Fabrication of high-performance p-type thin film transistors using atomic-layer-deposited SnO films

Abstract

Here, we demonstrate high-performance p-type thin film transistors (TFTs) with a SnO channel layer grown by atomic layer deposition (ALD). The performance of the SnO TFTs relies on hole carriers and defects in SnO and near the back-channel surface of SnO as well as the quality of the gate dielectric/SnO interface. The growth of SnO films at a high temperature of 210 degrees C effectively suppresses the hole carrier concentration, leading to a high on-current/off-current (Ion/Ioff) ratio. In addition, the SnO films grown at 210 degrees C achieve high field effect mobility (mFE) compared with the SnO films grown at lower temperatures because of their large grain size and lower impurity contents. However, the SnO films grown at 210 degrees C still contain defects and hole carriers, especially near the back-channel surface. The post-deposition process - back-channel surface passivation with ALD-grown Al2O3 followed by post-deposition annealing at 250 degrees C - considerably alleviates the defects and hole carriers, resulting in superior TFT performance (I-on/I-off: 2 x 10(6), subthreshold swing: 1.8 V dec(-1), mu(FE): similar to 1 cm(2) V-1 s(-1)). We expect that the SnO ALD and subsequent process will provide a new opportunity for producing high-performance p-type oxide TFTs.