Abstract:
A method for producing a light reflecting structure in a transflective or reflective liquid crystal display uses one or two masks for masking a photoresist layer in a back-side exposing process. The pattern on the masks is designed to produce rod-like structures or crevices and holes on exposed and developed photoresist layer. After the exposed photoresist is developed, a heat treatment process or a UV curing process is used to soften the photoresist layer so that the reshaped surface is more or less contiguous but uneven. A reflective coating is then deposited on the uneven surface. One or more intermediate layers can be made between the masks, between the lower mask and the substrate, and between the upper masks and the photoresist layers. The masks and the intermediate layers can be made in conjunction with the fabrication of the liquid crystal display panel.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a liquid crystal display panel and, more particularly, to a reflective or transflective liquid crystal display panel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Due to the characteristics of thin profile and low power consumption, liquid crystal displays (LCDS) are widely used in electronic products, such as portable personal computers, digital cameras, projectors, and the like. Generally, LCD panels are classified into transmissive, reflective, and transflective types. A transmissive LCD panel uses a back-light module as its light source. A reflective LCD panel uses ambient light as its light source. A transflective LCD panel makes use of both the back-light source and ambient light. 
         [0003]    As known in the art, a color LCD panel  1  has a two-dimensional array of pixels  10 , as shown in  FIG. 1 . Each of the pixels comprises a plurality of sub-pixels, usually in three primary colors of red (R), green (G) and blue (B). These RGB color components can be achieved by using respective color filters.  FIG. 2  illustrates a plan view of the pixel structure in a conventional transflective liquid crystal panel, and  FIG. 3  is a cross sectional view of the pixel structure. As shown in  FIG. 2 , a pixel can be divided into three sub-pixels  12 R,  12 G and  12 B and each sub-pixel can be divided into a transmission area (TA) and a reflection area (RA). In the transmission area as shown in  FIG. 3   a , light from a back-light source enters the pixel area through a lower substrate  30 , and goes through a liquid crystal layer, a color filter R and the upper substrate  20 . In the reflection area, light encountering the reflection area goes through an upper substrate  20 , the color filter R and the liquid crystal layer before it is reflected by a reflective layer  52 . Alternatively, part of the reflection area is covered by a non-color filter (NCF), as shown in  FIG. 3   b.    
         [0004]    As known in the art, there are many more layers in each pixel for controlling the optical behavior of the liquid crystal layer. These layers may include a device layer  50  and one or two electrode layers. The device layer is typically disposed on the lower substrate and comprises gate lines  31 ,  32 , data lines  21 - 24  ( FIG. 2 ), transistors, and passivation layers (not shown). 
         [0005]    It is advantageous and desirable to provide a method for making the reflective layer in a transflective or reflective liquid crystal display panel. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a method for producing a light reflecting structure for use in the pixels of a transflective or reflective liquid crystal display. One or two masks are disposed on a substrate for producing an uneven surface pattern in a photoresist layer disposed on the mask when the photoresist layer is exposed by a light beam through the mask and developed. The exposed and developed photoresist layer is softened in a heat treatment process or a UV curing process to produce a reshaped surface. A reflective coating is disposed on the reshaped surface. In particular, when two masks are used for partially blocking the light beam in the exposure process, both masks have light-blocking areas and non-blocking areas. These areas are arranged such that the combined non-blocking areas are smaller than the non-blocking areas in either one of the masks. The masks are designed such that at least part of the uneven surface comprises rod-like bumps. These bumps are partially joined when the photoresist layer is softened in the reshaping process. The masks can also be designed such that at least part of the uneven surface comprises crevices or holes. These crevices or holes are partially filled when the photoresist layer is softened in the reshaping process. The light reflecting structure may have one or more intermediate layers disposed between the masks, between the photoresist layer and the upper mask, and between the substrate and the lower mask. 
         [0007]    Thus, the first aspect of the present invention is a method for producing a light reflective structure on a substrate in a liquid crystal display panel. The method comprises the steps of: 
         [0008]    providing a mask on the substrate, the mask having light-blocking areas and non-light blocking areas; 
         [0009]    disposing a photoresist layer on the mask; 
         [0010]    exposing the photoresist layer through the mask for providing an exposed photoresist layer having exposed layer areas; 
         [0011]    developing the exposed photoresist layer for producing an uneven surface; 
         [0012]    reshaping the uneven surface for producing a reshaped surface; and 
         [0013]    disposing a light reflective coating on the reshaped surface, wherein the reshaping step can be a heating process or a UV curing process for softening the photoresist layer. 
         [0014]    Advantageously, the method further comprises the step of disposing one or more intermediate layers between the substrate and the mask, and/or disposing one or more intermediate layers between the photoresist layer and the mask. 
         [0015]    Advantageously, the method also comprises the step of providing a further mask between the intermediate layers and the photoresist layer, wherein the further mask has light-blocking areas at least partially different from the light-blocking areas in the mask so as to reduce the exposed layer areas. 
         [0016]    Advantageously, the method further comprises the step of disposing one or more different intermediate layers between the photoresist layer and the further mask. 
         [0017]    The second aspect of the present invention is a light reflecting structure in a pixel in a liquid crystal display having a substrate. The light reflecting structure comprises: 
         [0018]    a first mask disposed on the substrate, the first mask having light-blocking areas and non-light blocking areas; 
         [0019]    one or more intermediate layers disposed on the first mask; 
         [0020]    a second mask disposed on the intermediate layers, wherein the second mask has further light blocking areas and further non-light blocking areas; 
         [0021]    a photoresist layer disposed on the second mask; wherein the further light-blocking areas are at least partially different from the light blocking areas and the further non-light blocking areas are partially overlapped with the non-light blocking areas so as to allow a light beam to expose at least part of the photoresist layer through the first and second masks in an exposing process; and 
         [0022]    a reflective coating disposed on the photoresist layer. 
         [0023]    Advantageous, the masks and the intermediate layers are some of the layers for producing the gate lines, the common electrodes and the transistors in the liquid crystal display. For example, each of the first and second masks is made of a metal layer, one or more of the intermediate layers comprises a dielectric layer, an amorphous silicon layer or a passivation layer. 
         [0024]    The third aspect of the present invention is a liquid crystal display panel comprising two substrates and a liquid crystal layer between the substrates to form a plurality of pixels, wherein at least some pixels comprise the light reflecting structure as described above. The liquid crystal display panel can be a reflective LCD panel or a transflective LCD panel. 
         [0025]    The present invention will become apparent upon reading the description taken in conjunction with  FIGS. 4   a  to  13 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0026]      FIG. 1  is a schematic representation showing a typical LCD display. 
           [0027]      FIG. 2  is a plane view showing the pixel structure of a conventional transflective color LCD display. 
           [0028]      FIG. 3   a  is a cross sectional view showing the reflection and transmission of light beams in the pixel as shown in  FIG. 2 . 
           [0029]      FIG. 3   b  is a cross sectional view showing the reflection and transmission of light beams in another prior art transflective display. 
           [0030]      FIGS. 4   a  to  4   c  illustrate the general method of producing a reflective layer, according to the present invention. 
           [0031]      FIGS. 5   a  to  5   g  illustrate the steps in making the reflective layer on a substrate, according to one embodiment of the present invention. 
           [0032]      FIGS. 6   a  to  6   g  illustrate the steps in making the reflective layer on a substrate, according to another embodiment of the present invention. 
           [0033]      FIGS. 7   a  to  7   g  illustrate the steps in making the reflective layer on a substrate, according to a different embodiment of the present invention. 
           [0034]      FIGS. 8   a  and  8   b  illustrate the result of using two masks in producing the reflective layer. 
           [0035]      FIGS. 9   a  to  9   c  show an example of dual masks for making the reflective layer. 
           [0036]      FIGS. 10   a  to  10   c  show another example of dual masks for making the reflective layer. 
           [0037]      FIG. 11   a  to  11   c  show yet another example of dual masks for making the reflective layer. 
           [0038]      FIG. 12  illustrates an example of using the various layers in a typical LCD panel for producing the basis of the reflective layer, according to the present invention. 
           [0039]      FIG. 13  shows a reflective coating deposited for producing the reflective layer, according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    It is generally preferred that the reflective layer in the reflection area in a transflective or reflective liquid crystal display (LCD) panel has an uneven surface such as the reflective layer  52  shown in  FIGS. 3   a  and  3   b . The present invention provides a method in making such a reflective layer. As shown in  FIG. 4   a , the reflective layer is formed from a plurality of discrete bumps, or rod-like objects  60 . The rod-like objects are partially softened in a re-flow process so that they join with each other to become a single layer  70  having a wavy surface as shown in  FIG. 4   b . The surface is then coated with a reflective material to form a reflective layer  62 , as shown in  FIG. 4   c . In order to form the single layer  70 , the rod-like objects  60  must behave like a viscid fluid during the re-flow process and become solidified after the process. Furthermore, the rod-like objects should be simple to make. According to the present invention, the rod-like objects  60  are made of a photoresist material which can be softened in a heat treatment process or a UV curing process. After the single layer  70  has been formed, a layer of metal such as Al or Ag is coated to form the reflective layer  62 . 
         [0041]    In one embodiment of the present invention, the rod-like objects  60  are fabricated in a number of photolithography and etching processes (PEPs) on a substantially transparent substrate. As shown in  FIG. 5   a , a mask  90  is produced on a substrate  100 . The mask  90  has opaque areas  91  to partially block a light beam  100  in a backside exposure process ( FIG. 5   d ). In an optional step, one or more intermediate layers  80  are disposed on top of the mask  90 , as shown in  FIG. 5   b . A layer of photoresist  82 , such as a positive-type photoresist material, is provided on top of the optional layers  80 , as shown in  FIG. 5   c . A backside exposure procedure using a light beam  110  is carried out as shown in  FIG. 5   d . As part of the light beam is allowed to transmit through the intermediate layers  80  and the non-blocking areas on the mask  90 , it interacts with part of the photoresist layer. After the partially exposed photoresist layer is developed, the exposed part is removed and the remaining photoresist layer has a plurality of discrete bumps or rod-like objects  60 , as shown in  FIG. 5   e . The rod-like objects are softened so that they join each other to form a single layer  70 , as shown in  FIG. 5   f . Depending on the photoresist material, the rod-like objects  60  can be softened in a heat treatment process or a UV curing process, for example. The surface of the single layer  70  is then coated with a reflective layer  62 , as shown in  FIG. 5   g.    
         [0042]      FIGS. 6   a  to  6   g  show another embodiment of the present invention in which the order of disposing the mask  90  and the intermediate layers  80  is reversed. As shown in  FIG. 6   a , one or more intermediate layers  80  are disposed on a substrate  100 . A mask  90  is disposed on top of the intermediate layers  80 . The mask  90  has opaque areas  91  to partially block a light beam  100  in a backside exposure process ( FIG. 6   d ). A layer of photoresist  82 , such as a positive-type photoresist material, is provided on top of the optional layers  80 , as shown in  FIG. 6   c . A backside exposure using a light beam  110  is carried out as shown in  FIG. 6   d . As part of the light beam is allowed to transmit through the intermediate layers  80  and the non-blocking areas on the mask  90 , it interacts with part of the photoresist layer. After the partially exposed photoresist layer is developed, the exposed part is removed and the remaining photoresist layer has a plurality of discrete bumps or rod-like objects  60 , as shown in  FIG. 6   e . The rod-like objects are softened so that they join each other to form a single layer  70 , as shown in  FIG. 6   f . Depending on the photoresist material, the rod-like objects  60  can be softened in a heat treatment process or a UV curing process, for example. The surface of the single layer  70  is then coated with a reflective layer  62 , as shown in  FIG. 6   g.    
         [0043]    In a different embodiment, two masks are used in the photoresist exposure process as shown in  FIGS. 7   a  to  7   g . As shown in  FIG. 7   a , a mask  92  is produced on a substrate  100 . The mask  92  has opaque areas  93  to partially block a light beam  100  in a backside exposure process ( FIG. 7   d ). In an optional step, one or more intermediate layers  80  are disposed on top of the mask  92 , as shown in  FIG. 7   b   1 . In an additional step, a second mask  96  is disposed on top of the optional intermediate layers  80 , as shown in  FIG. 7   b   2 . The mask  96  also has opaque areas  97  to partially block the light beam  110 . A layer of photoresist  82 , such as a positive-type photoresist material, is provided on top of the second mask, as shown in  FIG. 7   c . The opaque areas  97  areas and the opaque areas  93  have some non-overlapping sections, but they still have non-blocking areas to allow part of the light beam  110  to reach the photoresist layer. A backside exposure using a light beam  110  is carried out as shown in  FIG. 7   d . As part of the light beam is allowed to transmit through both the masks  92  and  96 , it interacts with part of the photoresist layer. After the partially exposed photoresist layer is developed, the exposed part is removed and the remaining photoresist layer has a plurality of discrete bumps or rod-like objects  60 , as shown in  FIG. 7   e . The rod-like objects are softened so that they join each other to form a single layer  70 , as shown in  FIG. 7   f . Depending on the photoresist material, the rod-like objects  60  can be softened in a heat treatment process or a UV curing process, for example. The surface of the single layer  70  is then coated with a reflective layer  62 , as shown in  FIG. 7   g.    
         [0044]    As mentioned above, the opaque areas  97  areas on the mask  92  and the opaque areas  93  on the mask  92  have some non-overlapping sections, but they still have non-blocking areas to allow part of the backside exposure light beam to transmit through the masks. As shown in  FIG. 8   a , the mask  92  has opaque or light-blocking areas  93  and non-blocking areas  94 . Likewise, the mask  96  has opaque or light-blocking areas  97  and non-blocking areas  98 . The masks  92  and  96  are designed and arranged such that the non-blocking areas  94  and the non-blocking areas  96  have overlapping areas so as to allow part of the light beam  110  to transmit through the masks. As such, the masks  92  and  96 , together, act like a composite mask  190  having non-blocking areas  194 . The non-blocking areas  194  are smaller than either the non-blocking areas  94  or the non-blocking areas  98 . 
         [0045]      FIGS. 9   a  to  9   c  show an example of using two shifted mask patterns to produce a composite mask having reduced non-blocking areas. As shown in  FIGS. 9   a  and  9   b , the masks  92  and  96  are similar except that the non-blocking areas are slightly shifted from one mask to another. When the masks  92  and  96  are used together for partially blocking the back-side exposure light beam, the resulting non-blocking areas  194  are reduced, as shown in the composite mask  190  in  FIG. 9   c.    
         [0046]      FIGS. 10   a  to  10   c  show another example of using two masks to reduce the non-blocking areas. As shown in  FIGS. 10   a  and  10   b , the mask  92  and the mask  96  have different mask patterns. When the mask  92  and mask  96  are used together for partially blocking the backside exposure light beam, the blocking areas  97  on the mask  96  overlap with the non-blocking areas  94  on the mask  92 . As such, the resulting non-blocking areas  194 ′ are reduced, as shown in the composite mask  190 ′ in  FIG. 10   c.    
         [0047]      FIGS. 11   a  to  11   c  show yet another example of using two masks to make the basis of the reflective layer. As shown in  FIG. 11   a  and  FIG. 11   b , the masks  92  and the mask  96  are similar except that the light-blocking patterns  93  and  97  are slightly shifted from one mask to another. When the masks  92  and  96  are used together for partially blocking the back-side exposure light beam, the resulting non-blocking areas  194 ″ are reduced to crevices and holes, as shown in the composite mask  190 ″ in  FIG. 11   c.    
         [0048]    In the fabrication of an LCD panel, many of the layers on the rear substrate can serve as the masks  90 ,  92 ,  96  and the intermediate layers  80  for making the reflective layer, according to the present invention.  FIG. 12  shows an example of using the generally available layers disposed on the substrate  100  as the masks and the intermediate layers in a transflective LCD panel. As shown in  FIG. 12 , the metal layer for producing the gate line  102 , reflective pattern  202  and common electrode (not shown) can also be used to provide the mask  92  of  FIG. 7 . The dielectric layer  104 , the amorphous silicon (a-Si) layer  106 ,  206  and the doped amorphous silicon (N+ a-Si) layer  108 ,  208  can also be used to provide the intermediate layers  80 . The source-drain metal layer  110 ,  112 ,  210  can be also used to provide the mask  96 . As shown in  FIG. 12 , an indium Tin oxide (ITO) layer  114  and a passivation layer  116  made of silicon oxide or silicon nitride may also present in the various layers disposed on the rear substrate  100 . Because these layers are substantially transparent, they do not significantly affect the partial exposure of the photoresist layer to the backside exposure light beam. Thus, after the photoresist layer is exposed through the metal layer  102 ,  110 ,  112 ,  202 ,  210  and developed, the remaining photoresist layer  118 ,  218  has a number of discrete portions, substantially aligned to the underlying metal layer  102 ,  110 ,  112 ,  202 ,  210 . After being softened and reshaped by a heat treating process or a UV process, the width of the remaining photoresist portions  118   a ,  218   b  would increase. In the process of making a transflective type liquid crystal panel (see  FIGS. 3   a  and  3   b ), the reshaped photoresist layer  118   a ,  218   b  can be used as a mask for etching away part of the passivation layer  116  to leave the remaining passivation portions  116   a ,  216   b  in order to expose part of the ITO layer in transmission area  300 .  FIG. 13  shows a reflective coating, such as Al and Ag, deposited and patterned on the reshaped photoresist  118   a ,  218   b  to form a reflective layer  120  in the reflection area (including a portion of the reflective layer  220   b  in the bump reflection area) of a transflective LCD panel. The exposed ITO area can be used as part of the transmission area  300  in a transflective LCD panel. 
         [0049]    It should be noted that the present invention has been disclosed as using one or two masks for masking the photoresist layer in the back-side exposure process. Additional masks can also be used. Furthermore, the exposed and developed photoresist layer is softened by a heat treating process or a UV curing process for reshaping the surface. A different process may also be used to reshape the surface. 
         [0050]    Thus, although the present invention has been described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.