JP2003150943A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader used in a fingerprint collation system or the like and adapted to start the operation on detecting the contact of a detected body, capable of obtaining good image quality by overcoming the disadvantages of the resistance detection system. SOLUTION: This image reader includes a transparent conductive film (a transparent electrode layer 30) integrally covering an image read surface of an image sensor part, a good conductor (a case member 50) mounted in an outer edge of the transparent conductive film or in an arbitrary position on the outer edge thereof, an insulator (e.g. air) for electrically insulating the transparent conductive film from the good conductor, and a determination means (a detecting circuit 60) for determining the contact of the detected body according to a change in resistance value between the transparent conductive film and the good conductor. The contact surface of the detected body is formed by the transparent conductive film and the good conductor.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, the biological characteristics of the human body that cannot be arbitrarily changed (eg:
An image reading apparatus applicable to a so-called biometric authentication system that authenticates an individual by means of facial features, fingerprints, and blood vessel patterns of the retina. Specifically, a start signal for automating the reading start (authentication start) of biological characteristics is provided. The present invention relates to an image reading device capable of generating and outputting.

[0002]

2. Description of the Related Art Fingerprint authentication, which is one type of biometric authentication, is a personal authentication method that uses a fingerprint unique to an individual, and is an authentication technology that has much higher security than a password method or the like. A fingerprint authentication system using this technology can be applied to a wide range of applications, such as an entrance / exit management system for specific areas at business establishments, home security, payment systems on the Internet, or business application usage authentication systems. it can.

FIG. 10A is a simplified block diagram of the fingerprint authentication system 1. Generally, the fingerprint authentication system 1 includes an image reading device 2 and a fingerprint collation device 3, and uses the collation result (personal authentication result) of the fingerprint collation device 3 to determine whether or not the above various systems can be used or not. .

The image reading device 2 is a compact, lightweight, low power consumption image pickup device such as a CCD (Charge Cou
It is configured by a two-dimensional solid-state imaging device such as a pled device) and reads a fingerprint image of the authentication target person 4 and outputs the fingerprint image to the fingerprint collation device 3. The fingerprint matching device 3 extracts, for example, a feature point extraction method, that is, a fingerprint feature point (a fingerprint end point or a branch point) from a fingerprint image read by the image reading device 2, and the feature point is registered in advance. It is determined whether or not it matches the feature point information of the registered person who is authenticated, and the person-to-be-authenticated 4 is authenticated, and the verification result (personal authentication result) is output to, for example, the above-described various authentication systems.

Here, the start of reading a fingerprint image by the image reading device 2 and the start of the fingerprint matching operation by the fingerprint matching device 3 (hereinafter collectively referred to as "authentication start" for convenience) are the image reading device. 2 is preferably performed automatically when the finger of the authentication subject 4 is placed (when the fingertip is touched) from the viewpoint of operability. Examples of such one-touch type authentication start technology include:
"Resistance detection method" and "capacity detection method" are known.

FIG. 10B is a conceptual diagram of the resistance detection method. The image reading device 2 is partitioned by, for example, a transparent insulating film 2b via an insulating film (protective insulating film) not shown on the image reading surface (upper surface in the figure) of the image sensor unit 2a such as CCD. Alternatively, two transparent conductive films 2c, 2c which are arranged apart from each other with a slight gap therebetween.
It has a structure in which d is stacked. The planar sizes of the two transparent conductive films 2c and 2d including the transparent insulating film 2b are set to be slightly larger than the fingertip area of the authentication target person 4, and the finger of the authentication target person 4 touches the image reading device 2. When this is done, the fingertip is in contact with both of the two transparent conductive films 2c and 2d.

In such a structure, the resistance value between the two transparent conductive films 2c and 2d when the fingertip is not touched (when the fingertip is not touched) is the resistance value of the transparent insulating film 2b, that is, the resistance value of approximately infinity. The same resistance value at the time of touching (touching) a fingertip is obtained by the value
given by the skin resistance of the fingertip in contact with both of d,
Since this skin resistance is lower than the resistance value of the transparent insulating film 2b, the one-touch type authentication start technology can be realized by utilizing the change in the resistance value.

FIG. 10C is a conceptual diagram of the capacity detection method. The image reading device 2 has a structure in which a transparent conductive film 2e having the same size as the image reading surface is laminated on the image reading surface (the upper surface in the figure) of the image sensor unit 2a such as CCD. Transparent conductive film 2e when the fingertip is not touched
Capacity is smaller than the same capacity when touched with a fingertip (the same capacity when touched with a fingertip increases with the capacity of the human body), so one-touch authentication start technology should be realized by utilizing the change in capacity. You can

[0009]

However, the above conventional image reading apparatus 2 has the following problems.

(1) Problems of the resistance detection method In the resistance detection method, the transparent insulating film 2b and the two transparent conductive films 2c, 2 which are electrically separated from each other by a gap.
It is possible to satisfactorily detect the contact state of the fingertip and start the image reading operation based on the resistance value when the fingertip which is the detected body comes into contact with both d, but at this time, the human body is charged. Static electricity is discharged to a predetermined potential (ground potential or the like) not shown through the transparent conductive films 2c and 2d. here,
Generally, a conductive oxide film such as ITO described later is often used as a film material applied to a transparent conductive film, and such a conductive oxide film has a higher resistance value than a metal material. Since the material has material characteristics, the static electricity is not sufficiently discharged to the ground potential when the fingertip is touched, and the image sensor unit 2
There is a problem that electrostatic breakdown of the two-dimensional solid-state imaging device constituting a is caused. Further, since the image reading surface of the image sensor portion 2a has a structure in which the transparent insulating film 2b and the two transparent conductive films 2c and 2d partitioned by a gap are laminated, a fingerprint read by the image sensor portion 2a is formed. There is a problem in that an unnecessary partition line (a boundary line between the transparent insulating film 2b and the gap) is included in the image and the image quality is impaired, resulting in deterioration of fingerprint collation performance.

(2) Problems of the capacitance detection method This detection method is based on the transparent conductive film 2 when the fingertip is not touched.
It is based on a capacitance change between the capacitance A of e (the capacitance between the image sensor unit 2a and the transparent conductive film 2e) and the capacitance B when the fingertip is touched. For example, the capacitance A is about 6000 pF. , Capacity B is capacity A (6000 pF
(About 100 pF) of the human body, and the above-mentioned capacitance change amount is only about 1/60 of the capacitance A, the detection performance must be sufficiently high, and the cost increases. There is a problem.

Therefore, in view of the above-mentioned problems, the present invention overcomes the drawbacks of the conventional resistance detection method so that a good image quality can be obtained. For example, when applied to a fingerprint collation system, It is an object of the present invention to provide an image reading device that does not cause deterioration in matching performance.

[0013]

An image reading apparatus according to a first aspect of the present invention has an image sensor section for reading an image of a detection object brought into contact with an image reading surface and outputting an image signal thereof. In the image reading device, a transparent conductive film that integrally covers an image reading surface of the image sensor unit, an outer edge of the transparent conductive film, or a good conductor provided at an arbitrary position on the outer edge, and the transparent conductive film. An insulator that electrically insulates the good conductor from each other, and a determination unit that determines contact of the detected object based on a change in resistance value between the transparent conductive film and the good conductor. It is characterized in that the transparent conductive film and the good conductor form a contact surface of the object to be detected.

Here, the transparent conductive film has transparency,
Moreover, it is a film-like substance that also has conductivity. Typical examples are tin oxide (SnO ₂ ) film and ITO (Indium-Tin-Oxide) film, and an appropriate film material should be selected in consideration of light transmittance and conductivity. You can Insulators and good conductors are those with electrical insulation in the former and electrical conductivity in the latter (especially "good").
Since it does not need to take optical characteristics such as transmittance into consideration, it has good conductivity of air or insulators such as rubber or Teflon (registered trademark), or metal or metal-plated thin film. The bodies can each be applied.

In the present invention, the contact surface of the object to be detected is formed by the transparent conductive film and the good conductor, and the electric resistance value between the transparent conductive film and the good conductor at this contact surface is detected. It is equivalent to almost infinity when the body is not in contact, and the surface resistance of the body to be detected (the skin resistance when the body is a finger of the body) when the body is in contact with it. A binary change in electrical resistance value can be obtained. Therefore, the contact of the detected object is determined from the change in the resistance value.

Further, according to the present invention, since the image reading surface of the image sensor section is integrally covered with the transparent conductive film, it is not necessary for the image of the detected object read by the image sensor section as in the prior art. The partition line (in the case of the conventional technique, the boundary line between the transparent insulating film 2b and the gap) does not enter, and as a result, good image quality can be obtained. For example, when applied to a fingerprint matching system, fingerprint matching can be performed. There is no reduction in performance.

An image reading apparatus according to a second aspect of the present invention is the image reading apparatus according to the first aspect, wherein the good conductor is made of metal for protecting the image reading surface of the image sensor section. It is characterized by being a case.

In the present invention, the protective metal case is also used as the good conductor. Therefore, a separate good conductor is not required, so that the number of parts can be reduced and the manufacturing cost can be reduced.

An image reading apparatus according to a third aspect of the present invention is the image reading apparatus according to the first aspect, wherein the determining means determines that the resistance value between the transparent conductive film and the good conductor is When the resistance value of the insulator falls below a reference resistance value that is set lower by a predetermined margin, the contact of the object to be detected is determined.

In the present invention, the contact of the object to be detected is determined based on the change in the resistance value between the transparent conductive film and the good conductor when the object is not in contact and when the object is in contact.

An image reading apparatus according to a fourth aspect of the present invention is the image reading apparatus according to the first aspect, wherein the determination means resistance-divides a predetermined DC constant voltage to generate a divided voltage. A voltage dividing unit is provided, and the divided voltage is applied to either one of the transparent conductive film and the good conductor, and the other is set to the ground potential, and the potential difference between the transparent conductive film and the good conductor is When the insulator is used as a load resistance, the contact of the object to be detected is determined when the voltage falls below a reference voltage value set lower by a predetermined margin than the voltage value across the load resistance.

According to the present invention, the contact of the object to be detected is determined based on the change in the potential difference between the transparent conductive film and the good conductor when the object is not in contact and when the object is in contact.

An image reading device according to a fifth aspect of the present invention is the image reading device according to the first aspect, wherein the image sensor portion includes a source electrode and a source electrode formed by sandwiching a channel region made of a semiconductor layer. A drain electrode,
A first gate electrode and a second gate electrode formed at least above and below the channel region via an insulating film, respectively, and applying a reset pulse to the first gate electrode to operate the sensor. After initializing and applying a pre-charge pulse to the drain electrode, a read pulse is applied to the second gate electrode, so that the channel region is charged during a charge accumulation period from the end of initialization to the application of the read pulse. Outputs a voltage corresponding to the electric charge accumulated in the output voltage, and the image reading device,
The difference between the signal voltage related to the precharge pulse and the output voltage is observed as the image signal.

According to the present invention, the image sensor section applies the reset pulse to the top gate electrode (first gate electrode) and the read pulse to the bottom gate electrode (second gate electrode) at a predetermined timing. Thus, during the charge accumulation period, charges corresponding to the amount of incident light in the channel region are accumulated, and a voltage corresponding to the accumulated amount of charges is output as an image signal. As a result, each pixel of the image sensor unit is thinned and miniaturized, and as a result, it is possible to increase the number of pixels of the image sensor unit and improve the reading accuracy of the fingerprint image.

According to a sixth aspect of the present invention, there is provided the image reading apparatus according to the first aspect, wherein the good conductor is such that an object to be detected comes into regular contact with the transparent conductive film. It may have a guide function for guiding.

That is, a good conductor such as a conductive case member provided around the sensor array and the transparent electrode film is arranged so that the object to be detected such as a finger contacts the transparent conductive film serving as the detection surface in a good and normal manner. In order to guide or guide the touch position, direction, etc. of the detection target, for example, it may be formed to have an oval opening or the like corresponding to the shape of the finger.

As a result, since the object to be detected is always touched at a predetermined position on the detection surface, the image pattern can be accurately read under certain conditions, and
Since the object to be detected can surely and satisfactorily be brought into contact with both the transparent conductive film and the good conductor such as the case member, the start operation of the image reading operation can be satisfactorily executed.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of an image reading apparatus according to the present invention will be described in detail with reference to the drawings as an application example to a fingerprint authentication system.

<Structure of Image Sensor Section> First, a good sensor structure applied to the image reading apparatus according to the present invention will be described. As the sensor applied to the image reading apparatus according to the present invention, as described at the beginning, a solid-state imaging device such as CCD can be used in terms of small size, light weight, and low power consumption.

As is well known, the CCD is a photodiode or a thin film transistor (TFT).
r) and other photosensors are arranged in a matrix, and the amount of electron-hole pairs (charge amount) generated corresponding to the amount of light applied to the light receiving portion of each photosensor is determined by the horizontal scanning circuit. And the vertical scanning circuit to detect the brightness of the irradiation light.

By the way, in such a photosensor system using a CCD, it is necessary to individually provide a selection transistor for bringing each scanned photosensor into a selected state. Therefore, as the number of pixels increases, an image is increased. It has a disadvantage that the sensor section becomes large.

Therefore, in recent years, as a structure for solving such a problem, a thin film transistor having a double gate structure in which a photo sensor itself has a photo sensing function and a selection transistor function (hereinafter, referred to as "double gate type transistor"). Has been developed, and attempts have been made to reduce the size of the system and increase the density of pixels.
Therefore, it is extremely preferable to apply this double gate type transistor also to the image reading apparatus of the present invention. This is because the number of pixels can be increased without increasing the size of the image sensor unit and the reading accuracy of the fingerprint image can be significantly improved.

Here, a photosensor using a double gate type transistor applied to the image reading apparatus according to the present invention (hereinafter referred to as "double gate type photosensor").
Will be described with reference to the drawings.

<Structure of Double Gate Photo Sensor> FIG. 1 is a sectional structural view showing a schematic structure of a double gate photo sensor. As shown in FIG. 1A, the double-gate photosensor (image sensor unit) 10 is made of amorphous silicon or the like in which electron-hole pairs are generated when excitation light (here, visible light) is incident. Semiconductor layer (channel layer)
11 and n ⁺ provided on both ends of the semiconductor layer 11, respectively.
A pair of impurity layers 17 and 18 made of silicon, and a drain electrode 1 formed on the impurity layers 17 and 18, respectively.
2 and the source electrode 13, a top gate electrode (first gate electrode) 21 formed above the semiconductor layer 11 (above the drawing) via a block insulating film 14 and an upper (top) gate insulating film 15, and a semiconductor Below layer 11 (below the drawing)
And a bottom gate electrode (second gate electrode) 22 formed via a lower (bottom) gate insulating film 16 on a transparent insulating substrate 19 such as a glass substrate.

Here, the drain electrode 12 and the source electrode 13 are formed of a metal material opaque to visible light selected from chromium, a chromium alloy, aluminum, an aluminum alloy and the like, and the top gate electrode ( The first gate electrode (21) is made of a transparent electrode film such as ITO that is transparent to visible light and has conductivity, and the bottom gate electrode (second gate electrode) 22 is It is made of a metal material that is opaque to visible light and is selected from chrome, chrome alloys, aluminum, aluminum alloys, and the like.

That is, in FIG. 1A, the uppermost transparent electrode layer (transparent conductive film) 30, the lower layer protective insulating film (derivative) 20, the top gate insulating film 15, the block insulating film 14, and the bottom gate. Each of the insulating films 16 is formed of a transparent thin film having a high light transmittance for visible light that excites the semiconductor layer 11, and has a structure for detecting only light incident from above the drawing.

The double gate type photosensor 10 is generally represented by an equivalent circuit as shown in FIG. Here, TG is the top gate electrode 21.
A bottom gate terminal electrically connected to the bottom gate electrode 22, S a source terminal electrically connected to the source electrode 13, and D electrically connected to the drain electrode 12. Drain terminal that is electrically connected.

Next, a drive control method of the above-mentioned double gate type photo sensor will be described with reference to the drawings. FIG. 2 is a timing chart showing an example of a basic drive control method of the double gate type photo sensor, FIG. 3 is an operation conceptual diagram of the double gate type photo sensor, and FIG. 4 is a double gate type photo sensor. It is a figure which shows the optical response characteristic of the output voltage of. Here, description will be given with reference to the configuration of the above-described double-gate photosensor (FIG. 1) as appropriate.

First, in the reset operation (initialization operation), as shown in FIGS. 2 and 3A, a pulse voltage (hereinafter referred to as “reset pulse”) is applied to the top gate terminal TG of the double-gate photosensor 10. Note: For example, Vtg = +
A high level of 15 V) φTi is applied to the semiconductor layer 1
1 and carriers (here, holes) accumulated near the interface between the block insulating film 14 and the semiconductor layer 11 are released (reset period Trst).

Next, in the light accumulation operation (charge accumulation operation), as shown in FIGS. 2 and 3B, a bias voltage φTi of low level (for example, Vtg = −15V) is applied to the top gate terminal TG. By doing so, the reset operation is completed and the light accumulation period Ta by the carrier accumulation operation is started. During the light accumulation period Ta, electron-hole pairs are generated in the effective incident region of the semiconductor layer 11, that is, in the carrier generation region, according to the amount of light incident from the top gate electrode 21 side, and the semiconductor layer 11 and the block insulation. Membrane 1
Holes are accumulated in the vicinity of the interface with the semiconductor layer 11 in 4, that is, around the channel region.

In the precharge operation, as shown in FIGS. 2 and 3C, a predetermined voltage (precharge) is applied to the drain terminal D in parallel with the light accumulation period Ta based on the precharge signal φpg. Voltage) Vpg is applied to hold electric charge in the drain electrode 12 (precharge period Tpr
ch).

Next, in the read operation, as shown in FIG.
As shown in FIG. 3D, after the precharge period Tprch has passed, a high-level (eg, Vbg = + 10V) bias voltage (read selection signal; hereinafter referred to as “read pulse”) is applied to the bottom gate terminal BG. By applying φBi (selected state), the double gate photosensor 10 is turned on (reading period Tread).

Here, in the read period Tread,
Carriers (holes) accumulated in the channel region act in the direction of relaxing Vtg (-15V) applied to the top gate terminal TG having the opposite polarity, and thus Vbg of the bottom gate terminal BG.
(+ 15V) forms an n-channel, and the voltage of the drain terminal D (drain voltage) VD according to the drain current.
Shows a tendency of gradually decreasing from the precharge voltage Vpg with time, as shown in FIG.

That is, when the light accumulation state in the light accumulation period Ta is the bright state, carriers (holes) corresponding to the amount of incident light are trapped in the channel region as shown in FIG. 3D. , The negative bias of the top gate terminal TG is canceled, and the positive bias of the bottom gate terminal BG corresponds to the canceled bias, and the double gate type photosensor 10 is turned on. Then, according to the ON resistance corresponding to the incident light amount, the drain voltage VD is lowered as shown in FIG.

On the other hand, when the light storage state is dark and no carriers (holes) are stored in the channel region, a negative bias is applied to the top gate terminal TG as shown in FIG. 3 (e). As a result, the positive bias of the bottom gate terminal BG is canceled and the double gate type photo sensor 1
0 is in the OFF state, and the drain voltage VD is maintained almost as it is, as shown in FIG.

Therefore, as shown in FIG.
The change tendency of the drain voltage VD depends on the top gate terminal TG.
To the bottom gate terminal BG until the read pulse φBi is applied to the bottom gate terminal BG (light accumulation period Ta) from the end of the reset operation by applying the reset pulse φTi to the bottom gate terminal BG. When it is large (bright state), it tends to decrease sharply, and when the accumulated carriers are small (dark state), it tends to decrease gently. Therefore, the drain voltage VD after the elapse of a predetermined time from the start of the read period Tread
By detecting (= Vrd), or by detecting the time until the voltage reaches a predetermined threshold voltage, the double gate type photo sensor 10 is detected.
The amount of light (illumination light) incident on is converted.

The double gate type photo sensor operates as a two-dimensional sensor system by repeating the same processing procedure for the double gate type photo sensor 10 in the i + 1th row with the series of image reading operations described above as one cycle. Can be made.

In the timing chart shown in FIG. 2, after the precharge period Tprch has elapsed, the timing chart shown in FIG.
As shown in (f) and (g), if the low level (for example, Vbg = 0V) is applied to the bottom gate terminal BG (non-selected state), the double gate photosensor 10 is kept in the OFF state. Then, as shown in FIG.
The drain voltage VD holds a voltage close to the precharge voltage Vpg. In this way, the selection function of switching the reading state of the double-gate photosensor 10 to the selected / non-selected state is realized depending on the state of the voltage applied to the bottom gate terminal BG.

<Photo Sensor System> Next, a photo sensor system having a photo sensor array configured by arranging the above-mentioned double gate type photo sensors in a predetermined format will be described with reference to the drawings. here,
A photosensor array configured by arranging a plurality of double gate type photosensors in a two-dimensional manner will be shown and described. However, a plurality of double gate type photosensors are arranged in a one-dimensional manner in the X direction to form a line sensor array. Needless to say, the two-dimensional area may be scanned by moving the line sensor array in the Y direction orthogonal to the X direction.

FIG. 5 shows a double-gate type photosensor having two components.
FIG. 1 is a schematic configuration diagram of a photosensor system including a photosensor array configured in a two-dimensional array. As shown in FIG. 5, the photo sensor system is roughly classified into a photo sensor array in which a large number of double gate photo sensors 10 are arranged in a matrix of, for example, n rows × m columns (n and m are arbitrary natural numbers). 100 and the top gate terminal TG (top gate electrode 2 of each double gate photosensor 10).
1) and the bottom gate terminal BG (bottom gate electrode 2)
2) are connected in the row direction to extend, and a top gate line 101 and a bottom gate line 102, and a drain line (data line) in which the drain terminal D (drain electrode 12) of each double-gate photosensor 10 is connected in the column direction ) 103, the source terminal S (source electrode 13) in the column direction, and the source line (common line) 104 connected to the ground potential, the top gate driver 110 connected to the top gate line 101, and the bottom. A bottom gate driver 120 connected to the gate line 102 and a drain driver 130 including a column switch 131, a precharge switch 132, and an amplifier 133 connected to the drain line 103 are included.

Here, the top gate line 101 is integrally formed with a transparent electrode layer such as ITO together with the top gate electrode 21 shown in FIG.
02, drain line 103 and source line 104
Are the bottom gate electrode 22 and the drain electrode 1, respectively.
2. The source electrode 13 and the source electrode 13 are integrally formed of a material that is opaque to the same excitation light. Further, a constant voltage Vss set according to a precharge voltage Vpg described later is applied to the source line 104, but may be a ground potential (GND).

In FIG. 5, φtg is a control signal for generating signals φT1, φT2, ... φTi, ... φTn, which are selectively output as either the reset voltage or the photocarrier storage voltage, and φbg. Is a control signal for generating signals φB1, φB2, ... φBi, ... φBn that are selectively output as either the read voltage or the non-read voltage, and φpg controls the timing of applying the precharge voltage Vpg. This is a precharge signal.

In such a structure, from the top gate driver 110 through the top gate line 101,
By applying a signal φTi (i is an arbitrary natural number; i = 1, 2, ... N) to the top gate terminal TG, the photo sense function is realized, and the bottom gate driver 12
The signal φBi is applied to the bottom gate terminal BG from 0 through the bottom gate line 102, and the drain line 10
The detection signal is taken into the drain driver 130 via the output signal V and the output voltage V of the serial data or parallel data is output.
By outputting as out, the selective reading function is realized.

FIG. 6 is a cross-sectional view of the essential parts of a fingerprint image reading apparatus (image sensor section) to which the above-described photo sensor system is applied. Here, for convenience of explanation and illustration, hatching showing a cross-sectional portion of the photo sensor system is omitted. As shown in FIG. 6, in an image reading device that reads an image pattern such as a fingerprint, a backlight (surface light source) provided below an insulating substrate 19 such as a glass substrate on which the double-gate photosensor 10 is formed. ) Irradiation light La is made incident from BL, and this irradiation light La is generated by the double gate photosensor 10 (specifically, bottom gate electrode 22, drain electrode 12, source electrode 1).
The transparent insulating substrate 19 and the insulating films 15, 16 and 20 except the region 3) are penetrated and the finger (covered) placed on the fingerprint detection surface (image reading surface) 30a on the transparent electrode layer 30. It is irradiated to the detection body) 40.

When the fingerprint is detected by the fingerprint reader, the semi-transparent layer of the skin surface layer 41 of the finger 40 is
By contacting the transparent electrode layer 30 formed on the uppermost layer of the photosensor array 100, the air layer having a low refractive index disappears at the interface between the transparent electrode layer 30 and the skin surface layer 41. Here, since the thickness of the skin surface layer 41 is thicker than 650 nm, the light La incident inside the convex portion 42 a of the fingerprint 42 propagates while being scattered and reflected inside the skin surface layer 41. A part of the propagated light Lb is transmitted through the transparent electrode layer 30, the transparent insulating films 20, 15, 14 and the top gate electrode 21, and the semiconductor layer 1 of the double-gate photosensor 10.
1 is incident as excitation light. As described above, the carriers (holes) generated by the incident light are accumulated in the semiconductor layer 11 of the double-gate photosensor 10 arranged at the position corresponding to the convex portion 42a of the finger 40, and The image pattern of the finger 40 can be read as the light and dark information according to the series of drive control methods described above.

In the concave portion 42b of the fingerprint 42,
The radiated light La is applied to the fingerprint detection surface 30 of the transparent electrode layer 30.
a passing through the interface between a and the air layer, the finger 40 at the tip of the air layer
Reach the surface and are scattered in the skin surface layer 41,
Has a higher refractive index than air, light Lc in the skin surface layer 41 incident on the interface at an angle is less likely to escape to the air layer, and the semiconductor layer of the double-gate photosensor 10 arranged at the position corresponding to the recess 42b. Incident on 11 is suppressed.

Thus, ITO is used as the transparent electrode layer 30.
By applying a transparent conductive material such as, for example, the light radiated to the finger 40 placed on the transparent electrode layer 30, scattered, and reflected is favorably applied to the semiconductor layer 11 of each double-gate photosensor 10. Therefore, the reading sensitivity characteristic in the reading operation of the finger (object to be detected) 40 is not deteriorated, and the image pattern (fingerprint) of the object to be detected is satisfactorily read.

Next, the image reading apparatus according to the present invention will be described with reference to specific embodiments. In the embodiment described below, a case where the above-mentioned double gate type photo sensor is applied as a sensor will be described.

FIG. 7 is a schematic view showing a state where a finger is placed on the image reading apparatus according to this embodiment. Note that, here, description will be given with reference to the configurations of the above-described photosensor and photosensor system (FIGS. 1 and 6) as appropriate. Further, regarding the configuration equivalent to the configuration shown in FIGS. 1 and 6,
The same reference numerals are given and the description thereof is simplified or omitted.

As shown in FIG. 7, in the image reading apparatus according to the present embodiment, the double-gate type photosensor 10 having the above-mentioned structure is formed on one surface side of the translucent insulating substrate 19 in a matrix form. Photo sensor array 1
00, and a sensor device PD including a transparent electrode layer (transparent conductive film) 30 formed through a protective insulating film 20 over the entire array region in which the double-gate photosensors 10 are arranged, and a translucent insulation. The surface light source BL, which is arranged on the other surface side of the substrate 19 and irradiates the finger (object to be detected) 40 that is in contact with the upper surface (fingerprint detection surface 30a) of the sensor device PD with uniform light, is separated from the sensor device PD. And a metal case member 50 as a good conductor provided so as to surround the sensor device PD.
And a detection circuit 60 that detects a change in resistance value between the transparent electrode layer 30 and the case member 50.

Here, a ground potential (GND) is applied to the case member 50, and the case member 50 is spaced apart from the sensor device PD with a predetermined gap, and the air in the gap serves as an insulating layer. It is electrically isolated. Alternatively, a predetermined insulator other than air (for example, rubber or Teflon (registered trademark)) may be interposed in the gap. In short, the case member 50 and the transparent electrode layer 30 of the sensor device PD are essential.
It suffices if there is an electrical insulation between and.

Further, the case member 50 surrounds the sensor device PD and is provided with an opening 50a having a predetermined shape for exposing the fingerprint detecting surface 30a on the transparent electrode layer 30. The material of the case member 50 is selected from, for example, chromium, aluminum, tungsten, or the like, and is made of a material (that is, a good conductor) having a lower resistivity than the transparent conductive material such as ITO of the transparent electrode layer 30, It is composed of a layer or a plurality of layers of conductors.

Specifically, the opening 50 of the case member 50
a is the finger 4 on the fingerprint detection surface 30a on the sensor device PD.
In a state in which 0 is placed, the finger 40 has a shape such that the finger 40 also contacts the case member 50 near the end of the opening 50a. That is, the finger 40 has a shape suitable for contacting both the transparent electrode layer 30 and the case member 50.

The case member 50 may have a function as a shield case for protecting the sensor device PD from an electric disturbance element, a physical shock or the like, which will be described later. As described above, it may have a function as a guide member for guiding or guiding the finger, which is the detected object, so as to make good contact with the fingerprint detection surface 30a on the sensor device PD.

Since the case member 50 is made of a material having a resistivity lower than that of the conductor material forming the transparent electrode layer 30, it is possible to obtain a sufficient sheet resistance with a small thickness, so that the signal-to-noise ratio is low. (S / N) can be made sufficiently large. Further, the case member 50 has a property of reflecting or absorbing visible light and ultraviolet rays, and thus the top gate driver 1
10, the bottom gate driver 120 and the drain driver 130 are arranged so as to be covered, so that it is possible to prevent external light from directly entering the drivers 110, 120, and 130, and suppress deterioration. it can.

FIG. 8 is a specific configuration diagram of the detection circuit 60. The detection circuit 60 includes a transparent electrode layer 30 and a ground potential (G
Input protection diode 61 connected in parallel with ND)
And the first protection diode 61 connected in parallel
A resistance element 62 and a second resistance element 63 having one end connected to the first resistance element 62 and the other end connected to a DC constant voltage Vcc.
And a voltage follower 64 that amplifies the potential at the connection point (hereinafter referred to as “point A”) between the first resistance element 62 and the second resistance element 63 with ANF (amplification factor) 1, the DC constant voltage Vcc, and the ground potential. The variable resistance element 65 connected between the variable resistance element 65 and the variable voltage Vr extracted from the variable resistance element 65 is compared with the output potential Vo of the voltage follower 64, and the binary logic signal Vf corresponding to the comparison result is output. Comparator 6
6 and a pull-up resistor 6 for the output potential of the comparator 66.
7 and 7. Here, the first resistance element 62 and the second resistance element 63 form a voltage dividing means 68.

In such a structure, the case member 50
When the finger 40 is not in contact with the transparent electrode layer 30, the electrical resistance value R between the case member 50 and the transparent electrode layer 30.
L has a high resistance value (hereinafter referred to as “Rmax”) that is substantially infinite. The potential at point A (hereinafter referred to as “Vmax”) of the voltage dividing means in this high resistance state is R ₆₂ when the resistance value of the first resistance element 62 is R ₆₂ , and R is the resistance value of the second resistance element 63.
_{If it is 63} , it is given by the following equation (1).

Vmax = i × R ₆₂ (1) Here, since i = Vcc / (R ₆₂ + R ₆₃ ) ... (2), Vmax = [Vcc / (R ₆₂ + R _63). )] × R ₆₂ ... (3)

Now, in order to simplify the explanation, "R ₆₂ = R
₆₃ = 1 kΩ ”, the above formula (3) becomes Vmax = (Vcc / 2kΩ) × 1kΩ ... (4), and Vmax = Vcc / 2 ... (5).

On the other hand, when the finger 40 contacts the case member 50 and the transparent electrode layer 30, the electrical resistance value RL between the case member 50 and the transparent electrode layer 30 is as low as the skin resistance of the finger 40. It has a value (hereinafter referred to as "Rmin"). The potential at point A of the voltage dividing means (hereinafter referred to as “Vmin”) in the low resistance state is Rmin = 0.5 for convenience of explanation.
If kΩ, it is given by the following equation (6).

[0071] Becomes

That is, the case member 50 and the transparent electrode layer 3
The potential at point A (Vmax) of the voltage dividing means when the finger 40 is not in contact with 0 and the potential at point A of the voltage dividing means when the finger 40 is in contact with the case member 50 and the transparent electrode layer 30. (Vmi
Since n) has a relationship of Vmax> Vmin from the equations (5) and (6), it is necessary to set the threshold voltage Vr to an appropriate value that is smaller than Vmax and larger than Vmin. The comparator 66 can convert the potential change at the point A into a binary logic signal Vf and output it.

Therefore, according to the present embodiment, the upper surface of the sensor device PD is covered with the transparent electrode layer 30, and
It is not necessary for the fingerprint image because the transparent electrode layer 30 is integrated without being disposed separately from the transparent insulating film 2b or the gap as in the prior art (see FIG. 10B). It is possible to obtain a special effect that the collation performance can be improved by making the read image quality good without introducing such an image.

Whether or not the finger 40 is in contact with the case member 50 and the transparent electrode layer 30 can be detected by the change in the electrical resistance value RL between the case member 50 and the transparent electrode layer 30. It is possible to generate and output a one-touch activation signal (binary logic signal Vf) for instructing the start of the matching operation.

Further, an excessive input voltage such as static electricity applied to the image reading device (sensor device PD, detection circuit 60 side) via the finger 40 can be released to the ground potential via the input protection diode 61. The reader can be protected. The input protection diode 61
Is a unidirectional diode in the illustrated example, but is not limited to this. A bidirectional diode may be formed by connecting a pair of diodes in parallel in opposite directions. on the other hand,
Excessive input voltage such as static electricity applied to the case member 50 via the finger 40 is directly discharged to the ground potential.

Further, in the above-described embodiment, FIG.
As described above, the case member 50 having a rectangular opening 50a which surrounds the sensor device PD and exposes the transparent electrode layer 30 has been described as the shape of the case member 50. In the present invention, since it is necessary for the finger to contact both the transparent electrode layer 30 and the case member 50, the case member 50 serves as a guiding or guiding member for bringing the object to be detected into good contact with the fingerprint detection surface 30a. You may apply what added the function of.
Specifically, for example, as shown in FIG.
As a shape of 0, a substantially elliptical or elliptical opening 50b is provided in correspondence with the shape of the finger 40 to be detected, and the placement position, direction, etc. of the finger 40 are provided to the user of the fingerprint reading device. By visually recognizing that the finger 40 is brought into good contact with the fingerprint detection surface 30a of the opening 50b of the ellipse, and the finger 40 is also brought into contact with the end portion of the case member 50. It is possible to satisfactorily obtain the function and effect of the form.

Further, in the above-described embodiment, the case member 50 is connected to the ground potential (GND) and the transparent electrode layer 30 is connected to the detection circuit 60, but this can be reversed. . That is, the case member 50 is connected to the detection circuit 60, and the transparent electrode layer 30 is connected to the ground potential (GND).
You may connect to. However, as shown in the above embodiment, by adopting the configuration in which the case member 50 is connected to the ground potential, the transparent electrode layer 30 made of ITO or the like having a higher resistance value than metal is connected to the ground potential. Compared to the configuration, the static electricity of the human body can be discharged to the ground potential satisfactorily via the case member 50 formed of a metal such as a good conductor. Therefore, from the viewpoint of electrostatic discharge (elimination of static electricity) of the human body, preferable.

Further, in the above-mentioned embodiment, the case where the double gate type photosensor is applied as the sensor is shown, but the sensor applied to the present invention is not limited to this double gate type photosensor. The same can be applied to a photo sensor system using a photo sensor having another configuration such as a photodiode or a TFT. Further, in the above-described embodiment, the optical so-called photo sensor is used. However, for example, it is possible to read a capacitance that is displaced according to the unevenness of a finger, and to apply a capacitive sensor in which a threshold value is set. , The signal component (voltage, displacement voltage, etc.) output from each of the multiple sensors is detected, and the number of sensors (frequency) for each signal component
If the sensor system has a configuration and a method for determining a characteristic portion included in the image pattern of the detected object, based on the tendency of change in frequency with respect to the signal component obtained by observing The reader can be applied well.

In the above description, the "fingerprint" is taken as an example, but the present invention is not limited to this. In short, it is a biological characteristic of the human body that cannot be arbitrarily changed. , As long as it can read images,
For example, it can be applied to reading "face" and "vascular pattern of retina".

[0080]

According to the image reading apparatus of the present invention, the contact surface of the object to be detected is formed by the transparent conductive film and the good conductor, and the contact surface between the transparent conductive film and the good conductor is formed. The electrical resistance value of is equivalent to infinity when the object is not in contact, and the surface resistance of the object when the object is in contact (the skin resistance when the object is a human finger) That is, since a binary change in the electric resistance value can be obtained at the time of non-contact and at the time of contact, it is possible to judge the contact of the detection object with one touch from the change in the resistance value. Therefore, it is possible to avoid the problem that the determination of the contact state of the detection target becomes unstable or difficult due to the influence of the capacitance of the sensor device itself, as in the image reading apparatus of the capacitance detection method described in the related art. You can

Furthermore, since the image reading surface of the image sensor section is integrally covered with the transparent conductive film, unnecessary partition lines (conventional partition lines) are conventionally added to the image of the object read by the image sensor section as in the prior art. In the case of technology, transparent insulating film 2b
And a boundary line of a gap are not included, and as a result, good image quality is obtained, and for example, when applied to a fingerprint matching system, the performance of fingerprint matching is not deteriorated.

Further, in the above-mentioned image reading apparatus, since the good conductor is a metal case for protecting the image reading surface of the image sensor section, the number of parts can be reduced and the manufacturing cost can be reduced. .

Further, in the above-mentioned image reading apparatus, the judging means is a criterion that the resistance value between the transparent conductive film and the good conductor is set lower than the resistance value of the insulator by a predetermined margin. When it is lower than the resistance value, the contact of the detected object is determined, and therefore, the contact of the detected object can be determined based on the change in the resistance value when the detected object is not in contact and the contact value. it can.

Further, in the above-mentioned image reading apparatus, the judging means includes a voltage dividing means for resistance-dividing a predetermined DC constant voltage to generate a divided voltage, and the divided voltage is supplied to the transparent conductive film and the transparent conductive film. A reference voltage applied to a good conductor, and a voltage value between the transparent conductive film and the good conductor is set lower than a voltage value across the load resistance when the insulator is a load resistance by a predetermined margin. When it is less than a value, the contact of the detected object is determined, so that the contact of the detected object can be determined based on the change between the voltage value when the detected object is not in contact and the voltage value when the detected object is in contact. . Therefore, unlike the capacitance detection type image reading apparatus shown in the prior art, it is not necessary to have a highly sensitive and complicated structure for determining the contact state of the object to be detected from a minute change in capacitance. It is possible to simplify the configuration of the (detection circuit) and reduce the product cost.

In the above-mentioned image reading apparatus, the sensor includes a source electrode and a drain electrode formed by sandwiching a channel region made of a semiconductor layer, and at least an insulating film above and below the channel region. A first gate electrode and a second gate electrode which are formed, a reset pulse is applied to the first gate electrode to initialize the sensor, and a precharge pulse is applied to the drain electrode; By applying a read pulse to the gate electrode of, the voltage corresponding to the charge accumulated in the channel region is output as an output voltage during the charge accumulation period from the end of initialization to the application of the read pulse, and the image reading apparatus described above The difference between the signal voltage related to the precharge pulse and the output voltage may be observed as the image signal.

As a result, the sensors forming the sensor array can be made thin and compact, and the density of the read pixels can be increased to read the image pattern of the object to be detected as a high-definition image. In this case, the thinning of the sensor reduces the static electricity resistance, but the above-mentioned transparent electrode layer and the case member are connected to the ground potential via the antiparallel diode circuit, and the structure for static electricity removal is provided. With the above configuration, the sensor array including the double gate type photo sensor can be favorably applied to the image reading apparatus according to the present invention.

Further, in the above-mentioned image reading apparatus, the metal case as the good conductor may have a guide function for guiding the object to be detected so as to make regular contact with the transparent conductive film. Well, for example, it is configured to guide or guide the placement position, direction, etc. of the detection target so that the detection target such as a finger can contact the transparent electrode film serving as the detection surface satisfactorily and normally. .

As a result, the object to be detected is always placed at a predetermined position on the detection surface, so that the image pattern can be accurately read under certain conditions, and the object to be detected is a transparent conductive film and a transparent conductive film. Since it is possible to reliably and satisfactorily contact both of the metal cases, it is possible to satisfactorily execute the startup operation of the image reading operation.

[Brief description of drawings]

FIG. 1 is a cross-sectional structural view showing a schematic configuration of a double-gate type photosensor applied to an image reading apparatus according to the present invention.

FIG. 2 is a timing chart showing an example of a basic drive control method of a double gate type photo sensor.

FIG. 3 is an operation conceptual diagram of a double gate type photo sensor.

FIG. 4 is a diagram showing an optical response characteristic of an output voltage of a double gate type photo sensor.

FIG. 5 is a schematic configuration diagram of a photosensor system including a photosensor array configured by arranging double-gate photosensors two-dimensionally.

FIG. 6 is a cross-sectional view of a main part of an image reading device (fingerprint reading device) to which a photo sensor system including a double gate type photo sensor is applied.

FIG. 7 is a schematic configuration diagram showing an embodiment when the image reading device according to the present invention is applied to a fingerprint reading device.

FIG. 8 is a configuration diagram of a detection circuit.

FIG. 9 is an equivalent circuit showing a circuit function in a non-contact state and a contact state of an object to be detected (finger) to the fingerprint reading device according to the present embodiment. It is a distribution characteristic diagram.

FIG. 10 is a schematic configuration diagram showing a configuration example of an image reading apparatus in a conventional technique.

[Explanation of symbols]

Vcc DC constant voltage 10 Double gate type photo sensor (image sensor section) 11 Semiconductor layer (channel region) 12 drain electrode 13 Source electrode 21 Top gate electrode (first gate electrode) 22 Bottom gate electrode (second gate electrode) 30 Transparent electrode layer (transparent conductive film) 30a Fingerprint detection surface (image reading surface) 40 fingers (object to be detected) 50 case members (good conductor, metal case) 60 Detection circuit (determination means) 68 partial pressure means

Claims (6)

[Claims] 1. An image reading apparatus having an image sensor section for reading an image of a detection object brought into contact with the image reading surface and outputting an image signal thereof, wherein the image reading surface of the image sensor section is integrally covered. A transparent conductive film, an outer edge of the transparent conductive film or a good conductor provided at an arbitrary position on the outer edge, an insulator electrically insulating between the transparent conductive film and the good conductor, A determination means for determining contact of the detection object based on a change in resistance value between the transparent conductive film and the good conductor, the transparent conductive film and the good conductor of the detection object An image reading apparatus characterized in that it is configured to form a contact surface. 2. The image reading device according to claim 1, wherein the good conductor is a metal case for protecting an image reading surface of the image sensor unit. 3. The determination means, when a resistance value between the transparent conductive film and the good conductor is lower than a reference resistance value set lower than a resistance value of the insulator by a predetermined margin, The image reading apparatus according to claim 1, wherein the contact of the detected object is determined. 4. The determining means includes voltage dividing means for resistively dividing a predetermined direct current constant voltage to generate a divided voltage, and the divided voltage is either one of the transparent conductive film and the good conductor. And the other is ground potential, the potential difference between the transparent conductive film and the good conductor is set lower than the voltage value across the load resistance when the insulator is a load resistance by a predetermined margin. The image reading apparatus according to claim 1, wherein the contact of the object to be detected is determined when the value is lower than the reference voltage value. 5. The image sensor unit includes a source electrode and a drain electrode formed by sandwiching a channel region made of a semiconductor layer, and a first electrode formed at least above and below the channel region with an insulating film interposed therebetween. A gate electrode and a second gate electrode, wherein a reset pulse is applied to the first gate electrode to initialize the sensor, and a precharge pulse is applied to the drain electrode, and then the second gate By applying a read pulse to the electrodes, a voltage corresponding to the charge accumulated in the channel region is output as an output voltage during the charge accumulation period from the end of initialization to the application of the read pulse, and the image reading device Is observing the difference between the signal voltage related to the precharge pulse and the output voltage as the image signal. Image reading apparatus of claim 1, wherein. 6. The image reading apparatus according to claim 1, wherein the good conductor has a guide function for guiding the detected body so as to come into regular contact with the transparent conductive film. .