Sputter deposition of phosphors for electroluminescent flat panel displays

Abstract

Thin film electroluminescent (TFEL) phosphors for flat panel displays have been produced by several different growth methods including atomic layer epitaxy, chemical vapor deposition, and sputter deposition. There is a great deal of interest in sputter deposition due to the extensive knowledge base and equipment from other existing thin film manufacturing. However, deposition of sulfide-based TFEL phosphors by conventional radio frequency magnetron sputtering has proven to be difficult due to the formation of negative sulfur ions near the target which are accelerated to the growing film by the self-bias developed on the target. This negative-ion resputtering can result in amorphization or re-sputtering of the phosphor films. In severe cases, a net sputtering of the substrate can result. In order to remedy this negative ion resputtering 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 require a postdeposition anneal which adds to expense and can cause other problems for the flat panel display. Ion-beam assist during deposition of undoped ZnS was studied as a method to induce surface-atom mobility and a more crystalline as-deposited film for use in monochrome TFEL displays.