Patent Publication Number: US-11391971-B2

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/395,263, filed on Apr. 26, 2019, which claims the priority benefit of China Application No. 201820635679.5, filed on Apr. 28, 2018. The entirety of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a display device, and in particular to a display device which has an anti-peeping mode and a sharing mode controlled in an electrical manner. 
     BACKGROUND OF THE INVENTION 
     At present, when anti-peeping is required for a display device, usually a light control film is placed on the display panel or the backlight module to filter out the large-angle light; when anti-peeping is not required, the light control film must be manually removed. The general light-control films on the market are usually the optical films having a black fine louver structure such as the light control film (LCF) containing a screen privacy film or the advanced light control film (ALCF) of 3M. 
     However, the optical film described above is relatively expensive and increases product cost. The optical film must be manually placed on or removed from the display panel, which is inconvenient. In addition, the light control film has a periodic structure and is liable to generate a Moiré pattern with the display panel. Furthermore, the light control film causes a decreased brightness of the display device, for example, a decrease of about 30%. 
     The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The invention provides a display device, which has an anti-peeping mode and a sharing mode switched by an electrically controlled manner. 
     Other advantages and objects of the invention may be further illustrated by the technical features broadly embodied and described as follows. 
     In order to accomplish one or a part or all of the above or other purposes, the display device provided by the invention has a viewing angle control direction. The display device comprises a backlight module, a display panel and an electrically controlled viewing angle switching device. The display panel is disposed on the backlight module. The display panel comprises a panel module and a first polarizer. The electrically controlled viewing angle switching device is disposed on the backlight module and disposed in a stacking manner with the display panel. There is an air layer between the electrically controlled viewing angle switching device and the display panel. The panel module is disposed between the first polarizer and the electrically controlled viewing angle switching device. The electrically controlled viewing angle switching device comprises a liquid crystal cell, at least one phase compensation film and two second polarizers. The liquid crystal cell is disposed between the two second polarizers. The at least one phase compensation film is disposed at least between one of the second polarizers and the liquid crystal cell. 
     In order to accomplish one or a part or all of the above or other purposes, the display device provided by the invention has a viewing angle control direction. The display device comprises a backlight module, a display panel and an electrically controlled viewing angle switching device. The display panel is disposed on the backlight module. The display panel comprises a panel module and a first polarizer. The electrically controlled viewing angle switching device is disposed on the backlight module and disposed in a stacking manner with the display panel. There is a bonding layer between the electrically controlled viewing angle switching device and the display panel. The panel module is disposed between the first polarizer and the electrically controlled viewing angle switching device. The electrically controlled viewing angle switching device comprises a liquid crystal cell, at least one phase compensation film and two second polarizers. The liquid crystal cell is disposed between the two second polarizers. The at least one phase compensation film is disposed at least between one of the second polarizers and the liquid crystal cell, wherein the refraction index of the bonding layer is equal to or less than the refraction index of the two second polarizer of the electrically controlled viewing angle switching device. 
     The display device of the embodiments of the invention adopts the electrically controlled viewing angle switching device disposed in the stacking manner with the display panel and on the backlight module, wherein there is an air layer between the electrically controlled viewing angle switching device and the display panel, and together with the situation that at least one phase compensation film is disposed between the liquid crystal cell of the electrically controlled viewing angle switching device and the two second polarizers to achieve anti-peeping control. Therefore, the switching between the anti-peeping mode and the sharing mode of the display device can be achieved through the condition whether voltage is applied to the liquid crystal cell of the electrically controlled viewing angle switching device or not. 
     The display device of the other embodiments of the invention adopts the electrically controlled viewing angle switching device disposed in the stacking manner with the display panel and on the backlight module, wherein there is a bonding layer between the electrically controlled viewing angle switching device and the display panel, wherein the refraction index of the bonding layer is no higher than the refraction index of the two second polarizers of the electrically controlled viewing angle switching device, and together with the situation that at least one phase compensation film is disposed between the liquid crystal cell of the electrically controlled viewing angle switching device and the two second polarizers to achieve anti-peeping control. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this 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 explosive view of the display device of a first embodiment of the invention; 
         FIG. 2  is a schematic cross-sectional view of the display device of a first embodiment of the invention; 
         FIG. 3  is a schematic structural view of the electrically controlled viewing angle switching device of an embodiment of the invention; 
         FIG. 4A  and  FIG. 4B  are respectively schematic diagrams showing correspondence of different alignment directions and axial directions of the absorption axis of the polarizers according to an embodiment of the invention; 
         FIG. 5A  and  FIG. 5B  are schematic cross-sectional views of the electrically controlled viewing angle switching device of the display device of an embodiment of the invention under the sharing mode and the anti-peeping mode, respectively; 
         FIG. 6  is a schematic view of a configuration of a liquid crystal cell, a second upper polarizer and a second lower polarizer of the electrically controlled viewing angle switching device of an embodiment of the invention; 
         FIG. 7  is a schematic structural view of the display panel of an embodiment of the invention; 
         FIG. 8  is a schematic cross-sectional view of the display device of another embodiment of the invention; 
         FIG. 9  is a schematic structural view of a frame of an embodiment of the invention; 
         FIG. 10  is a schematic view of positions of the frame and frame glues of the liquid crystal cell of an embodiment of the invention; 
         FIG. 11  is another schematic cross-sectional view of the display device of the first embodiment of the invention; 
         FIG. 12  is a schematic cross-sectional view of a reflector of an embodiment of the invention; 
         FIG. 13  is a schematic cross-sectional view of the reflector of another embodiment of the invention; 
         FIG. 14A ,  FIG. 14B  and  FIG. 14C  are respectively schematic views of microstructure patterns of the reflector of an embodiment of the invention; 
         FIG. 15  is a schematic explosive view of the display device of a second embodiment of the invention; and 
         FIG. 16  is a schematic view of the display panel and the electrically controlled viewing angle switching device connected to a circuit board according to an embodiment of the invention; 
         FIG. 17  is another schematic cross-sectional view of the display device of the first embodiment of the invention; 
         FIG. 18  is another schematic cross-sectional view of the display device of the embodiment shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top”, “bottom”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) being described. The components of the invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected”, “coupled”, and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing”, “faces”, and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component facing “B” component directly or one or more additional components is between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components is between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG. 1  is a schematic explosive view of the display device of a first embodiment of the invention. As shown in the figure, the display device  10  comprises a backlight module  12 , a display panel  14  and an electrically controlled viewing angle switching device  16 . The electrically controlled viewing angle switching device  16  and the display panel  14  are disposed in a stacking manner and are disposed on the backlight module  12 . In the first embodiment, the electrically controlled viewing angle switching device  16  is disposed between the display panel  14  and the backlight module  12  but not limited thereto. In the display device  10 A of a second embodiment described afterwards, the display panel  14  is disposed between the electrically controlled viewing angle switching device  16  and the backlight module  12 . The display panel  14  comprises a panel module  18  and a first polarizer  20 . The panel module  18  is located between the first polarizer  20  and the electrically controlled viewing angle switching device  16 . The electrically controlled viewing angle switching device  16  comprises a liquid crystal cell  22 , at least one phase compensation film  24  and two second polarizers. In one embodiment, the two second polarizers are a second upper polarizer  26  and a second lower polarizer  28 , respectively. The liquid crystal cell  22  is disposed between the second upper polarizer  26  and the second lower polarizer  28 , and the phase compensation film  24  is disposed between the second upper polarizer  26  and the liquid crystal cell  22  but not limited thereto. In other embodiments, the phase compensation film  24  may be of one layer or a plurality of layers, and be disposed between the second upper polarizer  26  and the liquid crystal cell  22 , and/or between the second lower polarizer  28  and the liquid crystal cell  22 .  FIG. 2  is a schematic cross-sectional view of the display device of the first embodiment of the invention. Please refer to  FIG. 2  concurrently, that the electrically controlled viewing angle switching device  16  is located between the display panel  14  and the backlight module  12 , wherein there is an air layer  30  between the electrically controlled viewing angle switching device  16  and the display panel  14 . 
     Continued from the above illustration, that a switching by means of the electrically controlled viewing angle switching device  16  makes the display device  10  be in an anti-peeping mode in a viewing angle control direction P.  FIG. 3  is a schematic structural view of the electrically controlled viewing angle switching device of an embodiment of the invention. As shown in the figure, the liquid crystal cell  22  of the electrically controlled viewing angle switching device  16  comprises two substrates, two electrode layers, two alignment layers and a liquid crystal material layer  228 . In one embodiment, the two substrates are an upper substrate  221  and a lower substrate  222 , respectively. The two electrode layers are an upper electrode layer  223  and a lower electrode layer  224 , respectively. The two alignment layers are an upper alignment layer  225  and a lower alignment layer  226 , respectively. As shown in  FIG. 3 , the upper substrate  221  and the lower substrate  222  are disposed between the second upper polarizer  26  and the second lower polarizer  28 . In one embodiment, the phase compensation film  24  is located between the upper substrate  221  and the second upper polarizer  26  but not limited thereto. The upper electrode layer  223  and the lower electrode layer  224  are disposed between the upper substrate  221  and the lower substrate  222 . In one embodiment, the upper electrode layer  223  and the lower electrode layer  224  are disposed on an interior surface of the upper substrate  221  and an interior surface of the lower substrate  222 , respectively, wherein the interior surface of the upper substrate  221  is opposite to the interior surface of the lower substrate  222 . The upper alignment layer  225  and the lower alignment layer  226  are disposed between the upper electrode layer  223  and the lower electrode layer  224 . In one embodiment, the upper alignment layer  225  is adjacent to the upper electrode layer  223  and the lower alignment layer  226  is adjacent to the lower electrode layer  224 . The liquid crystal material layer  228  is disposed between the upper alignment layer  225  and the lower alignment layer  226 , wherein the liquid crystal material layer  228  comprises a plurality of liquid crystal molecules  229 , and a direction B of an optical axis  230  of the liquid crystal molecules  229  relative to the viewing angle control direction P forms an included angle θ 1  of 70-110 degrees. In one embodiment, as shown in  FIG. 3 , an axial direction of an absorption axis A 26  of the second upper polarizer  26  and an axial direction of an absorption axis A 28  of the second lower polarizer  28  are parallel to the viewing angle control direction P. 
     Further, each of the upper alignment layer  225  and the lower alignment layer  226  has an alignment direction. The two alignment directions form respectively included angles of 90±20 and 270±20 degrees with the viewing angle control direction P, and included angles formed between the axial directions of the absorption axis (or transmission axis) of the second upper polarizer  26  and the second lower polarizer  28  and the two alignment directions are selected from one of 0±5 degrees and 90±5 degrees. For example, when the viewing angle control direction P is represented by being toward the azimuth angles of 0 and 180 degrees, the alignment directions of the upper alignment layer  225  and the lower alignment layer  226  may be 90 degrees and 270 degrees respectively, or 90 degrees and 270±20 degrees respectively, or 90±20 degrees and 270 degrees respectively, or 90±20 degrees and 270±20 degrees respectively. The axial directions of the absorption axis (or transmission axis) of the second upper polarizer  26  and the second lower polarizer  28  are arranged corresponding to the alignment directions and perpendicular (or parallel) to the alignment directions. In one embodiment, as shown in  FIG. 4A , when the alignment direction I 1  of the upper alignment layer  225  and the alignment direction I 2  of the lower alignment layer  226  are such as 270 degrees and 90 degrees, respectively, both the axial direction of the absorption axis A 26  of the second upper polarizer  26  and the axial direction of the absorption axis A 28  of the second lower polarizer  28  are toward 0 and 180 degrees. As shown in  FIG. 4B , when the alignment directions I 1  and I 2  are deflected counterclockwise by an angle θ 2 , the axial directions of the absorption axis A 26  and A 28  are also deflected counterclockwise by an angle θ 2 , wherein the angle θ 2  is less than 20 degrees. 
       FIGS. 5A and 5B  are schematic cross-sectional views of the electrically controlled viewing angle switching device of the display device of an embodiment of the invention under a sharing mode and the anti-peeping mode, respectively. It is taken as an example that the included angle between the direction B (not shown) of the optical axis  230  of the liquid crystal molecules  229  and the viewing angle control direction P is 90 degrees and both the axial direction of the transmission axis T 26  of the second upper polarizer  26  and the axial direction of the transmission axis T 28  of the second lower polarizer  28  are parallel to the direction B. For example, the optical axis  230  of the liquid crystal molecules  229 , the transmission axis T 26  of the second upper polarizer  26  and the transmission axis T 28  of the second lower polarizer  28  are all parallel to a first direction D 1 . The viewing angle control direction P is a second direction D 2 , which is perpendicular to the first direction D 1 , and a reversed direction of the second direction D 2 . Also, a third direction D 3  represents a stacking direction of the electrically controlled viewing angle switching device  16  and the display panel  14 . The third direction D 3  is perpendicular to the first direction D 1  and the second direction D 2 . When the electrically controlled viewing angle switching device  16  is powered off, there is no voltage between the upper electrode layer  223  and the lower electrode layer  224 . As shown in  FIG. 5A , the optical axis  230  of the liquid crystal molecules  229  is perpendicular to the viewing angle control direction P. In such case, whether a light L 1  in a central view angle (i.e. the light which enters the electrically controlled viewing angle switching device in a forward direction) or a light L 2  in the viewing angle control direction (i.e. the light which enters the electrically controlled viewing angle switching device at a large angle), a polarized light generated by passing through the second lower polarizer  28  does not experience a phase transition of the liquid crystal molecules  229  and thus a polarization direction is not changed by the liquid crystal material layer  228 , thereby all the lights being able to pass through the second upper polarizer  26 . At this time, the display device  10  is in the sharing mode. When the electrically controlled viewing angle switching device  16  is powered on, the liquid crystal molecules  229  in the liquid crystal material layer  228  are subjected to an effect of an electric field between the upper electrode layer  223  and the lower electrode layer  224 . As shown in  FIG. 5B , the optical axis  230  of the liquid crystal molecules  229  rotate at an angle with the viewing angle control direction P as an axis. The lights passing through the electrically controlled viewing angle switching device  16  with different incident angles are subjected to different phase transitions at the liquid crystal material layer  228 . For example, when the light L 1  in the direction of central view angle passes through the liquid crystal material layer  228 , the light L 1  has no changed polarization direction and can therefore pass through the second upper polarizer  26 . The light L 2  in the viewing angle control direction entering the electrically controlled viewing angle switching device at a larger angle has changed polarization direction due to the liquid crystal material layer  228  and is unable to pass through the second upper polarizer  26 . At this time, the display device  10  is in the anti-peeping mode. 
     Further, as shown in  FIG. 6 , the second upper polarizer  26  and the second lower polarizer  28  of the electrically controlled viewing angle switching device  16  are attached above and below the liquid crystal cell  22 , respectively. The second upper polarizer  26  includes two opposite long sides  261  and two opposite short sides  262 . The second lower polarizer  28  includes two opposite long sides  281  and two opposite short sides  282 . In one embodiment, the axial direction of the absorption axis A 26  of the second upper polarizer  26  and the axial direction of the absorption axis A 28  (not shown) of the second lower polarizer  28  are parallel to the long sides  261 ,  281  so that a stress direction S of the second upper polarizer  26  and a stress direction S of the second lower polarizer  28  counteract each other and the electrically controlled viewing angle switching device  16  is therefore not liable to warp or bend. In addition, as shown in  FIG. 7 , the first polarizer  20  of the display panel  14  also includes two opposite long sides  201  and two opposite short sides  202 . In one embodiment, an axial direction of the absorption axis A 20  of the first polarizer  20  is parallel to the short side  202  and therefore a stress direction S of the first polarizer  20  is parallel to the short side  202  so that the display panel  14  is not liable to warp or bend though only one first polarizer  20  is attached on the panel module  18 . 
       FIG. 8  is a schematic cross-sectional view of the display device of another embodiment of the invention. The following is also an illustration in that both the transmission axis T 26  of the second upper polarizer  26  and the transmission axis T 28  of the second lower polarizer  28  are perpendicular to the viewing angle control direction P. As shown in  FIG. 8 , after the light L 1  or the light L 2  in the viewing angle control direction P emitted from the backlight module  12  passes through the second lower polarizer  28  of the electrically controlled viewing angle switching device  16 , the polarization direction of the polarized light, i.e. a S-polarized light, is perpendicular to the viewing angle control direction P. Generally speaking, an interface transmittance of S-polarized light is much lower than an interface transmittance of P-polarized light. For example, taking the light L 2  incident on the electrically controlled viewing angle switching device  16  at an angle of 45 degrees as an example, after the light L 2  enters the electrically controlled viewing angle switching device  16 , a traveling direction of the light L 2  is deflected from 45 degrees to, for example, 28.1 degrees. The interface transmittance of the S-polarized light is, for example, 90.7% of the interface transmittance of the P-polarized light at an interface of the second upper polarizer  26  and the air layer  30 . When the light L 2  enters the air layer  30 , the traveling direction of the light L 2  is deflected back to 45 degrees. When the light L 2  proceeds to a side of the display panel  14  adjacent to the air layer  30 , the interface transmittance of the S-polarized light is, for example, 91.6% of the interface transmittance of the P-polarized light. That is, for the light L 2  which enters the electrically controlled viewing angle switching device  16  at a 45-degree angle, the transmittance of the S-polarized light is about 17% lower than that of the P-polarized light and therefore the anti-peeping effect is improved. Further speaking, the air layer  30  located between the electrically controlled viewing angle switching device  16  and the display panel  14  conduces to decrease the interface transmittance of the light L 2  in the viewing angle control direction (i.e. the light which enters the electrically controlled viewing angle switching device at a large angle) at the interface of the second upper polarizer  26  and the air layer  30  and the interface of the air layer  30  and the display panel  14  when the polarized light of the light L 1  or the light L 2  passing though the electrically controlled viewing angle switching device  16  is the S-polarized light and therefore improves the anti-peeping effect. 
     Continued from the above illustration, in the first embodiment, as shown in  FIG. 2  and  FIG. 8 , the electrically controlled viewing angle switching device  16  is disposed between the display panel  14  and the backlight module  12 , wherein a frame  32  with adhesiveness is disposed between the electrically controlled viewing angle switching device  16  and the display panel  14  to connect the same (the electrically controlled viewing angle switching device  16  and the display panel  14 ), and the air layer  30  is therefore formed between the electrically controlled viewing angle switching device  16  and the display panel  14 . A thickness of the air layer  30  is such as 0.1 mm, 0.2 mm or 0.3 mm. Since a surface of the panel module  18  of the display panel  14  is generally a transparent glass surface or has an optical film attached thereon, a structure of concave-convex unevenness (not shown) is disposed on a side or a surface of the second upper polarizer  26  facing the panel module  18  to prevent Newton&#39;s ring effect when the electrically controlled viewing angle switching device  16  and the panel module  18  are too close. The structure of concave-convex unevenness is located between the second upper polarizer  26  and the panel module  18  and is able to prevent a large-area contact between the surface of the second upper polarizer  26  and the surface of the panel module  18  to prevent the Newton&#39;s ring effect. In addition, the surface of the second upper polarizer  26  having the structure of concave-convex unevenness is designed to have an exterior haze of lower than 50% to prevent a destroyed polarization state of the polarized light from the second upper polarizer  26  due to a scattering by the structure of concave-convex unevenness, which therefore results in a lowered contrast of the display panel  14 . Preferably, the exterior haze of the second upper polarizer  26  is less than 20%. More preferably, the exterior haze of the second upper polarizer  26  is less than 5%. 
     The frame  32  with adhesiveness mentioned above comprises a double-sided glue having a square framed shape. The frame  32  is preferably black to shield scattered light from an optical plate below the frame  32  or from an edge of a reverse prism sheet and to prevent scattering of light on an edge of the frame  32 , thereby preventing aureola on a border of a display area. In one embodiment, as shown in  FIG. 9 , the frame  32  comprises four frame edges  321 ,  322 ,  323  and  324 . Each of the frame edges  321 ,  322 ,  323  and  324  has step structures  325  at two opposite ends. The frame edges  321 ,  322 ,  323  and  324  are connected at the ends by means of the step structures  325  so as to constitute a square framed shape. With the design of the step structures  325 , the dust can be effectively prevented from entering the air layer  30  through the joints between the frame edges  321 ,  322 ,  323  and  324 . 
     Referring to  FIG. 10 , a position of the frame  32  is further illustrated together with the structure of the liquid crystal cell.  FIG. 10  is a schematic view of positions of the frame and frame glues of the liquid crystal cell according to an embodiment of the invention. As shown in  FIG. 10 , the liquid crystal cell  22  has a display area  40  and a frame glue area  42 . The frame glue area  42  surrounds the display area  40 , wherein the liquid crystal material layer  228  (shown in  FIG. 3 ) of the liquid crystal cell  22  is located in the display area  40 . A first frame glue  44  is located in the frame glue area  42  between the upper substrate  221  (shown in  FIG. 3 ) and the lower substrate  222  (shown in  FIG. 3 ) and surrounds the display area  40  to seal the liquid crystal material layer  228 . In one embodiment, the frame  32  is disposed between the electrically controlled viewing angle switching device  16  (shown in  FIG. 2 ) and the display panel  14  (shown in  FIG. 2 ), and surrounds the frame glue area  42  and overlaps partially with the frame glue area  42 , particularly overlapping partially with the first frame glue  44 . Both the frame  32  and the first frame glue  44  are black. Through the disposition of the black first frame glue  44  and the black frame  32 , the aureola on a periphery of the display device  10  can be effectively shielded. 
     Further, as shown in  FIG. 10 , in addition to the first frame glue  44  which is disposed in the frame glue area  42  between the upper substrate  221  and the lower substrate  222  to seal the liquid crystal material layer  228 , a second frame glue  46  is disposed in the frame glue area  42 . The second frame glue  46  is only disposed at a local position of the frame glue area  42 . A plurality of conductive balls  48  such as gold balls are distributed in the second frame glue  46  so that the upper electrode layer  223  (shown in  FIG. 3 ) and the lower electrode layer  224  (shown in  FIG. 3 ) are electrically connected through the conductive balls  48  while the upper substrate  221  is connected to the lower substrate  222  by the second frame glue  46 . In one embodiment, a drive signal of the lower electrode layer  224  is originated from an external signal, which is electrically separated by the upper electrode layer  223  and then conducted to the lower electrode layer  224  through the conductive balls  48  in the second frame glue  46 . In such design, an electrical connection area between the upper electrode layer  223  and the lower electrode layer  224  is electrically separated from other areas of the upper electrode layer  223  to serve as a signal entry area of the lower electrode layer  224 . In another embodiment, a drive signal of the upper electrode layer  223  is originated from an external signal, which is electrically separated by the lower electrode layer  224  and then conducted to the upper electrode layer  223  through the conductive balls  48  in the second frame glue  46 . In such design, an electrical connection area between the lower electrode layer  224  and the upper electrode layer  223  is electrically separated from other areas of the lower electrode layer  224  to serve as a signal entry area of the upper electrode layer  223 . 
     Continued from the above illustration, in the invention, the phase compensation film  24  of the electrically controlled viewing angle switching device  16  may be a Negative C-plate, an A-plate and a Bi-axial plate. The phase compensation film  24  may be of one-layer film or stacked film (i.e. being multilayer film construction) but not limited thereto. No matter what kind of phase compensation film  24  is used, a compensation value of the in-plane retardation (R o ) thereof is between 0 nm and 150 nm, and a compensation value of the out-of-plane retardation (R th ) thereof is between 100 nm and 600 nm. The lower the R o , the better. The optimal R th  is 400 nm. The phase compensation film  24  improves the anti-peeping range of the electrically controlled viewing angle switching device  16 . 
     Since the A-plate and the Bi-axial plate are of directivity, a refractive index distribution of the Bi-axial plate must satisfy Nx&gt;Ny&gt;Nz when the phase compensation film  24  is the Bi-axial plate, wherein Nx, Ny and Nz represent refractive indexes of the Bi-axial plate in the x-axis, the y-axis and the z-axis, respectively, and a thickness direction of the phase compensation film  24  is in the z-axis direction. The phase compensation film  24  may comprise stacking multiple layers of Bi-axial plates. The Bi-axial plates can be located such as between the second upper polarizer  26  and the liquid crystal cell  22  (as shown in  FIG. 2 ), or between the second lower polarizer  28  and the liquid crystal cell  22 . The Bi-axial plates can also be located both between the liquid crystal cell  22  and the second upper polarizer  26 , and between the liquid crystal cell  22  and the second lower polarizer  28 . The x-axis direction of each Bi-axial plate forms an included angle of 0±30 degrees with the absorption axis A 26 /A 28  or the transmission axis T 26 /T 28  of the adjacent second upper polarizer  26 /second lower polarizer  28 , wherein a better anti-peeping effect is accomplished when the x-axis direction of the Bi-axial plate is parallel to the absorption axis A 26 /A 28  or the transmission axis T 26 /T 28 . 
     When the phase compensation film is the A-plate, a pair of A-plates is required. In one embodiment, as shown in  FIG. 11 , the phase compensation film  24  comprises a first A-plate  241  and a second A-plate  242 . An included angle between an optical axis (not shown in the figure) of the first A-plate  241  and an optical axis (not shown in the figure) of the second A-plate  242  is 90±20 degrees. The first A-plate  241  is disposed between the second lower polarizer  28  and the liquid crystal cell  22 , and an included angle between the optical axis of the first A-plate  241  and the absorption axis A 28  (not shown in the figure) of the second lower polarizer  28  is 45±10 degrees. The second A-plate  242  is disposed between the second lower polarizer  28  and the first A-plate  241 , and an included angle between the optical axis of the second A-plate  242  and the absorption axis A 28  (not shown in the figure) of the second lower polarizer  28  is 45±10 degrees. A better anti-peeping effect is accomplished when the included angle between the optical axis of the first A-plate  241  (the second A-plate  242 ) and the absorption axis A 26  (A 28 ) of the second upper polarizer  26  (the second lower polarizer  28 ) is 45 degrees. When the R o  and the R th  of the first A-plate  241  and the second A-plate  242  are low and do not reach the above mentioned values, an elevated R o  and an elevated R th  can be reached by stacking a plurality of first A-plates  241  and/or a plurality of second A-plates  242 . 
     In addition to a disposition of the phase compensation film  24  to improve the anti-peeping effect of the display device  10 , in one embodiment, the structure of the backlight module  12  is also one of the factors that prevent a decreased anti-peeping effect. Please refer to  FIG. 1 . The backlight module  12  comprises a light source and an optical plate. The light source in the embodiment is such as a linear light source assembly  50 . The optical plate is such as a light guide plate  52 . The light guide plate  52  has a light-incident surface  521  and a light-emitting surface  522 . In the first embodiment, the light-emitting surface  522  is disposed opposite to the electrically controlled viewing angle switching device  16  but not limited thereto. In the display device  10 A of the second embodiment to be described later, the light-emitting surface  522  is disposed opposite to the display panel  14 . As shown in  FIG. 1 , the linear light source assembly  50  is disposed beside the light-incident surface  521 . The linear light source assembly  50  comprises a plurality of light-emitting diodes  501  arranged along a predetermined direction C 1 , and the predetermined direction C 1  is parallel to the viewing angle control direction P. In one embodiment, the backlight module  12  further comprises a reverse prism sheet  54  disposed on the light-emitting surface  522 . The reverse prism sheet  54  has a plurality of prisms  541  arranged in parallel. The prisms  541  face the light-emitting surface  522  and extending directions C 2  of the prisms  541  are parallel to the viewing angle control direction P. 
     Continued from the above illustration, the backlight module  12  further comprises a reflector  56  disposed at an opposite side of the light-emitting surface  522  of the light guide plate  52 , i.e. the reflector  56  is disposed below the light guide plate  52 .  FIG. 12  is a schematic cross-sectional view of the reflector of one embodiment of the invention. As shown in the figure, the reflector  56  comprises a substrate  561  and a metal layer  562 . The metal layer  562  is formed on the substrate  561 . The metal layer  562  is a silver metal layer or an aluminum metal layer, so that the reflector  56  is not a white reflector in order to prevent scattering of reflected light due to the use of a white reflector, which results in a deficiency of decreased anti-peeping effect caused by the increase of large-angle light of the backlight module  12 . 
       FIG. 13  is a schematic cross-sectional view of the reflector of another embodiment of the invention. As shown in the figure, the reflector  56  comprises a metal layer  562  and a protection layer  563 . The metal layer  562  is a silver metal layer or an aluminum metal layer. The protection layer  563  covers the metal layer  562 . A microstructure pattern  564  is formed on a side of the protection layer  563  facing the light guide plate  52  (shown in  FIG. 1 ). Since the microstructure pattern  564  is asymmetrical to scattered light, adjustment of the microstructure pattern  564  requires consideration of the viewing angle control direction P, so as to have a lower proportion of scattered light in the viewing angle control direction P.  FIG. 14A ,  FIG. 14B , and  FIG. 14C  are schematic views of the microstructure patterns of the reflector respectively according to one embodiment of the invention. As shown in  FIG. 14A , the microstructure pattern  564  comprises a plurality of strip-like convex portions  565 , and an extension direction of each strip-like convex portion  565  is parallel to the viewing angle control direction P. As shown in  FIG. 14B , the microstructure pattern  564  comprises a plurality of strip-like convex portions  565 , and an extension direction of each strip-like convex portion  565  is perpendicular to the viewing angle control direction P. As shown in  FIG. 14C , the microstructure pattern  564  comprises a plurality of convex portions  565 , and each convex portion  565  has an elliptical shape, and a long axis L 565  of the elliptical shape is parallel to the viewing angle control direction P. In other embodiment, the reflector  56  can also be a specular reflector (ESR) having multilayer film construction. 
     The reflector  56  of the embodiment is characterized by low scattering. In one embodiment, a ratio of a light scattered by the reflector  56  to a light not scattered by the reflector  56  is less than 0.25. Therefore the large-angle light emitted from the backlight module  12  can be reduced, and especially the large-angle light of the backlight module  12  in the viewing angle control direction P can be reduced. In addition, the design of the protection layer  563  mentioned above can prevent the reflector  56  from being damaged during transportation or during assembly into the backlight module  12 . 
     Continued from the above illustration, in the first embodiment, as shown in  FIG. 2 ,  FIG. 8  and  FIG. 11 , the electrically controlled viewing angle switching device  16  is disposed between the display panel  14  and the backlight module  12 , wherein a frame  32  with adhesiveness is disposed between the electrically controlled viewing angle switching device  16  and the display panel  14  to connect the same (the electrically controlled viewing angle switching device  16  and the display panel  14 ), and the air layer  30  is therefore formed between the electrically controlled viewing angle switching device  16  and the display panel  14 . As shown in  FIG. 17 , alternatively, there is no air layer  30  and frame  32  between the electrically controlled viewing angle switching device  16  and the display panel  14 . Moreover, there is a bonding layer  34  between the electrically controlled viewing angle switching device  16  and the display panel  14 . 
     As shown in  FIG. 18 , when the light L 2  proceeds from  16  to the bonding layer  34  and then proceeds to a side of the display panel  14  adjacent to the bonding layer  34 , if the refraction index of the bonding layer  34  is equal to or less than the second upper polarizer  26  of the electrically controlled viewing angle switching device, the transmittance of the S-polarized light is lower than that of the P-polarized light. Further speaking, the bonding layer  34  with lower refraction index located between the electrically controlled viewing angle switching device  16  and the display panel  14  conduces to decrease the interface transmittance of the light L 2  in the viewing angle control direction when the polarized light of the light L 1  or the light L 2  passing though the electrically controlled viewing angle switching device  16  is the S-polarized light and therefore improves the anti-peeping effect. 
       FIG. 15  is a schematic explosive view of the display device of a second embodiment of the invention. As shown in the figure, the display device  10 A comprises the backlight module  12 , the display panel  14  and the electrically controlled viewing angle switching device  16 . A difference from the first embodiment is that in the second embodiment, the display panel  14  is between the backlight module  12  and the electrically controlled viewing angle switching device  16 , and the light-emitting surface  522  of the optical plate (such as the light guide plate  52 ) of the backlight module  12  is disposed opposite to the display panel  14 . Regarding the switching modes of the electrically controlled viewing angle switching device  16 , the formation of the air layer  30  between the display panel  14  and the electrically controlled viewing angle switching device  16 , and the structure of the backlight module  12 , they are the same as or similar to those in the first embodiment and are not further elaborated herein. Furthermore, air layer  30  can be a bonding layer  34  with lower refraction index. 
       FIG. 16  is a schematic view of the display panel and the electrically controlled viewing angle switching device connected to a circuit board according to an embodiment of the invention. As shown in  FIG. 16 , the display device  10 / 10 A further comprises a circuit board  58  having a control circuit assembly and a plurality of flexible printed circuit  60 . The display panel  14  and the electrically controlled viewing angle switching device  16  are electrically connected to the circuit board  58  by using the flexible printed circuit  60  so that the display panel  14  and the electrically controlled viewing angle switching device  16  are driven and controlled by the control circuit assembly of the circuit board  58 . 
     In view of illustration set forth above, the invention can achieve the following effects:
     1) When the display device of the embodiment is in use, a viewing angle of images of the display device can be switched by the electrically controlled viewing angle switching device to accomplish the switching between the anti-peeping mode and the sharing mode. The display device of the embodiment improves the disadvantage of inconvenient use caused by the conventional requirement that the optical film must be manually placed on or removed from the display panel to achieve anti-peeping or sharing demands.   2) The anti-peeping effect can be enhanced through the selection and the disposition of the phase compensation film and the improvement of the structure of the reflector.   3) The electrically controlled viewing angle switching device is not liable to warp or bend and has a longer lifespan.   

     The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “The invention” or the like is not necessary limited the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. Moreover, these claims may refer to use “first”, “second”, etc. following with noun or element. Such terms should be understood as a nomenclature and should not be construed as giving the limitation on the number of the elements modified by such nomenclature unless specific number has been given. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the invention as defined by the following claims. Moreover, no element and component in the disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims. Furthermore, the terms such as the first polarizer, the second polarizer, the first A-plate, the second A-plate, the second upper polarizer, the second lower polarizer, the first frame glue, and the second frame glue are only used for distinguishing various elements and do not limit the number of the elements.