Abstract:
A transmissive liquid crystal display having two driving matrix modes is disclosed. A first insulating layer, a first lower electrode, a second insulating layer, a second lower electrode and a first alignment film are formed subsequently on a lower substrate with a plurality of transistors fabricated thereon, whereas a first upper electrode, a third insulating layer, a second upper electrode and a second alignment film are formed subsequently on an upper substrate with color filters attached thereon. A liquid crystal layer is sandwiched between the first alignment film and the second alignment film. One of the first lower electrode and the second lower electrode is electrically connected to drain areas of transistors.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a transmissive type liquid crystal display (LCD). More particularly, the present invention relates to a transmissive type LCD having two operating matrix modes, active and passive, converged within a panel.  
       BACKGROUND OF THE INVENTION  
       [0002]     Since the explosive growth in wireless communications is a worldwide phenomenon, the next generation of mobile phones, also known as 3G (third generation) or UMTS (Universal Mobile Telecommunication Services), is a technology that allows users to access e-mails, videos and webs via a mobile phone.  
         [0003]     Many companies, such as Motorola and Samsung, have provided 3G mobile phones that possess two displays. These kinds of mobile phones offer people two viewing options. A large interior display is used for standard functions and an exterior one just shows a caller&#39;s ID or, time and date. According to this, the resolution of the interior display is much higher than the exterior one. The interior display with higher resolution is sometimes an active matrix liquid crystal display (AMLCD). The exterior display with less electrical consumption is a passive matrix LCD (PMLCD).  
         [0004]     A liquid crystal (LC) layer of the PMLCD is sandwiched between an upper glass substrate and a lower glass substrate. A first set of electrical lines (electrodes) aligned in a row configuration and a second set of electrical lines aligned in a column configuration are located between the LC layer and the upper glass substrate, and the LC layer and the lower glass substrate, respectively, to form a matrix mode. In the matrix mode, each intersection of the electrical lines aligned in the row configuration and the electrical lines aligned in the column configuration is a pixel. When applying a voltage difference between the row and column electrical lines, alignments of the LC molecules change and the gray scale of the pixel is thus determined.  
         [0005]     AMLCD is similar to the PMLCD. The major difference between the AMLCD and the PMLCD is that the AMLCD further comprises a switching device (e.g. thin film transistor; TFT) at its each pixel so as to provide faster switching rate and more image displays.  
         [0006]     Referring to  FIG. 1 , a simple comparison between the AMLCD and PMLCD is shown. The electrical consumption of PMLCD is much less than that of AMLCD. The resolution and contrast ratio of AMLCD are higher those of AMLCD. In addition, the manufacturability of the AMLCD is much more complex than that of the PMLCD.  
         [0007]     In order to include all the advantages that AMLCD and PMLCD have within a mobile phone but reduce the weight and the thickness of the mobile phone, it is required to integrate the active and the passive matrix modes within one LCD panel.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     Accordingly, an object of the present invention is to provide a transmissive type liquid crystal display with at least two matrix modes converged within a LCD panel.  
         [0009]     Another object of the present invention is to provide a transmissive type liquid crystal display with at least two matrix modes converged within a panel, wherein at least one matrix mode comprises an active matrix mode.  
         [0010]     A transmissive type liquid crystal display comprises a first substrate, a second substrate, a first insulating layer, a first lower electrode, a first upper electrode, a second insulating layer, a third insulating layer, a second lower electrode, a second upper electrode, a first alignment film, a second alignment film and a liquid crystal layer. A plurality of thin film transistors (TFT) are fabricated on the first substrate and a color filter is attached on the second substrate. The first insulating layer is formed on the first substrate to cover the TFTs and to provide insulation and planarization. The first lower electrode is formed on the first insulating layer. The first upper electrode is located on the second substrate. The second insulating layer and the third insulating layer are formed on the first lower electrode and the first upper electrode, respectively. The second lower electrode is located on the second insulating layer, and the second upper electrode is located on the third insulating layer. One of the first lower electrode and the second lower electrode is electrically connected to the TFTs. The first alignment film is formed on the second lower electrode, whereas the second alignment film is fabricated on second upper electrode. The liquid crystal layer is sandwiched between the first and the second alignment films. 
     
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0011]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated and understood by referencing the following detailed description in conjunction with the accompanying drawings, wherein:  
         [0012]      FIG. 1  shows a simple comparison between the AMLCD and PMLCD.  
         [0013]      FIG. 2  is a cross-sectional view of a transmissive type liquid crystal display in accordance with the present invention.  
         [0014]      FIG. 3 (A) is a top plan view, illustrating a configuration of a first upper electrode and a second upper electrode on a second substrate in accordance with the present invention.  
         [0015]      FIG. 3 (B) is a top plan view, illustrating a configuration of a first lower electrode and a second lower electrode on a first substrate in accordance with the present invention.  
         [0016]      FIG. 3 (C) is a cross-sectional view of the transmissive type liquid crystal displaye in accordance with the present invention.  
         [0017]      FIG. 4  is a cross-sectional view of the transmissive type liquid crystal display in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The invention disclosed herein is directed to a transmissive type liquid crystal display (LCD) with at least two matrix modes converged within a liquid crystal display (LCD) panel, wherein one of the two matrix modes is an active matrix mode. When the transmissive type LCD is applied to a portable terminal device, the different demand from users can be satisfied with the switch between different matrix modes. For example, the passive matrix mode is activated to display low resolution images for lowing the electrical consumption. The active matrix mode is activated for displaying high resolution images and satisfying the demand of high resolution and fast switching rate. The embodiments of the present invention are now described in detail below.  
       Embodiment 1  
       [0019]     Referring to  FIG. 2 , the transmissive type LCD  50  comprises a first substrate  52 , an second substrate  54 , a color filter  56 , a first insulating layer  58 , a set of first electrodes  60  with a passive matrix mode, a second insulating layer  64 , a third insulating layer  66 , a set of second electrodes  68  with a active matrix mode, a first alignment film  70 , a second alignment film  72  and a liquid crystal layer  74 . The first electrodes  60  include a first lower electrode  60   a  and a first upper electrode  60   b , while the second electrodes  68  encompass a second lower electrode  68   a  and a second upper electrode  68   b . A plurality of thin film transistors (TFTs; not shown herein) served as electronic switches and a color filter  56  are fabricated on the inner surfaces of the second substrate  54 , and both first and second substrate can be made of glass, plastics or the like. The first insulating layer  58  is located on the first substrate  52  to cover the TFTs and to provide insulation and planarization.  
         [0020]     As shown in  FIG. 2 , the first lower electrode  60   a  is located on the first insulating layer  58  and conductive patterned electrodes inlay within an insulating material. In this embodiment of the present invention, the conductive patterns of the first lower electrode  60   a  are made of indium tin oxide (ITO) with high transparence. The first upper electrode  60   b  is located on the forementioned color filter  56 . Like the first lower electrode  60   a , the first upper electrode  60   b  preferably comprises conductive ITO patterns and inlay within an insulating material. The second insulating layer  64  and the third insulating layer  66  are located on the first lower electrode  60   a  and the first upper electrode  60   b , respectively.  
         [0021]     Still referring back to  FIG. 2 , the second lower electrode  68   a  is located on the second insulating layer  64 , and the second upper electrode  68   b  is located on the third insulating layer  66 . In one preferred embodiment of the present invention, the second lower electrode  68   a  and second upper electrode  68   b  are conductive ITO patterns. The first alignment film  70  and the second alignment film  72  are located on the second lower electrode  68   a  and the second upper electrode  68   b , respectively. The liquid crystal (LC) layer  74  is sandwiched between the first and the second alignment films,  70  and  72 .  
         [0022]     While one of the two sets of the electrodes described above are activated, to contribute to alignments of liquid crystal molecules within the LC layer, a voltage originally applied to the first lower electrode  60   a  is interfered by the second lower electrode  68   a  since the first lower electrode  60   a  and the second lower electrode  68   a  are both comprise conductive materials and the parasitic voltage is thus generated. For example, when applying 5 volts to the first lower electrode  60   a , the second lower electrode  68   a  over the first lower electrode  60   a  is induced to have a parasitic voltage of about 1 volt. Thus, the displaying image triggered by the first lower electrode  60   a  will have undesirable interference due to the parasitic voltage.  
         [0023]     In order to address the problem, dispositions of the first lower electrode  60   a  and the second lower electrode  68   a  are staggered in a preferred embodiment of the present invention.  
         [0024]      FIG. 3 (A) is a top plan view illustrating a configuration of the first upper electrode  60   b  and the second upper electrode  68   b  on the second substrate  54 .  
         [0025]      FIG. 3 (C) shows a top plan view illustrating a configuration of the first lower electrode  60   a , the second lower electrode  68   a , a plurality of scan lines  71  and data lines  73  on the first substrate  52 .  FIG. 3 (C) is a cross-sectional view of an LCD provided by the present invention when assembling layers shown in  FIG. 3 (A) with layers shown in  FIG. 3 (B) (section P⇄P′).  
         [0026]     As shown in  FIG. 3 (B), the first lower electrode  60   a  and the second lower electrode  68   a  located over the first substrate  52  are staggered to prevent the undesired electric interference occurred between two conductive layers.  
         [0027]     Referring to  FIG. 3 (A), the first upper electrode  60   b  is a column electrode which comprises a plurality of patterns aligned in column direction. The first lower electrode  60   a  shown in  FIG. 3 (B) is a row electrode includes plural patterns aligned in row direction. This configuration forms a matrix mode. When applying two respective voltages to the column electrode and the row electrode, aligning state of the liquid crystal molecules within the LC layer are changed by a potential difference produced at an intersection between the row and column electrodes (i.e. the intersection is so-called pixel). As shown in the figure, the second lower electrode  68   a  is electrically connected to drains of the TFTs. Sources and gates of the TFTs are in contact with the data lines  73  and the scan lines  71 , respectively. While the TFTs are turned on, alignments of the liquid crystal molecules are altered by a potential difference in each pixel.  
         [0028]     In another embodiment, a 1 volt of negative voltage is supplied to the second lower electrode  68   a  at the time of applying 5 volts of positive voltage to the first lower electrode  60   a  for neutralizing 1 volt of positive parasitic voltage and preventing the generation of undesired electric interference. By this way, the resolution of the image displayed on the LCD is improved.  
         [0029]     The object of the present invention is to integrate at least two matrix modes within an LCD panel. However, modifications can be made as illustrated below.  
       Embodiment 2  
       [0030]     The difference between Embodiment 2 and Embodiment 1 is that only one of the first upper electrode  60   b  and second upper electrode  68   b  is located on the second substrate  54  to serve as a common electrode for both of the first lower electrode  60   a  and second lower electrode  68   a . When applying two respective voltages to the first lower electrode  60   a  and the common electrode, the first lower electrode  60   a  serves as the row electrode and the common electrode serves as the column electrode. When the second lower electrode  68   a  is supplied with a voltage and the common electrode is electrically connected to a reference voltage, a potential difference between the common electrode and the second lower electrode  68   a  triggers alignments of liquid crystal molecules.  
       Embodiment 3  
       [0031]     Referring to  FIG. 4 , the differences between Embodiment 3 and Embodiment 1 are that locations of the first lower electrode  60   a  and the second lower electrode  68   a  are interchanged. In addition, the locations of the first upper electrode  60   b  and the second upper electrode  68   b  are interchanged.  
         [0032]     Since two sets of electrodes of the present invention are integrated within a LCD panel, the size and the weight of the portable terminal device can be reduced. When the portable terminal device is standby, the passive matrix mode is activated optionally to save electrical consumption; while the portable terminal device is in use, the active matrix mode is activated optionally to obtain a higher resolution. In addition, two sets of electrodes of the present invention are converged within one panel, so that the cost and complexity of the manufacturability can be reduced.  
         [0033]     Various other modifications will be apparent to and can be readily mad by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.