The commonly used dielectrics, Y2O3, Al2O3, Si3N4, and Ta2O5, were evaluated for use in ac thin-film electroluminescent displays, along with a composite dielectric SiAlON. Adhesion, stress cracking, charge storage capacity, and display brightness and efficiency were studied for devices with ZnS: Mn layers fabricated under identical conditions. A combination of SiAlON and Ta2O5appears to be optimum as a double-layer dielectric system for ACTFEL displays.