Abstract:
A vacuum flat panel display has a plurality of associated pixels each having a phosphor and nanotubes and a surrounding control frame. When a pixel voltage is negative relative to the frame then a plurality of electrons emitted by the nanotubes are attracted to the frame whereby electrons strike gas atoms in transit to the frame and produce ions and additional electrons; wherein said ions returning to the pixel result in phosphor illumination. The invention is also a process for illuminating a phosphor in a flat panel display comprising: a plurality of associated pixels each having a phosphor and nanotubes; applying a pixel voltage negative relative to a frame; attracting to the frame a plurality of electrons emitted by the nanotubes; whereby electrons strike atoms of a gas in transit to the frame producing ions resulting in phosphor illumination.

Description:
RELATED APPLICATIONS  
       [0001]    Co-pending applications entitled “Passive Matrix Phosphor Based Cold Cathode Display”, Ser. No. 60/999,783, filed on Oct. 19, 2007, “Active Matrix Phosphor Cold Cathode Display”, Ser. No. 61/000,958, filed on Oct. 30, 2007, A Matrix Phosphor Cold Cathode Display Employing Secondary Emission, Ser. No. 12/079,658 filed on Mar. 28, 2008 and other pending applications regarding flat panel display technology. 
     
    
     FIELD OF THE INVENTION  
       [0002]    This application is generally related to the field of displays and more particularly to flat panel displays employing phosphor pixels, frame and cold cathode emission sources, and providing excitation of the phosphor by ion bombardment resulting in a simplification of the display construction especially in the electronic configuration of the display and in a cost reduction due to the lower voltages required to operate the display. 
       BACKGROUND OF THE INVENTION  
       [0003]    Flat panel display (FPD) technology is one of the fastest growing display technologies in to the world. As a result of this growth, a large variety of FPDs exist, which range from very small virtual reality eye tools to large hang-on-the-wall television displays. Copytele, the applicant herein, has many patents and applications relating to such displays. 
         [0004]    It is desirable to provide a display device that may be operated in a cold cathode field emission configuration such as nanotubes, edge emitters, etc. and that exhibits a uniform, enhanced and adjustable brightness with good electric field isolation between pixels. Such a device would be particularly useful as a low voltage FPD, incorporating a cold cathode electron emission system, a pixel control system, and phosphor based pixels, with or without memory and active devices such as transistors including those of the thin film construction. It is further desirable to provide a brighter display and, therefore, there is described means for exciting the phosphor by ion bombardment. 
       SUMMARY OF THE INVENTION  
       [0005]    In one exemplary embodiment, a flat panel display including: a plurality of electrically addressable pixels; a plurality of thin film transistor driver circuits each being electrically coupled to an associated at one of the pixels, respectively; a passivating layer on the thin-film transistor driver circuits and at least partially around the pixels; a conductive frame on the passivating layer; and a plurality of cold cathode emitters and phosphor deposited on top of the pixel material wherein, exciting the conductive frame and addressing one of the pixels using the associated driver circuit causes the cold cathode emitters to emit electrons which electrons go to the frame; wherein some emitted electrons strike gas atoms enroute to the frame producing ions and additional electrons. The ions return to the pixel causing the phosphor to illuminate and additional electrons to be released. 
         [0006]    In one exemplary embodiment, there is provided a thin, phosphor-based active TFT matrix flat panel display. Adjacent each pixel in the matrix is a control conductive frame. The control frame surrounds pixels, which pixels consist of a conductive layer coated with a phosphor (Red, Green or Blue) and nanotubes. The frame consists of a conductive material (chrome, aluminum and so on). The frame and pixel voltages are controlled by a TFT circuit to cause electrons emitted by the nanotubes to go to the frame. Some electrons strike gas atoms en route to the frame producing ions and additional electrons. The ions return to the pixel causing the phosphor to illuminate and additional electrons to be released. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]    It is to be understood that the accompanying drawings are solely for purposes of illustrating the concepts of the invention and are not drawn to scale. The embodiments shown in the accompanying drawings, and described in the accompanying detailed description, are to be used as illustrative embodiments and should not be construed as the only manner of practicing the invention. Also, the same reference numerals, possibly supplemented with reference characters where appropriate, have been used to identify similar elements. 
           [0008]      FIG. 1  illustrates a circuit for driving the pixels according to an aspect of the present invention. 
           [0009]      FIG. 2  illustrates a timing diagram depicting circuit driver operation. 
           [0010]      FIG. 3  illustrates an exemplary display device according to an aspect of the present invention. 
           [0011]      FIG. 4  illustrates a control frame around each pixel and having a DC, AC or pulsed voltage applied according to an aspect of the present invention. 
           [0012]      FIG. 4   a  illustrates a control frame according to another aspect of the present invention. 
           [0013]      FIG. 5  illustrates a top view of a control frame according to another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purpose of clarity, many other elements found in typical display (e.g. FPD) systems and methods of making and using the same. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. Furthermore, while the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. 
         [0015]    Before embarking on a more detailed discussion, it is noted that there are other passive matrix displays and active matrix displays that are used in laptop and notebook computers. In a passive matrix display, there is a matrix of solid-state elements in which each element or pixel is selected by applying a potential voltage to a corresponding row and column line that forms the matrix. In an active matrix display, each pixel is further controlled by at least one transistor and a capacitor that is also selected by applying a potential to a corresponding row and column line. Part of the invention lies in the recognition that a TFT-based display device with a control frame disposed thereon exhibits enhanced performance and effects useful for display devices. Electron emission sources may be used with such a frame to form a cold cathode configuration, such as one including edge emitters, or nanotube emitters, and or other cold cathode electron emitters. Cold cathode emitters may also be used which are not associated with the frame. This has been disclosed in pending applications (see Related Applications). Here there is described increased secondary emission of an FED display for enhancing illumination of the display. 
         [0016]    According to an aspect of the present invention, a pixel matrix control system having a control frame around each pixel associated with a thin film transistor (TFT) circuit of a display device is used to provide a display characterized as having a good uniformity, adjustable brightness, and a good electric field isolation between pixels, regardless of the type of electron source used. For purposes of completeness, a TFT is a type of field effect transistor made by depositing thin films for the metallic contacts, semiconductor active layer, and dielectric layer. TFT&#39;s are widely used in liquid crystal display (LCD) FPDs. 
         [0017]    The control frame surrounds the pixel and hence, the TFT, and is disposed in an inactive area between the pixels (e.g. on an insulating substrate over the respective columns and rows). The pixels have a thin layer of a conductive material on a metal pad deposited at the pixel location. Carbon nanotubes (CNT) and Phosphor are deposited on top of the pixel area. During operation electrons emitted by the nanotubes go to the frame. Some electrons strike gas atoms producing ions and more electrons. The ions return to the frame causing the pixel to illuminate and additional electrons to be released. When the ions strike the pixel covered with phosphor and nanotubes more electrons are released. 
         [0018]    According to an aspect of the present invention, the control frame includes a plurality of conductors, typically arranged in a matrix having parallel horizontal conductors and parallel vertical conductors. Each pixel is bounded by the intersection of vertical and horizontal conductors, such that the conductors surround the corresponding pixels to the right, left, top, and bottom in a matrix fashion. One or more conductive pixel pads are electrically connected to the control frame. The control frame may be fabricated of a metal including, for example, chrome, molybdenum, aluminum, and/or combinations thereof. 
         [0019]    According to an aspect of the present invention, the control frame can be formed using standard lithography, deposition and etching techniques. 
         [0020]    In one exemplary configuration, conductors parallel to columns and rows are electrically connected together, and a voltage is applied thereto. In another exemplary configuration, conductors parallel to columns are electrically connected together, and have a voltage applied thereto. Conductors parallel to the rows are also connected together, with a voltage applied thereto. In yet another exemplary configuration, a voltage is only applied to one of the parallel rows or columns of conductors. 
         [0021]    According to an aspect of the present invention, a vacuum FPD or a FPD containing a noble gas in the hollow of the display, incorporating a TFT circuit may be provided. Associated with each pixel element is a TFT circuit that is used to selectively address that pixel element in the display. In one configuration the TFT circuit includes first and second active device electrically cascaded, and a capacitor coupled to an output of the first device and an input of the second device. 
         [0022]    Referring to  FIG. 1 , there is shown a TFT circuit  300  for driving a pixel  140  according to this invention, the TFT substrate of the display consists of the desired number of pixels each having the configuration shown in  FIG. 1 . The pixels consist of conductive layer coated with phosphor (red, green, or blue) and nanotubes  180 . The Frame  120  consists of a conductive material (for ex. chrome, aluminum, etc.). The nanotubes can be deposited first on the phosphor or they can be mixed and then deposited. 
         [0023]    According to an aspect of the present invention, control of one or more of the TFTs associated with the display device of the present invention may be accomplished using an active matrix location  300  as shown in  FIG. 1 . The circuit comprising the active matrix location  300  includes transistors TFT  330  and TFT  310  and capacitor  320  electrically interconnect to a pixel  140 , e.g., pad  140 ,  FIGS. 1 and 3 . 
         [0024]    The TFT substrate of the display consists of the desired number of pixels  140  each having the active matrix location  300  configuration as shown in  FIG. 1 . The pixels  140  are comprised of conductive layer coated with a phosphor (RGB) and nanotubes  180 . Referring to  FIG. 1  and  FIG. 2  at time t 1  when a row driver output  324  is selected (e.g., V row-high =15V in  FIG. 4   b ) TFT  310  turns “on” enabling new column data  327  (e.g., V col-high =15V in  FIG. 4   a ) to be stored in capacitor  320  at time t 1  (e.g., V pixel-on =15V in  FIG. 2   d ). If row  324  is at zero volts (e.g., V row-low =0V at t 0 , t 3 , t 6 , t 9 , in  FIG. 2   b ) the particular active matrix location  300  is not selected and new column data from the column driver output  327  cannot be written to capacitor  320 . It should be noted that the row  324  shown at a potential of V row-high =15V may be any other voltage sufficient enough to turn “on” transistor  310 . It should also be noted that row  324  shown at a potential V row-low  may be any other voltage sufficient to turn “off” transistor  310 . The voltages used are a function of the minimum voltage requirement of the drivers (not shown) and the TFT  310  used. 
         [0025]    When the data stored at location capacitor  320 , is represented by greater than the threshold voltage of transistor  330  this turns “on” transistor  330  allowing current to flow through transistor  330 . When the data stored represented by the voltage at capacitor  320  is less than the threshold voltage of transistor  330  the, transistor  330  is cut “off’ and current cannot flow through transistor  330 . When transistor  330  is in an “on” state this applies ground or any voltage negative relative to the frame  120  voltage to the pixel pad  140 . The frame  120  has a positive voltage relative to the pixel pad. 
         [0026]    Since the pixel pad  140  voltage is negative relative to the frame  120  (V pixel  less positive than V frame ) the electrons emitted by the nanotubes (see,  FIG. 1 ) are attracted to the frame  120 . Some electrons strike gas atoms in transit to the frame  120  producing ions and additional electrons. The ions will return to the pixel  140  causing the phosphor  180  to illuminate and additional electrons to be released. 
         [0027]    The column driver output  327 , which output voltage represents the data to be displayed is connected to transistor  310 . The row driver output  324  is connected to the gate of transistor  310 . The output of transistor  310  is connected to the gate transistor  330 . The output of transistor  330  is connected to pixel  140 . When the data as represented by a voltage is in a low state (e.g., V co     —     low =0V at t 5 , in  FIG. 4   a ), transistor  330  does not conduct and there is no pixel  140  current since no ions are attracted to the pixel  140  (e.g., V pixel     —     OFF =0V at t 5 , in  FIG. 4   d ). When the column driver output  327  is high (e.g., V col-high =15V in  FIG. 4   a ) transistor  330  conducts and ions are attracted to the pixel  140  and the phosphor  180  illuminates. 
         [0028]    TFT  330  acts as a switch which is operated at low voltage thereby eliminating the need for high voltage drivers and reducing the cost of the display. In addition, since all voltages (column 327, row 324, frame  120  and anode  325 ) are positive or at ground, the insulating layers are not required to sustain high voltage gradients and are considerably less likely to breakdown. This invention may be implemented with displays, which use noble gases and with displays which do not use noble gases. Essentially the invention may be used with any display which uses a phosphor to produce an image. 
         [0029]      FIG. 3  illustrates a schematic cross-sectional view of a TFT anode based FPD  100  according to one aspect of the present invention. In the exemplary embodiment, display  100  is composed of an assembly  110  that includes an anode and that employs TFT circuitry (as shown in  FIG. 1 ) and a control frame structure  120  is disposed on an anode passivation layer  130 . The control frame substantially surrounds and is adjacent to each of the pixel element. In the illustrated embodiment, the pixel metal  140  attracts ions as explained above. Those of ordinary skill in the art may recognize that other configurations with cold cathode emitter in various other locations are possible. 
         [0030]    Assembly  110  of  FIG. 3  includes a plurality of conductive pixel pads  140  fabricated in a matrix of substantially parallel rows and columns on a substrate  150  using conventional fabrication methods. Each pixel pad ( FIG. 1 ) is covered with a phosphor and carbon nanotubes  180 . Substrate  150  may be formed of a transparent material, such as glass, or a flexible material (such as a plastic with no internal outgassing during sealing and vacuumization processing), but may be opaque. Substrate  170 , which serves to confine the FPD housing in an evacuated or an inert or noble gas environment may also be made of a transparent (or at least translucent) material, such as glass or flexible material, but alternatively may be opaque. In the exemplary embodiment depicted in  FIG. 3 , substrate  170  has a layer of metal (ML)  172  secured on or otherwise formed on the surface. The ML layer  172  as shown and configured relative to assembly  110 . The ML layer  172  is transparent and may be ITO or some other metal. The substrates  150  and  170  are bonded or sealed at the peripheries to form an enclosed hollow which may be filled with an inert gas, a vacuum or a noble gas. Conductive pixel pads  140  may be composed of a transparent conductive material, such as ITO (Indium Titanium Oxide) or a non-transparent conductor such as Chrome (CR), Moly Chrome (MoCr) or aluminum. 
         [0031]    In any event, deposited on each conductive pixel pad  140  is a phosphor layer and nanotubes  180 . Each phosphor layer(s) is selected from materials that emit light  190  ( FIG. 3 ) of a specific color, wavelength, or range of wavelengths. In a conventional RGB display, phosphor layer  180  is selected from materials that produce red light, green light or blue light when struck by electrons. In the illustrated embodiment, light (i.e. photons) is emitted in the direction of substrate  170  for viewing. If the pixel metal is of a transparent (or translucent) material (such as ITO) rather than opaque, light emissions  190  would be transmitted in both the directions of substrates  150  and  170  (rather than being reflected via the pixel metal to substrate  170  only, for example). 
         [0032]    Incorporated in the TFT circuit ( FIG. 1 ) are conductive pixel column and row addressing lines associated with each of the corresponding conductive pixel pads  140 . The pixel row and column addressing lines may be substantially perpendicular to one another. Such a matrix organization of conductive pixel pads and phosphor layers allows for X-Y addressing each of the individual pixel elements in the display as will be understood by those possessing an ordinary skill in the pertinent arts. 
         [0033]    Associated with each conductive pixel pad  140 /phosphor layer  180  pixel is a TFT circuit  200  ( FIG. 3 ) ( 300  of  FIG. 1 ) that operates to apply an operating voltage proportional to the data to the associated conductive pixel pad  140 /phosphor layer  180  pixel element. TFT circuit  200  operates to apply either a first voltage to bias an associated pixel element to maintain it in an “off” state or a second voltage to bias the associated pixel element to maintain it in an “on” state as required by the data, or any intermediate state as described in  FIG. 1 . 
         [0034]    TFT circuitry  200  biasing conductive pixel pad  140  provides for dual functions of addressing pixel elements and maintaining the pixel elements in a condition to attract ions for a desired time period, i.e., time-frame or sub-periods of time-frame. 
         [0035]    Referring now also to  FIG. 4  there is shown a plan view of a control frame  220  suitable for use as control frame  120  of  FIG. 1 . Control frame  220  includes a plurality of conductors arranged in a rectangular matrix having parallel vertical conductive lines  230  and parallel horizontal conductive lines  240 , respectively. Each pixel  250  (e.g. pad  140  and phosphor  180  of  FIG. 1 ) is bounded by vertical and horizontal conductors or lines  230 ,  240 , such that the conductors substantially surround each pixel  250  to the right, left, top, and bottom. One or more conductive pads  260  or conductive bars electrically connect conductive frame  220  to a conventional power source. In the illustrated embodiment of  FIG. 2 , four conductive pads  260  are coupled to the conductive lines  230 ,  240  of frame  220 . In an exemplary embodiment, each pad  260  is around 100×200 micrometers (microns) in size. 
         [0036]      FIG. 4   a  shows another exemplary configuration of a control frame structure similar to that of  FIG. 2  (wherein like reference numerals are used to indicate like parts), but wherein two of the pads  260  of  FIG. 2  are replaced by a single conductive bar or bus  260 ′. The conductive bar  260 ′ is coupled to each of the parallel horizontal conductive lines  240   a ,  240   b ,  240   c , . . .  240   n  at corresponding positions  260   a ,  260   b ,  260   c , . . .  260   n  along the bar. In the illustrated configuration, the row lines are substantially identical to one another and interconnect to the bar at uniform spacings along the length of the bar. This configuration provides for an equipotential frame configuration with minimal voltage drops as a function of frame position. 
         [0037]    In the illustrated embodiment control frame  220  (or  220 ′) is formed as a metal layer above the final passivation layer (e.g.  130 ,  FIG. 1 ). Pads  260  and metal lines that provide the control frame structure  220  remain free from passivation in the illustrated embodiment. In an exemplary configuration, the control frame metal layer has a thickness of less than about 1 micron (um), and a width may be used depending on particular design criteria. 
         [0038]    According to one aspect of the present invention, nanostructures are provided upon the pixels  250  which are coated with a phosphor. The nanostructures may take the form of carbon nanotubes, for example. The nanostructures may take the form of SWNTs or MWNTs. The nanostructures may be applied to the control frame using any conventional methodology, such as spraying, growth, or printing, for example. Other cold cathode emitters may be used. 
         [0039]    While the vertical line conductors  230  and horizontal line conductors  240  frame each pixel  250  above the plane of the pixels  250  in the illustrated embodiment (see, e.g.  FIG. 1 ), other configurations are contemplated, such as where the conductors are disposed in the same plane as the pixels. Further yet, conductors  230 ,  240  may be connected in a number of configurations. For example, in one configuration, all horizontal and vertical conductors are joined together as shown in  FIG. 2  and a voltage is applied to the entire control frame configuration. In another configuration, all horizontal conductors  240  are joined and separately all vertical conductors  230  are joined. In this connection configuration the horizontal conductors  240  and vertical conductors  230  are not electrically interconnected. Thus, a voltage may be applied to the horizontal conductor array, and a separate voltage may be applied to the vertical conductor array. Other configurations are also contemplated, including for example: a configuration of all horizontal conductors only, or a configuration of all vertical conductors only. For example, the control frame may include only metal lines parallel to the columns or only metal lines parallel to the rows. 
         [0040]    By negatively biasing the pixel voltage (V PIXEL ) relative to the voltage of the frame, electrons emitted by the nanotubes go to the frame. Some electrons strike gas atoms en route to the frame producing ions and additional electrons. The ions return to the pixel causing the phosphor to illuminate and additional electrons to be released. The wavelength of the emitted light depends upon the phosphor (Red, Green, Blue). 
         [0041]    According to an aspect of the present invention, control of one or more of the TFTs associated with the display device of the present invention may be accomplished using the circuit  300  of  FIG. 1 . Circuit  300  includes first and second transistors  310 ,  330  and capacitor  320  electrically interconnect with a pixel, e.g. pad  140 ,  FIG. 1 . 
         [0042]    In general, the voltage used to select the row (V ROW ) is equal to the fully “on” voltage of the column (Vc). The row voltage in this case causes the pass transistor  310  to conduct. The resistance of pass transistor  310 , capacitor  320  and the write time of each selected pixel row determines the voltage at the gate of transistor  330 , as compared to Vc. V ANODE    325  the power supply voltage, and may be on the order of about 10-40 volts. 
         [0043]    Referring to  FIG. 4 , the conductive part of frame  220  may be widened (e.g. by about 4 um) and an insulating layer  450  (e.g. SiN) provided at each edge for preventing electrical short circuits from the frame to the pixels, and to encapsulate the frame edge which is associated with high field intensity. Accordingly, the exposed part  430  of the frame may have a width of about 12-15 um. 
         [0044]    Emissive displays using phosphor to emit light in order to display an image including: a source of electrons, pixels including phosphor on a conductive surface, and a conductive layer capable of extracting electrons from the display surfaces. In a cold cathode display, as described herein, the source of electrons may be nanotubes, edge emitters, tips, and so on. The phosphor and nanotubes are placed on the pixels and light is emitted from the phosphor when ions emitted strike the phosphor. The amplitude of the illumination is a linear function of the power consumed by the phosphor. The power is a linear function of the number of ions arriving at the phosphor for a given voltage. 
         [0045]    Therefore, any means to maximize the electron flow from the cold cathode to the phosphor will optimize the illumination and performance of the display. 
         [0046]    By varying the voltage applied to ML  172  ( FIG. 3 ) and optimizing the effect of the field generated by the ML voltage, depending on the physical configuration of the display, will result in an increase of the electron flow from the cold cathodes, resulting in increased brightness and optimum display performance. 
         [0047]    The DC, AC or pulsed voltage on ML for optimum performance is a function of the geometry of the components in the display and must be determined independently for the physical structure of the particular display. 
         [0048]    The introduction of a noble gas, such as argon and/or mixtures of noble or ionizable gases at low pressure into the display, and applying a DC, AC or pulsed voltage to ML to create a plasma and coating the frame and pixel metal with an insulator creating a sheath results in multiplication of the current produced by the cold cathode electron emitting source, such as nanotubes, edge emitters, etc. by order of magnitude while the applied voltage is virtually constant. The coating with the insulator causes increased secondary emission as described while the creation of the sheath in the plasma cause electron multiplication and thus increases the brightness of the display without an increase in the cold cathode voltage applied. Since the photons (light level) emitted by the phosphor is a linear function of the power then the brightness, at a constant voltage on the pixel, is a linear function of the current. Since the current increases order of magnitude then the brightness will increase at the same rate. The creation of the plasma is a function of the DC, AC or pulsed voltage applied to the ML. 
         [0049]    While there has been shown, described, and pointed out fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the apparatus described, in the form and details of the devices disclosed, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, the control frame described previously may be used with any display which uses electrons or charged particles to form an image. As discussed above, it is also understood that the present invention may be applied to flexible displays in order to form an image thereon. 
         [0050]    It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.