Abstract:
A flexible display panel device includes a plastic substrate with a display region and a peripheral region, a plurality of ribs disposed in the peripheral region and/or the display region, a discontinuous buffer layer disposed on the plastic substrate, and an active matrix component layer on a pixel disposed on the discontinuous buffer layer. During the fabrication of the flexible panel, a plastic substrate is first disposed on a carrier substrate for performing device fabrication. After the panel is finished, the plastic substrate is departed from the carrier substrate to form a flexible panel. Through the integration design of the ribs and discontinuous buffer layer, the flexible panel has preferred warp resistance and low stress, thereby enhancing the reliability and life time of the panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 095150058 filed in Taiwan, R.O.C. on Dec. 29, 2006, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a display panel, and more particularly, to a flexible plastic substrate with preferred warp resistance and low warp displacement formed by a geometrical structure design of the plastic substrate and active matrix component, so as to enhance the reliability of the display panel. 
         [0004]    2. Related Art 
         [0005]    As for portable products, such as notebooks, personal digital assistants (PDAs), cell phones, digital cameras, and E-Books, the weight and space of the panel are mostly considered. Currently, the thickness of a glass substrate is about 0.5 mm; but, the plastic substrate is thinner and flexible, approximately 0.05 mm, and is lighter than the glass substrate, thus the plastic substrate has been a focus of attention as a next generation flexible display. Currently, the developing trends of plastic display process technology include a roll to roll printing process and an existing vacuum process apparatus. The vacuum process method is advantageous of not redesigning the process apparatus, and a glass substrate can be directly used as a carrier substrate (a carrier) of the plastic substrate. However, as the thermal expansion coefficients of the materials of a plastic and a glass substrate or an inorganic thin film transistor (TFT) component are significantly different, the plastic and glass substrates are seriously warped after a high temperature process, which may cause a severe offset in lithography, and thus influence the performance and yield of the inorganic TFT element. 
         [0006]    Furthermore, as the Young&#39;s coefficient (elastic coefficient) and thickness of the plastic substrate is very small and thin, the plastic substrate shows a poor strain-resistance property. When the internal residual stresses are generated during a high temperature process, the plastic substrate may wrap and cannot be subjected to the subsequent processes, and thus influence the device performance. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, how to reduce the stress of the display panel, enhance the strain-resistance property=of the plastic substrate, and maintain certain flexibility have become important issues for flexible display. 
         [0008]    As embodied and broadly described herein, a flexible display panel is provided. The flexible display panel includes a plastic substrate having a display region and a peripheral region, in which the display region is used for displaying images and the peripheral region is used for placing=drive IC chips; a plurality of ribs disposed on the peripheral region of the plastic substrate and/or between the active matrix component; the plastic substrate covered on a carrier substrate and the plurality of ribs; a discontinuous buffer layer disposed on the plastic substrate; and an active matrix component on a pixel disposed on the discontinuous buffer layer. The ribs, used for increasing the structural rigidity of the plastic substrate, are made of a plastic material having a high elastic coefficient and low thermal expansion coefficient. Furthermore, the discontinuous buffer layer can not only block gases and isolate impurities from entering the display panel, but also reduce the stress of the plastic substrate. With the integration design of the ribs and discontinuous buffer layer, the flexible panel shows better=warp resistance and low stress properties, thereby enhancing the reliability and life time of the panel. 
         [0009]    Therefore, the present invention discloses a structure that may alleviate the warpage of the plastic substrate used for flexible display panel. Compared with a prior art, the present invention can reduce the internal stress of the plastic substrate, so as to reduce the warpage probability of the display panel in the high temperature process. Further, due to the ribs on the plastic substrate, the plastic substrate is not easily warpaged after a high temperature process. Moreover, the discontinuous buffer layer on the plastic substrate can disperse the structural stress of the entire plastic substrate, and can block gases and isolate impurities from entering the display panel. In addition, an active matrix component having a discontinuous pixel or discontinuous material layer can be used to alleviate the stress of the flexible panel in the prior art, thereby enhancing the reliability of the display panel. 
         [0010]    The features and practice of the preferred embodiments of the present invention will be illustrated in detail below with the accompanying drawings. (The objectives, structures, features, and functions of the present invention will be illustrated in detail below accompanied with the embodiments.) 
         [0011]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus is not limitative of the present invention, and wherein: 
           [0013]      FIG. 1A  is a side view of a carrier substrate with ribs according to the present invention; 
           [0014]      FIGS. 1B to 1D  are top views of a carrier substrate with ribs according to the present invention; 
           [0015]      FIG. 1E  is a side view of the ribs disposed between the active matrix component according to the present invention; 
           [0016]      FIG. 2A  is a side view of the plastic substrate disposed on the carrier substrate and on the plurality of ribs in the peripheral region of the carrier substrate according to the present invention; 
           [0017]      FIG. 2B  is a side view of the plastic substrate disposed on the carrier substrate and on the plurality of ribs between the active matrix components according to the present invention; 
           [0018]      FIGS. 3A to 3C  are schematic views of the process of forming a discontinuous buffer layer on the plastic substrate according to the present invention; 
           [0019]      FIG. 4  is a schematic view of the relation between the warp displacement of the plastic substrate with the ribs disposed thereon and the thickness of the ribs according to the present invention; 
           [0020]      FIG. 5A  is a side view of forming a discontinuous pixel on the discontinuous buffer layer according to the present invention; 
           [0021]      FIG. 5B  is a top view of an array structure formed by the stacking of the discontinuous buffer layer and the discontinuous pixel according to the present invention; and 
           [0022]      FIG. 6  is a schematic view of the active matrix component on the pixel disposed on the discontinuous buffer layer according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The embodiments of the present invention disclose a flexible display panel which integrates a liquid crystal or an organic light-emitting material and composed of an active matrix component (a-Si TFT/poly-Si TFT/thin film diode (TFD)/organic-TFT)) and a plastic substrate.  FIG. 1A  is a side view of a display panel substrate disclosed in the present invention.  FIGS. 1B to 1D  are top views of each example of a plurality of ribs placed on the substrate.  FIG. 1E  is a side view of a plurality of ribs disposed between the active matrix components. First, referring to  FIG. 1A , a plastic substrate (or a carrier)  10  has a display region  102  and a peripheral region  104 , in which the display region  102  is used for displaying images, and the peripheral region  104  is used for placing driving integrated circuit chips (drive IC chips). The thickness of the carrier substrate  10  is approximately 700 μm, and the carrier substrate  10  can be a glass substrate or other substrates of rigid materials, such as metal or ceramic materials, for carrying a plastic substrate (not shown). 
         [0024]    As shown in  FIG. 1B , in an embodiment, a plurality of ribs  12  is discontinuously disposed at two symmetrical corners on the peripheral region  104  of the carrier substrate  10 . Or, in another preferred embodiment, as shown in  FIG. 1C , the plurality of ribs  12  is respectively an L shaped configuration disposed at the four corners of the peripheral region  104  of the carrier substrate  10 . Further, as shown in  FIG. 1D , the ribs  12  of a continuous rectangular structure, for example, quadrate or square are placed on the peripheral region  104  of the carrier substrate  10 . In this embodiment, the thickness of the ribs  12  disposed on the carrier substrate  10  is approximately 0.1 to 120 μm, and the width thereof is about 10% to 100% of that of the peripheral region  104 . In  FIG. 1E , according to another preferred embodiment of the present invention, a plurality of ribs  12  is disposed between the active matrix components (not shown) of the carrier substrate  10 . 
         [0025]    In the above embodiments, the ribs  12  are made of a plastic material, for example, polyimide (PI), with the elastic coefficient of approximately 7.5 to 250 GPa and thermal expansion coefficient of approximately 10 to 200 ppm. As the ribs  12  are disposed on the peripheral region  104  of the carrier substrate  10  for increasing the rigidity of the subsequent plastic substrate (not shown), such that the plastic substrate will not be wrapped during the subsequent high temperature process. Further, as the peripheral region  104  is used for placing drive IC chips thereon, the display of images and the transmission of a back light source will not be affected. It should be particularly noted herein that in this embodiment, the stated low thermal expansion coefficient indicates that the thermal expansion coefficient of the material is lower than 15 ppm (1×10 −6 ). 
         [0026]    Next,  FIGS. 2A and 2B  are side views illustrating the plastic substrate covered on a carrier substrate and the ribs, respectively. First, referring to  FIG. 2A , the plastic material of the plastic substrate  14  is coated on the carrier substrate  10  and the plurality of ribs  12  in the peripheral region  104  of the carrier substrate  10 . The thickness of the coated plastic material is approximately 20 to 200 μm, so the total thickness of the entire plastic substrate  14  and the peripheral region  104  of the ribs is 0.1 mm thicker than that of the display region  102 . Further, referring to  FIG. 2B , likewise, the plastic substrate  14  is coated on the carrier substrate  10  and the plurality of ribs  12  disposed on an active matrix component (not shown). In this embodiment, the elastic coefficient of the plastic substrate  14  is approximately 50 GPa to 250 GPa, the thermal expansion coefficient is approximately 10 ppm to 200 ppm, and the material thereof is, for example, PI. In this embodiment, the plastic substrate  14  and the ribs  12  with different elastic coefficients and thermal expansion coefficients are used in purpose, in which the ribs  12  of a higher elastic coefficient may enhance the rigidity of the structure of the plastic substrate  14  and the plastic substrate  14  of a lower elastic coefficient may make the display region  102  of the plastic substrate  14  maintain a high light transmittance property and flexibility. 
         [0027]    Afterwards,  FIGS. 3A to 3C  are schematic views of the process of forming a discontinuous buffer layer  16  on the plastic substrate  14 . First, referring to  FIG. 3A , a buffer layer  16  is disposed on the plastic substrate  14 . Next, as shown in  FIG. 3B , a discontinuous buffer layer  16  is formed on the plastic substrate  14  and above the display region  102  by means of patterning, such as lithography and etching. Further, it can be seen from the top view of  FIG. 3C  that the discontinuous buffer layer  16  is arranged in an array on the plastic substrate (not shown) and located above the display region  102  (marked by the dashed line in the figure) of the plastic substrate. As such, the discontinuous buffer layer  16  can be used to disperse the structural stress of the entire display panel, and meanwhile enhance the reliability of the display panel. Moreover, the discontinuous buffer layer  16  can be used to block gases or isolate impurities from entering the display panel, and it can be an inorganic or an organic/inorganic mixed material, such as SiO 2 , Si 3 N 4 , SiO x N y , Al 2 O 3 , TiO 2 , and Parylene/SiN x . 
         [0028]    In view of the above, according to the research results, if the ribs  12  are placed on the peripheral region of the plastic substrate  14 , the warp displacement of the panel can be reduced.  FIG. 4  is a schematic view illustrating the relation between the warp displacement of the plastic substrate  14  with the ribs  12  disposed thereon and the thickness of the ribs  12 . As shown in  FIG. 4 , a layer of 3000 Å thick SiO 2  thin film is coated on the plastic substrate  14  with an area of approximately 10 cm×10 cm. If the ribs  12  are not disposed on the peripheral region  104  of the plastic substrate  14 , the warp displacement of the plastic substrate  14  (center and edge) may reach about 26 mm. If the ribs  12  are added, with the increase of the thickness of the ribs  12 , the warp displacement of the plastic substrate  14  can be reduced by a factor of 4, i.e., only about 6 mm. If the buffer layer  16  is coated on the display region  102  only, the warp displacement of the plastic substrate  14  can be further reduced by a factor of 3, i.e., only about 2 mm. If the buffer layer  16  of the display region  102  is further designed into a discontinuous thin film, the warp displacement of the plastic substrate  14  can be further reduced by a factor of 3, i.e., only about 0.7 mm. Compared with the situation in the absence of the above design, after the structures of the plastic substrate  14  and the buffer layer  16  are re-designed, the warp displacement of the plastic substrate  14  can be reduced by a factor of 36. 
         [0029]    After that, referring to  FIG. 5A , a discontinuous pixel  20  is formed on the discontinuous buffer layer  16  by means of vacuum coating, spin coating, screen printing, or ink jet printing. As shown  FIG. 5B , a structure of discontinuous bright regions and dark regions is disposed on the plastic substrate  14 . The bright regions are pixel regions formed by a plurality of pixels  20 , and are light transmissive regions. The pixel regions are separately disposed in the display region of the plastic substrate. The dark regions are an active matrix component  30  and the buffer layer  16 , in which the buffer layer  16  covers an area from the active matrix component  30  to the pixel regions. 
         [0030]    Next, referring to  FIG. 6 , the active matrix component  30  on the pixel  20  is disposed on the discontinuous buffer layer  16 , and the active matrix component  30  can be a transistor array element. Moreover, the structure of the active matrix component  30  includes a channel layer (not shown), a gate insulator layer (not shown), and a transparent conductive layer (not shown), which are discontinuously stacked on the discontinuous buffer layer  16  and located above the display region  102 . The buffer layer  16  covers an area from the active matrix component  30  to the pixel regions. In this embodiment, the channel layer, gate insulator layer, and transparent conductive layer form a discontinuous structure because the channel layer, gate insulator layer, and transparent conductive layer respectively have a certain elastic coefficient. 
         [0031]    It should be noted that extensibility refers to a ratio u between the breaking strain ε E  and the yield strain ε y  in a stress-strain curve of the material, i.e., u=ε E /ε y . When the value of u of the material is lower than 5, it can be referred to as a material of poor extensibility. Moreover, the material of the channel layer can be a-Si or poly-Si, the material of the gate insulator layer can be SiNx or SiOx, and the material of the transparent conductive layer can be ITO or IZO. 
         [0032]    Thus, according to the above embodiments, the structural rigidity of the plastic substrate can be enhanced by the ribs. Moreover, the discontinuous buffer layer and the discontinuous pixel can be used to disperse the structural stress between the plastic substrate and the active matrix component and also reduce the warp stress. As such, through the improvement of the structure of the plastic substrate, the reliability and life time of the entire flexible display panel is enhanced. 
         [0033]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.