Patent Publication Number: US-2019179190-A1

Title: Flexible liquid crystal display

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201711314917.9, filed on Dec. 12, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     1. Field of the Invention 
     This disclosure is related to liquid crystal displays, especially related to flexible liquid crystal displays. 
     2. Description of Related Art 
     With the widespread use of portable displays, the development of flexible displays has become more active. Currently, flexible displays are mainly organic light-emitting diode (OLED) displays. However, compared with the liquid crystal displays (LCDs), manufacturing costs of OLED displays are high and moisture resistance thereof is poor, so various manufacturers are still committed to the development of flexible LCDs. 
     At present, most of the substrates used in LCD are glass-based. To meet flexible requirements, the substrate needs to be thinned to have a substantial degree of flexibility. However, the thinned substrate may be damaged due to the insufficient strength of the substrate during manufacturing, such as handling, cleaning, or the like. 
     Therefore, how to improve the substrate strength of a flexible LCD is one of the most pressing issues to be solved by current researchers. 
     SUMMARY 
     A flexible liquid crystal display (LCD) is provided. The substrate of the flexible LCD has good strength and can block the laser from irradiating to the active component layer, thereby preventing the active components or circuits in the active component layer from being damage. 
     According to an embodiment of this invention, the flexible LCD comprises a first substrate, a second substrate, and a liquid crystal layer. The first substrate comprises a first flexible substrate, a second flexible substrate, a reflective layer, and an active component layer. The second flexible substrate is disposed on the first flexible substrate. The reflective layer is disposed between the first flexible substrate and the second flexible substrate. The active component layer is disposed on the second flexible substrate. The second substrate is disposed on the first substrate. The liquid crystal layer is disposed between the first substrate and the second substrate. 
     According to another embodiment of this invention, the first substrate further comprises a first barrier layer disposed between the second flexible substrate and the active component layer. 
     According to yet another embodiment of this invention, the second substrate comprises a third flexible substrate and a color filter pattern. The third flexible substrate is disposed on the liquid crystal layer. The color filter pattern is disposed between the third flexible substrate and the liquid crystal layer. 
     According to yet another embodiment of this invention, the second substrate further comprises a second barrier layer disposed between the third flexible substrate and the color filter pattern. 
     According to yet another embodiment of this invention, a material of the first barrier layer or the second barrier layer comprises silicon oxide, silicon nitride, or a combination thereof. 
     According to yet another embodiment of this invention, a material of the reflective layer comprises a metal, a metal compound, or a combination thereof. 
     According to yet another embodiment of this invention, the liquid crystal layer comprises polymer dispersed liquid crystal. 
     According to yet another embodiment of this invention, the flexible LCD further comprises a first polarizer and a second polarizer. The first polarizer is disposed on a surface of the first substrate away from the liquid crystal layer. The second polarizer is disposed on a surface of the second substrate away from the liquid crystal layer. 
     According to yet another embodiment of this invention, the active component layer comprises thin film transistors. 
     According to yet another embodiment of this invention, the flexible LCD is a reflective LCD. 
     In light of the foregoing, in the flexible LCD according to the above embodiments, the first substrate comprises the first flexible substrate, the second flexible substrate, and the reflective layer disposed therebetween to form a sandwich structure, thereby the strength of the first substrate can be increased. In addition, since the reflective layer is disposed between the first and second flexible substrates, when a laser is used to perform a release process to separate the carrier and the first flexible substrate, the laser can be blocked from irradiating to the active component layer, thereby preventing the active components or circuits in the active component layer from being damage. 
     The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are used to further understand this invention, and the drawings are incorporated herein to form a part of the specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic cross-sectional view showing a flexible LCD according to an embodiment of this invention. 
         FIG. 2  is a schematic cross-sectional view showing a flexible LCD in a release process according to an embodiment of this invention. 
         FIG. 3  is a schematic cross-sectional view showing a flexible LCD according to another embodiment of this invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the invention, 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. However, this invention may be practiced in many different forms and should not be construed to be limited to the embodiments. 
     The relative thicknesses and locations of layers, regions, and/or structures may be reduced or enlarged for clarity. In addition, in the drawings, similar or identical elements are used to represent similar or same elements or features. Therefore, the same reference numerals in the drawings denote the same elements and will not be redundantly described. 
       FIG. 1  is a schematic cross-sectional view showing a flexible LCD according to an embodiment of this invention.  FIG. 2  is a schematic cross-sectional view showing a flexible LCD in a release process according to an embodiment of this invention.  FIG. 3  is a schematic cross-sectional view showing a flexible LCD according to another embodiment of this invention. 
     Please refer to  FIG. 1 . A flexible LCD  100  comprises a first substrate  102 , a second substrate  104 , and a liquid crystal layer  106 . In some embodiment, the flexible LCD  100  may be a reflective LCD, a transmissive LCD, or a trans-reflective LCD. 
     The first substrate  102  comprises a first flexible substrate  108 , a second flexible substrate  110 , a reflective layer  112 , and an active component layer  114 . In some embodiments, the first substrate  102  may be an active array substrate having switching elements, such as thin film transistors, for controlling the electro-optical property of the liquid crystal, scan lines for providing signals to the gates of the switching elements, data lines for providing signals to the drains of the switching elements, and common lines for connecting the drains and the pixel electrodes of the switching elements. 
     In this embodiment, a material of the first flexible substrate  108  may be polyimide (PI), but this invention is not limited thereto. In some other embodiments, the material of the first flexible substrate  108  may also be selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), or poly(ether sulfones) (PES). Therefore, even if the thickness of the first flexible substrate  108  is thin, such as 10 μm, it does not cause damage during manufacturing, such as handling or cleaning. 
     The second flexible substrate  110  is disposed on the first flexible substrate  108 . In this embodiment, a material of the second flexible substrate may be polyimide, but this invention is not limited thereto. In some other embodiments, the second flexible substrate  110  may also be selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), or poly(ether sulfones) (PES). In some embodiments, the material of the second flexible substrate  110  may be the same as the first flexible substrate  108 . The thickness of the second flexible substrate  110  may be the same as or different from the thickness of the first flexible substrate  108 . In some embodiments, the thickness of the second flexible substrate  110  may be 10 μm. 
     The reflective layer  112  may be disposed between the first flexible substrate  108  and the second flexible substrate  110  to form a sandwich structure, thereby the strength of the first substrate  102  can be increased. Moreover, as shown in  FIG. 2 , when a laser L is used to perform a release process to separate the carrier  116  for carrying the first substrate  102  and the first flexible substrate  108 , the reflective layer  112  can block the laser L from irradiating to the active component layer  114 , thereby preventing the active components or circuits in the active component layer  114  from being damage. In some embodiments, a material of the reflective layer  112  may be a metal, a metal compound, or a combination thereof to further increase the strength of the first substrate  102  and the effect of protecting the active component layer  114  by increasing the blocking efficiency of the laser. For example, the material of the reflective layer  114  may be Au, Ag, Al, Mo, Ta, a metal compound of these metals, or any combinations thereof. In some other embodiments, the reflective layer  112  may also be a material with light-reflecting property. In some embodiments, the reflective layer  112  may be used to reflect environmental light. Therefore, no backlight modules are needed (i.e. a reflective LCD), so that the flexible LCD  100  has no problem of light leakage during bending. The thickness of the reflective layer  112  is 2 μm, for example. In some embodiments, the two opposite sides of the reflective layer  112  are respectively in direct contact with the first flexible substrate  108  and the second flexible substrate  110 . 
     The active component layer  114  is disposed on the second flexible substrate  110 . The component layer  114  may comprise thin film transistors (not shown), scan lines (not shown), data lines (not shown), common lines (not shown), common electrodes (not shown), and pixel electrodes (not shown). The scan lines and the data lines are interlaced and connected to the corresponding thin film transistors, respectively. The pixel electrodes are also connected to the corresponding thin film transistors. The common electrodes and the pixel electrodes may belong to the same layer or different layers. For example, when the flexible LCD  100  is an in-plane switching (IPS) LCD, the common electrodes and the pixel electrodes may belong to the same layer. When the flexible LCD  100  is a fringe field switching (FFS) LCD, the common electrode and the pixel electrode may belong to different layers. 
     In some embodiments, the first substrate  102  may further comprise a first barrier layer  118  disposed between the second flexible substrate  110  and the active component layer  114 . Therefore, moisture and oxygen can be prevented from entering the active component layer  114  to improve the stability of the flexible LCD  100 . In another aspect, since the first flexible substrate  108  and the second flexible substrate  110  are flexible substrates, and the reflective layer  112  located therebetween also has a considerable degree of flexibility (thinner thickness), the sandwich structure (the first flexible substrate  108 /the reflective layer  112 /the second flexible substrate  110 ) still has flexibility, resulting in a situation where the surface may have insufficient flatness. Based on this, when the first barrier layer  118  is disposed between the second flexible substrate  110  and the active component layer  114 , the first barrier layer  118  may serve as a planarization layer to improve the flatness of the sandwich structure. So that the active component layer  114  on the stacked layer of the sandwich structure has better film-forming property. A material of the first barrier layer  118  may be an inorganic material, such as silicon oxide, silicon nitride, or a combination thereof. 
     The second substrate  104  is disposed on the first substrate  102 . In this embodiment, the second substrate  104  is disposed on the side of the first substrate  102  adjacent to the active component layer  114 . In this embodiment, the second substrate  104  may be a color filter substrate having a color filter pattern thereon, but the present invention is not limited thereto. In other embodiments, the color filter pattern can also be integrated on the first substrate  102 , that is, a technique of integrating a color filter on a thin film transistor array (i.e. color filter on array, abbreviated as COA). In this embodiment, the second substrate  104  comprises a third flexible substrate  120  and a color filter pattern  122 . 
     The third flexible substrate  120  is disposed on the first substrate  102 . In this embodiment, a material of the third flexible substrate  120  may be polyimide, but this invention is not limited thereto. In some other embodiments, the material of the third flexible substrate  120  may also be selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), or poly(ether sulfones) (PES). In some embodiments, the material of the third flexible substrate  120  may be the same as the first flexible substrate  108  or the second flexible substrate  110 . The thickness of third flexible substrate  120  may be the same as or different from the thickness of the first flexible substrate  108  or the second flexible substrate  110 . In some embodiments, the thickness of the third flexible substrate  120  may be 10 μm. 
     The color filter pattern  122  is disposed between the third flexible substrate  120  and the first substrate  102 . The color filter pattern  122  may comprise a plurality of color filters of the same or different colors, which respectively correspond to the sub-pixels of the active component layer  114 . A light shielding structure  124  may further comprise between two adjacent color filters to define a plurality of sub-pixel regions of the third flexible substrate  120 . A material of the light shielding structure  124  may be a black matrix material, such as a metal chrome material or a black resin. 
     In some embodiments, the second substrate  104  may further comprise a second barrier layer  126  disposed between the third flexible substrate  120  and the color filter pattern  122  to block moisture and oxygen from the external environment, thereby enhancing the stability of the flexible LCD  100 . On the other hand, since the third flexible substrate  120  has flexibility, the surface thereof may have insufficient flatness. Based on this, when the second barrier layer  126  is disposed between the third flexible substrate  120  and the color filter pattern  122 . The second barrier layer  126  may also serve as a planarization layer to improve the flatness of the third flexible substrate  120 , so that the color filter pattern  122  formed thereon has better film formability. The material of the second barrier layer  126  may be an inorganic material, such as silicon oxide, silicon nitride, or a combination thereof. A material of the second barrier layer  126  may be the same as or different from the material of the first barrier layer  118 , and this invention is not limited thereto. 
     The liquid crystal layer  106  is disposed between the first substrate  102  and the second substrate  104 . That is, in this embodiment, the third flexible substrate  120  of the second substrate  104  is disposed on the liquid crystal layer  106 , and the color filter pattern  122  is disposed between the third flexible substrate  120  and the liquid crystal layer  106 . In other embodiments, the color filter pattern  122  may also be disposed between the liquid crystal layer  106  and the active component layer  114  (for example, a technology of using COA). In this embodiment, the liquid crystal layer  106  may comprise polymer dispersed liquid crystal (PDLC), so that the liquid crystals in the liquid crystal cells are irregularly arranged when no driving voltage is applied, thereby the light cannot penetrate the liquid crystal layer  106 ; and the liquid crystals in the liquid crystal cells are arranged in a regular pattern when a driving voltage (for example, 5 V) is applied, so that the light can penetrate the liquid crystal layer  106 . Accordingly, the flexible LCD  100  does not need any polarizer, and the second substrate  104  does not need to comprise any alignment structure layer, so that the flexible LCD  100  shows relatively high penetration, and the manufacturing cost of the flexible LCD  100  can be saved. In some embodiments, the polymer dispersed liquid crystal may be prepared by using nematic liquid crystals, a photopolymerizable material, and a photoinitiator. The photopolymerizable material may be a monomer or oligomer of an unsaturated thiol ester, an acrylic acid group-containing monomer or oligomer, or an epoxy group-containing monomer or oligomer, for example, but is not limited thereto. Specifically, a nematic liquid crystal, a photopolymerizable material, and a photoinitiator may be preliminarily mixed and subjected to an ultraviolet ray irradiation treatment to form a plurality of liquid crystal cell droplets. In other embodiments, the liquid crystal layer  106  may also adopt a liquid crystal material in which the liquid crystal molecules are arranged horizontally or vertically when no voltage is applied. However, it is necessary to add a polarizer. For example, as shown in  FIG. 3 , the flexible LCD  100  may further comprise a first polarizer  128  and a second polarizer  130 . The first polarizer  128  is disposed on the surface of the first substrate  102  away from the liquid crystal layer  106 , and the second polarizer is disposed on the surface of the second substrate away from the liquid crystal layer  106 . In addition, when the liquid crystal layer  106  adopts a liquid crystal material in which the liquid crystal molecules are arranged horizontally when no voltage is applied, the transmittance of light is poor. Therefore, a backlight module (not shown) is also required to improve the brightness of the display. In some embodiments, the first substrate  102  and the second substrate  104  are in direct contact with the liquid crystal layer  106 . 
     In light of the foregoing, in the flexible LCD, the first substrate comprises the first flexible substrate, the second flexible substrate, and the reflective layer between the first and the second flexible substrates to form a sandwich structure to increase the strength of the first substrate. In addition, since the reflective layer is disposed between the first and second flexible substrates, when a laser is used to perform a release process to separate the carrier and the first flexible substrate, the laser can be blocked from irradiating to the active component layer to prevent the damage of the active components or circuits of the active component layer. 
     Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present invention, but not for limiting the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions described in the foregoing embodiments may still be modified or replaced by equivalent to some or all of the technical features. These modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments in this invention.