Enhancement-mode amorphous indium gallium zinc oxide (alpha-IGZO) channel thin film transistors (TFTs) with a 6 mu m gate length and a 100 mu m gate width were fabricated on glass substrates by rf magnetron sputtering near room temperature. The resistivities of the alpha-IGZO films were controlled from 10(-1) to 10(3) Omega cm by varying the deposition power of 75-300 W. The n-type carrier concentration in the channel was 6.5x10(17) cm(-3). The gate oxide was 90-nm-thick SiNx, deposited by plasma enhanced chemical vapor deposition at 70 degrees C. The bottom-gate TFTs had saturation mobility of similar to 17 cm(2) V-1 s(-1) and the drain current on-to-off ratio of similar to>10(5), a subthreshold gate-voltage swing of similar to 0.5 V decade(-1), and a threshold voltage of 2.1 V. In the TFT with a gate length of 6 mu m and a gate width of 100 mu m, the relative change of saturation mobility and threshold voltage was less than +/- 1.5% after 500 h aging time at room temperature. This demonstrates that alpha-IGZO films are promising semiconductor materials for long-term-stable transparent TFT applications. (C) 2008 American Vacuum Society.