Low-Temperature Poly-Si Thin-Film Transistor with High-k ZrAlOx Gate Insulator with SiO2 Blocking Layer

Low-power electronic devices are of increasing interest with high-k gate insulators (GI). Herein, the performance and stability of low-temperature poly-Si (LTPS) thin-film transistors (TFTs) are investigated with two different GIs: spray pyrolyzed zirconiumaluminum oxide (ZAO) directly deposited on poly-Si, and SiO2/ZAO stack GI. The LTPS TFT with SiO2/ZAO stack GI exhibits hysteresis free characteristics with a threshold voltage of -0.2 V, field-effect mobility of 114.4 cm(2) V-1 s(-1), subthreshold swing of 0.10 V dec(-1), and high on/off current ratio of 7.3 x 10(8), at a gate voltage sweeping +/- 6 V. The TFT exhibits very stable operation under negative bias temperature stress. The X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses demonstrate that the diffusion of Zr and Al into poly-Si deteriorates device performance with ZAO only GI. A thin SiO2 on LTPS blocks the diffusion of Zr and Al, resulting the high-performance and stable p-type LTPS TFT with a high-k SiO2/ZAO stack GI. Finally, a 7-stage ring oscillator using LTPS TFTs with SiO2/ZAO stack GI is demonstrated, exhibiting an oscillation frequency of 7.49 MHz and a propagation delay of 9.54 ns at a supply voltage of 6 V, indicating its suitability for low-power consumption TFT electronics and displays.