SPUTTER-DEPOSITION OF PHOSPHORS FOR ELECTROLUMINESCENT FLAT-PANEL DISPLAYS

Thin film electroluminescent (TFEL) phosphors for flat panel displays have been produced by several different growth methods including atomi c layer epitaxy, chemical vapor deposition, and sputter deposition. Th ere is a great deal of interest in sputter deposition due to the exten sive knowledge base and equipment from other existing thin film manufa cturing. However, deposition of sulfide-based TFEL phosphors by conven tional radio frequency magnetron sputtering has proven to be difficult due to the formation of negative sulfur ions near the target which ar e accelerated to the growing film by the self-bias developed on the ta rget. This negative-ion resputtering can result in amorphization or re -sputtering of the phosphor films. In severe cases, a net sputtering o f the substrate cap result. In order to remedy this negative ion respu ttering problem, modifications of the magnetron geometry and ion-beam sputtering have been evaluated for production of CaxSr1-xGa2S4:Ce and SrS:Ce TFEL phosphors. Sputter deposited TFEL films also typically req uire a post-deposition anneal which adds to expense and can cause othe r problems for the flat panel display. Ion-beam assist during depositi on of undoped ZnS was studied as a method to induce surface-atom mobil ity and a more crystalline as-deposited film for use in monochrome TFE L displays.