conversion device of example 7 of the fourth embodiment;
fig. 12 is a diagram showing a photoelectric conversion device of example 7 of a fourth embodiment;
fig. 13 is a diagram showing a photoelectric conversion apparatus according to a fifth embodiment;
fig. 14A to 14C are diagrams showing light sensing characteristics of the light sensor element;
fig. 15A and 15B are diagrams showing light sensing characteristics of the light sensor element;
fig. 16 is a sectional view of the photoelectric conversion apparatus; and
fig. 17 is a sectional view of the photoelectric conversion device.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(first embodiment)
Fig. 1 is a sectional view of a photosensor according to a first embodiment. The photosensor according to the first embodiment is formed using an oxide semiconductor. In the optical sensor (optical sensor element) according to the first embodiment, the following structure is formed on the glass substrate 6. In this structure, a first insulating film (insulating film) 2 and a first conductive electrode (gate electrode) 3 formed of a material transparent to visible light are provided on one side of an oxide semiconductor film (oxide semiconductor active layer) 1, and a second insulating film (insulating film) 4 and a second conductive electrode (gate electrode) 5 are provided on the other side of the oxide semiconductor film 1. As an element constituting the oxide semiconductor film 1, at least indium or zinc is contained. In the example shown in fig. 1, the first conductive electrode 3 on the upper side of the oxide semiconductor film 1 is made of a transparent material. However, the second conductive electrode 5 on the lower side of the oxide semiconductor film 1 may be made of a transparent material, and both the first conductive electrode 3 and the second conductive electrode 5 may be made of a transparent material. That is, in order to make light incident on the oxide semiconductor film 1, at least one of the two conductive electrodes 3 and 5 may be formed of a transparent material.
In the structure shown in fig. 1, a first potential 7 is applied to the first conductive electrode 3 formed of a transparent material, a second potential 8 is applied to the second conductive electrode 5, and light 9 is irradiated from the first conductive electrode 3 side to the oxide semiconductor film 1 in a state where a potential gradient in the film thickness direction in the oxide semiconductor film 1 is increased. At this time, even in the case where the oxide semiconductor film 1 is irradiated with light having a wavelength of energy equal to or larger than the band gap energy (typically, 3.0eV to 3.5eV) of the oxide semiconductor film 1, and light having a wavelength of energy smaller than the band gap energy (for example, red light having a wavelength of 600nm to 800 nm), photo carriers contributing to conduction are generated in the oxide semiconductor film 1 due to a potential gradient in the oxide semiconductor film 1. In the related art disclosed in non-patent document 1, photo carriers cannot be generated in the oxide semiconductor film 1 by irradiating the oxide semiconductor film 1 with red light, but photo carriers can be generated in a photosensor using an oxide semiconductor as shown in fig. 1.
In general, it is known that an energy level due to oxygen vacancy exists in the band gap of an oxide semiconductor. In the case where the oxide semiconductor film 1 is irradiated with light having energy smaller than the band gap energy, electrons are excited to an energy level, and the electrons open a channel from the energy level to a conduction band and serve as carriers due to a potential gradient in the oxide semiconductor film 1. This is a physical mechanism that generates photo carriers in the oxide semiconductor film 1 even when light having a wavelength of energy smaller than the band gap energy is irradiated, and this mechanism is achieved for the first time by the present invention.
(example 1)
Hereinafter, example 1 relating to an optical sensor formed using the oxide semiconductor of the first embodiment will be described. As described above, the photosensor functions by reading out the photo carriers generated in the oxide semiconductor film 1 as a current signal or a voltage signal. Fig. 2 is a sectional view of a photosensor according to example 1 of the first embodiment. Fig. 2 shows a structure in which the first readout electrode 10 and the second readout electrode 11 are added to the left and right sides of the oxide semiconductor film 1, respectively, in the photosensor shown in fig. 1. The generated photo-carriers are read out as a current signal or a voltage signal using the electrodes 10 and 11. Based on this, the irradiation light intensity can be sensed.
In the photosensor of embodiment 1, as the oxide semiconductor film 1, an InGaZnO film including indium (symbol of element: In), gallium (symbol of element: GA), zinc (symbol of element: Zn), and oxygen (symbol of element: O) is used. In addition, a silicon oxide film is used as the first insulating film 2 and the second insulating film 4, an Indium Tin Oxide (ITO) film is used as the first conductive electrode 3, and an electrode formed of an aluminum alloy is used as the second conductive electrode 5. Therefore, in embodiment 1, a silicon oxide film as the first insulating film 2 is formed on the upper side of the InGaZnO film as the oxide semiconductor film 1, and an ITO film as the first conductive electrode 3 is further formed on the upper side of the silicon oxide film as the first insulating film 2. In addition, a silicon oxide film as the second insulating film 4 and a second conductive electrode 5 formed of an aluminum alloy are formed on the lower side of the InGaZnO film. As described above, the oxide semiconductor film 1 in which the first insulating film 2, the first conductive electrode 3, the second insulating film 4, and the second conductive electrode 5 are formed is formed on the upper surface of the glass substrate 6 with the second conductive electrode 5 on the lower side. Further, a readout electrode 10 and a readout electrode 11 formed of a molybdenum alloy are formed on the left end and the right end of the InGaZnO film (oxide semiconductor film 1), respectively. The photosensor of embodiment 1 includes a mechanism (voltage applying unit) that applies a first potential 7 to the first conductive electrode 3 and a second potential 8 to the second conductive electrode 5.
Next, a method for manufacturing the optical sensor of example 1 will be described.
First, an aluminum alloy film is formed on the glass substrate 6 according to a sputtering method and patterned into a predetermined shape to form the second conductive electrode 5. Then, according to the use of SiH4(silane, hydrosilicon) and N2The second insulating film 4 (silicon oxide film) is formed at a temperature of 350 ℃ by a plasma Chemical Vapor Deposition (CVD) method using a mixed gas of O (nitrous oxide) as a raw material. Next, an InGaZnO film was formed according to a sputtering method, and patterned into a desired island shape by etching to form the oxide semiconductor film 1. The composition ratio of the oxide semiconductor film 1, including In: ga: zn: o is 1: 1: 1: 4, it can be designed in an arbitrary manner based on etching processability and the like.
After the oxide semiconductor film 1 is formed, annealing treatment is performed at a temperature of 350 ℃ to 500 ℃ for 1 hour in the atmosphere. Thereafter, a molybdenum alloy film is formed according to a sputtering method and patterned into a predetermined shape to form the first and second sensing electrodes 10 and 11.
In addition, according to the use of SiH4And N2The first insulating film 2 (silicon oxide film) is formed at a temperature of 200 ℃ by a plasma CVD method using a mixed gas of O as a raw material. After forming the first insulating film 2, annealing treatment is performed at a temperature of 350 ℃ to 400 ℃. Thereby, the film quality of the silicon oxide film can be improved. After that, an ITO film is formed according to a sputtering method and patterned into a desired shape to form the first conductive electrode 3 formed of a transparent material.
In the photosensor configured as described above, the first potential 7 is applied to the first conductive electrode 3, and the second potential 8 is applied to the second conductive electrode 5, so that a potential difference is generated between the readout electrode 10 and the readout electrode 11. At this time, the photosensor functions by detecting the light intensity dependence of the current flowing between the readout electrode 10 and the readout electrode 11. In addition, the oxide semiconductor film 1 has the following characteristics. That is, in the case where the first potential 7 is applied to one gate electrode (the first conductive electrode 3) and the second potential 8 is applied to the other gate electrode (the second conductive electrode 5), the amount of visible light absorbed by the oxide semiconductor film 1 increases as compared with the case where no voltage is applied (the case where no voltage is applied).
In the optical sensor of embodiment 1, the conductive electrode (3 or 5) to which the lower potential of the first potential 7 and the second potential 8 is applied may be formed of a transparent material, and light 9 may be irradiated from the side of the conductive electrode (3 or 5) formed of a transparent material.
As the oxide semiconductor film 1, a ZnO film, an InZnO film, an InSnZnO film, an InAlZnO film, or the like may be used in addition to the InGaZnO film described above. The method of forming these films is not limited to the sputtering method, and a pulse laser film-forming method, a coating and baking method using a liquid material, and the like can be used.
As the first insulating film 2 and the second insulating film 4, a silicon nitride film, an aluminum oxide film, a tantalum oxide film, or a laminate in which a plurality of films are laminated can be used in addition to the silicon oxide film described above. The method for forming these films is not limited to the plasma CVD method, and a sputtering method, a vapor deposition method, an Atomic Layer Deposition (ALD) method, or the like may be used.
(second embodiment)
Fig. 3A and 3B are diagrams showing a photosensor according to a second embodiment. Fig. 3A is a sectional view of a photosensor according to the second embodiment, and fig. 3B is a graph showing a light sensing characteristic in a case where the photosensor according to the second embodiment is irradiated with light having a wavelength of 400nm ± 10 nm. The photosensor according to the second embodiment is formed using a double gate type oxide semiconductor TFT.
In the photosensor of the second embodiment, the protective insulating film 22 and the first insulating film (insulating film, first gate insulating film) 2 are formed on the upper side of the oxide semiconductor film (oxide semiconductor active layer) 1, and the transparent top gate electrode (gate electrode, first gate electrode) 12 that is transparent to visible light is further formed on the upper side of the first insulating film 2. Further, a second insulating film (insulating film, second gate insulating film) 4 and a bottom gate electrode (gate electrode, second gate electrode) 18 are formed below the oxide semiconductor film 1. The oxide semiconductor film 1 having the films and electrodes formed on the upper and lower sides thereof is formed on the glass substrate 6 with the bottom gate electrode 18 on the lower side. In addition, the source electrode 14 is formed in contact with the left end of the oxide semiconductor film 1 and the left end of the protective insulating film 22, and the drain electrode 16 is formed in contact with the right end of the oxide semiconductor film 1 and the right end of the protective insulating film 22. The material of the oxide semiconductor film 1 is the same as that of the first embodiment.
In the optical sensor shown in fig. 3A, blue light 20-1 (light having a wavelength of 400nm ± 10nm, for example) enters the oxide semiconductor film 1 from the transparent top gate electrode 12 side. At this time, the transparent top gate electrode potential 13 applied to the transparent top gate electrode 12 is made lower than the source electrode potential 15 applied to the source electrode 14. The drain electrode potential 17 applied to the drain electrode 16 is set higher than the source electrode potential 15, and the bottom gate electrode potential 19 applied to the bottom gate electrode 18 is set higher than the source electrode potential 15.
Fig. 3B shows characteristics (Vbg-Id characteristics) of the drain current (Id) with respect to the bottom gate electrode potential 19(Vbg) when the drain electrode potential 17(Vd) is set to 1V and the source electrode potential 15(Vs) is set to 0V. Fig. 3B shows Vbg-Id characteristics when the transparent top gate electrode potential 13(Vtg) is set as a parameter and Vtg is set to 0V, -10V, -20V. The broken line in fig. 3B indicates the characteristic in the state where light irradiation is not performed (dark state), and the solid line indicates the characteristic in the state where light having a wavelength of 400nm ± 10nm is irradiated (light irradiation state). Further, monochromatic light (a bandwidth of the center wavelength ± 10 nm) generated by a halogen light source (a halogen lamp unit AT-100 HG manufactured by SHIMADZU CORPORATION) and a spectroscope (a spectroscope SPG-120S manufactured by shimadzuporition CORPORATION) was irradiated from the transparent top gate electrode 12 side using an optical fiber.
As is clear from fig. 3B, the subthreshold current (current in a state of transition from off to on) in the characteristics in the light irradiation state is larger as compared with the characteristics in the dark state as the transparent top gate electrode potential 13(Vtg) is set lower than the source electrode potential 15(Vs is 0V). In addition, even in the operating state, the bottom gate electrode potential 19(Vbg) is higher than the source electrode potential 15 (Vs). Fig. 3B shows that the lower the transparent top gate electrode potential 13(Vtg) is set, the higher the light sensitivity of the dual-gate oxide semiconductor TFT. This is caused by the following phenomenon. Specifically, in the case where a first voltage is applied to one gate electrode and a second voltage is applied to the other gate electrode, the amount of visible light absorbed in the oxide semiconductor film 1 increases as compared with the case where no voltage is applied (the case where no voltage is applied). In the second embodiment, the transparent top gate electrode potential 13(Vtg) is set lower than the source electrode potential 15(Vs) as described above to amplify the light sensitivity of the oxide semiconductor TFT, thereby using the oxide semiconductor TFT as a photosensor. In addition, by appropriately controlling the value of the transparent top gate electrode potential 13(Vtg), the light sensitivity function can be controlled in an arbitrary manner. Therefore, in the photosensor element formed using an oxide semiconductor, the light sensitivity function can be controlled, and light sensitivity can be realized in the entire visible light region.
(example 2)
Hereinafter, example 2 relating to an optical sensor formed using the double-gate oxide semiconductor TFT according to the second embodiment will be described.
In the photosensor of example 2, an InGaZnO film is used as the oxide semiconductor film 1, as in the first embodiment. In addition, a silicon oxide film is used as the protective insulating film 22, the first insulating film 2, and the second insulating film 4, an ITO film is used as the transparent top gate electrode 12, and an electrode formed of an aluminum alloy is used as the bottom gate electrode 18. In addition, electrodes in which a molybdenum alloy film and an aluminum alloy film are laminated are used as the source electrode 14 and the drain electrode 16.
In embodiment 2, a silicon oxide film made of silicon oxide is formed as the protective insulating film 22 and the first insulating film 2 on the upper side of the InGaZnO film as the oxide semiconductor film 1, and an ITO film as the transparent top gate electrode 12 is further formed on the upper side of the first insulating film 2. In addition, a silicon oxide film as the second insulating film 4 and a bottom gate electrode 18 formed of an aluminum alloy are formed on the lower side of the InGaZnO film. The oxide semiconductor film 1 formed as described above is formed on the upper surface of the glass substrate 6 with the bottom gate electrode 18 on the lower side. Further, a source electrode 14 and a drain electrode 16 are formed on the left and right ends of the InGaZnO film (oxide semiconductor film 1). The source electrode 14 is formed in a region overlapping with a part of the left end of the protective insulating film 22 and in direct contact with the left end side of the oxide semiconductor film 1. The drain electrode 16 is formed in a region which overlaps with a part of the right end of the protective insulating film 22 and is in direct contact with the right end side of the oxide semiconductor film 1. The source electrode 14 and the drain electrode 16 have a structure in which a molybdenum alloy film and an aluminum alloy film are stacked, and are provided so that the molybdenum alloy film is in contact with the oxide semiconductor film 1.
The photosensor of example 2 includes a mechanism for applying a transparent top gate electrode potential 13 to the transparent top gate electrode 12, a source electrode potential 15 to the source electrode 14, a drain electrode potential 17 to the drain electrode 16, and a bottom gate electrode potential 19 to the bottom gate electrode 18. The photosensor of example 2 includes a mechanism (voltage applying means) for applying a transparent top gate electrode potential 13 lower than a source electrode potential 15 to the transparent top gate electrode 12, and a mechanism for applying a drain electrode potential 17 higher than the source electrode potential 15 to the drain electrode 16. The photosensor of example 2 includes a mechanism (voltage applying means) for applying a bottom gate electrode potential 19 higher than the source electrode potential 15 to the bottom gate electrode 18. The photosensor configured as above includes a mechanism for introducing blue light 20-1 into the oxide semiconductor film 1 from the transparent top gate electrode 12 side.
Next, a method for manufacturing the optical sensor of example 2 will be described.
First, an aluminum alloy film is formed on the glass substrate 6 according to a sputtering method and patterned into a predetermined shape to form the bottom gate electrode 18. Next, according to the reaction of Tetraethoxysilane (TEOS) and oxygen (O)2) The second insulating film 4 (silicon oxide film) having a film thickness of 400nm was formed at a temperature of 350 ℃ by the plasma CVD method using the mixed gas of (2) as a raw material. Next, an InGaZnO film having a film thickness of 50nm was formed according to a sputtering method, and the InGaZnO film was patterned into a desired island shape by etching to form the oxide semiconductor film 1. As the composition ratio of the oxide semiconductor film 1, In: ga: zn: o is 1: 1: 1: 4.
after the oxide semiconductor film 1 is formed, annealing treatment is performed at 400 ℃ for 1 hour in the atmosphere. Then, according to the use of SiH4And N2A plasma CVD method using a mixed gas of O as a raw material forms a silicon oxide film with a film thickness of 100nm at a temperature of 200 ℃, and patterns the silicon oxide film into a desired shape to form the protective insulating film 22. Next, a molybdenum alloy film and an aluminum alloy film are sequentially formed according to a sputtering method, and the molybdenum alloy film and the aluminum alloy film are patterned into a desired shapeA source electrode 14 and a drain electrode 16.
After that, according to the use of SiH4And N2The first insulating film 2 (silicon oxide film) having a film thickness of 300nm was formed by a plasma CVD method using a mixed gas of O as a raw material at a temperature of 200 ℃. After the first insulating film 2 is formed, annealing treatment may be performed at a temperature of 300 to 400 ℃ in order to improve the protective insulating film 22 and the first insulating film 2 formed at a temperature of 200 ℃. After that, an ITO film is formed according to a sputtering method, and the ITO film is patterned into a desired shape to form the transparent top gate electrode 12.
In the photosensor configured as described above, blue-violet light having a wavelength of 400nm ± 10nm is irradiated from the transparent top gate electrode 12 side to the oxide semiconductor film 1. The energy density of the irradiated light was 78. mu.W/cm2. At this time, the transparent top gate electrode potential 13(Vtg) is set to be lower than the source electrode potential 15(Vs), and the drain electrode potential 17(Vd) and the bottom gate electrode potential 19(Vbg) are set to be higher than the source electrode potential 15 (Vs).
As is clear from fig. 3B, when Vtg is-10V or-20V, that is, when Vtg < Vs (Vs ═ 0V), a positive potential is applied to the bottom gate electrode potential 19(Vbg), and the subthreshold current is further increased during the irradiation with blue-violet light, as compared with the dark state, and a higher light sensitivity is obtained. In addition, in the method of setting Vtg to-20V, the difference between the characteristics in the dark state and the characteristics in the light irradiated state becomes larger than when Vtg is set to-10V, which means that the light sensitivity can be controlled by changing the value of Vtg. Further, even when Vtg is set to 0V, slight light sensitivity is provided. However, since the energy of light having a wavelength of 400nm is approximately equal to the band gap energy of the InGaZnO film, direct excitation of electrons to the conduction band causes slight photosensitivity. As described above, one of the effects of the present invention is that the light sensitivity of the oxide semiconductor TFT can be controlled by changing the value of the transparent top gate electrode potential 13 (Vtg). The oxide semiconductor TFT can be used as a photosensor by amplifying the light sensitivity of the oxide semiconductor TFT using this effect. (third embodiment)
Fig. 4A and 4B are diagrams showing a photosensor according to a third embodiment. Fig. 4A is a cross-sectional view of a photosensor according to a third embodiment, and fig. 4B is a graph showing a light sensing characteristic in the case where light having a wavelength of 700nm ± 10nm is irradiated to the photosensor according to the third embodiment. The photosensor according to the third embodiment is formed by using a double gate type oxide semiconductor TFT.
The optical sensor of the third embodiment has the same configuration as the optical sensor of the second embodiment. In the photosensor of the third embodiment, red light 21 (for example, light having a wavelength of 700nm ± 10 nm) is incident on the oxide semiconductor film 1 from the transparent top gate electrode 12 side which is transparent to visible light. At this time, the transparent top gate electrode potential 13 is set to be lower than the source electrode potential 15, the drain electrode potential 17 is set to be higher than the source electrode potential 15, and the bottom gate electrode potential 19 is set to be higher than the source electrode potential 15.
Fig. 4B shows characteristics (Vbg-Id characteristics) of the drain current (Id) with respect to the bottom gate electrode potential 19(Vbg) when the drain electrode potential 17(Vd) is set to 1V and the source electrode potential 15(Vs) is set to 0V. Fig. 4B shows Vbg-Id characteristics when Vtg is set to 0V, -10V, -20V, with transparent top gate electrode potential 13(Vtg) set as a parameter. The broken line in fig. 4B indicates the characteristic in a state where light irradiation is not performed (dark state), and the solid line indicates the characteristic in a state where light irradiation with a wavelength of 700nm ± 10nm is performed (light irradiation state). Further, monochromatic light (a bandwidth of the center wavelength ± 10 nm) generated by a halogen light source (a halogen lamp unit AT-100 HG manufactured by SHIMADZU CORPORATION) and a spectroscope (a spectroscope SPG-120S manufactured by SHIMADZU CORPORATION) was irradiated from the transparent top gate electrode 12 side using an optical fiber.
As is clear from fig. 4B, when the transparent top gate electrode potential 13(Vtg) is set lower than the source electrode potential 15(Vs ═ 0V), particularly when Vtg is set to-20V, the subthreshold current in the characteristics in the light irradiation state becomes larger than the characteristics in the dark state. In addition, even in the operating state, the bottom gate electrode potential 19(Vbg) is set higher than the source electrode potential 15 (Vs). This represents the following phenomenon. Specifically, as in the case of irradiation with blue light described in the second embodiment, even when irradiation with red light is performed, the lower the transparent top gate electrode potential 13(Vtg) is set, the higher the light sensitivity of the oxide semiconductor TFT. Since typical band gap energies of oxide semiconductors are 3.0 to 3.5eV, the result in fig. 4B shows a light sensitivity function capable of applying light having a much smaller energy than the band gap energy of the oxide semiconductor to the oxide semiconductor TFT (the energy of light having a wavelength of 700nm is about 1.8 eV).
In the related art technology, there is no oxide semiconductor TFT having sensitivity to red light having energy smaller than the band gap energy. This is disclosed in non-patent document 1. In addition, data that The oxide semiconductor TFT does not have sensitivity to Light having a wavelength of 550nm or more is also disclosed in Masashi Tsukuku and another 8 people "Photo-Current Response and Negative Bias Stability Under Light Irradationis IGZO-TFT" (Proceedings of The 17th interactive Display workstations 2010(IDW2010), The Institute of Image Information and Television Engineers,2010, 12 rd month, volume 3, 1841-1844).
In the third embodiment, as described above, the transparent top gate electrode potential 13(Vtg) is set lower than the source electrode potential 15(Vs), and the oxide semiconductor TFT is given photosensitivity to light of energy lower than the band gap energy. Therefore, the oxide semiconductor TFT can be used as a photosensor over the entire visible light region.
(example 3)
Hereinafter, example 3 relating to an optical sensor formed using the dual-gate oxide semiconductor TFT of the third embodiment will be described.
In the photosensor of example 3, an InGaZnO film is used as the oxide semiconductor film 1, as in the second embodiment. In addition, a silicon oxide film is used as the protective insulating film 22 and the first insulating film 2, an ITO film is used as the transparent top gate electrode 12, and an electrode formed of an aluminum alloy is used as the bottom gate electrode 18. In embodiment 3, a laminated film in which a silicon oxide film and a silicon nitride film are laminated is used as the second insulating film 4, and electrodes in which three layers (including a titanium film, an aluminum alloy film, and a titanium film) are laminated are used as the source electrode 14 and the drain electrode 16.
In embodiment 3, a silicon oxide film made of silicon oxide is formed as the protective insulating film 22 and the first insulating film 2 on the upper side of the InGaZnO film as the oxide semiconductor film 1, and an ITO film as the transparent top gate electrode 12 is further formed on the upper side of the first insulating film 2. Further, a laminated film in which a silicon oxide film and a silicon nitride film are laminated as the second insulating film 4, and a bottom gate electrode 18 made of an aluminum alloy are formed below the InGaZnO film. The oxide semiconductor film 1 formed as described above is formed on the upper surface of the glass substrate 6 with the bottom gate electrode 18 facing downward. Further, a source electrode 14 and a drain electrode 16 are formed on the left and right ends of the InGaZnO film (oxide semiconductor film 1). The source electrode 14 is formed in a region overlapping with a part of the left end of the protective insulating film 22 and in direct contact with the left end side of the oxide semiconductor film 1. The drain electrode 16 is formed in a region which overlaps with a part of the right end of the protective insulating film 22 and is in direct contact with the right end side of the oxide semiconductor film 1. The source electrode 14 and the drain electrode 16 have a structure in which a titanium film, an aluminum alloy film, and a titanium film are stacked, and are arranged so that the titanium film on the lower layer side is in contact with the oxide semiconductor film 1.
The photosensor of example 3 includes a mechanism that applies a transparent top gate electrode potential 13 lower than a source electrode potential 15 to a transparent top gate electrode 12, and a mechanism that applies a drain electrode potential 17 higher than the source electrode potential 15 to a drain electrode 16. The photosensor of example 3 has a function of applying a bottom gate electrode potential 19 higher than the source electrode potential 15 to the bottom gate electrode 18. The photosensor configured as above includes a mechanism for introducing red light into the oxide semiconductor film 1 from the transparent top gate electrode 12 side.
Next, a method for manufacturing the optical sensor of example 3 will be explained.
First, an aluminum alloy film is formed on the glass substrate 6 according to a sputtering method and patterned into a predetermined shape to form the bottom gate electrode 18. Next, the second insulating film 4 was formed according to the plasma CVD method at a temperature of 350 ℃ in such a manner that the silicon nitride film and the silicon oxide film were formed in this order to have a total film thickness of 400 nm. Next, an InGaZnO film having a film thickness of 30nm was formed according to a sputtering method, and the InGaZnO film was patterned into a desired island shape by etching to form the oxide semiconductor film 1. As the composition ratio of the oxide semiconductor film 1, In: ga: zn: o is 1: 1: 1: 4.
after the oxide semiconductor film 1 is formed, annealing treatment is performed at 400 ℃ for 1 hour in the atmosphere. After that, according to the use of SiH4And N2A plasma CVD method using a mixed gas of O as a raw material forms a silicon oxide film with a film thickness of 100nm at a temperature of 200 ℃, and patterns the silicon oxide film into a desired shape to form the protective insulating film 22. Next, a three-layer film was formed by a sputtering method in the order of a titanium film, an aluminum alloy film, and a titanium film, and the three-layer film was patterned into a desired shape to form the source electrode 14 and the drain electrode 16.
After that, according to the use of SiH4And N2The first insulating film 2 (silicon oxide film) having a film thickness of 300nm was formed by a plasma CVD method using a mixed gas of O as a raw material at a temperature of 200 ℃. After the first insulating film 2 is formed, annealing treatment may be performed at a temperature of 300 to 400 ℃ in order to improve the protective insulating film 22 and the first insulating film 2 formed at a temperature of 200 ℃. After that, an ITO film is formed according to a sputtering method and patterned into a predetermined shape to form the transparent top gate electrode 12.
In the photosensor constituted as described above, the oxide semiconductor film 1 is irradiated from the transparent top gate electrode 12 side with light having a wavelength of 700nmRed light 21 of ± 10 nm. The energy density of the irradiated light was 78. mu.W/cm2. At this time, the transparent top gate electrode potential 13(Vtg) is set to be lower than the source electrode potential 15(Vs), and the drain electrode potential 17(Vd) and the bottom gate electrode potential 19(Vbg) are set to be higher than the source electrode potential 15 (Vs).
As can be seen from fig. 4B, when Vtg is set to 0V or-10V, the difference between the characteristics in the dark state and the characteristics in the light-irradiated state is small (i.e., the light sensitivity is very small). However, in the case where Vtg is set to-20V, when a positive potential is applied to the bottom gate electrode potential 19(Vbg), the subthreshold current during irradiation with red light is further increased compared to that in the dark state, and high light sensitivity is achieved.
As described above, the present invention is an important effect that cannot be achieved in the related art technology in that a red light (energy of light having a wavelength of 700nm is about 1.8eV) having a light sensitivity function can be applied to an oxide semiconductor TFT with energy sufficiently smaller than a band gap energy (3.0 to 3.5eV) of an oxide semiconductor. In addition, when the measurement as shown in fig. 4B was performed in the temperature range of 20 ℃ to 80 ℃, it was found that the current value during light irradiation hardly changed with respect to the temperature change. This small temperature dependence is caused by the unique physical properties of the oxide semiconductor and is an important effect of the present invention. By utilizing this effect, the light sensitivity of the oxide semiconductor TFT can be amplified, and the oxide semiconductor TFT can be used as a blue-violet to red visible light sensor.
(example 4)
Hereinafter, example 4 relating to the optical sensor of the third embodiment will be described. Further, embodiment 4 is a modification of embodiment 3, and is also a modification of embodiment 2 described in the second embodiment.
In example 2 of the second embodiment and example 3 of the third embodiment, a photosensor using an etching stopper type (channel protection type) oxide semiconductor TFT including a protective insulating film 22 is described. The structure of the oxide semiconductor TFT used in the photosensor is not limited to the etching stop type, and may be a so-called channel etching type not including the protective insulating film 22. Therefore, in embodiment 4, a photosensor formed using a channel-etched oxide semiconductor TFT will be described. Example 4 has the same structure as example 3 of the third embodiment and example 2 of the second embodiment, except that the protective insulating film 22 is not provided.
Fig. 5A is a cross-sectional view of a photosensor according to example 4 of the third embodiment.
In embodiment 4, as in embodiments 2 and 3, an InGaZnO film is used as the oxide semiconductor film 1, a silicon oxide film is used as the first insulating film 2, an ITO film is used as the transparent top gate electrode 12, and an electrode formed of an aluminum alloy is used as the bottom gate electrode 18. In addition, as in example 3, an electrode in which three layers (including a titanium film, an aluminum alloy film, and a titanium film) are stacked was used as the source electrode 14 and the drain electrode 16. In embodiment 4, a stacked film in which a silicon oxide film and an aluminum oxide film are stacked is used as the second insulating film 4.
In embodiment 4, a silicon oxide film as the first insulating film 2 is formed on the upper side of the InGaZnO film as the oxide semiconductor film 1, and an ITO film as the transparent top gate electrode 12 is further formed on the upper side of the first insulating film 2. Further, a stacked film in which a silicon oxide film and an aluminum oxide film are stacked and a bottom gate electrode 18 made of an aluminum alloy are formed as the second insulating film 4 on the lower side of the InGaZnO film. The oxide semiconductor film 1 formed as described above is formed on the upper surface of the glass substrate 6 with the bottom gate electrode 18 on the lower side. In addition, a source electrode 14 and a drain electrode 16 are formed in regions that are in contact with the left and right ends of the InGaZnO film (oxide semiconductor film 1), respectively.
The photosensor of example 4 includes a mechanism for applying a transparent top gate electrode potential 13 lower than a source electrode potential 15 to the transparent top gate electrode 12, and a mechanism for applying a drain electrode potential 17 higher than the source electrode potential 15 to the drain electrode 16. The photosensor of example 4 has a function of applying a bottom gate electrode potential 19 higher than the source electrode potential 15 to the bottom gate electrode 18. The photosensor configured as above includes a mechanism for introducing light 9 into the oxide semiconductor film 1 from the transparent top gate electrode 12 side.
Next, a method for manufacturing the optical sensor of example 4 will be described.
First, an aluminum alloy film is formed on the glass substrate 6 according to a sputtering method and patterned into a predetermined shape to form the bottom gate electrode 18. Next, the second insulating film 4 was formed according to the plasma CVD method at a temperature of 350 ℃ in such a manner that the silicon oxide film and the aluminum oxide film were formed in this order to have a total film thickness of 400 nm. Next, an InGaZnO film having a film thickness of 70nm was formed according to a sputtering method, and the InGaZnO film was patterned into a desired island shape by etching to form the oxide semiconductor film 1. As the composition ratio of the oxide semiconductor film 1, In: ga: zn: o is 1: 1: 1: 4.
after the oxide semiconductor film 1 is formed, annealing treatment is performed at 400 ℃ for 1 hour in the atmosphere. Next, a three-layer film was formed according to a sputtering method in the order of a titanium film, an aluminum alloy film, and a titanium film, and the three-layer film was patterned into a desired shape to form the source electrode 14 and the drain electrode 16. Then, according to the use of SiH4And N2The first insulating film 2 (silicon oxide film) having a film thickness of 300nm was formed at a temperature of 250 ℃ by a plasma CVD method using a mixed gas of O as a raw material. After the first insulating film 2 is formed, in order to improve the first insulating film 2 formed at a temperature of 250 ℃, annealing treatment may be performed at a temperature of 300 to 400 ℃. After that, an ITO film is formed according to a sputtering method, and the ITO film is patterned into a desired shape to form the transparent top gate electrode 12.
Even in the structure including no protective insulating film as shown in fig. 5A, when a potential lower than the source electrode potential 15 is applied as the transparent top gate electrode potential 13 to the transparent top gate electrode 12, the light sensitivity function as shown in fig. 3B and 4B can be applied to the oxide semiconductor TFT. In a bias state in which the transparent top gate electrode potential 13(Vtg) is set to be lower than the source electrode potential 15(Vs) and the drain electrode potential 17(Vd) and the bottom gate electrode potential 19(Vbg) are set to be higher than the source electrode potential 15(Vs), when light 9 is irradiated from the transparent top gate electrode 12 side to the oxide semiconductor film 1, the subthreshold current during irradiation with red light is further increased than in the dark state, and high light sensitivity is achieved.
Fig. 5B and 5C are sectional views of a photosensor according to a modification of example 4 of the third embodiment. In the example shown in fig. 5A, the light 9 is irradiated from the transparent top gate electrode 12 side, but as shown in fig. 5B, the light 9 may be irradiated from the opaque bottom gate electrode 18 side. In this case, since the bottom gate electrode 18 is opaque, the light 9 is blocked by the bottom gate electrode 18, but the light is introduced into the oxide semiconductor film 1 due to diffraction of the light on the edge portion (peripheral portion) of the bottom gate electrode 18. Due to the introduced light, electrons are excited inside the oxide semiconductor film 1. Therefore, the same light sensitivity as in the case of performing the irradiation of the light 9 from the transparent top gate electrode 12 side is obtained, thereby achieving the effect of the present invention.
In addition, as shown in fig. 5C, the transparent top gate electrode 12 on the upper side of the oxide semiconductor film 1 and the bottom gate electrode 18 on the lower side of the oxide semiconductor film 1 may be transparent electrodes. In this case, the light 9 can be irradiated from both the transparent top gate electrode 12 side and the bottom gate electrode 18. A structure in which the light 9 is irradiated from either side may be employed.
(example 5)
Hereinafter, example 5 relating to the optical sensor of the third embodiment will be described. Further, embodiment 5 is a modification of embodiments 3 and 4, and is also a modification of embodiment 2 described in the second embodiment.
In example 2 of the second embodiment and examples 3 and 4 of the third embodiment, a configuration in which a potential (transparent top gate electrode potential 13) lower than the source electrode potential 15 is applied to the transparent top gate electrode 12 is described. The transparent gate electrode may be provided not only on the top side (upper side) of the oxide semiconductor film 1 but also on the bottom side (lower side) of the oxide semiconductor film 1. Therefore, in example 5, a configuration in which a bottom gate electrode is formed of a transparent gate electrode and light 9 is irradiated from the bottom gate electrode side is described.
Fig. 6 is a sectional view of a photosensor according to example 5 of the third embodiment.
In embodiment 5, an InGaZnO film is used as the oxide semiconductor film 1, a silicon oxide film is used as the first insulating film 2, a laminated film in which a silicon oxide film and a silicon nitride film are laminated is used as the second insulating film 4, and electrodes in which three layers (including a titanium film, an aluminum alloy film, and a titanium film) are laminated are used as the source electrode 14 and the drain electrode 16. In example 5, an aluminum-neodymium alloy film was used as the top gate electrode 21, and an InZnO film was used as the transparent bottom gate electrode 20.
In embodiment 5, a silicon oxide film as the first insulating film 2 is formed on the upper side of the InGaZnO film as the oxide semiconductor film 1, and an aluminum-neodymium alloy film as the top gate electrode 21 is further formed on the upper side of the first insulating film 2. Further, a laminated film in which a silicon oxide film and a silicon nitride film are laminated as the second insulating film 4, and an InZnO film as the transparent bottom gate electrode 20 are formed on the lower side of the InGaZnO film. The oxide semiconductor film 1 formed as described above is formed on the upper surface of the glass substrate 6 with the transparent bottom gate electrode 20 set to the lower side. In addition, a source electrode 14 and a drain electrode 16 are formed on the left and right ends of the InGaZnO film (oxide semiconductor film 1).
The photosensor of example 5 includes a mechanism that applies a transparent bottom gate electrode potential 22-2 lower than the source electrode potential 15 to the transparent bottom gate electrode 20, and a mechanism that applies a drain electrode potential 17 higher than the source electrode potential 15 to the drain electrode 16. The photosensor of example 5 has a function of applying a top gate electrode potential 23 higher than the source electrode potential 15 to the top gate electrode 21. The photosensor configured as described above includes a mechanism for introducing light 9 into the oxide semiconductor film 1 from the transparent bottom gate electrode 20 side.
Next, a method for manufacturing the optical sensor of example 5 will be described.
First, an InZnO film is formed on the glass substrate 6 according to a sputtering method, and the InZnO film is patterned into a predetermined shape to form the transparent bottom gate electrode 20. Next, the second insulating film 4 was formed according to the plasma CVD method at a temperature of 350 ℃ in such a manner that the silicon nitride film and the silicon oxide film were formed in this order to have a total film thickness of 400 nm. Next, an InGaZnO film having a film thickness of 70nm was formed according to a sputtering method, and the InGaZnO film was patterned into a desired island shape by etching to form the oxide semiconductor film 1. As the composition ratio of the oxide semiconductor film 1, In: ga: zn: o is 1: 1: 1: 4.
after the oxide semiconductor film 1 is formed, annealing treatment is performed at 400 ℃ for 1 hour in the atmosphere. Next, a three-layer film was formed by a sputtering method in the order of a titanium film, an aluminum alloy film, and a titanium film, and the three-layer film was patterned into a desired shape by plasma etching to form the source electrode 14 and the drain electrode 16. After that, according to the use of SiH4And N2The first insulating film 2 (silicon oxide film) having a film thickness of 300nm was formed at a temperature of 250 ℃ by a plasma CVD method using a mixed gas of O as a raw material. After the first insulating film 2 is formed, in order to improve the first insulating film 2 formed at a temperature of 250 ℃, annealing treatment may be performed at a temperature of 300 ℃ to 400 ℃. Next, an aluminum-neodymium alloy film is formed according to a sputtering method, and the aluminum-neodymium alloy film is patterned into a desired shape to form the top gate electrode 21.
As described above, when the transparent conductive material is used for the bottom gate electrode 20, the light 9 can be irradiated from the glass substrate 6 side. In this case, when a transparent bottom gate electrode potential 22-2 lower than the source electrode potential 15 is applied to the transparent bottom gate electrode 20 and a top gate electrode potential 23 higher than the source electrode potential 15 is applied to the top gate electrode 21, the light sensitivity function as shown in fig. 3B or fig. 4B can be realized.
In embodiments 4 and 5, a manufacturing method in which the source electrode 14 and the drain electrode 16 are formed after the oxide semiconductor film 1 is formed is described. However, a method of forming the oxide semiconductor film 1 after forming the source electrode 14 and the drain electrode 16 on the second insulating film 4 may be employed.
(example 6)
Hereinafter, example 6 relating to the optical sensor of the third embodiment will be described. Further, example 6 is a modification of example 3 to example 5 of the second embodiment and the third embodiment.
The structure in which the etching stopper type (channel protection type) oxide semiconductor TFT is used for the optical sensor in example 2 of the second embodiment and example 3 of the third embodiment, and the channel etching type oxide semiconductor TFT is used for the optical sensor in example 4 and example 5 is described. The structure of the oxide semiconductor TFT used for the photosensor is not limited thereto, and the following self-aligned structure may be employed. In embodiment 6, a photosensor using a self-aligned oxide semiconductor TFT will be described.
Fig. 7A and 7B are sectional views of a photosensor according to example 6 of the third embodiment.
In embodiment 6, as shown in fig. 7A, a silicon oxide film as a first insulating film 2 is formed on the upper side of an InGaZnO film as an oxide semiconductor film 1, and an aluminum alloy film as a top gate electrode 21 is further formed on the upper side of the first insulating film 2. In addition, the first insulating film 2 (silicon oxide film) and the top gate electrode 21 are formed in the same shape in a self-aligned manner. Further, a laminated film in which a silicon oxide film and a silicon nitride film are laminated as the second insulating film 4, and an ITO film as the transparent bottom gate electrode 20 are formed on the lower side of the InGaZnO film. The oxide semiconductor film 1 formed as described above is formed on the upper surface of the glass substrate 6 with the transparent bottom gate electrode 20 set to the lower side. Further, a source electrode 14 and a drain electrode 16 are formed on the left end side and the right end side of the InGaZnO film (oxide semiconductor film 1). The source electrode 14 and the drain electrode 16 are formed using an electrode in which three layers including a titanium film, an aluminum alloy film, and a titanium film are stacked, and are arranged so that the lower titanium film is in contact with the oxide semiconductor film 1.
The photosensor of embodiment 6 includes a mechanism that applies a transparent bottom gate electrode potential 22-2 lower than the source electrode potential 15 to the transparent bottom gate electrode 20, and a mechanism that applies a drain electrode potential 17 higher than the source electrode potential 15 to the drain electrode 16. The photosensor of example 6 has a function of applying a top gate electrode potential 23 higher than the source electrode potential 15 to the top gate electrode 21. The photosensor configured as above includes a mechanism for introducing light 9 into the oxide semiconductor film 1 from the transparent bottom gate electrode 20 side.
Next, a method for manufacturing the optical sensor of example 6 will be described.
First, an ITO film is formed on the glass substrate 6 according to a sputtering method and patterned into a predetermined shape to form the transparent bottom gate electrode 20. Next, the second insulating film 4 was formed according to the plasma CVD method at a temperature of 350 ℃ in such a manner that the silicon nitride film and the silicon oxide film were formed in this order to have a total film thickness of 400 nm. Next, an InGaZnO film having a film thickness of 70nm was formed according to a sputtering method, and the InGaZnO film was patterned into a desired island shape by etching to form the oxide semiconductor film 1.
After the oxide semiconductor film 1 is formed, annealing treatment is performed at 450 ℃ for 1 hour. Then, according to the use of SiH4And N2The first insulating film 2 (silicon) having a film thickness of 300nm was formed at a temperature of 250 ℃ by plasma CVD using a mixed gas of O as a raw materialOxide film). After the first insulating film 2 is formed, in order to improve the first insulating film 2 formed at a temperature of 250 ℃, annealing treatment may be performed at a temperature of 300 ℃ to 400 ℃. After that, an aluminum alloy film is formed according to a sputtering method, and the aluminum alloy film and a silicon oxide film (first insulating film 2) are patterned into a desired shape to form a laminated film of the top gate electrode 21 and the first insulating film 2. When the first insulating film 2 is etched, in the exposed portion of the surface of the InGaZnO film, the oxygen vacancy density is increased by a chemical reaction with the etching gas or the etchant, and thus the resistivity is decreased. Thus, the portion serves as a source/drain region.
Then, according to the use of SiH4And N2The interlayer film 23-2 (silicon oxide film) having a film thickness of 300nm was formed at a temperature of 250 ℃ by a plasma CVD method using a mixed gas of O as a raw material. A contact hole is formed at a desired position of the interlayer film 23-2. Next, a three-layer film was formed in the contact hole according to a sputtering method in the order of a titanium film, an aluminum alloy film, and a titanium film to form the source electrode 14 and the drain electrode 16. Further, as the passivation film 23-3, a silicon nitride film having a film thickness of 200nm was formed at a temperature of 250 ℃ by a plasma CVD method.
Even in embodiment 6, as in embodiments 1 to 5, when the transparent bottom gate electrode 22-2 lower than the source electrode potential 15 is applied to the transparent bottom gate electrode 20 and the top gate electrode potential 23 higher than the source electrode potential 15 is applied to the top gate electrode 21, the light 9 irradiated from the transparent bottom gate electrode 20 side can be sensed.
Further, a photosensor having a structure in which a transparent electrode (transparent top gate electrode 12) is arranged on the upper side of the oxide semiconductor film 1 as shown in fig. 7B can be produced in the same manner, and detailed description thereof will not be repeated.
The structure of the thin film transistor is not limited to the structure shown in fig. 3A to 7B, and a structure in which the bottom gate electrode 18 is added to a planar structure including the transparent top gate electrode 12 may be employed. As the structure of the thin film transistor, any structure can be applied as long as an insulating film and a gate electrode are provided on both sides of the oxide semiconductor film 1 in the vertical direction, at least one gate electrode is formed of a transparent conductive material, and a source electrode and a drain electrode are provided on both sides of the oxide semiconductor film 1 in the horizontal direction.
(fourth embodiment)
Fig. 8 and 9 are diagrams showing a photoelectric conversion device according to a fourth embodiment. Fig. 8 shows a photoelectric conversion device of one pixel, the upper side of fig. 8 shows an equivalent circuit, and the lower side of fig. 8 shows a cross-sectional view. Fig. 9 shows a photoelectric conversion apparatus in which a plurality of pixels constituted by photosensor elements (photoelectric conversion elements) 24 and switching elements 25 as shown in fig. 8 are arranged in a two-dimensional matrix by using switching wirings and signal readout wirings. In the photoelectric conversion device according to the fourth embodiment, each of the photosensor element 24 and the switching element 25 is formed of an oxide semiconductor TFT, and the photosensor element 24 is formed of a double-gate oxide semiconductor TFT.
In fig. 8, the oxide semiconductor TFT serving as the photosensor element 24 is provided with a transparent top gate electrode 12 transparent to visible light on its light-receiving surface side. The drain electrode 16 of the oxide semiconductor TFT for the photosensor element 24 is connected to a predetermined power supply 26, and the source electrode 14 is connected to the source electrode of the oxide semiconductor TFT serving as the switching element 25. In the oxide semiconductor TFT for the photosensor element 24, when irradiation of light 9 is performed from the transparent top gate electrode 12 side, a transparent top gate electrode potential 13(Vtg) lower than the source electrode potential 15(Vs) is applied to the transparent top gate electrode 12 to provide a photosensitivity function. This structure utilizes the phenomenon that: when Vtg lower than Vs is applied to the transparent top gate electrode 12 and a positive voltage is applied to the bottom gate electrode 18 on the other side, the amount of visible light absorbed in the oxide semiconductor film 1 (oxide semiconductor active layer) further increases as compared to when no voltage is applied. At this time, the switching element 25 is also irradiated with the light 9, but the oxide semiconductor TFT for the switching element 25 is not provided with the transparent top gate electrode 12. Therefore, the oxide semiconductor TFT for the switching element 25 does not have a photosensitivity function and is used as a simple switch without photosensitivity. This structure is different from non-patent document 1 in that a light shielding layer is provided above an oxide semiconductor TFT for a switching element.
In the refresh period of the photoelectric conversion device, the oxide semiconductor TFT for the switching element 25 is turned on, and a bias (bias) for making both Vbg- | Vtg | and Vs- | Vtg | negative is applied to the oxide semiconductor TFT for the photosensor element 24, so that the oxide semiconductor film 1 is consumed. Then, the oxide semiconductor TFT for the photosensor element 24 is charged. Then, when the oxide semiconductor TFT for the switching element 25 is turned off and the oxide semiconductor TFT for the photosensor element 24 is irradiated with light 9, the amount of charge decreases according to the amount of light irradiation. The oxide semiconductor TFT for the switching element 25 is turned on again, and the charge variation amount is detected by the integrator 27 for sensing.
As described above, the structure of reading out the signal charges generated due to light irradiation using a current is the same as that of the related art. However, when the oxide semiconductor TFT including the transparent top gate electrode 12 as the photosensor element 24 is used as in the present invention, the following effects are obtained. First, the off-current of the oxide semiconductor TFT is much smaller than that of the silicon-based TFT in the related art. Therefore, in the switching element 25 and the photosensor element 24, the off current in the dark state is much lower, and therefore, a high-performance photoelectric conversion device having a relatively high signal-to-noise (S/N) ratio can be manufactured as compared with the related art. In addition, the temperature dependence of the electrical characteristics of the oxide semiconductor TFT is much smaller than that of the silicon-based TFT of the related art. That is, even when the temperature of the surrounding environment changes, the electrical characteristics of the oxide semiconductor TFT hardly change. Therefore, a photoelectric conversion device that does not depend on changes in the ambient environmental temperature even in various temperature environments and can achieve stable performance can be manufactured. From the viewpoint of manufacturing, the oxide semiconductor TFT for the switching element 25 and the oxide semiconductor TFT for the photosensor element 24 can be manufactured in the same process, and only the process of adding the transparent top gate electrode 12 to the oxide semiconductor TFT for the photosensor element 24 is added. Therefore, the manufacturing process can be further shortened as compared with the related art, thereby achieving cost reduction and high productivity.
Fig. 9 shows an example of the structure of a photoelectric conversion device having 3 × 3 pixels. In the photoelectric conversion apparatus shown in fig. 9, the gate signal G1 of the shift register circuit is turned on, and the oxide semiconductor TFTs (S11 to S13) for the switching elements 25 in the 1 st row from the upper side are turned on. A desired bottom gate electrode potential 19(Vbg) and transparent top gate electrode potential 13(Vtg) are applied to each of the oxide semiconductor TFTs (P11 to P13) for the photosensor element 24, thereby giving a light sensitivity function to the oxide semiconductor TFTs (P11 to P13) and performing photocharge charging. The photocharges of the oxide semiconductor TFTs (P11 to P13) for the photosensor element 24 are output to the signal wiring, and the photocharges of the oxide semiconductor TFTs (P11 to P13) for the photosensor element 24 are read out in time series from the integrator 27 by sequentially turning on the transfer switches M1 to M3. The above-described processing is repeated in order of the oxide semiconductor TFT for the switching element 25 (S21 to S23) and the oxide semiconductor TFT for the photosensor element 24 (P21 to P23) in the 2 nd row from the upper side, the oxide semiconductor TFT for the switching element 25 (S31 to S33) and the oxide semiconductor TFT for the photosensor element 24 (P31 to P33) in the 3 rd row from the upper side, thereby two-dimensionally reading out the photocharge of each pixel. Thus, the photoelectric conversion device functions as a two-dimensional photoelectric conversion device.
(example 7)
Hereinafter, example 7 relating to the photoelectric conversion device of the fourth embodiment will be described.
Fig. 10 is a diagram showing a photoelectric conversion device of example 7 of the fourth embodiment. In fig. 10, the upper side shows an equivalent circuit of the photoelectric conversion device corresponding to one pixel, and the lower side shows a cross-sectional view thereof. Fig. 11A to 11C are diagrams showing light sensing characteristics of a photosensor element used in a photoelectric conversion device of example 7 of the fourth embodiment. Further, FIG. 11A shows the light sensing characteristics when light having a wavelength of 400 nm. + -. 10nm is irradiated, and FIG. 11B shows the irradiation wavelengthThe light sensing characteristics when the wavelength was 500 nm. + -.10 nm, and the light sensing characteristics when the wavelength was 700 nm. + -.10 nm. Note that solid lines in fig. 11A to 11C show characteristics in a state where light irradiation is not performed (a dark state), and broken lines in fig. 11A to 11C show characteristics in a state where light irradiation with different intensities (energy densities) is performed. In addition, regarding the intensity of the irradiated light, in FIG. 11A, the small broken line is 10.98. mu.W/cm2The middle dotted line is 30.06. mu.W/cm2The large dotted line is 78.03. mu.W/cm2. In FIG. 11B, the small broken line is 58.67. mu.W/cm2The dotted line is 104.34 μ W/cm2The large dotted line is 175.14 μ W/cm2. In FIG. 11C, the small broken line is 78.03. mu.W/cm2The dotted line is 154.91 μ W/cm2The large dotted line is 241.04 μ W/cm2。
As is apparent from fig. 11A to 11C, the light sensitivity of the photosensor element 24 (oxide semiconductor TFT) can be controlled by changing the value of the transparent top gate electrode potential 13(Vtg) for each wavelength. For example, to make the light sensitivity uniform at each wavelength, Vtg can be set to-10V for the most sensitive blue, and-20V for green and red. As described above, in the present invention, the value of the transparent top gate electrode potential 13(Vtg) can be controlled according to the sensitivity with respect to light of each wavelength. In contrast, in the photosensor constituted by the silicon PIN diode of the related art, the light sensitivity with respect to each wavelength is uniquely determined based on the diode characteristics, and thus it is difficult to control the sensitivity to each color.
As shown in fig. 10, the photoelectric conversion device has a structure in which filters for three primary colors are provided on the light receiving surface side of the external light 28 (only filters for red and green are shown in fig. 10). In this case, by independently controlling the voltage (Vtg1) applied to the transparent top gate electrode 12 of the oxide semiconductor TFT for the photosensor element 24 existing at the position irradiated with the green light 20-2 transmitted through the green filter 29 and the voltage (Vtg2) applied to the transparent top gate electrode 12 of the oxide semiconductor TFT for the photosensor element 24 existing at the position irradiated with the red light 21 transmitted through the red filter 30, it is possible to make the sensitivities to the lights of the respective colors uniform.
For example, in consideration of the characteristics in fig. 11A to 11C, the transparent top gate electrode potential (Vtg2) of the oxide semiconductor TFT for the photosensor element 24 existing at the position of the red filter 30 can be set smaller than the transparent top gate electrode potential (Vtg) of the oxide semiconductor TFT for the photosensor element 24 existing at the position of the blue filter. Thus, by further amplifying the sensitivity to red light, a balance between the sensitivity to blue light and the sensitivity to red light can be maintained.
Fig. 12 is a diagram showing a photoelectric conversion device of example 7 of the fourth embodiment. Fig. 12 shows a photoelectric conversion device in which blue pixels, green pixels, and red pixels are arranged. In the photoelectric conversion device shown in fig. 12, a blue filter, a green filter, and a red filter are provided in a pixel including the switching element 25 and the photosensor element 24. As shown in fig. 11A to 11C, the light sensitivity of the photosensor element 24 depends on the wavelength of light and the values of the bottom gate electrode potential 19(Vbg) and the transparent top gate electrode potential 13(Vtg) in the oxide semiconductor TFT for the photosensor element 24. Therefore, by changing the values of the bottom gate electrode potential 19(Vbg) and the transparent top gate electrode potential 13(Vtg) in accordance with the wavelength band of light to be sensed, it is possible to control the light sensitivity in each wavelength band. Therefore, the photoelectric conversion device of embodiment 7 includes a mechanism (voltage control unit) which controls the voltages (Vbg and Vtg) respectively applied to the two gate electrodes in the oxide semiconductor TFT for the photosensor element 24 in accordance with the wavelength band of light to be sensed.
Referring to FIGS. 11A to 11C, the method of using 78.03. mu.W/cm2When the blue light (light having a wavelength of 400 nm) of energy density (intensity) of (1) is irradiated, the irradiation is carried out so as to obtain a wavelength of 1X 10-8The photocurrent (Id) of a requires a bias voltage of Vtg-20V and Vbg + 12V. On the other hand, the resin composition is used at 78.03. mu.W/cm2When red light (light having a wavelength of 700 nm) having an energy density (intensity) of (1) is irradiated, the irradiation is carried out so as to obtain a wavelength of 1X 10-8A ofThe photocurrent (Id) requires a bias voltage of Vtg-20V and Vbg + 15V. That is, in order to obtain the same photocurrent at the same irradiation intensity when the wavelengths of light are different, the difference between Vtg and Vbg is increased for light having a longer wavelength (in this example, the difference between Vtg and Vbg is 32V in the case of blue light, and 35V in the case of red light). As described above, when an operation method is used in which the difference between Vtg and Vbg is set large as the wavelength of light to be sensed becomes longer, it is possible to maintain a balance of sensitivities to light of various wavelengths.
(fifth embodiment)
Fig. 13 is a diagram showing a photoelectric conversion device according to a fifth embodiment. Fig. 13 shows an equivalent circuit of the photoelectric conversion device of one pixel constituted by the photosensor element 24 and the switching element 25 shown in fig. 10. A two-dimensional photoelectric conversion device can be configured by arranging a plurality of pixels as shown in fig. 13 in a two-dimensional matrix using switching wirings and signal readout wirings. In the photoelectric conversion device according to the fifth embodiment, each of the photosensor element 24 and the switching element 25 is formed of an oxide semiconductor TFT, and the photosensor element 24 is formed of a double-gate oxide semiconductor TFT.
In fig. 13, the oxide semiconductor TFT serving as the photosensor element 24 is provided with a transparent gate electrode 36 on the light receiving surface side. The oxide semiconductor TFT for the photosensor element 24 has a source electrode grounded and a drain electrode connected to a source electrode of the oxide semiconductor TFT serving as the switching element 25. In the oxide semiconductor TFT for the photosensor element 24, when light is irradiated from the transparent gate electrode 36 side, a transparent gate electrode potential Vtg lower than a source electrode potential Vs (in fig. 13, ground potential) is applied to the transparent gate electrode 36, thereby realizing a photosensitivity function. A bias voltage that makes Vbg- | Vtg | and Vs- | Vtg | both become negative is applied to the oxide semiconductor TFT for the photosensor element 24 to consume the oxide semiconductor film 1, and a photosensitivity function is provided to the oxide semiconductor TFT for the photosensor element 24, and then the oxide semiconductor TFT is charged. At this time, the switching element 25 is also irradiated with light, but the oxide semiconductor TFT for the switching element 25 is not provided with a top gate electrode. Therefore, the oxide semiconductor TFT for the switching element 25 does not have a photosensitivity function and is used as a simple switch without photosensitivity.
As described above, the potential of the floating node 31 of the source terminal of the oxide semiconductor TFT for the switching element 25 is changed due to the signal charge converted into electricity at the oxide semiconductor TFT for the photosensor element 24 by the light irradiation. With this potential change, the potential of the gate electrode of the amplifying TFT32 connected to the floating node 31 changes, and the potential of the drain node of the readout TFT33 connected to the amplifying TFT32 changes. At this time, when a selection signal is input to the gate electrode of the readout TFT33 via the selection signal input line 34, a potential difference due to signal charges generated in the photosensor element 24 is output to the readout line 35. Thus, sensing is performed.
As described above, the structure of reading out the signal charges due to light irradiation by the potential difference is the same as that of the related art. However, as in the present invention, when an oxide semiconductor TFT including the transparent gate electrode 36 is used as the photosensor element 24, the following effects are obtained. First, the off-current of the oxide semiconductor TFT is much smaller compared to the related art silicon-based TFT. Therefore, in the switching element 25 and the photosensor element 24, the off current in the dark state becomes much lower. Further, since the signal is read based on the potential difference, a high-performance photoelectric conversion device having a much higher signal-to-noise (S/N) ratio can be manufactured as compared with the related art. In addition, the temperature dependence of the electrical characteristics of the oxide semiconductor TFT is much smaller than that of the silicon-based TFT of the related art. That is, even when the temperature of the surrounding environment changes, the electrical characteristics of the oxide semiconductor TFT hardly change. Therefore, it is possible to manufacture a photoelectric conversion device in which a potential difference signal does not depend on a change in ambient temperature even in various temperature environments and stable output performance can be achieved. In addition, needless to say, the amplifying TFT32 and the reading TFT33 are also realized by oxide semiconductor TFTs.
Means for further improving the light sensitivity of the photosensor element 24 and further improving the performance of the photoelectric conversion device will be described below.
In fig. 8, the oxide semiconductor film 1 of the oxide semiconductor TFT serving as the photosensor element 24 and the oxide semiconductor film of the oxide semiconductor TFT serving as the switching element 25 are formed in the same layer. Therefore, the film thicknesses of the oxide semiconductor films are the same. The present inventors have found that, in order to further improve the light sensitivity of the photosensor element 24, it is effective to increase the film thickness of the oxide semiconductor film 1 of the oxide semiconductor TFT used as the photosensor element 24.
Fig. 14A to 14C are diagrams showing light sensing characteristics of the light sensor element 24. Fig. 14A shows the photo-sensing characteristics of the photo-sensor element 24 using an InGaZnO film with a film thickness of 35nm as the oxide semiconductor film 1, fig. 14B shows the photo-sensing characteristics of the photo-sensor element 24 using an InGaZnO film with a film thickness of 70nm as the oxide semiconductor film 1, and fig. 14C shows the photo-sensing characteristics of the photo-sensor element 24 using an InGaZnO film with a film thickness of 100nm as the oxide semiconductor film 1. Accordingly, fig. 14A to 14C show the oxide semiconductor film thickness dependence of the light sensing characteristics of the light sensor element 24. Specifically, fig. 14A to 14C show characteristics (Vbg-Id characteristics) of the drain current (Id) with respect to the bottom gate electrode potential 19(Vbg) when the drain electrode potential 17(Vd) is set to 1V and the source electrode potential 15(Vs) is set to 0V. Note that the solid line in fig. 14A to 14C indicates the Vbg-Id characteristic when the transparent top gate electrode potential 13(Vtg) is set to 0V, and the broken lines in fig. 14A to 14C indicate the Vbg-Id characteristic in the dark state and the blue light irradiation state when the transparent top gate electrode potential 13(Vtg) is set to-20V.
When comparing the characteristics shown in fig. 14A to 14C, if Vtg is set to-20V, in the case of 70nm or 100nm, it can be seen that the difference between the characteristics in the dark state and the characteristics in the light-irradiated state is large as compared with the case of 35 nm. From the results, it is seen that increasing the film thickness of the InGaZnO film is effective for improving the sensitivity, and such a structure is very important for the function of the photosensor element. When Vtg is set to 0V, the Vbg value, at which the drain current rapidly increases, tends to shift to the negative side as the film thickness of the InGaZnO film increases. This tendency is not preferable for the function of the switching element. In view of the above, the inventors of the present application found that the film thickness of the oxide semiconductor film 1 of the photosensor element 24 is preferably increased, and the film thickness of the oxide semiconductor film of the switching element 25 is preferably decreased.
Fig. 15A and 15B are diagrams showing light sensing characteristics of the light sensor element 24. Fig. 15A and 15B show characteristics (Vbg-Id characteristics) of the drain current (Id) with respect to the bottom gate electrode potential 19(Vbg) when the drain electrode potential 17(Vd) is set to 1V and the source electrode potential 15(Vs) is set to 0V. Fig. 15A shows the characteristics of the photosensor element 24 using an InGaZnO film having a film thickness of 35nm as the oxide semiconductor film 1, in which the transparent top gate electrode potential 13(Vtg) is set to-20V. In fig. 15A, the solid line indicates Vbg-Id characteristics in the dark state, and the broken line indicates Vbg-Id characteristics in the blue light irradiation state. Fig. 15B shows characteristics when the transparent top gate electrode potential 13(Vtg) is set to-15V in the photosensor element 24 using the InGaZnO film having a film thickness of 70nm as the oxide semiconductor film 1. In fig. 15B, the solid line indicates Vbg-Id characteristics in the dark state, and the broken line indicates Vbg-Id characteristics in the blue light irradiation state.
When comparing the characteristics shown in fig. 15A and 15B, it can be seen that the sensitivities are approximately the same between the case where Vtg of-20V is applied to the photosensor element 24 using the InGaZnO film having the film thickness of 35nm and the case where Vtg of-15V is applied to the photosensor element 24 using the InGaZnO film having the film thickness of 70 nm. This indicates that the absolute value of Vtg required to obtain the same sensitivity can be reduced by increasing the film thickness of the InGaZnO film. When the absolute value of Vtg is reduced as described above, the stress caused by Vtg in consideration of long-term use as a photosensor element can be reduced, whereby a long operating life can be achieved. As described above, the present inventors have found that it is also effective to increase the thickness of the oxide semiconductor film 1 of the photosensor element 24 from the viewpoint of a long operating life of the photosensor element.
As described above, from the viewpoint of improving the sensitivity of the photosensor element and improving the long-term reliability, it is effective to adopt a structure in which the thickness of the oxide semiconductor film 1 of the photosensor element 24 is increased and the thickness of the oxide semiconductor film of the switching element 25 is decreased. Means for realizing the structure are described below.
Fig. 16 is a sectional view of the photoelectric conversion device. In the photoelectric conversion device shown in fig. 16, the switching element 25 including the thin oxide semiconductor film 47 and the photosensor element 24 including the thick oxide semiconductor film 48 are formed on a single glass substrate 6.
In the case of manufacturing the photoelectric conversion device shown in fig. 16, after the first bottom gate electrode 41 and the first bottom gate insulating film 42 are formed on the glass substrate 6, the oxide semiconductor TFT used as the switching element 25 is formed using the same process as that of the switching element of the fourth embodiment (i.e., the process of manufacturing the optical sensor described in examples 1 to 6). At this time, the film thickness of the oxide semiconductor film 47 of the oxide semiconductor TFT is set to be less than 70nm, preferably equal to or less than 50 nm.
Next, after the second bottom gate electrode 44 for the photosensor element 24 is formed on the first passivation film 43 in the oxide semiconductor TFT for the switching element 25, the oxide semiconductor TFT for the photosensor element 24 is formed by the same process as that for the switching element 25. At this time, the film thickness of the oxide semiconductor film 48 of the oxide semiconductor TFT is set to 70nm or more, preferably 100nm or more. In addition, the transparent top gate electrode 12 for the photosensor element 24 is formed on the second passivation film 46 in the oxide semiconductor TFT for the photosensor element 24.
Further, the source and drain electrodes of the oxide semiconductor TFT for the photosensor element 24 are formed so as to be connected to the source and drain electrodes of the oxide semiconductor TFT for the switching element 25 via contact holes formed in the first passivation film 43 and the second bottom gate insulating film 45. In the photoelectric conversion device shown in fig. 16, the source and drain electrodes of the oxide semiconductor TFT for the photosensor element 24 and the source and drain electrodes of the oxide semiconductor TFT for the switching element 25 are formed in different layers from each other. In this way, an oxide semiconductor TFT for the switching element 25 including the thin oxide semiconductor film 47 and an oxide semiconductor TFT for the photosensor element 24 including the thick oxide semiconductor film 48 can be formed on the glass substrate 6, respectively.
Fig. 17 is a sectional view of the photoelectric conversion device. The photoelectric conversion apparatus shown in fig. 17 is a modification of the photoelectric conversion apparatus shown in fig. 16. In the photoelectric conversion device shown in fig. 17, the bottom gate electrode (first bottom gate electrode 41) of the oxide semiconductor TFT for the switching element 25 and the bottom gate electrode (second bottom gate electrode 44) of the oxide semiconductor TFT for the photosensor element 24 are formed of the same metal layer. After the bottom gate electrode 41 and the bottom gate electrode 44 are formed, a third insulating film 51 is formed as a bottom gate insulating film of the oxide semiconductor TFT for the switching element 25.
Next, the thin oxide semiconductor film 47 is formed as an active layer of an oxide semiconductor TFT for the switching element 25. At this time, the film thickness of the oxide semiconductor film 47 is set to less than 70nm, preferably equal to or less than 50 nm.
Next, a fourth insulating film 52 is formed over the third insulating film 51 and the oxide semiconductor film 47, and a thick oxide semiconductor film 48 is formed as an active layer of an oxide semiconductor TFT for the photosensor element 24. At this time, the film thickness of the oxide semiconductor film 48 is set to 70nm or more, preferably 100nm or more. In addition, the third insulating film 51 and the fourth insulating film 52 each function as a bottom gate insulating film of the oxide semiconductor TFT for the photosensor element 24.
After a fifth insulating film 53 is formed over the fourth insulating film 52 and the oxide semiconductor film 48, contact holes for a source electrode and a drain electrode are simultaneously opened in both the oxide semiconductor TFT for the switching element 25 and the oxide semiconductor TFT for the photosensor element 24. The source electrode 49 and the drain electrode 50 of each element 24, 25 are formed so that the source electrode 49 of the switching element 25 and the drain electrode 50 of the photosensor element 24 are connected to each other via a contact hole.
Next, the sixth insulating film 54 is formed, and the transparent top gate electrode 12 of the photosensor element 24 is formed. The fifth insulating film 53 and the sixth insulating film 54 both function as a top gate insulating film of the oxide semiconductor TFT for the photosensor element 24.
In the case of being formed as shown in fig. 17, the bottom gate electrodes 44 and 41 and the source electrode 49 and the drain electrode 50 of the respective elements 24 and 25 can be formed in the same layer, unlike the case of fig. 16, whereby simplification of the process and reduction in cost can be achieved. In this way, the oxide semiconductor TFT for the switching element 25 including the thin oxide semiconductor film 47 and the oxide semiconductor TFT for the photosensor element 24 including the thick oxide semiconductor film 48 can be formed on the glass substrate 6 at low cost, respectively.
Needless to say, the means of forming the oxide semiconductor TFT for the switching element 25 including the thin oxide semiconductor film 47 and the oxide semiconductor TFT for the photosensor element 24 including the thick oxide semiconductor film 48 on the glass substrate 6 as shown in fig. 16 and 17, respectively, is also applicable to any of the photoelectric conversion devices shown in fig. 9, 12, and 13. The process of forming the switching element 25 and the photosensor element 24 each including the oxide semiconductor films 47 and 48 having different thicknesses, and the structure of the thin film transistor are not limited to the above-described structure, and may be any combination of a bottom gate type, a top gate type, a staggered type, and a planar type.
In all the embodiments and examples described above, both gate electrodes of the double-gate type oxide semiconductor TFT used as the photosensor element 24 may be formed of a transparent conductive film. In this case, light may be incident from either side of the two gate electrodes. Further, it is not necessary that light enters the gate electrode side formed of the transparent conductive film, and for example, in the case of using diffracted light as shown in fig. 5B, light may enter the opaque gate electrode side.
The optical sensor of the present invention can be used as an optical sensor or an image sensor that detects received light, an image sensor for a radiation image capturing apparatus, or the like. In addition, the light sensor may be used in flat panel displays such as liquid crystal displays and organic Electroluminescent (EL) displays having a light input function using light sensing.
According to the present invention, in the optical sensor formed using an oxide semiconductor, the light sensitivity function can be controlled, and the light sensitivity can be realized over the entire visible light region.
As the present invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims, rather than by the description, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are intended to be embraced by the claims.
Furthermore, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
Description of reference numerals
1 oxide semiconductor film (oxide semiconductor active layer)
2 first insulating film (insulating film)
3 first conductive electrode (grid electrode)
4 second insulating film (insulating film)
5 second conductive electrode (Gate electrode)
6 glass substrate
7 first potential
8 second potential
12 transparent top gate electrode (gate electrode, first gate electrode)
13 transparent top gate electrode potential
14 source electrode
15 source electrode potential
16 drain electrode
17 drain electrode potential
18 bottom gate electrode (gate electrode, second gate electrode)
19 bottom gate electrode potential
24 light sensor element
25 switching element
41 first bottom gate electrode
42 first bottom gate insulating film
43 first passivation film
44 second bottom gate electrode
45 second bottom gate insulating film
46 second passivation film
47 oxide semiconductor film
48 oxide semiconductor film
49 source electrode
50 drain electrode
51 third insulating film
52 fourth insulating film
53 fifth insulating film
54 sixth insulating film

Claims (21)

1. A photosensor element including gate electrodes arranged on an upper side and a lower side of an oxide semiconductor active layer with an insulating film interposed therebetween, respectively, the photosensor element comprising:
a voltage applying unit that applies a first voltage to one of the gate electrodes and a second voltage to the other of the gate electrodes,
wherein,
in a case where the voltage applying unit applies the first voltage to the one gate electrode and the second voltage to the other gate electrode, an amount of light absorbed by the oxide semiconductor active layer increases as compared with when no voltage is applied,
the gate electrode to which at least the lower of the first voltage and the second voltage is applied is transparent with respect to visible light,
light is incident on the oxide semiconductor active layer from the gate electrode side which is transparent with respect to visible light, an
The constituent element of the oxide semiconductor active layer includes at least indium or zinc.
2. A photosensor element including gate electrodes arranged on an upper side and a lower side of an oxide semiconductor active layer with an insulating film interposed therebetween, respectively, the photosensor element comprising:
a source electrode;
a drain electrode; and
a voltage applying unit that applies a first voltage lower than a voltage applied to the source electrode to one of the gate electrodes and applies a second voltage higher than the voltage applied to the source electrode to the other of the gate electrodes, and
wherein, in a case where the first voltage and the second voltage are applied to the gate electrode, an amount of light absorbed by the oxide semiconductor active layer is increased as compared to a case where the first voltage and the second voltage are not applied to the gate electrode.
3. A photosensor element including gate electrodes arranged on an upper side and a lower side of an oxide semiconductor active layer with an insulating film interposed therebetween, respectively, the photosensor element comprising:
a source electrode;
a drain electrode; and
a voltage applying unit that applies a first voltage lower than a voltage applied to the source electrode to one of the gate electrodes and applies a second voltage higher than the voltage applied to the source electrode to the other of the gate electrodes, and
wherein in a case where the first voltage and the second voltage are applied to the gate electrode, photo carriers are generated in the oxide semiconductor active layer as compared to a case where the first voltage and the second voltage are not applied to the gate electrode.
4. A photosensor element including gate electrodes arranged on an upper side and a lower side of an oxide semiconductor active layer with an insulating film interposed therebetween, respectively, the photosensor element comprising:
a source electrode;
a drain electrode; and
a voltage applying unit that applies a first voltage lower than a voltage applied to the source electrode to one of the gate electrodes and applies a second voltage higher than the voltage applied to the source electrode to the other of the gate electrodes, and
wherein, in a case where the first voltage and the second voltage are applied to the gate electrode, an amount of current flowing to the oxide semiconductor active layer is increased as compared to a case where the first voltage and the second voltage are not applied to the gate electrode.
5. The photosensor element according to claim 4, wherein an amount of current flowing to the oxide semiconductor active layer is increased in a case of irradiation with light having a wavelength of 400nm to 700 nm.
6. The light sensor element according to any one of claims 2 to 5,
at least one of the two gate electrodes is transparent with respect to visible light.
7. The light sensor element of claim 6,
light is incident on the oxide semiconductor active layer from at least one of the two gate electrodes.
8. The light sensor element according to any one of claims 2 to 5,
at least a second gate electrode, a second gate insulating film, the oxide semiconductor active layer, the source and drain electrodes, a first gate insulating film, and a first gate electrode are disposed in this order on the substrate.
9. The light sensor element of claim 8,
the first gate electrode is transparent with respect to visible light, an
The voltage applying unit applies a voltage lower than the voltage applied to the source electrode to the first gate electrode.
10. The light sensor element of claim 8,
the second gate electrode is transparent with respect to visible light, an
The voltage applying unit applies a voltage lower than the voltage applied to the source electrode to the second gate electrode.
11. The light sensor element according to claim 9 or 10,
light is incident on the oxide semiconductor active layer from the gate electrode side which is transparent to visible light.
12. The light sensor element of claim 11,
the voltage applied to the transparent gate electrode by the voltage applying unit is lower than the voltage applied to the source electrode and corresponds to a wavelength of light incident to the oxide semiconductor active layer.
13. The light sensor element according to any one of claims 2 to 5,
the constituent element of the oxide semiconductor active layer includes at least indium or zinc.
14. A photoelectric conversion apparatus comprising:
a plurality of pixels including a photosensor element and a switching element, respectively, the plurality of pixels being arranged on an insulating substrate in a two-dimensional manner using switching wirings and signal readout wirings;
wherein the photosensor element and the switching element are each constituted by an oxide semiconductor thin film transistor, an
The light sensor element is according to any one of claims 2 to 5.
15. The photoelectric conversion apparatus according to claim 14, further comprising:
a voltage control unit that changes the voltage applied by the voltage applying unit to the two gate electrodes of the oxide semiconductor thin film transistor of the photosensor element according to a wavelength band of light to be sensed.
16. The photoelectric conversion apparatus according to claim 15,
the voltage control unit increases a difference between the voltages applied to the two gate electrodes by the voltage applying unit as the wavelength of the light to be sensed becomes longer.
17. The photoelectric conversion apparatus according to claim 14,
the film thickness of the oxide semiconductor active layer of the oxide semiconductor thin film transistor constituting the photosensor element is larger than the film thickness of the oxide semiconductor active layer of the oxide semiconductor thin film transistor constituting the switching element.
18. The photoelectric conversion apparatus according to claim 17,
the film thickness of the oxide semiconductor active layer of the oxide semiconductor thin film transistor constituting the photosensor element is equal to or greater than 70nm, and the film thickness of the oxide semiconductor active layer of the oxide semiconductor thin film transistor constituting the switching element is less than 70 nm.
19. The photoelectric conversion apparatus according to claim 17,
the source electrode and the drain electrode of the oxide semiconductor thin film transistor constituting the photosensor element and the source electrode and the drain electrode of the oxide semiconductor thin film transistor constituting the switching element are each formed of a metal layer formed in a layer different from each other.
20. The photoelectric conversion apparatus according to claim 17,
the source electrode and the drain electrode of the oxide semiconductor thin film transistor constituting the photosensor element and the source electrode and the drain electrode of the oxide semiconductor thin film transistor constituting the switching element are formed of metal layers formed in the same layer.
21. The photoelectric conversion apparatus according to claim 17,
one of the gate electrodes of the oxide semiconductor thin film transistor constituting the photosensor element and the gate electrode of the oxide semiconductor thin film transistor constituting the switching element are formed of a metal layer formed in the same layer.
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