JP2003242488A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus suitable for obtaining an image of an object such as a fingertip touching the imaging surface. <P>SOLUTION: A fingerprint reader 3 includes an image pickup element 8 for converting the shading due to projecting and recessed parts of the fingertip 100 to obtain a fingerprint image of the fingertip 100. A photocatalyst film 33 having transparency and a photocatalyst function is formed on the surface of the image pickup element 8. The photocatalyst 33 mainly contains titanium oxide. By the photocatalyst function of the photocatalyst film 33, sebum of the fingertip adhering to the surface of the surface is decomposed so that the fingerprint will not remain on the surface of the image pickup element 8. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device for obtaining an optical image of a subject.

[0002]

2. Description of the Related Art Conventionally, a fingerprint reading device has been known as an image pickup device for picking up a fingerprint defined by minute unevenness of a fingertip of a subject. This fingerprint reading device supplies an image sensor for converting the degree of light and darkness of light due to unevenness of a finger tip to an electric signal and a drive signal for driving the image sensor which is arranged in the vicinity of the image sensor and supplies it to the finger tip. And a driver circuit for acquiring the fingerprint image data of. In this fingerprint reading device, when reading a fingerprint of a fingertip, the fingertip is brought into contact with an image sensor, and the difference in the unevenness of the skin forming the fingerprint is optically recognized by the image sensor so that the fingerprint can be read. There is. Since a fingerprint has a pattern peculiar to an individual, the fingerprint reading device is often used for an authentication device that performs individual authentication by collating with fingerprint image data of a registered registrant.

[0003]

By the way, since the fingertip is in contact with the image pickup device, the sebum and sweat of the convex portion of the fingertip adhere to the surface of the image pickup device, leaving a fingerprint. If a fingerprint remains on the surface of the image sensor, the fingerprint left on the surface of the image sensor may be captured, and a malicious third party may copy the fingerprint onto paper or the like. Furthermore, a third party may be authenticated by the paper on which the registrant's fingerprint is drawn. That is, the conventional imaging device as a fingerprint reading device has a possibility of leaking fingerprint data from the viewpoint of security when applied to a device that directly obtains a fingerprint image by directly contacting a fingertip which is a subject.

Therefore, an object of the present invention is to provide an image pickup apparatus suitable for obtaining an image of an object such as a fingertip which is in contact with the image pickup surface.

[0005]

In order to solve the above-mentioned problems, the invention according to claim 1 is an image pickup device for obtaining an optical image of a subject by causing light from the subject to enter at an incident surface. A photocatalytic film having a light-transmitting property and a photocatalytic function is formed on the incident surface.

Here, as in the second aspect of the invention, a plurality of photoelectric conversion elements provided under the photocatalytic film, having electrical characteristics according to the amount of incident light, and arranged in a matrix. Further comprising: a driver that drives the plurality of photoelectric conversion elements and detects electrical characteristics of the plurality of photoelectric conversion elements according to light from the subject, thereby obtaining image data of the subject. You can do it.

In the invention of claim 1 or 2, since the photocatalytic film has a light-transmitting property, light from the subject is incident on the incident surface. Therefore, an optical image of the subject can be acquired by the imaging device. Furthermore, since the photocatalytic film has a photocatalytic function, active oxygen is generated on the surface by external light. Therefore, even if dirt or dust adheres to the incident surface from the object due to the contact of the subject with the incident surface, the dirt or dust is decomposed and the dirt or dust does not remain on the incident surface. Therefore, the image pickup apparatus according to the present invention is suitable for acquiring an image of a subject in contact with the incident surface. In particular, the image pickup apparatus according to the present invention is suitable for use mainly for obtaining a fingerprint image of a fingertip. That is, the fingerprint patterned by the sebum attached to the incident surface from the fingertip does not remain on the incident surface because the sebum is decomposed by the photocatalytic function of the photocatalytic film. Therefore, since a malicious third party cannot copy a fingerprint onto paper or the like, when the image pickup apparatus according to the present invention is applied to a personal identification device, a third party who is not registered in the personal identification device is not authenticated. .

According to a third aspect of the present invention, in an image pickup device that acquires an optical image of the subject by making light from the subject incident on an incident surface, the image pickup device has a light-shielding property when the temperature is lower than the threshold temperature, and the threshold temperature. A thermochromic film, which is transparent at a higher temperature, is formed on the incident surface.

According to the third aspect of the invention, when the thermochromic film has a temperature lower than the threshold temperature, the thermochromic film has a light-shielding property, and therefore, the optical image of the object cannot be obtained by the imaging device. On the other hand, when the temperature of the thermochromic film is higher than the threshold temperature, the thermochromic film has a light-transmitting property, so that an optical image of the subject can be obtained by the imaging device. By the way, when the subject is higher than the threshold temperature, the temperature of the thermochromic film rises when the subject comes into contact with the incident surface, and an optical image of the subject can be acquired by the imaging device. On the other hand, when the subject is lower than the threshold temperature, the temperature of the thermochromic film decreases when the subject comes into contact with the incident surface, and the optical image of the subject cannot be acquired by the imaging device. That is, according to the present invention, it is possible to specify what can be applied as a subject by the temperature. Therefore, the image pickup apparatus according to the present invention is suitable for acquiring an image of a specific subject in contact with the incident surface, and an image other than the specific subject cannot be acquired.

According to a fourth aspect of the present invention, in the image pickup device according to the third aspect, the threshold temperature of the thermochromic film is 30 ° C. or higher and 40 ° C. or lower.

According to the invention of claim 4, the threshold temperature is 30.
Since the temperature is not lower than 40 ° C and not higher than 40 ° C, a part of the human body such as a fingertip is suitable as the subject. In other words, the thermochromic film does not become higher than the threshold temperature even if it contacts the incident surface with the temperature lower than the threshold temperature, that is, the body temperature only when it is normally present in the outside air, such as paper, so an image of the lower temperature is imaged. I can't. On the other hand, for example, when a part of the human body such as a fingertip contacts the incident surface, the thermochromic film has a temperature higher than the threshold temperature, so that a part of the human body can be imaged. Therefore, the image pickup apparatus according to the present invention is suitable for the main purpose of acquiring the fingerprint image of the fingertip. Therefore, for example, even if a malicious third party copies a fingerprint on paper and touches the paper with the incident surface,
Since the fingerprint pattern on the paper cannot be picked up, when the image pickup apparatus according to the present invention is applied to the personal identification device, a third person who is not registered in the personal identification device is not authenticated.

Here, as in the invention described in claim 5, in the invention described in claim 3 or 4, it is provided under the thermochromic film, has electrical characteristics according to the amount of incident light, and has a matrix. A plurality of photoelectric conversion elements arranged in a pattern, by driving the plurality of photoelectric conversion elements, by detecting the electrical characteristics of the plurality of photoelectric conversion elements according to the light from the subject, A driver for acquiring image data may be further provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[First Embodiment] FIG. 1 shows an authentication device 1 to which the present invention is applied. The authentication device 1
An arithmetic processing unit 2 including a CPU 4, a RAM 5, a ROM 6, a storage medium 7, an interface, a bus connecting these, and the like, and a fingerprint reading device 3 as an imaging device are provided.

The fingerprint reading device 3 is a device for acquiring the difference in light and shade of light corresponding to the unevenness of the fingerprint as image data converted into an electric signal. The ROM 6 of the arithmetic processing device 2 stores a control program for controlling the entire authentication device 1. The CPU 4 performs various operations according to the control program stored in the ROM 6 using the RAM 5 as a work area, so that the arithmetic processing device 2 performs various functions. For example, C
The arithmetic processing unit 2 performs a process of causing the fingerprint reading device 3 to acquire image data of a subject such as the fingertip 100 (illustrated in FIG. 3) by a calculation of the PU 4, and a process of capturing the acquired image data from the fingerprint reading device 3. You can do it.

Further, the storage medium 7 stores collation image data which is data for reference collation. And
The arithmetic processing unit 2 performs processing of the CPU 4 to determine whether the optical image data input from the fingerprint reading device 3 matches the collation image data, and authenticates when the optical image data and the collation image data match. It is possible to perform processing such as outputting a signal or a command signal for releasing a predetermined restriction that has been locked.

As shown in FIGS. 1 and 2, the fingerprint reader 3 has, as a basic configuration, a fingertip 1 to obtain a fingerprint image of the fingertip 100 by optically sensing.
An image pickup device (photosensor unit) 8 for converting light and darkness due to unevenness of 00 into image data converted into an electric signal, a fingertip holding unit 9 for holding a ball of the fingertip 100, and fingerprint image data from the image pickup device 8 is acquired, An image pickup circuit 10 for outputting fingerprint image data to the arithmetic processing unit 2, a top gate driver 11, a bottom gate driver 12 and a drain driver 13 for driving the image pickup device 8 according to a control signal from the image pickup circuit 10, and emits light. Backlight 14 that emits light
And a light guide plate 15 that guides the light of the backlight 14 to the image pickup element 8. The top gate driver 11, the bottom gate driver 12, and the drain driver 13 are each connected to the image pickup circuit 10 so that signals can be input and output.

The fingertip holder 9 is attached to the surface of the image pickup device 8. The fingertip holding portion 9 is formed with a substantially elliptical opening 16 that is open to the size of the belly of the fingertip 100. The fingertip holding portion 9 is formed in a shape such that the inner circumference of the opening 16 fits the fingertip 100. The fingertip holder 9 is made of an opaque material that blocks the transmission of light, and the light passes through only the opening 16.

The light guide plate 15 has a substantially flat plate shape and is provided with the image pickup device 8.
Is arranged on the back side of the image pickup element 8 so as to face the. A backlight 14 that emits light is arranged around the light guide plate 15. The light guide plate 15 is covered with a reflective member except for the side surface facing the backlight 14 and the surface facing the image sensor 8, and the light from the backlight 14 irradiates the back surface of the image sensor 8 via the light guide plate 15. To be done. That is, the light from the backlight 14 is surface-diffused by the light guide plate 15, and the image sensor 8
Is evenly illuminated on the back surface of.

The image pickup device 8 has a plurality of double gate type thin film transistors (hereinafter, referred to as thin film transistors) arranged in a matrix of n rows and m columns (n and m are integers) on a transparent substrate 17 having a light transmitting property and an insulating property. , DG-TFT.) 2
0, 20, ... Have a basic configuration. Each DG-TFT2
0 will be described with reference to FIG.

As shown in FIG. 3, each DG-TFT 20
Is the bottom gate electrode 21 and the bottom gate insulating film 22.
A semiconductor film 23, a channel protective film 24, impurity semiconductor films 25 and 26, a source electrode 27, a drain electrode 28, a top gate insulating film 29, a top gate electrode 30, and a protective insulating film 31. This is an n-channel thin film transistor that is provided and has a laminated structure.

The bottom gate electrode 21 is formed on the transparent substrate 17. As shown in FIG. 1, the bottom gate electrodes 21 of each DG-TFT 20 arranged in the same row in the horizontal direction.
Are connected to a common bottom gate line 41 extending in the lateral direction and are electrically conductive with each other. N bottom gate lines 41 are arranged. Bottom gate electrode 2
1 and the bottom gate line 41 have an insulating property and a light shielding property, and are made of, for example, chromium, a chromium alloy, aluminum or an aluminum alloy, or a compound or mixture thereof.

As shown in FIG. 3, the bottom gate insulating film 2
2 is formed on the bottom gate electrode 21, the transparent substrate 17 and the bottom gate line 41 so as to cover the bottom gate electrode 21 and the transparent substrate 17. The bottom gate insulating film 22 has an insulating property and a light-transmitting property, and is made of, for example, silicon nitride or silicon oxide. In addition,
The bottom gate insulating film 22 is formed on one surface and is a common layer of the DG-TFTs 20.

The semiconductor film 23 is formed on the bottom gate insulating film 22, and the semiconductor film 23 is formed on the bottom gate electrode 2.
It is arranged so as to face 1. The semiconductor film 23 is a layer made of amorphous silicon or the like, and when visible light or infrared light is incident, an amount of electron-hole pairs according to the amount of light is generated mainly in the vicinity of the interface with the channel protective film 24.

The channel protection film 24 is formed on the semiconductor film 23. The channel protective film 24 has a function of protecting the interface in the channel region of the semiconductor film 23 from an etchant used for patterning, has insulating properties and translucency, and is made of, for example, silicon nitride or silicon oxide.

The impurity semiconductor film 25 is formed so as to overlap one end of the semiconductor film 23, and the impurity semiconductor film 26 is formed so as to overlap the other end of the semiconductor film 23. Are separated from each other. Part of the impurity semiconductor film 25 overlaps one end of the channel protective film 24, part of the impurity semiconductor film 26 overlaps the other end of the channel protective film 24, and the impurity semiconductor films 25 and 26 are step-shaped. Has become. Impurity semiconductor film 2
Reference numerals 5 and 26 are made of amorphous silicon (n + silicon) containing n-type impurity ions.

The source electrode 27 is formed so as to overlap the impurity semiconductor film 25. The drain electrode 28 is formed so as to overlap the impurity semiconductor film 26. As shown in FIG. 1, each DG-TFT 2 arranged in the same column in the vertical direction.
The zero source electrode 27 is connected to a common source line 42 extending in the vertical direction. Similarly, the drain electrodes 28 of the respective DG-TFTs 20 arranged in the same column in the vertical direction have the common drain line 4 extending in the vertical direction.
Connected to 3. M source lines 42 and m drain lines 43 are arranged. Source electrode 2
7, the drain electrode 28, the source lines 42, 42, ... And the drain lines 43, 43, ... Have conductivity and light shielding properties, and are, for example, chromium, chromium alloys, aluminum or aluminum alloys, or compounds thereof. Consists of.

As shown in FIG. 3, the top gate insulating film 2
9 is formed so as to cover the channel protective film 24, the source electrode 27, the drain electrode 28, the source lines 42, 42, ... And the drain lines 43, 43 ,. The top gate insulating film 29 has an insulating property and a light transmitting property, and is made of, for example, silicon nitride or silicon oxide. The top gate insulating film 29 is formed on one surface and is a common layer of the DG-TFTs 20.

The top gate electrode 30 is formed on the top gate insulating film 29 and is arranged so as to face the bottom gate electrode 21 and the semiconductor film 23. Figure 1
, Each DG-TF arranged in the same row in the horizontal direction.
The top gate electrodes 30 of T20 are connected to a common top gate line 44 extending in the lateral direction, and are electrically conductive with each other. N top gate lines 44 are arranged. The top gate electrode 30 and the top gate line 44 have conductivity and translucency. For example, the top gate electrode 30 and the top gate line 44 are made of In2
It is made of an oxide such as O3, SnO2, Cd2SnO4 or CdO, but mainly made of ITO (Indium-Tin-Oxide).

3, the protective insulating film 31 is formed on the entire surface so as to cover the top gate electrode 30, the top gate lines 44, 44, ... And the top gate insulating film 29. The protective insulating film 31 has insulating properties and translucency,
For example, it is made of silicon nitride or silicon oxide. The upper surface of the protective insulating film 31 serves as the incident surface.

Each of the above DG-TFTs 20 is a double-gate type photosensor having the following photoelectric conversion element and MOS type transistor. The photoelectric conversion element includes a semiconductor film 23, a channel protective film 24, a source electrode 27, a drain electrode 28, a top gate insulating film 29, and a top gate electrode 30, and has electrical characteristics according to the amount of incident light. That is, the semiconductor film 23 serves as a light receiving portion, and the amount of carriers according to the amount of incident light on the semiconductor film 23 is accumulated near the interface between the semiconductor film 23 and the channel protective film 24. The MOS transistor is composed of a semiconductor film 23, a source electrode 27, a drain electrode 28, a bottom gate insulating film 22 and a bottom gate electrode 21. The semiconductor film 23 functions as a channel region of the photoelectric conversion element and the MOS transistor.

In the present embodiment, the subject touches the fingertip holder 9
When held at, the fingertip 100 comes into contact with the surface of the image sensor 8, and the fingerprint reading device 1 optically senses with the image sensor 8 to acquire a fingerprint image of the fingertip 100. That is, since the image sensor 8 is a contact type sensor, dust adheres to the surface of the image sensor 8 and becomes an obstacle for reading the light and shade of light according to the unevenness of the finger, or a charged object is captured by the image sensor 8. DG-TFT2 only by approaching the surface of
0 electrodes 21, 27, 28, 30, bottom gate lines 41, 41, ..., Source lines 42, 42, ..., Drain lines 43, 43 ,.
A malfunction may occur due to the current flowing through 4, 44, .... Since the image pickup device 8 uses the fingertip 100 as a subject in particular, sebum and sweat of the fingertip 100 tend to adhere to the surface of the image pickup device 8 and remain in the form of fingerprints on the surface of the image pickup device 8. Therefore, in the present embodiment, the image sensor 8 is subjected to surface treatment in order to suppress erroneous authentication and malfunction due to adhesion of dust and static electricity.

That is, the conductive film 32 is formed on the entire surface of the protective insulating film 31, and the photocatalytic film 33 is formed on the entire surface of the conductive film 32. The conductive film 32 has a light-transmitting property and also has a conductive property. The conductive film 32 is, for example, I
Although it is made of an oxide containing any one of n2O3, SnO2, Cd2SnO4, CdO, etc., it is made of, for example, ITO, and a weak pulse signal is periodically input from an external signal generation circuit. The reference potential of this pulse signal is the ground potential, and the pulse signal is displaced to a weak positive or negative voltage for a predetermined period at a predetermined interval. The conductive film 32 is connected to the arithmetic processing unit 2 via a detection circuit. This detection circuit has a conductive film 3
By detecting the electrical change of No. 2, the fact that the fingertip is in contact with the conductive film 32 is detected, and a signal to that effect is output to the arithmetic processing unit 2. For example, when a fingertip comes into contact with the conductive film 32, static electricity is discharged from the finger through the conductive film 32, and the weak input to the conductive film 32 is caused by the finger of a person having a specific resistance value range and capacitance range. The waveform of the pulse signal is delayed, or the waveform is blunted, which shows a particular tendency. The detection circuit detects the disturbance of the waveform and determines whether the placed object is a human finger, and a determination result signal is output from the detection circuit to the arithmetic processing unit 2. Further, for example, the conductive film 32 is composed of two regions which are insulated from each other and have different potentials, and when a fingertip contacts the two regions of the conductive film 32, a minute current flows through the conductive film 32 through the fingertip, and a minute current flows. The current is detected by the detection circuit, and a signal indicating that the ground has been detected is output from the detection circuit to the arithmetic processing device 2. When a subject having a capacity different from that of the fingertip comes into contact with the conductive film 32, the detection circuit detects electrical displacement, and a signal indicating that the subject is not the fingertip is output from the detection circuit to the arithmetic processing unit 2. .

The photocatalyst film 33 has a photocatalytic function and also has translucency. That is, the photocatalyst film 33 contains at least a substance that is brought into an excited state by light and can give its excitation energy to another, for example, a metal oxide semiconductor. When a metal oxide semiconductor absorbs light having a hand gap energy or more,
The electrons of the valence band are excited in the conduction band, and holes are formed in the valence band. The electrons react with oxygen (O2) in the outside air, and the holes react with water (H2O) in the outside air. As a result, two types of active oxygen, superoxide ions and hydroxyl radicals, are generated on the surface of the photocatalyst film 33. Since superoxide ions and hydroxyl radicals have a function of decomposing organic substances, dust adhering to the surface of the image sensor 8 (that is, the surface of the photocatalyst film 33), particularly sebum adhering from the fingertip 100, is decomposed. As a result, no fingerprint remains on the surface of the image sensor 8.

For example, the photocatalyst film 33 is made of titanium oxide (TiO2) as a metal oxide. Further, the photocatalyst film 33 may be made of titanium oxide with a slight amount of zirconium oxide, aluminum oxide, silicon oxide, or the like mixed therein. The titanium oxide is preferably rutile type titanium oxide or brookite type titanium oxide, and more preferably anatase type titanium oxide. Titanium oxide has a barrier property against ultraviolet rays. Therefore, the ultraviolet rays do not reach the semiconductor film 23 and the like, and the deterioration of the semiconductor film 23 (in particular, the change in the electrical characteristics) can be suppressed. The semiconductor film 23 is a part of the light from the backlight 14.
The photocatalyst film 33 does not hinder the carrier generation of the semiconductor film 23 because it is excited mainly by visible light or infrared light, which has a wavelength longer than ultraviolet light, to generate electron-hole pairs.

When the photocatalytic film 33 is irradiated with light,
Oxygen component (titanium oxide (Ti
In the case of O2), one of the two O's reacts with H2O in the outside air. As a result of the reaction between O and H2O, a hydroxyl group that is very compatible with water is generated. Therefore, the surface of the image sensor 8 becomes superhydrophilic, and H2O in the outside air enters the surface of the image sensor 8 with dust. Therefore, it becomes easier to remove dust from the surface of the image sensor 8, and the surface of the image sensor 8 has a self-cleaning function.

Even if the fingertip 100 contacts the photocatalyst film 33 (that is, the surface of the image pickup device 8), the grounded conductive film 32 is interposed between the electrodes 21, 27, 28, 30 of each DG-TFT 20. Therefore, no current flows through the electrodes 21, 27, 28, 30 and the like due to the charged fingertip 100. Also,
Since the photocatalyst film 33 is formed on the conductive film 32, sebum of the fingertip 100 or sweat containing sebum or protein does not adhere to the conductive film 32. In particular, the photocatalyst film 33 decomposes sebum or sweat. Therefore, sebum or sweat does not penetrate into the conductive film 32. Therefore, it is possible to prevent the conductive film 32 from increasing in resistance due to promotion of oxidation or the like, and to prevent deterioration of the electrostatic discharge property of the conductive film 32.

Next, the circuit configuration of the fingerprint reading device 3 will be described. As shown in FIG. 1, each source line 42 is
It is kept at a constant voltage, for example, grounded and kept at 0 [V]. Each bottom gate line 41 is connected to the bottom gate driver 12. Each top gate line 44 is connected to the top gate driver 11.

The top gate driver 11 is a so-called shift register. That is, according to the control signal output from the image pickup circuit 10 to the top gate driver 11, the top gate driver 11 causes the top gate line 44 in the first row to the top gate line 44 in the n-th row (n-th row: A high level reset pulse is selectively output to the first line). The bottom gate driver 12 is a so-called shift register. That is, the bottom gate driver 12 causes the bottom gate driver 12 to output the bottom gate line 4 in the first row by the control signal output from the imaging circuit 10 to the bottom gate driver 12.
A high-level read pulse is selectively output in the order of the bottom gate line 41 of the 1st to nth rows. After the top gate driver 11 outputs a reset pulse to the top gate line 44 of the i-th row (i is an integer of 1 to n), the bottom gate driver 12 outputs a read pulse to the bottom gate line 41 of the i-th row. , The top gate driver 11 and the bottom gate driver 12 shift the output signal.

In accordance with the control signal output from the image pickup circuit 10, the drain driver 13 predetermines all the drain lines 43, 43, ... Between the output of the reset pulse and the output of the read pulse. The level (high level) precharge pulse is output. Further, the drain driver 13 includes the drain lines 43, 4
The voltages of 3, ... Are amplified and output to the image pickup circuit 10. The imaging circuit 10 detects the voltage of the drain lines 43, 43, ... After a lapse of a predetermined time from the output of the read pulse, or detects the voltage of the drain lines 43, 43 ,. An optical image (that is, a fingerprint pattern) of the fingertip 100 is acquired by detecting the time required to reach a predetermined threshold voltage and output to the arithmetic processing device 2 as digital data.

Fingerprint reader 3 constructed as described above
Is a top gate driver 11, a bottom gate driver 12, and a drain driver 13 for each DG-TFT.
20 is driven by the active matrix system.

That is, when a reset pulse is output to the top gate line 44 on the i-th row, each DG-TF on the i-th row is output.
The carriers accumulated in the vicinity of the interface between the semiconductor film 23 of T20 and the channel protection film 24 are repelled by the voltage of the top gate electrode 30 and ejected. Then, when the reset pulse of the top gate line 44 ends, the amount of carriers corresponding to the amount of the reflected light reflected by the fingertip 100 is accumulated near the interface between the semiconductor film 23 and the channel protective film 24. Here, of the light that has entered the fingertip 100 from the light guide plate 15, the light that has entered at an angle less than the critical angle of total reflection is the fingertip 10
0, the interface between the convex portion 101 and the photocatalytic film 33, or the fingertip 1
00 reflected in the skin, the reflected light enters the photocatalyst film 33 and the protective insulating film 31, and the DG-TFT
20 to the semiconductor film 23 (see arrow A shown in FIG. 3).
On the other hand, the light incident on the groove 102 of the fingertip 100 is mainly transmitted through the inside of the epidermis of the finger having a higher refractive index than the air, and then repeatedly reflected to proceed in the direction in which the air intervenes.
And the air are reflected again and attenuated inside the skin, or attenuated in the air while diffusely reflected between the groove 102 and the surface of the photocatalyst film 33, so that a sufficient amount of light is emitted from the semiconductor film 2.
3 does not enter (see arrow B shown in FIG. 3). That is, the reflected light corresponding to the fingerprint pattern of the fingertip 99 is incident on the semiconductor film 23, and the amount of carriers generated and accumulated in the semiconductor film 23 is determined according to the amount of incident light on the semiconductor film 23.

Then, the precharge pulse is output from the drain driver 13 to all the drain lines 43, 43, .... At this time, the reset pulse is not output to the top gate electrode 30 of each DG-TFT 20 in the i-th row and the read pulse is not output to the bottom gate electrode 21, so that the n-channel is not formed in the semiconductor film 23. Therefore, the precharge pulse charges the drain electrode 28 with electric charges.

When a read pulse is output to the bottom gate line 41 of the i-th row almost at the same time as the end of the precharge pulse, a channel is formed in the semiconductor film 23 by the voltage of the bottom gate electrode 21 of each DG-TFT 20 in the i-th row. After being formed, each DG-TFT 20 in the i-th row is turned on. Therefore, the drain electrode 28 of each DG-TFT 20 in the i-th row
, And the voltages of the drain lines 43, 43, ... tend to gradually decrease with the passage of time due to the drain-source current.

Here, the smaller the amount of light incident on the semiconductor film 23, the less holes out of the carriers accumulated at the interface of the semiconductor film 23 due to the negative electric field of the top gate electrode 30, so that the semiconductor film 23 has a smaller number of holes. Since the inner depletion layer becomes wider, the semiconductor film 23 has a higher resistance even when a read pulse is input to the bottom gate electrode 21, and the DG-TFT
At 20, the current value between the source and the drain is low, and the displacement of the voltage of the drain line 43 during a predetermined period is small.
On the contrary, as the amount of light incident on the semiconductor film 23 increases, the number of holes among the carriers accumulated on the interface of the semiconductor film 23 increases, and the negative charge of the top gate electrode 30 for inhibiting the formation of the n-channel is increased. Since the depletion layer inside the semiconductor film 23 becomes narrower in order to relax or cancel the electric field, when the read pulse is input to the bottom gate electrode 21, the semiconductor film 2
3 has a lower resistance, an n-channel is not formed, and DG-
In the TFT 20, the value of the current flowing between the source and the drain becomes high, and the voltage of the drain line 43 largely changes during a predetermined period. Therefore, the change tendency (rate of change) of the voltage of the drain line 43 is closely related to the amount of light incident on the semiconductor film 23 from the fingertip. The drain driver 13 detects the voltage of each drain line 43 after a lapse of a predetermined time from the output of the read pulse and outputs it to the image pickup circuit 10, or reaches a predetermined threshold voltage of each drain line 43. The image pickup circuit 10 converts the light amount of the reflected light from the fingertip by detecting the time up to and outputting it to the image pickup circuit 10.

By repeating the same processing procedure for each DG-TFT 20 in all rows, the fingerprint image of the fingertip is formed in the image pickup circuit 10, and the fingerprint image is converted from the image pickup circuit 10 to the arithmetic processing unit 2 as digital data. Is output to. The arithmetic processing unit 2 collates the fingerprint image input from the imaging circuit 10 with the reference image data, determines whether the fingerprint image and the reference image data match, and authenticates when they match.

If the fingerprint of the fingertip of the registrant is stored in the storage medium 7 of the arithmetic processing unit 2 as the reference image data, the authentication apparatus 1 as described above can be used for personal authentication of the registrant. it can. In particular, since the surface of the image sensor 8 is the photocatalytic film 33, the fingerprint of the fingertip does not remain on the surface of the image sensor 8 even after the registrant touches the image sensor 8 with the fingertip. Therefore, a third party cannot copy the registrant's fingerprint from the surface of the image sensor 8, and the authentication device 1 is very excellent as a device for personal authentication.

Further, it becomes easy to remove fingerprints from the surface of the image pickup device 8. Therefore, for example, a fingerprint wiping device for wiping off fingerprints attached to the surface of the image sensor 8 is provided.
Since the fingerprints can be easily wiped off even when the wiper is provided at the position, the wiping device can be simplified. Therefore, a third party cannot copy the registrant's fingerprint from the surface of the image sensor 8, and the authentication device 1 is very excellent as a device for personal authentication. Although the conductive film 32 is provided below the photocatalytic film 33 in the above embodiment, the photocatalytic film 33 may be provided directly on the protective insulating film 31 without the conductive film 32. Further, the light for decomposing the organic matter or the like attached to the photocatalyst film 33 may be light from the backlight 14 or external light. In the former case, after the fingertip 100 is separated from the photocatalyst film 33, the fingerprint is given to a third party. The decomposition may be promoted by causing the backlight 14 to emit light for a predetermined period of time so quickly that it cannot be read.

Second Embodiment Next, another example of the authentication device will be described. In the authentication device 1 of the first embodiment, the photocatalytic film 33 is formed above the protective insulating film 31, but in the authentication device of the second embodiment, the protective insulating film 31.
A thermochromic film is formed on it. As for the other configuration of the authentication device of the second embodiment, the same components as those of the authentication device 1 of the first embodiment are designated by the same reference numerals.

FIG. 4 is a cross-sectional view of the image pickup device included in the authentication device of the second embodiment. A thermochromic film 34 is formed on one surface of the protective insulating film 31 of the DG-TFTs 20, 20, ... Arranged in a matrix.
The thermochromic film 34 contains a substance having a thermochromic property, that is, a substance whose color reversibly changes with temperature change (thermochromic substance).
The thermochromic film 34 has a DG-
When the light in the wavelength range that excites the semiconductor film 23 of the TFT 20 is absorbed or reflected to such an extent that the semiconductor film 23 is not sufficiently excited, for example, in a colored state, and when the temperature is higher than the threshold temperature, the DG-TFT 20 For example, a colorless state is shown in which light in the wavelength range that excites the semiconductor film 23 is transmitted to the extent that the semiconductor film 23 is sufficiently excited. The threshold temperature may be the temperature of the subject. Since the fingertip is the subject in the present embodiment, the threshold temperature is preferably higher than room temperature (outside air) and lower than the human body temperature, for example, 30 ° C. to 40 ° C.
℃, more preferably 35 ℃. In particular,
Examples of thermochromic substances include di-α, β-
Naphthoisospiropyran, benzo-β-naphthoisospiropyran, 3-alkyl-di-β-naphthospiropyran, bianthrone, dixanthylene, xanthylideneanthrone and the like can be used. These thermoclock materials are in the form of ink, for example, trade name "Daithermo DI" (dye type), "Daithermo DR".
(Dye-based), "Dythermo PR" (inorganic), "Dythermo PI" (inorganic), "Dythermo PI" (inorganic,
It is also possible to use commercially available products such as metal complex salt type) and “Dythermo PF” (inorganic type).

5 and 6 are plan views for explaining changes in the state of the image sensor 8. As shown in FIG. 5, when the fingertip which is the subject is not in contact with the thermochromic film 34 and the thermochromic film 34 is at room temperature (below the threshold temperature), the thermochromic film 34 is colored. Therefore, the thermochromic film 34 has a light shielding property, and the light from the outside is blocked by the thermochromic film 34. Therefore, the semiconductor film 2 of the DG-TFTs 20, 20 ,.
Since no light is incident on the image pickup device 3, it is impossible to image the subject.

On the other hand, as shown in FIG. 6, when the fingertip which is the subject contacts the thermochromic film 34, the temperature of the thermochromic film 34 becomes higher than the threshold temperature due to the body temperature of the fingertip, and the thermochromic film 34 becomes colorless and transparent. (The area α in FIG. 6 is colorless). Therefore, the reflected light from the fingertip passes through the thermochromic film 34, enters the protective insulating film 31, and reaches the semiconductor film 23 of the DG-TFTs 20, 20 ,. Therefore, it is possible to image the fingertip. When the fingertip is separated from the thermochromic film 34, the temperature of the thermochromic film 34 returns to the threshold temperature or lower due to the surrounding atmosphere, so that the thermochromic film 34 again develops color so as not to sufficiently transmit the excitation light. 5 and 6, the illustration of the fingertip holder 9 is omitted.

As described above, in the second embodiment, when the fingertip is not in contact with the thermochromic film 34, it is impossible to capture an image of the subject. Therefore, contact with the fingertip is indispensable. That is, for example, since it is impossible for a third party to sense the image sensor 8 with a sheet of paper or the like on which the fingerprint of the registrant's finger is copied, the authentication device of the second embodiment also has a security aspect as a device for personal authentication. Is very good at. In the present embodiment, if necessary, the thermochromic film 34
Conductive film above or below (ITO having translucency and conductivity)
May be laminated.

[Third Embodiment] Next, an authentication apparatus according to a third embodiment will be described. In the authentication device 1 of the first embodiment, the photocatalyst film 33 is formed above the protective insulating film 31, and in the authentication device 1 of the second embodiment, the thermochromic film 34 is formed, but the third embodiment. In the authentication device, the thermochromic film is formed above the protective insulating film 31, and a heating resistor that heats the thermochromic film to a predetermined temperature is provided around the thermochromic film.

FIG. 7 shows a sectional view of an image pickup device provided in the authentication apparatus of the third embodiment. A thermochromic film 35 is formed on almost the entire surface of the protective insulating film 31 of the DG-TFTs 20, 20, ... Arranged in a matrix. The thermochromic film 35 can be selected from the substantially same material group as the thermochromic film 34 of the second embodiment, and may have the same shape and the same size. Further, a conductive film 36 is formed on the entire surface of the thermochromic film 35. Further, the thermochromic film 35
A heating resistor 37 is formed on the protective insulating film 31 around the area.

Similar to the conductive film 32 of the first embodiment, the conductive film 36 has conductivity and translucency, is made of ITO or the like, and is periodically weak pulsed from an external signal generating circuit. A signal is input. The reference potential of this pulse signal is the ground potential, and the pulse signal is displaced to a weak positive or negative voltage for a predetermined period at a predetermined interval. The conductive film 36 is connected to the arithmetic processing unit 2 via a detection circuit. This detection circuit detects an electrical change in the conductive film 36,
The fact that the fingertip has come into contact with the conductive film 36 is detected and a signal to that effect is output to the arithmetic processing unit 2. For example, when a fingertip comes into contact with the conductive film 36, static electricity is discharged from the finger through the conductive film 36, and the weak input to the conductive film 36 is made by the finger of a person having a specific resistance value range and capacitance range. The waveform of such a pulse signal shows a unique tendency of being delayed or blunted for a predetermined period. The detection circuit detects the disturbance of the waveform and determines whether the placed object is a human finger, and a determination result signal is output from the detection circuit to the arithmetic processing unit 2. Further, for example, the conductive film 36 is composed of two regions which are insulated from each other and have different potentials. When the fingertip contacts the two regions of the conductive film 36, a minute current flows through the conductive film 36 via the fingertip, and a minute current flows. The detection circuit detects the current, and a signal indicating that the ground has been detected is output from the detection circuit to the arithmetic processing unit 2
Is output to. When a subject having a capacity different from that of the fingertip comes into contact with the conductive film 36, the detection circuit detects an electrical displacement, and a signal indicating that the subject is not the fingertip is output from the detection circuit to the arithmetic processing unit 2. .

The heating resistor 37 recognizes that the fingertip 100 is placed on the basis of the signal from the detection circuit 2 as the arithmetic processing unit 2.
Generates heat by a current flowing through the operational amplifier in response to a heating command signal output from the thermochromic film 35, and heats the thermochromic film 35 above a threshold temperature.

The thermochromic film 35 contains a thermochromic substance whose color reversibly changes with a change in temperature, is colored below the threshold temperature, and is colorless when the temperature is higher than the threshold temperature. The threshold temperature of the thermochromic film 35 has only to be higher than room temperature and may be higher than the human body temperature.

If the fingertip, which is the subject, is not in contact with the conductive film 36, that is, even if a finger having a resistance value range and a capacitance range different from the human finger is in contact, the detection circuit does not recognize that the fingertip 100 is placed. Since the heating resistor 37 does not generate heat, the thermochromic film 35 remains colored, the thermochromic film 35 remains light-shielding, and external light is blocked by the thermochromic film 35. Therefore, D
No light is incident on the semiconductor film 23 of the G-TFTs 20, 20 ,.

On the other hand, when the fingertip, which is the subject, comes into contact with the conductive film 36, the arithmetic processing unit 2 recognizes that fact and the electric current from the arithmetic processing unit 2 causes the heating resistor 37 to generate heat.
When the thermochromic film 35 is heated by the heating resistor 37 and the temperature of the thermochromic film 35 becomes higher than the threshold temperature, the thermochromic film 35 becomes colorless and transparent. Therefore, the reflected light from the fingertip is reflected by the thermochromic film 34.
Through the protective insulating film 31 and then DG-
The light enters the semiconductor film 23 of the TFT 20, 20, .... Therefore, it is possible to image the fingertip. After a lapse of a predetermined time, the arithmetic processing unit 2 stops supplying the current to the heating resistor 37, the temperature of the thermochromic film 35 is lowered, and the thermochromic film 35 is colored.

As described above, when the fingertip 100 does not come into contact with the conductive film 36, it is impossible to capture an image of the subject, so that contact with the fingertip is indispensable. In other words, for example, it is impossible for a third party to sense the image sensor 8 with a paper or the like on which the fingerprint of the registrant's finger is copied. Therefore, the authentication device according to the second embodiment is also extremely useful as a device for personal authentication. Are better. In particular, even when the fingertip 100 does not reach the threshold temperature due to internal conditions such as constitution and external conditions such as winter and cold regions, the subject can be imaged and the range of application of the authentication device can be expanded. In the above embodiment,
Although the conductive film 36 is provided above the thermochromic film 35 so that the finger directly contacts the conductive film 36, the thermochromic film 35 is provided above the conductive film 36 so that the finger directly contacts the thermochromic film 35. The conductive film 36 may be omitted.

[Fourth Embodiment] Next, an authentication apparatus according to a fourth embodiment will be described. In the authentication device of the present embodiment, the thermochromic film and the heating resistor are provided above the protective insulating film 31. In addition, about the other structure of the authentication device of 4th Embodiment, the same code | symbol is attached | subjected with respect to the structure similar to the authentication device 1 of the said 1st embodiment.

On the protective insulating film 31 of each DG-TFT 20, three layers of a conductive film 32, a thermochromic film 38 and a photocatalytic film 39 are laminated. Thermochromic film 38
Is almost the same as the thermochromic film 34 in the second embodiment, and the threshold temperature of the thermochromic film 38 is, for example, 30 ° C. to 40 ° C., more preferably 35 ° C. The photocatalyst film 39 is almost the same as the photocatalyst film 33.

That is, the fingertip 100 first comes into contact with the photocatalyst film 39 located at the uppermost portion, so that the fingertip 100 is first contacted.
The static electricity charged on the display device is discharged through the conductive film 32 to electrostatically destroy the authentication device 1 (mainly, each DG-TFT 20, the imaging circuit 10, the top gate driver 10, the bottom gate driver 12, and the drain driver 13). The heat of the fingertip 100 that exceeds the threshold temperature is transmitted to the thermochromic film 38 via the photocatalyst film 39,
-The thermochromic film 38 is discolored so that light in the wavelength range that excites the semiconductor film 23 of the TFT 20 is sufficiently transmitted.
After the detection circuit detects the contact of the fingertip 100, the arithmetic processing unit 2 drives the DG-TFT 20 and the backlight 14 to capture an image.

When the fingertip 100 is separated from the photocatalyst film 39 after the completion of image pickup, organic substances such as sebum adhered to the photocatalyst film 39 are decomposed by the catalytic action of the photocatalyst film 39 which receives the light from the backlight 14 or the external light.

As described above, in the present embodiment, the thermochromic film 38 transmits light by the contact of the fingertip 100, so that even if the one having a temperature different from that of the fingertip 100 is placed (contacted). The photocatalyst film 39 can protect the fingerprint information from being read by a third party. Although the conductive film 32 for electrostatic protection is provided below the thermochromic film 38 in the present embodiment, the conductive film 32 may be provided above the thermochromic film 38. Similarly, a heating resistor 37 (similar to the third embodiment) may be provided around the thermochromic film 38.

The present invention is not limited to the above-described embodiments, and various improvements and design changes may be made without departing from the spirit of the present invention. The image pickup device 8 has the DG-TFTs 20 arranged in a matrix, but may be, for example, a charge-coupled device (CCD) having photodiodes arranged in a matrix. Further, in each of the above-described embodiments, the subject is optically imaged by the light of the backlight, but only the external light or both the external light and the backlight may be used as the light source. When the organic substance on the surface of the photocatalyst film 33 or the photocatalyst film 39 is decomposed from the backlight, in order to optimize, the wavelength range of the light to be decomposed and the wavelength range of the light irradiated at the time of imaging are mutually at least partially. You may set up differently.

[0068]

As described above, according to the present invention as set forth in claim 1 or 2, when the subject comes into contact with the incident surface, even if dirt or dust adheres to the incident surface from the subject, the photocatalytic film causes Dirt and dust are decomposed by the generated active oxygen, and no dirt or dust remains on the incident surface. Therefore, the image pickup apparatus according to the present invention is suitable for acquiring an image of a subject in contact with the incident surface.

According to the invention described in any one of claims 3 to 5, for example, when the subject is higher than the threshold temperature,
When the subject comes into contact with the incident surface, the temperature of the thermochromic film rises, and an optical image of the subject can be acquired by the imaging device. On the other hand, when the subject is lower than the threshold temperature, the temperature of the thermochromic film decreases when the subject comes into contact with the incident surface, and the optical image of the subject cannot be acquired by the imaging device. That is, according to the present invention, it is possible to specify what can be applied as a subject by the temperature. Therefore, the image pickup apparatus according to the present invention is suitable for acquiring an image of a specific subject in contact with the incident surface, and an image other than the specific subject cannot be acquired.

[Brief description of drawings]

FIG. 1 is a drawing mainly showing a circuit configuration of an authentication device.

FIG. 2 is a cross-sectional view taken along the line C-C in FIG.

FIG. 3 is a sectional view showing a part of FIG. 2 in an enlarged manner.

FIG. 4 is a cross-sectional view showing an enlarged part of an image sensor included in a fingerprint reading device of another example of the authentication device.

FIG. 5 is a plan view of the image sensor.

FIG. 6 is a plan view of the image sensor.

FIG. 7 is a cross-sectional view of a fingerprint reading device of another example of the authentication device.

FIG. 8 is an enlarged cross-sectional view of a part of an image sensor included in a fingerprint reading device of another example of the authentication device.

[Explanation of symbols]

1 Authentication device 2 Processor 3 Fingerprint reader (imaging device) 8 image sensor 10 Imaging circuit (driver) 11 Top gate driver (driver) 12 Bottom gate driver (driver) 13 Drain driver (driver) 20 Double gate transistor (photoelectric conversion element) 33 Photocatalytic film 34 Thermochromic film 35 Thermochromic film 100 fingertips

Claims (5)

[Claims] 1. An image pickup device for obtaining an optical image of a subject by entering light from the subject on the incident face, wherein a photocatalytic film having a light-transmitting property and a photocatalytic function is formed on the incident face. An imaging device characterized by the above. 2. A plurality of photoelectric conversion elements provided under the photocatalytic film, having electrical characteristics according to the amount of incident light, and arranged in a matrix, and driving the plurality of photoelectric conversion elements. The imaging device according to claim 1, further comprising: a driver that acquires image data of the subject by detecting electrical characteristics of the plurality of photoelectric conversion elements according to light from the subject. apparatus. 3. An image pickup device for obtaining an optical image of a subject by entering light from the subject on an incident surface, which has a light-shielding property when the temperature is lower than a threshold temperature, and is transparent when the temperature is higher than the threshold temperature. An imaging device, wherein a thermochromic film having optical property is formed on an incident surface. 4. The threshold temperature of the thermochromic film is 30.
The image pickup device according to claim 3, wherein the image pickup device has a temperature of not less than 40 ° C and not more than 40 ° C. 5. A plurality of photoelectric conversion elements provided under the thermochromic film, having electrical characteristics according to the amount of incident light, and arranged in a matrix, and driving the plurality of photoelectric conversion elements. And a driver for acquiring image data of the subject by detecting electrical characteristics of the plurality of photoelectric conversion elements according to light from the subject. The imaging device described.