Patent Application
20060113888
1. Field of the Invention
The present invention generally relates to field emission display panels or devices, and more particularly, relates to a field emission display device having at least one reduction plate or electrode which deflects ionic emission gas away from the field emission components of the device to prevent damage to the field emission components.
2. Background of the Invention
In recent years, flat panel display devices have been developed and used in electronic applications such as personal computers. One of the popularly-used flat panel display devices is an active matrix liquid crystal display which provides improved resolution. However, liquid crystal display devices have many inherent limitations that render them unsuitable for a number of applications. For instance, liquid crystal displays have numerous fabrication limitations including a slow deposition process for coating a glass panel with amorphous silicon, high manufacturing complexity and low yield. Moreover, the liquid crystal display devices require a fluorescent back light which draws high power while most of the light generated is wasted. A liquid crystal display image may be difficult to see under bright light conditions or at wide viewing angles which further limit its use in many applications.
Other flat panel display devices have been developed in recent years to replace the liquid crystal display panels. One of such devices is a field emission display device that overcomes some of the limitations of LCD and provides significant advantages over the traditional LCD devices. For instance, the field emission display devices have higher contrast ratio, larger viewing angle, higher maximum brightness, lower power consumption and a wider operating temperature range when compared to conventional thin film transistor (TFT) liquid crystal display panels.
A most drastic difference between an FED and an LCD is that, unlike the LCD, the FED utilizes colored phosphors to produce its own light. The FEDs do not require complicated, power-consuming back lights and filters and, as a result, almost all the light generated by an FED is visible to the user. Moreover, the FEDs do not require large arrays of thin film transistors, and thus, a major source of high cost and yield problems for active matrix LCDs is eliminated.
In an FED, electrons are emitted from a cathode and impinge on phosphors coated on the back of a transparent cover plate to produce an image. Such a cathodoluminescent process is known as one of the most efficient methods for generating light. In contrast to a conventional CRT device, each pixel or emission unit in an FED has its own electron source, i.e., typically an array of emitting microtips. A voltage difference exists between a cathode and a gate electrode which extracts electrons from the cathode and accelerates them toward the phosphor coating. The emission current, and thus, the display brightness, is strongly dependent on the work function of the emitting material. To achieve the necessary efficiency of an FED, the cleanliness and uniformity of the emitter source material are very important.
In order for electrons to travel in an FED, most FEDs are evacuated to a low pressure such as 10−7 torr in order to provide a log mean free path for the emitted electrons and to prevent contamination and deterioration of the microtips. The resolution of the display can be improved by using a focus grid to collimate electrons drawn from the microtips.
In the early development for field emission cathodes, a metal microtip emitter of molybdenum was utilized. In such a device, a silicon wafer is first oxidized to produce a thick silicon oxide layer and then a metallic gate layer is deposited on top of the oxide. The metallic gate layer is then patterned to form gate openings, while subsequent etching of the silicon oxide underneath the openings undercuts the gate and creates a well. A sacrificial material layer such as nickel is deposited to prevent deposition of nickel into the emitter wall. Molybdenum is then deposited at normal incidence such that a cone with a sharp point grows inside the cavity until the opening closes there above. An emitter cone is left when the sacrificial layer of nickel is removed.
In an alternative design, silicon microtip emitters are produced by first conducting a thermal oxidation on silicon, followed by patterning the oxide and selectively etching to form silicon tips. Further oxidation or etching protects the silicon and sharpens the point to provide a sacrificial layer. In another alternate design, the microtips are built onto a substrate of a desirable material such as glass, as an ideal substrate for large area flat panel displays. The microtips can be formed of conducting materials such as metals or doped semi-conducting materials. In this alternate design for a FED device, an interlayer that has controlled conductivity deposited between the cathode and the microtips is highly desirable. A proper resistivity of the interlayer enables the device to operate in a stable condition. In fabricating such FED devices, it is therefore desirable to deposit an amorphous silicon film which has electrical conductivity in an intermediate range between that of intrinsic amorphous silicon and n+ doped amorphous silicon. The conductivity of the n+ doped amorphous silicon can be controlled by adjusting the amount of phosphorous atoms contained in the film.
Generally, in the fabrication of an FED device, the device is contained in a cavity of very low pressure such that the emission of electrons is not impeded. For instance, a low pressure of 10−7 torr is normally required. In order to prevent the collapse of two relatively large glass panels which form the FED device, spacers must be used to support and provide proper spacing between the two panels. For instance, in conventional FED devices, glass spheres or glass crosses have been used for maintaining such spacings in FED devices. Elongated spacers have also been used for such purposes.
A completed FED structure 30, including an anode 28 mounted on top of the structure 30, is shown in
The conventional FED devices formed with microtips shown in
In a co-pending application Ser. No. 09/377,315, filed Aug. 19, 1999, assigned to the common assignee of the present invention, a field emission display device and a method for fabricating such device of a triode structure using nanotube emitters as the electron emission sources were disclosed. In the triode structure FED device, the device is constructed by a first electrically insulating plate, a cathode formed on the first electrically insulating plate by a material that includes metal, a layer formed on the cathode of a high electrical resistivity material, a layer of nanotube emitters formed on the resistivity layer of a material of carbon, diamond or diamond-like carbon wherein the cathode, the resistivity layer and the nanotube emitter layer form an emitter stack insulated by an insulating rib section from adjacent emitter stacks, a dielectric material layer perpendicularly overlying a multiplicity of the emitter stacks, a gate electrode on top of the dielectric material layer, and an anode formed on a second electrically insulating plate overlying the gate electrode. The FED device proposed can be fabricated advantageously by a thick film printing technique at substantially lower fabrication cost and higher fabrication efficiency than the FEDs utilizing microtips.
In another co-pending application Ser. No. 09/396,536, filed Sep. 15, 1999, assigned to the common assignee of the present invention, a field effect emission display device and a method for fabricating the diode structure device using nanotube emitters as the electron emission sources were disclosed. In the diode structure FED device, the device is constructed by a first glass plate that has a plurality of emitter stacks formed on a top surface. Each of the emitter stacks is formed parallel to a transverse direction of the glass plate and includes a layer of electrically conductive material such as silver paste and a layer of nanotube emitter on top. The first glass plate has a plurality of rib sections formed of an insulating material in-between the plurality of emitter stacks to provide electrical insulation. A second glass plate is positioned over and spaced-apart from the first glass plate with an inside surface coated with a layer of an electrically conductive material such as indium-tin-oxide. A multiplicity of fluorescent powder coating strips is then formed on the ITO layer each for emitting a red, green or blue light when activated by electrons emitted from the plurality of emitter stacks. The field emission display panel is assembled together by a number of side panels that join the peripheries of the first and second glass plate together to form a vacuum-tight cavity therein.
During operation of the FED device 40, oxygen and nitrogen are typically present at low pressures between the cathode 42 and the anode 46. When the FED device 40 is energized, a voltage potential is applied by the voltage source 48, between the cathode 42 and the anode 46, to establish the electric field 50. High-energy electrons 52 are emitted from the field emission elements 44, toward the anode 46. These high-energy electrons 52 strike the nitrogen and oxygen gas and form positive nitrogen and oxygen ions, as shown in
An object of the present invention is to provide a novel protection structure for preventing burn-out damage to field emission elements in a field emission display device.
Another object of the present invention is to provide a novel field emission display device provided with a protection structure having at least one reduction plate or electrode for altering the discharge path of ionized gases and preventing the gases from inducing an electrical surge which may otherwise cause burnout damage to field emission elements in the device.
Still another object of the present invention is to provide a novel field emission display device having a protection structure which may include multiple reduction plates or electrodes interspersed among field emission elements on a cathode in the device to alter the discharge path of ionized gases in the device and prevent current-induced burnout damage to the field emission elements.
A still further object of the present invention is to provide a novel field emission display device which includes a protection structure that substantially prolongs the lifetime of field emission elements in the device.
Another object of the present invention is to provide a novel field emission display device having a protection structure which may include multiple, elongated reduction plates or electrodes that run parallel to and between rows of field emission elements in the device.
Yet another object of the present invention is to provide a novel field emission display device having a protection structure that is arranged in a meshwork- or net-shaped configuration among field emission elements in the device.
In accordance with these and other objects and advantages, the present invention is generally directed to a novel protection structure for protecting field emission elements in a field emission display device from burnout damage due to electrical current surges induced to the device cathode by ionized gases in the device.
The structure includes one or multiple reduction plates or electrodes which are typically provided on the cathode. A voltage source is electrically connected to the reduction plate or plates to alter the discharge path of the ionized gases from the device cathode to the reduction plate or plates. Consequently, induction of electrical current surges to the cathode is avoided, thereby preventing burnout damage to the field emission elements.
In a typical embodiment of the invention, multiple reduction plates or electrodes are interspersed among the field emission elements in the device. In one embodiment, the multiple reduction plates or electrodes are elongated and run parallel and adjacent to rows of field emission elements in the device. In another embodiment, the multiple reduction plates or electrodes are arranged in a meshwork- or net-shaped configuration among the field emission elements in the device.
The present invention is directed to a field emission display device which includes a structure for deflecting the discharge path of gas ions away from a cathode. This prevents surges in electrical current from being drawn to the cathode and inducing burnout damage to field emission elements provided in electrical communication with the cathode. Consequently, the lifetime of the device is substantially prolonged.
Referring initially to
In accordance with the present invention, a protection structure 68 includes at least one reduction plate or electrode 70 which is provided in the field emission device 54, typically on the cathode 56. The reduction plate 70 is preferably any electrically-conductive metal. An insulation layer 72, which is an electrically-insulating material, typically separates the reduction plate 70 from the cathode 56. A bias voltage source 74 is electrically connected to the reduction plate 70 for applying a negative voltage thereto, as hereinafter further described.
In operation of the FED device 54, the operating voltage source 62 applies an operating voltage potential of typically about 1000V between the cathode 56 and the anode 60, to establish the electric field 64. Simultaneously, the bias voltage source 74 applies a negative bias voltage of typically about −1 to −30 V to the reduction plate 70. High-energy electrons 66 are emitted from the field emission elements 58 and strike a phosphors target (not shown) provided on the anode 60, to emit light from the target. These high-energy electrons 66, in transit from the field emission elements 58 to the target, strike molecular nitrogen and oxygen in the device 54, thereby ejecting electrons from the nitrogen and oxygen and forming N+ and O+ ions.
Due to the negative charge of the reduction plate 70, applied by the bias voltage source 74, the N+ and O+ ions are deflected away from the cathode 56, along a gas discharge path 76, to the reduction plate 70. Accordingly, the N+ and O+ ions are prevented from contacting the cathode 56, thereby preventing ion-induced surges in electrical current to the cathode 56 which would otherwise tend to damage the field emission elements 58. At the reduction plate 70, the N+ and O+ ions are reduced back to molecular nitrogen and oxygen as follows:
N2++e−→N2
O2++e−→O2
A first exemplary structure of FED device according to the present invention is illustrated in
A protection structure 87 of the FED device 80 includes multiple, elongated reduction plates or electrodes 89 that are provided on the cathode plate 81. The reduction plates 89 extend parallel and adjacent to the cathode strips 82 on which the field emission elements 83 are provided. A bias voltage source 90 is electrically connected to each reduction plate 89 of the protection structure 87 for applying a negative bias voltage to the reduction plate 89. Accordingly, the negative bias voltage applied by the bias voltage source 90 imparts a negative charge to the reduction plates 89 which attracts positive nitrogen and oxygen ions thereto and prevents current-induced damage to the field emission elements 83, as heretofore described with respect to the protection structure 68 of
The reduction plates 89 may be fabricated on the cathode plate 81 at the same as the cathode strips 82. In manufacture, a metal material, i.e., the metal cathode plate 81, is first deposited on a substrate (not shown), using conventional deposition techniques. Photolithography techniques are then used to form a first mask (not shown) which defines the location and geometry of the cathode strips 82 and the reduction plates 89 on the cathode plate 81. The cathode plate 81 is then etched to form the cathode strips 82 and the reduction plates 89 according to the pattern defined by the first mask. A wet etching method may be used to precisely control the geometry and size of the cathode strips 82. Next, a second mask (not shown) is formed on the cathode strips 82 and the reduction plates 89 to define the geometry and location of the field emission elements 83 on the cathode strips 82, followed by etching and fabrication of the field emission elements 83. In this structure, the reduction plates 89 and the cathode strips are formed on a same plane and are parallel and alternately spaced-apart. Each of the reduction plate 80 provides protection for its adjacent field emission elements 83.
In addition to the elongated and parallel structure described above, the reduction plates 89 can also be formed in a meshwork-shape or a net-shape according to another exemplary embodiment of the present invention, which is shown in
A meshwork-shaped or net-shaped protection structure 99 including reduction plates 101 is provided on the cathode plate 93 of the FED device. The reduction plates 101 are formed on the top of the cathode plate 93 and is separated from the cathode strips 94 by an insulation layer 100. Accordingly, the reduction plates 101 along with the underlying insulation layer 100 impart a meshwork- or net-shaped configuration to the protection structure 99.
A bias voltage source 103 is electrically connected to the reduction plates 101 of the protection structure 99. The bias voltage source 103 applies a negative voltage to the protection structure 99 to attract positive nitrogen and oxygen ions formed by the high-energy electrons emitted by the field emission elements 95. This prevents the ions from contacting the cathode strips 94 and inducing surging of an excessive electrical current to the cathode strips 94 and field emission elements 95, as heretofore described with respect to the FED device 54 of
The manufacturing of the FED device 92 is described below. Initially, a first metal layer is deposited on a substrate (not shown) to form the cathode plate 93. A first mask (not shown) is then patterned on the cathode plate 93 to etch the cathode strips 94 therein. After the first mask is removed from the cathode plate 93, the insulator layer 100 is deposited over the cathode plate 93 and cathode strips 94. Next, a second metal layer for the reduction plates 101 is deposited on the insulator layer 100, followed by formation of a second mask (not shown) using a negative photoresist to define the geometry and location of the light emission elements 95. The second metal layer is then etched away the region for forming the field emission elements 95, leaving the reduction plates 101. Afterward, keeping the second mask unremoved, the regions where the second metal layer is removed are then deposited with materials for the light emission elements 95. After the light emission elements 95 are formed, the structure of the FED device 92 as shown in
The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.
Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.
