JP2007059504A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus having high protection performance to external pressure applied to a photosensor array, and capable of satisfactorily reading an image pattern of an object while preventing damage to an insulating substrate. <P>SOLUTION: The image reading apparatus comprises in lamination a sensor array 110 composed of a plurality of photosensors PS (double gate type photosensors) arranged two-dimensionally on one surface side of an insulating substrate SUB; and a prism sheet PRM including a detection surface DTC having a crosssectional structure where there are regularly and repeatedly arranged mount parts and valley parts, on an upper surface of the sensor array 110 via a protective insulating film. It is herein set that a separation interval Lb between the adjacent mount parts (or valley parts) formed on the prism sheet PRM is the same as an adjacent separation distance La between the photosensors PS arranged on the photosensor array 110. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus applicable to reading a fingerprint image.

  2. Description of the Related Art Conventionally, as an image reading device that reads a male image pattern of a subject such as a printed matter, a photograph, or a fingerprint, for example, a photosensor array in which photoelectric conversion elements (photosensors) such as a CCD (Charge Coupled Device) are arranged in a line or matrix The object image is read by irradiating the object placed on the detection surface on the photosensor array with irradiation light, detecting the reflected light by each photosensor and converting it into an electrical signal. The structure is known.

  Here, as is well known, the CCD calculates the amount (charge amount) of electron-hole pairs generated corresponding to the amount of light incident on the light receiving portion of each photosensor (corresponding to the reflected light). It is detected using a horizontal scanning circuit and a vertical scanning circuit to detect light and dark data of an image pattern of a subject, and is applied to various imaging devices and image reading devices such as a digital video camera and a copying machine. In such an image reading apparatus using a CCD, it is necessary to provide a selection transistor for selecting each scanned photosensor individually for each photosensor. When the number of detection pixels (reading pixels) is increased, there is a problem that the apparatus scale increases.

  Therefore, in recent years, as a configuration for solving such a problem, for example, as described in Patent Document 1, etc., it has a double gate type thin film transistor structure, and the photo sensor itself has a photo sensing function (light quantity detection). Function) and a selection transistor function have been developed, so-called double gate type photosensors have been developed, and attempts have been made to reduce the size of the system and increase the density of read pixels (higher resolution of the read image). Yes.

  The element structure and drive control method of the double-gate photosensor described in Patent Document 1 and the like will be described in detail later, but generally, a single semiconductor layer is formed on one side of an insulating substrate such as a glass substrate. A top gate electrode and a bottom gate electrode are provided above and below the (channel region), and are configured to receive only light from the one surface side and shield light from the other surface side of the insulating substrate. ing. A plurality of such double gate type photosensors are two-dimensionally arranged on an insulating substrate, and a light transmissive insulating film is formed to electrically insulate the double gate type photosensors, Moreover, it is configured to protect against damage caused by external pressure or the like.

  Then, an image reading operation (fingerprint reading operation) in an image reading apparatus provided with a photosensor array in which such double gate type photosensors are two-dimensionally arranged, as shown in FIG. 7, is the other side of the insulating substrate SUB. Light Ra is emitted from a backlight (light source) BL provided on the back side (lower surface side of the drawing), and detection is provided above the photosensor array (on one side of the insulating substrate SUB (upper surface side of the drawing)). A subject (for example, a finger) FGP placed on the surface DTC is irradiated, reflected according to an image pattern (uneven pattern) of the subject FGP, and reflected on a light receiving region (channel region) of each double-gate photosensor PSP. By detecting the amount of incident light (reflected light) Rb, the image pattern of the subject FGP is read as light and dark data.

  Here, in the image reading apparatus shown in FIG. 7, light is reflected and scattered between the photosensor array and the subject FGP in the convex region FGa of the subject FGP in close contact with the detection surface DTC. A part of the light Rb is incident on the light receiving area of the double-gate photosensor PSP, and a charge amount corresponding to the light quantity is accumulated. On the other hand, in the recessed area FGb of the subject FGP that is not in close contact with the detection surface DTC, the light Ra is Since the light is transmitted and does not reflect or scatter, the light Rb does not enter the double-gate photosensor PSP, and charge accumulation does not occur.

Therefore, the image signal (fingerprint image) of the subject FGP is brought into close contact with the detection surface DTC by reading out an electrical signal corresponding to the amount of charge accumulated in each of the plurality of double-gate photosensors PSP constituting the photosensor array. It can be read out as light / dark data consisting of a region (dark data) that is not in close contact with the region (bright data).
FIG. 7 is a conceptual cross-sectional view for explaining an image reading operation (fingerprint reading operation) in an image reading apparatus to which a double gate type photosensor is applied. Here, for the sake of illustration, hatching representing a cross section is omitted.

JP 2002-259955 A (page 3, FIG. 10)

However, the conventional techniques as described above have the following problems.
That is,
(1) In the image reading apparatus as shown in FIG. 7, in order to prevent damage due to external pressure or the like, a protective insulating film (over film) made of a silicon nitride film or the like on the photosensor array (double gate type photosensor PSP). (Coat film) PRT is provided, and a detection surface DTC on which the subject FGP is directly placed and adhered is formed on the protective insulating film PRT. Here, for example, when the thickness of the protective insulating film PRT is thin or the film quality is deteriorated, defects such as pinholes are likely to exist (or occur) in the protective insulating film PRT. When this image reading device is applied to a fingerprint reading device, a photosensor array is composed of salt or contaminants (erodible materials) contained in sweat secreted from the finger, which is the subject FGP, or dirt attached to the finger. The double gate type photosensor PSP and its wiring member are corroded, resulting in a malfunction and failure of the image reading apparatus.

  Therefore, after completion of the image reading device or after completion of the image reading unit including the photosensor array, an image reading operation is repeatedly performed by dropping an erodible substance such as salt water on the detection surface, and the photosensor and its wiring It has been necessary to carry out a test for inspecting the occurrence of corrosion or the like in the member, which has the problem that the manufacturing process becomes extremely complicated.

  (2) Further, if the protective insulating film PRT is damaged by hitting or coming into contact with the detection surface DTC, the double gate type photosensor PSP or its wiring may be disconnected or poorly connected. In order to prevent such a problem, it is conceivable to apply a structure in which the protective insulating film PRT is formed thick. However, a transparent insulating film (silicon nitride film or the like) applied to the protective insulating film PRT is thick. If formed, the manufacturing (film formation) time becomes longer, and the light insulating property is reduced due to the thick insulating film, and the contrast of the image pattern (fingerprint image) of the imaged subject is lowered. . For this reason, the protective insulating film is formed to have a thickness of approximately 10 μm (10000 mm) or less in consideration of the above-described defects such as pinholes, film quality deterioration, film forming conditions, and permeability.

  (3) Further, when a stronger external pressure is applied to the detection surface DTC (photo sensor array), the insulating substrate SUB may be broken (cracked). In this case, the image reading device ( There has also been a problem that there is a possibility that the user (fingerprint collector) of the fingerprint reader may be injured.

  Therefore, in view of the above problems, the present invention has a high protection performance against external pressure applied to the photosensor array, and prevents an image pattern of a subject from being damaged while preventing damage to the photosensor, wiring, and insulating substrate. An object of the present invention is to provide an image reading apparatus that can be read favorably.

  According to a first aspect of the present invention, in an image reading apparatus for reading an image pattern of a subject, a light transmission type sensor array in which a plurality of photosensors are two-dimensionally arranged on one surface side of a transparent insulating substrate, and one surface is An optical sheet having a detection surface disposed on one surface side of the insulating substrate and having the subject placed on the other surface, and disposed on the other surface side of the insulating substrate, via the sensor array. A light source for irradiating the optical sheet with light, and the detection surface of the optical sheet has a cross-sectional shape in which crests and troughs having inclined surfaces are alternately provided, and is irradiated from the light source. The reflected light is reflected by the inclined surface and enters the photosensor in a region where the subject placed on the detection surface is not in close contact with the detection surface.

According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the light emitted from the light source is emitted from the inclined surface in a region where a subject placed on the detection surface is in close contact with the detection surface. It is incident on the subject.
According to a third aspect of the present invention, in the image reading apparatus according to the first or second aspect, the subject has a convex portion and a concave portion, the convex portion is in close contact with the inclined surface, and the concave portion is in close contact with the inclined surface. It is characterized by not.

According to a fourth aspect of the present invention, in the image reading apparatus according to the first aspect, the inclined surfaces of the peak portion and the valley portion of the optical sheet are formed symmetrically with each other, and are formed by the inclined surfaces. Is set to be 90 °.
According to a fifth aspect of the present invention, in the image reading apparatus according to the first aspect of the present invention, the distance between the crests or the troughs provided adjacent to each other in the optical sheet is arranged in the sensor array. It is set so that it may become the same as the separation distance of each of these photosensors.

  According to a sixth aspect of the present invention, in the image reading device according to any one of the first to fifth aspects, the photosensor includes a source electrode and a drain electrode formed with a channel region made of a semiconductor layer interposed therebetween, and the channel. It has the 1st gate electrode and the 2nd gate electrode which were each formed through the insulating film on the said one surface side and the said other surface side of the area | region, It is characterized by the above-mentioned.

  That is, in the image reading apparatus according to the present invention, a protective insulating film is interposed on a sensor array in which a plurality of photosensors (double gate type photosensors) are two-dimensionally arranged on one side of a transparent insulating substrate. Since it has a configuration in which optical sheets (prism sheets) made of a transparent member with a detection surface on the upper surface are stacked, secretions and deposits from subjects (such as fingers) placed directly on the detection surface The phenomenon that the photosensors and their wiring members constituting the sensor array are corroded by salt or erodible substances contained in (dirt) etc. can be suppressed, and the malfunction or failure of the image reading apparatus can be prevented. In addition, it is possible to eliminate the inspection process and simplify the manufacturing process and improve the product yield.

  In addition, since it has a configuration in which an optical sheet made of a transparent member (acrylic resin or the like) having a film hardness higher than that of a protective insulating film (silicon nitride film or the like) generally applied on the sensor array is disposed. The protective insulating film does not need to be formed thicker than necessary, and the manufacturing (deposition) time of the protective insulating film can be shortened, and the phenomenon that the sensor array and the insulating substrate are damaged by an external pressure or the like is suppressed. Even if the glass substrate applied to the insulating substrate is damaged, the optical sheet can prevent the glass fragments from being scattered and ensure the safety of the user of the image reading apparatus. be able to.

  Furthermore, the detection surface of the upper surface of the optical sheet has a cross-sectional shape in which crests and troughs having inclined surfaces are alternately provided, and the crossing angle between the inclined surfaces constituting the crests and troughs to be provided is 90 °. And the separation distance between adjacent peaks (or valleys) is set to be the same (match) with the adjacent separation distance of the photosensors arranged in the sensor array. As a result, the light emitted from the light source (backlight) is almost equal to the inclined surface of the optical sheet in the area where the subject (fingerprint) placed on the detection surface does not adhere to the inclined surface (concave portion of the fingerprint). In a region where the light is totally reflected and enters the photosensor at the corresponding position and the subject is in close contact with the inclined surface (the convex portion of the fingerprint), the light is incident on the subject from the inclined surface and diffused within the subject. Suppresses attenuation and improves It is possible to capture an image pattern (fingerprint image) of the subject in the last.

Hereinafter, an image reading apparatus according to the present invention will be described in detail with reference to embodiments.
First, the overall configuration (sensor array and its peripheral circuit) of the image reading apparatus according to the present invention will be described.
FIG. 1 is a schematic configuration diagram showing an embodiment of an overall configuration (sensor array and its peripheral circuit) of an image reading apparatus according to the present invention, and FIG. 2 is an image reading apparatus (sensor array) according to the present embodiment. It is a schematic sectional drawing which shows the principal part structure of this. Here, components equivalent to those of the above-described prior art will be described with the same or equivalent reference numerals.

  In the present embodiment, the case where the double gate type photosensor referred to in the related art is applied as the photosensor constituting the sensor array will be described, but the present invention is not limited to this, in short, A light-transmitting sensor array is configured, and light from a light source disposed on the back side is transmitted through the sensor array so that a sufficient amount of light is applied to a subject (finger) placed on the detection surface. It may have other element structure or circuit configuration as long as it is well irradiated and receives the reflected light and outputs an electrical signal corresponding to the image pattern (fingerprint image) of the subject. Needless to say.

  As shown in FIGS. 1 and 2, the image reading apparatus according to the present invention has, for example, n rows × m columns (on the upper surface side in FIG. 2) on a transparent insulating substrate SUB such as a glass substrate. A plurality of photosensors (double-gate photosensors described later) PS arranged in a matrix of n and m are arbitrary positive integers, and top gate terminals TG of each photosensor PS are connected in the row direction. The top gate line TL provided, the bottom gate line BL arranged by connecting the bottom gate terminal BG of each photosensor PS in the row direction, and the drain terminal D of each photosensor PS connected in the column direction A drain line (data line) DL disposed, and a source line (common line) SL disposed so as to commonly connect the source terminal S to a predetermined low potential voltage (for example, ground potential) Vss. The sensor array 110 is provided.

  Here, above the sensor array 110 (the front side in FIG. 1 and the upper side in FIG. 2), as shown in FIG. 2, photosensors (double-gate type photosensors) that are two-dimensionally arranged in the sensor array 110. ) A prism sheet (optical sheet) PRM having a detection surface DTC provided on the upper surface is disposed through a protective insulating film (protective insulating film 19 shown in FIG. 3) formed so as to cover PS. is doing.

  In particular, the detection surface DTC provided on the upper surface of the prism sheet PRM applied to the present embodiment has regular crests and troughs composed of inclined surfaces formed symmetrically on the left and right sides of the paper as shown in FIG. It has a cross-sectional structure arranged repeatedly. The pair of inclined surfaces constituting the crests or troughs is the direction in which the insulating substrate, the sensor array and the prism sheet are stacked (the vertical direction in the drawing) or the direction in which the surface of the subject placed on the detection surface DTC extends ( The angle formed by the inclined surfaces (intersecting angle between the inclined surfaces) α is set to 90 °, for example.

  Specifically, such a prism sheet PRM has, for example, a groove portion having a V-shaped cross section on the upper surface of a transparent plate member made of an acrylic resin material on a polyester film having a film thickness of about 100 μm. The prism layer in which the valley portion is formed can be laminated, and the total film thickness of the prism sheet PRM can be set to about 150 μm, for example.

  Furthermore, the spacing (pitch) Lb between adjacent ridges or valleys (V-shaped grooves) formed on the prism sheet PRM applied to the present embodiment is a photosensor arranged in the sensor array 110. It is set to be the same as the adjacent spacing distance La between PSs. Specifically, for example, La = Lb = 50 μm can be set.

  In the sensor array 110 and the prism sheet PRM having such a configuration, one surface side of the backlight (light source) BL (the drawing in FIG. 2) disposed on the other surface side (the lower surface side in the drawing in FIG. 2) of the insulating substrate SUB. Planar light radiated from the upper surface side passes through the insulating substrate SUB, the photosensor PS of the sensor array 110, and the region where the respective lines are not formed (inter-element region), and the prism sheet PRM Irradiates the lower surface. As will be described later, a part of the irradiated light is totally reflected in the prism sheet PRM and enters the photosensor PS, and a part is irradiated to the subject placed on the detection surface DTC via the prism sheet PRM. The Details of the light irradiation state on the subject and the light incident state on the photosensor in the image reading apparatus according to the present embodiment will be described later.

  Further, as shown in FIG. 1, the image reading apparatus according to the present invention is connected to the top gate driver 120 connected to each top gate line TL disposed in the sensor array 110 and to each bottom gate line BL. The bottom gate driver 130 and the drain driver 140 connected to each drain line DL are configured.

  The top gate driver 120 or the bottom gate driver 130 determines the start signal as a reference clock signal based on a start signal, a reference clock signal, an output enable signal, etc. supplied as a top gate control signal (or bottom gate control signal). The shift signal is sequentially output to the next stage at the timing based on the output signal and is output as the shift signal corresponding to the top gate line TL or the bottom gate line BL of each row at the timing based on the output enable signal or the like. Is output to the top gate line TL or the bottom gate line BL as a reset pulse φTi or a read pulse φBi.

  The drain driver 140 precharges a predetermined precharge pulse (precharge voltage Vpg) simultaneously applied to each drain line DL at a timing (a precharge period described later) based on a precharge signal supplied as a drain control signal. Each data voltage Vrd (drain line voltage) corresponding to the carrier accumulated in each photosensor PS via each drain line DL at the timing based on the operation and a sampling signal supplied as a drain control signal (a readout period described later). VD) is read out in parallel, and at the timing based on the shift signal output corresponding to each drain line DL, the data voltage Vrd is taken out in time series and converted into a serial signal and output as a read data signal Vdata. Read operation is performed at a predetermined timing. Configured to run.

  In other words, the top gate control signal shown in FIG. 1 is selectively output as signals φT1, φT2,... ΦTi,. This is a control signal for generating φTn (i is an arbitrary positive integer satisfying 1 ≦ i ≦ n), and the bottom gate control signal is used as either a read voltage or a non-read voltage described later in the bottom gate driver 130. , ΦBn,..., And φBn, which are selectively output signals, are applied to each photosensor PS by a drain driver 140 that applies a precharge voltage Vpg, which will be described later, to the drain driver 140. At the same time, the data voltage Vrd corresponding to the carrier stored in each photosensor PS is read. It is a control signal for controlling the. All of these control signals are generated and supplied by, for example, a system controller (timing control means) (not shown).

Next, the element structure of the photosensor applicable to this embodiment will be described in detail.
FIG. 3 is a schematic configuration diagram showing an element structure of a photosensor applicable to the sensor array of the image reading apparatus according to the present invention. Here, FIG. 3A is a schematic cross-sectional view showing one configuration example of the photosensor, and FIG. 3B is an equivalent circuit diagram of the photosensor shown in FIG.

For example, as shown in FIG. 3A, the photosensor PS applicable to the sensor array 110 described above is roughly amorphous in which an electron-hole pair is generated by incidence of excitation light (here, visible light). A semiconductor layer (channel region) 11 such as silicon and both ends of the semiconductor layer 11 are formed via impurity layers (ohmic contact layers) 17 and 18 made of n ⁺ silicon, respectively. Chromium, chromium alloy, aluminum, aluminum A drain electrode 12 (drain terminal D) and a source electrode 13 (source terminal S) which are made of a conductive material selected from an alloy or the like and are opaque to visible light, and block insulation above the semiconductor layer 11 (upward in the drawing) Transparent electrodes such as a tin oxide film and an ITO film (indium-tin oxide film) are formed through the film (stopper film) 14 and the upper gate insulating film 15. A top gate electrode TGx (first gate electrode; top gate terminal TG), which is composed of a polar layer and is transparent to visible light, and a lower gate insulating film 16 below the semiconductor layer 11 (downward in the drawing). A bottom gate electrode BGx (second gate electrode; bottom gate terminal) formed of a conductive material selected from chrome, chromium alloy, aluminum, aluminum alloy, etc., and opaque to light (having a light shielding property) BG).

  That is, the photosensor PS is a photosensor having a so-called double gate type thin film transistor structure (double gate type photosensor). As shown in FIG. A thin film is formed on a transparent insulating substrate SUB. Further, a protective insulating film (overcoat film) 19 is formed on the entire surface (upper side of the drawing) of the insulating substrate SUB including the photosensor PS.

  Here, in the photosensor PS shown in FIG. 3A, the top gate insulating film 15, the block insulating film 14, the insulating film constituting the bottom gate insulating film 16, and the protective insulation provided on the top gate electrode TGx. Each of the films 19 is made of a material having a high transmittance for visible light that excites the semiconductor layer 11, for example, silicon nitride, silicon oxide, or the like, so that the insulating substrate SUB side (downward in the drawing) is formed. The light emitted from the provided light source (not shown; corresponding to the above-described backlight BL) is transmitted upward in the drawing, and the upper surface of the prism sheet PRM (not shown) provided on the protective insulating film 19 The light reflected according to the image pattern of the subject placed on the detection surface DTC is incident on the photosensor PS (specifically, the semiconductor layer 11). It has been made.

  Note that a photosensor PS having an element structure as shown in FIG. 3A is generally represented by an equivalent circuit as shown in FIG. Here, TG is a top gate terminal electrically connected to the top gate electrode TGx, BG is a bottom gate terminal electrically connected to the bottom gate electrode BGx, and D is a drain electrically connected to the drain electrode 12. A terminal S is a source terminal electrically connected to the source electrode 13.

Next, a drive control method for the image reading apparatus having the above-described configuration will be described with reference to the drawings.
FIG. 4 is a timing chart showing an example of a sensor array drive control method applied to the image reading apparatus according to the present embodiment. FIG. 5 is a conceptual diagram showing an operation (fingerprint reading operation) when reading a fingerprint in the image reading apparatus according to the present embodiment. Here, in FIG. 5, for the convenience of illustration, a part of hatching representing a cross section is omitted.

  For example, as shown in FIG. 4, the drive control method in the sensor array 110 (photosensor PS) described above includes a reset period Trst, a charge accumulation period Ta, and a precharge period Tprch in a predetermined processing operation period (one processing cycle). This is realized by setting the reading period Tread.

  First, in the reset period Trst, a reset pulse φTi (for example, a top gate voltage (= reset pulse voltage) Vtg) is applied to the top gate terminal TG of the i-th photosensor PS by the top gate driver 120 via the top gate line TL. = 15V (high level) is applied, and a reset operation (initialization operation) for releasing carriers (here, holes) accumulated in the semiconductor layer 11 is executed.

  Next, in the charge accumulation period Ta, the top gate driver 120 applies a low level bias voltage φTi (for example, the top gate voltage Vtg = −15 V) to the top gate terminal TG, thereby terminating the reset operation, The accumulation operation (carrier accumulation operation) is started.

  In this charge accumulation period Ta, as shown in FIG. 5, a part of the light Rx emitted from the backlight BL disposed on the back side of the transparent insulating substrate SUB is converted into the insulating substrate SUB and the sensor array 110. To the image pattern of the subject (finger) FG (fingerprint pattern) that is incident on the prism sheet PRM through the inter-element region and placed in close contact with the detection surface DTC provided on the upper surface of the prism sheet PRM. The light (reflected light) Rz reflected accordingly passes through the top gate electrode TGx made of the transparent electrode layer constituting the photosensor (double gate type photosensor) PS shown in FIG. 3 and enters the semiconductor layer 11. Thereby, electron-hole pairs are generated in the incident effective region (carrier generation region) of the semiconductor layer 11 according to the amount of light incident on the semiconductor layer 11 during the charge accumulation period Ta, and the semiconductor layer 11 and the block insulating film 14 Carriers (holes) are accumulated in the vicinity of the interface (around the channel region).

  Here, when the image reading apparatus according to the present embodiment is applied as a fingerprint reading apparatus, the subject (fingerprint) FG has a convex region FGa and a concave region FGb as shown in FIG. When such a subject (fingerprint) FG is placed on the detection surface DTC, the convex region FGa is in close contact with the detection surface DTC, but the concave region FGb is not in contact with the detection surface DTC. That is, in the convex region FGa of the subject FG, the subject FG is in close contact with the inclined surfaces constituting the peaks and valleys of the detection surface DTC, and the refractive indexes of the prism sheet PRM and the finger approximate, The light Rx emitted from the backlight BL passes through the interface between the prism sheet PRM and the finger, enters the skin surface layer of the finger, and is reflected and diffused within the skin surface layer (see the light Ry in the figure). For this reason, almost no light is incident on each photosensor PS in the convex region FGa.

On the other hand, in the fingerprint recessed area FGb, the subject FG is not in contact with the inclined surfaces constituting the peaks and valleys of the detection surface DTC, and the prism sheet PRM is in contact with the air layer. The angle formed by the inclined surfaces constituting the peaks and valleys provided on the detection surface DTC is set to be 90 ° (intersection angle between the inclined surfaces), and is adjacent to each other. Since the distance between the peaks (or between the valleys) is set to be the same (match) as the adjacent distance between the photosensors arranged in the sensor array, it is emitted from the backlight BL. The light Rx is not emitted to the subject FG side, but is substantially totally reflected by the inclined surface of the prism sheet PRM (see the light Rz in the figure) and enters each photosensor PS.
As a result, the amount of light incident on each of the plurality of photosensors PS arranged in the sensor array 110 differs depending on the concave / convex pattern of the fingerprint, and the amount of accumulated charge also differs.

  In the precharge period Tprch, the drain driver 140 precharges the drain terminal D via the drain line DL based on the precharge signal φpg supplied as a drain control signal in parallel with the charge accumulation period Ta. A pulse (for example, precharge voltage Vpg = + 5 V) is applied, and a precharge operation for holding the charge in the drain electrode 12 is executed.

  Next, in the read period Tread, after the precharge period Tprch has elapsed, the bottom gate driver 130 applies a read pulse φBi (for example, bottom gate voltage (= read pulse voltage) to the bottom gate terminal BG via the bottom gate line BL. ) Vbg = + 10V) is applied, so that the drain voltage VD (data voltage Vrd; voltage signal) corresponding to the carriers (holes) accumulated in the channel region during the charge accumulation period Ta is applied to the drain line DL. A read operation is performed by the drain driver 140 via the.

  Here, the change tendency of the drain voltage VD (data voltage Vrd) during the application period (readout period) of the read pulse φBi is when there are many carriers accumulated in the charge accumulation period Ta (bright state; fingerprint recessed area FGb). Shows a tendency for the voltage to drop sharply, while on the other hand, when there is a small amount of accumulated carriers (dark state; convex region FGa of the fingerprint), the voltage tends to drop gradually. By detecting the data voltage Vrd after elapse of a predetermined time from the above, it is possible to detect the amount of light incident on the photosensor PS, that is, lightness data (light / dark information) corresponding to the uneven pattern of the subject.

  Then, a series of brightness data detection operations for such a specific row (i-th row) is regarded as one processing cycle, and it is equivalent to each row (i = 1, 2,... N) of the sensor array 110 described above. By repeatedly executing the above-described operation processing, the image reading apparatus including the sensor array 110 including the photosensor PS having the double-gate thin film transistor structure is used to read the subject image pattern (uneven pattern of fingerprints) as brightness data. Type image reading apparatus. Note that the drive control operation of the series of image reading apparatuses described above is controlled by, for example, a system controller (not shown).

  Therefore, the image reading apparatus according to the present embodiment has a configuration in which a prism sheet (optical sheet) made of a transparent member is laminated on the sensor array via a protective insulating film. Phenomenon in which the photosensors and their wiring members constituting the sensor array are corroded by salt or erodible substances contained in secretions or deposits (dirt) from the subject placed directly on the detection surface And the occurrence of malfunction and failure of the image reading apparatus can be prevented, and it is not necessary to carry out an inspection process therefor, thereby greatly simplifying the manufacturing process and improving the product yield. be able to.

  In addition, since the prism sheet made of a transparent member (acrylic resin or the like) having a higher film hardness than the protective insulating film is disposed on the sensor array, the sensor array and the insulating substrate are damaged by external pressure or the like. The phenomenon can be suppressed, and even if the glass substrate applied to the insulating substrate is damaged, the prism sheet can prevent the glass fragments from being scattered. Can be secured.

  In this case, the prism sheet provided with the detection surface has a sufficient function to protect the sensor array (photosensor and its wiring member), so that the protective insulating film provided on the sensor array is thicker than necessary. There is no need to form the film (for example, it can be formed relatively thin with a film thickness of about 2 μm), and the manufacturing (film formation) time of the protective insulating film can be shortened. Thus, attenuation of light applied to the subject placed on the detection surface can be suppressed, and an image pattern (fingerprint image) of the subject can be captured with good contrast.

  In the above-described embodiment, the configuration in which the prism sheet is laminated on the sensor array via the protective insulating film is shown, but the present invention is not limited to this, and the sensor array and the prism sheet are not limited to this. Further, an optical member may be interposed. For example, an optical fiber condensing body is provided between the protective insulating film formed on the sensor array and the prism sheet so that the light emitted from the backlight is suppressed from being attenuated and propagated in a direction perpendicular to the sensor array. It may be configured as follows.

  In the above-described embodiment, as the cross-sectional shape of the upper surface of the prism sheet, the ridges and valleys are regularly arranged, and the crossing angle between the inclined surfaces constituting the ridges or valleys is, for example, approximately Although the configuration set to be 90 ° is shown, the present invention is not limited to this. For example, as shown in FIG. 6, as a cross-sectional shape of the upper surface of the prism sheet PRM, a curved portion of a waveform May be regularly arranged, and the crossing angle α between the tangents of the curved surfaces of the inclined portions constituting the waveform may be set to be approximately 90 °.

  According to the image reading apparatus having such a configuration, when the image reading apparatus according to the present invention is applied to the fingerprint reading apparatus, the adhesion between the convex portion of the finger as the subject and the prism sheet PRM is improved, Since dirt and the like adhering to the groove (valley) can be wiped off easily and satisfactorily, the image pattern (fingerprint image) of the subject can be taken with good contrast. FIG. 6 is a schematic sectional view showing another example of the sectional shape of the upper surface (detecting surface) of the prism sheet applied to the image reading apparatus according to the present invention. Also in FIG. 6, for convenience of illustration, a part of hatching representing a cross section is omitted.

1 is a schematic configuration diagram illustrating an embodiment of an overall configuration (sensor array and its peripheral circuit) of an image reading apparatus according to the present invention. It is a schematic sectional drawing which shows the principal part structure of the image reading apparatus (sensor array) which concerns on this embodiment. It is a schematic block diagram which shows the element structure of the photosensor applicable to the sensor array of the image reading apparatus which concerns on this invention. 6 is a timing chart illustrating an example of a sensor array drive control method applied to the image reading apparatus according to the embodiment. FIG. 5 is a conceptual diagram showing a drive control method (fingerprint reading operation) when reading a fingerprint in the image reading apparatus according to the present embodiment. It is a schematic sectional drawing which shows the other example of the cross-sectional shape of the prism sheet upper surface (detection surface) applied to the image reading apparatus which concerns on this invention. It is a conceptual sectional view for explaining an image reading operation (fingerprint reading operation) in an image reading apparatus to which a double gate type photosensor is applied.

Explanation of symbols

PS Photosensor SUB Insulating substrate PRM Prism sheet DTC Detection surface FG Subject FGa Convex region FGb Concave region 110 Sensor array BL Backlight

Claims (6)

In an image reading device that reads an image pattern of a subject,
A light transmission type sensor array in which a plurality of photosensors are two-dimensionally arranged on one side of a transparent insulating substrate;
An optical sheet having a detection surface on which one surface is disposed facing one surface side of the insulating substrate and the subject is placed on the other surface;
A light source disposed on the other surface side of the insulating substrate and irradiating the optical sheet with light through the sensor array;
With
The detection surface of the optical sheet has a cross-sectional shape in which crests and troughs having inclined surfaces are alternately provided, and the light emitted from the light source is emitted from the subject placed on the detection surface. An image reading apparatus that is reflected by the inclined surface and enters the photosensor in a region that is not in close contact with the detection surface. The image reading according to claim 1, wherein the light emitted from the light source is incident on the subject from the inclined surface in a region where the subject placed on the detection surface is in close contact with the detection surface. apparatus. The image reading apparatus according to claim 1, wherein the subject has a convex portion and a concave portion, the convex portion is in close contact with the inclined surface, and the concave portion is not in close contact with the inclined surface. The inclined surface of the peak portion and the valley portion of the optical sheet is formed symmetrically with each other, and an angle formed by the inclined surfaces is set to 90 °. The image reading apparatus according to 1. In the optical sheet, the separation distance between the crests or the troughs provided adjacent to each other is the same as the separation distance of each of the plurality of photosensors arranged in the sensor array. The image reading apparatus according to claim 1, wherein the image reading apparatus is set. The photosensor includes a source electrode and a drain electrode formed across a channel region made of a semiconductor layer, and a first gate formed on the one surface side and the other surface side of the channel region via an insulating film, respectively. 6. The image reading apparatus according to claim 1, further comprising an electrode and a second gate electrode.

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