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.
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.
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.
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.
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.
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.
a illustrates a control frame according to another aspect of the present invention.
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.
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.
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's are widely used in liquid crystal display (LCD) FPDs.
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.
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.
According to an aspect of the present invention, the control frame can be formed using standard lithography, deposition and etching techniques.
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.
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.
Referring to
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
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
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.
Since the pixel pad 140 voltage is negative relative to the frame 120 (Vpixel less positive than Vframe) the electrons emitted by the nanotubes (see,
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., Vco
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.
Assembly 110 of
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 (
Incorporated in the TFT circuit (
Associated with each conductive pixel pad 140/phosphor layer 180 pixel is a TFT circuit 200 (
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.
Referring now also to
a shows another exemplary configuration of a control frame structure similar to that of
In the illustrated embodiment control frame 220 (or 220′) is formed as a metal layer above the final passivation layer (e.g. 130,
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.
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.
By negatively biasing the pixel voltage (VPIXEL) 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).
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
In general, the voltage used to select the row (VROW) 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. VANODE 325 the power supply voltage, and may be on the order of about 10-40 volts.
Referring to
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.
Therefore, any means to maximize the electron flow from the cold cathode to the phosphor will optimize the illumination and performance of the display.
By varying the voltage applied to ML 172 (
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.
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.
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.
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.
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.
Number | Date | Country | |
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60999783 | Oct 2007 | US | |
61000958 | Oct 2007 | US |