(1) Field of the Invention
The invention relates to flat panel displays, and more particularly to a field emission display provided with a repair capability, and a method for repairing the display to isolate defective elements from the remainder of the display.
(2) Description of the Related Art
In display technology, there is an increasing need for flat, thin, lightweight displays to replace the traditional cathode ray tube (CRT) device. One of several technologies that provide this capability is field emission displays (FED). An array of very small, conical emitters is formed on a back plate, typically using a semiconductor or insulator substrate as the base, and the emitters are addressed via a matrix of columns and lines. These emitters are connected at their base to a conductive cathode, and the tips of the emitters are in close proximity to and are surrounded by a second conductive surface, usually referred to as the gate. When the proper voltages are applied to the cathode and gate, electron emission occurs from the emitter tips, with the electrons attracted to a third conductive surface, the anode, formed on an opposite face plate on which there is cathodoluminescent material that emits light when excited by the emitted electrons. A display image is formed and viewed on the face plate and by selecting certain of the emitters via the matrix addressing.
FIG. 1 is a cross-sectional view of a back plate of a prior art field emission display (FED). Column electrodes 12, also called the cathode, are formed on a baseplate 10, and have emitter tips 14 mounted thereon. The emitters are separated by insulating layer 16. A row electrode 18, or gate, with openings 17 for the emitter tips, is formed on the insulating layer 16 and is formed perpendicular to the row electrodes.
Referring now to FIG. 2, during manufacturing of the FED backplate, a conductive particle 20 may accidentally become lodged between emitter tip 14 and gate 18. If this defect in the display manufacture is not corrected, during operation of the display a short circuit condition will occur between the emitter and gate, causing loss of the pixel at which the emitter is located (where a pixel is typically formed of from one to many thousands of emitters), or even an entire row of the display.
Workers in the art are aware of this problem and have attempted to resolve it. In U.S. Pat. No. 5,194,780 (Meyer), the cathode is formed in a meshed pattern and separated from the emitter tips by a resistive layer, so that in the event of a short circuit between the emitter and gate, the resistive layer prevents a dead short. However, if the short circuit is not repaired, this leads to increased loading of the driving circuit. If one short occurs, there is a resultant leakage current of about 10 microamps at the point of the short. In general, the specification of the driving IC (integrated circuit) provides an output power of about 1 watt over a total of about 100 outputs. For an typical output voltage of 100 volts, the current limit per output is about 100 microamps. It can readily be seen, then, that several short circuits would overload the driver and lead to driver failure.