A vacuum-deposited thin film metal-insulator-metal (Al-SiO-Au) device, after an electro-forming process, emits hot electrons,and constitutes a cold cathode. An array of 25 of these Al-SiO-Au cold cathodes, each of approximately 0.1 cm2 area, is used with a phosphor screen in an alpha-numeric display panel, which is clearly visible under normal laboratory lighting conditions. The normal cathode bias is about 12 V. The normal screen potential is about 3 kV. Screen brightness varies directly with the screen potential and exponentially with cathode bias. Pulse operation shows th t the rise and decay times of the light output are limited only by the phosphor used. The thickness and composition of the cathode insulator film determine the operating characteristics, notably life. Cathodes of high emission current density, for example, 250 ???????μA cm????????2, may operate for about 1 hour. Some with initial high ratio of emission current to current circulating through the cathode, for example, up to one per cent, may operate for 1000 hours. Cathodes of emission current density that is approximately uniform over the cathode area, and therefore suitable for a display, operate for several hundred hours. Failure mechanisms are due to continued forming during operation,and dielectric breakdown.
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