Low temperature high k dielectric on poly-Si TFTs

Abstract

In this work, it is demonstrated the application of a high k dielectric, as hafnium oxide (HfO2), in poly-Si thin film transistors (TFTs) obtained by metal induced lateral crystallization (MILC). The dielectric layer was deposited at room temperature by sputtering, using argon and oxygen as process gases. As produced TFTs exhibit field effect mobility around 45cm2V−1s−1and Ion/Ioff ratio of about 2×105. After annealing in a forming gas atmosphere for about 1h at 200°C, the threshold voltage and the sub-threshold slope are reduced, respectively from 4.8 to 2V and from 1.6 to 1.4V/dec. Nevertheless, by doing so, we notice a reduction on the field effect mobility of about 45% and a decrease of about 2.5 times on the Ion/Ioff ratio. Longer annealing time will not improve the TFT’s performance.