Patent Publication Number: US-9847367-B2

Title: Digital x-ray detector and method for repairing a bad pixel thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 14/700,752, filed Apr. 30, 2015; which claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2015-0014359, filed Jan. 29, 2015, which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field of Invention 
     The following description relates to a digital x-ray detector wherein a PIN diode may be prevented from being damaged in a process of repairing a bad pixel using laser, and a method for repairing the bad pixel thereof. 
     Description of Related Art 
     Methods for detecting an x-ray include a method of directly detecting an x-ray and a method of indirectly detecting an x-ray by converting the x-ray into a visible ray and then detecting the x-ray using the visible ray. 
     An x-ray detector using the aforementioned indirect method consists of an element to convert an x-ray into a visible ray, an element to convert the visible ray into an electronic signal, and an element to convert the electronic signal into an image signal. In other words, the x-ray detector using the indirect method is an apparatus configured to convert an emitted x-ray eventually into an image signal. 
     Hereinafter, a conventional indirect type digital x-ray detector (hereinafter referred to as a ‘digital x-ray detector’) will be explained with reference to the drawings attached. 
       FIG. 1  is a schematic cross-sectional view illustrating a conventional digital x-ray detector;  FIG. 2  is a schematic top view of the conventional digital x-ray detector; and  FIG. 3  is an enlarged view of major parts of  FIG. 2 . 
     As illustrated in  FIGS. 1 to 3 , the conventional digital x-ray detector includes a substrate  10 , a gate line  20  and a data line  30  disposed on the substrate  10  such that the gale line and the data line intersect each other, a thin film transistor  40  formed on an intersecting region of the gate line  20  and the data line  30 , a PIN diode  50  disposed on a pixel domain, a bias line  60  disposed above the PIN diode  50  such that it is parallel to the data line  30 , and a scintillator  70 . 
     The thin film transistor  40  is formed on the substrate  40 , and includes a gate electrode  21 , an active layer  41 , a source electrode  42  and a drain electrode  43 . 
     The PIN diode  50  includes a lower electrode  51  that is electrically connected to the thin film transistor  20 ; a layer  52  that includes a P (Positive) type semiconductor layer, an I (Intrinsic) type semiconductor layer, and an N (Negative) type semiconductor layer successively deposited on the lower electrode  51 ; and an ITO upper electrode  53 . 
     The scintillator  70  is formed on the PIN diode  50  and serves to convert an x-ray into a visible ray. 
     Hereinafter, operations of such a conventional digital x-ray detector will be explained. 
     When an x-ray is emitted to the scintillator  70 , the x-ray is converted into a visible ray in the scintillator  70 , and then the visible ray is transmitted to the PIN diode  50 . The visible ray transmitted to the PIN diode  50  is converted into an electronic signal in the PIN diode  50 , and the converted electronic signal is converted into an image signal through the thin film transistor, and is then displayed. 
     Generally, in a digital x-ray detector, from a minimum of tens of thousands up to a maximum of tens of millions of pixels are formed with different sizes and resolutions, and thus it would take too much failure cost to manufacture an array substrate such that all those tens of thousands or tens of millions of pixels operate normally. Therefore, array substrates of fair quality if not the best quality are being manufactured as long as they satisfy minimum requirements. 
     However, due to the recent increasing demand from customers to improve the display quality, efforts are being made for processes that could repair bad pixels. 
     Specifically, after an x-ray is converted into a visible ray in a scintillator, the visible ray is converted into an electronic signal in a PIN diode, and then the converted electronic signal is displayed as an image signal after going through a thin film transistor. Herein, should there be a bad pixel that retains its state of being bright spot, the bright spot will be clearly recognizable. Accordingly, efforts are being made to provide a repair process that could keep the bad pixel in a state of a dark spot. 
     It is generally easy for a human eye to recognize a white spot on a black background than a black spot on a white background, and thus to reduce the recognizability of a bad pixel, it is general to darkening or blackening the bad pixel. 
     Therefore, when manufacturing an array substrate for a digital x-ray detector, a bright bad pixel is repaired to appear darker while leaving a dark bad pixel as it is, thereby reducing the recognizability of the bad pixels. 
     In an array substrate for a conventional digital x-ray detector, darkening a bad pixel is performed by cutting a drain electrode  43  (“A” part shown in dotted lines in  FIG. 3 ) of the thin film transistor  40  by emitting a laser. 
     However, in the pattern design of an array substrate of such a conventional digital x-ray detector, the distance between the drain electrode  43  and a PIN diode is too close to perform the repair process, and thus the PIN diode  50  may be damaged by the laser in the process of cutting the drain electrode  43  using the laser, and when the PIN diode  50  is damaged, the unstable state of a current may affect a PIN diode of a neighboring pixel as well, causing the PIN diode  50  of the neighboring pixel to malfunction. Thus, performing the process of repairing a bad pixel is not easy. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     A purpose of the present disclosure is to resolve the aforementioned problems of prior art, that is to provide a digital x-ray detector with an increased distance between a drain electrode and a PIN diode so that the PIN diode may be prevented from being damaged during a process of repairing a bad pixel wherein laser is used, and a method for repairing the bad pixel thereof. 
     According to an aspect, there is provided a digital x-ray detector comprising: a substrate; a gate line and a data line formed on the substrate such that the gate line and the data line intersect each other to form a pixel domain; a thin film transistor formed within the pixel domain such that the thin film transistor is adjacent to a portion where the gate line and the data line intersect each other, the thin film transistor including a gate electrode, an active layer, a source electrode and a drain electrode; a PIN diode which is formed within the pixel domain and which includes a lower electrode connected to the source electrode of the thin film transistor, a PIN layer formed on the lower electrode, and an upper electrode formed on the PIN layer; a bias line connected to the upper electrode of the PIN diode; and a scintillator arranged above the PIN diode, wherein on at least one of a surface of the drain electrode which faces the PIN diode and a surface of the PIN diode which faces the drain electrode, a groove is formed such that it expands a distance between the drain electrode and the PIN diode. 
     Herein, the groove may be formed on an area between the data line and the active layer of the thin film transistor. 
     Furthermore, the groove may include a first groove formed on the drain electrode side, and a second groove formed on the PIN diode side, the first groove and the second groove facing each other. 
     According to another aspect, there is provided a method for repairing a bad pixel of a digital x-ray detector comprising a substrate; a gate line and a data line formed on the substrate such that the gate line and the data line intersect each other to form a pixel domain; a thin film transistor formed within the pixel domain such that the thin film transistor is adjacent to a portion where the gate line and the data line intersect each other, the thin film transistor including a gate electrode, an active layer, a source electrode and a drain electrode; a PIN diode which is formed within the pixel domain and which includes a lower electrode connected to the source electrode of the thin film transistor, a PIN layer formed on the lower electrode, and an upper electrode formed on the PIN layer; a bias line connected to the upper electrode of the PIN diode; and a scintillator arranged above the PIN diode, wherein on at least one of a surface of the drain electrode which faces the PIN diode and a surface of the PIN diode which faces the drain electrode, a groove is formed such that it expands a distance between the drain electrode and the diode, the method comprising the following steps: detecting the bad pixel by inspecting the digital x-ray detector; and darkening the detected bad pixel by cutting the drain electrode using laser at the position of the drain electrode corresponding to the groove. 
     Various aforementioned aspects of the present disclosure have an effect of providing a digital x-ray detector with an increased distance between a drain electrode and a PIN diode so that the PIN diode may be prevented from being damaged during a process of repairing a bad pixel wherein laser is used, and a method for repairing the bad pixel thereof. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating a conventional digital x-ray detector. 
         FIG. 2  is a schematic top view of the conventional digital x-ray detector. 
         FIG. 3  is an enlarged view of the main parts of  FIG. 2 ; 
         FIG. 4  is a schematic top view of the digital x-ray detector according to the present disclosure. 
         FIG. 5  is an enlarged view of the main parts of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the systems, apparatuses, and/or methods described herein will be apparent to one of ordinary skill in the art. The progression of processing steps and/or operations described is an example; however, the sequence of and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
     The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
     Hereinafter, a digital x-ray detector according to a first embodiment of the present disclosure will be explained in detail with reference to the drawings attached. 
       FIG. 4  is a schematic top view of a digital x-ray detector of the present disclosure; and  FIG. 5  is an enlarged view of the main parts of  FIG. 4 . 
     The digital x-ray detector according to the first embodiment of the present disclosure illustrated in  FIGS. 4 and 5  includes a substrate  110 , a gate line  120 , a data line  130 , a thin film transistor  140 , a PIN diode  150 , a bias line  160  and a scintillator (not illustrated). 
     The gate line  120  is arranged on the substrate HO in a first direction, for example, an X axis direction of the figure, and the data line  130  is arranged on the substrate  110  in a second direction that is perpendicular to the first direction, for example, a Y axis direction. That is, the gate line  120  and the data line  130  are arranged such that they intersect each other and form a pixel domain. 
     The thin film transistor  140  is arranged within the pixel domain such that it is adjacent to where the gate line  120  and the data line  130  intersect each other, and the thin film transistor  140  includes a gate electrode  121  protruding from one side of the gate line  120 , an active layer  141  formed above the gate electrode  121 , a drain electrode  143  protruding from one side of the data line  130  and super posed on one side of the active layer  141 , and a source electrode  142  superposed on the other side of the active layer  141 . 
     Herein, the gate electrode  121  extends from the gate line  120 . Therefore, the gate electrode  121  may be made of a same substance and in the same process as the gate line  120 . 
     The active layer  141  is formed on the gate electrode  121  and below the source electrode  142  and drain electrode  143 , and may include an ohmic contact layer doped with an impurity formed on a region where it contacts the source electrode  142  and drain electrode  143 . That is, the active layer  141  is formed on a middle layer between the gate electrode  121 , and the source electrode  142  and drain electrode  143 , so as to serve as a channel through which electrons move. 
     The source electrode  142  is formed on one side of the active layer and is electrically connected to the PIN diode. Therefore, an electronic signal converted at the PIN diode  150  is transmitted to the active layer through the source electrode  142  of the thin film transistor  140 . 
     The drain electrode  143  is formed on the other side of the active layer that faces the source electrode  142 . The drain electrode  143  may be electrically connected to the data line  130  through a predetermined contact hole. Therefore, the electronic signal goes through the drain electrode  143  of the thin film transistor  140  and through the data line  130  connected to the drain electrode  143 , and is then displayed as an image signal. 
     The PIN diode  150  is electrically connected to the source electrode  142  of the thin film transistor  140 . The PIN diode  150  converts the visible ray into an electronic signal and transmits the converted electronic signal to the source electrode  142 . 
     The PIN diode  150  includes a lower electrode  151  electrically connected to the source electrode  142 , a PIN layer  152  formed on the lower electrode  151 , and an upper electrode  153  formed on the PIN layer  152 . The PIN layer  152  serves to convert the visible ray into the electronic signal. Specifically, the PIN layer  152  includes a P (Positive) type semiconductor layer, an I (Intrinsic) type semiconductor layer, and an N (Negative) type semiconductor layer, and the N type semiconductor layer, the I type semiconductor layer, and the P type semiconductor layer may be deposited successively on the lower electrode  151 . When a visible ray is emitted to such a PIN layer  152 , the I type semiconductor layer is depleted by the P type semiconductor layer and the N type semiconductor layer, and generates an electric field inside thereof. A positive hole and electron generated by the ray are drifted by the electric field, and then collected in the P type semiconductor layer and N type semiconductor layer, respectively. 
     The bias line  160  may be electrically connected to the upper electrode  153  of the PIN diode  150  through a predetermined contact hole  161 . 
     The scintillator (not illustrated) is formed above the PIN diode  150 , and serves to convert an x-ray into a visible ray. 
     According to the embodiment of the present disclosure, on a surface of the drain electrode  143  facing the PIN diode  150 , a first groove  144  is formed that partially reduces a width of the drain electrode  143  in the first direction (X axis). Herein, the first groove  144  is desirably formed where the drain electrode  143  is cut off in a repairing process using laser aimed at making a bad pixel darker, that is between the data line  130  and the active layer  141 . 
     Furthermore, on a surface of the PIN diode facing the drain electrode  143 , a second groove  154  is formed to distance the PIN diode  150  away from the drain electrode  143 . Herein, the second groove  154  faces the first groove  144 . 
     The first groove  144  and the second groove  154  expands the distance between the drain electrode  143  and the PIN diode  150 , thereby distancing the drain electrode  143  away from the PIN diode  150 . Accordingly, it is possible to prevent the PIN diode from being damaged in a process of cutting the drain electrode using laser when repairing a bad pixel. 
     A width of the first groove  144  and the second groove  154  in the first direction (X axis) and a depth of the first groove  144  and the second groove  154  in the second direction (Y axis) are desirably set up such that they minimize a photo-electronic signal conversion efficiency of the PIN diode  150  and electrical characteristics of the drain electrode  143  within a range that the Pin diode  150  is not damaged during the repairing process using laser. 
     A method for repairing a bad pixel by making the bad pixel darker in the aforementioned digital x-ray detector is explained hereinafter. 
     The method for repairing a bad pixel by making the bad pixel darker according to the embodiment of the present disclosure includes a step of detecting the bad pixel, and a step of making the bad pixel darker. 
     The detecting the bad pixel may involve evenly emitting an x-ray on an entirety of surface of the digital x-ray detector, and detecting the bad pixel by determining whether or not there is the bad pixel using an image signal being output from the digital x-ray detector. 
     The making the bad pixel darker may involve cutting the drain electrode  143  of the bad pixel detected in the detecting of the bad pixel using laser, and making the bad pixel darker. Herein, the cut portion of the drain electrode  143  using laser may be the portion where the first groove  144  is formed (“B” part shown in dotted lines in  FIG. 5 ). 
     In such a method for repairing a bad pixel of the digital x-ray detector of the present disclosure, during the process of cutting the drain electrode  143  using laser, the laser is distanced away from the PIN diode  150  as much as the depth of the first groove  144  in the second direction (Y axis). Therefore, it is possible to prevent the PIN diode  150  from being damaged in the repairing process, thereby increasing the yield rate of the panel. 
     Furthermore, since on the surface of the PIN diode  150  facing the drain electrode  143 , the second groove  154  is formed such that it corresponds to the first groove  144 , the PIN diode  150  is further distanced from the drain electrode  143  that is subjected to the cutting by the laser, by as much as the depth of the second groove  154  in the second direction (Y axis). Therefore, it is possible to significantly reduce the possibility that the PIN diode  150  is damaged by the laser in the process of repairing the bad pixel by cutting the drain electrode  143  with laser. 
     While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure. 
     REFERENCE NUMERALS 
     
         
           110 : SUBSTRATE 
           120 : GATE LINE 
           121 : GATE ELECTRODE 
           130 : DATA LINE 
           140 : THIN FILM TRANSISTOR 
           141 : SOURCE ELECTRODE 
           142 : ACTIVE LAYER 
           143 : DRAIN ELECTRODE 
           144 : FIRST GROOVE 
           150 : PIN DIODE 
           151 : LOWER ELECTRODE 
           152 : PIN LAYER 
           153 : UPPER ELECTRODE 
           154 : SECOND GROOVE 
           160 : BIAS LINE 
           161 : CONTACT HOLE