Microsecond Crystallization of Amorphous Silicon Films on Glass Substrates by Joule Heating

Joule-heating-induced crystallization (JIC) of amorphous silicon (a-Si) films was conducted by applying an electric pulse to a conductive layer located beneath or above the films. Crystallization occurs across the whole substrate surface within few tens of microseconds. The phase-transformation phenomena during the JIC process were detected electrically and optically by the in-situ measurements of input voltage/current and normal reflectance at wavelength of 532 nm. We devised a method for the crystallization of a-Si films while preventing arc generation; this method consisted of pre-patterning an a-Si active layer into islands and then depositing a gate oxide and gate electrode. Electric pulsing was then applied to the gate electrode formed using a Mo layer. JIC-processed poly-Si thin-film transistors were fabricated successfully, and the proposed method was found to be compatible with the standard processing of coplanar top-gate poly-Si TFTs. The p-channel JIC poly-Si TFT with W/L = 7 μm/7 μm exhibited a field effect mobility of 38.9 cm2/V-s, a threshold voltage of −2.8 V, and a gate voltage swing of 0.35 V/dec.