Abstract:
A structure of an interference display cell is provided. The cell comprises a first plate and a second plate, wherein a support is located between the first plate and the second plate. The second plate is a deformable and reflective plate. An incident light from one side of the first plate is modulated and only specific frequency light reflects by the second plate. The frequency of the reflected light is related to the distance between the first plate and the second plate. The support has at least one arm. The arm&#39;s stress makes the arm hiking upward or downward. The distance between the first plate and the second plate is also changed. Therefore, the frequency of the reflected light is altered.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a structure of an optical interference display. More particularly, the present invention relates to a structure of an optical interference display with posts of arms.  
         BACKGROUND OF THE INVENTION  
         [0002]    Planar displays are popular for portable displays and displays with space limits because they are light and small in size. To date, planar displays in addition to liquid crystal displays (LCD), organic electro-luminescent displays (OLED), plasma display panels (PDP) and so on, as well as a mode of the optical interference display are of interest.  
           [0003]    U.S. Pat. No. 5,835,255 discloses an array of display units of visible light that can be used in a planar display. Please refer to FIG. 1, which depicts a cross-sectional view of a display unit in the prior art. Every optical interference display unit  100  comprises two walls,  102  and  104 . Posts  106  support these two walls  102  and  104 , and a cavity  108  is subsequently formed. The distance between these two walls  102  and  104 , that is, the length of the cavity  108 , is D. One of the walls  102  and  104  is a hemi-transmissible/hemi-reflective layer with an absorption rate that partially absorbs visible light, and the other is a light reflective layer that is deformable when voltage is applied. When the incident light passes through the wall  102  or  104  and arrives in the cavity  108 , in all visible light spectra, only the visible light with the wavelength corresponding to the formula 1.1 can generate a constructive interference and can be emitted, that is,  
           2D=Nλ  (1.1)  
           [0004]    where N is a natural number.  
           [0005]    When the length D of cavity  108  is equal to half of the wavelength times any natural number, a constructive interference is generated and a sharp light wave is emitted. In the meantime, if the observer follows the direction of the incident light, a reflected light with wavelength λ 1  can be observed. Therefore, the display unit  100  is “open”.  
           [0006]    The first wall  102  is a hemi-transmissible/hemi-reflective electrode that comprises a substrate, an absorption layer, and a dielectric layer. Incident light passing through the first wall  102  is partially absorbed by the absorption layer. The substrate is made from conductive and transparent materials, such as ITO glass or IZO glass. The absorption layer is made from metal, such as aluminum, chromium or silver and so on. The dielectric layer is made from silicon oxide, silicon nitrite or metal oxide. Metal oxide can be obtained by directly oxidizing a portion of the absorption layer. The second wall  104  is a deformable reflective electrode. It shifts up and down by applying a voltage. The second wall  104  is typically made from dielectric materials/conductive transparent materials, or metal/conductive transparent materials.  
           [0007]    [0007]FIG. 2 depicts a cross-sectional view of a display unit in the prior art after applying a voltage. As illuminated in FIG. 2, while driven by the voltage, the wall  104  is deformed and falls down towards the wall  102  due to the attraction of static electricity. At this time, the distance between wall  102  and  104 , that is, the length of the cavity  108  is not exactly zero, but is d, which can be zero. If we use d instead of D in formula 1.1, only the visible light with a wavelength satisfying formula 1.1, which is λ 2 , can generate a constructive interference, and be reflected by the wall  104 , and pass through the wall  102 . Because wall  102  has a high light absorption rate for light with wavelength λ 2 , all the incident light in the visible light spectrum is filtered out and an observer who follows the direction of the incident light cannot observe any reflected light in the visible light spectrum. The display unit  100  is now “closed”.  
           [0008]    An array comprising the display unit  100  controlled by voltage operation is sufficient for a single color planar display, but not for a color planar display. A method known to the art is to manufacture a pixel which comprises three display units with different lengths of the cavities. FIG. 3 and FIG. 4 are cross-section views for the color planar displays comprising display unit known to the arts. FIG. 3 illuminates a cross-section view for a prior art multi-layered color planar display. Multi-layered color planar display  200  comprises three layers, display units  202 ,  204  and  206 . An incident light  208  is reflected by display units  202 ,  204  and  206 . The wavelengths of the reflected light are different, for example, they can be red light, green light and blue light. The reasons to have reflected light with three different wavelengths is that the length of the cavities of display units  202 ,  204  and  206  are different, and also different reflective mirrors are used. One of the disadvantages of a multi-layered color planar display is its poor resolution. Also, as illuminated in FIG. 3, the blue light is less bright than the red light.  
           [0009]    [0009]FIG. 4 illuminates a cross-section view for a prior at matrix color planar display. Three display units, display units  302 ,  304  and  306  are formed on a substrate  300 . An incident light  308  is reflected by display units  302 ,  304  and  306 . The wavelengths of the reflected light are different, for example, they are red light, green light and blue light. The reason to have reflected light with three different wavelengths is that the lengths of the cavities of display units  302 ,  304  and  306  are different. It is not required to use different reflective mirrors. The resolution is good, and the brightness of every color light is similar. However, display units with three different lengths of cavities need to be manufactured separately, for example, the region for forming the display units  304  and  306  is shielded by photo-resist while the process for forming the display unit  302  is performed. The manufacturing process is complicated and the yield is low. Moreover, the errors introduced during the manufacturing process, for instance, the errors of the lengths of cavities may cause red shift or blue shift. The mistake is uncorrectable and the substrate is wasted.  
           [0010]    Therefore, it is important to develop a color optical interference display plate which has high resolution and brightness and is easy to manufacture.  
         SUMMARY OF THE INVENTION  
         [0011]    It is therefore an objective of the present invention to provide an optical interference display unit structure used to form a color optical interference display. The resolution and brightness of the color optical interference display is high.  
           [0012]    One objective of this invention is to provide an optical interference display unit structure applied in the production color optical interference display plate. The manufacturing process is simple and the yield of the manufacture is high.  
           [0013]    It is another an objective of the present invention to provide an optical interference display unit structure applied in the production color optical interference display plate. The posts of the optical interference display unit structure have at least one arm.  
           [0014]    In accordance with the foregoing objectives of the present invention, one preferred embodiment of the invention provides an optical interference display unit structure. The optical interference display unit structure has a first electrode and a second electrode. Posts are located between the two electrodes and support the electrodes to form a cavity. The length of the cavity is D. The post is consisted by a support and at least an arm. The first plate is a semi-transparent electrode, and the second plate is a deformable reflective electrode.  
           [0015]    In accordance with the foregoing objectives of the present invention, one preferred embodiment of the invention provides an optical interference display unit structure. The optical interference display unit structure has a first electrode and a second electrode. Posts are located between the two electrodes and support the electrodes to form a cavity. The post has at least an arm and the shape of the post is T-shape or ┌-shape. After a thermal process, such as a backing, the arm may generate displacement by stress action. The arm may generate displacement as the pivot of the support caused by stress action. An end of the arm adjacent to the support has less displacement, but another end of the arm has more displacement. The displacement of the arm may change the position of the second wall. The length of the cavity in the prior art is decided by the thickness of a sacrificial layer. In the present invention, the length of the cavity is decided by the displacement of the arm(s).  
           [0016]    In the present invention, the arms with the ratios of various lengths to thicknesses have various amounts of stress, and displacements and directions generated by arms are various during baking. Therefore, the arms with the ratios of various lengths to thicknesses may be used for controlling the length of the cavity, instead of the various thicknesses of the sacrificial layers used in the various processes of the display units to control various wavelengths of light reflected in the prior art. There are many advantages in the above way. First of all, the cost drops drastically. The thickness of the cavity in the prior art is the thickness of the sacrificial layer, and the sacrificial layer needs to be removed at the end of the process. However, using an upward displacement of the arms in the present invention increases the length of the cavity, so that the length of the cavity is greater than the thickness of the sacrificial layer, even if the thickness of the sacrificial layer is substantially decreased while forming the same length of cavities. Therefore, the material used for manufacturing the sacrificial layer is substantially reduced. The second, the process time is shortened. The release etch process of the metal sacrificial layer in the prior art consumes lots of time, because the sacrificial layer is removed by an etching gas that must permeate the spaces between the posts. The present invention utilizes a mask for a front exposure, so the sacrificial layer can be transparent materials such as dielectric materials, instead of opaque materials such as metal and the like as in the prior art. Besides, the thickness used by the sacrificial layer can be substantially reduced, so the time required for the release etch process can be also drastically decreased. Third, the color optical interference display formed by using posts can substantially reduce complexity of the process. The difference in the ratios of lengths to thicknesses of arms of posts is used for changing the stress of the arms. After baking, various optical interference display units have various lengths of the cavities due to the displacement of arms, such that reflected light is changed with various wavelengths, such as red, green, and blue lights, so as to obtain various color lights.  
           [0017]    In accordance with another an objective of the present invention, one preferred embodiment of the invention provides a matrix color planar display structure. Each matrix color planar display unit has three optical interference, display units. Every optical interference display unit comprises at least a first plate and a second plate. The two plates are set in parallel. The first plate is a semi-transparent electrode, and the second plate is a deformable reflective electrode. The two plates are supported by posts and a cavity is formed. Each arm of the T-shaped post of the optical interference display unit has variable length/ thickness ratio and stress. Therefore, after baking, each optical interference display unit has various cavity lengths due to the various displacements of arms, such that reflected light is changed with different wavelengths, such as red, green, and blue light. These in turn provide various color lights for a matrix color planar display structure.  
           [0018]    In accordance with the color planar display consisting of an array of optical interference display units disclosed by the present invention, the advantages of a matrix color planar display according to the prior art are retained, including high resolution and high brightness, as well as the advantages of a multi-layered color planar display with a simple process and high yield in the prior art. It is understood that the present invention discloses an optical interference display unit which not only keeps all advantages of the prior optical interference color planar display such as high resolution, high brightness, simple process and high yield during forming arrays, but also increases the window during processing and raises the yield of the optical interference color planar display.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    These and other features, aspects, and advantages of the present invention will be more fully understood by reading the following detailed description of the preferred embodiment, with reference made to the accompanying drawings as follows:  
         [0021]    [0021]FIG. 1 depicts a cross-sectional view of a display unit in the prior art;  
         [0022]    [0022]FIG. 2 depicts a cross-sectional view of a display unit in the prior art after applying a voltage;  
         [0023]    [0023]FIG. 3 depicts a cross-sectional view of a multi-layered color planar display in the prior art;  
         [0024]    [0024]FIG. 4 depicts a cross-sectional view of a matrix color planar display in the prior art;  
         [0025]    [0025]FIG. 5 depict an optical interference display unit structure according to the first preferred embodiment of this invention; and  
         [0026]    [0026]FIG. 6 depict an optical interference display unit according to the second preferred embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    In order to provide more information of the optical interference display unit structure, the first embodiment is provided herein to explain the optical interference display unit structure in this invention. In addition, the second embodiment is provided to give further description of the optical interference color planar display formed with an array of the optical interference display unit.  
       Embodiment 1  
       [0028]    [0028]FIG. 5 depict an optical interference display unit structure according to the first preferred embodiment of this invention. Please refer to FIG. 5, an optical interference display unit  500  which functions as a color changeable pixel comprises at least a first plate  502  and a second plate  504 . The two plates are set in parallel. The first plate  502  and the second plate  504  are selected from the group consisting of narrowband mirrors, broadband mirrors, non-metal mirrors, metal mirrors and the combination thereof.  
         [0029]    The first plate  502  is a semi-transparent electrode which comprises a conductive substrate  5021 , an absorption layer  5022 , and a dielectric layer  5023 . An incident light going through light incidence electrode  502  is partially absorbed by the absorption layer  5022 . The conductive substrate  5021  is made from a conductive transparent material, such as ITO and IZO. The absorption layer  5022  is made from metal, such as aluminum or silver. The dielectric layer  5023  is made from silicon oxide, silicon nitrite or metal oxide, which can be obtained by oxidation of part of the absorption layer  5022 . The second plate  504  is a deformable reflective electrode. It shifts by the voltage applied. The second plate  504  is made from a dielectric material/conductive semi- or non-transparent material, or metal/conductive transparent material.  
         [0030]    The two plates  502  and  504  are supported by a post  512 . The post  512  has a support  514 , which is located in an opening  508  and arms  5121 ,  5122 . The length and thickness of the arms  5121  and  5122  depend on desired demand. Sequentially, a thermal process, such as baking, is performed. The arms  5121  and  5122  of the post  512  may generate displacement as the pivot of the support  514  caused by stress action, where ends of the arm  5121  and the arm  5122  adjacent to the support  514  have less displacement, but another ends of the arm  5121  and  5122  have more displacement. The displacement of the arm  5121  and  5122  may change the position of the second electrode  504 .  
         [0031]    The length of the cavity of the optical interference display unit in the prior art is decided by the thickness of a sacrificial layer. The length of the cavity is D if the thickness of the sacrificial layer is D. In this embodiment, a cavity  510  is formed between the first electrode  502  and the second electrode  504  supported by posts  512 . The posts  512  have the arms  5121  and  5122 . The ratio of lengths to thicknesses of the arms  5121  and  5122  decide stress thereof, and a dotted line  5121 ′ and a dotted line  5122 ′ label the positions prior to performing a thermal process of the arms  5121  and  5122 . After performing the thermal process, the arms  5121  and  5122  may generate displacement; therefore the position of the second electrode  504  changes from the original position labeled by the dotted line  504 ′, and the length D′ of the cavity  510  between the first electrode  502  and the second electrode  504  changes from the original length D. Since the length of the cavity  520  is changed, the frequency of a reflected light changes following the length of the cavity  520 . In general, when post  512  is made from polyamide compounds, the ratio of lengths to thicknesses of the arms  5121  and  5122  is between 5 and 50, and the length D′ of the cavity  510  is approximately 1.5 to 3 times the length D of the thickness of the sacrificial layer. Of course, the ratio of lengths to thicknesses of the arms  5121  and  5122  can be changed to make the length D′ of the baked cavity  510  smaller than the thickness of the sacrificial layer.  
         [0032]    In this invention, the materials suitable for forming posts  512  include positive photoresists, negative photoresists, and all kinds of polymers such as acrylic resins and epoxy resins.  
       Embodiment 2  
       [0033]    Referring is made to FIG. 6, FIG. 6 shows a cross-section view of an array of the optical interference display unit provided in the second embodiment of this invention. An array of modulation 600 comprises three optical interference display units: optical interference display unit  602 , optical interference display unit  604  and optical interference display unit  606 . Every optical interference display unit is a color changeable pixel. The structure of optical interference display unit is the same as the one provided in embodiment 1. The difference of the three optical interference display units is the arms of the posts of the optical interference display unit. The optical interference display unit  602  is supported by arms  608  and  610 , the optical interference display unit  604  is supported by arms  612  and  614 , and the optical interference display unit  606  is supported by arms  616  and  618 . The length and the thickness of the arms  608  and  610 , arms  612  and  614 , and arms  616  and  618  are the same, therefore, the stress of every pair of arms is the same, too. After a thermal process, such as baking, is performed. The arms  608 ,  610 ,  612 ,  614 ,  616 , and  618  of the optical interference display units  602 ,  604 , and  606  may generate displacement caused by stress action. The displacements of the arms  608  and  610  are the same, the displacements of the arms  612  and  614  are the same, and the displacements of the arms  616  and  618  are the same. But there are various displacements among three above pairs of the arms. Therefore, the cavity  6102  of the optical interference display unit  602 , the cavity  6104  of the optical interference display unit  604  and the cavity  6106  of the optical interference display unit  606  have different length d 1 , d 2  and d 3 . As shown in formula 1.1, the wavelength of the reflected light is altered due to the change of the length of cavity. Light with different color, such as red light, green light or blue light is obtained.  
         [0034]    The lengths of the cavities, d 1 , d 2  and d 3 , are not decided by the thickness of the sacrificial layer. Therefore, using complicated manufacturing process to form the sacrificial layers with different thickness to define the length of the cavity is not necessary.  
         [0035]    In accordance with the color planar display consisting of an array of optical interference display units disclosed by the present invention, the advantages of a matrix color planar display according to the prior art are retained, including high resolution and high brightness, as well as the advantages of a multi-layered color planar display with a simple process and high yield in the prior art. It is understood that the present invention discloses an optical interference display unit which not only keeps all advantages of the prior optical interference color planar display such as high resolution, high brightness, simple process and high yield during forming arrays, but also increases the window during processing and raises the yield of the optical interference color planar display.  
         [0036]    The color planar display with an array of optical interference display unit provided in this invention retains the advantages of a prior art matrix color planar display known to the art, high resolution and brightness, and as well has the advantages of a multi-layered color planar display known to the art, simple manufacturing process and high yield. Comparing to a matrix color planar display known to the art, the lengths of the cavities of all optical interference display units are not decided by the thickness of the sacrificial layer. Therefore, using complicated manufacturing process to form the sacrificial layers with different thickness to define the length of the cavity is not necessary. The manufacturing process is simple and yield is high. Compared to a multi-layered color planar display known to the art, all the optical interference display units are on the same plane, therefore an incident light does not need to go through multi-layered optical interference display units. The resolution and brightness are high. Besides, in a prior art multi-layered color planar display, in order to make an incident light to go through a first optical interference display unit and be reflected by a second optical interference display unit efficiently, the composition and thickness of the first plate and the second plate of three types of optical interference display units are different. The manufacturing process is actually more complicated than expected. Manufacturing optical interference display units provided in this invention is less difficult than the optical interference display unit known to the art.  
         [0037]    Although the present invention has been described in considerable detail with reference certain preferred embodiments thereof, other embodiments are possible. Therefore, their spirit and scope of the appended claims should no be limited to the description of the preferred embodiments container herein. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.