JP2002094041A - Two-dimensional image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-dimensional image reading device where an wrong reading operation and damages to a device are suppressed significantly, while the discomfort caused by the electrical shock that follows electrostatic discharge is reduced by appropriately discharging the static electricity charged at an object to be detected which is placed on a photosensor device. SOLUTION: The two-dimensional image reading device comprises a photosensor array 100 comprising a plurality of double gate photosensors 10 arrayed in a matrix form on an insulating substrate 19, an electrostatic removing layer 30 comprising a first conductive layer 31 and a second conductive layer 32 sequentially laminated on a protective insulating film 20 is provide so as to cover the plurality of photosensors 10, and a lead-out wiring 33 for connecting the first conductive layer 31 to a ground electrical potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional image reading apparatus, and more particularly, to a method of reading an image pattern by bringing a subject into contact with a photosensor array in which a plurality of photosensors are arranged in a matrix. The present invention relates to a three-dimensional image reading device.

[0002]

2. Description of the Related Art Conventionally, as a two-dimensional image reading device for reading the shape of fine irregularities such as a printed matter, a photograph, or a fingerprint, a photo-sensor constructed by arranging photoelectric conversion elements (photo sensors) in a matrix. The object to be detected is placed on and brought into contact with the detection surface provided on the sensor array, and the object to be detected 2
There is a structure that reads a two-dimensional image. In a two-dimensional image reading apparatus having a structure in which the detection target directly contacts the detection surface, various methods have been considered in order to suppress malfunction or damage due to static electricity or the like charged on the detection target. .

[0003] For example, Japanese Patent Application Laid-Open No. 11-259638 discloses a surface light source 2 as shown in FIGS.
01, and a plurality of photosensors 20
A fingerprint reader in which a transparent conductive layer 203 is formed on a photosensor device 202 in which 2a are arranged in a matrix is described. In such a fingerprint reader, the upper surface (detector contact surface) 203a of the transparent conductive layer 203 is provided.
The surface light source 2 is applied to the finger (detected body) 210
By irradiating light Lp from 01, the light Lp is reflected in accordance with the concave and convex pattern of the fingerprint, and based on the reflected light Lr incident on the photosensor 202a, light and dark information is detected to generate a fingerprint image. .

Here, the transparent conductive layer 203 is made of ITO (In
formed of a transparent conductive material such as dium Tin Oxide (indium tin oxide);
Is formed in a thin film shape over the entire upper surface or with a predetermined shape pattern. Such a transparent conductive layer 203
Plays a role of the finger 210 contacting the detection object contact surface 203a.
Fingerprint reader (two-dimensional image reader) by discharging static electricity charged to
Erroneous reading and damage of the photo sensor device 202 are prevented.

[0005]

However, in the conventional two-dimensional image reading apparatus as described above, the conditions for forming the transparent conductive layer, which can discharge the static electricity charged on the object to be detected sufficiently and reliably, and the like. Since the specific configuration has not been determined yet, there has been a problem that the electrostatic withstand voltage is not sufficient, and it is not possible to reliably prevent the reading malfunction or breakage of the two-dimensional image reading apparatus due to the static electricity.

In particular, an object to be detected is directly placed on the transparent conductive layer formed on the photosensor device as described above,
In the configuration for removing the charged static electricity by contact, a large discharge current flows temporarily at the moment when the detection target is brought into contact with the transparent conductive layer, so that a photo sensor device immediately below the transparent conductive layer is configured. The laminated film (for example, a protective insulating film, etc.) is liable to be deteriorated or damaged. In addition, for example, in the case of a configuration in which a human body is in direct contact with a fingerprint reader, the user is extremely liable to be hit by electric shock due to electrostatic discharge. Had the problem of having discomfort.

In view of the above-mentioned problems, the present invention appropriately discharges static electricity charged on a detection target placed on a photosensor device, and significantly suppresses a reading malfunction and device damage. It is another object of the present invention to provide a two-dimensional image reading apparatus capable of alleviating discomfort caused by electric shock caused by electrostatic discharge.

[0008]

According to a first aspect of the present invention, there is provided a two-dimensional image reading apparatus in which an object to be detected is mounted on a photosensor device having a plurality of photosensors arranged on one surface of an insulating substrate. Reading the image pattern of the object to be detected 2
In the two-dimensional image reading device, the photo sensor device includes, on the photo sensor device, a first conductive layer for removing static electricity charged on the detection target, and a second conductive layer having higher resistivity than the first conductive layer. It is characterized in that a static electricity removing layer is provided.

According to the first aspect of the present invention, a static electricity removing layer composed of a plurality of conductive layers is provided on the photo sensor device. Static electricity charged to the detection body is removed from the first conductive layer made of a relatively low resistivity material, and a second conductive layer made of a high resistivity material is used to remove static electricity between the detection body and the second conductive layer. Since the flow of the large current is suppressed, it is possible to prevent the object to be detected and the photosensor device from being impacted by static electricity. As a result, the static electricity charged on the detection target can be reliably discharged, so that the photo sensor device can be prevented from being destroyed by static electricity, and the two-dimensional image reading device may malfunction due to the static electricity, or the photo sensor device may be damaged. Can be suppressed.

When an object to be detected such as a finger (human body) is placed on and comes into contact with the second conductive layer, static electricity charged on the object is discharged from the second conductive layer having a high resistivity to a low level. It moves through the first conductive layer having resistivity and is discharged to a predetermined potential such as a ground potential. Therefore, when the discharge current due to the static electricity charged to the detection object flows down to the predetermined potential, a large discharge current is suppressed from flowing primarily through the second high-resistivity conductive layer. Since the discharge current quickly flows to a predetermined potential from the second conductive layer having a low resistivity through the first conductive layer having a low resistivity, it is possible to suppress damage to the photosensor device during electrostatic discharge. At the same time, discomfort caused by electric discharge at the time of contact of the detection target can be reduced.

That is, if the static electricity removing layer is composed only of the low resistivity material, the discharge current becomes large and the discomfort is strong. On the other hand, if the static electricity removing layer is composed only of the high resistivity material, the current flow is too slow. Although the photosensor device is likely to be destroyed, the present invention can suppress the destruction of the photosensor device and alleviate discomfort. Note that if the resistance of the second conductive layer is merely increased, a sufficiently high resistance can be obtained by increasing the thickness of the layer even if a material having a lower resistivity is used. And it becomes difficult to read the image pattern of the object to be detected by the photo sensor. In the present invention, since the second conductive layer is configured to have a high resistivity, it is possible to set a sufficiently high resistance even if the thickness of the layer is small, and to increase the light transmittance in the sensitivity region of the photosensor. It is possible to do.

Preferably, the first conductive layer is set to have a sheet resistance of approximately 50 Ω / □ or less in order to quickly and sufficiently discharge static electricity. The layer is desirably formed of a material mainly containing indium tin oxide. Accordingly, the first conductive layer (ITO) can be formed to be relatively thin, so that the object is irradiated and reflected while the actual withstand voltage of the photosensor device is increased (about -10 kV). The transmitted light satisfactorily passes through the first conductive layer and is incident on the photosensor. Therefore, deterioration of the reading sensitivity characteristics due to light attenuation can be suppressed, and the image pattern of the detection target can be read well. .

The second conductive layer is formed to have a resistivity of about 10 ⁶ Ω · cm or more in order to maintain high transmittance and reduce discomfort caused by electrostatic discharge. Preferably, for example, amorphous silicon, amorphous silicon containing impurities, amorphous silicon doped with impurities, silicon nitride, silicon oxide, diamond, a polymer thin film, or a conductive polymer is used as a material. Can be. Of these materials, the insulating material preferably has a thickness of about 500 ° or less in order to sufficiently discharge static electricity.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a two-dimensional image reading apparatus according to the present invention will be described in detail. First,
The configuration of a good photosensor applied to the two-dimensional image reading apparatus according to the present invention will be described. The photo sensor applied to the two-dimensional image reading device according to the present invention includes CC
A solid-state imaging device such as D (Charge Coupled Device) can be used.

As is well known, a CCD is a photodiode or a thin film transistor (TFT).
And the like (the charge amount) of electron-hole pairs generated corresponding to the amount of light applied to the light receiving portion of each photosensor. The luminance of the irradiation light is detected by a scanning circuit. By the way, in a photo sensor system using such a CCD, it is necessary to separately provide a selection transistor for setting each scanned photo sensor to a selected state. There is a problem of increasing the size.

Therefore, in recent years, as a configuration for solving such a problem, a thin film transistor having a so-called double gate structure (hereinafter, referred to as a “double gate”) in which a photo sensor itself has a photo sensing function and a selection transistor function. Type transistors) have been developed, and attempts have been made to reduce the size of the system and increase the density of pixels. Therefore, the double-gate transistor can also be favorably applied to the two-dimensional image reading device of the present invention.

Here, a photo sensor (hereinafter, referred to as a "double gate photo sensor") using a double gate transistor applied to the two-dimensional image reading apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the basic structure of a double-gate photosensor.

As shown in FIG. 1A, a double-gate photosensor 10 has a semiconductor layer of amorphous silicon or the like in which electron-hole pairs are generated when excitation light (here, visible light) is incident. (Channel layer) 11 and semiconductor layer 11
And impurity layers 17 and 18 made of n ⁺ silicon, provided at both ends of the semiconductor substrate, and opaque to visible light selected from chromium, chromium alloy, aluminum, aluminum alloy and the like formed on the impurity layers 17 and 18. A block insulating film 14 and an upper (top) gate insulating film 1 above the drain layer 12 and the source electrode 13 and above the semiconductor layer 11 (above the drawing).
5 made of a transparent conductive film such as ITO formed through
A top gate electrode 21 that transmits visible light,
Chromium, a chromium alloy, formed below the semiconductor layer 11 (below the drawing) via the lower (bottom) gate insulating film 16;
And a bottom gate electrode 22 that is opaque to visible light such as aluminum or an aluminum alloy. And
Double gate type photo sensor 1 having such a configuration
Numeral 0 is formed on a transparent insulating substrate 19 such as a glass substrate.

Here, in FIG. 1A, the protective insulating film 20 provided on the top gate insulating film 15, the block insulating film 14, the bottom gate insulating film 16, and the top gate electrode 21 is the same as the semiconductor layer 11 shown in FIG. The static electricity removing layer 30 formed of an insulating material having a high transmittance to the exciting visible light, for example, silicon nitride, silicon oxide, or the like, provided on the protective insulating film 20 includes a semiconductor layer 11.
A material having high transmittance to visible light that excites, for example,
Since it includes a plurality of layers made of amorphous silicon, ITO, or the like, it has a structure for detecting only light incident from above the drawing. The double-gate photosensor 10 is generally represented by an equivalent circuit as shown in FIG. Here, TG is a top gate terminal, BG is a bottom gate terminal, S is a source terminal, and D is a drain terminal.

Next, a photo sensor system provided with a photo sensor array (photo sensor device) configured by two-dimensionally arranging the above-described double gate type photo sensors will be briefly described with reference to the drawings. FIG.
1 is a schematic configuration diagram of a photosensor system including a photosensor array configured by two-dimensionally arranging double-gate photosensors.

As shown in FIG. 2, the photo sensor system is roughly divided into a large number of double gate type photo sensors 10.
Are arranged in a matrix of, for example, n rows × m columns, and a top gate terminal TG (top gate electrode 2) of each double gate type photo sensor 10.
1) and the bottom gate terminal BG (bottom gate electrode 2)
2), a top gate line 101 and a bottom gate line 102 extending in a row direction, and a drain line 103 connecting a drain terminal D (drain electrode 12) of each double gate type photosensor 10 in a column direction.
, A source line 104 connecting source terminals S (source electrodes 13) in a column direction, a top gate driver 110 connected to a top gate line 101, and a bottom gate driver 12 connected to a bottom gate line 102.
0, a column switch 132, a precharge switch 133, and an amplifier 134 connected to the drain line 103.
And a drain driver (output circuit unit) 130 composed of

Here, the top gate line 101 is formed integrally with the top gate electrode 21 by a transparent conductive film such as ITO, and the bottom gate line 102, the drain line 103 and the source line 104 are formed by the bottom gate electrode 22 respectively. , The drain electrode 12 and the source electrode 13 are integrally formed of the same material opaque to the same excitation light. Further, the source line 104 is connected to the ground potential. In FIG. 2, φtg and φbg are:
Reset pulses φT1, φT2,... ΦTi,.
φTn and readout pulses φB1, φB2,.
A control signal for generating Bi,... ΦBn, φpg is a precharge signal for controlling the timing of applying the precharge voltage Vpg.

In such a configuration, from the top gate driver 110 via the top gate line 101,
By applying a voltage to the top gate terminal TG, a photo sensing function is realized, and the bottom gate driver 11
2, a voltage is applied to the bottom gate terminal BG via the bottom gate line 102, the detection signal is taken into the train driver 130 via the drain line 103, and output as serial data or parallel data (Vout)
By doing so, a selective reading function is realized.

Next, a drive control method for the above-described photo sensor system will be described with reference to the drawings. FIG.
FIG. 4 is a timing chart illustrating an example of a drive control method of the photosensor system. FIG. 4 is a conceptual diagram of the operation of the double-gate photosensor, and FIG. FIG. Here, the configuration of the above-described double-gate photosensor and photosensor system (FIGS. 1 and 2) will be described with appropriate reference.

First, in the reset operation, as shown in FIGS. 3 and 4A, a pulse voltage (reset pulse; for example, Vtg =
+15 V (high level) φTi is applied, and carriers (here, holes) accumulated near the semiconductor layer 11 of each double gate type photosensor 10 and the interface with the semiconductor layer 11 in the block insulating film 14 are applied. (Reset period Treset).

Next, in the light accumulation operation, as shown in FIGS. 3 and 4B, a low level (for example, Vtg = −15 V) bias voltage φT is applied to the top gate line 101.
By applying i, the reset operation ends, and the light accumulation period Ta due to the carrier accumulation operation starts. In the light accumulation period Ta, an electron-hole pair generated in the incident effective area of the semiconductor layer 11, that is, the carrier generation area is generated according to the amount of light incident from the top gate electrode side, and the semiconductor layer 11 and Holes are accumulated near the interface between the block insulating film 14 and the semiconductor layer 11, that is, around the channel region.

In the precharge operation, as shown in FIGS. 3 and 4C, in parallel with the light accumulation period Ta, the drain line 1 is controlled based on the precharge signal φpg.
03, a predetermined voltage (precharge voltage) Vpg is applied,
The charge is held in the drain electrode 12 (precharge period Tprch). Next, in the read operation, FIG.
As shown in FIG. 4D, after a precharge period Tprch has elapsed, a high-level (for example, Vbg = + 10 V) bias voltage (read selection signal; hereinafter, referred to as a read pulse) φBi is applied to the bottom gate line 102. As a result, the double-gate photosensor 10 is turned on (readout period Tread).

Here, in the reading period Tread,
Carriers (holes) accumulated in the channel region act in a direction to reduce Vtg (−15 V) applied to the top gate terminal TG having the opposite polarity, and therefore, Vbg of the bottom gate terminal BG is reduced.
As a result, an n-channel is formed, and the drain line voltage VD of the drain line 103 changes according to the drain current as shown in FIG.
As shown in (a), it tends to gradually decrease from the precharge voltage Vpg over time.

That is, when the light accumulation state during the light accumulation period Ta is a dark state and no carriers (holes) are accumulated in the channel region, as shown in FIGS. 4 (e) and 5 (a). By applying a negative bias to the top gate terminal TG, the positive bias of the bottom gate terminal BG is canceled and the double gate type photosensor 10 is turned off, and the drain voltage, that is, the drain line 1
The voltage VD of 03 is maintained almost as it is.

On the other hand, when the light accumulation state is the bright state, carriers (holes) corresponding to the amount of incident light are captured in the channel region as shown in FIGS. 4D and 5A. Therefore, it acts to cancel the negative bias of the top gate terminal TG, and the bottom gate terminal B
Due to the positive bias of G, the double gate photosensor 10 is turned on. Then, the voltage VD of the drain line 103 is determined according to the ON resistance according to the amount of incident light.
Will decrease.

Therefore, as shown in FIG.
The tendency of the change in the voltage VD of the drain line 103 depends on the time from the end of the reset operation by the application of the reset pulse φTi to the top gate terminal TG to the application of the read pulse φBi to the bottom gate terminal BG (the light accumulation period Ta). ) Is closely related to the amount of light received, and tends to decrease gradually when the amount of accumulated carriers is small,
Further, when the amount of accumulated carriers is large, it tends to decrease sharply. Therefore, by detecting the voltage VD of the drain line 103 after a predetermined time has elapsed after the start of the read period Tread, or by detecting a time required to reach the voltage based on a predetermined threshold voltage. By doing so, the amount of irradiation light is converted.

The above-described series of image reading operations is defined as one cycle, and the same processing procedure is repeated for the double-gate photosensor 10 in the (i + 1) -th row, so that the double-gate photosensor 10 is formed as a two-dimensional sensor system. Can work. In the timing chart shown in FIG. 3, the precharge period Tprch
After a lapse of time, as shown in FIGS. 4F and 4G, when the state where a low level (for example, Vbg = 0 V) is applied to the bottom gate line 102 is continued, the double gate type photosensor 10 keeps the OFF state. Then, as shown in FIG. 5B, the voltage VD of the drain line 103 holds the precharge voltage Vpg. As described above, the selection function of selecting the read state of the double-gate photosensor 10 is realized by the voltage application state to the bottom gate line 102.

FIG. 6 is a sectional view of a main part of a two-dimensional image reading apparatus (fingerprint reading apparatus) to which the above-described photo sensor system is applied. Here, for the sake of explanation and illustration, hatching indicating a cross-sectional portion of the photosensor system is omitted. As shown in FIG. 6, in an image reading apparatus that reads a two-dimensional image such as a fingerprint, a glass substrate (insulating substrate) on which a double-gate photosensor 10 is formed.
Irradiation light La is made incident from a backlight (surface light source) 40 provided on the lower side of the double-gate photosensor 10 (specifically, the bottom gate electrode 2).
2. Except for the regions where the drain electrode 12 and the source electrode 13) are formed, the transparent insulating substrate 19 and the insulating films 15, 16, 20
Irradiates the finger (detected object) 50 placed on the detection object contact surface 30 a on the transparent static electricity removing layer 30.

When a fingerprint is detected by the fingerprint reader, the translucent layer of the skin surface layer 51 of the finger 50 contacts the transparent layer (static electricity removing layer 30) formed on the uppermost layer of the photosensor array 100. By doing so, there is no air layer having a low refractive index at the interface between the static electricity removing layer 30 and the skin surface layer 51. Here, the thickness of the skin surface layer 51 is 65
Since it is thicker than 0 nm, the light La incident inside the convex portion 52a of the fingerprint 52 propagates while scattering and reflecting inside the skin surface layer 51. Part of the transmitted light Lb passes through the transparent static electricity removing layer 30, the transparent insulating films 20, 15, 14 and the top gate electrode 21 and enters the semiconductor layer 11 of the double gate photosensor 10 as excitation light. Is done.
As described above, the semiconductor layer 11 of the double-gate photosensor 10 disposed at a position corresponding to the convex portion 52a of the finger 50
By accumulating carriers (holes) generated by light incident on the finger 50, the image pattern of the finger 50 can be read as light / dark information according to the above-described series of drive control methods.

In the concave portion 52b of the fingerprint 52,
The irradiated light La is applied to the fingerprint detecting surface 3 of the static electricity removing layer 30.
0a and the air layer, and reaches the finger at the tip of the air layer and is scattered in the skin surface layer 51. However, since the skin surface layer 51 of the finger 50 has a higher refractive index than air, it has a certain angle. The light Lc in the skin surface layer 51 incident on the interface is hard to escape to the air layer, and the incidence on the semiconductor layer 11 of the double-gate photosensor 10 arranged at a position corresponding to the concave portion 52b is suppressed. In the embodiment described below, a case will be described in which the above-described double-gate photosensor is applied as a photosensor. However, the present invention is not limited to this, and a well-known photodiode, TFT, or the like may be used. Needless to say, it can be applied well.

Next, a two-dimensional image reading apparatus according to the present invention will be described with reference to specific embodiments. FIG.
1 is a schematic configuration diagram illustrating an embodiment of a two-dimensional image reading device according to the present invention. In addition, about the structure equivalent to the above-mentioned structure (FIG. 1, FIG. 6), the same code | symbol is attached | subjected and the description is simplified or abbreviate | omitted.

As shown in FIG. 7, in the two-dimensional image reading apparatus according to the present embodiment, a plurality of double-gate photosensors 10 having the above-described configuration are arranged in a matrix on an insulating substrate (glass substrate) 19. A photosensor array (photosensor device) 100 formed in an array and a light-transmitting protective insulating film 20 formed so as to cover the entire array region in which at least a plurality of double-gate photosensors 10 are arranged. A static electricity removing layer 30 composed of a first conductive layer 31 and a second conductive layer 32 sequentially stacked thereon
A lead wiring 33 for connecting the first conductive layer 31 to a ground potential (predetermined potential); and a rear surface side (lower side in the drawing) of the photosensor array 100, and an upper surface side of the photosensor array 100 (static discharge). A surface light source 40 that irradiates a finger (detected body) 50 that has come into contact with the upper surface of the layer 30 with uniform light.
And is configured.

Here, the first of the static electricity removing layers 30 is formed.
Has a high transmittance (light transmittance) with respect to visible light that excites the semiconductor layer 11 of each double-gate photosensor 10, and has a high conductivity (in other words,
(Low resistance). Specifically, for example, the above-described ITO, tin oxide (SnO ₂ ), indium and zinc having a film thickness set so that the sheet resistance is approximately 50 Ω / □ or less (preferably, 20 Ω / □ or less). A transparent conductive material such as an oxide is applied.

Further, the second conductive layer 32 is formed on the first conductive layer 31 so that the object to be detected does not directly contact the first conductive layer 32.
Has a high transmittance (light transmittance) with respect to visible light for exciting the semiconductor layer 11 of the first conductive layer 31.
It is configured to have a higher resistivity than that of.
Here, it is desirable that the second conductive layer 32 can be made thinner and has uniform film quality and electrical characteristics (resistance characteristics) even when it is made thinner. Specifically, for example, amorphous silicon (α-Si) having a resistivity of about 10 ⁶ to 10 ⁸ Ω · cm is applied, and the first conductive layer 31 is formed by a known film forming method such as a plasma CVD method.
A predetermined film thickness is formed thereon. It is desirable that the static electricity removing layer 30 composed of the first conductive layer 31 and the second conductive layer 32 has a transmittance of about 75% or more to visible light for exciting the semiconductor layer 11. Other configurations (materials) applied to the second conductive layer 32 will be described later.

On the other hand, the lead wiring 33 connects the first conductive layer 31 to the ground potential, and discharges static electricity supplied to the first conductive layer 31 via the second conductive layer 32 as described later. It is made of a low-resistance wiring material that can be discharged well to the ground potential, for example, a lead wire or a metal layer. Here, the wiring resistance (insertion resistance) of the extraction wiring 33
33a is a sheet resistance of the first conductive layer 31 (about 50Ω).
/ □ or less).

In such a two-dimensional image reading apparatus,
An object to be detected, that is, a finger (human body) is formed on the second conductive layer 32.
When the device 40 is placed and contacted, static electricity charged on the finger 40 is discharged from the high-resistance second conductive layer 32 to the ground potential via the low-resistance first conductive layer 31 and the lead-out wiring 33. Flow down. At this time, since the second conductive layer 32 is made of a material having a high resistivity so as to have a high resistance, even if a high electric field is generated due to static electricity charged on the finger 40, the second conductive layer 32 has a high resistance. The amount of current flowing through the layer 32 is suppressed. Also, the first conductive layer 3 via the second conductive layer 32
The current flowing to 1 is sufficiently and reliably discharged to the ground potential via the first conductive layer 31 and the lead-out wiring 33 having lower resistance.

As a result, a phenomenon in which a large discharge current temporarily flows through the static electricity removing layer 30 at the moment when the finger 40 is placed on and touches the second conductive layer 32 is suppressed. The influence (damage) on the photosensor device, for example, the malfunction due to the fluctuation of the potential and the occurrence of deterioration or breakage of the laminated film (for example, the protective insulating film 20 or the like) are suppressed, and the electrostatic withstand voltage of the photosensor device is improved. In addition, when the two-dimensional image reading device is applied to a fingerprint reading device, it is possible to greatly reduce the discomfort felt by the user at the fingertip due to the electric shock caused by the discharge of the static electricity.

Further, according to the two-dimensional image reading apparatus of the present embodiment, a transparent conductive material such as ITO is applied as the first conductive layer 31 forming the static electricity removing layer 30, By using a material that is transparent and has a high resistivity such as amorphous silicon and is easy to form a film as the conductive layer 32, the finger 4 placed on the static electricity removing layer 30 can be used.
0, scattered and reflected light is satisfactorily incident on the semiconductor layer 11 of each double-gate photosensor 10, so that the reading sensitivity characteristics of the photosensor device are not deteriorated and the photosensor device is well covered. The image pattern (fingerprint) of the detection object can be read.

Here, the static electricity removing layer 3 according to the present embodiment
The configuration and operation of the first conductive layer 31 applied to 0 will be described. As described above, the static electricity removing layer 30 applied to the present embodiment is connected to the ground potential, and has a lower sheet resistance (a sheet resistance of approximately 50Ω / □ or less) than the second conductive layer 32. 31 is directly in contact with the object to be detected, and has a higher resistivity than the first conductive layer 31 (for example, approximately 10 ⁶ Ω).
(Resistivity of about cm or more). For such a configuration, the sheet resistance of the ITO layer and the actual withstand voltage (electrostatic withstand voltage) of the photosensor device are measured using an experimental model in which the ITO layer forming the first conductive layer 31 is connected to the ground potential via a lead wire. )
Verify the relationship with

FIG. 8 shows an experimental result showing the relationship between the sheet resistance of the ITO layer or the like applied to the first conductive layer according to the present embodiment and the actual withstand voltage, and FIG. 9 shows the film thickness of the ITO layer. 6 is a correspondence table showing a relationship between the sheet resistance and the sheet resistance. In this verification experiment, the actual withstand voltage was such that a strong electric field was generated by an electrostatic gun on the first conductive layer, and some or all of the circuits of the photosensor system shown in FIG. Is defined as the applied voltage.

As shown in FIG. 8, as the first conductive layer, I
The relation between the sheet resistance and the actual withstand voltage when the TO layer is applied is that the sheet resistance is generally high (45 to 50Ω /) even though the resistance up to the ground potential (wiring resistance) is almost unified.
□), the absolute value of the actual withstand voltage is lower (−5 to −7 kV),
On the other hand, the sheet resistance is low (15-30Ω / □)
The tendency was observed that the absolute value of the actual withstand voltage became higher (−8 to −9 kV).

In comparison with other materials under the same experimental conditions, when a carbon paste or a copper tape having a relatively low sheet resistance (approximately 20 to 30 Ω / □) is applied as the first conductive layer. Since the actual withstand voltage is −10 kV or less and the absolute value of the actual withstand voltage is greater than 10 kV, it was found that the lower the sheet resistance, the higher the absolute value of the actual withstand voltage. Note that the absolute value of the discharge voltage due to contact with a finger is approximately 3 to 4 kV, so that if the absolute value is 5 kV or more, damage to the photosensor device can be suppressed and the photosensor device can function satisfactorily.

Here, the sheet resistance of the ITO film is ITO
It is controlled by changing the thickness of the layer and the abundance ratio of oxygen. The relationship between the thickness of the ITO layer and the sheet resistance generally has a correspondence as shown in FIG. Therefore, as described above, in order to set the sheet resistance as low as approximately 20 Ω / □ in order to increase the actual withstand voltage, the film thickness needs to be set to 150Ω
It is necessary to form it at 0 ° or more. The ITO layer is made of a transparent conductive material. However, even in the case of ITO, light absorption and scattering in the layer occur, so that the thickness of the ITO layer is reduced in order to realize a low sheet resistance. If the thickness is unconditionally increased, the reading sensitivity characteristic of the image pattern of the detection target (finger) is deteriorated. Therefore, it is desirable to set the thickness of the ITO layer based on certain conditions.

Therefore, in order to realize a higher absolute value of the actual withstand voltage (approximately -10 kV) and to maintain good image pattern reading sensitivity characteristics while realizing a higher absolute value of the actual withstand voltage (approximately -10 kV) by the above verification experiment, I constituting the conductive layer of
The thickness of the TO layer is approximately 500 ° or more, preferably 15
When the sheet resistance is about 15 to
It turned out that it is more desirable to set it to about 20Ω / □. In this case, the thickness of the first conductive layer (ITO layer) may be relatively thin, about 1500 to 2000 °, so that the above-described large attenuation of light in the ITO layer is suppressed.

In this verification experiment, the case where an ITO layer is applied as the first conductive layer 31 has been described. However, the present invention is not limited to this.
As the first layer, in addition to the above-mentioned ITO, a material such as tin oxide (SnO ₂ ) having a light transmitting property and oxides of indium and zinc is used, and the sheet resistance is as low as 50Ω / □ or less. The structure (setting of film thickness, adjustment of components, etc.) can be applied favorably.

Next, the static electricity removing layer 3 according to the present embodiment
Another configuration of the second conductive layer 32 applied to 0 will be described. As described above, the second embodiment applied to the present embodiment
Since the conductive layer 32 is configured to have a high resistance, the function of suppressing the amount of current flowing through the second conductive layer 32 even when a high electric field is generated by static electricity charged in the finger 40 (Large current suppression function). Meanwhile, the first
The conductive layer 31 has a function (discharge function) of sufficiently and reliably discharging the current supplied through the second conductive layer 32 to the ground potential.

Therefore, the second embodiment applied to the present embodiment
The conductive layer 32 has film characteristics capable of favorably realizing the above-described functions, that is, has a high transmittance for visible light incident on the photosensor, and has a higher transmittance than the first conductive layer 31. And high resistance, it is easy to form a thin film, and even if it is thinned, it is only necessary to have uniform film quality and electrical characteristics (resistance characteristics). A silicon nitride film (SiN) or a silicon oxide film (Si
O ₂ ), a silicon thin film containing n-type impurities (n ⁺ -S
i) a semi-insulating diamond thin film, polystyrene or polyvinyl alcohol formed to a thickness of 500 ° or less,
Polymer thin film such as polymethyl methacrylate, or
A conductive polymer thin film such as polyvinyl carbazole or a triphenyldiamine derivative can be favorably applied.

In the above-described embodiment, a two-layer structure in which the first conductive layer and the second conductive layer are laminated is shown as the structure of the static electricity removing layer. However, the present invention is not limited to this. Rather, it is sufficient that the device has a configuration capable of at least satisfactorily realizing the large current suppressing function and the discharging function described above. For example, the static electricity removing layer may be configured by two or more layers.

[0054]

According to the first aspect of the present invention, the static elimination layer includes at least a first conductive layer provided on at least a region where the subject is placed on the photo sensor device; And a second conductive layer having a higher resistivity than the first conductive layer. Therefore, when an object to be detected such as a finger (human body) is placed on the second conductive layer and brought into contact therewith, Static electricity charged on the detection body moves from the high-resistance second conductive layer via the low-resistance first conductive layer, and is discharged to a predetermined potential such as a ground potential.

Therefore, when the discharge current due to the static electricity charged to the detection object flows to the predetermined potential, a large discharge current is prevented from flowing through the high resistance second conductive layer temporarily. Since the discharge current quickly flows from the high-resistance second conductive layer to the predetermined potential via the low-resistance first conductive layer, damage to the photosensor device at the time of electrostatic discharge can be suppressed. At the same time, it is possible to reduce the discomfort caused by the electric shock at the time of the contact of the detected object.

The first conductive layer has a thickness of about 50 Ω /
□ It is desirable to set the following sheet resistance,
Further, it is preferable that the first conductive layer is formed of a material mainly containing indium tin oxide.
Accordingly, the first conductive layer (ITO) can be formed to be relatively thin, so that the object is irradiated and reflected while the actual withstand voltage of the photosensor device is increased (about -10 kV). The transmitted light satisfactorily passes through the first conductive layer and is incident on the photosensor. Therefore, deterioration of the reading sensitivity characteristics due to light attenuation can be suppressed, and the image pattern of the detection target can be read well. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic structure of a double gate type photo sensor.

FIG. 2 is a schematic configuration diagram of a photosensor system including a photosensor array configured by two-dimensionally arranging double-gate photosensors.

FIG. 3 is a timing chart illustrating an example of a drive control method of the photo sensor system.

FIG. 4 is an operation conceptual diagram of a double gate type photo sensor.

FIG. 5 is a diagram showing a light response characteristic of an output voltage of the photo sensor system.

FIG. 6 is a cross-sectional view of a main part of a two-dimensional image reading apparatus to which a photo sensor system including a double gate type photo sensor is applied.

FIG. 7 is a schematic configuration diagram showing one embodiment of a two-dimensional image reading device according to the present invention.

FIG. 8 shows I applied to the first conductive layer according to the embodiment.
It is an experimental result which shows the relationship between the sheet resistance of a TO layer etc. and actual withstand voltage.

FIG. 9 is a correspondence table showing the relationship between the thickness of the ITO layer and the sheet resistance.

FIG. 10 is a schematic configuration diagram of a fingerprint reader having an electrostatic discharge structure according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Double gate type photo sensor 11 Semiconductor layer 20 Protective insulating film 21 Top gate electrode 22 Bottom gate electrode 30 Static electricity removal layer 31 First conductive layer 32 Second conductive layer 33 Lead-out wiring 40 Surface light source 50 Finger 100 Photo sensor array

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 AA08 AB10 BA05 CA02 CA11 CA34 CB14 DD12 FB09 FB13 FB16 GA02 GB11 5C024 CX00 EX23 GX02 GY31 5F088 AA01 AA09 AB05 BA20 BB03 EA04 HA20 5F110 AA22 AA30 BB01 EE03 EE30 FF02 FF03 GG02 GG15 HK03 HK04 HK06 HK21 NN23 NN24 NN80

Claims (6)

[Claims] An object is placed on a photosensor device having a plurality of photosensors arranged on one surface side of an insulating substrate, and an image pattern of the object is read.
In the three-dimensional image reading apparatus, a first conductive layer for removing static electricity charged on the object to be detected and a second conductive layer having higher resistivity than the first conductive layer are provided on the photosensor device. A two-dimensional image reading device comprising a static electricity removing layer. 2. The two-dimensional image reading apparatus according to claim 1, wherein the first conductive layer has a sheet resistance of about 50 Ω / □ or less. 3. The method according to claim 1, wherein the first conductive layer is made of indium oxide.
The two-dimensional image reading device according to claim 1, wherein the two-dimensional image reading device is formed of a material mainly composed of tin. 4. The two-dimensional image reading device according to claim 1, wherein the first conductive layer is connected to a ground potential. 5. The second conductive layer has a resistivity of 10 ⁶ Ω.
The two-dimensional image reading device according to any one of claims 1 to 4, wherein the size is not less than cm. 6. The second conductive layer comprises a material selected from amorphous silicon, amorphous silicon containing impurities, silicon nitride, silicon oxide, diamond, a polymer thin film, or a conductive polymer. The two-dimensional image reading device according to claim 1.