We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180 degrees C. The AZTO TFT exhibited a field effect mobility (mu(FET)) of 10.1 cm(2)/V s, a turn-on voltage (V-on) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (I-on/I-off) of 10(9). (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2998612]