Patent Abstract:
A double-sided fiber-based display includes a plasma tube array sandwiched between two electro-optic materials. The electro-optic materials are preferably sandwiched between two fiber arrays. The two fiber arrays contain wire electrodes to set the charge in the plasma tubes and are parallel to each other and orthogonal to the plasma tube array. The fibers can be alternatively coated with a transparent conductive coating, such as a carbon nanotube film, to spread the voltage across the surface of the fiber. The plasma tubes contain wire electrodes to ignite a plasma along its entire length. The tube surfaces that are in contact with the electro-optic materials are preferably thin and flat. The fiber and plasma tube wire electrodes are preferably directly connected to a circuit board which houses electronics to address the display.

Full Description:
REFERENCE TO RELATED APPLICATIONS 
   This application claims an invention which was disclosed in Provisional Application No. 60/665,781, filed Mar. 28, 2005, entitled “DOUBLE-SIDED FIBER-BASED DISPLAYS”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention pertains to the field of fiber-based displays and methods of manufacture. More particularly, the invention pertains to actively addressing two electro-optic materials using a single array of plasma tubes. 
   BACKGROUND OF THE INVENTION 
   There are several different methods of producing a reflective and transmissive display. The most well known and widely used method uses liquid crystal molecules as the electro-optic material. In the liquid crystal family, a vast range of molecules could potentially be used to create the electro-optic modulated material. Some of these liquid crystal molecules include, but are not limited to, twisted nematic, cholesteric-nematic, dichroic dye (or guest-host), dynamic scattering mode, and polymer dispersed molecules. Most of these liquid crystal molecules require other films, such as alignment layers, polarizers, and reflective films. 
   Another type of reflective display composing an electro-optic material is an electrophoretic display. Early work such as that described in U.S. Pat. No. 3,767,392, “ELECTROPHORETIC LIGHT IMAGE REPRODUCTION PROCESS”, used a suspension of small charged particles in a liquid solution. The suspension is sandwiched between two glass plates with electrodes on the glass plates. If the particles have the same density as the liquid solution then they will not be effected by gravity, therefore the only way to move the particles is using an electric field. By applying a potential to the electrodes, the charged particles are forced to move in the suspension to one of the contacts. The opposite charge moves the particles to the other contact. Once the particles are moved to one of the contacts they reside at that point until they are moved by another electric field, therefore the particles are bistable. The electrophoretic suspension is designed such that the particles are a different color than the liquid solution. Therefore, moving the particles from one surface to the other will change the color of the display. One potential problem with this display is the agglomeration of the small charged particles when the display is erased, i.e., as the pixel is erased, the particles are removed from the contact in groups rather than individually. Microencapsulating the electrophoretic suspension in small spheres solves this problem, as shown in U.S. Pat. No. 5,961,804, “MICROENCAPSULATED ELECTROPHORETIC DISPLAY”.  FIG. 1  shows the typical operation of a microencapsulated electrophoretic display. In this display the particles are positively charged and are attracted to the negative terminal of the display by applying a voltage  7  across the electrophoretic material  37 . The charged particles are white and the liquid solution they are suspended in is dark, therefore contrast in the display is optionally achieved by selectively moving some of the particles from one contact  5  to the other  5 . In this type of display, the electro-optic material is the electrophoretic material and any casing used to contain the electrophoretic material. 
   A similar type of electro-optic display, a twisting ball display or Gyricon display, was invented by N. Sheridon at Xerox, and is shown in U.S. Pat. No. 4,126,854, “TWISTING BALL DISPLAY”. It was initially called a twisting ball display because it is composed of small spheres, one side coated black, the other white, sandwiched between two electroded  5  glass plates. Upon applying an electric field  7 , the spheres with a positive charged white half and relative negative charged black half are optionally addressed (rotated), as shown in  FIG. 2 . Once the particles are rotated they stay in that position until an opposite field is applied. This bistable operation requires no electrical power to maintain an image. A follow on patent, U.S. Pat. No. 5,739,801, disclosed a multithreshold addressable twisting ball display. In this type of display, the electro-optic material is the bichromal spheres and any medium they may reside in to lower their friction in order to rotate. 
   Most electro-optic displays have problems with addressing the display. Since most of the electro-optic materials do not have a voltage threshold, displays fabricated with the materials have to be individually addressed. Some of the liquid crystal materials use an active transistor back plane to address the displays, but these type of displays are presently limited in size due to the complicated manufacturing process. Transmissive displays using liquid crystal materials and a plasma addressed back plane have been demonstrated in U.S. Pat. No. 4,896,149 and are shown in  FIG. 3 . A pair of parallel electrodes  36  are deposited in each of the channels  35 , and a very thin glass microsheet  33  forms the top of the channels. Channels  35  are defined by ribs  34 , which are typically formed by screen printing or sand blasting. A liquid crystal layer  32  on top of the microsheet  33  is the optically active portion of the display. A cover sheet  30  with transparent conducting electrodes  31  running perpendicular to the plasma channels  35  lies on top of the liquid crystal  32 . Conventional polarizers, color filters, and backlights, like those found in other liquid crystal displays, are also commonly used. Displays fabricated using the plasma addressed back plane shown in  FIG. 3  are also limited in size due to availability of the thin microsheet  33 . One potential solution for producing large size displays is to use fibers to create the plasma cells as shown in  FIG. 4 . Using tubes to create a plasma cell was first disclosed in U.S. Pat. No. 3,964,050, and using fibers with wire electrodes to create the column driving plane in a transmissive plasma addressed liquid crystal display was disclosed in U.S. Pat. No. 5,984,747. 
   All of the above mentioned prior art focuses on creating a single display viewable on the surface of the panel. Therefore, there is a need in the art for a structure that can be used to create two independent images on both surfaces of a display panel. 
   SUMMARY OF THE INVENTION 
   A double-sided fiber-based display includes a plasma tube array sandwiched between two electro-optic materials. The two electro-optical materials are preferably sandwiched between two fiber arrays. The two fiber arrays contain wire electrodes to set the charge in the plasma tubes and are parallel to each other and orthogonal to the plasma tube array. The fibers may be alternatively coated with a transparent conductive coating, such as a carbon nanotube film or a transparent conductive polymer coating, to spread the voltage across the surface of the fiber. Two electroded sheets may also be used to set the charge in the plasma tubes, where the electroded sheets are formed by placing wire electrodes into the surface of a polymer substrate and connecting patterned transparent conductive coating to the wire electrodes to spread the voltage placed on the wire electrodes across the surface of the pixels. The plasma tubes preferably contain wire electrodes to ignite a plasma along its entire length. The plasma tube surfaces that are in contact with the electro-optic materials are preferably thin and flat. The electro-optic material includes a liquid crystal material, an electrophoretic material, a bichromal sphere material, or any electro-optic material that can be modulated in an electrostatic field. The wire electrodes in the plasma tubes and column electrode plane are preferably directly connected to a circuit board, which houses electronics to address the display. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically shows a cross-section and addressing of an electrophoretic display, in accordance with the prior art. 
       FIG. 2  schematically shows a cross-section and addressing of a bichromal sphere display in accordance with the prior art. 
       FIG. 3  illustrates a traditional PALC display in accordance with the prior art. 
       FIG. 4  illustrates a fiber-based plasma-addressed electro-optic display in accordance with the prior art. 
       FIG. 5  is a photograph of an operating 46″ diagonal, 20 dpi, fiber-based plasma-addressed display using Gyricon paper as an electro-optic material. 
       FIG. 6   a  schematically shows a cross-section of a single pixel in a plasma-addressed fiber-based display. 
       FIG. 6   b  schematically shows the charge generation in a plasma tube when a plasma is ignited. 
       FIG. 6   c  schematically shows a layer of negative charge built-up on the inner surface of the plasma tube after being addressed. 
       FIG. 7  illustrates a fiber-based plasma-addressed electro-optic display containing two electro-optic viewing surfaces and a single plasma tube array. 
       FIG. 8  schematically shows a cross-section of the active addressing region in the double-sided display in  FIG. 5 . 
       FIG. 9  schematically shows a cross-section of a plasma tube used in the double-sided display. 
       FIG. 10   a  is a photograph of side A of an operating 6.4″×6.4″, 20 dpi, double-sided fiber-based plasma-addressed display using Gyricon paper as an electro-optic material. 
       FIG. 10   b  is a photograph of side B of an operating 6.4″×6.4″, 20 dpi, double-sided fiber-based plasma-addressed display using Gyricon paper as an electro-optic material. 
       FIG. 11  schematically shows a cross-section of a plasma tube similar to that shown in  FIG. 9  with a larger separation between charge depositing surfaces. 
       FIG. 12  schematically shows a cross-section of a plasma tube used in a double-sided display with the plasma electrodes located closer to the center of the tube to create an electrode plane to block the electrostatic field from a plated out charge on one side from affecting the plated out charge on the other side. 
       FIG. 13  schematically shows a cross-section of a tube used in a double-sided display with a center glass barrier to act as a charge neutral region in the tube. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 4  shows a schematic of a reflective plasma-addressed electro-optic display using both a top fiber array  17  and a bottom plasma tube array  27  to create the structure in the display, as disclosed in U.S. Pat. No. 6,459,200, incorporated herein by reference. Using this structure a 46 inch diagonal (25.5″×38.4″) 20 dots-per-inch display was fabricated, as shown in  FIG. 5 . The 46″ diagonal display was fabricated using Gyricon paper  37  (shown in  FIG. 2 ) as an electro-optic material  37 . Gyricon paper  37  is reflective and bistable, which means once the image is written it is displayed with no power until another image is written. Note that the image in  FIG. 5  shows the structure of the display shown in  FIG. 4 . The display has an addressable area of 25.55″×38.4″ (46″ diagonal) at a resolution of 20 dpi. The display was constructed using 511 plasma tubes and 768 top fibers. The display was assembled using an array of plasma tubes  27  placed on a bottom substrate  30   b . A sheet of Gyricon paper  37  is then applied to the top surface of the plasma tubes  27  and sandwiched with an array of rectangular top fibers  17  with co-drawn wire electrodes  31 . The top fiber array  17  is placed orthogonal to the plasma tube array  27  and a pixel is defined at every point where a top fiber  17  and plasma tube  27  cross. A top plate  30   t  is placed over the top fiber array  17  to complete the panel. The wire electrodes ( 31  and  36 ) from the plasma tubes  27  and top fibers  17  are connected directly to a circuit board, which houses the drive electronics. 
     FIG. 6  shows how the electro-optic material  37  (Gyricon paper) is addressed or an image is written on the display.  FIG. 6   a  shows the cross-sectional structure of a single pixel of a plasma-addressed display with a random orientation of the bichromal spheres in the Gyricon paper  37 . The display is addressed a row at a time by igniting a plasma in the first tube  27  of the panel generating a multitude of electrons (e) and positive ions (Ne + )  99 , as shown in  FIG. 6   b . During the plasma firing, positive or negative voltages are placed on each of the top fiber  17  column electrodes  31 . This voltage attracts electrons or positive ions  99  toward the electrodes  31 . However, the electrons or positive ions  99  are stopped by the inner surface of the plasma tube  27  where they stay and build up charge  99 , as shown in  FIG. 6   c . To plate out electrons  99 , as shown in  FIG. 6   c , a positive voltage needs to be applied to the column electrodes  31  during the plasma firing step, shown in  FIG. 6   b . Once the charge  99  is set-up on the inner surface of the plasma tube  27  and the plasma is extinguished, the charge  99  remains there until it bleeds off (&gt;10 sec). By repeating this addressing process for each of the remaining tubes  27 , charge  99  can be deposited at each pixel in the panel. Then when the voltage on all the column electrodes  31  are grounded, an electric field is set up through the electro-optic material  37  (Gyricon paper) from the charge  99  plated out in the tubes  27  to the grounded electrodes  31 . This electric field causes the electro-optic material  37  to be modulated and an image to be generated. Note in the above example the black side of the bichromal spheres in the Gyricon paper  37  is charged positive with respect to the white side of the bichromal spheres. 
   By modifying the structure of the plasma tubes  27  to have a first fiber array  17   a  and a second fiber array  17   b , a tube with two thin walled sides for depositing charge  99  is fabricated. By placing an electro-optic material  37  and the second fiber array  17   b  against this second surface, a double-sided display is fabricated, as depicted in  FIG. 7 . Addressing both surfaces of this double-sided display is done similar to the single-sided display explained above, except, in addition to positive and negative voltage being applied to the first side electrodes  31   a  in the first fiber array  17   a  to plate-out charge  99   a , positive and negative voltages are also applied to the second side electrodes  31   b  in the second fiber array  17   b  to plate-out charge  99   b  on the other side of the plasma tubes  27  during the plasma tube firing step. 
     FIG. 8  schematically shows a cross-section of the active addressing area of four adjacent pixels with the four different combinations of plated out charges. The four different charge combinations creates black or white pixels on both sides of the panel assuming Gyricon papers  37   a  and  37   b  are used for the two electro-optic addressable materials. Creating two independently addressable surfaces using a single array of plasma tubes  27  and one set of drive electronics drastically reduces the overall cost of generating a display with two viewing surfaces as opposed to manufacturing two separate displays. In another embodiment, a double-sided display using two separate panels like the one shown in  FIG. 5  preferably share the same high voltage drive electronics to reduce costs. 
   Many different electro-optic materials  37  can be used for the two light modulation regions. The use and operation of the display usually dictates which electro-optic materials  37   a  and  37   b  to use in both sides of the display. If a simple double-sided reflective display is desired, then there are many choices, such as, Gyricon paper, an electrophoretic material (for example the materials E-ink Corporation and SiPix Imaging, Inc. are developing), a suspended particle material (for example the materials Research Frontiers Incorporated are developing), or one of many different liquid crystal materials. However, if a transflective display or a display that operates in a transmissive and reflective mode is desired then the panel will have to have a reflective electro-optic material  37   a  on one side and a transmissive electro-optic material  37   b  on the other side. This transflective display would be viewed from one side but have two different addressable electro-optic materials  37   a  and  37   b . If at least one of the two electro-optic materials  37  are used in a transmissive mode then the tube walls  27   w  have to be thinner, similar to that shown in  FIG. 9 , so the tube walls  27   w  do not protrude into the center of the tube where the wall  27   w  or plasma electrodes  36  would scatter or absorb light transmitting through the tube  27 . Color could also be added to the display by coloring the fibers or tube similar to that disclosed in U.S. Pat. No. 6,459,200 entitled REFLECTIVE ELECTRO-OPTIC FIBER-BASED DISPLAYS, and U.S. Pat. No. 6,452,332 entitled FIBER-BASED PLASMA ADDRESSED LIQUID CRYSTAL DISPLAY. These patents are incorporated herein by reference. The sides  27   w  of the plasma tubes  27  could also be reflective to help guide the light traveling through the display. 
   In order to address thin electro-optic materials like liquid crystal or electrophoretic materials, the voltage on the column electrodes  31  has to be spread across the entire pixel width. In order to spread the charge across the pixel width or across the fiber  17 , a transparent conductive coating has to be added to the fiber  17  and connected to the wire address electrode  31  as discussed in U.S. patent application Ser. No. 11/236,904, filed Sep. 28, 2005, entitled “ELECTRODE ENHANCEMENT FOR FIBER-BASED DISPLAYS”, incorporated herein by reference. The fiber arrays  17  used to address the plasma (set the charge) and act as a ground plane may also be replaced with an electroded sheet, as discussed in U.S. Provisional Patent Application Ser. No. 60/749,446, filed Dec. 12, 2005, entitled “ELECTRODE ADDRESSING PLANE IN AN ELECTRONIC DISPLAY”, and U.S. Provisional Patent Application Ser. No. 60/759,704, filed Jan. 18, 2006, entitled “ELECTRODE ADDRESSING PLANE IN AN ELECTRONIC DISPLAY AND PROCESS”. These applications are incorporated herein by reference. 
     FIG. 10  shows photographs of a double-sided display using a structure similar to that shown in  FIG. 7 . The electro-optic material  37  is Gyricon paper and the substrates  30  are 0.002″ Mylar, which form a display that is only 2.3 mm thick and is flexible. The two images,  FIG. 10   a  and  10   b , were written one tube at a time, similar to that discussed above. A small amount of cross-talk can be observed in the two images. This small “ghost” image from the one side showing up in the other side is a result of the charge  99   a  plated out on one side causing some spheres to rotate in the Gyricon paper  37   b  on the other side. The plasma electrodes  36  are supposed to shield the electric field from this charge  99 , however the tube height  27   h  ( FIG. 9 ) is not large enough to allow the plasma electrodes  36  to completely block the electric field from the charge  99 . Charge deposited on the tube surface creates field lines which decrease in magnitude as you radially move away from the charge. These field lines have to impinge on the plasma electrodes  36  before they come close to reaching the other surface or they will affect the charge (electric field) on that surface in turn effecting the modulation of electro-optic material  37  on that surface. One method that solves this cross-talk issue increases the height  27   h  of the plasma tubes with respect to the width or pixel pitch, as shown in  FIG. 11 . Another method moves the plasma electrodes  36  in toward the center of the plasma tubes  27 , as shown in  FIG. 12 . Moving the plasma electrodes  36  away from the edge of the tubes  27  allows for a lower profile tube to be fabricated.  FIG. 13  shows another method of creating an inner web that acts as a charge neutralization barrier in the center of the tube  27 . A glass barrier  47  collects neutralization charge to cancel the electric field from the electro-optic modulation charge  99 . 
   The above examples show that there are several different methods and structures for creating an actively addressed electro-optic region on both sides of a single plasma tube array. The above figures are only used as an example and are not intended to limit the scope of creating a double-sided display using a single plasma tube array. 
   Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Technology Classification (CPC): 6