Patent Publication Number: US-6657226-B1

Title: Thin-film transistor array and method for manufacturing same

Description:
This application is a division of 09/092,944, filed Jun. 8, 1998, now U.S. Pat. No. 6,121,632. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a thin-film transistor array and, more particularly, to a thin-film transistor array that can be used with advantage for an active matrix liquid crystal display panel. 
     DISCUSSION ON THE RELATED ART 
     The following specific analyses have been given on the related art by the inventors in the course of the investigation toward the present invention. 
     An active matrix type liquid crystal display device, employing a thin-film transistor (‘TFT’) as a switching device, is made up of a TFT substrate comprised of a matrix array of TFTs and pixel electrodes and an opposing substrate electrode, arranged opposing the TFT substrate with a liquid crystal material interposed in-between. The opposing substrate electrode includes a light-shielding film (so-called black matrix), a color filter and a common electrode. 
     FIG. 15 shows a plan view illustrating the structure for one pixel of a typical thin-film transistor array, and FIG. 16 shows a cross-sectional view taken along line G-G′ of FIG.  15 . This structure is referred to as ‘a first conventional technique’. 
     Referring to FIGS. 15 and 16, the structure of the first conventional technique is explained. 
     The active matrix type liquid crystal display device, employing the TFT as an active device, has a structure in which a gate bus line  111 , wired in the horizontal direction from a gate driver, and a drain bus line  112 , wired in the vertical direction from a source driver, are connected to a gate electrode  101  and a drain electrode  103  of the TFT device, respectively, and in which a pixel electrode  106  is connected to a source electrode  104  of the TFT device. 
     When a given gate line  111  goes high, the TFTs connected to this gate bus line  111  are turned on in unison. The pixel electrode  106 , connected to this TFT, is charged to a signal voltage applied to the drain bus line  112 . 
     If then the gate bus line  111  goes low, the TFT in the on-state is turned off. However, the pixel electrode  106  keeps on to maintain its charging voltage. This maintained voltage is rewritten by the next signal voltage when the corresponding TFT again goes on. 
     If the active matrix type liquid crystal display device employing this TFT substrate is to make display of satisfactory quality, it is necessary for the pixel electrode  106  to hold the charging voltage sufficiently until next rewriting. 
     FIG. 17 shows a cross-sectional view illustrating, step-by-step, the process for manufacturing a typical thin-film transistor array (first conventional technique) shown in FIG.  16 . Referring to FIG. 17, the manufacturing method according to the first conventional technique is explained. 
     A gate electrode  101  formed by a metal film of Cr or Al is patterned on a glass substrate  100 , as shown in FIG. 17 a . A gate insulating film  114 , a channel layer  102  of intrinsic semiconductor amorphous silicon ‘a-Si(n+)’ and a contact layer  107  of n+ semiconductor amorphous silicon (‘a-Si (n+)’ are formed sequentially thereon. 
     The semiconductor layer is then etched (FIG. 17 b ) and the gate insulating film  114  of the contact area interconnecting the gate layer and the drain layer are removed by patterning, so that a through-hole, not shown, is formed for interconnecting a metal film forming the gate electrode  101  and a metal film forming the drain electrode  103 , source electrode  104  and the drain bus line  112 . 
     Similarly to the drain electrode  101 , the drain electrode  103 , source electrode  104 , drain bus line  112  and the pixel electrode  106  are formed (see FIGS. 17 c  and  17   d ) and subsequently a passivation film  115  is formed to complete a TFT array substrate (see FIG. 17 e ). 
     Meanwhile, a storage capacitance electrode  108  is formed simultaneously with the gate electrode  101  in the course of the patterning step for forming the gate electrode  101 . The storage capacitance electrode  108  faces the pixel electrode  106  via the gate insulating film  114  operating as a storage capacitance insulating film in-between to constitute a storage capacitance. 
     The opposing substrate side is manufactured by forming a counter-electrode on a glass substrate, not shown. 
     Finally, orientation films, not shown, are formed on the TFT array substrates and the opposing substrate, by way of orientation processing, after which a sealing pattern is formed and the substrates are then stacked together and fired. Into the fired product is injected a liquid crystal, not shown, and the injection inlet is sealed to complete a liquid crystal panel. 
     To this liquid crystal panel are added a light polarization plate, a driving circuit and a casing to complete a liquid crystal display device. 
     FIG. 18 shows a plan view illustrating the structure of one pixel of a representative thin-film transistor array characterized in that the storage capacitance is formed between it and the gate electrode (this structure is referred to as a ‘second conventional technique). The number of patterning steps and the manufacturing method in this structure are the same as those of the first conventional technique explained in accordance with FIG.  17 . 
     In the TFT of the structure shown in the first conventional technique and in the second conventional technique, the drain bus line  112  and the pixel electrode  106  are both electrically conductive layers each extending over the gate insulating film  114 , and are spaced apart from each other by a pre-set distance. However, if residual patterning troubles would occur in any patterning process, shorting is likely to occur between the drain bus line  112  and the pixel electrode  106 . 
     If shorting occurs between the drain bus line  112  and the pixel electrode, charging/discharging of the pixel electrode  106  cannot be controlled by on/off control of the TFT such that the pixels become visible as bright-point defect. 
     For reducing this shorting, there has been proposed in, for example, JP Patent Kokai JP-A-7-325314 a liquid crystal device in which, as shown in FIG. 19 a , by a step difference of the storage capacitance electrode  108 , the pixel electrode  106  in the vicinity of the storage capacitance electrode  108  is constricted or retracted, as shown in FIG. 19 b , relative to residual a-Si  116 , so that the drain bus line  112  and the pixel electrode  106  become difficult to get conductive by the residual a-Si  116 . The structure, however, cannot be applied to other than the case of residual a-Si attributable to the step difference of the storage capacitance electrode  108 . 
     There has also been proposed a TFT structure in which the drain bus line  112  and the pixel electrode  106  are laminated via an insulating film interposed in-between for reducing occurrences of shorting. FIG. 20 shows, in a plan view, the structure for one pixel of a TFT array aimed at reducing the shorting between the drain bus line  112  and the pixel electrode  106 . FIG. 21 is a cross-sectional view taken along line H-H′ in FIG. 20 (third conventional technique). 
     Referring to FIGS. 20 and 21, the structure of the third conventional technique is explained. 
     In this third conventional technique, the drain bus line  112  is provided on the gate insulating film  114 , whilst the pixel electrode  106  is formed on a passivation film  115 . The drain bus line  112  and the pixel electrode  106  are separated on the layer basis by the passivation film  115 . 
     FIG. 22 is a process diagram showing, step-by-step, the manufacturing process for a thin-film transistor array (third conventional technique) aimed at reducing shorting between the drain bus line  112  and the pixel electrode  106  as shown in FIG.  21 . Referring to FIG. 22, the manufacturing method for this third conventional technique is explained. 
     On the glass substrate  100  was patterned a gate electrode  101  of a metal film, such as Cr or Al (see FIG.  22 a), after which the gate insulating film  114  and the channel layer  102  formed of a-Si(I) and a contact layer  107  formed of a-Si(n+) are formed sequentially. 
     The semiconductor layer is then etched (see FIG. 22 b ) and a patterning step of removing the gate insulating film  114  of the contact area interconnecting the gate layer and the drain layer is then carried for forming a through-hole, not shown, for interconnecting the metal film forming the gate electrode  101  and the metal film forming the source electrode  104  and the drain bus line  112 . 
     Then, similarly to the gate electrode  101 , the drain electrode  103  formed by a metal layer, such as Cr or Al, source electrode  104  and the drain bus line  112  are formed, as shown in FIG. 22 c.    
     The passivation film  115  is then formed thereon and the through-hole  110  interconnecting the source electrode  104  and the pixel electrode  106  is provided (FIG. 22 d ). The pixel electrode  106  is then formed to provide a TFT array substrate (FIG. 22 e ). 
     In this structure, the storage capacitance electrode  108  is formed simultaneously with the gate electrode  101  by the patterning process forming the gate electrode  101 . The number of the patterning steps is equal to that used in the first conventional technique. 
     Another conventional technique characterized in that occurrences of shorting between the drain bus line  112  and the pixel electrode  106  is reduced and the storage capacitance electrode serves simultaneously as the gate electrode (referred to as a ‘fourth conventional technique’), as in the third conventional technique, is shown as a plan view in FIG.  23 . FIG. 9 shows a cross-section taken along line D-D′ in FIG.  23 . The number of the patterning steps is equal to that used in the third conventional technique (see FIG.  22 ). 
     For explaining the effect of the third and fourth conventional techniques, FIG. 24 shows, in a plan view, the state of generation of a-Si residuals on a pixel. FIG. 25 shows a cross-sectional view taken along line I-I′ in FIG.  24 . 
     In the above-mentioned conventional technique, since the drain bus line  112  and the pixel electrode  106  are separated on the layer basis by the passivation film  115 , no shorting occurs between the drain bus line  112  and the pixel electrode  106  even on occurrence of patterning defects in the course of the respective patterning steps. This reduces occurrences of point defects, that is bright and dark points. 
     However, even with this structure in which the drain bus line  112  and the pixel electrode  106  are separated form each other on the layer basis, electrically conductive foreign substances, such as a-Si, are left on occurrence of patterning defects, as shown in FIG.  26 . Moreover, parasitic capacitances Ca between the drain bus line  112  contacted with the pixel electrode  106  and the pixel electrode  106  are increased. If there exist parasitic capacitances between the drain bus line  112  and the pixel electrode  106 , the maintained voltage of the pixel Vp is modulated (ΔVp) as shown by the following equation 
      (1):Δ Vp =( Ca/Ct )Δ V   D   (1) 
     where Ca: drain-to-pixel capacitance 
     Ct: total capacitance of the pixel 
     ΔVp: voltage modulation of a pixel 
     ΔV D : drain amplitude 
     If the drain-to-pixel capacitance Ca is increased by the interposed electrically conductive foreign substances, the pixel voltage is lowered by 2×ΔVp as compared to that for regular pixels, so that point defects of semi-bright spots tend to be increased. 
     SUMMARY OF THE DISCLOSURE 
     In the structure of the above-described third and fourth conventional techniques, in which, for suppressing shorting between the drain bus line and the pixel electrode, the drain bus line and the pixel electrode are separated on the layer basis by an insulating film, the residual a-Si, if produced as shown in FIGS. 24 and 25, leads to such an inconvenience that, since the residual a-Si is electrically connected to the drain bus line  112 , the parasitic capacitance between the drain bus line  112  and the pixel electrode  106  is increased to increase point defects of semi-bright spots, that is points that have no optimum brightness. 
     It is therefore an object of the present invention to provide a transistor array in which occurrences of point defects of bright and dark spots ascribable to shorting between the drain bus line and the pixel electrode may be reduced. 
     It is a further object of the present invention to provide a transistor array in which a residual a-Si produced by patterning defects may be removed without increasing the number of patterning steps. 
     It is a still further object of the present invention to provide a transistor array in which the occurrences of point defects of bright and dark spots ascribable to increased parasitic capacitance between the drain bus line and the pixel electrode caused by electrical connection of residual a-Si to the drain bus line in order to reduce production loss and in order to improve yield and product quality. 
     Other objects of the present invention will become apparent in the entire disclosure. 
     According to one aspect of the present invention there is provided a thin-film transistor array comprising a matrix array of thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent glass substrate, and pixel electrodes disposed on the passivation film and which are electrically connected with the source electrode via an opening portion of the passivation film, and a storage capacitance electrode provided on the same layer as the gate electrode opposing each pixel electrode. The improvement resides in that an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the passivation film in at least a partial area. 
     The present invention provides a second aspect of thin-film transistor array comprising a matrix array of thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent glass substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source elect rode via an opening port ion in the passivation film, and a storage capacitance provided between each pixel electrode and the gate bus line of the previous stage. The improvement resides in that an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the passivation film in at least a partial area. 
     The present invention provides a third aspect of thin-film transistor array in which an insulating film for the pixel electrode is formed only by the passivation film in a slit area extending along the side of the pixel electrode. 
     The present invention provides a fourth aspect of thin-film transistor array comprising a matrix array of: thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source elect rode and a passivation film on a transparent glass substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source elect rode via an opening portion of the passivation film, and a storage capacitance electrode provided on the same layer as the gate electrode for opposing each pixel electrode. The improvement resides in that an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the gate insulating film in at least a partial area. 
     The present invention provides a fifth aspect of thin-film transistor array comprising a matrix array of thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent glass substrate; and pixel electrodes arranged on the passivation film and electrically connected with the source elect rode via an opening port ion in the passivation film, and a storage capacitance provided between each pixel electrode and the gate bus line of the previous stage. The improvement resides in that an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the gate insulating film in at least a partial area. 
     The present invention provides a sixth aspect of the thin-film transistor array according to the fourth and fifth aspects in which the insulating film for the pixel electrode is formed only by the gate insulating film in a slit area extending along the side of the pixel electrode. 
     Also, for accomplishing the above object, the present invention provides, as a seventh aspect, a first method for manufacturing a thin-film transistor array comprising: patterning a gate electrode and a storage capacitance electrode on a transparent glass substrate, sequentially forming a gate insulating film, a channel layer formed of an amorphous silicon of an intrinsic semiconductor and a contact layer of amorphous silicon of a n-type semiconductor. The method further comprises: patterning the amorphous silicon layer to the shape of an island, forming in the gate insulating film a through-hole serving for interconnecting a metal film forming the gate electrode and a metal film forming a drain electrode, a source electrode and a video signal line, and forming the drain electrode and the source electrode. The method further comprises: providing a passivation film and forming in the passivation film a through-hole for interconnecting the pixel electrode and the source electrode, and forming thereon the pixel electrode so as to interconnect to the source electrode. 
     In this method, the gate insulating film of at least a partial area of the insulating film for the pixel electrode, interposed between the pixel electrode of each pixel and the glass substrate and made up of the gate insulating film and the passivation film, is removed by the same patterning process as the patterning process used for forming the through-hole serving for interconnecting the metal film forming the gate electrode and the metal film forming the drain electrode, source electrode and the video signal line. 
     As a eight aspect, the present invention also provides a second method for manufacturing a thin-film transistor array comprising: patterning a gate electrode and a storage capacitance electrode on a transparent glass substrate, and sequentially forming a gate insulating film, a channel layer formed of an amorphous silicon of an intrinsic semiconductor and a contact layer of amorphous silicon of a n-type semiconductor. The method further comprises: patterning the amorphous silicon layer to the shape of an island, forming in the gate insulating film a through-hole serving for interconnecting a metal film forming the gate electrode and a metal film forming a drain electrode, a source electrode and a video signal line, and forming the drain electrode and the source electrode. The method further comprises providing a passivation film and forming in the passivation film a through-hole for interconnecting the pixel electrode, and the source electrode and forming thereon the pixel electrode so as to interconnect to the source electrode. 
     In this method, the passivation film of at least a partial area of the insulating film for the pixel electrode, interposed between the pixel electrode of each pixel and the glass substrate and which is made up of the gate insulating film and the passivation film, is removed by the same patterning process as the patterning process used for forming a through-hole adapted for interconnecting the pixel electrode and the source electrode. 
     According to the present invention, residual a-Si overlapped between the drain bus line or the gate bus line and the pixel electrode can be removed simultaneously by etching off the gate insulating film which is interposed between the transparent glass substrate and the pixel electrode, thus suppressing the reject ratio of point defects to improve the product yield. The gate insulating film has conventionally served as an insulating film for the pixel electrode. 
     According to further aspects of the present invention, the capacitive interconnection between the pixel electrodes and neighboring bus lines (e.g., gate bus lines and/or drain bus lines) by providing a boundary separating layer portion and/or slit portion which interrupts or breaks the capacitive coupling which might result from defective patterning, e.g., residual a-Si layer left at the boundary area between the pixel electrodes and neighboring bus lines. The slit portion may be filled with an insulating layer material, e.g., a passivation film or a gate insulating layer material. 
     In a ninth aspect there is provided a display device having gate bus lines, drain bus lines, and a thin-film transistor array disposed on a transparent substrate, the thin-film transistor array comprising a matrix array of: thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a drain electrode, a source electrode and a passivation film on the substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source electrode, with a storage capacitance elect rode being provided the substrate opposing each pixel electrode, wherein an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the substrate, is formed only by the passivation film in at least a partial area neighboring the gate bus lines and/or drain bus lines. 
     In a tenth aspect, there is provided a display device having gate bus lines, drain bus lines and a thin-film transistor array disposed on a transparent substrate, the thin-film transistor array comprising a matrix array of: thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a drain electrode, a source electrode and a passivation film on the substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source electrode, with a storage capacitance being provided between each pixel electrode and the gate bus line of the previous stage, wherein an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the passivation film in at least a partial area neighboring the gate bus lines and/or drain bus lines. 
     In an eleventh aspect, there is provided a display device having gate bus lines, drain bus lines and a thin-film transistor array disposed on a transparent substrate, the thin-film transistor array comprising a matrix array of: thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source electrode via an opening portion of the passivation film, with a storage capacitance elect rode being provided on the same layer as the gate electrode opposing each pixel electrode, wherein an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the substrate, is formed only by the gate insulating film in at least a partial area neighboring the gate bus lines and/or drain bus lines. 
     In a twelfth aspect, there is provided a display device having gate bus lines, drain bus lines and a thin-film transistor array disposed on a transparent substrate, the thin-film transistor array comprising a matrix array of: thin-film transistors, each made up of a gate electrode, a gate insulating film, a channel layer, a drain electrode, a source electrode and a passivation film on the substrate, and pixel electrodes disposed on the passivation film and electrically connected with the source electrode, with a storage capacitance being provided between each pixel electrode and the gate bus line of the previous stage, wherein an insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the substrate, is formed only by the gate insulating film in at least a partial area neighboring the gate bus lines and/or drain bus lines. 
    
    
     BRIEF DESCRIPTION F THE DRAWINGS 
     FIG. 1 is a plan view of a thin-film transistor array according to a first embodiment of the present invention. 
     FIG. 2 is a cross-sectional view taken along line A-A′ of FIG.  1 . 
     FIG. 3 is a cross-sectional view showing the manufacturing process of a thin-film transistor array according to the first embodiment of the present invention. 
     FIG. 4 is a plan view showing a thin-film transistor array according to the first embodiment of the present invention and particularly showing the state of occurrence of residual a-Si. 
     FIG. 5 is a cross-sectional view taken along line B-B′ of FIG.  4 . 
     FIG. 6 is a plan view of a thin-film transistor array according to a second embodiment of the present invention. 
     FIG. 7 is a cross-sectional view taken along line C-C′ of FIG.  6 . 
     FIG. 8 is a plan view of a thin-film transistor array according to a third embodiment of the present invention. 
     FIG. 9 is a cross-sectional view taken along line D-D′ of FIGS. 8 and 22. 
     FIG. 10 is a plan view showing a third embodiment of the present invention and particularly showing the state of occurrence of residual a-Si. 
     FIG. 11 is a cross-sectional view taken along line E-E′ of FIG.  10 . 
     FIG. 12 is a plan view of a thin-film transistor array according to a fourth embodiment of the present invention. 
     FIG. 13 is a cross-sectional view taken along line F-F′ of FIG.  12 . 
     FIG. 14 is a cross-sectional view showing the manufacturing process for the thin-film transistor array according to the fourth embodiment of the present invention. 
     FIG. 15 is a plan view showing a pixel of an active matrix type liquid crystal display device according to a conventional technique (first conventional technique). 
     FIG. 16 is a cross-sectional view taken along line G-G′ of FIG.  15 . 
     FIG. 17 is a cross-sectional view showing the manufacturing process for the first conventional technique. 
     FIG. 18 is a plan view showing a pixel of an active matrix type liquid crystal display device according to another conventional technique (second conventional technique). 
     FIG. 19 illustrates a structure of JP Patent Kokai JP-A-7-325314. 
     FIG. 20 is a plan view showing a pixel of an active matrix type liquid crystal display device according to still another conventional technique (third conventional technique). 
     FIG. 21 is a cross-sectional view taken along line H-H′ of FIG.  20 . 
     FIG. 22 is a cross-sectional view showing the manufacturing process for the third conventional technique. 
     FIG. 23 is a plan view showing a pixel of an active matrix type liquid crystal display device according to yet another conventional technique (fourth conventional technique). 
     FIG. 24 is a plan view of the fourth conventional technique showing the state in which residual a-Si has been produced. 
     FIG. 25 is a cross-sectional view taken along line I-I′ of FIG.  24 . 
     FIG. 26 illustrates the principle of generation of semi-bright spots by residual a-Si. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Preferred embodiments of the present invention are hereinafter explained. 
     In its preferred form, a first thin-film transistor array of the present invention includes a matrix array of inverted staggered a-Si thin-film transistors, constituted by a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent glass substrate, and pixel electrodes arranged on the passivation film and electrically connected with the source electrode via an opening portion of the passivation film. A storage capacitance electrode is provided on the same layer as the gate electrode for facing each pixel electrode. An insulating film for the pixel electrode, which is comprised of the gate insulating film ( 114  of FIG. 2) and the passivation film ( 115  of FIG. 2) and which is interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the passivation film ( 115  of FIG. 2) in at least a part of the entire area. 
     In its preferred form, a first thin-film transistor array of the present invention includes a matrix array of thin-film transistors, constituted by a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source elect rode and a passivation film on a transparent glass substrate, and pixel electrodes arranged on the passivation film and which are electrically connected with the source electrode via an opening portion in the passivation film. A storage capacitance electrode is provided between each pixel electrode ( 106  of FIG.  6 ). and the gate bus line of the previous stage ( 111  of FIG.  6 ). An insulating film for the pixel electrode, which is comprised of the gate insulating film and the passivation film and which is interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the passivation film in at least a part of the entire area (see FIG.  7 ). 
     In its preferred from, a third thin-film transistor array of the present invention is an embodiment of the first and second thin-film transistor arrays in which the insulating film for the pixel electrode is formed only by the passivation film in a slit area ( 117  in FIG. 8) extending along a side of the pixel electrode neighboring the drain bus line. 
     In its preferred form, a fourth thin-film transistor array of the present invention includes a matrix array of thin-film transistors, constituted by a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain elect rode, a source electrode and a passivation film on a transparent glass substrate, and pixel electrodes, arranged on the passivation film and electrically connected with the source elect rode via an opening portion in the passivation film. A storage capacitance electrode is provided on the same layer as the gate electrode for facing each pixel electrode. An insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, is formed only by the gate insulation film in at least a partial area (see FIG.  13 ). 
     In its preferred form, a fifth thin-film transistor array of the present invention includes a matrix array of thin-film transistors, constituted by a gate electrode, a gate insulating film, a channel layer, a contact layer, a drain electrode, a source electrode and a passivation film on a transparent glass substrate, and pixel electrodes arranged on the passivation film and which are electrically connected with the source electrode via an opening portion of the passivation film. A storage capacitance electrode is provided between each pixel electrode and the gate bus line of the former stage. An insulating film for the pixel electrode, comprised of the gate insulating film and the passivation film and interposed between the pixel electrode of each pixel and the glass substrate, may be formed only by the gate insulation film in at least a partial area. 
     In its preferred from, a sixth thin-film transistor array of the present invention is an embodiment in the fourth and fifth thin-film transistor arrays in which the insulating film for the pixel electrode is formed only by the gate insulation film in a slit area extending along a side of the pixel electrode neighboring the drain bus line. 
     A first manufacturing method according to the present invention comprises the steps of: 
     (a) patterning a gate electrode and a storage capacitance electrode on a transparent glass substrate (see FIG. 3 a ); 
     (b) sequentially forming a gate insulating film, a channel layer formed of an amorphous silicon of intrinsic semiconductor and a contact layer of amorphous silicon of n-type semiconductor and patterning the amorphous silicon layer to the shape of an island (see FIG. 3 b ); 
     (c) forming in the gate insulating film a through-hole serving for interconnecting a metal film forming the gate electrode and a metal film forming a drain electrode, a source electrode and a video signal line (see FIG. 3 c ); 
     (d) forming a drain electrode and a source electrode (see FIG. 3 d ); 
     (e) providing a passivation film and forming in the passivation film a through-hole for interconnecting the pixel electrode and the source electrode (see FIG. 3 e ); and 
     (f) forming thereon a pixel electrode for interconnection to the source electrode (see FIG. 3 f ); 
     In above steps, the gate insulating film of at least a partial area of the insulating film for the pixel electrode which is interposed between the pixel electrode of each pixel and the glass substrate and which is made up of the gate insulating film and the passivation film, is removed by the same patterning process as the patterning process for forming the through-hole used for interconnecting the metal film forming the gate electrode and the metal film forming the drain electrode, source electrode and the video signal line. 
     A second manufacturing method according to the present invention includes the steps of: 
     (a) patterning a gate electrode and a storage capacitance electrode on a transparent glass substrate (see FIG. 14 a ); 
     (b) sequentially forming a gate insulating film, a channel layer formed of an amorphous silicon of intrinsic semiconductor and a contact layer of amorphous silicon of n-type semiconductor and patterning the amorphous silicon layer to the shape of an island (see FIG. 14 b ); 
     (c) forming in the gate insulating film a through-hole serving for interconnecting a metal film forming the gate electrode and a metal film forming a drain electrode, a source electrode and a video signal line and subsequently forming the drain electrode and the source electrode (see FIG. 14 c ); 
     (d) forming a passivation film (see FIG. 14 d ); 
     (e) forming in the passivation film a through-hole for interconnecting a pixel elect rode and the source electrode (see FIG. 14 e ); and 
     (f) forming thereon a pixel electrode for interconnection to the source electrode (see FIG. 14 f ); 
     In the above steps, the passivation film of at least a partial area of the insulating film for the pixel electrode, which is interposed between the pixel electrode of each pixel and the glass substrate and which is made up of the gate insulating film and the passivation film, is removed by the same patterning process as the patterning process used for forming the through-hole serving for interconnecting the pixel electrode and the source electrode. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, preferred embodiments of the present invention will be explained in detail. 
     Embodiment 1 
     FIGS. 1 and 2 show a plan view illustrating a first embodiment of a thin-film transistor array of the present invention and a cross-sectional view taken along line A-A′ of FIG. 1, respectively. 
     Referring to FIGS. 1 and 2, the structure of the first embodiment of the present invention is explained. 
     In the first embodiment of the present invention, there exist two layers, namely a gate insulating film  114  and a passivation film  115  as upper layers of the gate electrode  101  and the gate bus line  111 . However, the insulating film for the pixel electrode disposed below the pixel electrode  106  is made up only of the passivation film  115 . Namely  117  termed as “removing pattern” designates an area where the gate insulating film  114  has been removed. 
     The passivation film  115 , as an insulating film, is interposed between a drain bus line  112  and the pixel electrode  106 . Namely, the drain bus line  112  is disposed below the passivation film  115 , whereas the pixel electrode  106  is above the passivation film. 
     FIG. 3 shows a cross-sectional view for illustrating, step-by-step, the manufacturing process for manufacturing a thin-film transistor array of a first embodiment of the present invention. Referring to FIG. 3, the manufacturing method for the first embodiment of the present invention is explained. 
     The gate bus line  111  formed by a metal film of metals, such as Cr or Al, and the gate electrode  101 , are patterned on a glass substrate  100 , at the same time as a storage capacitance electrode  108  is formed thereon by the same patterning process (see FIG. 3 a ). 
     After sequentially forming the gate insulating film  114 , channel layer  102  formed of a-Si(I) and a contact layer  107  formed of a-Si(n + ), the semiconductor layer is etched (see FIG. 3 b ) for removing the gate insulating film  114  of the contact area interconnecting the gate layer and the drain layer for forming a through-hole (not shown) used for interconnecting a metal film forming the gate bus line  101  and a metal film forming the drain electrode  103 , source electrode  104  and the drain bus line  112  by way of patterning. During this patterning process, the gate insulating film  114  of an area  117  lying below the pixel electrode of each unit pixel is simultaneously removed so as not to stride on the gate bus line  101  and the storage capacitance electrode  108  (see FIG. 3 c ). 
     In the above process, if there is any residual pattern of the gate metal, this residual metal pattern can be removed by immersion in the etching solution of the gate metal after etching the gate insulating film  114 . This simultaneously prevents increase in the parasitic capacitance or shorting. 
     Then, similarly to the gate bus line  101 , the drain electrode  103  formed by a metal film, such as Cr or Al film, source electrode  104  and the drain bus line  112  are formed (see FIG. 3 d ). 
     The passivation film  115  then is formed and a through-hole  110  for interconnecting the source electrode  104  and the pixel electrode  106  is formed (see FIG. 3 e ). 
     The pixel electrode  106  is formed for interconnection to the source elect rode  104  to give a TFT array substrate (see FIG. 3 f ). 
     As for a counter-substrate, a black matrix layer, not shown, formed by a metal film, such as a Cr film, is provided on a glass substrate, not shown, and a counter-electrode, not shown, is formed thereon. 
     Finally, an orientation film (not shown) is formed on each of the TFT array substrate and the counter-substrate and subjected to orientation processing. After forming a seal pattern, the two substrates are stacked and fired. The liquid crystal is then injected and sealed to complete a liquid crystal display panel. 
     By way of illustrating the operation and effect of the first embodiment of the present invention, FIGS. 4 and 5 show a plan view illustrating residual-Si produced on a pixel and a cross-sectional view taken along line B-B′ of FIG.  4 . 
     In the first embodiment of the present invention, the gate insulating film  114  of the area  117  lying below the pixel electrode can be removed by the contact step and simultaneously removing residual a-Si  116  produced by defective patterning during the island process as shown in the plan view of FIG.  4  and in the cross-sectional view of FIG.  5 . Thus, as shown in FIG. 5, the passivation film  115  extends at the end of the pixel electrode  106  from its lower side to the upper side to form a boundary layer, and further extends to the upper side of the drain bus line  112 . 
     This reduces occurrence of point defects of semi-bright spots caused by interconnection of the pixel electrode  106  to the drain bus line  112  and the resultantly increased parasitic capacitance between the drain bus line and the pixel electrode  106  to suppress the reject ratio as well as to increase production yield. 
     Also, in the first embodiment of the present invention, since the gate insulating film  114  of the area  117  lying below the pixel electrode is etched off using the patterning step which is the same as that used for producing the through-hole serving for interconnecting the metal film forming the gate bus line  101  and the metal film forming the source electrode  104  and the drain bus line  112 , the number of the patterning steps is the same as that of the conventional manufacturing method, thus avoiding complication of the manufacturing process. 
     Also, in the first embodiment of the present invention, a thin residual layer  116 , if any, of the gate metal resulting from patterning can be removed to a certain extent by immersion of the gate metal etching liquid after etching the gate insulating film for a short time such as not to cause significant etching of the lower layer of the gate interconnection. 
     Moreover, since there is insulating the passivation film  115  as a boundary separating film between the drain bus line  112  and the pixel electrode  106 , the structure for reducing the occurrences of the point defects, such as bright or dark spots, ascribable to shorting between the drain bus line  112  and the pixel electrode  106 , is realized. In addition, since the drain bus line  112  and the pixel electrode  106  are formed in separate layers, the pixel electrode  106  can be increased in area, thus simultaneously increasing the opening ratio. 
     FIG. 6 shows a plan view illustrating the structure of the second embodiment of the thin-film transistor array of the present invention and FIG. 7 is a cross-sectional view taken along line C-C′ of FIG.  6 . 
     Referring to FIGS. 6 and 7, the structure and the manufacturing method of the second embodiment of the present invention are explained. 
     The second embodiment of the present invention is characterized in that the storage capacitance electrode  108  is used simultaneously as the gate bus line  101  and is otherwise the same as the above-described first embodiment. 
     In the second embodiment of the present invention, the insulating film for the pixel electrode, extending over a partial area  117  lying below the pixel electrode  106 , is constituted solely by the passivation film  115 , as in the first embodiment, so that residual a-Si produced due to patterning defects during the island forming step can be removed simultaneously. This reduces occurrences of defects of semi-bright spots, otherwise caused by increased parasitic capacitance between the drain bus line  112  and the pixel electrode  106  on interconnection to the drain bus line  112  to suppress the reject ratio to improve the production yield. 
     Moreover, since there is the insulating passivation film  115  as a boundary separating film between the drain bus line  112  and the end of the pixel electrode  106 , as in the above-described first embodiment, the structure for reducing the occurrences of the point defects, such as bright or dark spots, ascribable to shorting between the drain bus line  112  and the pixel electrode  106 , is realized. Also, the storage capacitance electrode  108  serves simultaneously as the gate bus line  101 , the area of the metal film of the storage capacitance electrode can be suppressed to a minimum value. 
     In addition, since the drain bus line  112  and the pixel electrode  106  are formed in separate layers, the pixel electrode  106  can be increased in area, thus simultaneously increasing the opening ratio. 
     FIG. 8 shows a plan view illustrating the structure of a third embodiment of the thin-film transistor array of the present invention and FIG. 9 is a cross-sectional view taken along line D-D′ of FIG.  8 . 
     Referring to FIGS. 8 and 9, the structure and the manufacturing method of the third embodiment of the present invention are explained. 
     The third embodiment of the present invention is characterized in that, in removing the gate insulating film  114  lying below the pixel electrode of each unit pixel, there is formed a removing pattern  117  in the form of a slot a few micrometers in width along the drain bus line  112  and is otherwise the same as the above-described first embodiment. 
     For illustrating the operation and result of the third embodiment of the present invention, FIG. 10 shows a plan view illustrating the state of residual a-Si produced on a pixel. FIG. 11 shows a cross-sectional view taken along line E-E′ of FIG.  10 . 
     With the third embodiment of the present invention, the gate insulating film  114  of a partial area  117  lying below the pixel electrode is removed in the contact step in the form of slits several micrometers in width along the drain bus line  112  for simultaneously removing residual a-Si  116  produced due to patterning defects during the island step. This reduces occurrences of point defects of semi-bright spots otherwise produced by increased parasitic capacitances between the drain bus line  112  and the pixel electrode  106  by interconnection to the drain bus line  112  to suppress the reject ratio to improve the product yield. 
     In the third embodiment, since the residual a-Si removing pattern is slit-shaped, there is no necessity for the pixel electrode to stride over the step at the TFT pixel electrode leadout portion as in the first and second embodiments thus suppressing disconnection failure of the pixel electrode. 
     In the third embodiment, the residual a-Si removing pattern is formed as slit along the drain bus line  112 . However, a similar slit may be formed along the gate bus line  111  simultaneously with the drain bus line  112  for encircling the pixel electrode. 
     In the third embodiment of the present invention, the storage capacitance electrode is used simultaneously as the gate electrode. However, the third embodiment may be configured for application to an independent type. 
     If the storage capacitance electrode is used simultaneously as the gate electrode  101 , the area of the metal film of the storage capacitance electrode can be suppressed to the smallest value possible. In addition, since the drain bus line  112  and the pixel electrode  106  are formed in separate layers, the pixel electrode  106  can be increased in area, thus simultaneously increasing the opening ratio. 
     Embodiment 4 
     FIG. 12 shows a plan view illustrating the structure of a fourth embodiment of the thin-film transistor array of the present invention and FIG. 13 is a cross-sectional view taken along line F-F′ of FIG.  12 . 
     Referring to FIGS. 12 and 13, the structure of the fourth embodiment of the present invention are explained. 
     The fourth embodiment of the present invention is characterized in that, although two layers of the gate insulating film  114  and the passivation film  115  are present as upper layers for the gate bus line  111  and the gate bus lime  111 , an insulating film lying in an area of “removing pattern”  118  lying below the pixel electrode  106  is constituted solely by the gate insulating film  114 . 
     FIG. 14 shows a cross-sectional view for illustrating, step-by-step, the manufacturing process for manufacturing a thin-film transistor array of a fourth embodiment of the present invention shown in FIG.  13 . Referring to FIG. 14, the manufacturing method for the fourth embodiment of the present invention is explained. 
     The gate bus line  111  formed by a metal film of metals, such as Cr or Al, and the gate electrode  101 , are patterned on a glass substrate  100 , at the same time as a storage capacitance electrode  108  is formed by the same patterning process (see FIG. 14 a ). 
     After sequentially forming the gate insulating film  114 , channel layer  102  formed of a-Si(I) and a contact layer  107  formed of a-Si(n + ), the semiconductor layer is etched (see FIG. 14 b ) for removing the gate insulating film  114  of the contact area interconnecting the gate layer and the drain layer (not shown). 
     As the gate electrode  101 , the drain electrode  103 , source electrode  104  and the drain bus line  112 , formed by layers of metals, such as Cr or Al, are formed (see FIG. 14 c ) 
     The passivation film  115  is then formed and, in the patterning step of forming the through-hole  110  used for interconnecting the source electrode  104  and the pixel electrode  106 , only the passivation film of an area  118  lying below the pixel electrode of each unit device is simultaneously removed, at the same time as the etching rate is adjusted, so that the gate electrode  101  or the storage capacitance electrode  108  will remain unaffected (see FIGS. 14 d  and  14   e ). 
     The pixel electrode  106  is formed for interconnection to the source electrode  104  to complete a TFT array substrate (see FIG. 14 f ). The structure and the manufacturing method are otherwise the same as those of the above-described first embodiment. 
     In the fourth embodiment of the present invention, since the insulating film for the pixel electrode below the pixel electrode  106  is constituted solely by the gate insulating film  114 , it becomes possible to remove residual a-Si produced due to patterning defects during the island-forming step. This reduces occurrences of point defects of semi-bright spots caused due to the increased parasitic capacitances between the drain bus line  112  and the pixel electrode  106  on interconnection to the drain bus line  112  to suppress the reject ratio to improve the product yield. 
     In the fourth embodiment of the present invention, a thin residual patterning layer, if any, of the drain metal can be removed to a certain extent by immersion of the gate metal etching liquid after etching the passivation film for a short time such as not to cause significant etching of the drain layer. 
     Also, in the fourth embodiment of the present invention, only the passivation film of the area  118  lying below the pixel electrode is etched off by the same patterning step as that used for providing the through-hole  110  serving for interconnecting the source electrode  104  with the pixel electrode  106 . Thus, the number of the patterning steps remains the same as that of the conventional process thus evading complication of the manufacturing process. 
     Moreover, since there exists the insulating passivation film  115 , as a boundary separating film, between the drain bus line  112  and the pixel electrode  106 , as in the first embodiment, the structure of reducing occurrences of point defects of bright and dark spots otherwise caused due to shorting between the drain bus line  112  and the pixel electrode  106  is achieved. 
     Meanwhile, the fourth embodiment of the present invention is applied to an independent type storage capacitance electrode system. However, the present invention can, of course, be applied to the storage capacitance electrode type in which the storage capacitance electrode is used simultaneously as the gate electrode. In this case, the area of the metal film of the storage capacitance electrode can be suppressed to the smallest value possible. Since the drain bus line  112  and the pixel electrode  106  are formed in separate layers and hence the pixel electrode  106  can be increased in area, the opening ratio can be increased simultaneously. 
     The present invention is not limited to the above-described embodiments which are given only by way of illustration. For example, the gate electrode, storage capacitance electrode or the source or drain electrodes can be formed by other metal materials or composite films. The gate insulating films or the passivation film may be formed by a variety of insulating films or compound films. 
     Effects of the Invention are summarized as follows, but not limiting thereto. 
     According to the present invention, as described above, the following meritorious effects may be achieved: 
     (1) According to the present invention, since the gate insulating lying below the pixel electrode in roughly its entirety or a slit-like area thereof extending along the drain bus line is removed simultaneously during the step of etching the contact hole, it becomes possible to remove the residual a-Si produced due to patterning defects during the island-forming step. Thus, with the present invention, the point defects of semi-bright spots, otherwise produced by interconnection to the drain bus line and resulting capacitative coupling to the pixel electrode, can be suppressed, thereby reducing the reject ratio to improve product yield. 
     (2) Also, according to the methods of the present invention, since the entire gate insulating film below the gate electrode of the gate insulating film or a slit-like area of the gate insulating film along the drain bus line is etched off by the same patterning step as that used for providing the through-hole serving for interconnecting the metal film forming the gate electrode and the metal film forming the drain and source electrodes and the drain bus line, the number of the patterning steps is the same as that required in the conventional process, thus evading complication of the manufacturing process. 
     (3) Moreover, according to the present invention, since there is the passivation film as an insulating/boundary separating film extending between the drain bus line and the pixel electrode, such a structure is obtained in which point defects such as bright and dark spots ascribable to the shorting between the drain bus line and the pixel elect rode can be reduced. Further, since the drain bus line and the pixel electrode are provided in different layers, the pixel electrodes can be increased in area thus simultaneously increasing the opening area. 
     Various aspects, embodiments and any features or elements thereof may be combined together according to the gist of the present invention. Also it should be noted any modifications may be introduced within the gist and scope of the present invention herein disclosed and claimed as appended.