Displays, such as those commonly used in lap-top computer screens function as a result of energy or voltage responsive substances (whether liquid crystals, plasma, phosphors, electrochemic, electrophoretic and other materials) disposed between electrodes at least one of which is transparent. When the energy or voltage responsive substances are excited, they either permit light to pass through a transparent electrode and onto the viewer, or generate light which passes through a transparent electrode and onto the viewer. Liquid crystal displays (LCD), electroluminescent displays (EL), plasma displays, and electrochromic displays are among the devices using at least one transparent electrode at a pixel site. These displays employ orthogonal electrically conductive row and column electrodes in various ways to induce a visible pixel site to a viewer. The electrodes are commonly patterned, i.e., arranged in rows and columns. Energy or voltage responsive materials are disposed between the electrodes. When a voltage is created between the electrodes, and the materials respond, light is transmitted toward the viewer. In order for light to pass through the electrode and onto the viewer, the row electrodes, the column electrodes, or both electrodes must be fabricated from a transparent material. As stated in U.S. Pat. No. 5,342,477 assigned to the assignee of the present invention and which is hereby incorporated by reference, the transparent electrode material must also be highly conductive. In these types of devices, the transparent electrodes are not bombarded with electrons (having energies ranging from a few hundred to thousands of volts) and consequently a variety of materials which are conductive and transparent may be utilized, for example, indium tin oxide and tin oxide. Indium tin oxide is more conductive for a given thickness, it is more transparent for a given thickness, and it is easier to etch than tin oxide. In addition, indium tin oxide forms very smooth thin films. Consequently, indium tin oxide is preferred for these types of displays.
A promising technology is the use of a matrix-addressable array of cold cathode emission devices to excite phosphors on a screen. These field emission displays operate on the principle of cathodoluminescent phosphors excited by cold cathode field emission electrons. The faceplate having a cathodoluminescent phosphor coating receives patterned electron bombardment from an opposing baseplate thereby providing a light image which can be seen by a viewer. The faceplate is separated from the baseplate by a vacuum gap, an outside atmospheric pressure is prevented from collapsing the two plates together by physical standoffs between them, often referred to as spacers. Arrays of electron emission sites (emitters) are typically sharp cones that produce electron emission in the presence of an intense electric field. A positive voltage is applied to an extraction grid relative to the sharp emitters to provide the intense electric field required for generating cold cathode electron emission. The electrons bombard and strike the transparent conductor on which the phosphors are located. In the case of indium tin oxide conductors, it has been found that over a period of time, there is a visible deterioration of the field emission display which is exhibited by a browning of the conductor and an increase in resistivity of the conductor.
Consequently, there is a need for a transparent conductor which does not deteriorate over time due to electron bombardment. Moreover, there is a need for a transparent conductor whose resistivity does not increase over time due to electron bombardment.
USPTO Backgrounds
USPTO Backgrounds