Reflective electro-optic fiber-based displays with barriers

[0002] This is a continuation-in-part of U.S. patent application Ser. No. 09/517,759, filed Mar. 2, 2000, now U.S. Pat. No. 6,459,200 entitled REFLECTIVE ELECTRO-OPTIC FIBER-BASED DISPLAYS, which is a continuation-in-part of U.S. patent application Ser. No. 09/299,372, filed Apr. 26, 1999, now U.S. Pat. No. 6,452,332 entitled FIBER-BASED PLASMA ADDRESSED LIQUID CRYSTAL DISPLAY. The aforementioned applications are hereby incorporated herein by reference.

[0003] 1. Field of the Invention

[0004] The invention pertains to the field of reflective displays and methods of manufacture. More particularly, the invention pertains to electrophoretic displays containing barrier walls and barrier electrodes, and fabricating such displays using fibers and/or hollow tubes.

[0005] 2. Description of the Related Art

[0006] There are several different methods of producing a reflective display, however when fabricating very large, energy efficient flat panel displays the most promising method uses an electrophoretic switching material. 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 (electrophoretic suspension) for displaying a light image. 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 by 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.

[0007] It is very difficult to address most electrophoretic displays. Since electrophoretic materials do not have a voltage threshold, displays fabricated with the electrophoretic materials have to be individually addressed at each pixel. One method to combat this problem is to use active devices that have a voltage threshold. There are two different types of active devices. One type is a transistor array similar to that used in an active matrix liquid crystal display. The second type is a plasma similar to that disclosed in U.S. patent application Ser. No. 09/517,759, entitled REFLECTIVE ELECTRO-OPTIC FIBER-BASED DISPLAYS, hereby incorporated herein by reference.

[0008] Active devices are complicated and expensive to fabricate and are usually limited in size. Therefore, an addressing scheme where the display can be passively addressed is desired. One such addressing scheme was introduced by Philips in U.S. Pat. No. 4,203,106 where they added a third control electrode to create a voltage threshold to manage the migration of particles. This third electrode is patterned with holes and is placed over and orthogonal to the attraction electrode. Controlling the voltage on the control electrode causes the particles to migrate into the holes in the control electrode, in turn, changing the color of the display.

[0009] Another passively addressed display was invented at Copytele, U.S. Pat. No. 5,345,251. This display is constructed using interleaved electrodes and an orthogonal electrode. The movement of the particles is in the plane between the interleaved electrode and is controlled by the orthogonal electrode. The addressing electrode controls the movement of the particles in all of these passively addressed displays. Since the particles do not have a voltage threshold, it makes it very difficult to matrix address the display. In order to achieve passive matrix addressing, a barrier must be added to the cell between the two driving electrodes.

[0010] A display which uses a barrier between drive electrodes was disclosed by E. Kishi, et al., “Development of In-Plane EPD”, SID 00 Digest, pp. 24-27. Two types of barriers were disclosed: a physical barrier 48, shown in FIG. 1, and an electrical barrier 44, shown in FIG. 2. Both displays are constructed by building up the structure on a top 30B and a bottom 30T substrate. A separator 45 is used to create the cell that houses the electrophoretic material 37. The drive electrodes 43 and 42 are electrically isolated from the cell and each other using dielectric layers 46 and 47. The operation of these displays is achieved by placing voltages on both driving electrodes 43 and 42 and controlling the flow of particles over the barriers using the control electrode 41.

[0011] Assuming the particles 37 are positively charged, then the display is in a holding state when a large positive voltage is applied to the control electrode 41, a small positive voltage is applied to the 1^stdriving electrode 43, and a negative voltage is applied to the 2^nddriving electrode 42. In the case where the barrier is created by an electric field (FIG. 2), a positive voltage is applied to the barrier electrode 44. To move the particles 37 from the 1^stdriving electrode 43 to the 2^nddriving electrode 42, the positive voltage on the control electrode 41 is reduced. In this case, the particles 37, which are repelled from the 1^stdriving electrode 43, are allowed to flow over the barrier to the 2^nddriving electrode 42.

[0012] This passive method of addressing by adding barriers helps in addressing the pixel, but has problems addressing more than one row in a display. In addition, the display will have a high manufacturing cost because of the multiple steps needed to create the structure and pattern the electrodes in the display. The display will also be limited in size since the structure is built-up on a substrate. The following invention solves the manufacturing and addressing issues and is cost effective in a large panel display.

[0013] The invention includes the use of hollow tubes filled with an electrophoretic material sandwiched between two plates to form a reflective display. The hollow tubes have either barrier walls or an electrostatic barrier, which restricts the flow of electrophoretic particles within the hollow tubes. The flow of electrophoretic particles over these barriers is controlled using electric fields, which makes it possible to matrix address the electrophoretic displays. Wire electrodes built into the hollow tubes and electrodes on the two plates are used to create the electric field and address the display. The electrodes on the plates can be replaced with wire electrodes or wire electrodes contained within a fiber. The plates are preferably composed of glass, glass-ceramic, polymer/plastic or metal, while the hollow tubes are preferably composed of glass, polymer/plastic or a combination of glass and polymer/plastic. In addition, color is optionally imparted into the display using colored tubes, adding a color coating to the surface of the tubes, or adding the color to the electrophoretic material. Reflectivity within the display is accomplished by using a reflective material to fabricate the tubes, coating the tubes with a reflective material or coating one of the two plates with a reflective material. The display can also function in a transmissive mode by applying an illuminating back to the display.

[0014] FIG. 1 schematically shows a structural barrier type in plane switching electrophoretic display, in accordance with the prior art.

[0015] FIG. 2 schematically shows an electrical barrier type in plane switching electrophoretic display, in accordance with the prior art.

[0016] FIG. 3 schematically shows a structural barrier type in plane switching electrophoretic display using hollow tubes containing barrier walls and wire drive electrodes.

[0017] FIG. 4 illustrates voltage waveforms to address a pixel in the display shown in FIG. 3.

[0018] FIG. 5A schematically shows a cross-sectional view of a single pixel of the in plane switching electrophoretic display using hollow tubes containing barrier walls and wire drive electrodes in the unwritten hold state.

[0019] FIG. 5B schematically shows a cross-sectional view of a single pixel of the in plane switching electrophoretic display using hollow tubes containing barrier walls and wire drive electrodes during a writing state.

[0020] FIG. 5C schematically shows a cross-sectional view of a single pixel of the in plane switching electrophoretic display using hollow tubes containing barrier walls and wire drive electrodes in the written hold state.

[0021] FIG. 6 schematically shows a cross-sectional view of a hollow tube containing a wire drive electrode and a wire barrier electrode.

[0022] FIG. 7 schematically shows a cross-sectional view of a hollow tube containing a wire drive electrode, a barrier wall and a wire barrier electrode attached to the top of the barrier wall.

[0023] FIG. 8 schematically shows a cross-sectional view of a hollow tube containing a wire drive electrode, a wire barrier electrode and a wire control electrode at the top of the hollow tube directly above the wire barrier electrode.

[0024] FIG. 9A schematically shows a cross-sectional view of a hollow tube containing a wire drive electrode, a barrier wall and a wire control electrode at the top of the hollow tube directly above the barrier wall.

[0025] FIG. 9B schematically shows a cross-sectional view of a hollow tube containing a wire drive electrode, a barrier wall and a wire control electrode in the top corner of the hollow tube.

[0026] FIG. 10A schematically shows a cross-sectional view of a hollow tube composed of absorbing sidewalls to serve as a black matrix.

[0027] FIG. 10B schematically shows a cross-sectional view of a hollow tube coated with an absorbing film on the sidewalls to serve as a black matrix.

[0028] FIG. 10C schematically shows a cross-sectional view of a skewed hollow tube coated with an absorbing film on the side-walls to block all unwanted light through the display.

[0029] FIG. 11A schematically shows a cross-sectional view of a hollow tube composed of a colored material to add color to the display.

[0030] FIG. 11B schematically shows a cross-sectional view of a hollow tube containing colored electrophoretic particles to add color to the display.

[0031] FIG. 11C schematically shows a cross-sectional view of a hollow tube composed of a colored material and containing colored electrophoretic particles to add color to the display.

[0032] FIG. 12A schematically shows a cross-sectional view of a hollow tube composed of a reflective material to add reflectivity to the display.

[0033] FIG. 12B schematically shows a cross-sectional view of a hollow tube coated with a reflective material to add reflectivity to the display.

[0034] FIG. 13A schematically shows a cross-sectional view of the top plate with transparent address electrodes, shown in FIG. 3.

[0035] FIG. 13B schematically shows a cross-sectional view of the address electrodes composed of an array of wire electrodes.

[0036] FIG. 13C schematically shows a cross-sectional view of an array of fibers containing one wire address electrode per fiber to replace the top plate.

[0037] FIG. 13D schematically shows a cross-sectional view of an array of fibers containing three-wire address electrode per fiber to replace the top plate.

[0038] FIG. 14A illustrates the change in cross-sectional shape of the preform/fiber in the root during the draw process.

[0039] FIG. 14B schematically shows a cross-sectional view of the top of the root shown in FIG. 14A.

[0040] FIG. 14C schematically shows a cross-sectional view of the bottom of the root shown in FIG. 14A.

[0041] FIG. 15A illustrates how the angle of the barrier wall changes after the draw process.

[0042] FIG. 15B illustrates how the angle of the barrier wall changes after the draw process if it is positioned against the drive electrode.

[0043] FIG. 16 schematically shows a cross-sectional view of a hollow tube with the wire drive electrode and barrier wall in the top corner of the hollow tube.

[0044] FIG. 17 schematically shows a cross-sectional view of a hollow tube with an additional wire drive electrode.

[0045] FIG. 18 schematically shows a cross-sectional view of a hollow tube with three wire drive electrodes in the bottom section of the tube.

[0046] The invention includes the use of fibers mainly in the form of hollow tubes with wire electrodes and barriers to construct reflective fiber-based displays. Modulating an electro-optic material within the display forms the reflectivity. The wire electrodes are contained within the fiber or on the surface of the fiber. The barriers are either structural barrier walls or created by an electric field from a wire electrode and assist in matrix addressing the display. The fibers or tubes are optionally colored to impart color to the display and can also be partially black to serve a black matrix function which enhances the contrast and sharpness of the display. Alternatively, the fibers or tubes can be white to enhance the reflectivity of the display. The electrophoretic material may also be colored to add color to the display. The fibers or tubes are preferably composed of glass, glass ceramic, plastic/polymer, metal, or a combination of the above.

[0047] FIG. 3 shows a schematic of a structural barrier type in plane switching electrophoretic display using hollow tubes 27 containing barrier walls 68 and wire drive electrodes 63. The height of the physical barrier wall 68 extends less than 100% of the height of the inside of the hollow tube 27, leaving a gap between the barrier wall 68 and the top of the hollow tube 27. The array of tubes 27 are sandwiched between two plates 60T and 60B. The top plate 60T has parallel address electrodes 61 to modulate the flow of electrophoretic particles 37 in the hollow tubes 27. The bottom plate 60B is blanket coated with a second planar drive electrode 62, which is used to attract the particles to the bottom of the hollow tubes 27. Addressing the display is accomplished by applying voltages on the wire drive electrodes 63 and the address electrodes 61 to create an electric field to force the electrophoretic particles 37 to flow over the barrier walls 68, if the pixel is to be dark (a written state).

[0048] FIG. 4 shows typical voltage waveforms to address a pixel in the display. The three periods of addressing, the refresh period, the write period and the hold period, are pictorially represented in FIGS. 5A, 5B, and 5C, respectively. The voltage pulses and representative figures assume that the electrophoretic particles are positively charged. During the refresh period a negative holding voltage, −V_h, is applied to the wire drive electrode 63 to attract the particles 37 and a positive refresh voltage, +V_f, is applied to the planar drive electrode 62 to repel the particles 37. Under these voltage conditions, the particles 37 collect around the wire drive electrode 63, as shown in FIG. 5A. To place the pixel in a written state, particles must flow over the barrier wall and be collected on the surface of the hollow tube. This flow of particles is accomplished by applying a positive repulsive voltage, +V_r, to the wire drive electrode 63 to repel the particles 37 from the wire drive electrode 63. A second positive write voltage, +V_w, is applied to the orthogonal address electrode(s) 61 to control the flow of particles 37 over the barrier wall 68, as shown in FIG. 5B. The magnitude of the write voltage, +V_w, determines if the particles 37 flow over the barrier wall 68 or not. If a large write voltage, ++V_w, is applied to the address electrode 61, then the particles 37 are forced to stay below the barrier wall 68 and the cell is in an unwritten state. Whereas, if a small write voltage, +V_w, is applied, then the positive voltage from the wire drive electrode 63, +V_r, creates a large enough repulsive field to force the particles 37 to flow over the barrier wall 68. A negative voltage, −V_h, is also applied to the planar drive electrode 62 to attract the particles 37 that flow over the barrier wall 68 to the bottom of the hollow tube(s) 27, as shown in FIG. 5C. Once the cell has been written (or not), the voltage on the wire drive electrode 63 is reduced to a negative holding voltage, −V_h, to attract any remaining particles 37 that have not made it over the barrier wall 68 and allow the next hollow tube 27 row of the display to be addressed. The address voltages, +V_w, are then modulated to address the subsequent rows (hollow tubes) in the displays. Note that the planar drive electrode 62 stays at a negative hold voltage, −V_h, until the remainder of the display is written and the display is ready to be refreshed.

[0049] Gray scale images are optionally created in the display by controlling the write voltage, +V_w, on the address electrode 61. Controlling the magnitude of this voltage controls the strength of the repulsive electric field, hence controlling the amount of particles 37 that flow over the barrier wall(s) 68. Reducing the magnitude of the write voltage, +V_w, on the address electrode 61 in turn leads to an increased number of particles that surmount the barrier wall(s) 68.

[0050] Another method of creating a gray scale image divides the addressing time into sections or bits, similar to the addressing scheme of a plasma display. The amount of time that the write voltage, +V_w, on the address electrode 61 is reduced to near zero voltage during the addressing period of a single frame determines the amount of particles 37 that flow over the barrier wall(s) 68. In a preferred embodiment, this time modulating addressing scheme is combined with a JPEG image and the image on the display is written similar to the flow of information from a JPEG image (i.e. the image is written in an intensity map sequence). A third method of creating gray scale breaks the address electrode 61 into several electrodes, similar to that shown in FIG. 13D. The multiple address electrodes can have different widths to control the flow of particles from a larger area.

[0051] The barrier wall 68 in the hollow tube(s) 27 may be replaced with a barrier electrode 69, similar to that shown in FIG. 6. This barrier electrode 69 serves the same purpose as the barrier wall 68 discussed above. The barrier is created by applying a positive voltage to the barrier electrode 69 in turn creating a repulsive barrier for the particles to cross over. The size or height of the barrier is determined by the magnitude of the voltage applied to the barrier electrode 69. The barrier wall 68 and barrier electrode 69 can both be combined into one hollow tube 27 to create a compound barrier, as shown in FIG. 7. This compound barrier yields a much tighter control on the movement of particles 37 across the barrier region. The barrier electrode 69 can be combined with the barrier wall 68 at any location within the barrier wall 68.

[0052] FIG. 8 shows a cross-section of a hollow tube 27 where the barrier is a gate created by a barrier electrode 69 and a control electrode 71. There are two different methods of operating this type of barrier. The first method creates a gate using the barrier electrode 69 and the control electrode 71. This gate is large enough to keep any particles 37 from passing through it. Then, by applying a negative voltage on the orthogonal address electrode(s) 61 (not shown, see FIG. 3), the gate is locally reduced and particles 37 can pass through it. The other method uses the barrier electrode 69 and control electrode 71 to create a gate weak enough for particles 37 to penetrate through it. Then, by applying a positive voltage on the orthogonal address electrode(s) 61 the gate can be selectively closed to particle 37 flow. The wire drive electrode 63 can be attached to the sides of the hollow tube between the barrier electrode 69 and the control electrode 71 so the particles have a more direct line of sight to the center of the electrostatic gate.

[0053] FIG. 9 shows a gate that is created using the barrier wall 68 and a control electrode 71. FIG. 9A shows the control electrode 71 located directly above the barrier wall 68 and FIG. 9B shows the control electrode 71 in the corner of the hollow tube 27. Adding a control electrode 71 allows for many different addressing schemes. But, the largest advantage of adding a control electrode 71 is to even out the particles 37 along the length of the hollow tube 27. During the operation of the display, particles start to aggregate to one location in the hollow tube as the image in that area of the display is continuously written dark. Applying an alternating voltage between the control electrode 71 and the wire drive electrode 63 evenly redistributes the particles. This reconditioning of the distribution of particles is imperative for a display with an even gray scale and color distribution across the display. In addition, the control electrode 71 greatly assists in returning the particles to the wire drive electrode 63. Due to the blocking of the barrier wall, applying a negative voltage to the control electrode 71 pulls the particles 37 from the large volume of the hollow tube 27 much easier than applying the voltage to the wire drive electrode 63.

[0054] In order to increase the contrast of the display, light absorbing regions 75 must be added to the sides of the hollow tubes 27, as shown in FIG. 10. These light absorbing regions 75 function as a black matrix and keep light from penetrating through the unmodulated regions of the display. FIG. 10A shows that the black absorbing region 75 is contained within the hollow tube 27. Alternatively, the black absorbing region 75 is coated on the ends of the hollow tube 27, as shown in FIG. 10B. Both FIGS. 10A and 10B block the unwanted light within the hollow tube, but light still can be transmitted between the hollow tubes 27 if they are not in intimate contact. However, by designing the hollow tubes 27 in an interlocking mechanism or simply slanting the side of the hollow tubes 27, similar to that shown in FIG. 10C, the light transmission between the hollow tubes 27 is blocked.

[0055] FIG. 11 shows several ways to add color to the display. Color is added to the display by fabricating the hollow tubes (27R, 27G, 27B) from a color material, as shown in FIG. 11A, or by coating the hollow tubes with a colored die. The color die is coated on either the inside or outside of the hollow tubes. The colored die and/or black matrix can be coated on the tubes (27R, 27G, 27B) during the draw process. This can be done using several different methods, the most promising method being spraying or drawing the tubes (27R, 27G, 27B) over or past a coating system.

[0056] Coating the tubes (27R, 27G, 27B) with both the black matrix material 75 and color filter material requires two different coating systems. The first system coats the sides with an absorbing black matrix material 75, while the second system coats the top, bottom or both top and bottom with a particular color film (red, green, or blue) to create the color in the display. Color can also be added to the display by either making the particles (37R, 37G, 37B) different colors in the hollow tubes, as shown in FIG. 11B, or by making the liquid medium the particles 37 reside in colored. To achieve the best color quality in the display, both the hollow tubes (27R, 27G, 27B) and electrophoretic particles (37R, 37B, 37G) have to be colored, as shown in FIG. 11C.

[0057] Reflectivity in the display is achieved by using a reflective conductive planar drive electrode 62, shown in FIG. 3. Using a highly reflective metal film for this electrode 62 yields a high reflectivity, however the display only functions in a reflective mode. To fabricate a transflective display that can be operated in both a reflective and transmissive mode, the reflecting material must be both transmissive and reflective. An example of one such material is a conductive coating that is used in a one-way mirror, where the mirror side faces the viewer. Therefore, when there is a high level of incident light on the display, it functions in a reflective mode, but when the background illumination level is low, the display is back illuminated and functions in a transmissive mode. The reflectivity of the display can also be included in the hollow tubes 27, as shown in FIG. 12. FIG. 12A shows the reflective layer 77 as part of the hollow tube 27. If the hollow tube 27 is composed of glass, this reflective layer 77 is preferably an opal glass. Alternatively, if the hollow tube is composed of plastic, then white pigment or colorant could be added to the polymer blend to form the hollow tube(s) 27. The reflective layer 77 could also be added to the surface of the hollow tube 27, as shown in FIG. 12B. This reflective coating 77 could be a simple white paint and/or could be conductive and serve as the planar drive electrode 62.

[0058] In order to create very large displays, it is advantageous to replace the patterned address electrodes 61 on the top plate 60T with wire address electrodes 61W, as shown in FIG. 13. FIG. 13A shows a cross-section of a typical patterned top plate 60T with the transparent address electrodes 61, similar to that shown in FIG. 3. These address electrodes 61 are replaced with an array of wires 61W, as shown in FIG. 13B. One potential problem with using individual wires as the address electrodes 61W is holding the wires on a given pitch or separation. To alleviate this problem, the wires are held in the exact location by adding a transparent flowable film between the top plate 60T and the hollow tubes 27. This flowable film not only holds the wire address electrodes 61W in place but also removes the light reflection at that interface.

[0059] Another method to maintain the correct pitch is to include the wire address electrodes 61W in a fiber similar to that shown in FIG. 13C. In this case, arraying the fibers 17 into a compact sheet places the wire address electrodes 61W on a specified pitch. Since the wire is made as thin as possible to allow for the maximum amount of light to be transmitted through the display, the electric field created by the wire is narrow. One potential solution to this problem is to add more than one wire address electrode 61W per fiber 17, as shown in FIG. 13D. Multiple wire electrodes 61W spread out the electric field and the thin or small diameter of the wire minimizes the obstruction of light passing through the display.

[0060] Another potential problem with fabricating a high quality reflective display is the reflection at the interfaces between the plates 60 and the hollow tubes 27 or fibers 17. These additional surfaces create reflections, which lowers the contrast ratio of the display. To reduce or eliminate these reflections, a flowable polymer material is optionally included into the structure between the plates 60 and the hollow tubes 27 or fibers 17. A polymer material, such as, for example, ethylvinyl acetate (EVA), is optionally used to remove these reflections. In addition, it is advantageous to match the index of refraction of the plates, fibers/tubes, and electrophoretic solution to reduce reflections.

[0061] To fabricate the hollow tubes 27 and fibers 17, larger size preforms 127 are drawn into smaller sizes 27, as shown in FIG. 14A. The art of including the wire electrodes and forming the arrays of hollow tubes 27 or fibers 17 is explained in copending U.S. application Ser. No. 09/299,350, filed Apr. 26, 1999, entitled “PROCESS FOR MAKING ARRAY OF FIBERS USED IN FIBER-BASED PLASMA”, which is hereby incorporated herein by reference. During the “fiber draw” process, the shape of the hollow tubes and barrier wall 68 is altered. This shape change is a result of forces exerted on the tube and wall in reducing the size from a preform 127 to a hollow tube 27. The section of the “fiber draw” where the “fiber” is reduced in size is called the root of the draw. In the root of the draw, there are two normal forces that act on the “fiber”. At the top of the root the force (F1) acts to pull all points to the centerline of the preform/fiber. This force (F1) is present until the root goes through the point of inflection (POI), the point at which the curvature of the root goes from concave outward to concave inward. The resulting change in shape of the hollow tube and barrier wall 68 is shown in FIG. 14B, a cross-sectional view of FIG. 14A. Note that the force (F1) pulls the top of the barrier wall 68 and the sides of the hollow tube to the centerline of the cross-sectional shape. After the point of inflection, a force (F2) tends to “push” all parts of the preform/fiber away from the centerline. This force (F2) creates a final hollow tube and barrier wall 68 shape as shown in FIG. 14C, a cross-sectional view of FIG. 14A. Note that the force (F2) pushes the top of the barrier wall 68 and the sides of the hollow tube outward from the centerline of the cross-sectional shape.

[0062] By applying a small negative pressure or vacuum in the centerline of the hollow tube preform 127 during the draw process, the hollow tube 27 is kept from bowing outward, however the barrier wall 68 is still tilted outward, similar to that shown in FIG. 15A. Tilting of the barrier wall 68 during the draw process is advantageous in that it creates a better barrier for the electrophoretic particle 37 flow. Connecting the barrier wall 68 to the small square tube 64, housing the wire drive electrode 63, causes the barrier wall 68 to be bent over top of the wire drive electrode 63 during the draw process, as shown in FIG. 15B.

[0063] FIG. 16 represents a method of placing the wire drive electrode 63 and barrier wall 68 in the top corner of the hollow tube 27 and the control electrode 71 in the bottom corner of the hollow tube 27. Addressing this type of display could be similar to that discussed above or the top plate 60T with address electrodes 61 (shown in FIG. 3) could be placed below the hollow tubes 27 to replace the bottom plate 60B and planar drive electrode 62. The lines in the display are addressed along the length of the hollow tubes 27 by applying a voltage on the address electrode 61 and modulating the particle flow using the control electrode 71. In addition, the barrier wall 68 is optionally replaced with a barrier electrode, similar to that shown in FIG. 8.

[0064] FIG. 17 shows the addition of a second wire drive electrode 73. Adding a second wire drive electrode 73 to the structure of the hollow tube 27 eliminates the need for the planar drive electrode 62 (shown in FIG. 3). Using a second wire drive electrode 73 enhances the addressability of each row of hollow tubes 27 in the display by locally controlling the voltage in each hollow tube 27. Unfortunately, using a second wire drive electrode 73 instead of a planar drive electrode 62 localizes the field and tends to attract the electrophoretic particles 37 toward the second wire drive electrode 62.

[0065] One method to spread out the electrophoretic particles once the cell has been written is to apply a high frequency AC voltage between the two wire drive electrodes 63 and 73. If this high frequency AC voltage is faster than the time it takes the electrophoretic particles 37 to traverse the hollow tubes 27 then it acts as an electronic shaker to spread out the particles. Another method which uses a second wire drive electrode 73 included in the structure of the hollow tubes 27 is to use multiple second wire drive electrodes 73, as shown in FIG. 18. Placing multiple second wire drive electrodes 73 below the center of the hollow tube 27 spreads out the electric field and creates a more uniform attraction potential for the electrophoretic particles 37.

[0066] 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.