Abstract:
A flat panel display device displays an image using a micro-shutter electrode and a diffusive reflection layer. The display device has a wide viewing angle and reduces a loss of light to thus improve light efficiency. In addition, gray levels can be determined by an electrostatic force between the pixel electrode and the micro-shutter electrode. An opening/closing operation of the micro-shutter electrode is fast so that the response speed can be improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Korean Patent Application No. 10-2008-0086896 filed in the Korean Intellectual Property Office on Sep. 3, 2008, the entire contents of which are herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present disclosure is directed to a display device and, more particularly, to a new type of transmissive display device. 
         [0004]    (b) Discussion of the Related Art 
         [0005]    Display devices have evolved from cathode ray tube (CRT) devices to flat panel display devices such as a liquid crystal displays (LCDs), plasma display panels (PDPs), and the like. The CRT display device displays images by allowing electron beams to collide with a fluorescent material (e.g., phosphor). The CRT display device is disadvantageous in that an increase in its screen size is accompanied by an increase in its depth, making it difficult to enlarge the display device. 
         [0006]    Thus, to overcome such shortcomings, a plurality of flat panel display devices have been developed. Of them, the LCD and the PDP are typical flat panel display devices. The flat panel display devices are advantageous in that the devices can be increased in size without increasing their depth, so that they can be hung on a wall. 
         [0007]    However, the LCD has a slow response speed, and the PDP consumes much power. 
         [0008]    Thus, to address these issues of existing flat panel display devices, there is a need to develop a new type of flat panel display device. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention provide a flat panel display device with a new structure using a micro-shutter electrode and a diffusive reflection layer. 
         [0010]    An exemplary embodiment of the present invention provides a display device including: a first substrate; a pixel electrode formed on the first substrate and made of a transparent conductive material; a protrusion formed to be adjacent to the pixel electrode and having a reflection face; a diffusive reflection layer formed on the protrusion and diffusively reflecting incident light; and a micro-shutter electrode moved by an electrostatic force with the pixel electrode and reflecting incident light. 
         [0011]    The diffusive reflection layer may be formed as a white reflection film obtained by depositing a powder such as silicon oxide, aluminum oxide, or the like. 
         [0012]    The micro-shutter electrode may have a fixed end with a convex structure. 
         [0013]    The micro-shutter electrode may have a fixed end, and the fixed end may be connected by a connection ring. 
         [0014]    The connection ring may be made of an elastic material such as silicon. 
         [0015]    Gray levels may be displayed according to an opening and closing degree of the micro-shutter electrode. 
         [0016]    A gray level may be represented by controlling a time interval duration during which the micro-shutter electrode is open. 
         [0017]    The display device may further include a backlight unit including a light source at an outer side of the first substrate. 
         [0018]    The display device may further include a light-recycle layer formed below the pixel electrode and the protrusion on the first substrate to reflect incident light to the backlight unit. The light-recycle layer may be made of a metal or may be formed as a white reflection film obtained by depositing a powder such as silicon oxide, aluminum oxide, or the like. 
         [0019]    The backlight unit may include red, blue, and green light sources, and each light source may be operated at different intervals. 
         [0020]    The device may further include a second substrate facing the first substrate, a color filter formed on the second substrate, and a black matrix formed at a region on the second substrate where the color filter is not formed. 
         [0021]    The micro-shutter electrode may be positioned above the pixel electrode on the first substrate. 
         [0022]    The device may further include a layer made of the same material as that of the diffusive reflection layer on the micro-shutter electrode. 
         [0023]    The device may further include a layer formed between the protrusion and the diffusive reflection layer and made of the same material as that of the micro-shutter electrode. 
         [0024]    The device may further include a passivation layer formed between the pixel electrode and the micro-shutter electrode. 
         [0025]    The micro-shutter electrode may be positioned below the second substrate and above the pixel electrode. 
         [0026]    The device may further include a light absorption layer formed on the first substrate where the pixel electrode is not formed. 
         [0027]    One or more micro-shutter electrodes may be formed per pixel. 
         [0028]    Another embodiment of the present invention provides a display device including: a first substrate; a pixel electrode formed on the first substrate and made of a transparent conductive material; a protrusion formed to be adjacent to the pixel electrode and having a reflection face with a depressed portion and an embossed portion; and a micro-shutter electrode moved by an electrostatic force with the pixel electrode and reflecting incident light. 
         [0029]    The display device may be driven in an active mode in which signals are transferred by using switching elements formed at respective pixels, or driven in a passive mode in which pixels selected by selecting a horizontal axis and a vertical axis of pixels are driven without a switching element for each pixel. 
         [0030]    Yet another embodiment of the present invention provides a method for manufacturing a display device, including: coating an insulation material on a first substrate and patterning the insulation material to form an electrode structure; stacking a metal layer on the electrode structure; and lifting off the electrode structure. 
         [0031]    The method may further include removing the metal layer formed on one of inclined planes of the electrode structure between the stacking of the metal layer and the lifting-off of the electrode structure. 
         [0032]    The method may further include forming a protrusion with a reflection face is at the side of the electrode structure when forming the electrode structure, and stacking the metal layer on the protrusion when stacking the metal layer on the electrode structure, and forming a white reflection film on the electrode structure and the protrusion after stacking the metal layer on the electrode structure and before lifting-off the electrode structure. 
         [0033]    The method may further include removing the metal layer and the white reflection film formed on one of inclined planes of the electrode structure after forming the white reflection film and before lifting-off the electrode structure. 
         [0034]    A depression portion and an embossed portion may be formed on the reflection face of the protrusion. 
         [0035]    The white reflection film may be formed by depositing a powder such as silicon oxide, aluminum oxide, or the like. 
         [0036]    The method may further include forming a color filter covering pattern for covering the color filter may be formed at the side of the electrode structure, and stacking the metal layer on the color filter covering pattern. 
         [0037]    The method may further include: coating an insulation material on a second substrate facing the first substrate and patterning the coated insulation material to form a protrusion and a pixel electrode covering pattern; forming a white reflection film on the protrusion and the pixel electrode covering pattern; and lifting off the pixel electrode covering pattern. 
         [0038]    The white reflection film may be formed by depositing a powder such as silicon oxide, aluminum oxide, or the like. 
         [0039]    The electrode structure may have a protrusion structure formed at one end thereof. 
         [0040]    The method may further include forming a micro-shutter electrode with a convex structure corresponding to the protrusion structure. 
         [0041]    A display device according to the present invention is a flat panel display device with a micro-shutter electrode and a diffusive reflection layer, which improves luminance by enhancing efficiency of light used for displaying images. Gray levels may be determined by electrostatic forces between the pixel electrode and the micro-shutter electrode, and because the opening/closing operation of the micro-shutter electrode is fast, the response speed can be improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1  is a cross-sectional view of a display device according to an embodiment of the present invention. 
           [0043]      FIGS. 2 to 7  show a method of forming each layer on a lower substrate of a display device according to an embodiment of the present invention. 
           [0044]      FIG. 8  is a cross-sectional view showing a state of a micro-shutter electrode when black is displayed in the embodiment of  FIG. 1 . 
           [0045]      FIG. 9  is a cross-sectional view showing a state of the micro-shutter electrode when a gray scale of a certain level is represented in the embodiment of  FIG. 1 . 
           [0046]      FIG. 10  is a cross-sectional view showing a state of the micro-shutter electrode when white is displayed in the embodiment of  FIG. 1 . 
           [0047]      FIG. 11  is a cross-sectional view of a display device according to another embodiment of the present invention. 
           [0048]      FIG. 12  is a cross-sectional view of a display device according to still another embodiment of the present invention in which one micro-shutter is open and another micro-shutter is almost closed. 
           [0049]      FIGS. 13 to 16  show a method of forming each layer of a lower substrate of the display device according to the embodiment of  FIG. 12 . 
           [0050]      FIGS. 17 to 20  show a method of forming each layer on an upper substrate of the display device according to the embodiment of  FIG. 12 . 
           [0051]      FIG. 21  is a cross-sectional view showing a state of the micro-shutter electrode when black is displayed according to the embodiment of  FIG. 12 . 
           [0052]      FIG. 22  is a cross-sectional view showing a state of the micro-shutter electrode when a certain level of gray scale is represented according to the embodiment of  FIG. 12 . 
           [0053]      FIG. 23  is a cross-sectional view showing a state of the micro-shutter electrode when white is displayed in the embodiment of  FIG. 12 . 
           [0054]      FIG. 24  is a cross-sectional view of the display device according to another embodiment of the present invention. 
           [0055]      FIG. 25  is a cross-sectional view of the display device according to another embodiment of the present invention. 
           [0056]      FIG. 26  shows a method of forming an electrode structure and a shutter electrode on a lower substrate of the display device according to another embodiment of the present invention. 
           [0057]      FIG. 27  shows a protrusion according to another embodiment of the present invention. 
           [0058]      FIGS. 28 and 29  show micro-shutter electrodes according to another embodiment of the present invention. 
           [0059]      FIG. 30  is a cross-sectional view of a display device according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0060]    Embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
         [0061]    In the drawings, the thickness of layers, films, panels, regions, etc., may be exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present 
         [0062]    A display device according to an embodiment of the present invention will now be described in detail with reference to  FIG. 1 . 
         [0063]      FIG. 1  is a cross-sectional view of a display device according to an embodiment of the present invention in which one micro-shutter is open and another micro-shutter is almost closed. 
         [0064]    The display device can be divided into a display panel and a backlight unit  300 . The display panel includes a lower substrate  110  and an upper substrate  210  formed at outermost portions thereof, and a thin film transistor (not shown), a pixel electrode  191 , a micro-shutter electrode  192 , a diffusive reflection layer  196 , a color filter  230 , a black matrix  220 , and the like, are formed between the lower substrate  110  and the upper substrate  210 . The backlight unit  300  necessarily includes a light source, and may further include a light guide plate (not shown), a reflection plate (not shown), and the like, according to embodiments of the invention. 
         [0065]    The display panel including the elements of the present invention will now be described in detail. 
         [0066]    The display panel according to an embodiment of the present invention includes the upper substrate  210  and the lower substrate  110 . 
         [0067]    A light-recycle layer  130  is formed on the lower substrate  110 . The light-recycle layer  130  blocks light emitted from the backlight unit  300  that is incident to an unused portion of the display, and returns it to the backlight unit  300 . The light returned to the backlight unit  300  is again reflected from the reflection plate (not shown) of the backlight unit  300  to be incident to the display panel again. Thus, light efficiency can be increased. The light-recycle layer  130  may be formed as a metal layer or as a white reflection film formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film has better reflection efficiency than the metal layer. 
         [0068]    In addition to the light-recycle layer  130 , a gate line (not shown), a data line (not shown), and a thin film transistor (TFT) (not shown) are formed on the lower substrate  110 . The light-recycle layer  130  may be formed together when the gate line and the data line are formed, and the gate line and the data line may also serve as the light-recycle layer  130  according to other embodiments of the invention. 
         [0069]    An insulating layer  140  is formed to cover the gate line, the data line, the TFT, and the light-recycle layer  130 , and includes a contact hole (not shown) exposing a drain electrode of the TFT. 
         [0070]    A pixel electrode  191  is formed on the insulating layer  140  and is connected with the TFT via the contact hole. The pixel electrode  191  is formed of a transparent conductor such as indium tin oxide (ITO), indium zinc oxide (IZO), or the like. 
         [0071]    A passivation layer  180  is formed on the pixel electrode  191 . The passivation layer  180  may be formed over the entire region of the lower substrate. 
         [0072]    The micro-shutter electrodes  192 , protrusions  185 , and the diffusive reflection layer  196  are formed on the passivation layer  180 . 
         [0073]    The micro-shutter electrodes  192  are formed at positions corresponding to the pixel electrodes  191 , and may be moved by an electrostatic force with the pixel electrodes  191 . In this case, the micro-shutter electrodes  192  may be formed such that the regions corresponding to the pixel electrodes  191  can be opened or closed. The micro-shutter electrode  192  may be formed as a thin metal layer to mirror-reflect light that has passed through the transparent pixel electrode  191 . White (or a maximum luminance of a corresponding color) or black may be displayed according to the position of the micro-shutter electrode  192 . A layer  197  made of the same material as the diffusive reflection layer  196  may be formed on the micro-shutter electrodes  192 . The layer  197  is formed in a fabrication process and may be omitted according to other embodiments of the invention. 
         [0074]    Each protrusion  185  is formed at a region that does not correspond to a pixel electrode  191  on the passivation layer  180 . The protrusion  185  is made of an insulating material and has a triangular structure with at least one inclined plane. In an exemplary embodiment of the invention, although the section has a triangular cross-section, a side (i.e., the right inclined plane of the protrusion  185  in  FIG. 1 ) that is not used for image display is not sloped. On the other hand, a side (i.e., the left inclined plane of the protrusion  185  in  FIG. 1 , hereinafter referred to as a “reflection face”) used for displaying an image may be an inclined plane formed at an angle. The reflection face may have various shapes according to the operational shape of the micro-shutter electrode  192 . 
         [0075]    A layer  195  made of the same material as the micro-shutter electrode  192  is formed on a same side of the protrusion  185  on which the diffusive reflection layer  196  is formed. The layer  195  is formed in the same process as the micro-shutter electrode  192 , and may be omitted according to other embodiments of the invention. Unlike the micro-shutter electrode  192  that mirror-reflects light, the diffusive reflection layer  196  diffusively reflects light. Specifically, the diffusive reflection layer  196  can distributedly reflect light in various directions, to thus improve a viewing angle of the display device. The diffusive reflection layer  196  may be formed as a white reflection film obtained by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). 
         [0076]    The structure including the protrusion  185  and the diffusive reflection layer  196  may serve as a spacer that uniformly maintains the space with the upper substrate  210  as shown in  FIG. 1 , and an extra spacer may be additionally formed according to other embodiments of the invention. 
         [0077]    The black matrix  220  and the color filter  230  are formed on the upper substrate  210 . The color filter  230  is formed at a portion through which light that has been reflected from the diffusive reflection layer  196  mostly passes, to add a color to the corresponding light. Thus, the color filter  230  may be formed at a position corresponding to the structure of the protrusion  185  and the diffusive reflection layer  196 . 
         [0078]    The black matrix  220  is formed at a region where the color filter  230  is not formed, blocks light incident from the outside, and eliminates light that is not required for image display. 
         [0079]    The color filter  230 , the black matrix  220 , and the upper substrate  210  have a structure similar to that of a liquid crystal display (LCD), so the upper substrate used in the LCD can be used. 
         [0080]    Also, the backlight unit  300  is similar to that of the LCD, so the backlight unit used in the LCD can also be used as is. In this respect, in an exemplary embodiment of the invention, a film is not required below the lower substrate  110 , reducing fabrication unit cost compared with the LCD. 
         [0081]    A method according to an embodiment of the invention for forming each layer on the lower substrate  110  will now be described with reference to  FIGS. 2 to 7 . 
         [0082]      FIGS. 2 to 7  show a method of forming each layer on a lower substrate of the display device according to an embodiment of the present invention. 
         [0083]      FIG. 2  shows that the gate line, the data line, the TFT, and the light-recycle layer  130  (hidden by the insulating layer  140 ) are formed on the lower substrate  110  on which the insulating layer  140  is stacked, and the contact hole (not shown) exposing the drain electrode of the TFT is formed on the insulating layer  140  and the pixel electrode  191  is formed on the insulating layer  140 . The pixel electrode  191  is formed to be connected with the TFT via the contact hole, and is formed as a transparent conductor such as ITO or IZO. 
         [0084]      FIG. 3  shows the passivation layer  180  covering the pixel electrode  191 . The passivation layer  180  may be formed as an inorganic insulating layer or an organic insulating layer. In this respect, to form the protrusions  185  on the passivation layer  180 , the passivation layer  180  may have a smooth upper surface, so the organic insulating layer may be formed as the passivation layer  180 . 
         [0085]      FIG. 4  shows a method of forming the protrusions  185 , in which an insulating material is stacked on the passivation layer  180  and then patterned to form the protrusions  185  and electrode structures  182  formed at the positions where the micro-shutter electrodes  192  are to be formed. The electrode structure  182  has a triangular sectional structure with a long hypotenuse and a vertical side. The vertical side of the electrode structure  182  may be excessively etched through overetching to have a reverse-tapered structure. This is because, when the electrode structure  182  is removed, a metal material should not be stacked on the vertical side, as shown in  FIG. 7 . For the reverse-tapered structure, the electrode structure  182  may be additionally dry-etched after being patterned. The protrusion  185  may be formed according to various methods such as an imprinting method, a photolithography method, a gravure method, and the like. 
         [0086]    Thereafter, as shown in  FIG. 5 , a metal material is stacked to form the micro-shutter electrode  192  and the layer  195  made of the same material as the micro-shutter electrode  192 . The micro-shutter electrode  192  is formed on the long inclined plane of the electrode structure  182 . 
         [0087]    Thereafter, as shown in  FIG. 6 , the white reflection film is formed by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). The white reflection film is formed on the protrusion  185  and the layer  195  to form the diffusive reflection layer  196 . The white reflection film is also formed on the micro-shutter electrode  192 . 
         [0088]    In steps as shown in  FIGS. 5 and 6 , the material stacked on the electrode structure  182  may be formed only on the longer inclined plane of the electrode structure  182 , but in the actual process, each layer may be formed on the shorter inclined plane. In this case, a step of removing the layers formed on the shorter inclined plane through etching may be additionally performed (see  FIG. 26 ). 
         [0089]    Thereafter, as shown in  FIG. 7 , the insulating material used for forming the protrusion  184  is removed by reflowing or the like. Then, the protrusion  185  remains, but the electrode structure  182  formed under the micro-shutter electrode  192  is removed, allowing the micro-shutter electrode  192  to move. 
         [0090]    A method for representing gray levels in a display device according to an embodiment of the invention formed as described above will now be described with reference to  FIGS. 8 to 10 . 
         [0091]      FIG. 8  is a cross-sectional view showing a state of the micro-shutter electrode when black is displayed in the embodiment of  FIG. 1 ,  FIG. 9  is a cross-sectional view showing a state of the micro-shutter electrode when a gray level is represented in the embodiment of  FIG. 1 , and  FIG. 10  is a cross-sectional view showing a state of the micro-shutter electrode when white is displayed in the embodiment of  FIG. 1 . 
         [0092]    First,  FIG. 8  shows the case of displaying black. 
         [0093]    The micro-shutter electrode  192  is positioned to be as close as possible to the passivation layer  180  due to electromagnetic attraction between the micro-shutter electrode  192  and the pixel electrode  191 . Hereinafter, this is called a case where the micro-shutter electrode  192  is closed. As a result, light emitted from the backlight unit  300  transmits through the pixel electrode  191  but is mirror-reflected by the micro-shutter electrode  192 , failing to further proceed upwardly. Thus, there is no light emitted at the upper portion of the display device, and accordingly black is displayed. 
         [0094]      FIGS. 9 and 10  show a case where the micro-shutter electrode  192  is open to display of a gray level and white, respectively. 
         [0095]    In the display device according to an exemplary embodiment of the invention, the gray levels may be represented depending on the degree of opening of the micro-shutter electrode  192  according to an electrostatic force between the micro-shutter electrode  192  and the pixel electrode  191 . When the micro-shutter electrode  192  is slightly open as shown in  FIG. 9 , light that has passed through the pixel electrode  191  is reflected from the micro-shutter electrode  192 , of which one portion is returned to the backlight unit  300  while another portion is made incident on the diffusive reflection layer  196  to be discharged upwardly at less than a maximum luminance. An image is displayed with the discharged light. 
         [0096]    If the micro-shutter electrode  192  is completely open as shown in  FIG. 10 , the light that has passed through the pixel electrode  191  is reflected from the micro-shutter electrode  192  to be upwardly discharged. As a result, a maximum luminance (white) is displayed. When white is displayed, a repulsive electrostatic force is maximized between the micro-shutter electrode  192  and the pixel electrode  191 .  FIG. 10  shows an exemplary angle of 135° for the micro-shutter electrode  192  is maximally open, but the angle may vary according to other embodiments of the invention. 
         [0097]      FIGS. 8 to 10  show the micro-shutter electrode  192  negatively charged, but without being limited thereto, the micro-shutter electrode  192  may be positively charged according to other embodiments of the invention. The same charges as those on the micro-shutter electrode  192  may be applied to the pixel electrode  191  to display white, while different charges may be applied to the pixel electrode  191  to display black. 
         [0098]      FIG. 11  is a cross-sectional view of a display device according to another embodiment of the present invention. 
         [0099]    Unlike the embodiment of  FIG. 1 , in the present exemplary embodiment of  FIG. 11 , the light-recycle layer  130  is formed separately from a gate line and a data line. 
         [0100]    The light-recycle layer  130  is formed on the lower substrate  110 . The light-recycle layer  130  blocks light emitted from the backlight unit  300  and incident to an unused portion of the display, and returns it to the backlight unit  300 . The light returned to the backlight unit  300  is again reflected from the reflection plate (not shown) of the backlight unit  300  to be incident to the display panel again. Thus, light efficiency can be increased. The light-recycle layer  130  may be formed as a metal layer or as a white reflection film formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film has better reflection efficiency than the metal layer. 
         [0101]    A light-recycle insulating layer  137  is formed on the light-recycle layer  130  to cover the light-recycle layer  130 . The light-recycle insulating layer may be formed on the entire region of the lower substrate  110 , and is formed as an inorganic insulating layer or an organic insulating layer. 
         [0102]    In addition to the light-recycle layer  130 , a gate line (not shown), a data line (not shown), and a TFT (not shown) are formed on the light-recycle insulating layer  137 . In an exemplary embodiment of the invention, the light-recycle layer  130  is separately formed with respect to the gate line, the data line, and the TFT, and the respective elements play only their own roles. 
         [0103]    The insulating layer  140  is formed on the gate line, the data line, and the TFT, covering them, and includes a contact hole (not shown) exposing a drain electrode of the TFT. 
         [0104]    The pixel electrode  191  is formed on the insulating layer  140  and is connected with the TFT via the contact hole. The pixel electrode  191  is formed as a transparent conductor such as ITO or IZO, and a data voltage is applied to the pixel electrode  191  via the TFT. 
         [0105]    The passivation layer  180  is formed on the pixel electrode  191 . The passivation layer  180  may be formed over the entire region of the lower substrate. 
         [0106]    The micro-shutter electrode  192  and the protrusion  185  are formed on the passivation layer  180 , and the diffusive reflection layer  196  is formed on the protrusion  185 . 
         [0107]    The micro-shutter electrodes  192  are formed at positions corresponding to the pixel electrode  191 , and may be moved by an electrostatic force with the pixel electrode  191 . In this case, the micro-shutter electrode  192  may be formed at the region corresponding to the pixel electrode  191 , so that the region can be opened or closed. The micro-shutter electrode  192  is formed as a thin metal layer to mirror-reflect light that has passed through the transparent pixel electrode  191 . White (or a maximum luminance of the corresponding color) or black may be displayed according to the position of the micro-shutter electrode  192 . The layer  197  made of the same material as the diffusive reflection layer  196  may be formed on the micro-shutter electrode  192 . The layer  197  is formed from a fabrication process and may be omitted according to other embodiments of the invention. 
         [0108]    Each protrusion  185  is formed at a region that does not correspond to the pixel electrode  191  on the passivation layer  180 . The protrusion  185  is made of an insulating material and has a triangular structure with at least one hypotenuse. In an exemplary embodiment of the invention, although the section has the triangular cross-section, the side (i.e., the right inclined plane of the protrusion  185  in  FIG. 11 ) that is not used for an image display is not sloped. On the other hand, the side (i.e., the left inclined plane of the protrusion  185  in  FIG. 11 , hereinafter referred to as a “reflection face”) used for displaying an image may be an inclined plane formed at an angle. The reflection face may have various shapes according to the operational shape of the micro-shutter electrode  192 . 
         [0109]    The layer  195  made of the same material as the micro-shutter electrode  192  is formed on a same side of the protrusion  185  on which the diffusive reflection layer  196  is formed. The layer  195  is formed in a same process as the micro-shutter electrode  192 , and may be omitted according to other embodiments of the invention. Unlike the micro-shutter electrode  192  that mirror-reflects light, the diffusive reflection layer  196  diffusively reflects light. Specifically, the diffusive reflection layer  196  can distributedly reflect light in various directions, to thus improve a viewing angle of the display device. The diffusive reflection layer  196  may be formed as a white reflection film obtained by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). 
         [0110]    The structure including the protrusion  185  and the diffusive reflection layer  196  may serve as a spacer that uniformly maintains the space with the upper substrate  210  as shown in  FIG. 11 , and an extra spacer may be additionally formed according to other embodiments of the invention. 
         [0111]    The black matrix  220  and the color filter  230  are formed on the upper substrate  210 . The color filter  230  is formed at a portion through which light that has been reflected from the diffusive reflection layer  196  mostly passes, to add a color to the corresponding light. Thus, the color filter  230  may be formed at a position corresponding to the structure of the protrusion  185  and the diffusive reflection layer  196 . 
         [0112]    The black matrix  220  is formed at a region where the color filter  230  is not formed, blocks light incident from the outside, and eliminates light that is not required for image display. 
         [0113]    The color filter  230 , the black matrix  220 , and the upper substrate  210  have a structure similar to that of a liquid crystal display (LCD), so the upper substrate used in the LCD can be used. 
         [0114]    Also, the backlight unit  300  is similar to that of the LCD, so the backlight unit used in the LCD can also be used as is. In this respect, in an exemplary embodiment of the invention, a film is not required below the lower substrate  110 , reducing fabrication unit cost compared with the LCD. 
         [0115]    As described above, in the exemplary embodiment of  FIG. 11 , the light-recycle layer  130  is formed to be separated from the layer in which the gate line, the data line, and the TFT are formed, and the respective elements play only their own role. 
         [0116]    According to another embodiment of the invention, the micro-shutter electrode may be formed on the upper substrate  210 . Hereinafter, an embodiment thereof will be described in detail with reference to  FIG. 12 . 
         [0117]      FIG. 12  is a cross-sectional view of a display device according to another embodiment of the present invention in which one micro-shutter is open and another micro-shutter is almost closed. 
         [0118]    A display device according to an exemplary embodiment of the invention may be divided into the display panel and the backlight unit  300 . The display panel includes the lower substrate  110  and the upper substrate  210  formed at the outermost portions thereof, and a thin film transistor (not shown), a pixel electrode  191 , a diffusive reflection layer  196 , a micro-shutter electrode  270 , a color filter  230 , a black matrix  220 , and the like, are formed between the lower substrate  110  and the upper substrate  210 . The backlight unit  300  necessarily includes a light source, and may further include a light guide plate (not shown), a reflection plate (not shown), and the like, according to embodiments. 
         [0119]    A display panel according to an embodiment of the present invention will now be described in detail. 
         [0120]    A display panel according to the embodiment of the present invention includes the upper substrate  210  and the lower substrate  110 . 
         [0121]    A light-recycle layer  130  is formed on the lower substrate  110 . The light-recycle layer  130  blocks light emitted from the backlight unit  300  and incident to an unused portion of the display, and returns it to the backlight unit  300 . The light returned to the backlight unit  300  is again reflected from the reflection plate (not shown) of the backlight unit  300  to be incident to the display panel again. Thus, light efficiency can be increased. The light-recycle layer  130  may be formed as a metal layer or as a white reflection film formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film has better reflection efficiency than the metal layer. 
         [0122]    In addition to the light-recycle layer  130 , a gate line (not shown), a data line (not shown), and a thin film transistor (TFT) (not shown) are formed on the lower substrate  110 . The light-recycle layer  130  may be formed together when the gate line and the data line are formed, and the gate line and the data line may also serve as the light-recycle layer  130  according to other embodiments of the invention. 
         [0123]    The insulating layer  140  is formed to cover the gate line, the data line, the TFT, and the light-recycle layer  130 , and includes a contact hole (not shown) exposing a drain electrode of the TFT. 
         [0124]    The pixel electrode  191  is formed on the insulating layer  140  and is connected with the TFT via the contact hole. The pixel electrode  191  is formed as a transparent conductor such as indium tin oxide (ITO), indium zinc oxide (IZO), or the like, and a data voltage is applied to the pixel electrode via the TFT. 
         [0125]    A light absorption layer  181  is formed on the insulating layer  140  at a region where the pixel electrode  191  is not formed. The light absorption layer  181  may be formed with the same material as the black matrix  220  of the upper substrate  210 , and absorbs incident light. 
         [0126]    The protrusion  185  and the diffusive reflection layer  196  are formed on the light absorption layer  181 . 
         [0127]    The protrusion  185  is made of an insulating material, and has a triangular cross section with at least one hypotenuse. Although the section has the triangular cross section, the side (i.e., the right inclined plane of the protrusion  185  in  FIG. 12 ) that is not used for an image display is not sloped. On the other hand, the side (i.e., the left inclined plane of the protrusion  185  in  FIG. 12 , hereinafter referred to as a “reflection face”) used for displaying an image may be an inclined plane formed at an angle. The reflection face may have various shapes according to other embodiments of the invention. 
         [0128]    The diffusive reflection layer  196  is formed on the protrusion  185 . Unlike using mirror-reflection to reflect incident light in one direction, the diffusive reflection layer  196  can distributedly reflect incident light in various directions. As a result, the viewing angle of the display device can be improved. The diffusive reflection layer  196  may be formed as a white reflection film obtained by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). 
         [0129]    The structure including the protrusion  185  and the diffusive reflection layer  196  may serve as a spacer that uniformly maintains the space with the upper substrate  210  as shown in  FIG. 12 , and an extra spacer may be additionally formed according to other embodiments of the invention. 
         [0130]    The black matrix  220 , the color filter  230 , and the micro-shutter electrode  270  are formed on the upper substrate  210 . 
         [0131]    The color filter  230  is formed at a position corresponding to the reflection face of the structure including the protrusion  185  and the diffusive reflection layer  196 , and allows light reflected from the reflection face to mostly pass therethrough. In addition, the color filter  230  adds a color to the light that passes therethrough. 
         [0132]    The black matrix  220  is formed at a region where the color filter  230  is not formed, blocks light incident from the outside, and eliminates light that is not required for image display. 
         [0133]    The micro-shutter electrode  270  is formed under the black matrix  220 . The micro-shutter electrode  270  is not formed on the color filter  230 . 
         [0134]    The micro-shutter electrode  270  is formed at an upper region of the pixel electrode  191 , and may be moved by an electrostatic force with the pixel electrode  191 . In this case, the micro-shutter electrodes  270  may be formed to open and close at the upper region of the pixel electrodes  191 . The micro-shutter electrode  270  may be formed as a thin metal layer to mirror-reflect light that has passed through the transparent pixel electrode  191 . White (or a maximum luminance of a corresponding color) or black may be displayed according to the opening/closing degree of the micro-shutter electrode  270 . 
         [0135]    The backlight unit  300  is similar to that of the LCD, so the backlight unit used in the LCD can also be used as is. In this respect, a film is not required below the lower substrate  110 , reducing fabrication unit cost compared with the LCD. 
         [0136]    A method of forming the respective layers of the display device according to the embodiment of  FIG. 12  will now be described with reference to  FIGS. 13 to 20 .  FIGS. 13 to 16  show a method of forming the respective layers of the lower substrate of the display device according to the embodiment of  FIG. 12 , and  FIGS. 17 to 20  show a method of forming the respective layers on the upper substrate of the display device according to the embodiment of  FIG. 12 . 
         [0137]    First, the method of forming the respective layers on the lower substrate  110  will be described. 
         [0138]      FIGS. 13 to 16  show a method of forming the respective layers of the lower substrate of the display device according to the embodiment of  FIG. 12 . 
         [0139]    With reference to  FIG. 13 , the gate line, the data line, the TFT, and the light-recycle layer  130  (hidden by the insulating layer  140 ) are formed on the lower substrate  110 , on which the insulating layer  140  is stacked to cover them. The contact hole (not shown) exposing the drain electrode of the TFT is formed on the insulating layer  140 , and then the pixel electrode  191  is formed on the insulating layer  140 . The light absorption layer  181  is formed at a region where the pixel electrode  191  is not formed. The pixel electrode  191  is formed to be connected with the TFT via the contact hole, and is formed of the transparent conductor such as ITO or IZO. The light absorption layer  181  may be made of the same material as the black matrix  220 , and absorbs incident light. 
         [0140]      FIG. 14  shows a method of forming the protrusion  185 . An insulating material is stacked on the pixel electrode  191  and the light absorption layer  181  and then patterned to form the protrusion  185  and a pixel electrode covering pattern  187 . Here, the protrusion  185  may be formed according to various methods such as an imprinting method, a photolithography method, a gravure method, and the like. 
         [0141]    Thereafter, as shown in  FIG. 15 , the white reflection film is formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film is formed as the diffusive reflection layer  196  on the protrusion  185 , and is also formed on the pixel electrode covering pattern  187 . 
         [0142]    In  FIG. 15 , a material  193  stacked on the pixel electrode covering pattern  187  may be formed only on the upper surface of the pixel electrode covering pattern  187 , but in the actual process, the material  193  may also be stacked on the side. In this case, a step of etching the material  193  formed on the side to remove it may be additionally performed (see  FIG. 26 ). 
         [0143]    Thereafter, as shown in  FIG. 16 , the insulating material used for forming the protrusion  185  and the material  193  formed on the protrusion  185  are removed by using a lift-off process or the like. In this case, because the protrusion  185  is covered by the white reflection film  196 , it is not removed, while the pixel electrode covering pattern  187  is removed to expose the pixel electrode  191 . 
         [0144]    A method of forming the respective layers on the upper substrate  210  will now be described. 
         [0145]      FIGS. 17 to 20  show a method of forming the respective layers on the upper substrate of the display device according to the embodiment of  FIG. 12 . 
         [0146]      FIG. 17  shows the black matrix  220  and the color filter  230  formed on the upper substrate  210 . The color filter  230  is formed at a position corresponding to the reflection face of the structure including the protrusion  185  and the diffusive reflection layer  196  when the upper substrate  210  and the lower substrate  110  are combined, and allows light reflected from the reflection face to mostly pass therethrough. The black matrix  220  is formed at a region where the color filter  230  is not formed, and absorbs light incident to the black matrix. 
         [0147]    With reference to  FIG. 18 , an insulating material is stacked on the black matrix  220  and the color filter  230  and then patterned to form an electrode structure  245  and a color filter covering pattern  188  at positions where the micro-shutter electrode  270  is to be formed. The electrode structure  245  has a triangular sectional structure with a long hypotenuse and a vertical side. The vertical side of the electrode structure  245  may be excessively etched through overetching to have a reverse-tapered structure. This is because a metal material should not be stacked on the vertical side when the electrode structure  245  is removed, as shown in  FIG. 20 . For the reverse-tapered structure, the electrode structure  245  may be additionally dry-etched after being patterned. Alternatively, the electrode structure  245  may be formed to not have a reverse-tapered structure. 
         [0148]    In this case, the material stacked on the electrode structure  245  may be formed only on the longer inclined plane of the electrode structure  245 , but in the actual process, it may be formed on the shorter inclined plane. In this case, a step of etching the layer formed on shorter inclined plane to remove it may be additionally performed (see  FIG. 26 ). 
         [0149]    Thereafter, as shown in  FIG. 19 , a metal material is stacked to form the micro-shutter electrode  270  and a layer  275 . The micro-shutter electrode  270  is formed on the long inclined plane of the electrode structure  245 . 
         [0150]    Thereafter, as shown in  FIG. 20 , the electrode structure  245  and the color filter covering pattern  188  made of the insulating material are removed by using a lift-off process or the like. The exposed electrode structure  245  and the color filter covering pattern  188  are completely removed. The electrode structure  245  formed under the micro-shutter electrode  270  is removed to allow the micro-shutter electrode  270  to move. 
         [0151]    A method of representing gray levels in the display device formed according to the above-described method will now be described with reference to  FIGS. 21 to 23 . 
         [0152]      FIG. 21  is a cross-sectional view showing a state of the micro-shutter electrode when black is displayed according to the embodiment of  FIG. 12 ,  FIG. 22  is a cross-sectional view showing a state of the micro-shutter electrode when a gray level is displayed according to the embodiment of  FIG. 12 , and  FIG. 23  is a cross-sectional view showing a state of the micro-shutter electrode when white is displayed in the embodiment of  FIG. 12 . 
         [0153]    First,  FIG. 21  shows displaying of black. 
         [0154]    The micro-shutter electrode  270  is positioned to be as close as possible to the upper substrate  210  due to electromagnetic repulsive force between the micro-shutter electrode  270  and the pixel electrode  191 . Hereinafter, this is called a case where the micro-shutter electrode  270  is closed. As a result, light emitted from the backlight unit  300  transmits through the pixel electrode  191  but is mirror-reflected by the micro-shutter electrode  270  to be transmitted back through the pixel electrode  191  or to be incident to the light absorption layer  181  to be absorbed therein. As a result, light cannot proceed upwardly. Thus, there is no light emitted at the upper portion of the display device, and accordingly, black is displayed. 
         [0155]      FIGS. 22 and 23  show the micro-shutter electrode  270  which is open to display a gray level of gray scale or white, respectively. 
         [0156]    In a display device according to an embodiment of the present invention, gray levels may be displayed depending on the degree of opening of the micro-shutter electrode  270  according to an electrostatic force between the micro-shutter electrode  270  and the pixel electrode  191 . When the micro-shutter electrode  270  is slightly open as shown in  FIG. 22 , light that has passed through the pixel electrode  191  is reflected from the micro-shutter electrode  270 , of which only a portion is incident on the diffusive reflection layer  196  to be upwardly discharged at less than a maximum luminance. An image is displayed with the discharged light. Meanwhile, light that is not emitted to outside is mostly incident to the light absorption layer  181  to be absorbed therein. 
         [0157]    When the micro-shutter electrode  270  is completely open as shown in  FIG. 23 , light that has passed through the pixel electrode  191  is reflected from the micro-shutter electrode  270  to be incident to the diffusive reflection layer  196  and then upwardly discharged. As a result, a maximum luminance (white) is displayed. When white is displayed, a repulsive electrostatic force is maximized between the micro-shutter electrode  270  and the pixel electrode  191 .  FIG. 23  shows an exemplary open angle of 135° at which the micro-shutter electrode  192  is maximally open, but the angle may vary according to other embodiments of the invention. 
         [0158]      FIGS. 21 to 23  show the micro-shutter electrode  270  negatively charged, but without being limited thereto, the micro-shutter electrode  270  may be positively charged according to other embodiments of the invention. Different charges may be applied to the micro-shutter electrode  270  and the pixel electrode  191  to display white, and the same charges may be applied to the pixel electrode  191  and micro-shutter electrode  270  to display black. 
         [0159]      FIGS. 24 and 25  show other embodiments of the present invention. 
         [0160]      FIG. 24  is a cross-sectional view of a display device according to yet another embodiment of the present invention. 
         [0161]    Unlike the embodiment of  FIG. 12 , in the embodiment as shown in  FIG. 24 , an upper insulating layer  183  is formed on the pixel electrode  191  and the light absorption layer  181 . The upper insulating layer  183  prevents the pixel electrode  191  and the micro-shutter electrode  270  from being electrically connected when the micro-shutter electrode  270  is completely open. 
         [0162]    The display device as shown in  FIG. 24  may be divided into the display panel and the backlight unit  300 . The display panel includes the lower substrate  110  and the upper substrate  210  formed at the outermost portions thereof, and the thin film transistor (not shown), the pixel electrode  191 , the diffusive reflection layer  196 , the micro-shutter electrode  270 , the color filter  230 , the black matrix  220 , and the like, are formed between the lower substrate  110  and the upper substrate  210 . The backlight unit  300  necessarily includes a light source, and may further include a light guide plate (not shown), a reflection plate (not shown), and the like, according to other embodiments of the invention. 
         [0163]    A display panel according to an embodiment of the present invention will now be described in detail. 
         [0164]    A display panel according to an embodiment of the present invention includes the upper substrate  210  and the lower substrate  110 . 
         [0165]    A light-recycle layer  130  is formed on the lower substrate  110 . The light-recycle layer  130  blocks light emitted from the backlight unit  300  that is incident to an unused portion of the display after being, and returns it to the backlight unit  300 . The light returned to the backlight unit  300  is again reflected from the reflection plate (not shown) of the backlight unit  300  to be incident to the display panel again. Thus, light efficiency can be increased. The light-recycle layer  130  may be formed as a metal layer or as a white reflection film formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film has better reflection efficiency than the metal layer. 
         [0166]    In addition to the light-recycle layer  130 , a gate line (not shown), a data line (not shown), and a thin film transistor (TFT) (not shown) are formed on the lower substrate  110 . The light-recycle layer  130  may be formed together when the gate line and the data line are formed, and the gate line and the data line may also serve as the light-recycle layer  130  according to other embodiments of the invention. 
         [0167]    The insulating layer  140  is formed to cover the gate line, the data line, the TFT, and the light-recycle layer  130 , and includes a contact hole (not shown) exposing a drain electrode of the TFT. 
         [0168]    The pixel electrode  191  is formed on the insulating layer  140  and connected with the TFT via the contact hole. The pixel electrode  191  is formed as a transparent conductor such as indium tin oxide (ITO), indium zinc oxide (IZO), or the like. 
         [0169]    The light absorption layer  181  is formed on the insulating layer  140  at a region where the pixel electrode  191  is not formed. The light absorption layer  181  may be formed with the same material as the black matrix  220  of the upper substrate  210 , and absorbs incident light. 
         [0170]    The upper insulating layer  183  is formed on the pixel electrode  191  and the light absorption layer  181 . The upper insulating layer  183  prevents the pixel electrode  191  from being electrically connected with the micro-shutter electrode  270 . 
         [0171]    The protrusion  185  and the diffusive reflection layer  196  are formed on the light insulating layer  183  at an upper portion of the upper insulating layer  183 . 
         [0172]    The protrusion  185  is made of an insulating material, and has a triangular cross section with at least one hypotenuse. Although the section has the triangular cross section, the side (i.e., the right inclined plane of the protrusion  185  in  FIG. 24 ) that is not used for an image display is not sloped. On the other hand, the side (i.e., the left inclined plane of the protrusion  185  in  FIG. 24 , hereinafter referred to as a “reflection face”) used for displaying an image may be an inclined plane formed at an angle. The reflection face may have various shapes according to other embodiments of the invention. 
         [0173]    The diffusive reflection layer  196  is formed on the protrusion  185 . Unlike a mirror-reflection to reflect incident light in one direction, the diffusive reflection layer  196  can distributedly reflect incident light in various directions. As a result, a viewing angle of the display device can be improved. The diffusive reflection layer  196  may be formed as a white reflection film obtained by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). 
         [0174]    The structure including the protrusion  185  and the diffusive reflection layer  196  may serve as a spacer that uniformly maintains the space with the upper substrate  210  as shown in  FIG. 24 , and an extra spacer may be additionally formed according to other embodiments of the invention. 
         [0175]    The black matrix  220 , the color filter  230 , and the micro-shutter electrode  270  are formed on the upper substrate  210 . 
         [0176]    The color filter  230  is formed at a position corresponding to the reflection face of the structure including the protrusion  185  and the diffusive reflection layer  196 , and allows light reflected from the reflection face to mostly pass therethrough. In addition, the color filter  230  adds a color to the light that passes therethrough. 
         [0177]    The black matrix  220  is formed at a region where the color filter  230  is not formed, blocks light incident from the outside, and eliminates light that is not required for image display. 
         [0178]    The micro-shutter electrode  270  is formed under the black matrix  220 . The micro-shutter electrode  270  is not formed on the color filter  230 . 
         [0179]    The micro-shutter electrode  270  is formed at an upper region of the pixel electrode  191 , and may be moved by the electrostatic force with the pixel electrode  191 . In this case, the micro-shutter electrodes  270  may be opened or closed at the upper region of the pixel electrodes  191 . The micro-shutter electrode  270  may be formed as a thin metal layer to mirror-reflect light that has passed through the transparent pixel electrode  191 . White (or a maximum luminance of a corresponding color) or black may be displayed according to the opening/closing degree of the micro-shutter electrode  270 . 
         [0180]    The backlight unit  300  is similar to that of the LCD, so the backlight unit used in the LCD can also be used as is. In this respect, a film is not required below the lower substrate  110 , reducing fabrication unit cost compared with the LCD. 
         [0181]      FIG. 25  is a cross-sectional view of a display device according to another embodiment of the present invention. 
         [0182]    Unlike the backlight unit  300  that emits white light in  FIG. 12 , the display device as shown in  FIG. 25  discriminates the blue, green, and red colors and emits light of each color for a certain time. Specifically, blue light is emitted during a first time period, green light is emitted during a next time period, and then blue light is emitted during the following time period. The time period duration is short, and light of each color is added to allow a color image to be visible. 
         [0183]    The display device as shown in  FIG. 25  may be divided into the display panel and the backlight unit  300 . The display panel includes the lower substrate  110  and the upper substrate  210  formed at the outermost portions thereof, and the thin film transistor (not shown), the pixel electrode  191 , the diffusive reflection layer  196 , the micro-shutter electrode  270 , the black matrix  220 , and the like, are formed between the lower substrate  110  and the upper substrate  210 . The backlight unit  300  necessarily includes a light source, and may further include a light guide plate (not shown), a reflection plate (not shown), and the like, according to other embodiments of the invention. 
         [0184]    A display panel according to an embodiment of the present invention will now be described in detail. 
         [0185]    A display panel according to an embodiment of the present invention includes the upper substrate  210  and the lower substrate  110 . 
         [0186]    The light-recycle layer  130  is formed on the lower substrate  110 . The light-recycle layer  130  blocks light emitted from the backlight unit  300  that is incident to an unused portion of the display, and returns it to the backlight unit  300 . The light incident to the backlight unit  300  is again reflected from the reflection plate (not shown) of the backlight unit  300  to be incident to the display panel again. Thus, light efficiency can be increased. The light-recycle layer  130  may be formed as a metal layer or as a white reflection film formed by depositing a powder such as silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The white reflection film has better reflection efficiency than the metal layer. 
         [0187]    In addition to the light-recycle layer  130 , a gate line (not shown), a data line (not shown), and a thin film transistor (TFT) (not shown) are formed on the lower substrate  110 . The light-recycle layer  130  may be formed together when the gate line and the data line are formed, and the gate line and the data line may also serve as the light-recycle layer  130  according to other embodiments of the invention. 
         [0188]    The insulating layer  140  is formed to cover the gate line, the data line, the TFT, and the light-recycle layer  130 , and includes a contact hole (not shown) exposing a drain electrode of the TFT. 
         [0189]    The pixel electrode  191  is formed on the insulating layer  140  and connected with the TFT via the contact hole. The pixel electrode  191  is formed as a transparent conductor such as indium tin oxide (ITO), indium zinc oxide (IZO), or the like. 
         [0190]    The light absorption layer  181  is formed at a region on the insulating layer  140  where the pixel electrode  191  is not formed. The light absorption layer  181  may be formed with the same material as the black matrix  220  of the upper substrate  210 , and absorbs incident light. 
         [0191]    The protrusion  185  and the diffusive reflection layer  196  are formed on the light absorption layer  181 . 
         [0192]    The protrusion  185  is made of an insulating material, and has a triangular structure with at least one hypotenuse. Although the section has a triangular structure, the side (i.e., the right inclined plane of the protrusion  185  in  FIG. 25 ) that is not used for an image display is not sloped. On the other hand, the side (i.e., the left inclined plane of the protrusion  185  in  FIG. 25 , hereinafter referred to as a “reflection face”) used for displaying an image may be an inclined plane formed at an angle. The reflection face may have various shapes according to other embodiments of the invention. 
         [0193]    The diffusive reflection layer  196  is formed on the protrusion  185 . Unlike a mirror-reflection to reflect incident light in one direction, the diffusive reflection layer  196  can distributedly reflect incident light in various directions. As a result, a viewing angle of the display device can be improved. The diffusive reflection layer  196  may be formed as a white reflection film obtained by depositing a powder such as silicon oxide (SiO 2 ) or aluminum oxide (Al 2 O 3 ). 
         [0194]    The structure including the protrusion  185  and the diffusive reflection layer  196  may serve as a spacer that uniformly maintains the space with the upper substrate  210  as shown in  FIG. 25 , and an extra spacer may be additionally formed according to other embodiments of the invention. 
         [0195]    The black matrix  220  and the micro-shutter electrode  270  are formed on the upper substrate  210 . 
         [0196]    In an exemplary embodiment of the invention, there is no need to form a color filter, because the backlight unit  300  emits light of each color. Thus, the portion where the color filter is generally formed is empty and the black matrixes  220  are formed at other regions. 
         [0197]    The black matrix  220  blocks light from the outside and removes light that is not required for image display. 
         [0198]    The micro-shutter electrode  270  may be formed under the black matrix  220 . The micro-shutter electrode  270  may be formed on the black matrix  220 . 
         [0199]    The micro-shutter electrode  270  is formed at an upper region of the pixel electrode  191 , and may be moved by the electrostatic force with the pixel electrode  191 . In this case, the micro-shutter electrodes  270  may be opened or closed at the upper region of the pixel electrodes  191 . The micro-shutter electrode  270  may be formed as a thin metal layer to mirror-reflect light that has passed through the transparent pixel electrode  191 . White (or a maximum luminance of a corresponding color) or black may be displayed according to the opening/closing degree of the micro-shutter electrode  270 . 
         [0200]    The backlight unit  300  includes blue, green, and red light sources  400 , and emits light of the colors at different time intervals. Specifically, the backlight unit  300  emits blue light during a first time period, emits green light during a next time period, and then emits blue light during the following time period. The time period duration is short, and light of each color is added to allow a color image to be visible. 
         [0201]    Such backlight unit  300  can be applicable to the embodiment of  FIG. 1 , and may be used to replace the structure with the color filter  230  in the embodiment of  FIG. 1 . 
         [0202]      FIGS. 8 to 10  and  FIGS. 21 to 23  show a method of displaying gray levels of the display device according to embodiments of the present invention. As shown in the drawings, to adjust the gray levels, the opening/closing degree of the micro-shutter electrodes  192  and  270  are adjusted. The opening/closing of the micro-shutter electrodes  192  and  270  relies on the electrostatic force with the pixel electrode  191 , and in this case, it may be challenging to control the thin micro-shutter electrodes  192  and  270 . In such a case, the gray levels can be displayed in the following manner. 
         [0203]    Specifically, a single frame is divided into a plurality of intervals, and the micro-shutter electrodes  192  and  270  are open during the intervals according to the corresponding gray levels and are closed in the remaining intervals. For example, if 64 gray levels are displayed, one frame is divided into 63 intervals, and when black is displayed, the micro-shutter electrodes  192  and  270  are all closed, and when a gray level of 1 is represented, the micro-shutter electrodes  192  and  270  are completely open during one interval. More gray levels can be expressed by increasing the number of open intervals of the micro-shutter electrodes  192  and  270 . Accordingly, the amount of exposed light during one frame can be controlled to display gray levels. 
         [0204]      FIG. 26  shows a method of forming an electrode structure and a shutter electrode on the lower substrate of a display device according to another embodiment of the present invention. 
         [0205]    Unlike the embodiment shown in  FIGS. 3 to 7 , an additional step of etching a layer stacked on the shorter inclined plane of the electrode structure  182  is performed. 
         [0206]    First, like those as shown in  FIGS. 3 and 4 , the protrusion  185  and the electrode structure  182  are already formed, and a metal material and a material for the white reflection film are stacked to form the micro-shutter electrode  192  as shown in  FIG. 26(   a ). As noted in  FIG. 26(   a ), the metal material and the material for the white reflection film are also stacked on the shorter inclined plane of the electrode structure  182 . 
         [0207]    Next, as shown in  FIG. 26(   b ), the metal layer on the shorter inclined plane of the electrode structure  182  is selectively etched through photolithography or the like. The etched region is indicated by “PT” in  FIG. 26(   b ). 
         [0208]    Then, as shown in  FIG. 26(   c ), the electrode structure  182  is removed by reflowing or the like. Thus, an erroneous formation of the micro-shutter electrode  192  can be prevented in advance. 
         [0209]    In  FIG. 26 , the electrode structure  182  is subjected to reflow, but other layers (e.g., the pixel electrode covering pattern  187 ) may be partially removed through etching in a step previous to the reflow. 
         [0210]      FIG. 27  shows a protrusion according to another embodiment of the present invention. 
         [0211]    The protrusion  185 - 1  according to the embodiment as shown in  FIG. 27  has an embossed reflection face. That is, the reflection face of the protrusion  185 - 1  includes depressed portions and embossed portions (protrusions and depressions). The protrusions and depressions formed on the reflection face facilitate a diffusive reflection, so the white reflection film may not need to be formed on the protrusion  185 - 1 . The protrusion  185 - 1  according to the embodiment of  FIG. 27  may be formed in various manners, and can be easily formed by changing the design of a mold used for imprinting. Only two depressed portions and embossed portions are shown in  FIG. 27 , but various numbers and patterns of depressed portions and embossed portions can be formed and their size can be varied according to other embodiments of the invention. 
         [0212]      FIGS. 28 and 29  show micro-shutter electrodes according to another embodiment of the present invention. 
         [0213]    The micro-shutter electrodes should have a structure that moves subject to an electrostatic force. Thus, a fixed end (its opposite end is called a free end) of the micro-shutter electrode is frequently stressed.  FIGS. 28 and 29  show a structure for reducing stress on the fixed end of the micro-shutter electrode  192 - 1 . 
         [0214]    First,  FIG. 28  shows an exemplary embodiment in which a convex structure is added to the fixed end of the micro-shutter electrode  192 - 1 .  FIG. 28(   a ) shows an electrode structure  182 - 1  for forming the micro-shutter electrode  192 - 1  of  FIG. 28 , and  FIG. 28(   b ) shows the micro-shutter electrode  192 - 1 . 
         [0215]    As shown in  FIG. 28(   a ), the electrode structure  182 - 1  is formed to have a protrusion structure at the side of the fixed end of the micro-shutter electrode  192 - 1 . Then, after a metal material and a material for the white reflection film are stacked, the electrode structure  182 - 1  is removed through reflow to form the micro-shutter electrode  192 - 1  with the convex structure as shown in  FIG. 28(   b ). 
         [0216]    As a result, although the micro-shutter electrode  192 - 1  moves, stress applied to the fixed end thereof can be reduced owing to the protrusion structure. 
         [0217]      FIG. 29  shows another structure for removing stress. 
         [0218]    With reference to  FIG. 29 , a fixed end of a micro-shutter electrode  192 - 2  is cut and fixed to the substrate by using a connection ring  197 - 5  made of an elastic material such as silicon. Because the micro-shutter electrode  192 - 2  is already separated, the micro-shutter electrode  192 - 2  itself is not stressed, while the connection ring  197 - 5  made of silicon or the like is stressed instead. In this respect, however, silicon is more resistant to stress compared with a metallic material, so the performance and life span of the display device can be improved. 
         [0219]      FIG. 30  is a cross-sectional view of a display device according to another embodiment of the present invention. 
         [0220]    The display device as shown in  FIG. 30  is similar to that of the embodiment as shown in  FIG. 1 , but unlike the embodiment of  FIG. 1 , the display device according to the embodiment as shown in  FIG. 30  includes two micro-shutter electrodes  192  in a single pixel. Two pixel electrodes  191  are formed to correspond thereto. 
         [0221]    With the structure as shown in  FIG. 30 , because two micro-shutter electrodes  192  are formed, the two micro-shutter electrodes  192  can be adjusted to represent gray levels, so gray level display can have a higher resolution. In addition, the display device can have a higher aperture ratio to improve performance. 
         [0222]    Although  FIG. 30  shows two micro-shutter electrodes in the single pixel, three or more micro-shutter electrodes may also be formed according to other embodiments of the invention. 
         [0223]    The structure of  FIG. 30  is a modification of the structure of  FIG. 1 , and the structure of  FIG. 12  may have two or more micro-shutter electrodes for a single pixel electrode. 
         [0224]    As described above, a display device using the micro-shutter electrode can not only be used in an active mode in which signals are transferred by using switching elements formed at respective pixels, but also in a passive mode in which a horizontal axis and a vertical axis of pixels are selected to select crossed pixels and apply voltage thereto without a switching element for each pixel. 
         [0225]    While embodiments of this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.