Abstract:
An input display is provided in the present invention. The input display includes a thin film transistor (TFT) and a light blocking layer. The TFT includes a low-field electrode, a high-field electrode connected to the low-field electrode with a connecting section, and a field-effect area positioned on the connecting section and connected to the high-field electrode, wherein a PN junction field is formed in the field-effect area when the TFT is switched off. The light blocking layer corresponds to the high-field electrode and hides the field-effect area from all incident light from the TFT.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an input display, and more particularly to an input display with a light detector array. 
     BACKGROUND OF THE INVENTION 
     Please refer to  FIG. 1 , which is a circuit diagram showing a light detector array of an input display according to the first prior art. 
     In  FIG. 1 , each unit of the light detector array includes a TFT switch. For example, the operation of the unit  11  in the position where the first read-out line intersects the first gate line is as follows. When the light detector array is OFF, the gate line  1  is at low voltage. The body diode of the TFT is reversely biased so that there is no current flowing through the TFT. When the gate line  1  turns to high voltage, the current flows from gate line  1  through read-out line  1  to the readout amplifier  12 . 
     A photo-induced ON current occurs when the light is emitted onto the TFT. When the light is emitted onto the TFT, the photo-induced ON current increases. Contrarily, when no light is emitted onto the TFT, the photo-induced ON current decreases. 
     When the input display with the light detector array is used, the touch of the display will influence the quantity of the incident light. Hence, which position of the display has been touched is able to be detected by sensing the quantity of the photo-induced ON current. 
     However, the drawback of the input display with the light detector array is the generation of the photo-induced leakage current, which also occurs when the light is emitted onto the TFT. The sensing and the detection of the display are seriously held back by the photo-induced leakage current. 
     To overcome the drawback, another implementation of the display has been provided. Please refer to  FIG. 2 , which is a circuit diagram showing a light detector array of an input display according to the second prior art. 
     In  FIG. 2 , each unit of the light detector array includes two TFT switches. The unit  21  in the position where read-out line # 1  intersects gate line # 1  is taken for example. The switch-TFT  11  is arranged for switching and the photo-TFT  11  is arranged for detecting the intensity of the incident light. 
     In  FIG. 2 , the additional TFT is unnecessary to be emitted by the incident light, so the photo-induced leakage current is able to be decreased. However, the increased number of TFT results in a lower process yield. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an input display with a light detector array. The input display is able to be fabricated in a higher aperture ratio and a higher production yield. Besides, the input display has enough photo-induced ON current when the TFTs are switched ON and has no photo-induced leakage current when the TFTs are switched OFF. 
     It is another object of the present invention to achieve the above-mentioned object by appropriately designing a pixel unit with a light blocking layer which hides a field-effect area positioning on a connecting section between a high-field electrode and a low-field electrode and near the high-field electrode from all incident light from the pixel unit. 
     Preferably, the light blocking layer is a black matrix positioning on a color filter or a metal layer positioning on a passivation layer in the pixel unit. 
     For the convenience of description, the embodiments of invention are illustrated in the structure of an n-type TFT. However, it is obvious to one skilled in the art to apply the technical characteristics of the invention in the applications of a p-type TFT, a poly-TFT, and a TFT-LCD. 
     Please refer to  FIG. 3(   a ) and  FIG. 3(   b ).  FIG. 3(   a ) is a cross-sectional view of an n-type TFT of a light detector array.  FIG. 3(   b ) is a diagram showing the band of the n-type TFT when it is switched ON and OFF respectively. In  FIG. 3(   a ), the partial n-type TFT structure  30  is composed of a substrate  301 , a metal layer  302 , a gate insulator layer  303 , an amorphous silicon layer  304 , a N +  amorphous silicon layer  305 , a drain terminal  306 , and a source terminal  307 . The metal layer  302  is used as a gate terminal. The band diagram in  FIG. 3(   b ) is shown with respect to the dotted line drawn in  FIG. 3(   a ). 
     In  FIG. 3(   b ), a conduction band  311 , a valence band  312 , a channel  313 , a drain terminal  314 , a source terminal  315 , holes  316 , and electrons  317  are symbolized in ON state  31 , while a conduction band  321 , a valence band  322 , a channel  323 , a drain terminal  324 , a source terminal  325 , holes  326  and  328 , electrons  327  and  329 , and PN junction  320  are symbolized in OFF state  32 . The band diagrams are both drawn corresponding to the n-type TFT structure  30  in  FIG. 3(   a ), so the high-field electrode is defined as a drain terminal and the low-field electrode is defined as a source terminal. 
     When the TFT is switched ON in the ON state  31 , the electrons  317  in the valence band  312  are transferred to the conduction band  311  due to the emitting of the incident light (not shown) and holes  316  are generated accordingly. Then the electrons  317  move toward the drain terminal  314  and the holes move toward the source terminal  315  due to the effect of the electric field, so that a photo-induced ON current (not shown) occurs between the drain terminal  314  and the source terminal  315 . 
     When the TFT is switched OFF in the OFF state  32 , the gate terminal (not shown) is connected to a low voltage. At this time, the bands  321  and  322  in most of the area between the drain terminal  324  and the source terminal  325  are almost horizontal. That is, there is no electric field existing in this area. The electrons  327  in this region will just be transferred from the valence band  322  to the conduction band  321  and will be combined with the holes  326  repeatedly, even though the light (not shown) has been emitted onto the electrons ( 327 ). There is no assistance for the increase of the current. However, the current formed by an electric field, which occurs due to the transferring of the holes  328  and the electrons  329 , in a PN junction  320  existing near the drain terminal  324  constitutes the aforementioned photo-induced leakage current. 
     According to the first aspect of the present invention, an input display is provided. The input display includes a thin film transistor (TFT) and a light blocking layer. The TFT includes a low-field electrode, a high-field electrode connected to the low-field electrode with a connecting section, and a field-effect area positioned on the connecting section and connected to the high-field electrode, wherein a PN junction field is formed in the field-effect area when the TFT is switched off. The light blocking layer corresponds to the high-field electrode and hides the field-effect area from all incident light from the TFT. 
     According to the second aspect of the present invention, an pixel unit is provided. The pixel unit is composed of the TFT and the light blocking mentioned in the previous paragraph. 
     According to the third aspect of the present invention, an elimination method for a photo-induced leakage current of an input display is provided. The elimination method includes steps of providing a thin film transistor (TFT) including a low-field electrode, a high-field electrode connected to the low-field electrode with a connecting section, and a field-effect area positioned on the connecting section and connected to the high-field electrode, and hiding the field-effect area from all incident light from the TFT so that the photo-induced leakage current produced by a plurality of electrons influenced by the incident light and the PN junction field formed in the field-effect area when the TFT is switched off is eliminated. 
     The every aspects of the present invention are suitable in the application of an n-type TFT, a p-type TFT, a poly-TFT, and an n-type transistor or a p-type transistor with a channel made of semiconductor layer, such as a-Si, poly-Si, single crystalline Si, III-V compounds . . . etc., or organic materials. Moreover, they are also suitable for the combination of the fabrication process of a TFT-LCD to widen the utility in the industrial application. 
     The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing a light detector array of an input display according to the first prior art; 
         FIG. 2  is a circuit diagram showing a light detector array of an input display according to the second prior art; 
         FIG. 3(   a ) is a cross-sectional view of an n-type TFT of a light detector array; 
         FIG. 3(   b ) is a diagram showing the band of the n-type TFT along the dotted line of  FIG. 3(   a ) when the TFT is switched ON and OFF respectively; 
         FIG. 4(   a ) is an upper view of an n-type TFT of a light detector array according to the first embodiment of the present invention; 
         FIG. 4(   b ) is a cross-sectional view showing the structure of  FIG. 4(   a ) along the dotted line; 
         FIG. 5(   a ) is an upper view of an n-type TFT of a light detector array according to the second embodiment of the present invention; 
         FIG. 5(   b ) is a circuit diagram showing the light detector array fabricated with the n-type TFT of  FIG. 5(   a ); 
         FIG. 6(   a ) is an upper view of a TFT of a light detector array according to the third embodiment of the present invention; 
         FIG. 6(   b ) is a circuit diagram showing the light detector array fabricated with the TFT of  FIG. 6(   a ) 
         FIG. 7(   a ) is an upper view of an n-type TFT of a light detector array according to the fourth embodiment of the present invention; and 
         FIG. 7(   b ) is a cross-sectional view showing the structure of  FIG. 7(   a ) along the dotted line. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Please refer to  FIG. 4(   a ) and  FIG. 4(   b ).  FIG. 4(   a ) is an upper view of an n-type TFT of a light detector array according to the first embodiment of the present invention, and  FIG. 4(   b ) is a cross-sectional view showing the structure of  FIG. 4(   a ) along the dotted line. In  FIG. 4(   a ), the TFT  40  is in the area surrounded by data line  1 , data line  2 , read-out line, gate line  1 , and gate line  2  while the remaining components in the area are omitted for the convenience of illustration. The TFT  40  in  FIG. 4(   a ) is implemented to correspond to the photo sensitive switch TFT  11  surrounded by gate line  1 , gate line  2 , and read-out line  1  shown in  FIG. 1 . In the upper view of  FIG. 4(   a ), only a part of the components of TFT  40  are shown. To clarify the structure of the TFT  40  of  FIG. 4(   a ), the description for  FIG. 4(   b ) is given firstly as follows. 
     The main object of the invention is to provide a pixel unit and an input display implemented with a plurality of such pixel unit. As the first embodiment of the present invention, both of the pixel unit and the input display are based on the TFT  40  shown in  FIG. 4(   b ). 
     In  FIG. 4(   b ), the TFT  40  includes at least a high-field electrode  401 , a low-field electrode  402 , a connecting section  403  for connecting the high-field electrode  401  and the low-field electrode  402 , and a metal layer  409 . The high-field electrode  401  is connected to the read-out line and the metal layer  409  is connected to the gate line  2 . As  FIG. 4(   b ) shows, the connecting section  403  is mainly composed of an amorphous silicon layer  407  and the whole TFT  40  is fabricated on a substrate  40 ′. 
     When the TFT  40  is switched OFF, a PN junction field occurs in a field-effect area  404  in part of the connecting section  403  near the high-field electrode  401 . When the light is emitted to the field-effect area  404 , the electrons would be affected by the incident light and the PN junction field so that a photo-induced leakage current is generated. The object of the invention is to eliminate the photo-induced leakage current. 
     The n-type TFT  40  is taken for example in  FIG. 4 , so the high-field electrode  401  and the low-field electrode  402  can be defined as a drain terminal and a source terminal respectively while the gate terminal  409  is at low voltage. If a p-type TFT, however, is taken for another embodiment of the present invention, then the high-field electrode  401  and the low-field electrode  402  should be defined as a drain terminal and a source terminal respectively while the gate terminal  409  is at high voltage. For one skilled in the art, the invention needs not be limited to the disclosed n-type TFT and is easy to be deduced in the applications of the p-type TFT and the poly-TFT. 
     In the n-type TFT  40  shown in  FIG. 4 , the high-field electrode  401  and the low-field electrode  402  are defined as a drain terminal and a source terminal respectively. There is a passivation layer  405  covering the high-field electrode  401 , the low-field electrode  402  and the connecting section  403 . Besides, below the high-field electrode  401  and the low-field electrode  402  are sequentially a N +  amorphous silicon layer  406 , an amorphous silicon layer  407 , a gate insulator layer  408  and the gate terminal  409 . There is further an indium-tin-oxide (ITO) layer  410  covering the passivation layer  405  corresponding to the source terminal  402 . The ITO layer  410  is also connected to the metal layer  409  so as to connect the low field electrode  402  to the metal layer  409 . The operation of the low voltage is as described in  FIG. 1  and will be omitted here. 
     According to the object of the invention, a light blocking layer is introduced in order to eliminate the photo-induced leakage current. In the first embodiment of  FIG. 4 , a color filter (CF)  41  composed of a first black matrix (BM)  411 , a second BM  412 , and a substrate  41 ′ is provided. The first BM is adopted as the light blocking layer to hide the field-effect area  404  from all incident light, so that the light will never emit to or through the field-effect area  404 . Hence, the photo-induced leakage current will be eliminated when the TFT  40  is switched OFF, and the photo-induced ON current will still be hold when the TFT  40  is switched ON. 
     In the practical fabrication process, the width of the field-effect area  404  is limited between 1 um and 5 um. Yet the key point of the first embodiment is not the value of the width but is that the BM  411  should be able to hide the field-effect area  404  from all incident light perfectly, as shown in  FIG. 4(   b ). 
     In the production process of a display, the defect of the shifting between layers often occurs. For solving such a defect, in the present invention, the TFT  40  is implemented as the L-type structure shown in  FIG. 4(   a ). The TFT structure  40  is set at an angle with respect to the electric field of the PN junction. The angle in this embodiment is 90°. 
     Although the first embodiment is given in the application of an n-type TFT, the present invention is still suitable for the application of a p-type TFT and a poly-TFT. Besides, it can also be utilized for the combination of the fabrication process of a TFT-LCD to widen the utility in the industrial application. 
     Please refer to  FIG. 5(   a ) and  FIG. 5(   b ).  FIG. 5(   a ) is an upper view of an n-type TFT of a light detector array according to the second embodiment of the present invention, and  FIG. 5(   b ) is a circuit diagram showing the light detector array fabricated with the n-type TFT of  FIG. 5(   a ). In  FIG. 5(   a ), the TFT  50  is in the area surrounded by data line  1 , data line  2 , read-out line, gate line  1 , and fixed voltage line while the remaining components in the area are omitted for the convenience of illustration. The TFT  50  in  FIG. 5(   a ) is implemented to correspond to the photo sensitive switch TFT  50  shown in  FIG. 5(   b ). 
     Similar to  FIG. 4(   a ) and  FIG. 4(   b ), the equivalent components are given the same symbols in  FIG. 5(   a ). To clarify the operation of the TFT  50  in  FIG. 5(   a ), the description will be given by referring to  FIG. 5(   b ) firstly. In  FIG. 5(   b ), because the voltage level of the fixed voltage line is lower than the voltage level (Vbias) of the read-out line, the TFT  50  is OFF and the body diode of the TFT  50  is reversely biased. When the gate line  1  turns to high voltage, the current flows from the fixed voltage line through read-out line  1  to the readout amplifier  12 . 
     The technical characteristic of this embodiment is also to adopt the BM  511  as the light blocking layer to hide the field-effect area near the drain terminal  501  from all incident light, so that the light will never emit to or through the field-effect area. Hence, the photo-induced leakage current will be eliminated when the TFT  50  is switched OFF, and the photo-induced ON current will still be hold when the TFT  50  is switched ON. However, the difference between  FIG. 5  and  FIG. 4(   a ) (or  FIG. 4(   b )) is that the source terminal  502  is not short-connected to the gate terminal  509  but is connected to the fixed voltage line as  FIG. 5(   a ) shows. The drain terminal is still connected to the read-out line. 
     The n-type TFT  50  is taken for example in  FIG. 5 , so the high-field electrode  501  and the low-field electrode  502  can be defined as a drain terminal and a source terminal respectively while the gate terminal  509  is at low voltage. If a p-type TFT, however, is taken for another embodiment of the present invention, then the high-field electrode  501  and the low-field electrode  502  should be defined as a drain terminal and a source terminal respectively while the gate terminal  509  is at high voltage. For one skilled in the art, the invention needs not be limited to the disclosed n-type TFT and is easy to be deduced in the applications of the p-type TFT and the poly-TFT. 
     Please refer to  FIG. 6(   a ) and  FIG. 6(   b ).  FIG. 6(   a ) is an upper view of a TFT of a light detector array according to the third embodiment of the present invention, and  FIG. 6(   b ) is a circuit diagram showing the light detector array fabricated with the TFT of  FIG. 6(   a ). In  FIG. 6(   a ), the TFT  60  is in the area surrounded by data line  1 , data line  2 , read-out line, gate line  1 , and fixed voltage line while the remaining components in the area are omitted for the convenience of illustration. The TFT  60  in  FIG. 6(   a ) is implemented to correspond to the photo sensitive switch TFT  60  shown in  FIG. 6(   b ). 
     Similar to  FIG. 4(   a ) and  FIG. 4(   b ), the equivalent components are given the same symbols in  FIG. 6(   a ). Although the technical characteristic of this embodiment is also to adopt the BM  611  as the light blocking layer to hide the field-effect area, the position of the BM  611  in  FIG. 6(   a ) is opposite to the position of the BM  511  in  FIG. 5(   a ). That is, the BM  611  is fabricated to hide the high-field electrode  601  which is connected to the fixed voltage line. The low-field electrode  602  is still connected to the read-out line. 
     To clarify the operation of the TFT  60  in  FIG. 6(   a ), the description will be given by referring to  FIG. 6(   b ) firstly. In  FIG. 6(   b ), because the voltage level of the fixed voltage line is now higher than the voltage level (Vbias) of the read-out line, the blocking fabrication of the BM  611  in  FIG. 6(   a ) is different from the blocking fabrication of the BM  511  in  FIG. 5(   a ). 
     The circuit implementation of the structure in  FIG. 5  is shown in  FIG. 6 . Compared with the circuit of the prior art shown in  FIG. 1 , the TFTs in  FIG. 6  are controlled by a constant voltage. 
     Please refer to  FIG. 7(   a ) and  FIG. 7(   b ).  FIG. 7(   a ) is an upper view of an n-type TFT of a light detector array according to the fourth embodiment of the present invention, and  FIG. 7(   b ) is a cross-sectional view showing the structure of  FIG. 7(   a ) along the dotted line. In  FIG. 7(   a ), the TFT  70  is in the area surrounded by data line  1 , data line  2 , read-out line, gate line  1 , and gate line  2  while the remaining components in the area are omitted for the convenience of illustration. The TFT  70  in  FIG. 7(   a ) is implemented to correspond to the photo sensitive switch TFT  71  surrounded by gate line  1 , gate line  2 , and read-out line  1  shown in  FIG. 1 . In the upper view of  FIG. 7(   a ), only a part of the components of TFT  70  are shown. To clarify the structure of the TFT  70  of  FIG. 7(   a ), the description for  FIG. 7(   b ) is given firstly as follows. 
     The main object of the invention is to provide a pixel unit and an input display implemented with a plurality of such pixel unit. As the fourth embodiment of the present invention, both of the pixel unit and the input display are based on the TFT  70  shown in  FIG. 7(   b ). 
     In  FIG. 7(   b ), the TFT  70  includes at least a high-field electrode  701 , a low-field electrode  702 , a connecting section  703  for connecting the high-field electrode  701  and the low-field electrode  702 , and a metal layer  709 . As  FIG. 7(   b ) shows, the connecting section  703  is mainly composed of an amorphous silicon layer  707  and the whole TFT  70  is fabricated on a substrate  70 ′. 
     When the TFT  70  is switched OFF, a PN junction field occurs in a field-effect area  704  in part of the connecting section  703  near the high-field electrode  701 . When the light is emitted to the field-effect area  704 , the electrons would be affected by the incident light and the PN junction field so that a photo-induced leakage current is generated. The object of the invention is to eliminate the photo-induced leakage current. 
     The n-type TFT  70  is taken for example in  FIG. 7 , so the high-field electrode  701  and the low-field electrode  702  can be defined as a drain terminal and a source terminal respectively while the gate terminal  709  is at low voltage. If a p-type TFT, however, is taken for another embodiment of the present invention, then the high-field electrode  701  and the low-field electrode  702  should be defined as a drain terminal and a source terminal respectively while the gate terminal  709  is at high voltage. For one skilled in the art, the invention needs not be limited to the disclosed n-type TFT and is easy to be deduced in the applications of the p-type TFT and the poly-TFT. 
     In the n-type TFT  70  shown in  FIG. 7 , the high-field electrode  701  and the low-field electrode  702  are defined as a drain terminal and a source terminal respectively. There is a passivation layer  705  covering the high-field electrode  701 , the low-field electrode  702  and the connecting section  703 . Besides, below the high-field electrode  701  and the low-field electrode  702  are sequentially a N +  amorphous silicon layer  706 , an amorphous silicon layer  707 , a gate insulator layer  708  and a metal layer  709 . There is further an indium-tin-oxide (ITO) layer  710  covering the passivation layer  705  corresponding to the source terminal  702 . The ITO layer is also connected to the metal layer  709  so as to connect the low-field electrode  702  to the metal. layer  709 . The operation of the low voltage is as described in  FIG. 1  and will be omitted here. 
     According to the object of the invention, a light blocking layer is introduced in order to eliminate the photo-induced leakage current. Instead of the BM  411  in  FIG. 4(   a ), an additional layer  711  is provided in the fourth embodiment of  FIG. 7 . The additional layer  711  located on the high-field electrode  701 , which is composed of a opaque material, e.g. a kind of metal, is adopted as the light blocking layer to hide the field-effect area  704  from all incident light, so that the light will never emit to or through the field-effect area  704 . Hence, the photo-induced leakage current will be eliminated when the TFT  70  is switched OFF, and the photo-induced ON current will still be hold when the TFT  70  is switched ON. 
     In the production process of a display, the defect of the shifting between layers often occurs. For solving such a defect, in the present invention, the TFT  70  is implemented as the L-type structure shown in  FIG. 7(   a ). The TFT structure  70  is set at an angle with respect to the electric field of the PN junction. The angle in this embodiment is 90°. 
     Although the fourth embodiment is given in the application of an n-type TFT, the present invention is still suitable for the application of a p-type TFT and a poly-TFT. Besides, it can also be utilized for the combination of the fabrication process of a TFT-LCD to widen the utility in the industrial application. 
     In conclusion, an input display is provided in the present invention. A light blocking layer, for example the black matrix  411  or the layer  711  in the above-mentioned embodiments, is able to hide the PN field-effect area near the high-voltage terminal from all incident light from the TFT. The incident light can not emit to or through the PN field-effect area so that the photo-induced leakage current is eliminated when the TFT is switched OFF. The photo-induced ON current remains almost identical when the TFT is switched ON, regardless of the presence of the light blocking layer. The input display fabricated with the light detector array and the TFT provided in the present invention is able to be fabricated in a higher aperture ratio and a higher production yield. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.