Properties of Oxide-Nitride-Oxide Stacked Films for Gate Insulation in Active Matrix Displays

Abstract

ABSTRACTOxide-nitride-oxide (ONO) stacked films deposited by plasma enhanced chemical vapor deposition (PECVD) have been studied for use as the gate dielectric in active matrix displays. Good electrical properties were obtained for cadmium selenide thin film transistors (TFTs) with either ONO or single layer SiO2 gate insulation. However, the dielectric strength was up to twice as large for the ONO films. This improvement was observed with both Al and Cr electrodes.The individual oxide layers had compressive stress, while the individual nitride layers had tensile stress. When combined in an ONO structure, a net tensile stress of relatively low magnitude was obtained. Index of refraction and infrared absorption measurements indicated that the oxide films were oxygen deficient. Hydrogen incorporation was present for both the oxide and nitride films.