Abstract:
By employing an ultra-micro scattering layer with a top surface in a nano-scale roughness resulted from the crystallization or the property of the material within the ultra-micro scattering layer in a pixel for a fringe field switching liquid crystal display, the mask steps to manufacture the liquid crystal display and the cost therefore are reduced. The nano-scale roughness of the top surface on the ultra-micro scattering layer results in larger scattering angle and smooth distribution for the scattering effect. Accordingly, the reflectivity will not vary violently with the viewing angle, and excellent anti-glare effect is obtained also.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a fringe field switching (FFS) liquid crystal display (LCD) and more particularly, to a pixel for an FFS-LCD with a nano-scale rough surface thereof and without more mask steps to manufacture therefore.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a conventional FFS-LCD, the electrode is made of ITO and in transmissive manner for the modulated light to pass therethrough, and on the other hand, the typical reflective twisted nematic (RTN) TFT-LCD employs metal to implement the reflector thereof for the light to be reflected thereby. When the reflector for an LCD is made of metal, the reflective surface is so smooth that mirror-like reflection is occurred for the light reflected by that reflector, and thus the viewing angle of the display is limited. To enhance the scattering effect to the light, an organic layer such as resin is introduced under the reflector so as to result in roughness on the reflective surface. However, to introduce the organic layer requires more mask steps, and thus the total mask steps to manufacture an LCD need about 8˜10 masks, whereby increasing the manufacturing cost. Moreover, organic material has bad thermal endurability, which is up to only around 250° C., and the rough surface formed thereof has great height difference in the range of 0.5-1.5 μm, which produces too large optical-path difference Δnd, and thereby lower efficiency of reflecting light from ideally 100% to between 60%˜85%.  
         [0003]     Therefore, it is desired an FFS-LCD with a nano-scale rough surface thereof and without more mask steps to manufacture therefore.  
       SUMMARY OF THE INVENTION  
       [0004]     An object of the present invention is to provide a pixel for an FFS-LCD with a nano-scale rough surface thereof.  
         [0005]     Another object of the present invention is to provide a pixel for an FFS-LCD with reduced mask steps to manufacture therefore.  
         [0006]     In a pixel for an FFS-LCD, according to the present invention, on a substrate an ultra-micro scattering layer with a top surface in a nano-scale roughness resulted from the crystallization or the property of the material within the ultra-micro scattering layer is formed, and a reflective layer is then formed on the ultra-micro scattering layer to be conformal to the top surface, so as to obtain a reflective surface in a nano-scale roughness thereon. As a result, no additional mask steps are required for the reflective surface to have scattering effect, thereby reducing the manufacturing cost. Moreover, the nano-scale roughness of the reflective surface improves the efficiency of reflecting light because of the reduced optical-path difference And thereof and larger scattering angle and smooth distribution for the scattering effect. Accordingly, the reflectivity of the LCD will not vary violently with the viewing angle, and excellent anti-glare effect is obtained additionally. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]     These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:  
         [0008]      FIG. 1  shows a schematic diagram of the cross-sectional view of a pixel for a reflective LCD according to the present invention;  
         [0009]      FIG. 2  shows a schematic diagram of the top view of an embodiment electrode for the pixel shown in  FIG. 1 ;  
         [0010]      FIG. 3  shows a schematic diagram of the top view of another embodiment electrode for the pixel shown in  FIG. 1 ;  
         [0011]      FIG. 4  shows a schematic diagram of the cross-sectional view of first embodiment pixel for a transflective LCD according to the present invention;  
         [0012]      FIG. 5  shows a schematic diagram of the cross-sectional view of second embodiment pixel for a transflective LCD according to the present invention;  
         [0013]      FIG. 6  shows a schematic diagram of the cross-sectional view of third embodiment pixel for a transflective LCD according to the present invention; and  
         [0014]      FIG. 7  shows a schematic diagram of the cross-sectional view of a thin-film transistor implemented with CMOS for an LCD.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]      FIG. 1  shows a schematic diagram of the cross-sectional view of a pixel  100  for a reflective LCD according to the present invention, in which a thin-film transistor  102  is formed on a substrate  104 , an ultra-micro scattering layer including a transparent conductive layer  106  and an insulator layer  108  is also formed on the substrate  104 . The transparent conductive layer  106  can be formed of ITO or IZO, and the insulator layer  108  is covered over the transparent conductive layer  106 . A metal layer  110  is covered over the insulator layer  108 , which is formed with the same metal layer of manufacturing the source/drain of the thin-film transistor  102 , and has a high reflectivity. A passivation layer  112  is further covered over the thin-film transistor  102  and the metal layer  110 . A reflective layer is formed with several high reflective metal stripes  114  on the passivation layer  112 , and each of the metal stripes  114  can be bent. An optical stack  116  is spaced from the reflective layer  114 , and a layer of liquid crystal  116  with a horizontal rubbing direction between the reflective layer  114  and the optical stack  116 . The optical stack  116  includes a color filter  120  and a polarizer  124  on the color filter  120 , and a black matrix  126  formed of black resin is arranged at the front end of the color filter  120 , which structure has no ITO thereof. The insulator layer  108  is made of for example silicon nitride, silicon oxide, and silicon oxide nitride.  
         [0016]     The insulator layer  108  of the pixel  100  shown in  FIG. 1  is formed by physical or chemical vapor depositions. When the insulator layer  108  is formed on the transparent conductive layer  106 , due to the property of the material to form the insulator layer  108 , its top surface will become of a nano-scale roughness simultaneously, by which the metal layer  110  formed afterwards on the insulator layer  108  will obtain a top surface in a nano-scale roughness because of its being conformal to the nano-scale rough surface of the insulator layer  108 . Likewise, the passivation layer  112  is conformal to the nano-scale rough surface of the metal layer  110  when it is deposited and thus has a top surface in a nano-scale roughness. The metal stripes  114  are also conformal to the nano-scale rough surface of the passivation layer  112 , so as to have top surface in a nano-scale roughness to enhance scattering effect without introducing additional mask steps. Obviously, the manufacturing cost for the LCD is reduced eventually.  
         [0017]     The variation of the top surface in a nano-scale roughness within the LCD according to the present invention is ranged from 1 to 500 nm, and whose variation pitch is between 10 to 1500 nm, much smaller than that of conventional reflector typically of 5 to 20 μm. As a result, the scattering angle becomes wider and more uniform, and the variation of the optical-path difference And is ranged between 0.1 and 0.5 μm, which further improves the efficiency of reflecting light. Alternatively, the ultra-micro scattering layer can be obtained by the formation of a seed layer in combination with the insulator layer  108  with crystallization process.  
         [0018]     As shown in  FIG. 1 , the metal strips  114  have a gap L between each two of them, and each of the metal stripes  114  has width W and thickness H. The gap L and width W each ranges from 0.3 to 15 μm, and the thickness H is between 0.01 to 2 μm. The designated d 1  and d 2  are the average cell gaps from the optical stack  116  to the reflective layer  114  and the passivation layer  112 , respectively, where d 2  ranges from 3 to 4.8 μm, and the ratio of d 1  to d 2  is about 0.45 to 1. The passivation layer  112  includes for example silicon nitride, silicon oxide, or silicon oxide nitride, and whose thickness is about 0.15 to 3 μm. The metal layer  110  can be made of silver, aluminum or any alloy of high reflectivity. The metal layer  110  can also be of partially transmissive metal. Since the passivation layer  112  is sandwiched between the metal stripes  114  and the metal layer  110 , a storage capacitor is obtained, and no extra design for storage capacitor is required, thereby keeping the aspect ratio of the pixel  100  at high.  
         [0019]     Referring to  FIG. 1 , when a voltage is applied to the pixel  100 , a fringe field  130  is generated between the metal layer  110  and the metal strips  114  to twist the liquid crystal molecules  128  in the layer  118 .  FIG. 2  shows a schematic diagram of the top view of an embodiment electrode for the pixel shown in  FIG. 1 . The direction of the metal strips  114  has an angle φ with the rubbing direction  134  of the liquid crystal molecules  128 . If negative liquid crystal is employed for the layer  118 , the angle φ is preferably ranged from 3 to 30 degrees. Contrarily, if positive liquid crystal is employed for the layer  118 , the angle φ is preferably ranged between 60 and 85 degrees. The metal stripes  114  can be bent, as shown in  FIG. 3 ., with a tilting angle of 3 to 30 degrees.  
         [0020]     Negative liquid crystal is preferred for the layer  118  within the pixel  100 , with dielectric constant Δε of −2.5 to −7 and birefringence Δn of 0.027 to 0.11.  
         [0021]      FIG. 4  shows a schematic diagram of the cross-sectional view of first embodiment pixel  200  for a transflective LCD according to the present invention, which is similar to the pixel  100  shown in  FIG. 1 , and comprises a thin-film transistor  102  on a substrate  104 , a transparent conductive layer  106  with an insulator layer  108  and a passivation layer  112  thereon, a reflective layer including several metal stripes  114 , and a layer  118  of liquid crystal molecules  128  with a horizontal rubbing direction sandwiched between the reflective layer  114  and an optical stack  116  including a color filter  120  and a polarizer  124 . However, the pixel  200  employs a transparent conductive layer  202  to replace the metal layer  110  of the pixel  100  shown in  FIG. 1 . Likewise, when the insulator layer  108  is formed on the transparent conductive layer  106 , due to the property of the material to form the insulator layer  108 , its top surface will become of a nano-scale roughness simultaneously, and by which the transparent conductive layer  202  formed on the insulator layer  108  will obtain a top surface in a nano-scale roughness because of its being conformal to the nano-scale rough surface of the insulator layer  108 . Since the passivation layer  112  is conformal to the nano-scale rough surface of the transparent conductive layer  202  when it is deposited, it thus has a top surface in a nano-scale roughness. The metal stripes  114  are also conformal to the nano-scale rough surface of the passivation layer  112 , so as to have top surface in a nano-scale roughness to enhance scattering effect without introducing additional mask steps.  
         [0022]     Likewise, the variation of the top surface in a nano-scale roughness within the LCD in this embodiment is ranged from 1 to 500 nm, and whose variation pitch is between 10 to 1500 nm. The variation of the optical-path difference Δnd is ranged between 0.1 and 0.5 μm. The metal strips  114  have a gap L between each two of them and width W ranged from 0.3 to 15 μm, and the thickness H of them is between 0.01 to 2 μm. The passivation layer  112  has a thickness of about 0.15 to 3 μm, and the average cell gap d 2  is in the range of 3 to 4.8 μm. The cell gap ratio of d 1  to d 2  is between 0.45 and 1. When a voltage is applied to the pixel  200 , a fringe field  130  is generated between the transparent conductive layer  202  and the metal stripes  114  to twist the liquid crystal molecules  128  in the layer  118 . The liquid crystal molecules  128  can be positive type or negative type, whereas the latter is preferred.  
         [0023]     Likewise, due to the passivation layer  112  sandwiched between the metal strips  114  and the transparent conductive layer  202 , a storage capacitor is obtained, and thus no more design on the storage capacitor is required, thereby keeping the aspect ratio of the pixel  200  at high.  
         [0024]      FIG. 5  shows a schematic diagram of the cross-sectional view of second embodiment pixel  210  for a transflective LCD according to the present invention, which comprises a thin-film transistor  102  on a substrate  104 , an ultra-micro scattering layer including a transparent conductive layer  106  and an insulator layer  108 , a passivation layer  112 , a reflective layer including several metal stripes  114 , a layer  118  of liquid crystal molecules  128  with a horizontal rubbing direction sandwiched between the reflective layer  114  and an optical stack  116  including a color filter  120  and a polarizer  124 , and a black matrix  126  at the front end of the color filter  120  to shield the thin-film transistor  102 . In the pixel  210 , the thin-film transistor  102  and the ultra-micro scattering layer are arranged on the substrate  104 , and the reflective layer  114  is formed on the ultra-micro scattering layer and is formed of the same metal layer to implement the source/drain of the thin-film transistor  102 . The passivation layer  112  is covered over the thin-film transistor  102 . As in the foregoing embodiments, the insulator layer  108  obtains a top surface in a nano-scale roughness when it is deposited on the transparent conductive layer  106  due to the property of the material to form the insulator layer  108 , and the metal strips  114  is conformal to the insulator layer  108 , so that the metal stripes  114  have a top surface in a nano-scale roughness to enhance scattering effect without introducing additional mask steps.  
         [0025]      FIG. 6  shows a schematic diagram of the cross-sectional view of third embodiment pixel  300  for a transflective LCD according to the present invention, which comprises a thin-film transistor  302  on a substrate  304 , an insulator layer  306  on the substrate  304 , an ultra-micro scattering layer including a transparent conductive layer  308  and an insulator layer  310  with the transparent conductive layer  308  sandwiched between the two insulator layers  306  and  310  and formed of the same metal layer to manufacture the drain  3022  of the thin-film transistor  302 , a reflective layer  312  including several high reflective metal stripes on the insulator layer  310 , an optical stack  314 , and a layer  316  of liquid crystal molecules  128  arranged between the optical stack  314  and the reflective layer  312 . The optical stack  314  includes a color filter  318  and a polarizer  322 , and a black matrix  324  is disposed at the front end of the color filter  318 . The insulator layer  310  is made of for example silicon nitride or silicon oxide.  
         [0026]     Likewise, the insulator layer  310  can be formed by physical or chemical vapor depositions. When the insulator layer  310  is deposited on the transparent conductive layer  308 , its top surface will become of a nano-scale roughness due to the property of the material to form the insulator layer  310 . The metal strips  312  are conformal to the nano-scale rough surface of the insulator layer  310 , it is thus required no extra mask steps for the metal stripes  312  to have a top surface in a nano-scale roughness.  
         [0027]     The thin-film transistors in the foregoing embodiments can be replaced with CMOS transistor, as shown in  FIG. 7 , illustrated by a pixel  400  manufactured by a low-temperature poly-silicon (LTPS), which comprises a CMOS thin-film transistor  402  on a substrate  404 , an insulator layer  406  on the substrate  404 , a transparent conductive layer  408  sandwiched between passivation layers  410  and  412  with the transparent conductive layer  408  made of ITO and the passivation layer  412  to implement an ultra-micro scattering layer, a reflective layer  414  including several metal stripes made of high reflective metal on the passivation layer  412 , an optical stack  416 , and a layer  418  of molecules  128  with a horizontal rubbing direction arranged between the optical stack  416  and the reflective layer  414 . The optical stack  416  includes a color filter  420 , a black matrix  426  and a polarizer  424 .  
         [0028]     The pixel for a reflective or transflective LCD according to the present invention can be applied to TFT-LCD, LTPS LCD, thin-film diode (TFD) LCD, and liquid crystal on silicon (LCoS) display.  
         [0029]     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.