Abstract:
The present invention discloses a transflective liquid crystal display device, including: a liquid crystal panel including: a) a first substrate having a color filter; b) a second substrate spaced apart from the first substrate, having a switching element, a reflective electrode, and a pixel electrode, the reflective electrode having at least one transmitting hole and reflecting ambient light, the transmitting hole transmitting light and being covered by the pixel electrode, the reflective electrode and the pixel electrode being electrically insulated each other; and c) a liquid crystal layer interposed between the upper and lower substrates; and a back light device providing light toward the transmitting hole.

Description:
CROSS REFERENCE 
     This application claims the benefit of Korean Patent Application No. 1999-51143, filed on Nov. 17, 1999, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device and a method of manufacturing the same. 
     2. Description of Related Art 
     Liquid crystal display (LCD) devices are in wide use as display devices capable of being reduced in weight, size and thickness. In general, the LCD device includes upper and lower substrates with a liquid crystal layer interposed therebetween. The upper substrate includes a common electrode and a color filter, and the lower substrate includes a pixel electrode and TFTs. An upper polarizer is arranged on a front surface of the upper substrate, and a lower polarizer is arranged on a bottom surface of the lower substrate. A back light device is arranged under the lower substrate as a light source. 
     The LCD device is divided into a transmissive LCD device and a reflective LCD device. The typical transmissive LCD device displays images using light from the back light device. However, the transmissive LCD device is a non-effective light converter that merely transmits about 3% to about 8% of light from the back light device. In other words, as shown in FIG. 1, the observer gets to see about 7% of light from the back light device. Therefore, the transmissive LCD device requires a back light device having high brightness, leading to high power consumption. 
     In order to achieve a back light device having high brightness, sufficient power must be supplied to the back light device, thereby increaseing battery weight. However, such a back light device cannot be used for a long time. 
     To overcome the problems described above, the reflective LCD device has been introduced. Since the reflective LCD device is possible to use the device for a long time, and it is easy to carry due to its light weight. 
     FIG. 2 is a plan view illustrating a lower array substrate of a conventional reflective LCD device. As shown in FIG. 2, data lines  2  and  4  are arranged in a longitudinal direction, and gate lines  6  and  8  are arranged in a transverse direction perpendicular to the data lines  2  and  4 . A reflective electrode  10  is arranged on a region defined by the gate and data lines. TFTs are arranged at a cross point of the gate and data lines. Each of the TFTs includes a gate electrode  18 , a source electrode  12  and a drain electrode  14 . The gate electrode  18  extends from the gate line  8 , and the source electrode  12  extends from the data line  2 . The drain electrode  14  is spaced apart from the source electrode  12  and contacts the reflective electrode  10  through a contact hole  16 . 
     FIG. 3 is a cross sectional view taken along line III—III of FIG.  2 . As shown in FIG. 2, the gate electrode  18  is formed on a substrate  1 , and a gate insulating layer  20  is formed on the gate electrode  18  and an exposed surface of the substrate  1 . A semiconductor layer  22  is formed on the gate insulating layer  20 . The source and drain electrodes  12  and  14  overlap both end portions of the semiconductor layer  22 . A passivation film  24  is formed over the whole surface of the substrate  1  while covering the source and drain electrodes  12  and  14 . The passivation film  24  has the contact hole  16  on a portion of the drain electrode  14 . The reflective electrode  10  is formed on the passivation film and contacts the drain electrode  14  through the contact hole  16 . The reflective electrode is made of a reflective material having a good reflectance. 
     As described above, since the reflective LCD device uses ambient light other than an internal light source such as a back light device, it can be used for a long time. In other words, the reflective LCD device is driven using light reflected from the reflective electrode  10 . 
     However, ambient light such as natural light and external light does not exist always. In other words, the reflective LCD device can be used during the day or in office where external light exists, but it can not be used during the night or in a dim place. 
     For the foregoing reasons, there is a need for a liquid crystal display device that its weight is light and that power consumption is low and that can be used during both the day and the night. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide a transflective liquid crystal display device that can be used during both the day and the night. 
     In order to achieve the above object, the preferred embodiments of the present invention provide a transflective liquid crystal display device, including: a liquid crystal panel including: a) a first substrate having a color filter; b) a second substrate spaced apart from the first substrate, having a switching element, a reflective electrode, and a pixel electrode, the reflective electrode having at least one transmitting hole and reflecting ambient light, the transmitting hole transmitting light and being covered by the pixel electrode, the reflective electrode and the pixel electrode being electrically insulated from each other; and c) a liquid crystal layer interposed between the upper and lower substrates; and a back light device providing light toward the transmitting hole. 
     The preferred embodiment of the present invention provides a transflective liquid crystal display device, including: a first substrate; a second substrate spaced apart from the first substrate, including: a) a gate electrode formed on the second substrate: b) a first insulating layer formed over the whole surface of the second substrate and covering the gate electrode; c) a semiconductor layer formed on the first insulating layer; d) source and drain electrodes spaced apart from each other and overlapping both end portions of the semiconductor layer; e) a second insulating layer formed over the whole surface of the second substrate and covering the source and drain electrodes; f) a pixel electrode formed on the second insulating layer and contacting the drain electrode; g) a third insulating layer formed ove the whole surface of the second substrate and covering the pixel electrode; and h) a reflective electrode formed on the thrid insulating layer and having at least one transmitting hole, the transmitting hole being covered by the pixel electrode; and a liquid crystal layer interposed between the first and second substrates. 
     The preferred embodiment of the present invention provides a method of manufacturing an array substrate of a transflective liquid crystal display device, the method including: forming a gate electrode on the substrate forming a first insulating layer, over the whole surface of the substrate while covering the gate electrode; forming a semiconductor layer on the first insulating layer; forming source and drain electrodes, the source and drain electrodes being spaced apart from each other and overlapping both end portions of the semiconductor layer; forming a second insulating layer over the whole surface of the substrate while covering the source and drain electrodes; forming a pixel electrode on the second insulating layer, the pixel electrode contacting the drain electrode; forming a third insulating layer over the whole surface of the substrate while covering the pixel electrode; and forming a reflective electrode on the third insulating layer, the reflective electrode having at least one transmitting hole, the transmitting hole being covered by the pixel electrode. 
     The reflective electrode is a made of an opaque metal. The pixel electrode is made of one of ITO and IZO. The first and third insulating layers are made of SiNx or SiO 2 . The second insulating layer is made of BCB (benzocyclobutene). The reflective electrode and the pixel electrode are electrically insulated by an insulating layer. 
     As described herein before, since the transflective LCD device according to the preferred embodiment of the present invention has both the reflective mode and the transmissive mode, it can be used in anytime and it everywhere regardless of a time and a place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which: 
     FIG. 1 is a graph illustrating transmittance after light passes through each layer of a conventional liquid crystal display device; 
     FIG. 2 is a plan view illustrating a lower array substrate of a conventional reflective LCD device; 
     FIG. 3 is a cross sectional view taken along line—of FIG. 2; 
     FIG. 4 is a plan view illustrating a transflective liquid crystal display device according to the preferred embodiment of the present invention; 
     FIGS. 5A to  5 D are cross-sectional views taken along line V—V of FIG. 4, illustrating a process of manufacturing a lower array substrate of the transflective LCD device according to the preferred embodiment of the present invention; 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG. 4; 
     FIG. 7 is an enlarged view of a portion “Z” of FIG. 6; and 
     FIG. 8 is a schematic view illustrating the inventive transflective LCD device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to a preferred embodiment of the present invention, example of which is illustrated in the accompanying drawings. 
     FIG. 4 is a plan view illustrating a transflective liquid crystal display device according to the preferred embodiment of the present invention. As shown in FIG. 4, gate lines  50  are arranged in a transverse direction, and data lines  60  are arranged in a longitudinal direction perpendicular to the gate lines  50 . TFTs are arranged at a cross point of the gate and data lines. Each of the TFTs includes a gate electrode  52 , a source electrode  62  and a drain electrode  64 . The gate electrode  52  extends from the gate line  50 , and the source electrode  62  extends from the data line  60 . The drain electrode  64  is spaced apart from the source electrode  62 . A pixel electrode  70  is arranged on a region defined by the gate and data lines  50  and  60  and contacts the drain electrode  64  through a contact hole  66 . A reflective electrode  68  is arranged to cover the pixel electrode  70 . The reflective electrode  68  includes a transmitting hole  72  located at its central portion. The reflective electrode  68  and the pixel electrode  70  are made of a different material from each other. In other words, the reflective electrode  68  is made of an opaque metal, while the pixel electrode  70  is made of a transparent conductive material. 
     The reflective electrode  68  overlaps a portion of the gate and data lines  50  and  60  in order to improve an aperture ratio. The pixel electrode  70  overlaps a portion of the gate line  50 . Preferably, the transmitting hole  72  has a rectangular shape. According to use of the inventive transflective LCD, the number and size of the transmitting hole  72  and size of the reflective electrode  68  can be adjusted. Therefore, size, number and shape of the transmitting hole  72  are limited by the present invention. 
     At this point, the reflective electrode  68  is electrically independent from the pixel electrode  70 . In other words, an insulating layer (not shown) is interposed between the reflective electrode  68  and the pixel electrode  70 . In a reflective mode using the reflective electrode  68 , the transflective LCD device is driven by electric field excited by the pixel electrode  70 . 
     FIGS. 5A to  5 D are cross-sectional view taken along line V—V of of FIG. 4, illustrating a process of manufacturing a lower array substrate of the transflective LCD device according to the preferred embodiment of the present invention. 
     First, as shown in FIG. 5A, the gate electrode  52  is formed on a substrate  1 . The gate electrode  52  is made of a metal having a high corrosion resistance such as Cr, W or the like and a low resistive aluminum alloy. 
     Next, as shown in FIG. 5B, a gate insulating layer  80  is formed over the whole surface of the substrate  1  while covering the gate electrode  52 . A semiconductor layer  82  is formed on the gate insulating layer  80 . Thereafter, the source and drain electrodes  62  and  64  are formed to overlap both end portions of the semiconductor layer  80 . 
     Subsequently, as shown in FIG. 5C, a passivation film  84  is formed over the whole surface of the substrate  1  while covering the source and drain electrodes  62  and  64 . The passivation film  84  includes the contact hole  66  that exposes a portion of the drain electrode  64 . The passivation film  84  is preferably made of a material that is excellent in light transmittance and moisture resistance, for example, BCB (benzocyclobutene). Then, the pixel electrode  70  is formed on the passivation film  84  and contacts the drain electrode  64  through the contact hole  66 . The pixel electrode  70  is made of a material having a high light transmittance such as ITO (indium tin oxide) and IZO (indium zinc oxide). 
     Finally, as shown in FIG. 5D, an inter-layer insulator  86  is formed over the whole surface of the substrate  1  while covering the pixel electrode  70 . The inter-layer insulator  86  is made of, for example, SiNx. Thereafter, the reflective electrode  68  is formed on the inter-layer insulator  86 . The reflective electrode  68  has a transmitting hole  72 . Therefore, most of important components of the lower array substrate are completed. 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG.  4 . As shown in FIG. 6, the gate insulating layer  80  is formed on the substrate  1 , and the data line  60  is formed on the gate insulating layer  80 . The passivation film  84  is formed over the whole surface of the substrate  1  while covering the data line  60 . The two adjacent pixel electrodes  70  are formed not to overlap the data line  60 . In other words, there is an interval between the data line  60  and the pixel electrode  70 , which are transversely distant from each other. The inter-layer insulator  86  is formed over the whole surface of the substrate  1  while covering the pixel electrode  70 . The reflective electrode  68  is formed on the interlayer insulator  86  to transversely overlap both end portions of the data line  60 . In other words, the reflective electrode  68  overlaps as far as a predetermined distance AL from both end portions of the data line  60 . Preferably, the reflective electrode  68  covers all portions of the pixel electrode  70 . At this point, the reflective electrode  68  and the pixel electrode  70  are electrically not connected with each other by the inter-layer insulator  86 . Further, there is a portion where the reflective electrode  68  and the pixel electrode  70  overlap each other. In other words, the reflective electrode  68  and the pixel electrode  70  do not overlap as a length L. 
     The pixel electrode  70  is electrically connected with the drain electrode  64  and thus can receive electrical signals from the TFT, whereas the reflective electrode  68  is independent from the pixel electrode  70  and therefore can not receive electrical signals. Therefore, in order to apply electrical signals to the reflective electrode  68 , electrical signals applied to the pixel electrode  70  from the TFT, i.e., electric field, are used. 
     FIG. 7 is an enlarged view of a portion “Z” of FIG.  6 . As shown in FIG. 7, a portion of the reflective electrode  68  overlapping the pixel electrode  70  is driven by vertical electric field, and a portion “L” of the reflective electrode  68  not overlapping the pixel electrode  70  is driven by parallel electric field. 
     FIG. 8 is a schematic view illustrating the inventive transflective LCD device. As shown in FIG. 8, the inventive transflective LCD device includes a liquid crystal panel having a back light device  102 . The liquid crystal panel includes upper and lower substrates  106  and  108  with a liquid crystal layer  100  interposed therebetween. The upper substrate  106  includes a color filter  104  and a common electrode (not shown). The lower substrate  108  includes a switching element (not shown), the reflective electrode  68  and the pixel electrode  70 . Even though not shown, the inter-layer insulator is substantially interposed between the reflective electrode  68  and the pixel electrode  70 . The reflective electrode  68  is made of a conductive material having a high reflectance to reflect ambient light  110 , and is substantially an opaque metal. The reflective electrode  68  includes the transmitting hole  72 . The transmitting hole  72  serves to transmit light from the back light device  102 . As described above, the transmitting hole  72  does not have a limitation in location, size, number, and shape. The pixel electrode  70  has an area large enough to cover the transmitting hole  72 . 
     Hereinafter, an operation of the transflective LCD device according to the preferred embodiment of the present invention is explained below in detail. 
     First, when the transflective LCD device is in a reflective mode, the reflective electrode  68  reflects ambient light  110  toward the upper substrate  106 . At this time, electrical signals from the switching element are applied to the reflective electrode  68 , and thus a phase of the liquid crystal layer  100  varies, leading to variation in the amount of reflected light. Reflected light is colored by the color filter  104 , whereby signals applied to the reflective electrode  68  are displayed as images. 
     Alternatively, when the transflective LCD device is in a transmissive mode, light generated from the back light device  102  transmits through a portion of the pixel electrode  70  corresponding to the transmitting hole  72 . At this time, similar to the reflective mode, when electrical signals from the switching element are applied to the pixel electrode  70 , a phase of the liquid crystal layer  100  varies. Light transmitting the liquid crystal layer  100  is colored by the color filter  104 , whereby signals applied to the pixel electrode  70  are displayed as color images. 
     As described herein before, since the transflective LCD device according to the preferred embodiment of the present invention has both a reflective mode and a transmissive mode, it can be used anytime, anywhere, regardless of the time or place. 
     While the invention has been particularly shown and described with reference to first preferred embodiment s thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.