Patent Publication Number: US-10332918-B2

Title: Pixel structure

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of priority to Taiwan Patent Application No. 105107744, filed Mar. 14, 2016. The entire content of the above identified application is incorporated herein by reference. 
     Some references, which may include patents, patent applications and various publications, are cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. 
     FIELD 
     The present invention relates to a pixel structure, and in particular, to a pixel structure in which adjacent pixel units share a common opening of the same common electrode. 
     BACKGROUND 
     A Head-mount Display (HMD) is a display worn on a human body. The head-mount display is a small-sized display in which a lens assembly is disposed at a position very close to the eyes so that a user can view through this display, therefore achieving an effect similar to that of watching a large-sized display located some distance away. Generally speaking, manners of viewing via a display include a double-eye manner and a single-eye manner, and the size of the display varies in accordance with different watching manners. To develop a head-mount display that meets the requirements of being thin, light, and close to the eyes, a pixel size needs to be further reduced to improve the resolution of the display, so as to achieve the purpose of reducing the size of the display. However, because of the limitation of the manufacturing process, a conductive structure in pixels may be short-circuited as gaps become smaller, making it difficult to implement a high-resolution pixel design. 
     SUMMARY 
     The present disclosure provides a pixel structure, which prevents short-circuiting of a conductive structure in a pixel unit. 
     The pixel structure of the present disclosure includes a first pixel unit, a second pixel unit, a first insulating layer, and a common electrode. The first pixel unit is disposed on a substrate, and comprises a first drain and a first pixel electrode. The second pixel unit is disposed on the substrate, and comprises a second drain and a second pixel electrode. The first insulating layer covers the first drain and the second drain. The first pixel electrode and the second pixel electrode are disposed on the first insulating layer, and the first insulating layer has a first contact hole uncovering a part of the first drain and a second contact hole uncovering a part of the second drain. The common electrode is disposed on the first insulating layer and electrically insulated from the first pixel electrode and the second pixel electrode, the common electrode has a common opening, and in a vertical projection direction onto the substrate, both the first contact hole and the second contact hole are located in a region of the common opening. 
     In an embodiment of the present disclosure, in the vertical projection onto the substrate, an edge of the first contact hole is located within an edge of the first drain. 
     In an embodiment of the present disclosure, the pixel structure further comprises a second insulating layer and a first signal line, the first drain and the second drain are disposed on the second insulating layer and are filled into a third contact hole and a fourth contact hole of the second insulating layer, and the first signal line is located between the first pixel unit and the second pixel unit. 
     In an embodiment of the present disclosure, in a horizontal direction, a symmetry center of the first contact hole has a shift distance relative to a symmetry center of the first drain, and an edge of the first contact hole is located within an edge of the first drain. 
     In an embodiment of the present disclosure, the pixel structure further comprises a first signal line, the first signal line is located between the first pixel unit and the second pixel unit, a symmetry center of the first contact hole is closer to the first signal line than the symmetry center of the first drain is, and a symmetry center of the second contact hole is closer to the first signal line than a symmetry center of the second drain is. 
     In an embodiment of the present disclosure, the pixel structure further comprises a second insulating layer, the first drain and the second drain are disposed on the second insulating layer, the first contact hole and the second contact hole uncovers a partial top portion of the second insulating layer, respectively. 
     In an embodiment of the present disclosure, the pixel structure further comprises a first signal line, the first signal line is located between the first pixel unit and the second pixel unit, a symmetry center of the first contact hole is closer to the first signal line than a symmetry center of the first drain is, and a symmetry center of the second contact hole is closer to the first signal line than a symmetry center of the second drain is. 
     In an embodiment of the present disclosure, the pixel structure further comprises a third insulating layer, disposed on the first insulating layer, covering a part of the common electrode, and having a fifth contact hole and a sixth contact hole, the fifth contact hole is in communication with the first contact hole, and the sixth contact hole is in communication with the second contact hole. 
     In an embodiment of the present disclosure, the first pixel electrode is disposed on the third insulating layer and is electrically connected to the first drain through the fifth contact hole and the first contact hole, and the second pixel electrode is disposed on the third insulating layer and is electrically connected to the second drain through the sixth contact hole and the second contact hole. 
     In an embodiment of the present disclosure, the first pixel unit further comprises a first source and a first channel layer, and the first source is electrically connected to the first channel layer through a seventh contact hole. 
     In an embodiment of the present disclosure, the pixel structure further comprises a third pixel unit having a third drain and a third pixel electrode, and the third pixel unit is disposed between the first pixel unit and the second pixel unit. 
     In an embodiment of the present disclosure, the first insulating layer further covers the third drain, the third pixel electrode is disposed on the first insulating layer, the first insulating layer further has an eighth contact hole uncovering the third drain, and in the vertical projection onto the substrate, the first contact hole, the second contact hole, and the eighth contact hole all are located in the region of the common opening. 
     In an embodiment of the present disclosure, in the vertical projection onto the substrate, the first contact hole and the first drain at least partially overlap, the second contact hole and the second drain at least partially overlap, and an edge of the eighth contact hole is located within an edge of the third drain. 
     In an embodiment of the present disclosure, the pixel structure further comprises a first signal line and a second signal line, the first signal line is located between the first pixel unit and the third pixel unit, the second signal line is located between the second pixel unit and the third pixel unit, in the vertical projection onto the substrate, distances from the eighth contact hole to the first signal line and to the second signal line are substantially the same, a symmetry center of the first contact hole is closer to the first signal line than a symmetry center of the first drain is, and a symmetry center of the second contact hole is closer to the second signal line than a symmetry center of the second drain is. 
     In an embodiment of the present disclosure, the pixel structure further comprises a third insulating layer, disposed on the first insulating layer, covering the common electrode, and having a fifth contact hole, a sixth contact hole, and a ninth contact hole, the fifth contact hole is in communication with the first contact hole, the sixth contact hole is in communication with the second contact hole, and the ninth contact hole is in communication with the eighth contact hole. 
     In an embodiment of the present disclosure, the first pixel electrode is disposed on the third insulating layer and is electrically connected to the first drain through the fifth contact hole and the first contact hole, the second pixel electrode is disposed on the third insulating layer and is electrically connected to the second drain through the sixth contact hole and the second contact hole, and the third pixel electrode is disposed on the third insulating layer and is electrically connected to the third drain through the ninth contact hole and the eighth contact hole. 
     Based on the description above, in the present disclosure, the insulating layer has respective contact holes that uncover drains of pixel units, and the common opening of the common electrode uncovers contact holes of two adjacent pixel units at the same time. In this way, a sufficient gap is maintained between the common opening and the contact hole, so as to avoid short-circuiting the common electrode and the drain. The pixel structure will therefore be equipped with good device properties. 
     To make the above characteristics and advantages of the present disclosure clearer and easier to understand, the following embodiments are described in detail in conjunction with accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the disclosure, and wherein: 
         FIG. 1A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 1B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 1A ; 
         FIG. 2A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 2B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 2A ; 
         FIG. 3A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 3B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 3A ; 
         FIG. 4A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 4B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 4A ; 
         FIG. 5A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 5B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 5A ; 
         FIG. 6A  is a partial schematic diagram of a pixel structure in the related art, and  FIG. 6B  to  FIG. 6D  are respective enlarged partial schematic diagrams of  FIG. 1A ,  FIG. 4A , and  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. Further, the term “connect” or “electrically connected,” as used herein, refers to the direct or indirect physical or electrical contact between or among two or more components, or the mutual operation or action of two or more components. 
       FIG. 1A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 1B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 1A . Please refer to  FIG. 1A  and  FIG. 1B  at the same time. In the present embodiment, a pixel structure  10  comprises a substrate  110 , two adjacent pixel units  100   a  and  100   b , a first insulating layer  180 , and a common electrode  190 . In the present embodiment, the pixel structure  10  further comprises scan lines  140 , data lines  160 , a gate insulating layer  130 , a second insulating layer  150 , and a third insulating layer  200 . A data line  160  is located, for example, between the two adjacent pixel units  100   a  and  100   b . In the present embodiment, a straight line is used as an example for the data line  160 , but the present disclosure is not limited thereto. In other embodiments, the data line  160  may also be a meander line or a line in a different shape. 
     In the present embodiment, the pixel units  100   a  and  100   b  are located, for example, on the substrate  110 . The pixel units  100   a  and  100   b  each includes, for example, a gate  142 , a channel layer  120 , a source  162 , a drain  164 , and a pixel electrode  210 , and the source  162  and the drain  164  are electrically connected to the channel layer  120  and form a thin-film transistor together with the gate  142 . In the present embodiment, the source  162  and the drain  164  are located, for example, at two ends of the channel layer  120 , and partially overlap with the channel layer  120 ; the drain  164  is located, for example, between the channel layer  120  and the pixel electrode  210  in a vertical direction relative to the substrate  110 , and partially overlaps with the channel layer  120  and the pixel electrode  210 . In the present embodiment, the drain  164  is, for example, a rectangular shape in top view, but the present disclosure is not limited thereto. In other embodiments, the drain  164  may also be circular, polygonal, or have an irregular shape. In the present embodiment, the source  162  and the drain  164  are electrically connected to the channel layer  120  through a contact hole  154  and a contact hole  152  of the second insulating layer  150  respectively, and the gate insulating layer  130  is also provided with contact holes at positions corresponding to the contact holes  152  and  154 , such that the channel layer  120  is electrically connected to the source  162  and the drain  164  respectively. For example, a contact hole  132  corresponds to the position of the contact hole  152 , such that the channel layer  120  is electrically connected to the drain  164 . In the present embodiment, a material of the channel layer  120  is, for example, a metal-oxide semiconductor material or an amorphous silicon material, such as Indium-Gallium-Zinc Oxide (IGZO), zinc oxide (ZnO), tin oxide (SnO), Indium-Zinc Oxide (IZO), Gallium-Zinc Oxide (GZO), Zinc-Tin Oxide (ZTO) or Indium-Tin Oxide (ITO), or another suitable material, or a combination thereof. In the present embodiment, the gate  142  is, for example, a part of the scan line  140 . The source  162  is electrically connected to the data line  160 , or the source  162  is a part of the data line  160 . It should be additionally noted that, in the present embodiment, a thin-film transistor  200  of a top gate type in which the channel layer  120  is located between the substrate  110  and the gate  142  is used as an example; however, a thin film transistor of a bottom gate type or another type may also be applied to the present disclosure. In the present embodiment, the pixel units  100   a  and  100   b  are, for example, two of a red pixel unit, a blue pixel unit, and a green pixel unit. 
     In the present embodiment, the first insulating layer  180  is formed, for example, completely above the substrate  110  and covers the thin-film transistors, the scan lines  140 , the data lines  160 , and the second insulating layer  150 . The first insulating layer  180  covers the drains  164 , and has contact holes  182   a  and  182   b  that uncover the drains  164 . As is described above, the drain  164 , for example, partially overlaps with the pixel electrode  210  in the vertical direction relative to the substrate  110 ; the first insulating layer  180  is disposed between the drain  164  and the pixel electrode  210 , and the contact holes  182   a  and  182   b  of the first insulating layer  180  uncover the drains  164 . In the present embodiment, in a horizontal direction, the symmetry centers of the contact holes  182   a  and  182   b , for example, substantially overlap with the symmetry centers of the drains  164 , as shown in  FIG. 1B ; and in a vertical projection direction onto the substrate  110 , edges of the contact holes  182   a  and  182   b  are located, for example, within edges of the drains  164 . The horizontal direction described herein may, for example, be an extension direction of the scan line  140 ; the symmetry center refers to a symmetry center of an object in the horizontal direction; and an extension direction of a symmetry axis is, for example, parallel to an extension direction of the data line. A material of the first insulating layer  180  is, for example, an organic material (such as a polyester (PET), a polyene, a polyacrylamide, a polycarbonate, a polyepoxide, a polystyrene, a polyether, a polyketone, a polyalcohol, a polyaldehyde, or another suitable material, or a combination thereof), an inorganic material (such as silicon oxide, silicon nitride, silicon oxynitride, another suitable material, or a stacked layer of at least two of the above materials), or another suitable material, or a combination thereof. 
     In the present embodiment, the common electrode  190  is located, for example, on the first insulating layer  180 , and has a common opening  192 ; the common opening  192  exposes or uncovers the drains  164  of the two adjacent pixel units  100   a  and  100   b  at the same time. In the present embodiment, the third insulating layer  200  is also formed, for example, completely above the common electrode  190 , and has contact holes  202  exposing or uncovering the drains  164 . In the present embodiment, the contact holes  202  are formed, for example, together with the contact holes  182   a  and  182   b , but the present disclosure is not limited thereto. A material of the third insulating layer  200  is, for example, different from that of the first insulating layer  180 . The material of the third insulating layer  200  is, for example, an inorganic material (such as silicon oxide, silicon nitride, silicon oxynitride, another suitable material, or a stacked layer of at least two of the above materials), an organic material, or another suitable material, or a combination thereof. In the present embodiment, the pixel electrodes  210  are located, for example, on the third insulating layer  200 , and are electrically connected to the drains  164  through the contacts holes  202  and the contact holes  182   a  and  182   b , respectively. The common electrode  190  is electrically insulated from the pixel electrodes  210 . Examples of materials of the common electrode  190  and the pixel electrode  210  include transparent conductive materials such as indium-tin oxide, but are not limited thereto; metal-containing materials may also be used according to design requirements. In the present embodiment, the pixel electrode  210  has a plurality of electrode strips  212  which are electrically connected, so as to produce higher-density electric field variations with the common electrode  190 , but the present disclosure is not limited thereto. In the present embodiment, the pixel electrode  210  has, for example, a boot shape in top view, where an angle θ less than 180 degrees is formed between one side  210   a  and another side  210   b  of the boot shape. In the present embodiment, a corner of the boot shape with the angle θ is located, for example, near the common opening  192 . In the present embodiment, a distance between the position of the corner and the common opening  192  is, for example, less than 5 μm. In the present embodiment, a distance between the position of the corner and the common opening  192  is, for example, less than 2 μm. In the present embodiment, a distance between the position of the corner and the common opening  192  is, for example, less than 1 μm. In an embodiment, an insulating layer located between the first insulating layer  180  and the third insulating layer  200  may further be included; the insulating layer may have a contact hole formed together with the contact holes  202 , and a material of the insulating layer is, for example, an inorganic material (such as silicon oxide, silicon nitride, silicon oxynitride, another suitable material, or a stacked layer of at least two of the above materials), an organic material, or another suitable material, or a combination thereof. 
     In the present embodiment, all of the contact holes  152 , the contact holes  182   a  and  182   b , and the contact holes  202  corresponding to the two adjacent pixel units  100   a  and  100   b  are, for example, completely located within the region of the common opening  192 . The two adjacent pixel units  100   a  and  100   b  are made to use the same common opening  192 , so that a sufficient distance b is provided between an edge of the common electrode  190  and edges of the contact holes  182   a  and  182   b ; the distance b is, for example, greater than a manufacturing process limitation, 2 μm. The sufficient distance can prevent the common electrode  190  from sliding into the contact holes  182   a  and  182   b , thus avoiding short-circuiting the drain  164  and the common electrode  190 . Therefore, in the present embodiment, when being electrically connected to the drain  164 , the pixel electrode  210  is not in contact with the common electrode  190 ; that is, the pixel electrode  210  and the common electrode  190  are spaced from each other and are not in contact. As a result, the pixel electrode  210  and the common electrode  190  may have different voltages such that an electric field is generated between the pixel electrode  210  and the common electrode  190 . In the present embodiment, distances b from the edges of the common electrode  190  to the edges of the contact holes  182   a  and  182   b  meets the design specifications of being greater than 2 μm, with no needs to reduce sizes of the contact holes  182   a  and  182   b  or the thickness of the insulating layer  180 . In addition, the pixel structure of the present embodiment may be used as a pixel structure of a Fringe Field Switching (FFS) liquid crystal display, and is applicable to a pixel structure required for high resolution while maintaining good electrical connection. 
       FIG. 2A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 2B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 2A . Please refer to  FIG. 2A  and  FIG. 2B  at the same time. In the present embodiment, the first and second pixel units  100   a  and  100   b  differ from the foregoing embodiment in that, in the horizontal direction, the symmetry centers of the contact holes  182   a  and  182   b , for example, deviate from the symmetry centers of the drains  164  or each has a shift distance relative to the symmetry centers of the first drains  164 , as is shown in  FIG. 2B . In other words, the two contact holes  182   a  and  182   b  are, for example, relative to the drains  164 , deviated toward and close to the data line  160  between the two pixel units  100   a  and  100   b , respectively, that is, the symmetry center of the contact hole  182   a  is closer to the data line  160  between the two pixel units  100   a  and  100   b  than the symmetry center of the drain  164  corresponding to the contact hole  182   a  is, and the symmetry center of the contact hole  182   b  is closer to the data line  160  than the symmetry center of the drain  164  corresponding to the contact hole  182   b  is; but in the vertical projection onto the substrate  110 , the edges of the contact holes  182   a  and  182   b  are still located within the edges of the drains  164 . In another embodiment, as shown in  FIG. 3A  and  FIG. 3B , the contact holes  182   a  and  182   b  are, for example, relative to the drains  164 , even closer to the data line  160 . Therefore, the contact holes  182   a  and  182   b  are disposed, for example, in a manner of being misaligned with the contact holes  152 . However, in the vertical projection onto the substrate  110 , the edges of the contact holes  182   a  and  182   b  are still located within the edges of the drains  164 . 
       FIG. 4A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 4B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 4A . Please refer to  FIG. 4A  and  FIG. 4B  at the same time. The present embodiment differ from the foregoing embodiment in that the contact holes  182   a  and  182   b  uncover or expose only a part of the drains  164 , such as uncovering an edge of the drains  164 ; and the contact holes  182   a  and  182   b  uncover regions other than the drains  164 . In other words, in the present embodiment, the two contact holes  182   a  and  182   b  are, for example, relative to the drains  164 , close to the data line  160  between the two pixel units  100   a  and  100   b , that is, the symmetry center of the contact hole  182   a  is closer to the data line  160  between the two pixel units  100   a  and  100   b  than the symmetry center of the drain  164  corresponding to the contact hole  182   a  is, and the symmetry center of the contact hole  182   b  is closer to the data line  160  than the symmetry center of the drain  164  corresponding to the contact hole  182   b  is, such that the contact holes  182   a  and  182   b  are disposed, for example, in a manner of being misaligned with the contact holes  152 ; and in the vertical projection onto the substrate  110 , at least one edge of each of the contact holes  182   a  and  182   b  falls outside the drains  164 ; that is, the contact holes  182   a  and  182   b  uncover or expose a partial top portion  150   a  of the insulating layer  150 . 
     In the foregoing embodiments of  FIG. 2A  to  FIG. 4B , the adjacent pixel units  100   a  and  100   b  are made to share one common opening  192  such that the contact holes  182   a  and  182   b  of the first insulating layer  180  can shift towards the data line  160  between the adjacent pixel units  100   a  and  100   b . In this way, it is ensured that a relatively large horizontal gap, for example, a gap greater than 2 μm, is maintained between the common electrode  190  and the edges of the contact holes  182   a  and  182   b.    
     Two adjacent pixel units are used as an example for description in the foregoing embodiments, but the present disclosure is not limited thereto.  FIG. 5A  is a schematic diagram of a pixel structure according to an embodiment of the present disclosure, and  FIG. 5B  is a cross-sectional schematic diagram along line A-A′ shown in  FIG. 5A . Please refer to  FIG. 5A  and  FIG. 5B  at the same time. In the present embodiment, the pixel structure  10  may further comprise a third pixel unit  100   c , located between the first and second pixel units  100   a  and  100   b . Components of the third pixel unit  100   c  are similar to those of the first and second pixel units  100   a  and  100   b , described above. In the present embodiment, the pixel units  100   a ,  100   b , and  100   c  are, for example, a red pixel unit, a blue pixel unit, and a green pixel unit. In the present embodiment, the common opening  192  exposes the contact holes  182   a ,  182   b , and  182   c  of the adjacent pixel units  100   a ,  100   b , and  100   c  at the same time. In other words, in the present embodiment, the three adjacent pixel units  100   a ,  100   b , and  100   c  share the common opening  192  of a common electrode  190 . In the present embodiment, the whole contact hole  182   c  corresponding to the third pixel unit  100   c  may, for example, expose or uncover a part of a drain  164 , and edges of the contact hole  182   c  are located, for example, within edges of the drain  164 . In the present embodiment, an edge of a contact hole  152  corresponding to the third pixel unit  100   c  is located, for example, within an edge of the contact hole  182   c . In the present embodiment, a data line  160   a  is located, for example, between the first pixel unit  100   a  and the third pixel unit  100   c ; and a data line  160   b  is located, for example, between the second pixel unit  100   b  and the third pixel unit  100   c . A distance between the contact hole  182   c  and the data line  160   a  is, for example, substantially the same as a distance between the contact hole  182   c  and the data line  160   b  in the vertical projection onto the substrate  110 . The contact hole  182   a  is, relative to the drain  164  of the first pixel unit  100   a , close to the data line  160   a , and the contact hole  182   b  is, relative to the drain  164  of the second pixel unit  100   b , close to the data line  160   b , that is, the symmetry center of the contact hole  182   a  is closer to the data line  160   a  than the symmetry center of the drain  164  of the first pixel unit  100   a  is, and the symmetry center of the contact hole  182   b  is closer to the data line  160   b  than the symmetry center of the drain  164  of the second pixel unit  100   b  is. The present embodiment uses the contact holes  182   a  and  182   b  having the same disposition manner as the one in  FIG. 4A  and  FIG. 4B  as an example, but the present disclosure is not limited thereto. In other embodiments, the contact holes  182   a  and  182   b  may have a disposition manner that is the same as or similar to the disposition manner in  FIG. 1A  and  FIG. 1B , or  FIG. 2A  and  FIG. 2B , or  FIG. 3A  and  FIG. 3B , or  FIG. 4A  and  FIG. 4B , or a combination thereof. It should be particularly noted that, the foregoing embodiment uses the contact holes  182   a  and  182   b  shifted towards the data lines  160 ,  160   a , and  160   b  as an example, but the present disclosure is not limited thereto; that is, the contact holes  182   a  and  182   b  may also deviate together towards another signal line (such as the scan line  140 ) between the two adjacent pixel units. 
     In the foregoing embodiment, because the adjacent pixel units use the same common opening of the common electrode, the width of the pixel unit can be further reduced. More specifically, please refer to  FIG. 6A , a conventional pixel structure; an opening  191  of a common electrode  190  of the pixel structure corresponds to one pixel unit  100 . Generally speaking, to prevent the common electrode  190  from falling into a contact hole  182  as to avoid short-circuiting a drain  164  and the common electrode  190 , a gap meeting the design specifications of 2˜2.5 μm is provided between the common electrode  190  and the contact hole  182 ; and a limitation on the contact hole  182  in the manufacturing process is 4 μm. Therefore, in an extension direction of a signal line (using the scan line  140  as an example, but is not limited thereto), assuming that a width a of the common electrode between two adjacent openings  191  is 2 μm, a distance b between an edge of the contact hole  182  and an edge of the opening  191  is 2 μm, and a size c of the contact hole  182  is 4 μm, the width of one pixel unit is therefore (a+2b+c), i.e., about 10 μm. 
     However, in the foregoing embodiment, as shown in  FIG. 6B , it is assumed that a width a of the common electrode  190  between two adjacent common openings  192  is 2 μm, a distance b between the edge of the contact hole  182   a  ( 182   b ) and the edge of the common opening  192  is 2 μm, a size c of the contact holes  182   a  and  182   b  is 4 μm, and a distance d between the two adjacent contact holes  182   a  and  182   b  is 3 μm; in this case, the width of one pixel unit is (½a+b+c+½d), i.e., about 8.5 μm. In another embodiment, as shown in  FIG. 6C , a width a of the common electrode  190  between two adjacent common openings  192  is 1.5 to 2 μm, a distance b between the edge of the contact hole  182   a ( 182   b ) and the edge of the common opening  192  is 2 to 2.5 μm, a size c of the contact holes  182   a  and  182   b  is 3 to 4 μm, and a distance d between the two adjacent contact holes  182   a  and  182   b  is 1.5 to 2 μm; in this case, the width of one pixel unit is (½a+b+c+½d), i.e., about 6.5 to 8.5 μm. In a further embodiment, as shown in  FIG. 6D , a width a of the common electrode  190  between two adjacent common openings  192  is 1.5 to 2 μm, a distance b between the edge of the contact hole  182   a ( 182   b ) and the edge of the common opening  192  is 2 to 2.5 μm, a size c of the contact holes  182   a ,  182   b  and  182   c  is 3 to 4 μm, and a distance d between two of the contact holes  182   a ,  182   b  and  182   c  is 4 μm; in this case, the width of one pixel unit is ⅓(a+2b+3c+2d), i.e., about 7.5 to 9 μm. It can be learned from above that the width of the pixel unit in the present embodiment can be further reduced compared with the conventional pixel structure; therefore, the pixel unit in the present embodiment is applicable to a pixel structure required for high resolution. 
     In conclusion, the insulating layer of the pixel structure in the present disclosure has respective contact holes that uncover drains of pixel units, and the common opening of the common electrode uncovers contact holes of two adjacent pixel units at the same time. In this way, a sufficient gap is maintained between the common opening and the contact hole, so as to avoid short-circuiting the common electrode and the drain. In addition, in an embodiment, adjacent pixel units are made to share one common opening, such that the contact hole of the insulating layer may has a shift distance relative to a signal line between the adjacent pixel units, so as to ensure that a relatively large gap exists between the edge of the contact hole and the common electrode, thus further avoiding short-circuiting the common electrode and the drain. The pixel structure will therefore be equipped with good device properties. 
     Even though the present disclosure has been disclosed with the above-mentioned embodiments, it is not limited thereto. Any person of ordinary skill in the art may make some changes and adjustments without departing from the spirit and scope of the present disclosure. Therefore, the scope of the present disclosure is defined in view of the appended claims.