Abstract:
A liquid crystal display apparatus comprises: a substrate; gate wires and source wires formed in a matrix fashion on the substrate; gate electrodes formed close to points of intersection between the gate wires and the source wires, the gate electrodes being connected electrically to the gate wires; a first insulating film formed on the gate wires and the gate electrodes, the first insulating film further carrying the source wires thereon; a semiconductor active film formed over the gate electrodes with the first insulating film interposed therebetween; source electrodes formed on the semiconductor active film and connected to the source wires; drain electrodes formed on the semiconductor active film and isolated from the source electrodes; an electrode film intended to generate capacity and formed on the first insulating film, the electrode film being close to and in parallel with at least the source wires; a second insulating film formed on the first insulating film which carries the electrode film, the source wires, the source electrodes, the drain electrodes and the semiconductor active film thereon; and pixel electrodes connected to the drain electrodes and formed on the second insulating film in order to generate capacity in cooperation with the electrode film.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display apparatus comprising thin film transistors. More particularly, the invention relates to a liquid crystal display apparatus having a structure with electrodes which are faced with pixel electrodes and which generate cumulative capacity. 
     2. Description of the Related Art 
     FIGS. 10 and 11 show a typical constitution of a thin film transistor array substrate used by a conventional thin film transistor liquid crystal display apparatus. The substrate carries on its surface gate wires G and source wires S. 
     The thin film transistor array substrate of FIGS. 10 and 11 is a transparent substrate  13  illustratively made of glass having gate wires G and source wires S deposited thereon in matrix fashion. Each of the areas surrounded by the gate wires C and source wires S serves as one pixel  1 . Each pixel is furnished with a thin film transistor T 100 . 
     The thin film transistors T 100  shown in FIGS. 10 and 11 are of common, inversely staggered type. Each gate wire G and a gate electrode  2  forming part of the gate wire G in question are covered with a gate insulating film  3 . On the gate insulating film  3  over the gate electrode  2  is a semiconductor active film  4  which is made of amorphous silicon (a-Si) and which faces the gate electrode  2 . A drain electrode  6  and a source electrode  7 , both made of a conductive material, are positioned face to face on two edges of the semiconductor active film  4 . The upper portions of the two edges of the active film  4  are covered with ohmic contact films  8 ,  8  formed illustratively of amorphous silicon doped with impurities (i.e., donors) such as phosphorus of a high density. 
     A passivation film  10  made of an insulating film is deposited over the gate insulating film  3 , source electrodes  6  and drain electrodes  7 . On the passivation film  10  are pixel electrodes  11  which, constituted by a transparent conductive material such as ITO (indium tin oxide), cover almost all pixels  1  ranging from top to side of the drain electrodes  6 . The pixel electrodes  11  and the passivation film  10  are covered with an oriented film, not shown. Above the oriented film are liquid crystal and an opposite substrate having common electrodes. The whole structure constitutes an active matrix liquid crystal display apparatus. When a transparent pixel electrode  11  applies an electric field to liquid crystal molecules, the orientation of the molecules is controlled as desired. 
     In the liquid crystal display apparatus having the constitution of FIGS. 10 and 11, auxiliary electrodes  12  formed simultaneously with the gate electrodes  2  on the substrate  13  are installed opposite to the pixel electrodes  11 . As illustrated in FIG. 11, the auxiliary electrodes  12  are furnished so as to surround the contour of each pixel  1  corresponding to the circumference of each pixel electrode  11 . Each pixel electrode  11  and its corresponding auxiliary electrode  12  sandwich the passivation film  10  to constitute a capacitor providing a cumulative capacity that is used to inhibit the adverse effects of a parasitic capacity generated naturally upon liquid crystal activation. 
     In the liquid crystal display apparatus of the above constitution, the transparent substrate  13  is usually backlighted. The backlight is shielded by, or allowed to transmit, the orientation-controlled liquid crystal to let the user recognize the contrast on display. 
     In the constitution shown in FIGS. 10 and 11, each pixel electrode  11  and its corresponding auxiliary electrode  12  sandwich the gate insulating film  3  and passivation film  10  to form the cumulative capacity. While advantageous in driving the liquid crystal, the above constitution is known to have the following major deficiencies: 
     The gate insulating film  3  is interposed between the gate electrodes  2  and the semiconductor active film  4  for insulation purposes. To attain the good insulating property of the gate insulating film  3  requires strictly managing conditions for forming the film. On the other hand, the passivation film  10  is generally formed under less severe conditions than the gate insulating film  3  because the quality demanded of the passivation film is not so high. 
     In the conventional structure of FIGS. 10 and 11 where each pixel electrode  11  and its corresponding auxiliary electrode  12  sandwich the gate insulating film  3  and passivation film  10  to form cumulative capacity, two insulating films constitute the cumulative capacity. This makes it difficult to secure appreciable quantities of cumulative capacity. It is also difficult to control the cumulative capacity level to a desired value. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a liquid crystal display apparatus for allowing its cumulative capacity to be set more easily than before to ensure signal stabilization and numerical aperture improvement, the apparatus being fabricated with a fewer number of masks in a more simplified fabrication setup than before. 
     In carrying out the invention and according to one aspect thereof, there is provided a liquid crystal display apparatus comprising: a substrate; gate wires and source wires formed in a matrix fashion on the substrate; gate electrodes formed close to points of intersection between the gate wires and the source wires, the gate electrodes being connected electrically to the gate wires; a first insulating film formed on the gate wires and the gate electrodes, the first insulating film further carrying the source wires thereon; a semiconductor active film formed over the gate electrodes with the first insulating film interposed therebetween; source electrodes formed on the semiconductor active film and connected to the source wires; drain electrodes formed on the semiconductor active film and isolated from the source electrodes; an electrode film intended to generate capacity and formed on the first insulating film, the electrode film being close to and in parallel with at least the source wires; a second insulating film formed on the first insulating film which carries the electrode film, the source wires, the source electrodes, the drain electrodes and the semiconductor active film thereon; and pixel electrodes connected to the drain electrodes and formed on the second insulating film in order to generate capacity in cooperation with the electrode film. 
     With the above structure, the cumulative capacity is formed not by a plurality of insulating films as is the case with conventional structures but by a single insulating film. This means that the inventive structure using a single film may have a reduced facing electrode area to provide the same cumulative capacity as that of the conventional structure utilizing a plurality of insulating films. Hence an improved numeral aperture for the liquid crystal display apparatus of the invention can be obtained. 
     In the above liquid crystal display apparatus, the single-film structure, if arranged to have the same facing electrode area as that of the conventional multiple-film structure, offers a greater cumulative capacity than the latter. The cumulative capacity thus enhanced ensures better signal stabilization. 
     In the inventive structure above, cumulative capacity is formed by the electrode film and pixel electrodes sandwiching the second insulating film which acts as a dielectric film. Because there is only one dielectric film for generating cumulative capacity, the inventive liquid crystal display apparatus may set the cumulative capacity level more accurately than the conventional structure that has a plurality of insulating films. 
     Furthermore, where the second insulating film is sandwiched by the edges of each pixel electrode and by the electrode film in the inventive structure, lines of electric force generated by the edge portion of the pixel electrode are different from those created in the middle portion of the pixel electrode. This permits slightly different states of liquid crystal orientation to occur reflecting the different lines of electric force on the fringe side and in the middle of each pixel electrode. In other words, the liquid crystal display apparatus has two different states of liquid crystal orientation in two domains: on the fringe, and in the middle of each pixel electrode, along the different lines of electric force generated thereby. Such a multi-domain display structure, with its differently oriented states of liquid crystal, helps ease the problem of the narrow angle of visibility characteristic of conventional liquid crystal displays. 
     In one preferred structure according to the invention, the electrode film may be arranged to penetrate the first insulating film so as to be connected directly with the gate wires. This preferred structure reduces the number of masks used for fabrication by photolithography, whereby the yield of the apparatus is improved. 
     In another preferred structure according to the invention, connecting paths may be formed simultaneously with the pixel electrodes in order to connect the electrode film electrically with the gate wires. This structure is characterized by its connecting paths connecting electrically the electrode film with the gate wires, the paths being formed at the same time as the pixel electrodes. 
     According to another aspect of the invention, there is provided a liquid crystal display apparatus comprising: a substrate; a plurality of source wires formed in parallel with one another on the substrate; source electrodes connected to the source wires and formed on the substrate; drain electrodes isolated from the source electrodes and formed on the substrate; a semiconductor active film for connecting the source electrodes with the drain electrodes; a first insulating film formed over the substrate which carries the source wires, the source electrodes, the drain electrodes and the semiconductor active film thereon; gate electrodes formed on the semiconductor active film with the first insulating film interposed therebetween; gate wires formed on the first insulating film to connect with the gate electrodes, the gate wires being arranged to intersect the source wires; an electrode film intended to generate capacity and formed on the first insulating film, the electrode film being close to and in parallel with at least the gate wires; a second insulating film formed on the first insulating film which carries the electrode film, the gate wires and the gate electrodes thereon; and pixel electrodes connected to the drain electrodes and formed on the second insulating film in order to generate capacity in cooperation with the electrode film. 
     In the above liquid crystal display apparatus, as is the case with the preceding apparatus of the invention, a single-film structure generates cumulative capacity. Thus the inventive structure may have a reduced facing electrode area to provide the same cumulative capacity as that of the conventional structure employing a plurality of insulating films. This provides an improved numeral aperture for the liquid crystal display apparatus. The single-film structure, when arranged to have the same facing electrode area as that of the conventional multiple-film structure, offers a greater cumulative capacity than the latter. This ensures better signal stabilization. 
     These and other objects, features and advantages of the invention will become more apparent upon a reading of the following description and appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a liquid crystal display apparatus of an inversely staggered type practiced as a first embodiment of the invention; 
     FIG. 2 is a plan view of the first embodiment; 
     FIG. 3 is a plan view of a liquid crystal display apparatus practiced as a second embodiment of the invention; 
     FIG. 4 is a plan view of a liquid crystal display apparatus practiced as a third embodiment of the invention; 
     FIG. 5 is a cross-sectional view of the third embodiment; 
     FIG. 6 is a cross-sectional view of a liquid crystal display apparatus practiced as a fourth embodiment of the invention; 
     FIG. 7 is a plan view of the fourth embodiment; 
     FIG. 8 is a cross-sectional view of a liquid crystal display apparatus of a forward staggered type practiced as another embodiment of the invention; 
     FIG. 9 is a plan view of the embodiment of FIG. 8; 
     FIG. 10 is across-sectional view of a thin film transistor array substrate included in a conventional liquid crystal display apparatus; and 
     FIG. 11 is a plan view of the thin film transistor array substrate of FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of this invention will now be described with reference to the accompanying drawings. These embodiments should not be construed as limiting the scope of the invention but as merely providing illustrations of the presently preferred embodiments of this invention. 
     FIGS. 1 and 2 show key portions of an inversely staggered type active matrix liquid crystal display apparatus  30  practiced as the first embodiment of the invention. The liquid crystal display apparatus  30  comprises a thin film transistor array substrate  31 , a transparent facing substrate  32  positioned parallel to and separate from the thin film transistor array substrate  31 , and liquid crystal  33  contained interposingly between the thin film transistor array substrate  31  and the facing substrate  32 . 
     On the thin film transistor array substrate  31 , as many source wires  35  and gate wires  36  as in the case of the conventional structure in FIGS. 10 and 11 are arranged in a matrix fashion (viewed from above) as shown in FIG.  2 . Each of the numerous areas surrounded by the source wires  35  and gate wires  36  forms a pixel part  37 . A pixel electrode  38  made of a transparent conductive material such as ITO (indium tin oxide) is formed in each of the areas representing the pixel parts  37 . In one corner of each of the pixel parts  37 , a thin film transistor T is formed so as to extend to part of an adjacent pixel part  37 . 
     FIG. 2 is a plan view showing a thin film transistor T and its surroundings corresponding to one pixel part  37  surrounded by source wires  35  and gate wires  36 . Numerous pixel parts  37  are arranged on the thin film transistor array substrate  31  to form a display screen of the liquid crystal display apparatus  30 . 
     More specifically, the thin film transistor array substrate  31  is structured as follows: numerous gate wires  36  made of a light-shielding conductive material such as Cr or Mo are formed in parallel with one another on a substrate  40 . Part of each gate wire  36  is used as a gate electrode  41 . The gate electrodes  41  and the substrate  40  are covered with a first insulating film (gate insulating film)  42 . Over the first insulating film  42  on the gate electrodes  41  is a semiconductor active film  43  deposited to face the gate electrodes  41 . On both edges of the semiconductor active film  43  are ohmic contact films  45 ,  46  which illustratively include an n+ film and which are formed apart to leave a gap in the middle portion of the semiconductor active film  43 . 
     In the structure above, one ohmic contact film  45  is positioned at one side of the gate electrode  41  and the other ohmic contact film  46  at another side of the gate electrode  41 . Thus if one ohmic contact film  45  is inside the area of one pixel part  37 , the other ohmic contact film  46  is within the area of an adjacent pixel part  37 . 
     Drain electrodes  48  made of a light-shielding conductive material such as Cr or Mo are each furnished so as to contact the ohmic contact film  45 . Source electrodes  49  also constituted by a light-shielding conductive material such as Cr or Mo are each formed to contact the ohmic contact film  46 . 
     A second insulating film (passivation film)  50  is provided to cover the thin film transistors T and the first insulating film  42 . Over the second insulating film  50  are pixel electrodes  38  covering the pixel parts  37 . The pixel electrodes  38  are connected to the drain electrodes  48  by a connecting conductive film  52  formed in conductive holes  51  made on the second insulating film  50  at edges of the drain electrodes  48  for the thin film transistors T. 
     As shown in FIG. 2, wire-like transistor-side first electrode films  53  are formed along the source wires  35  on the first insulating film  42  at the thin film transistor forming side of the source wires  35 . The transistor-side first electrode films  53  are covered with the second insulating film  50 , as depicted in FIG.  1 . 
     As illustrated in FIG. 2, the transistor-side first electrode films  53  are each constituted two by portions: a straight portion  55  extended parallel to the source wires  35  between adjacent thin film transistors T, T; and bent portion  56  continued to the straight portion  55  and bypassing each thin film transistor T. The straight portion  55  of the first electrode film  53  is located so as to face the edge of each pixel electrode  38 . The straight portion  55  is arranged so that its inner part will come slightly inside the edge of each pixel electrode  38  and that its outer part will appear slightly out of the edge of each pixel electrode  38 . The bent portion  56  is arranged likewise so that part of its inner part will be located slightly inside the edge of each pixel electrode  38  near the thin film transistor T; the bent portion  56  is also arranged so that part of its fringe part will be positioned slightly outside the edge of each pixel electrode  38 . 
     In FIG. 2, the first insulating film  42  opposite to the thin film transistor side of the source wires  35  is covered with source-side first electrode films  58  formed straight along the source wires  35 . On the first insulating film  42 , each source-side first electrode film  58  is arranged so that its inner part will come slightly inside the edge of each pixel electrode  38  and its outer part slightly outside the edge of each pixel electrode  38 . The source-side first electrode films  58  are also covered with the second insulating film  50 , as shown in FIG.  1 . 
     The first electrode films  53  . . . ,  58  . . . , are extended along the source wires  35  up to the edge of each source wire  35  on the substrate  40 . On the fringe of the substrate  40 , the first electrode films  53  . . . ,  58  . . . , are interconnected and grounded to bear ground potential. Extended up to the edge of each source wire  35 , the first insulating films  53 ,  58  are interconnected illustratively via contact holes made on the second insulating film  50 , the holes being connected through transparent conductive films used to form the pixel electrodes  38 . 
     Meanwhile, as shown in FIG. 1, the liquid crystal side of the facing substrate  32  includes a transparent substrate  61  on which a color filter  62  and a common electrode film  63  are deposited, in that order. The color filter  62  has two major components: a black matrix for shielding those thin film transistor portions, gate wire parts and source wire segments which do not contribute to display; and color pixel parts which allow the pixel parts  37  equipped with the pixel electrodes  38  to let light pass through display-contributing regions for color display. The color pixel parts are needed by liquid crystal display apparatuses of a color display structure and are attached to the pixel parts. Contiguous pixel parts need to be made different in color. Illustratively, pixels of three primary colors (red, green and blue) are laid out regularly or randomly to ensure consistent color distribution. 
     In the cross-section shown in FIG. 1, an oriented film installed on the liquid crystal side of the thin film transistor array substrate  31  and another oriented film on the liquid crystal side of the facing substrate  32  are not shown. Also omitted from the figure are polarized plates outside both the thin film transistor array substrate  31  and the facing substrate  32 . 
     Below is a description of how the liquid crystal display apparatus of the structure shown in FIGS. 1 and 2 works and what effects it provides. The display function of this structure is activated and deactivated by applying and removing a suitable voltage to and from the gap between the pixel electrodes  38  of the desired pixel parts  37  on the one hand and the common electrode film  63  of the facing substrate on the other hand. 
     The liquid crystal molecules in the areas corresponding to the pixel parts  37  that are given the voltage are controlled in orientation. Light from the backlight under the substrate  40  is introduced into the liquid crystal. The introduced light is either polarized or allowed to pass unmodified according to the oriented or nonoriented state of the liquid crystal molecules, whereby a dark state and a bright state are switched. 
     The first electrode films  53 ,  58  are faced with the edges of the pixel electrodes  38  with the second insulating film  50  interposed therebetween. This arrangement generates cumulative capacity between the components to cancel out part of the parasitic capacity created in the liquid crystal display apparatus. Partially negating the parasitic capacity helps stabilize the operation of the thin film transistors T. 
     The first electrode films  53 ,  58  face the pixel electrodes  38  with only the second insulating film  50  interposed therebetween. This single-film arrangement allows cumulative capacity to be established more accurately than the conventional structure using two insulating films of different physical properties for setting cumulative capacity. The enhanced level of accuracy in establishing cumulative capacity leads to more stable operation of the thin film transistors T. In other words, because the cumulative capacity of the first embodiment is formed not by a plurality of insulating films as is the case with conventional arrangements but by one insulating film, the inventive single-film structure may have a reduced facing electrode area (i.e., facing area formed by the edges of the pixel electrodes  38  and the first electrode films  53 ,  58 ) to provide the same cumulative capacity as that of the conventional multiple insulating film structure. This ensures an improved numeral aperture for the liquid crystal display apparatus of the invention. 
     With the first embodiment, the single-film structure, if arranged to have the same facing electrode area (i.e., facing area formed by the edges of the pixel electrodes  38  and the first electrode films  53 ,  58 ) as that of the conventional multiple insulating film structure, offers a greater cumulative capacity than the latter. The cumulative capacity increased in this manner ensures better signal stabilization. 
     The first electrode films  53 ,  58  bear ground potential. This means that an electric field generated by those edges of each pixel electrode  38  which face the grounded first electrode films  53 ,  58  differs from an electric field generated by the middle portion of the pixel electrode  38 . That is, the orientation of liquid crystal in the middle portion of each pixel electrode  38  is different from that in regions forming second electrode films  38 A,  38 B for the pixel electrode  38 . Such a multi-domain display structure helps ease the problem of the narrow angle of visibility characteristic of conventional liquid crystal displays. 
     Lines of electric force coming from the middle portion of each pixel electrode  38  are directed at the common electrode film  63  of the facing electrode  32 , whereas lines of electric force from the edges of the pixel electrode  38  in question are distorted, i.e., attracted toward the first electrode films  53 ,  58 . Because the liquid crystal molecules are torqued perpendicularly to the distorted lines of electric force, the molecules in the middle portion of each pixel electrode  38  constitute one domain while the molecules on those edges of the pixel electrode  38  which face the first electrode films  53 ,  58  make up another domain. The multi-domain structure maintains states of homogeneous liquid crystal molecule orientation. Applying a suitable voltage to the structure automatically creates a plurality of domains. As a result, each pixel part  37  may be switched automatically to have a plurality of domains comprising homogeneously oriented liquid crystal molecules having the same tilt angle. 
     The feature above invariably eases abrupt, asynchronous contrast changes of liquid crystal display elements in the vertical direction and thereby widens regions where inversion of gradation will not occur in half tone. This provides a liquid crystal display apparatus that is less restricted by the angle of visibility and offers wider angles of visibility than before. 
     FIG. 3 shows a liquid crystal display apparatus practiced as the second embodiment of the invention. What characterizes this embodiment is a ring-shaped first electrode film  70  formed on each pixel part  37  to correspond with the edges of each pixel electrode  38 ; the first electrode film  70  covers approximately the entire circumference of each pixel electrode  38 . The first electrode films  70  attached to the pixel parts  37  are interconnected by connecting conductors  71  arranged parallel to the source wires  35 . The connecting conductors  71  are extended up to the end of each source wire on the substrate. On the edge side of the substrate, the connecting conductors  71  are interconnected and grounded so that the first electrode films  70  bear ground potential. 
     The other structural details of the second embodiment are the same as those of the first embodiment shown in FIGS. 1 and 2. As such, the second embodiment offers the same effects as the first embodiment. 
     In the structure depicted in FIG. 3, lines of electric force from the pixel electrode  38  are distorted when attracted radially toward the first electrode film  70  surrounding approximately the whole circumference of the pixel electrode  38 . When the liquid crystal molecules are torqued perpendicularly to the radially distorted lines of electric force, the molecules constitute a plurality of domains while being homogeneously oriented. As a result, applying a suitable electric field to the structure automatically generates a plurality of domains. Each pixel part  37  may thus be switched automatically to have a plurality of domains comprising homogeneously oriented liquid crystal molecules having the same tilt angle. 
     In the second embodiment, approximately the entire circumference of each pixel electrode  38 , i.e., a wider area than in the first embodiment of FIGS. 1 and 2, distorts the lines of electric force. This means that the second embodiment is more conducive to a multi-domain display constitution than the first embodiment. The second embodiment thus reliably eases abrupt, asynchronous contrast changes of liquid crystal display elements in the vertical direction and thereby widens regions where inversion of gradation will not occur in half tone. This in turn provides a liquid crystal display apparatus that is less constrained by the angle of visibility and offers wider angles of visibility than before. 
     FIGS. 4 and 5 show a liquid crystal display apparatus  80  practiced as the third embodiment of the invention. FIG. 5 shows a cross-sectional view of the third embodiment, the view being taken on line  5 — 5  in FIG.  4 . The third embodiment differs from the first and second embodiments in terms of an electrode film structure for cumulative capacity generation. 
     The liquid crystal display apparatus  80  comprises a thin film transistor array substrate  81 , a transparent facing substrate  82  positioned parallel to and separate from the thin film transistor array substrate  81 , and liquid crystal  83  contained interposingly between the thin film transistor array substrate  81  and the facing substrate  82 . 
     On the thin film transistor array substrate  81 , as many source wires  85  and gate wires  86  as in the case of the conventional structure in FIGS. 10 and 11 are arranged in a matrix fashion as viewed from above. Each of the numerous areas surrounded by the source wires  85  and gate wires  86  forms a pixel part  87 . A pixel electrode  88  made of a transparent conductive material such as ITO (indium tin oxide) is formed in each of the areas representing the pixel parts  87 . In one corner of each of the pixel parts  87 , a thin film transistor T 2  is formed. 
     FIG. 4 is an enlarged plan view showing a thin film transistor T 2  and its surroundings corresponding to one pixel part  87  surrounded by source wires  85  and gate wires  86 . Numerous pixel parts  87  are arranged on the thin film transistor array substrate  81  to form a display screen of the liquid crystal display apparatus  80 . 
     More specifically, the thin film transistor array substrate  81  is structured as follows: at the pixel parts  87 , numerous gate wires  86  made of a light-shielding conductive material such as Cr or Mo are formed in parallel with one another on a substrate  90 . Part of each gate wire  86  is extended for use as a gate electrode  91 . The gate electrodes  91  and the substrate  90  are covered with a first insulating film (gate insulating film)  92 . Over the first insulating film  92  on the gate electrodes  91  is a semiconductor active film  93  deposited to face the gate electrodes  91 . On both edges of the semiconductor active film  93  are a drain electrode  98  and a source electrode  99  with an ohmic contact film (e.g., n+ film) interposed therebetween. The source wires  85  are formed on the first insulating film  92 . 
     A second insulating film (passivation film)  100  is provided to cover the thin film transistors T 2 , the first insulating film  92  and the source wires  85 . Each pixel electrode  88  is formed to cover most of that area on the second insulating film  100  which corresponds to a pixel part  87 . The pixel electrode  88  is connected to a drain electrode  98  through a connecting conductive film  88   a  in a contact hole  101  formed on the second insulating film  100  at the edge of the drain electrode  98  of the thin film transistor T 2 . Opposite to that portion of the pixel electrode  88  which is connected to the thin film transistor T 2  is an extension part  88 A extended up to that area of the gate wire  86  which corresponds to an adjacent pixel part  87 . Each extension part  88 A covers approximately half the length of the gate wire  86  corresponding to one pixel part  87 . 
     On that edge of the pixel electrode  88  which has no thin film transistor T 2  is a first electrode film  103  formed between right- and left-hand source wires  85  on the first insulating film  92 . The first electrode film  103  is covered with the second insulating film  100 . 
     The first electrode film  103  has an extension part  103 A extended up to that area of each gate wire  86  which corresponds to the adjacent pixel part  87  as in the case of the pixel electrode  88 . The extension part  103 A is formed to occupy a wider area than the extension part  88 A. A contact hole  105  reaching each gate wire  86  is formed on the second insulating film  100  and on that portion of the first insulating film  92  which is not covered with the extension part  103 A. Another contact hole  106  reaching the first electrode film  103  is formed on the second insulating film  100  adjacent to the contact hole  105 . A connecting path  107  spanning the contact holes  105  and  106  connects electrically each gate wire  86  with the first electrode film  103 . On the edge of each pixel electrode  88 , the first electrode film  103  faces the extension part (edge)  88 A of the pixel electrode  88  with the second insulating film  100  interposed therebetween. The first electrode film  103  and the edge  88 A serve as facing electrodes which, together with the second insulating film  100 , constitute cumulative capacity. 
     In the structure shown in FIGS. 4 and 5, the second insulating film  100  is sandwiched between the first electrode film  103  and the edge  88 A of each pixel electrode  88  to form cumulative capacity. The cumulative capacity thus generated cancels out part of the parasitic capacity created in the liquid crystal display apparatus. Partially negating the parasitic capacity helps stabilize the operation of the thin film transistors T 2 . 
     The first electrode film  103  faces the edge  88 A of each pixel electrode  88  with only the second insulating film  100  interposed therebetween. This arrangement allows cumulative capacity to be established more accurately than the conventional structure using two insulating films of different physical properties for setting cumulative capacity. The enhanced level of accuracy in establishing cumulative capacity ensures more stable operation of the thin film transistors T 2 . 
     Below is a description of major benefits made available when the structure of the thin film transistor array substrate shown in FIGS. 4 and 5 is adopted. The benefits of the inventive structure will be discussed in connection with a method for fabricating the structure in question. 
     The thin film transistor array substrate of FIGS. 4 and 5 is fabricated as follows: a light-shielding conductive metal film made illustratively of Cr or Mo is formed all over the substrate  90 . The film-covered substrate is subjected to a patterning process wherein unnecessary parts are removed by etching through the use of a first mask. The patterning process leaves gate electrodes and gate wires formed on the substrate  90  as shown in FIG. 4, viewed from above. 
     The etched substrate is covered with a first insulating film (gate insulating film), a semiconductor active film and an ohmic contact film. The substrate with its newly deposited films is subjected to another patterning process wherein island-like semiconductor active films and ohmic contact films are formed by use of a second mask. 
     With these conductive metal films deposited, the substrate undergoes another patterning process wherein a third mask is used to form source electrodes, source wires, drain electrodes, and first electrode films between adjacent source wires. Then the unnecessary portions of the island-like ohmic contact films between the source and drain electrodes and of the semiconductor active films are removed by etching to form channel parts in the form of thin film transistors. No special mask is needed to form the channels because the source electrodes, source wires, drain electrodes, and the first electrode films between adjacent source wires stemming from the preceding patterning are used as a mask. 
     The substrate is then covered with a second insulating film (passivation film). A fourth mask is deposited on the second insulating film before the substrate is etched to form contact holes reaching the gate wires, the first electrode films and the drain electrodes. Where the contact holes attaining the gate wires are formed, both the first and the second insulating films are etched and the etching process stops at the gate wires made of a conductive metal film. 
     Thereafter, a transparent conductive film (ITO) is deposited on the second insulating film where the contact holes have been made. The transparent conductive film is formed so as to cover the second insulating film and to fill the contact holes thereon. Then the transparent conductive film is patterned by use of a fifth mask to form pixel electrodes. What is left from this patterning process are transparent pixel electrode parts covering the contact holes. The process forms connecting paths that connect electrically the first conductive film under the second insulating film with the gate wires under the first insulating film. The result is the thin film transistor array substrate  81  whose structure is depicted in FIGS. 4 and 5. 
     The method above for fabricating the thin film transistor array substrate utilizes five masks. The smallest possible number of necessary masks simplifies the fabrication process and enhances the yield of products. Whereas a method to be discussed below employs six masks, the above method uses only five, which contributes to improving the yield rate. 
     FIGS. 6 and 7 show a liquid crystal display apparatus practiced as the fourth embodiment of the invention. This embodiment is basically the same as that in FIGS. 4 and 5 except for a different connecting structure between the gate wires  86  and edges  108   a  of the pixel electrodes  108 . 
     In the structure of the fourth embodiment, a first insulating film (gate insulating film)  122  and a second insulating film (passivation film)  128  are deposited. A first electrode film  123 , combined with the edge  108   a  of each pixel electrode  108  to form cumulative capacity, is structured and connected in ways different from those of the third embodiment. However, the major benefits in connection with the generation of cumulative capacity are the same as those of the third embodiment. 
     Contact holes  124  reaching the gate wires  86  are formed only on the first insulating film  122 . The contact holes  124  are used to form connecting paths  125  that connect the first electrode film  123  with the gate wires  86 . An extension part  108   a  at the edge of each pixel electrode  108  is as wide as one pixel part  87 . The extension part  108   a  is formed so as to cover most of the gate wire  86  corresponding to each pixel part  87 . The first electrode film  123  is also formed in an extended manner to cover most of the gate wire  86  corresponding to each pixel part  87 . 
     The thin film transistor array substrate shown in FIGS. 6 and 7 is fabricated as follows: on the substrate  90 , gate electrodes and gate wires are first formed by a patterning process using a first mask, as in the case of the third embodiment. A first insulating film is deposited likewise on the patterned substrate. A second mask is used to form island-like semiconductor active films and ohmic contact films on the substrate. 
     A third mask is then used on a gate insulating film for a patterning process whereby contact holes are made. With the contact holes provided, a conductive metal film is deposited to serve as source and drain electrodes. A fourth mask is used for another patterning process whereby source electrodes, source wires, drain electrodes, and electrodes for generating cumulative capacity are formed. The films thus patterned are used to etch channel parts out of the semiconductor active films. Then a passivation film of SiN x  is deposited on the whole assembly. 
     A fifth mask is used to etch the passivation film, whereby contact holes reaching the drain electrodes are formed. With the passivation film etched to form the contact holes, a transparent conductive film (ITO) is deposited in preparation for making up transparent pixel electrodes. A sixth mask is then used to fabricate both the transparent pixel electrodes and electrodes for generating cumulative capacity at the same time. The result is the structure whose cross-section is shown in FIG.  6 . In the manner described, six masks are used to fabricate the structure depicted in FIG.  6 . 
     FIGS. 8 and 9 are a cross-sectional view and a plan view of a liquid crystal display apparatus  130  of a forward staggered type practiced as another embodiment of the invention. The liquid crystal display apparatus  130  comprises a thin film transistor array substrate  131 , a transparent facing substrate  132  positioned parallel to and separate from the thin film transistor array substrate  131 , and liquid crystal  133  contained interposingly between the thin film transistor array substrate  131  and the facing substrate  132 . 
     On the thin film transistor array substrate  131 , as many source wires  135  and gate wires  136  as in the case of the conventional structure in FIGS. 10 and 11 are arranged in a matrix fashion as viewed from above. Each of the numerous areas surrounded by the source wires  135  and gate wires  136  forms a pixel part  137 . A pixel electrode  138  made of a transparent conductive material such as ITO (indium tin oxide) is formed in each of the areas representing the pixel parts  137 . In one corner of each of the pixel parts  137 , a thin film transistor T 1  is formed so as to extend to part of an adjacent pixel part  137 . 
     FIG. 9 is an enlarged plan view showing a thin film transistor T 1  and its surroundings corresponding to one pixel part  137  surrounded by source wires  135  and gate wires  136 . Numerous pixel parts  137  are arranged on the thin film transistor array substrate  131  to form a display screen of the liquid crystal display apparatus  130 . 
     More specifically, the thin film transistor array substrate  131  is structured as follows: at the pixel parts  137 , numerous source wires  135  are formed in parallel with one another on a substrate  140 . Part of each source wire  135  is used as a source electrode  149 . Opposite to each source electrode  149  is a drain electrode  148  formed on the substrate  140 . A semiconductor active film  143  is provided on the substrate  140  to connect each source electrode  149  with the corresponding drain electrode  148 . The electrodes and the film are covered with a first insulating film (gate insulating film)  142 . On the first insulating film  142  over the semiconductor active film  143  are gate electrodes  141  facing the semiconductor active film  143 . 
     A second insulating film (passivation film)  150  is deposited on the thin film transistors T 1  and first insulating film  142 . On the second insulating film  150  are pixel electrodes  138  covering the areas corresponding to the pixel parts  137 . The pixel electrodes  138  are connected to the drain electrodes  148  through the first insulating film  142  at the edge of the drain electrode  148  of each thin film transistor T 1  as well as through a connecting conductive film  152  in conductive holes  151  formed on the second insulating film  150 . 
     A first electrode film  170  furnished corresponding to the edge of each pixel electrode  138  is shaped like a ring at each pixel part  137 . As such, the first electrode film  170  surrounds approximately the entire circumference of each pixel electrode  138 . The first electrode films  170  at the pixel parts  137  are interconnected by connecting conductors  171  arranged parallel to the gate wires  136 . The connecting conductors  171  extending to the edge of each gate wire on the substrate are interconnected and grounded at the substrate fringe. This causes the first electrode films  170  to bear ground potential. That portion of each pixel electrode  138  which faces the first electrode film  170  constitutes a second electrode film  138 A. 
     The above liquid crystal display apparatus  130  using forward staggered type thin film transistors provides benefits equivalent to those offered by the second embodiment of FIG.  3 . Specifically, cumulative capacity is generated by the first electrode film  170  surrounding the entire circumference of each pixel electrode  138  and by the second electrode film  138  corresponding to the first electrode film  170 . This structure cancels out part of the parasitic capacity created inevitably in the liquid crystal display apparatus, thus helping to stabilize the operation of the thin film transistors T 1 . 
     The cumulative capacity of the above embodiment is formed not by a plurality of insulating films (i.e., gate insulating film and passivation film) as is the case with conventional arrangements but by one insulating film (passivation film  150  alone). The inventive structure may have a reduced facing electrode area (i.e., facing area formed by the edges of the pixel electrodes  138  and by the first electrode films  170 ) to provide the same cumulative capacity as that of the conventional multiple insulating film structure. This ensures an improved numeral aperture for the liquid crystal display apparatus of the invention. 
     With the above embodiment, the single-film structure, when arranged to have the same facing electrode area (i.e., facing area formed by the edges of the pixel electrodes  138  and by the first electrode films  170 ) as that of the conventional multiple insulating film structure, provides a greater cumulative capacity than the latter. The cumulative capacity increased in this manner ensures better signal stabilization. 
     In the structure depicted in FIGS. 8 and 9, lines of electric force from the pixel electrode  138  are distorted when attracted radially toward the first electrode film  170  surrounding approximately the whole circumference of each pixel electrode  138 . When the liquid crystal molecules are torqued perpendicularly to the radially distorted lines of electric force, the molecules constitute a plurality of domains while being homogeneously oriented. As a result, applying a suitable electric field to the structure automatically generates a plurality of domains. Each pixel part  137  may thus be switched automatically to have a plurality of domains comprising homogeneously oriented liquid crystal molecules having the same tilt angle. 
     In this manner, an area as wide as approximately the entire circumference of each pixel electrode  138  distorts the lines of electric force to bring about a multi-domain display arrangement. The multi-domain feature reliably eases abrupt, asynchronous contrast changes of liquid crystal display elements in the vertical direction and thereby widens regions where inversion of gradation will not occur in half tone. This in turn provides a liquid crystal display apparatus that is less constrained by the angle of visibility and offers wider angles of visibility than before. 
     EXAMPLE 
     The inventors compared in concrete terms the thin film transistor array substrate of the first embodiment in FIGS. 1 and 2 with the conventional thin film transistor array substrate in FIGS. 10 and 11. In the structure of FIGS. 1 and 2, the facing area between the first and the second electrode films for generative cumulative capacity at each pixel part was set for 675 μm 2 . A passivation film 0.4 μm thick and made of silicon nitride was placed interposingly as a dielectric film between the first and the second electrode films. This structure provided a capacity of 0.1 pF. 
     In the structure of FIGS. 10 and 11, by contrast, the facing area between the first and the second electrode films for generating cumulative capacity at each pixel part was set for 1,000 μm 2 . A passivation film 0.4 μm thick and made of silicon nitride and a gate insulating film 0.3 μm thick and composed of silicon nitride were placed interposingly as dielectric films between the first and the second electrode films. This structure yielded a capacity of 0.085 pF. 
     The comparison above showed that the inventive structure of FIGS. 1 and 2, given the same facing area as that of the conventional arrangement, boosts cumulative capacity by about 70% over the latter. The dielectric constant of the passivation film measured about 6.7, approximately the same for both the inventive and the conventional structures. 
     The above comparison also indicated that the inventive structure of FIGS. 1 and 2 having the same cumulative capacity as that of the conventional arrangement in FIGS. 10 and 11 may have a 1.5% reduction in the facing area between the first and the second electrode films in acquiring the capacity of 0.085 pF. Given the same cumulative capacity, this feature translated into an improvement of about 1% in numerical aperture for the inventive liquid crystal display apparatus over comparable conventional devices. 
     As described, the liquid crystal display apparatus having inversely staggered thin film transistors according to the invention comprises: a first insulating film separating a gate insulating film from a semiconductor active film; and a second insulating film furnished independently of the first insulating film and interposed between a first electrode film and pixel electrodes facing the first electrode film; wherein the second insulating film alone is used as a dielectric film to form cumulative capacity. Whereas the conventional structure needs two different insulating films sandwiched by electrode films to constitute cumulative capacity, the inventive single-film setup having the same facing electrode area as that of its conventional counterpart offers a higher cumulative capacity than the latter. This feature translates into more stable operation of the thin film transistors. If the cumulative capacity of the inventive structure is the same as that of the conventional setup, the inventive structure needs a less facing electrode area than the latter. This ensures an improved numerical aperture for the liquid crystal display apparatus. 
     In the liquid crystal display apparatus of the invention, the film for forming source and drain electrodes may also be used to constitute the first electrode film. That is, the film treatment for fabricating the source and drain electrodes, when combined with patterning, creates the first electrode film at the same time. The facing electrodes are also formed simultaneously through the film treatment for fabricating the pixel electrode in conjunction with patterning. The inventive structure thus provides the electrode film without complicating the fabrication process and with no decline in the yield rate. 
     Where connecting paths penetrating the first and the second insulating films are used in the inventive structure to connect the pixel electrodes with the gate wires, the connecting paths may be fabricated simultaneously with the pixel electrodes being patterned. With a smaller number of masks thus in use, the fabrication process may be made simpler than before. 
     Where the first electrode film is arranged to bear ground potential, the electric field stemming from that edge of each pixel electrode which faces the grounded first electrode film differs from the electric field from the middle of the pixel electrode in question. That is, the liquid crystal in the middle region of each pixel electrode is oriented differently from the liquid crystal in the second electrode film side area of the pixel electrode in question. Such a multi-domain arrangement is conductive to easing the problem of constrained angles of visibility that has plagued liquid crystal display apparatuses. 
     Lines of electric force stemming from the middle portion of each pixel electrode proceed unchanged to the corresponding common electrode film on the facing electrode, while lines of electric force from the edge of the pixel electrode in question are distorted when attracted to the first electrode film. Because liquid crystal molecules are torqued perpendicularly to the distorted lines of electric force, the molecules constitute a plurality of domains, i.e., in the middle region of each pixel electrode, and on its edge facing the first electrode film, while they are homogeneously oriented. As a result, applying a suitable electric field to the inventive structure automatically generates a plurality of domains. Each pixel part may thus be switched automatically to have a plurality of domains comprising homogeneously oriented liquid crystal molecules having the same tilt angle. 
     In this manner, the multi-domain feature reliably eases abrupt, asynchronous contrast changes of liquid crystal display elements in the vertical direction and thereby widens regions where inversion of gradation will not occur in half tone. This in turn provides a liquid crystal display apparatus that is less constrained by the angle of visibility and offers wider angles of visibility than before. 
     The above structure applies not only to liquid crystal display apparatuses having inversely staggered thin film transistors but also to those equipped with forward staggered thin film transistors. In both cases, the major benefits available from the invention are equivalent. 
     As many apparently different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.