High Channel Mobility a-Si:H Thin Film Transistors with Oxide/Nitride Dielectrics

Abstract

ABSTRACTWe describe: i) nitride-layer optimization; ii) device fabrication: and iii) electrical properties of a-Si:H thin film transistors, TFTs, that integrate oxide/nitride dielectrics into an inverted, staggered gate structure. We have systematically changed the concentrations of Si-Si, Si-H and Si-NH bonding groups within the deposited nitride layers by varying the source gas flow ratio, R = NH3/SiH4 from 2.5 to 12.5. The electrical characteristics of the TFTs improve significantly as the gas phase ratio R is increased from 2.5 to approximately 10, and then decrease as R is further increased. The performance of the TFTs peaks for a source gas ratio of -10, where the channel mobility is ∼1.4 cm2/V-s, the threshold voltage is 2.3 V; and the Ion to Ioff current ratio is > 105.These increases in performance can only realized in devices in which the back of the Si channel region is passivated with an oxy-nitride interfacial region.