Patent Publication Number: US-2006017862-A1

Title: Liquid crystal display device built-in finger printing device and method of manufacturing the same

Description:
TECHNICAL FIELD  
      The disclosure relates to a liquid crystal display device having a built-in fingerprint identification device and a method of manufacturing the liquid crystal display device.  
     BACKGROUND ART  
      An a-Si thin film transistor liquid crystal display (TFT-LCD) device is a flat panel display (FPD). The a-Si TFT-LCD device is used in a laptop computer, a monitor, a television set and a mobile phone.  
      The a-Si TFT-LCD device displays an image by means of switch thin film transistors. In addition, the a-Si TFT-LCD device has a photosensitive property and is used as an optical sensor in the field of biometrics.  
      In a personal authentication system, especially a fingerprint identification method using fingerprint identification devices is widely used because the fingerprint identification method may be accomplished at a low cost and has characteristics of high availability and high accuracy.  
      The conventional fingerprint identification device may be divided into an optical fingerprint identification device employing an optical sensor and a semiconductor type fingerprint identification device employing semiconductor sensors.  
      The optical fingerprint identification device provides a high quality of fingerprint image. However, the optical fingerprint identification device is sensitive to distortion of images, cannot be easily miniaturized and is manufactured at a high cost. Particularly, the optical fingerprint identification device is not suitable for mobile devices such as a cellular phone because the optical fingerprint identification device uses a plurality of lens such that the optical fingerprint identification device cannot be easily thinner and lighter.  
      The semiconductor type fingerprint identification device manufactured by a complementary metal oxide semiconductor (CMOS) process may be easily miniaturized. However, the fingerprint identification device manufactured by the CMOS process is sensitive to a static electricity and an external environment and has a low reliability. The fingerprint identification devices used in the mobile devices should have a thinner and lighter structure, long endurance and high reliability.  
      Recently, a-Si TFT fingerprint identification device satisfying the requirement for the mobile devices has been developed. The a-Si TFT fingerprint identification device uses a photosensitive property of a-Si channel in the a-Si TFT. The a-Si TFT fingerprint identification device has a relatively thin structure and has a high photosensitive property during the sensor operation.  
      In addition, a TFT-LCD device employing the a-Si TFT fingerprint identification device has been used in a cellular phone.  
       FIG. 1  is a perspective view showing a cellular (or mobile) phone having an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate, and  FIG. 2  is a cross-sectional view showing an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate of  FIG. 1 .  
      Referring to  FIGS. 1 and 2 , a TFT fingerprint identification substrate  10  using a-Si TFT is attached to a TFT-LCD panel  20 . The TFT-LCD panel  20  includes a color filter substrate having a plurality of color filters and a TFT substrate.  
      The TFT fingerprint identification substrate  10  includes a first transparent substrate  12 , a fingerprint identification thin film transistor  14  and an inter-layer insulation film  16 . The first transparent substrate comprises a transparent material such as glass. The fingerprint identification thin film transistor  14  is formed on the first transparent substrate  12  and includes a sensor TFT for sensing a fingerprint pattern and a switch TFT. The inter-layer insulation film  16  is formed on the resultant structure.  
      The conventional TFT-LCD panel  20  includes a TFT substrate  25 , a color filter substrate  32  and a liquid crystal layer  35  interposed between the TFT substrate  25  and the color filter substrate  32 . The TFT substrate  25  includes thin film transistors (not shown) formed on a second transparent substrate  22  comprised of a transparent material such as glass. The color filter substrate  32  includes red (R), green (G) and blue (B) color filters formed on a third transparent substrate  34  comprised of a transparent material such as glass. The color filter substrate  32  is attached to the TFT substrate  25  to be opposite to the TFT substrate  25  while the liquid crystal layer  35  is interposed between the color filter substrate  32  and the TFT substrate  25 .  
      The TFT fingerprint identification substrate  10  usually has a higher resolution than the TFT-LCD panel  20  for the purpose of accurate fingerprint identification operation. For example, n unit cells of TFTs having an aspect ratio of 1:1 corresponds to one pixel of the TFT-LCD panel having an aspect ratio of 1:n. Namely, n unit cells of TFTs having the aspect ratio of 1:1 are arranged over one pixel of the TFT-LCD panel having the aspect ratio of 1:n.  
      For example, a resolution of the TFT fingerprint identification substrate  10  is larger than that of the TFT-LCD panel  20  by n times. When the TFT fingerprint identification substrate  10  is not exactly aligned with the TFT-LCD panel  20 , an aperture ratio of the TFT fingerprint identification substrate  10  may decrease by n times compared with that of the TFT-LCD panel  20 .  
      Particularly, the aperture ratio is greatly decreased when the TFT substrate  25  of the TFT-LCD panel  20  is not exactly aligned with the color filter substrate  32  of the TFT-LCD panel  20 . Accordingly, little design margin may be left and management for manufacture process may be difficult.  
      In addition, exact aligning process may not be easily performed, and quality of image may be deteriorated due to the decrease in the aperture ratio when the TFT-LCD panel  20  mounted with the TFT fingerprint identification substrate  10  is designed in consideration of the miss-align between substrates.  
     DISCLOSURE OF THE INVENTION  
      Accordingly, the present invention is provided to substantially obviate one or more problems due to limitations and disadvantages of the related art.  
      It is a first feature of the present invention to provide a liquid crystal display device including a built-in fingerprint identification device, which has enhanced light transmissivity and increased aperture ratio by decreasing the miss-alignment between substrates.  
      It is a second feature of the present invention to provide a process of manufacturing a liquid crystal display device including a built-in fingerprint identification device, which has enhanced light transmissivity and increased aperture ratio by decreasing the miss-alignment between substrates.  
      According to one aspect of the first feature of the invention, there is provided a liquid crystal display device comprising: a first substrate including a plurality of unit cells, each of the unit cells having i) a sensor thin film transistor for receiving a light reflected from a fingerprint to generate electric charges corresponding to an intensity of the reflected light, ii) a storage device for storing the electric charges, iii) a first switch thin film transistor for receiving the electric charges from the storage device to output the electric charges in response to an external control signal; a first transparent electrode disposed on a lower surface of the first substrate; a second substrate including a pixel, the pixel having i) a second switch thin film transistor, ii) a data line electrically coupled with a first electrode of the second switch thin film transistor, iii) a gate line electrically coupled with a second electrode of the second switch thin film transistor, iv) a color filter layer formed on first portions of the gate line, the data line and the second switch thin film transistor, v) a second transparent electrode formed on the color filter layer and electrically coupled with a second portion of the first electrode; and a liquid crystal layer interposed between the first and second substrates.  
      According to another aspect of the first feature of the invention, there is provided a liquid crystal display device comprising: a first substrate including a plurality of unit cells, each of the unit cells having i) a sensor thin film transistor for receiving a light reflected from a fingerprint to generate electric charges corresponding to an intensity of the reflected light, ii) a storage device for storing the electric charges, iii) a first switch thin film transistor for receiving the electric charges from the storage device to output the electric charges in response to an external control signal; a first transparent electrode disposed on a lower surface of the first substrate; a second substrate; a pixel including i) a data wiring having a data line formed in the second substrate, ii) a color filter layer on the second substrate on which the data wiring is formed, the color filter layer covering a first portion of the data wiring, iii) an insulation layer covering the data wiring and the color filter layer, iv) a second switch thin film transistor formed on the insulation layer, and v) a second transparent electrode electrically coupled with a second portion of a first electrode of the second switch thin film transistor; and a liquid crystal layer interposed between the first and second substrates.  
      To accomplish the second feature of the invention, there is provided a method of manufacturing the liquid crystal display device, the method comprising: forming a sensor thin film transistor, a storage device and a first switch thin film transistor and on a first substrate comprised of an insulation material, the sensor thin film transistor receiving a light reflected from a fingerprint to generate electric charges corresponding to an intensity of the reflected light, the storage device storing the electric charges, and the first switch thin film transistor receiving the electric charges from the storage device to output the electric charges in response to an external control signal; forming a first transparent electrode on a lower surface of the first substrate; forming a second switch thin film transistor on a second substrate comprised of insulation material; forming a color filter layer on the second switch thin film transistor; forming a second transparent electrode on the color filter layer; aligning the first substrate over the second substrate base on a first aspect ratio for a first pixel unit of the first substrate and a second aspect ratio for a second pixel unit of the second substrate; and forming a liquid crystal layer between the first and second substrates.  
      According to the present invention, there is provided a liquid crystal display device in which the fingerprint identification device having sensor TFT for sensing the fingerprint is mounted on the TFT-LCD panel. The TFT-LCD panel has color-filter-on-array (COA) structure in which the color filters are self-aligned with the thin film transistors.  
      Accordingly, when the fingerprint identification device having the sensor TFT is mounted on the TFT-LCD panel, the number of glass substrate can be reduced such that the manufacturing cost may be reduced. The liquid crystal display device according to the present invention requires only two glass substrates while the conventional liquid crystal display device requires three glass substrates. Particularly, when the liquid crystal display device is employed in the mobile devices such as the cellular phone, the thickness and total weight of the mobile device can be reduced.  
      In addition, the transmissivity of the TFT-LCD panel having the fingerprint identification device is increased according to the decrease of the number of glass substrate, so that the sensitivity of fingerprint identification can be enhanced.  
      In addition, in the TFT-LCD panel having the fingerprint identification device, the TFT substrate has the color-filter-on-array structure. Accordingly, the miss-alignment between the color filters and the thin film transistors can be eliminated, the aperture ratio of the TFT-LCD panel having the fingerprint identification device can be increased, and the quality of image display can be enhanced.  
      In addition, when the liquid crystal display device having the fingerprint identification device is designed and manufactured, the design margin can be increased, and management for manufacturing process may be proceeded easily. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view showing a cellular phone having an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate;  
       FIG. 2  is a cross-sectional view showing an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view showing a color-filter-on-array structure of an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate according to one exemplary embodiment of the present invention;  
       FIG. 4  is a cross-sectional view showing a unit cell of the TFT fingerprint identification substrate of  FIG. 3 ;  
       FIG. 5  is an equivalent circuit diagram showing a unit cell of the TFT fingerprint identification substrate of  FIG. 4 ;  
       FIG. 6  is a schematic block diagram showing an arrangement between a TFT fingerprint identification substrate, a TFT substrate having a color-filter-on-array structure, a gate driver integrating circuit and a data driver integrating circuit according to one exemplary embodiment of the present invention;  
       FIG. 7  is a plan view showing a unit cell of the TFT fingerprint identification substrate of  FIG. 4 ;  
       FIG. 8  is a cross-sectional view taken along a line A-A′ of  FIG. 7 ;  
       FIGS. 9A  to  14 C are plan views and cross-sectional views illustrating a process of manufacturing a unit cell of the TFT fingerprint identification substrate of  FIG. 7 ;  
       FIG. 15A  is a plan view showing a pixel of the TFT fingerprint identification substrate of  FIG. 3 ;  
       FIG. 15B  is a cross-sectional view taken along a line B-B′ of  FIG. 15A ;  
       FIG. 15C  is a cross-sectional view taken along a line C-C′ of  FIG. 15A ; and  
       FIGS. 16A  to  20 C are plan views and cross-sectional views illustrating a process of manufacturing a pixel of the TFT fingerprint identification substrate of  FIG. 15A .  
       FIG. 21  is a cross-sectional view showing a pixel of the TFT-LCD panel mounted with a TFT fingerprint identification substrate of  FIG. 3  according to another exemplary embodiment of the present invention; 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Hereinafter the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
       FIG. 3  is a cross-sectional view showing a color-filter-on-array structure of an a-Si TFT-LCD panel mounted with a TFT fingerprint identification substrate according to one exemplary embodiment of the present invention.  
      The color-filter-on-array structure is referred to as a structure in which color filters are formed on the TFT substrate to be aligned with thin film transistors of the TFT substrate. Namely, the color filters and the thin film transistors have a self-aligned structure. Accordingly, an aperture ratio of the TFT-LCD panel is increased. In addition, the color filters may be exactly aligned with the thin film transistors on the TFT substrate.  
      Referring to  FIG. 3 , the TFT fingerprint identification substrate  400  is attached to the TFT-LCD panel having the color-filter-on-array structure.  
      The TFT fingerprint identification substrate  400  includes a first transparent substrate  412 , a fingerprint identification thin film transistor  410 , an inter-layer insulation film  440  and a common electrode  450 . The first transparent substrate  412  comprises transparent material such as glass. The fingerprint identification thin film transistor  410  is formed on the first transparent substrate  412  and includes a sensor TFT for sensing a fingerprint pattern and a switch TFT. The inter-layer insulation film  440  is formed on the resultant structure. The common electrode  450  comprises transparent conductive material such as indium tin oxide (ITO) and is formed on a lower surface of the first transparent substrate  412 .  
      In the TFT-LCD panel having the color-filter-on-array structure, red (R), green (G) and blue (B) color filters  336  instead of an insulation layer (for example, an organic insulating layer) is formed on the thin film transistors (not shown). In detail, the thin film transistors and data lines  334  electrically connected to the thin film transistors is formed on a second transparent substrate  330  comprised of a transparent material such as glass. Then, color filters  336  instead of the insulation layer are formed on the second transparent substrate on which the thin film transistors and data lines  334  are formed. A contact hole  345  is formed at the color filters so as to expose the data lines, and pixel electrodes  340  are formed on the resultant structure. However, an insulation layer  338  may be formed on the color filters having the contact holes  345 , and then the pixel electrodes  340  may be formed on the an insulation layer  338 .  
      The thin film transistor is formed on the second transparent substrate  330  and includes a gate electrode, a gate insulation layer, a source electrode, a drain electrode, an active pattern and an ohmic contact pattern. (refer to  FIGS. 4 and 15 B)  
       FIG. 4  is a cross-sectional view showing a unit cell of the TFT fingerprint identification substrate of  FIG. 3 ,  FIG. 5  is an equivalent circuit diagram showing a unit cell of the TFT fingerprint identification substrate of  FIG. 4 . Hereinafter, the principle of fingerprint identification is illustrated.  
      Referring to  FIGS. 4 and 5 , the TFT fingerprint identification substrate  400  includes the sensor TFT  410   b , the switch TFT  410   a  and a storage capacitor (Cst), which are formed on the first transparent substrate  412 .  
      A drain electrode  427  of the sensor TFT  410   b  is connected to an external power line V DD  (refer to FIG,  7 ), a source electrode  425  of the sensor TFT  410   b  and a source electrode  409  of the switch TFT  410   a  is connected with each other through a first electrode layer  432 . A drain electrode  407  of the switch TFT  410   a  is connected to a sensor signal output line (refer to  FIG. 5 ). A gate electrode  421  of the sensor TFT  410   b  is electrically connected to a gate line of the sensor TFT  410   b , and a gate electrode  401  of the switch TFT  410   a  is electrically connected to a gate line of the switch TFT  410   a . A second electrode layer  436  is electrically connected to the gate line of the sensor TFT (refer to  FIG. 5 ). The gate line and data line may be comprised of ITO so as to reduce the decrease of aperture ratio due to the miss-alignment between the TFT fingerprint identification substrate  400  and the TFT substrate.  
      The second electrode layer  436  faces the first electrode layer  432 , and the insulation layer  434  is disposed between the first and second electrode layers  432  and  436 . The first and second electrode layers functions as a storage capacitor (Cst). The storage capacitor (Cst) accumulates electric charges proportional to the quantity of the light inputted into the sensor TFT  410   b.    
      A channel region  423  is formed between the source electrode  425  and the drain electrode  427  of the sensor TFT  410   b . The channel region  423  comprises amorphous silicon (a-Si). Accordingly, when the channel region  423  receives light more than a predetermined amount of light, the source electrode  425  is electrically conducted with the drain electrode  427 .  
      When an user adhere his finger closely to the TFT fingerprint identification substrate  400 , the light generated from the backlight assembly (not shown) disposed under the first transparent substrate  412  is incident into the TFT fingerprint identification substrate  400  through the liquid crystal layer  350 . The light incident into the TFT fingerprint identification substrate  400  is reflected by ridges and valleys of the fingerprint and is incident into the channel region  423 . Accordingly, the sensor TFT is electrically conducted, and the storage capacitor (Cst) accumulates the charges proportional to the quantity of light incident into the channel region  423 .  
      A light shielding layer (or black matrix)  438  is formed over the drain electrode  407  and the source electrode  409  of the switching thin film transistor  410   a . The light shielding layer  438  prevents the light from being incident into a channel region  405  of the switching thin film transistor  410   a.    
      Hereinafter, the principle of fingerprint identification is illustrated with reference to  FIG. 5 .  
      A DC voltage (V DD ) having a predetermined voltage level is applied to the drain electrode (D) of the sensor thin film transistor  410   b , and a bias voltage having a predetermined voltage level is applied to the gate electrode (G) of the sensor TFT  410   b.    
      The gate electrode of the switching TFT  410   a  receives a gate driving signal from the gate driver part (not shown) and the switching TFT  410   a  is turned on or turn off in response to the gate driving signal. The gate driver part outputs the gate driving signal at every frame during which the fingerprint is scanned so as to turn on or turn off the switching TFT  410   a , thereby outputting image frames for each of the sensor TFTs  410   b . The image frame is formed using the fingerprint image inputted through the TFT fingerprint identification substrate  400 .  
      In addition, the drain electrode (D) of the switching TFT  410   a  is connected to an amplifying circuit of an external data reading part through the sensor signal output line. When the switch TFT  410   a  is turned on, the voltage proportional to the quantity of the charges electrically charged in the storage capacitor (Cst) is outputted. A signal outputted from the source electrode (S) of the sensor TFT  41   0   b  is amplified through the amplifying circuit. Output terminals of the amplifying circuit are connected to a multiplexer and a single signal is outputted from the multiplexer.  
       FIG. 6  is a schematic block diagram showing an arrangement between a TFT fingerprint identification substrate, a TFT substrate having a color-filter-on-array structure, a gate driver integrating circuit and a data driver integrating circuit according to one exemplary embodiment of the present invention. The gate driver part is integrated to be the gate driver integrating circuit, and the data driver part is integrated to be the data driver integrating circuit.  
      Referring to  FIG. 6 , a first data driver integrating circuit  612  may be disposed adjacent to an upper side face of the TFT-LCD substrate  610  to be connected to the upper side face of the TFT-LCD substrate  610 . A first gate driver integrating circuit  614  may be disposed adjacent to a left side face of the TFT-LCD substrate  610  to be connected to the left side face of the TFT-LCD substrate  610 . In addition, a second data driver integrating circuit  622  may be disposed adjacent to a lower side face of the TFT fingerprint identification substrate  620  to be connected to the lower side face of the TFT fingerprint identification substrate  620 . A second gate driver integrating circuit  624  may be disposed adjacent to a right side face of the TFT fingerprint identification substrate  620  to be connected to the right side face of the TFT fingerprint identification substrate  620 . The TFT fingerprint identification substrate  620  may be disposed over the TFT-LCD substrate  610 .  
      When the TFT-LCD substrate  610  is attached to the TFT fingerprint identification substrate  620 , the increase in the entire thickness of the TFT-LCD panel, which includes the TFT fingerprint identification substrate  620  having a gate driver integrating circuit and a data driver integrating circuit, should be prevented. Accordingly, the gate driver integrating circuits and data driver integrating circuits attached to the TFT-LCD substrate  610  and the TFT fingerprint identification substrate  620  are arranged not to be overlapped with each other. For example, when the first data driver integrating circuit  612  is disposed adjacent to an upper (or lower) side face of the TFT-LCD substrate  610 , the second data driver integrating circuit  622  may be disposed adjacent to a lower (or upper) side face of the TFT fingerprint identification substrate  620 . When a first gate driver integrating circuit  614  is disposed adjacent to a left (or right) side face of the TFT-LCD substrate  610 , the second gate driver integrating circuit  624  may be disposed adjacent to a right (or left) side face of the TFT fingerprint identification substrate  620 .  
      Hereinafter, a method of manufacturing a unit cell of TFT fingerprint identification substrate  400  is illustrated first, and then the method of manufacturing a pixel of TFT-LCD panel is illustrated.  
       FIG. 7  is a plan view showing a unit cell of the TFT fingerprint identification substrate of  FIG. 4 , and  FIG. 8  is a cross-sectional view taken along a line A-A′ of  FIG. 7 .  FIGS. 9A  to  14 C are plan views and cross-sectional views illustrating a process of manufacturing a unit cell of the TFT fingerprint identification substrate of  FIG. 7 .  
      Referring to  FIGS. 7 and 8 , the unit cell of the TFT fingerprint identification substrate includes a sensor TFT  410   b , a switch TFT  410   a  and a storage capacitor (Cst) having first and second electrode layer  432  and  436 . The gate electrode  421  of the sensor TFT  410   b  and the gate electrode  401  of the switch TFT  410   a  may be portions or branches of a gate line  470 - n  of the sensor TFT  410   b  and a gate line  460 - n  of the switch TFT  410   a , respectively. The second electrode layer  436  is connected to the gate line  470 - n  of the sensor TFT  410   b.    
      Referring to  FIGS. 9A and 9B , the gate electrode  421  of the sensor TFT  410   b  and the gate electrode  401  of the switch TFT  410   a  are formed on a first transparent substrate  412  comprised of glass, quartz or sapphire etc.  
      Referring to  FIGS. 10A and 10B , a gate insulation layer comprised of SiNx is formed on the gate electrode  421  of the sensor TFT  410   b  and the gate electrode  401  of the switch TFT  410   a . A channel region  423  of the sensor TFT  410   b  and a channel region  405  of the switch TFT  410   a  is formed on the gate insulation layer  403  by plasma enhanced chemical vapor deposition (PECVD). The channel regions  423  and  405  may be comprised of amorphous silicon (a-Si) and n +  amorphous silicon.  
      Referring to  FIGS. 11A and 11B , data wirings comprised of metal layer is formed on the resultant structure. The data wirings includes the source electrode  425  of the sensor thin film transistor  410   b , the drain electrode  427  of the sensor thin film transistor  410   b , the source electrode  409  of the switch thin film transistor  410   a , the drain electrode  407  of the switch thin film transistor  410   a , the sensor signal output line  480 - m  and the external power line (V DD )  485 - m . The sensor signal output line  480 - m  intersects the gate lines  460 - n  and  470 - n . For example, the gate lines  460 - n  and  470 - n  and the sensor signal output line  480 - m  comprises transparent electrode such as ITO.  
      Referring to  FIGS. 12A and 12B , the first electrode layer  432  comprised of ITO is formed on the resultant structure so as to form the storage capacitor (Cst).  
      Referring to  FIGS. 13A and 13B , the insulation layer  434  is formed on the data wirings and the first electrode layer  432 . The second electrode layer  436  comprised of ITO is formed on the insulation layer to face the first electrode layer  432  such that the storage capacitor (Cst) is formed.  
      Referring to  FIGS. 14A and 14B , the light shielding layer (or black matrix)  438  is formed on the insulation layer  434  to be disposed over the channel region  405 . The light shielding layer  438  may be formed as the same layer as the second electrode layer  438 . The light shielding layer  438  may be comprised of Cr/Cr x O y . The inter-layer insulation film  440  is formed on the light shielding layer  438 , the second electrode layer  436  and the insulation layer  434 . The inter-layer insulation film  440  protects the light shielding layer  438 , the second electrode layer  436  and the insulation layer  434  from external environment.  
      The light shielding layer  438  may not be formed as the same layer as the second electrode layer  438 . Referring to  FIG. 14C , after the inter-layer insulation layer  440  is formed, the light shielding layer  438  may be formed at a portion of the inter-layer insulation layer  440 . The third portion is disposed over the channel region  405  of the switch thin film transistor  410   a.    
       FIG. 15A  is a plan view showing a pixel of the TFT fingerprint identification substrate of  FIG. 3 ,  FIG. 15B  is a cross-sectional view taken along a line B-B′ of  FIG. 15A , and  FIG. 15C  is a cross-sectional view taken along a line C-C′ of  FIG. 15A .  
      Referring to  FIGS. 15A, 15B  and  15 C, the TFT-LCD panel has a color-filter-on-array structure. In the color-filter-on-array structure, the color filters  336  are aligned with the thin film transistors  310  and the data lines  334 - j  and  334 -(j+1). Namely, the color filters, the thin film transistors  310  and the data lines  334 - j  and  334 -(j+1) have a self-aligned structure.  
      A pixel of TFT-LCD panel includes the thin film transistor  310 , insulation layer  335 , gate line  321 - i , data line  334 - j , color filter  340 , organic insulating layer  338  and the pixel electrode  340 . The gate line  321 - i  and data line  334 - j  is electrically connected with the thin film transistor  310 .  
      In the TFT-LCD panel having the color-filter-on-array structure, photosensitive red (R), green (G) and blue (B) color filters  336  instead of the insulation layer (or organic insulating layer) is formed on the thin film transistor  310 . Namely, the switch thin film transistor  310  is formed on the second transparent substrate  330  comprised of glass, and the color filters  336  is formed on the second transparent substrate  330  on which the switch thin film transistor  310  is formed. Then, a first contact hole is formed at the color filters to expose a first portion of the drain electrode  311 .  
      The organic insulating layer  338  having a second contact hole is formed on the entire surface of the resultant structure including the first contact hole. The second contact hole exposes a second portion of the drain electrode  311  of the switch thin film transistor  310 . The second portion of the drain electrode  311  is disposed over the first portion of the drain electrode  311  to correspond to the first portion of the drain electrode  311 .  
      The pixel electrode  340  having a third contact hole is formed on the entire surface of the resultant structure including the second contact hole. The third contact hole exposes a third portion of the drain electrode  311  of the switch thin film transistor  310  to make electrical contact with the drain electrode  311 . The third portion of the drain electrode  311  is disposed over the second portion of the drain electrode  311  to correspond to the second portion of the drain electrode  311 .  
      However, the organic insulating layer may not be formed. Namely, after the color filters  336  is formed on the second transparent substrate  330  on which the switch thin film transistor  310  is formed, the pixel electrode  340  instead of the organic insulating layer may be formed on the entire surface of the resultant structure including the first contact hole.  
      The switch thin film transistor  310  includes a gate electrode  301 , a gate insulation layer  303 , an active pattern  305 , an ohmic contact pattern  307 , a source electrode  309  and a drain electrode  311 . The gate electrode  301 , gate insulation layer  303 , active pattern  305 , ohmic contact pattern  307 , source electrode and drain electrodes  311  are formed on the second transparent substrate  330  comprised of glass.  
       FIGS. 16A  to  20 C are plan views and cross-sectional views illustrating a process of manufacturing a pixel of the TFT fingerprint identification substrate of  FIG. 15A .  
      Referring to  FIGS. 16A and 16B , a first metal layer comprised of Al—Nd or Al—Nd/Cr is deposited by sputtering method on the second transparent substrate  330 . The first metal layer is patterned by a photolithography process using a first mask to form the gate line  321  and the gate electrode  301  branched from the gate line  321 .  
      Referring to  FIGS. 17A and 17B , the gate insulation layer  303  comprised of silicon nitride is formed on the entire surface of the second transparent substrate  330  on which the gate line  321  and the gate electrode  301  is formed. The active pattern  305  and the ohmic contact pattern  307  is formed on the gate insulation layer  303  using a second mask to be disposed over the gate electrode  301 . The active pattern  305  is composed of amorphous silicon and the ohmic contact pattern  307  is comprised of n +  doped amorphous silicon.  
      Referring to  FIGS. 18A, 18B  and  18 C, a second metal layer comprised of metal such as Cr is deposited on the ohmic contact pattern  307  and gate insulation layer  303  by a sputtering method. The second metal layer is patterned by photolithography process using a third mask to form the data wirings. The data wirings includes the drain electrode  311  of the switch thin film transistor  410   a , the source electrode  309  of the switch thin film transistor  410   a , the second electrode layer  323 , the data lines  334 - j  and  334 (j+1) and data pad (not shown). The second electrode layer  323  is referred to as a storage electrode and functions as a storage capacitor (Cst) together with the gate lines.  
      Referring to  FIGS. 19A, 19B  and  19 C, the ohmic contact pattern  307  is removed by a reactive ion etching using a fourth mask such that the channel region of the switch thin film transistor  410   a  is formed over the gate electrode  301 . Subsequently, the insulation layer  335  comprised of silicon nitride is deposited on the entire surface of the resultant structure. After the red (R), green (G) and blue (B) color filters  336  is formed on the insulation layer  335 , the color filters  336  is patterned by a photolithography process using a fifth mask such that the contact holes  345   a  and  345   b  are formed on the color filters  336 .  
      Referring to  FIGS. 20A, 20B  and  20 C, the organic insulating layer  338  comprised of acrylic resin is formed on the entire surface of the resultant structure, and then the organic insulating layer  338  is patterned by a photolithography process using a sixth mask. The pixel electrode  340  comprised of ITO is patterned by photolithography process using a seventh mask on the entire surface of the resultant structure. The pixel electrode  340  is electrically connected with a third electrode  323 .  
      In the structure of the TFT substrate of the TFT-LCD panel mounted with the TFT fingerprint identification substrate according to one exemplary embodiment of the present invention, the color filter layer may be formed on the thin film transistor, or the thin film transistor may be formed on the color filter layer.  
       FIG. 21  is a cross-sectional view showing a pixel of the TFT-LCD panel mounted with a TFT fingerprint identification substrate of  FIG. 3  according to another exemplary embodiment of the present invention;  
      Referring to  FIG. 21 , a TFT substrate  500  includes a lower transparent substrate  330 , a data wiring, a color filter layer  336 , an insulation layer  338 , a gate wiring, a thin film transistor  310  and a pixel electrode  340 .  
      The data wiring is formed on the lower transparent substrate  330  comprised of a transparent material such as glass and includes a data line  334   a  and  334   b  and a data pad (not shown). The data line, as shown in  FIG. 21 , may include a double layer having an upper film  334   a  and a lower film  334   b , or may include a single layer comprised of a conductive material. For example, the upper film  334   a  comprises a material easily forming junction with other material. For example, the upper film  334   a  comprises chrome (Cr). For example, the lower film  334   b  comprises a material having a low resistance such as aluminum (Al), aluminum alloy or copper (Cu). A portion of the data line may function as a light shielding layer (or black matrix) for blocking the light incident from the lower surface of the lower transparent substrate  330 .  
      The color filter  336  is formed on the lower transparent substrate  330  on which the data wiring is formed. The color filter  336  includes red (R), green (G) and blue (B) color filters. A peripheral portion of the color filter layer  336  covers the data line  334   a  and  334   b  and the data pad.  
      The insulation layer  338  is formed on the color filter layer  336  and may include organic insulation layer.  
      The gate wiring is formed on the insulation layer  338  and includes a gate line  321  and a gate pad (not shown).  
      The thin film transistor  310  includes a gate electrode  301 , a gate insulation layer  303 , an active pattern  305 , an ohmic contact pattern  307 , a source electrode  309  and a drain electrode  311 .  
      The pixel electrode  340  comprises a transparent conductive material such as ITO or IZO. The pixel electrode is electrically connected to the drain electrode  311  of the thin film transistor  310 .  
      A contact hole  345   c  is formed on the source electrode  309  and the source electrode  309  is electrically connected to the data line  334   a  and  334   b.    
      According to above embodiment of the present invention, since the gate line  321  and the data line  334   a  and  334   b  function as the light shielding layer, a light shielding layer may not be formed on a upper transparent substrate (not shown) disposed on the liquid crystal layer (not shown) interposed between the upper and lower transparent substrates. Therefore, the miss-alignment between the upper and lower transparent substrates may be reduced, the aperture ratio of the TFT-LCD panel may be increased, and the quality of image display may be enhanced.  
      The structure of the TFT fingerprint identification substrate disposed over the TFT substrate is the same or similar to that of the TFT fingerprint identification substrate according to above described embodiments.  
      This invention has been described with reference to the exemplary embodiments. It is evident, however, that many alternative modifications and variations will be apparent to those having skill in the art in light of the foregoing description. Accordingly, the present invention embraces all such alternative modifications and variations as fall within the spirit and scope of the appended claims.