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 increased secondary emission for excitation of the phosphor by electron bombardment.
Flat panel display (FPD) technology is one of the fastest growing display technologies in 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 the use of an insulator coating on the frame of such devices to cause increased electron emission for the purpose of exciting the phosphor by increased electron 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 thin layer of an insulator material deposited on the frame and pixel, and a plurality of cold cathode emitters deposited on top of the insulator material on the frame, and a phosphor deposited on the pixel which is surrounded by the frame; wherein, exciting the conductive frame and addressing one of the pixels using the associated driver circuit causes the cold cathode emitters to emit electrons that induce one of the pixels to emit light; wherein, some emitted electrons strike gas atoms on route to the pixel. The ions return to the frame causing additional electrons to be released especially in the area of the frame covered with insulator.
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 which contains cold cathode emitters and which frame is completely or partially covered with an insulator such as SiO2 or MgO, for producing additional electrons. The ions return to the frame causing additional electrons to be released. When the ions return to the frame covered with the insulator more electrons are released allowing for more efficient illumination of the phosphor. When the hollow of the display is filled with a noble gas and a plasma is produced in the gas, the insulator on the conductive frame forms a potential variation at the surface of the insulator or forms a boundary. This boundary is a sheath and when, as above, ions are produced they return to the frame and strike or hit the sheath to cause electrons to be released causing electron multiplication for further increasing the illumination. Each pixel has color or monochrome phosphors located on the layer of insulation on the pixel. The pixels are activated by electrons created by a voltage potential between the frame and the pixel. The electrons strike the phosphor and cause the phosphor to emit light. Each pixel is addressed through a TFT matrix structure (e.g. a memory TFT matrix). The apparatus causes increased secondary emission for the purpose of increased excitation of the phosphor by electron bombardment.
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 control frame can accommodate carbon nanotube or other electron emission sources. The control frame and pixel have a thin layer of insulator such as SiO2 or MgO deposited thereon. Carbon nanotubes (CNT) are then deposited on top of the insulator on the frame. Phosphor is deposited on top of the pixel area. During operation electrons emitted by the nanotubes go to the pixel. The electrons strike the phosphor on the pixel causing the phosphor to illuminate. Some electrons strike gas atoms producing ions and more electrons. The ions return to the frame causing additional electrons to be released. When the ions strike the frame covered with insulator more electrons are released. Another implementation is to first deposit the nanotubes and then cover the nanotubes with a thin layer of SiO2 or MgO.
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
Referring to
The potential variation at the surface of the walls of the insulator is a boundary between the plasma and the insulator (SiO2, MgO) Sheath is this boundary. The sheath unit forms around any probe that may be immersed in the plasma of the discharge is an example of such a boundary through which charges may flow. The sheath that forms at the surface of insulation will accrue from the presence of an excess number of electrons. However, sheaths may contain either electrons or positive ions. Sheaths are regions of rapidly varying potential. Sheaths may form around any object that may exist in the plasma as well as at the surface of the material envelope containing the discharge. An insulated conductor in a plasma of a discharge has potential variation in the plasma. As long as the conductor is negative with respect with the plasma, positive ion current is collected by the conductor. A positive ion sheath forms around the conductor. The gas is ionized and a plasma is formed with a sheath at the walls of the insulator. When ions return to the frame they hit the sheath and cause electrons to be released which is an electron multiplication effect.
Referring now to the figures,
Assembly 110 of
In any event, deposited on each conductive pixel pad 140 is phosphor layer 180 over the insulator. Each phosphor layer(s) is selected from materials that emit light 190 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).
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 electrons for a desire 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 control frame 220 which is coated with an insulator layer where the nanostructures are deposited on top of the insulator layer such as SiO2 or MgO (
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.,
The anode (pixel) voltage (VANODE) of each pixel partly determines the brightness or color intensity of 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
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 is 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 (ML) 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 is placed on the pixels and light is emitted from the phosphor when the electrons emitted by the cold cathode 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 electrons 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 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 cathode to the phosphor for a given pixel voltage, resulting in increased brightness and optimum display performance.
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, and other pending applications regarding flat panel display technology.
Number | Date | Country | |
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60999783 | Oct 2007 | US | |
61000958 | Oct 2007 | US |