High-performance polycrystalline SiGe thin-film transistors using Al2O3 gate insulators

The use of aluminum oxide as the gate insulator for low temperature (600 degrees C) polycrystalline SiGe thin-film transistors (TFT's) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N2O plasma. The composition of the deposited aluminum oxide was found to be almost stoichiometric (i.e., Al2O3), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured on devices with 50-nm-thick Al2O3 gate dielectric layers. Typically, a field effect mobility of 47 cm(2)/Vs, a threshold voltage of 3 V, a subthreshold slope of 0.44 V/decade, and an on/off ratio above 3 x 10(5) at a drain voltage of 0.1 V can be obtained, These results indicate that the direct 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.