High Performance Polycrystalline SiGe Thin Film Transistors Using Al2O3 Gate Insulator

The use of aluminum oxide as the gate insulator for low temperature (<600C) polycrystalline SiGe thin film transistors (TFTs) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N20 plasma. The composition of the deposited aluminum oxide was found to be almost stoichiomertic (i.e. Al2O3), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured on devices with 50nm thick Al2O3 gate dielectric layers. Typically, a field effect mobility of 47cm /Vs, a threshold voltage of 3V, a sub-threshold slope of 0.44V/decade, and an on/off ratio above 3×10 at a drain voltage of 0.1V can be obtained. These results indicate that the native interface between the Al2O3 and the SiGe channel layer is sufficiently passivated to make Al2O3 a better alternative to grown or deposited SiO2 for SiGe field effect devices. * Permanent address: Optoelectronic Lab, Dept. of Information Science and Electronic Eng., Zhejiang University, Hangzhou, China. Email: [email protected]. ** Corresponding author. Tel. +852 2358 7057, Fax. +852 2358 1485, Email: [email protected]