Abstract:
A flat panel display including: a film electron emitting cathode; and, an anode including: a plurality of pixels, a plurality of TFT circuits, each being associated with a corresponding one of the circuits; and a conductive frame laterally separating the pixels and substantially isolating their respective electric fields.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/417,631, filed May 4, 2006, now U.S. Pat. No. 7,728,506 entitled “Low Voltage Phosphor With Film Electron Emitters Display Device”, which is a continuation-in-part of U.S. patent application Ser. No. 10/974,311 entitled “Hybrid Active Matrix Thin-Film Transistor Display,” filed on Oct. 27, 2004, now U.S. Pat. No. 7,327,080 which is a continuation-in-part of U.S. patent application Ser. No. 10/782,580 entitled “Hybrid Active Matrix Thin-Film Transistor Display,” filed on Feb. 19, 2004, now U.S. Pat. No. 7,274,136 which is a continuation-in-part of U.S. patent application Ser. No. 10/763,030 entitled “Hybrid Active Matrix Thin-Film Transistor Display,” filed on Jan. 22, 2004, now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 10/102,472, now U.S. Pat. No. 7,129,626 entitled “Pixel Structure For an Edge-Emitter Field-Emission Display”, filed on Mar. 20, 2002, and claims priority of U.S. patent application Ser. No. 11/417,631, filed May 4, 2006 and Provisional application Ser. No. 60/698,047 entitled “Control Grid Arrangement For Display Panel,” filed on Jul. 11, 2005, the entire disclosures of which are hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This application is related to the field of displays. 
     BACKGROUND OF THE INVENTION 
     Flat panel display (FPD) technology is one of the fastest growing technologies in the world with a potential to surpass and replace conventional Cathode Ray Tubes (CRTs) in the foreseeable future. As a result of this growth, a large variety of FPDs exist, which range from very small virtual reality eye tools to large TV-on-the-wall displays. 
     Various types of FPDs utilize both hot and cold cathodes that produce electrons that activate phosphor, Structures are depicted in various patents issued by Copytele, Inc. the assignee herein, including for example, U.S. Pat. Nos. 4,655,897, 4,742,345, 5,053,763, and 5,561,443, the subject matter of these patents being incorporated by reference herein in their entirety. 
     It would be desirable to have a display device and method of fabricating the display device, that would be operable having a small thickness film emitter which emit electrons when a low voltage is applied in combination with a TFT matrix configuration, and that would produce a more uniform, enhanced, and adjustable brightness with greater electric field isolation between pixels. The film emitters are approximately 10 to 17 micrometers (microns) in diameter and emit electrons when the applied voltage is between approximately 5 to 15 volts. One embodiment utilizes an emitter having a thickness of 12 microns and having an applied voltage of 6 volts. This device would be useful as a FPO such as a thin CRT, incorporating virtually any electron emission system, a pixel control system, and pixels with or without memory and comprised of phosphor. 
     SUMMARY OF THE INVENTION 
     A flat panel display including: a cathode or film emitters which emit electrons when a low voltage is applied; and, an anode including: a plurality of pixels, a plurality of TFT circuits, each being associated with a corresponding one of the circuits; and a conductive frame laterally separating the pixels and substantially isolating their respective electric fields. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional plan-view of a display panel incorporating a hot cathode and anode supported control frame according to an embodiment of the present invention; 
         FIG. 2  illustrates a plan-view of the anode with the control frame of  FIG. 1 ; 
         FIG. 3  illustrates a schematic view of a circuit suitable for use with the anode of  FIGS. 1 and 2  according to an embodiment of the present invention; 
         FIG. 4  illustrates a cross-sectional plan-view of a display panel incorporating a hot cathode and anode supported control frame according to an embodiment of the present invention; and 
         FIG. 5  illustrates a cross-sectional plan-view of a display panel incorporating a cathode of film emitters which emit electrons when a low voltage is applied an anode supported control frame and a control grid according to an embodiment of the present invention. 
     
    
    
     It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not drawn to scale. The embodiments shown herein 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. 
     DETAILED DESCRIPTION OF THE INVENTION 
     According to an embodiment of the present invention, a display device having a cathode of film emitters which emit electrons when a low voltage is applied, TFT circuit, with a control frame disposed on the anode TFT circuit, may be provided. The control frame may be lithographically applied as a final layer surrounding the pixels, for example. In an exemplary configuration, the device operates as a thin flat Low Voltage Phosphor Display (LVPD). 
     The inventors have discovered that a TFT-based display device with a control frame disposed on the anode thereof exhibits enhanced performance and effects useful for display devices. Any type of electron emission source may be used with such device. According to an embodiment of the present invention, a cathode of film emitters which emit electrons when a low voltage is applied may be used. The emitters are extremely small in thickness, being between about 10 to 17 microns thick. There are “thin film” transistors (TFTs) which have thinner emitters. Such devices have thicknesses less than 5 microns and are ususually on the order of 0.01 to 1 micron thick. 
     Before embarking on a detailed discussion, it is noted that passive matrix displays and active matrix displays are flat panel display types that are used in various display devices, such as laptop and notebook computers, for example. 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. 
     According to an embodiment of the present invention, a vacuum flat panel display using a thin-film-transistor (TFT) circuit may be provided. Associated with each pixel element is a TFT circuit that, in one configuration, includes first and second electrically cascaded active devices and a capacitor in communication with an output of the first device and an output of the second device. The circuit selectively addresses pixel elements in the display. In an exemplary embodiment, a cathode of film emitters that emit electrons when a low voltage is applied, are used to emit electrons that are drawn to selected pixel elements that include phosphor pads, which emit light of a known wavelength when struck by the emitted electrons. 
       FIG. 1  illustrates a schematic cross-sectional view of a TFT anode/hot cathode. The cathode is an array of film emitters which emit electrons when a low voltage is applied. The cathode and anode are incorporated in a LVPD device  100  according to an embodiment of the present invention. In this exemplary embodiment, display  100  includes a cathode of film emitters  107  that acts as a source of electrons  140  when a low voltage is applied, an anode  104  that employs TFT circuitry to control the attraction of electrons  140  to corresponding pixel element on a substrate  160 , and a control frame  1800  disposed on a passivation layer  179  of the anode and surrounding each of pixels  170 / 175 . 
     A second substrate  110 , and side-walls (not shown) close the display  100  housing. Substrates  160 ,  110  may take the form of glass substrates, for example. 
     Anode  106  is composed of a plurality of conductive pads  170  fabricated in a matrix of substantially parallel rows and columns on substrate  160  using known fabrication methods. Column-oriented conductive lines  177  are associated with each of the corresponding conductive pads  170 . In the illustrated embodiment, conductive pads  170  are composed of an electrically conductive and transparent material, such as ITO (Indium Titanium Oxide). It should be recognized though that the conductive pads may be opaque or transparent depending upon desired application and/or viewing perspective (see, e.g.,  FIGS. 1 ,  4 ). 
     Deposited on each conductive pad  170  is a low voltage phosphor layer  175 . Phosphor layer  175  may be selected from materials that emit light  195  of a specific color. The low voltage phosphors emit light when activated by the voltage between 12 to 50 volts. In a conventional RGB display, phosphor layer  175  may be selected from materials that produce red light, green light or blue light  195  when struck by electrons  140 . As would be appreciated by those skilled in the art, the terms “light” and “photon” are synonymous and are used interchangeably herein. 
     A matrix organization of conductive pads  170  and phosphor layers  175  (e.g., pixels  170 / 175 ) allows for X-Y addressing of each of the individual pixel elements in the display. 
     Associated with each conductive pad  170 /phosphor layer  175  pixel is a TFT circuit  180  that is operable to apply a known voltage to the associated conductive pad  170 /phosphor layer  175  pixel. TFT circuit  180  operates to apply either a first voltage to bias the associated pixel element to maintain it in an “off” state or a second voltage to bias an associate pixel element to maintain it in an “on” state, or an intermediate sate. In this illustrated case, each conductive pad  170  is inhibited from attracting electrons  140  emitted by cathode  107  when in an “off” state, and attracts electrons  140  when in an “on” state or any intermediate state. 
     Using TFT circuitry  180  to bias conductive pads  170  provides for both addressing pixel elements and maintaining the pixel element in a condition to attract electrons for a desired time period, i.e., time-frame or one or more sub-periods of a time-frame. Co-pending patent application Ser. No. 10/782,580 entitled “Hybrid Active Matrix Thin-Film Transistor Display” filed on Feb. 19, 2004 and assigned to Copytele, Inc. the assignee, describes various TFT, anode, and cathode configurations useful in implementing the present invention, the subject matter thereof incorporated by reference herein in its entirety. 
     TFT circuits  180  and conductive lines  177  may be formed on substrate  160  using lithographic techniques, for example. TFT circuits  180  and conductive lines  177  may then be passivated by passivating layer  179 . Passivating layer  179  may be deposited over substrate  160 , circuits  180  and conductive lines  177 , for example. Control frame  1800  may then be formed over passivating layer  179 . 
     Referring now to  FIG. 2  in conjunction with  FIG. 1 , there is illustrated a conductive control frame  200 . Control frame  200  is suitable for use as control frame  1800  according to an embodiment of the present invention. Control frame  200  helps produce a uniform and adjustable brightness and a bright image by providing good electric field uniformity within display  100 . Further, where control frame  200  is essentially in the same plane as the pixels (see,  1800   FIG. 1 ), it does not obscure the produced image. 
     Control frame  200  comprises a plurality of conductors arranged in a rectangular matrix having substantially parallel vertical lines  230  and substantially parallel horizontal lines  240 , respectively. Each pixel  250  is generally bounded by the intersection of vertical conductor lines  230  and horizontal conductor lines  240 , such that the control frame conductors  230 ,  240  surround each of corresponding pixels  250  to the right, left, top, and bottom. One or more conductive pads  260  connect to the conductors  230 ,  240  to electrically power frame  200 . In one embodiment, four conducting pads connect to the metal lines, with each pad being about 100×200 micrometers (microns) in size. The control frame  200  may be provided as a metal layer above the TFT passivation layer  179  (see  FIG. 1 ). The pads  260  and metal lines which comprise the control frame structure  200  should remain free from passivation. In an exemplary configuration, the control frame metal layer has a thickness of less than about 1 micon, although it is understood that other thicknesses may be used depending on the particular application. 
     An appropriate voltage applied to the control frame prevents appearance of mutual field effects between neighboring pixels  250 , and thus enables a more uniform and greater brightness of each individual pixel. Typically, the voltage applied to the frame is between 5 to 15 volts. Prior art configurations are susceptible to the effects of undesirable electric fields between pixels, particularly when control voltages are operated to activate one pixel (“high”) while a neighboring pixel is inactive (“low”). The control frame of the present invention operates as a shield to suppress such undesirable electric fields between pixel structures and better isolate and stabilize each of the pixels. Note that in alternate configurations the control frame may include only metal lines parallel to the columns or only metal lines parallel to the rows. The conductors  230 ,  240  may be connected in a number of configurations. For example, in one configuration, all horizontal and vertical conductors are joined together 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 and the vertical conductors are not electrically connected. A voltage is applied to the horizontal conductor array, and a separate voltage is applied to the vertical conductor array. 
     Other configurations are also contemplated, including for example, a configuration powering horizontal conductors only, or a configuration powering vertical conductors only. In these configurations, the device shields the pixels from undesirable electric fields in only one direction. 
     In an embodiment of the present invention, the vertical line conductors  230  and horizontal line conductors  240  are framing each pixel  250  and are above the plane of the pixels  250 . However, it is understood that other configurations are contemplated where the conductors are disposed in the same plane as the pixels. 
     A control frame voltage of up to about one half the corresponding anode voltage may be applied to produce good brightness and uniformity conditions. However, the voltages may be varied to optimize other aspects and features of the TFT based display, such as contrast, gray scale, and color combinations, for example. 
     While a control frame voltage of about one half the corresponding anode voltage may generally produce optimum brightness and uniformity conditions, the anode voltage of each pixel determines the brightness or color intensity of each pixel. In order to control gray scale and/or color combinations, the control frame voltage of each pixel may be changed depending on an applied characteristic, such as the data amplitude applied to that pixel. 
     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. 3 . Circuit  300  includes first and second transistors  310 ,  330  and capacitor  320  electrically interconnected with a pixel, e.g., pad  340 ,  FIG. 1 . 
     According to an aspect of the present invention, a second TFT (see  FIG. 3  may be used to generate a control frame voltage which is equal to the column voltage (Vc) divided by a ratio factor (n). The second circuit also includes first and second transistors  340 ,  360  and a capacitor  350 . The factor (n) may be selected to produce the optimum results for a particular application. In an exemplary operation, data may be provided via the column driver (Vc) to produce an amplitude signal. If a predetermined amount (e.g. half) of the voltage of that signal is to be applied to the frame at the same time, then (n) equals 2. The control frame driver (Vc/n) thus applies to the control frame one half of the voltage as is applied at the corresponding particular pixel. The structure is driven using the same row driver (row) such that when a given row N (e.g. row  1 - 234 ,  FIG. 1 ) is turned on, the corresponding pixel N (e.g. pixel  1  of row) receives a voltage from the column driver, and the control frame around pixel  1  receives a voltage from the control frame driver which is a fraction of the voltage across pixel  1 . When pixel  2  is turned on, the corresponding control frame surrounding that pixel (i.e. the control frame surrounding pixel  2 ) receives a control frame voltage that is a fraction of the column driver voltage appearing at pixel  2 . Thus, for each column N (e.g. where n equals 960 columns), there exists a corresponding n equal to 960 frames, where each frame receives a control voltage each time the corresponding pixel associated with that control frame receives an applied column driver voltage. Storage, capacitors  320  and  350  operate to hold the charge on each of the pixel and the control frame for an entire frame. When processing proceeds to the next row (e.g. row  2 ), the row  1  pixels are still drawing current. In this manner, capacitor  350  “remembers” the frame voltage when proceeding from one row to the next (e.g. from the first row to the second row) while capacitor  330  “remembers” the pixel voltage when going to the next row. Such processing operations continue through the entire frame. 
     Control of one or more of the TFTs associated with the display device of the present invention may be accomplished in the following manner. In general, the voltage (Row) used to select the row is equal to the fully “on” voltage (Vc) of the column. The voltage Row in this case causes the pass transistor  310  to conduct. The resistance of transistor  310 , the capacitor  320  and the write time of each selected row determines the voltage at the gate of transistor  330  as compared to Vc. Using a voltage Row higher than the fully “on” voltage (Vc) increases the conduction of transistor  310 , reducing its resistance and resulting in an increase in pixel voltage and enhanced brightness. The same advantage will also apply to the control frame voltage applied to transistors  340 ,  360 . Thus, the selection voltage for the row is higher than the highest column voltage, thereby causing the transistors  310 ,  330  to conduct with a reduced resistance, thereby providing a greater voltage on the gates of transistors  340 ,  350 . 
     It is further understood that other circuit configurations may also be utilized. For example, the voltage applied to the control frame structure around each pixel may also be generated by using a voltage divider circuit at each pixel which produces a voltage which is proportional to the pixel voltage. 
     As is shown in  FIG. 1 , control frame  1800 , and associated horizontal and vertical lines illustrated in  FIG. 2 , may be utilized with a cathode film emitter as a source of electrons when current is passed through. The control frame may be formed in the following manner. Using a mask the control frame may be formed using the conventional method of imaging the desired structure on a photoresist layer which is placed on a metal layer, above the passivation layer, and then etching. A lift-off technique may also be employed. 
     Referring now also to  FIG. 4 , there is shown a display according to another embodiment of the present invention. Like elements of the displays of  FIGS. 2 and 4  have been labeled with like references. In such a case, substrate  160  need not be transparent as the viewing perspective is through substrate  110 , as opposed to substrate  160  (see, e.g.,  FIG. 1 ). 
     Referring now also to  FIG. 5 , there is shown a display according to another embodiment of the present invention. Again, like elements of the displays of  FIGS. 2 and 5  have been labeled with like references. The display of  FIG. 5  additional includes a grid  502 . Grid  502  may be composed of steel or a conductive metal or alloy having a low temperature coefficient of expansion, for example. Grid  502  may serve to further equalize the electric field between anode  106  and cathode  104 , resulting in improved display uniformity. 
     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, such as, a LVPD, Field Emission Display, Electrophoretic. 
     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.