Dielectrics for bright EL displays

Thin-film electroluminescence as a practical flat-panel technology is considered. It is shown that stacked dielectrics, which are more amenable to high-volume production than composite dielectrics, can give dielectric layers with high figures of merit and can be utilized to maximize the dielectric capacitance and the phosphor thickness. However, the fraction of the applied voltage that is applied across the ZnS layer must be limited to about 70%. Because of the nature of the breakdown mechanism in Ta/sub 2/O/sub 5/ and its adhesion properties, the use of this material must be limited, and its placement in the stack carefully chosen. Ta/sub 2/O/sub 5/ should not be sputter-deposited on top of ITO or ZnS and its contact with aluminum should be preferably avoided. Extra brightness improvements must come from the phosphor process. High brightness and efficiencies have been attained in the SiON/Ta/sub 2/O/sub 5/ (ST) and Al/sub 2/O/sub 3//Ta/sub 2/O/sub 5/ (AT) stacked dielectric systems. The ST system is preferable because of its tolerance to subsequent processing steps.<>