JP2004200490A - Image pickup unit and method for driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the corrosion of a photoelectric converting element formed under a protecting insulating film, especially, the electrode. <P>SOLUTION: A solid image pickup device 2 is provided with a transparent substrate 17, a plurality of DG-Tr20 arrayed like a matrix on the transparent substrate 17, a protecting insulating film 31 doped with phosphorous coating all the DG-Tr20, a conductive film 32 for discharge formed on the protecting insulating film 31, and drivers 11, 12 and 13. This DG-Tr20 is provided with a top gate electrode 30. A potential which is always higher than that of the conductive film 32 for discharge is impressed to the top gate electrode 30 by the driver 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging device in which a plurality of photoelectric conversion elements are arranged and a driving method thereof.
[0002]
[Prior art]
A fingerprint is a very useful means for performing personal authentication because it has a pattern peculiar to an individual. In recent years, fingerprint authentication devices that apply fingerprints to personal authentication have been developed. Specifically, the fingerprint authentication apparatus performs personal authentication by comparing a fingerprint image captured by a solid-state imaging device with fingerprint image data of a registrant registered in advance, and includes a PC (Personal Computer) and a PDA (Personal Computer). It is being considered to be installed in information devices such as Personal Digital Assistance and mobile phones.
[0003]
Patent Literature 1 describes a solid-state imaging device in which a plurality of photoelectric conversion elements are arranged in a matrix on a substrate. The solid-state imaging device detects a subject by detecting the intensity and light amount of light with each photoelectric conversion element. To obtain an image. In this photoelectric conversion element, a top gate electrode facing the semiconductor layer is formed of ITO (tin-doped indium oxide), which is a transparent metal oxide, in order to detect the intensity and intensity of light incident on the semiconductor layer. The photoelectric conversion element is covered together with the top gate electrode, and a transparent protective insulating film made of silicon nitride is formed.
[0004]
In general, a solid-state imaging device is used to acquire an image of a subject by entering reflected light of the subject via a lens away from the subject, but according to Patent Document 1, the protection is described. Attempts have been made to use a solid-state imaging device to obtain an image of a subject by directly contacting the subject with a transparent earth electrode layer formed on an insulating film.
[0005]
[Patent Document 1]
JP-A-2002-94040
[0006]
[Problems to be solved by the invention]
By the way, when the subject is a fingertip, sweat of the fingertip adheres to the ground electrode layer. When there is no defect in the protective insulating film and the earth electrode layer, there is no particular problem, but when the protective insulating film and the earth electrode layer have defects such as pinholes due to minute particles in the manufacturing process, which are very rare. There is. If there is a defect such as a minute pinhole in the protective insulating film and the ground electrode layer, sweat penetrates into the photoelectric conversion element through the defect, and the photoelectric conversion element, especially the top gate electrode and the top gate line cause sodium ions in the sweat. Corrosion may be caused by Since the top gate electrode and the top gate line are extremely small or thin as compared with the ground electrode layer, there has been a problem that the top gate electrode and the top gate line are easily broken due to corrosion.
[0007]
Therefore, an object of the present invention is to suppress corrosion of a photoelectric conversion element formed under a protective insulating film, particularly, its electrode, even if a defect exists in the protective insulating film.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, an imaging apparatus according to the first aspect of the present invention includes, for example, as shown in FIGS.
A control electrode (for example, a top gate electrode 30) for controlling a photoelectric conversion element (for example, a double-gate transistor 20);
A protective insulating film (for example, protective insulating film 31) formed on the upper surface of the control electrode;
A conductive film (for example, a conductive film 32 for discharge) formed on the protective insulating film;
A driver (for example, a top gate driver 11) that constantly applies a potential equal to or higher than the potential of the conductive film to the control electrode of the photoelectric conversion element.
[0009]
According to a second aspect of the present invention, in the imaging device according to the first aspect, the conductive film is grounded.
[0010]
According to a third aspect of the present invention, in the imaging device according to the first or second aspect, the control electrode is made of a transparent metal oxide.
[0011]
The invention according to claim 4 is, for example, as shown in FIGS.
A control electrode (for example, a top gate electrode 30) for controlling a photoelectric conversion element (for example, a double-gate transistor 20);
A protective insulating film (for example, protective insulating film 31) formed on the upper surface of the control electrode;
A conductive film formed on the protective insulating film (for example, a conductive film for discharge 32), the method comprising:
A driving method of an imaging device, wherein a potential equal to or higher than the potential of the conductive film is constantly applied to the control electrode of the photoelectric conversion element.
[0012]
When an object such as a fingertip comes into contact with the conductive film, an adverse substance including sodium or the like such as sweat adheres to the conductive film. However, if a defect exists in the conductive film and the protective insulating film, the adverse substance penetrates into the control electrode through the defect. . However, in the invention according to any one of claims 1 to 4, since the potential of the control electrode is higher than the potential of the conductive film, sodium ions are controlled when cations in the adverse substance, particularly when the adverse substance is sweat, are controlled. It repels the electrode, sodium ions do not reach the control electrode, and the control electrode is not corroded. In particular, if the control electrode is a transparent metal oxide as in the third aspect of the present invention, the control electrode is not reduced by cations and can prevent the transmittance from lowering, so that the photoelectric conversion element performs favorable photoelectric conversion. be able to.
[0013]
The invention according to claim 5, for example, as shown in FIGS.
A plurality of photoelectric conversion elements (for example, double-gate transistors 20, 20) are placed on a substrate (for example, transparent substrate 17) under a mounting surface (for example, surface 32a) on which a subject (for example, fingertip 100) is mounted. ,...) Are arranged (for example, the solid-state imaging device 2).
A transparent protective insulating film doped with phosphorus (for example, the protective insulating film 31) is formed on the plurality of photoelectric conversion elements.
[0014]
When an object such as a fingertip comes into contact with the protective insulating film, an adverse substance such as sweat adheres to the protective insulating film. However, if a defect exists in the protective insulating film, the adverse substance penetrates into the photoelectrically sensitive element through the defect. However, in the invention according to claim 5, since the protective insulating film is doped with phosphorus, cations in the harmful substance, especially when the harmful substance is sweat, sodium ions react with phosphorus, and the harmful substance is an electrolyte. Does not act as Therefore, the photoelectric conversion element is not corroded.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated example.
[0016]
FIG. 1 is a plan view showing a circuit configuration of a fingerprint authentication device 1 to which the present invention is applied, and FIG. 2 is a cross-sectional view taken along a broken line CC of FIG.
[0017]
The fingerprint authentication device 1 includes a solid-state imaging device 2 that is a driver-integrated imaging device that captures a fingerprint image of the fingertip 100 by converting the amount of light reflected from the fingertip 100 as a subject into an electric signal, and a solid-state imaging device 2. Circuit 10 for acquiring a fingerprint image of the fingertip 100 by detecting an electric signal from the CPU, and an arithmetic processing unit for determining whether or not the fingerprint image acquired by the imaging circuit 10 can be regarded as matching the registered fingerprint image 4, a light source 14 that emits light, and a light guide plate 15 that guides the light emitted from the light source 14 to the solid-state imaging device 2 and irradiates the solid-state imaging device 2 with light.
[0018]
The light guide plate 15 has a substantially flat shape, and is covered with a light reflecting material except for a side surface facing the light source 14 and a surface facing the back surface of the solid-state imaging device 2. Light from the light source 14 is diffused in the light guide plate 15, and light radiated from the surface of the light guide plate 15 is uniformly applied to the back surface of the solid-state imaging device 2. Note that, instead of the light guide plate 15 and the light source 14, a surface emitting element such as an organic EL element may be provided so as to face the back surface of the solid-state imaging device 2.
[0019]
The arithmetic processing device 4 includes a CPU, a RAM used as a work area in the arithmetic processing of the CPU, a ROM storing programs executable by the CPU, and a storage medium storing registered fingerprint images for the number of registrants. (Not shown). The CPU drives the imaging circuit 10 according to a program stored in the ROM, inputs a fingerprint image from the imaging circuit 10, and compares the input fingerprint image with a registered fingerprint image stored in a storage medium to obtain a fingerprint. It is determined whether or not the image can be regarded as matching the registered fingerprint image.
[0020]
The solid-state imaging device 2 will be described with reference to FIGS. FIG. 3A is a plan view illustrating one pixel of the solid-state imaging device 2, and FIG. 3B is a cross-sectional view taken along a line AA in FIG. 3A. .
[0021]
The solid-state imaging device 2 includes a substantially flat transparent substrate 17 and a plurality of doubles arranged on one surface of the transparent substrate 17 in a matrix of n rows and m columns (both n and m are positive integers). Gate transistors (hereinafter referred to as DG-Trs) 20, 20,... And a top gate driver formed on a transparent substrate 17 around the image input area 8 in which the DG-Trs 20, 20,. 11, a protective insulating film 31 covering the bottom gate driver 12 and the drain driver 13, the drivers 11, 12, 13 and the DG-Trs 20, 20,..., And a discharge conductive film 32 formed on the protective insulating film 31 And.
[0022]
The transparent substrate 17 has a light transmitting property (hereinafter, simply referred to as a light transmitting property) and an insulating property, and is a glass substrate such as quartz glass or a plastic substrate such as polycarbonate. The transparent substrate 17 forms the back surface of the solid-state imaging device 2, and the light guide plate 15 faces the transparent substrate 17.
[0023]
Each DG-Tr 20 is a photoelectric conversion element serving as a pixel. Each of the DG-Trs 20 includes a bottom gate electrode 21 formed on the transparent substrate 17, an interlayer insulating film 22 formed on the bottom gate electrode 21, a bottom gate electrode 21 and the interlayer insulating film 22 interposed therebetween, and A semiconductor film 23 facing the electrode 21, a channel protective film 24 formed on the center of the semiconductor film 23, and impurity semiconductor films 25 and 26 formed on both ends of the semiconductor film 23 so as to be separated from each other; A source electrode 27 formed on the impurity semiconductor film 25; a drain electrode 28 formed on the impurity semiconductor film 26; an interlayer insulating film 29 formed on the source electrode 27 and the drain electrode 28; A top gate electrode 30 sandwiching the interlayer insulating film 29 and the channel protection film 24 and facing the semiconductor film 23.
[0024]
On the transparent substrate 17, the bottom gate electrodes 21 are formed in a matrix for each DG-Tr 20. Also, n bottom gate lines 41, 41,... Extending in the horizontal direction are formed on the transparent substrate 17, and the bottom gate electrodes 21 of the DG-Trs 20 in the same row arranged in the horizontal direction are It is formed integrally with the common bottom gate line 41. The bottom gate electrode 21 and the bottom gate line 41 have conductivity and light shielding properties, and are made of, for example, chromium, a chromium alloy, aluminum, an aluminum alloy, or an alloy thereof.
[0025]
An interlayer insulating film 22 common to all the DG-Trs 20, 20,... Is formed on the bottom gate electrode 21 and the bottom gate line 41. The interlayer insulating film 22 has an insulating property and a light transmitting property, and is made of, for example, silicon nitride or silicon oxide.
[0026]
A semiconductor film 23 is formed for each DG-Tr 20 on the interlayer insulating film 22. The semiconductor film 23 has a substantially rectangular shape in plan view, and is a layer formed of amorphous silicon or polysilicon. On the semiconductor film 23, a channel protection film 24 is formed. The channel protective film 24 has a function of protecting the interface of the semiconductor film 23 from an etchant used for patterning, has insulating properties and translucency, and is made of, for example, silicon nitride or silicon oxide. When light is incident on the semiconductor film 23, electron-hole pairs in an amount corresponding to the amount of incident light are generated around the interface between the channel protective film 24 and the semiconductor film 23.
[0027]
On one end of the semiconductor film 23, an impurity semiconductor film 25 is formed so as to partially overlap the channel protective film 24, and on the other end of the semiconductor film 23, an impurity semiconductor film 26 is partially formed on the channel protection film. It is formed so as to overlap with the protective film 24. The impurity semiconductor films 25 and 26 are patterned for each DG-Tr 20. The impurity semiconductor films 25 and 26 are made of amorphous silicon (n) containing n-type impurity ions. ⁺ Silicon).
[0028]
On the impurity semiconductor film 25, a source electrode 27 patterned for each DG-Tr 20 is formed. A drain electrode 28 patterned for each DG-Tr 20 is formed on the impurity semiconductor film 26. Also, m source lines 42, 42, ... and drain lines 43, 43, ... extending in the vertical direction are formed on the interlayer insulating film 22, and each of the DG-s in the same column arranged in the vertical direction. The source electrode 27 of the Tr 20 is formed integrally with the common source line 42, and the drain electrode 28 of each DG-Tr 20 in the same column arranged in the vertical direction is formed integrally with the common drain line 43. The source electrode 27, the drain electrode 28, the source line 42, and the drain line 43 have conductivity and light-shielding properties, and are made of, for example, chromium, a chromium alloy, aluminum, an aluminum alloy, or an alloy thereof.
[0029]
, All the DG-Trs 20, 20,..., On the channel protective film 24, the source electrode 27, the drain electrode 28, and the source lines 42, 42,. Are formed in common with each other. The interlayer insulating film 29 has an insulating property and a light transmitting property, and is made of, for example, silicon nitride or silicon oxide.
[0030]
On the interlayer insulating film 29, a top gate electrode 30 patterned for each DG-Tr 20 is formed. Further, n top gate lines 44 extending in the horizontal direction are formed on the interlayer insulating film 29, and the top gate electrodes 30 of the DG-Trs 20 in the same row arranged in the horizontal direction share a common top. It is formed integrally with the gate line 44. The top gate electrode 30 and the top gate line 44 are conductive and light-transmitting metal oxides, for example, indium oxide, zinc oxide, tin oxide, or a mixture containing at least one of them (for example, ITO, zinc-doped indium oxide).
The DG-Tr 20 configured as described above is a photoelectric conversion element using the semiconductor film 23 as a light receiving unit.
[0031]
A common protective insulating film 31 is formed on the top gate electrodes 30 and the top gate lines 44, 44,... Of all the DG-Trs 20, 20,. ing. The protective insulating film 31 has an insulating property and a light transmitting property, and is made of silicon nitride or silicon oxide.
[0032]
On the protective insulating film 31, a discharge conductive film 32 is formed all over. The discharge conductive film 32 has conductivity and translucency, and is formed of, for example, indium oxide, zinc oxide, tin oxide, or a mixture containing at least one of them (for example, tin-doped indium oxide (ITO), zinc, or the like). (Doped indium oxide). The discharging conductive film 32 is grounded and kept at 0 [V], and serves to prevent electrostatic damage of the DG-Trs 20, 20,. . The surface 32a of the discharge conductive film 32 forms the surface of the solid-state imaging device 2 and is a mounting surface on which the fingertip 100 is mounted.
[0033]
Next, a driver of the solid-state imaging device 2 will be described with reference to FIGS. The source lines 42, 42,... Are maintained at a constant potential higher than the potential of the discharge conductive film 32, for example, at +17 [V]. The bottom gate lines 41, 41,... Are connected to the output of the bottom gate driver 12. The top gate lines 44 are connected to the output of the top gate driver 11.
[0034]
The top gate driver 11 is a shift register. In other words, the top gate driver 11 receives the control signal Tcnt from the imaging circuit 10 to sequentially operate from the top gate line 44 in the first row to the top gate line 44 in the nth row (the first row when the nth row is reached). The reset pulse is output. The level of the reset pulse is a high level of +32 [V]. On the other hand, the top gate driver 11 applies a low-level potential of +2 [V] to each top gate line 44 when not outputting a reset pulse. Therefore, while the fixed imaging device 2 is operating, the potentials of the top gate electrodes 30 and the top gate lines 44 of all the DG-Trs 20, 20,. Is getting higher.
[0035]
When a defect such as a pinhole exists in the conductive film for discharge 32 and the protective insulating film 31, sweat of the fingertip 100 in contact with the surface 32a penetrates into the top gate electrode 30 through the defect. However, since the potentials of the top gate electrode 30 and the top gate line 44 are higher than the potential of the discharge conductive film 32, sodium ions in the sweat repel the top gate electrode 30 and no reduction reaction occurs at the top gate electrode. Therefore, it is possible to prevent the top gate electrode 30 from becoming opaque due to reduction.
[0036]
The bottom gate driver 12 is a shift register. That is, a read pulse is output in order from the bottom gate line 41 in the first row to the bottom gate line 41 in the n-th row (return to the first row when reaching the n-th row). The level of the read pulse is a high level of +27 [V], and the level when no read pulse is output is a low level of +17 [V]. Therefore, while the fixed imaging device 2 is operating, the potentials of the bottom gate electrodes 21, 21,... And the bottom gate lines 41, 41, of all the DG-Trs 20, 20,. Is always higher than the potential.
[0037]
After the top gate driver 11 outputs a reset pulse to the top gate line 44 of the i-th row (i is an integer from 1 to n), the bottom gate driver 12 applies a read pulse to the bottom gate line 41 of the i-th row. The top gate driver 11 and the bottom gate driver 12 shift the output signal so as to output. That is, in each row, the timing at which the read pulse is output is later than the timing at which the reset pulse is output. Further, after the input of the reset pulse to the top gate line 44 of the i-th row (i is any one of 1 to n) starts, the input of the read pulse to the bottom gate line 41 of the i-th row. Is a selection period of the i-th row. The period from the end of the input of the read pulse to the bottom gate line 41 of the i-th row to the start of the input of the reset pulse to the top gate line 44 in the next selection period of the i-th row is the i-th row Is a non-selection period.
[0038]
The drain driver 13 outputs a precharge pulse to all the drain lines 43, 43,... Between the output of the reset pulse and the output of the read pulse in the selection period of each row. ing. The level of the precharge pulse is a high level of +27 [V], and the level when the precharge pulse is not output is a low level of +17 [V]. Therefore, while the fixed imaging device 2 is operating, the potentials of the drain electrodes 28 and the drain lines 43, 43,... Of all the DG-Trs 20, 20,. ing.
The drain driver 13 amplifies the voltages of the drain lines 43, 43,... After outputting the precharge pulse, and outputs the amplified voltage to the imaging circuit 10.
[0039]
The imaging circuit 10 is driven by the arithmetic processing unit 4 to output control signals Bcnt, Tcnt, and Dcnt to the bottom gate driver 12, the top gate driver 11, and the drain driver 13, respectively, so that the bottom gate driver 12, the top gate The driver 11 and the drain driver 13 output pulses as appropriate. Further, the imaging circuit 10 detects the voltage of the drain lines 43, 43,... After a lapse of a predetermined time from the output of the read pulse, or detects the voltage of the drain lines 43, 43,. A fingerprint image of the fingertip 100 is obtained by detecting a time until the voltage reaches a predetermined threshold voltage.
[0040]
The operation and usage of the solid-state imaging device 2 and the fingerprint authentication device 1 configured as described above will be described.
When the subject places the fingertip 100 on the discharge conductive film 32, the light source 14 emits light, the light emitted from the light guide plate 15 enters the fingertip 100 via the solid-state imaging device 2, and the reflected light reflected on the fingertip 100 becomes The DG-Tr 20, 20,... At this time, since the light-shielding bottom gate electrode 21 is interposed between the light guide plate 15 and the semiconductor film 23, light emitted from the light guide plate 15 does not directly enter the semiconductor film 23. .
[0041]
Here, the imaging circuit 10 outputs a control signal Tcnt to the top gate driver 11, and the top gate driver 11 sequentially outputs a reset pulse from the top gate line 44 of the first row to the top gate line 44 of the nth row. Further, the imaging circuit 10 outputs a control signal Bcnt to the bottom gate driver 12, and the bottom gate driver 12 sequentially outputs read pulses from the bottom gate line 41 of the first row to the bottom gate line 41 of the nth row. Further, the imaging circuit 10 outputs the control signal Dcnt to the drain driver 13, and the drain driver 13 performs a precharge between a reset period in which a reset pulse is output in each row and a period in which a read pulse is output in each row. The pulse is output to all the drain lines 43, 43,.
[0042]
The operation of each DG-Tr 20 in the i-th row will be described in detail. As shown in FIG. 4, when the top gate driver 11 outputs a reset pulse to the top gate line 44 in the i-th row, the top gate line 44 in the i-th row becomes high level. While the top gate line 44 in the i-th row is at a high level (this period is referred to as a reset period), the DG-Tr 20 in the i-th row accumulates near the interface between the semiconductor film 23 and the channel protection film 24. The generated carriers (here, holes) are repelled and discharged by the voltage of the top gate electrode 30.
[0043]
Next, the top gate driver 11 ends outputting the reset pulse to the i-th top gate line 44. From the end of the reset pulse of the top gate line 44 in the i-th row to the output of the read pulse to the bottom gate line 41 in the i-th row (this period is referred to as a carrier accumulation period), the reflection of the fingertip 100. An amount of electron-hole pairs corresponding to the amount of light that has entered the semiconductor film 23 is accumulated near the interface between the semiconductor film 23 and the channel protection film 24.
[0044]
Next, during the carrier accumulation period, the drain driver 13 outputs a precharge pulse to all the drain lines 43, 43,. While the precharge pulse is being output (referred to as a precharge period), in each DG-Tr 20 in the i-th row, the potential applied to the top gate electrode 30 is +2 [V], and the bottom gate electrode Since the potential applied to 21 is +17 [V], no channel is formed in the semiconductor film 23, and even if a potential of +27 [V] is applied to the drain electrode 28 in the precharge pulse, the drain electrode 28 No current flows between the gate electrode and the source electrode 27. Since no current flows between the drain electrode 28 and the source electrode 27 in the precharge period, the precharge pulse output to the drain lines 43, 43,. Charge is charged.
[0045]
Next, the drain driver 13 finishes outputting the precharge pulse, and the bottom gate driver 12 outputs a read pulse to the i-th bottom gate line 41. While the bottom gate driver 12 is outputting a read pulse to the i-th bottom gate line 41 (this period is referred to as a read period), +27 [+27 [ V], the DG-Trs 20 in the i-th row are turned on.
[0046]
In the read period, since the carriers accumulated in the carrier accumulation period work to reduce the voltage between the top gate electrode 30 and the bottom gate electrode 21, the voltage between the bottom gate electrode 21 and the top gate electrode 30 is reduced. As a result, a channel is formed in the semiconductor film 23, and current flows from the drain electrode 28 to the source electrode 27. Therefore, in the read period, the voltage of the drain lines 43, 43,... Tends to gradually decrease with the passage of time due to the drain-source current.
[0047]
Here, as the amount of reflected light incident on the semiconductor film 23 in the carrier accumulation period increases, the number of accumulated carriers also increases. As the amount of accumulated carriers increases, the drain electrode 28 moves from the drain electrode 28 to the source electrode 27 in the lead period. The level of the flowing current also increases. Therefore, the change tendency of the voltage of the drain lines 43, 43,... During the read period is deeply related to the amount of light incident on the semiconductor film 23 during the carrier accumulation period. Then, during a period from the read period of the i-th row to the precharge period of the next (i + 1) -th row, the imaging circuit 10 outputs a predetermined time after the start of the read period via the drain driver 13. The voltages of the drain lines 43, 43,... Are detected. This is converted into the intensity of the reflected light of the fingertip 100. Note that the imaging circuit 10 detects the time required to reach a predetermined threshold voltage via the drain driver 13 during the period from the read period of the i-th row to the precharge period of the next (i + 1) -th row. Is also good. Even in this case, it is converted into the intensity of the reflected light of the fingertip 100.
[0048]
With the series of image reading operations described above as one cycle, the same processing procedure is repeated for each DG-Tr 20 in all rows, so that the solid-state imaging device 2 and the imaging circuit 10 obtain a fingerprint image of the fingertip 100. Then, the fingerprint image of the fingertip 100 is output from the imaging circuit 10 to the arithmetic processing device 4. The arithmetic processing unit 4 authenticates the subject by determining whether or not the input fingerprint image can be regarded as matching the registered fingerprint image.
[0049]
As described above, in the above embodiment, when a defect such as a pinhole is present in the discharge conductive film 32 and the protective insulating film 31, sweat of the fingertip 100 in contact with the surface 32a penetrates into the top gate electrode 30 through the defect. However, since the potentials of the top gate electrode 30 and the top gate line 44 are higher than the potential of the discharge conductive film 32, sodium ions in sweat repel the top gate electrode 30 and no reduction reaction occurs at the top gate electrode. Therefore, it is possible to prevent the top gate electrode 30 from becoming opaque due to reduction.
[0050]
In the above embodiment, the low level by the top gate driver 11 is +2 [V], but the level is not particularly limited as long as the low level by the top gate driver 11 is 0 [V] or more. If the low level by the top gate driver 11 is not +2 [V], the potential applied by the top gate driver 11, the bottom gate driver 12, and the drain driver 13 and the potential of the source line need to be changed by the difference from the above embodiment. There is.
Further, the difference between the low level and the high level by the top gate driver 11, the difference between the low level and the high level by the bottom gate driver 12, and the difference between the low level and the high level by the drain driver 13 are not limited to the above embodiment. In any case, the potential applied to the top gate electrode 30 and the top gate line 44 only needs to be higher than the potential applied to the discharge conductive film 32.
[0051]
In the above embodiment, sodium ions contained in sweat from the finger are prevented from entering the top gate electrode 30 and the top gate line 44 by controlling the voltage applied to the DG-Tr 20, but other embodiments are described. This will be described below.
[0052]
The solid-state imaging device 2 of the present embodiment has the same structure as the solid-state imaging device 2 of the above-described embodiment except that the protective insulating film 31 on the DG-Tr 20 is doped with phosphorus. That is, the common protective insulating film 31 is in contact with the top gate electrode 30 and the top gate line 44 on the top gate electrode 30 and the top gate lines 44, 44,... Of all the DG-Trs 20, 20,. Is formed. The protective insulating film 31 has insulating properties and translucency, and is made of silicon nitride or silicon oxide doped with phosphorus (P). It is desirable that the phosphorus concentration be higher in the upper part of the protective insulating film 31.
[0053]
Next, a method for manufacturing the solid-state imaging device 2 will be described.
First, after forming a conductive layer on the transparent substrate 17 by a PVD method such as sputtering or vapor deposition or a CVD method, a conductive layer is patterned by a masking step such as a photolithography method and an etching method. By appropriately performing a shape processing step, a bottom gate electrode 21 and bottom gate lines 41, 41,... Are formed, and then an interlayer insulating film 22, a semiconductor film 23, and a channel protective film made of silicon nitride over substantially the entire surface of the transparent substrate 17. 24 is formed. After patterning the channel protective film 24, an n-type impurity a-Si layer is deposited and then patterned to form impurity semiconductor films 25 and 26, and the semiconductor film 23 thereunder is patterned. A conductive layer serving as a drain and a source electrode is formed and patterned to form a source electrode 27 and a drain electrode 28, source lines 42, 42, and a drain line 43, 43,. Subsequently, an interlayer insulating film 29 is formed on the transparent substrate 17, and a transparent conductor layer is formed on the upper surface of the transparent substrate 17 and then patterned to form the top gate electrode 30 and the top gate lines 44, 44. It is formed.
[0054]
Next, a protective insulating film 31 doped with phosphorus is formed on the DG-Trs 20, 20,... Using a film forming apparatus capable of forming a film by a CVD method or a PVD method. In other words, the transparent substrate 17 is set in a chamber of a film forming apparatus, and while a gas containing phosphorus such as phosphine (PH3) is supplied into the chamber, a mixture of a vapor of a material of the protective insulating film 31 and a gas containing phosphorus is supplied. Is deposited. As a result, the protective insulating film 31 doped with phosphorus is formed.
Next, a discharge conductive film 32 is formed on the protective insulating film 31 by a PVD method, a CVD method, or the like.
[0055]
In the present embodiment, the voltage applied by the drivers 11, 12, and 13 is set 17 [V] lower than the voltage in the waveform chart shown in FIG. The timing of the pulse is the same as in FIG.
That is, the top gate driver 11 outputs a reset pulse having a potential of +10 [V] to the top gate lines 44, 44,... During the reset period, and outputs a potential of -15 [V] during the carrier accumulation period. It is set as follows. The bottom gate driver 12 is set so as to output a potential of 0 [V] to the bottom gate lines 41, 41,... During the carrier accumulation period and to output a +10 [V] read pulse during the read period. I have. The drain driver 13 outputs a precharge pulse of +10 [V] to the drain lines 43, 43,... During the precharge period, and is set to 0 [V] during the other periods. A voltage of 0 [V] is constantly applied to the source lines 42, 42,... And the discharge conductive film 32.
[0056]
In the solid-state imaging device 2 of the present embodiment, when a defect such as a pinhole exists in the conductive film for discharge 32 and the protective insulating film 31, sweat of the fingertip 100 in contact with the surface 32a penetrates into the top gate electrode 30 through the defect. However, since the protective insulating film 31 is doped with phosphorus, sodium ions in sweat react with phosphorus, and sweat does not act as an electrolyte. Therefore, it is possible to prevent the top gate electrode 30 from becoming opaque due to reduction.
[0057]
The present invention is not limited to the above embodiments, and various improvements and design changes may be made without departing from the spirit of the present invention.
[0058]
In each of the above embodiments, the fingertip 100 is imaged. However, not limited to the fingertip 100, various other objects may be pressed against the surface 32a of the discharge conductive film 32 to image. When the subject is pressed against the surface 32a of the discharge conductive film 32, a pattern (including characters, numerals, pictures, etc.) drawn on the surface of the subject can be imaged by the solid-state imaging device 2, or the surface of the subject can be imaged. The solid-state imaging device 2 can image a pattern defined by the unevenness of the solid-state imaging device 2.
[0059]
In each of the above embodiments, the solid-state imaging device 2 using the DG-Tr 20, 20,... As the photoelectric conversion element has been described as an example. However, the present invention is applied to a solid-state imaging device using a photodiode as the photoelectric conversion element. May be applied. As a solid-state imaging device using a photodiode, there are a CCD image sensor and a CMOS image sensor.
[0060]
In a CCD image sensor, photodiodes are formed in a matrix on a substrate for each pixel, and a vertical CCD for transferring an electric signal photoelectrically converted by the photodiode is provided around each photodiode. , A horizontal CCD is formed. Further, similarly to the solid-state imaging device 2, a protective insulating film is formed on one surface so as to cover a plurality of photodiodes, and a discharge conductive film is formed on one surface on the protective insulating film. The protective insulating film is doped with phosphorus.
[0061]
In a CMOS image sensor, photodiodes are formed in a matrix on a substrate for each pixel, and a pixel circuit for amplifying an electric signal photoelectrically converted by the photodiode is provided around each photodiode. Is provided. Like the solid-state imaging device 2, a protective insulating film is formed on one surface so as to cover a plurality of photodiodes, and a discharge conductive film is formed on one surface on the protective insulating film. The film is doped with phosphorus.
[0062]
【The invention's effect】
According to the invention as set forth in any one of claims 1 to 4, since the control electrode having a higher potential than the conductive film and the cations in an adverse substance such as sweat repel, the conductive film and the protective insulating film may be temporarily defective. Even when the presence of the control electrode, the control electrode is not corroded by cations contained in sweat or the like.
According to the fifth aspect of the invention, even if a defect exists in the protective insulating film, the phosphor in the protective insulating film reacts with the cation in the adverse substance, so that the photoelectric conversion element is not corroded.
[Brief description of the drawings]
FIG. 1 is a plan view showing a circuit configuration of a solid-state imaging device to which the present invention has been applied.
FIG. 2 is a cross-sectional view of the solid-state imaging device cut away.
FIG. 3A is a plan view showing one pixel of the solid-state imaging device, and FIG. 3B is a cross-sectional view taken along the line AA.
FIG. 4 is a timing chart showing a transition of a level of an electric signal output by a driver of the solid-state imaging device.
[Explanation of symbols]
2 Solid-state imaging device (imaging device)
11 Top gate driver (driver)
17 Transparent substrate (substrate)
20 Double-gate transistor (photoelectric conversion element)
23 Semiconductor film
30 Top gate electrode (top electrode)
31 Protective insulating film
32 Discharge conductive film (conductive film)
100 fingertips (subject)

Claims (5)

A control electrode for controlling the photoelectric conversion element,
A protective insulating film formed on the upper surface of the control electrode,
A conductive film formed on the protective insulating film,
An imaging device, comprising: a driver that constantly applies a potential equal to or higher than the potential of the conductive film to the control electrode of the photoelectric conversion element. The imaging device according to claim 1, wherein the conductive film is grounded. The imaging device according to claim 1, wherein the control electrode is made of a transparent metal oxide. A control electrode for controlling the photoelectric conversion element,
A protective insulating film formed on the upper surface of the control electrode,
A conductive film formed on the protective insulating film, and a driving method of an imaging device comprising:
A driving method of an imaging device, wherein a potential equal to or higher than the potential of the conductive film is constantly applied to the control electrode of the photoelectric conversion element. In an imaging device in which a plurality of photoelectric conversion elements are arranged below a mounting surface on which a subject is mounted and on a substrate,
An imaging device, wherein a transparent protective insulating film doped with phosphorus is formed on the plurality of photoelectric conversion elements.

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