The Dependence of Poly-Si TFT Characteristics on the Relative Misorientation Between Grain Boundaries and the Active Channel

Abstract

ABSTRACTWe present device-related experimental results that quantitatively reveal the effect of varying the active channel/grain-boundary misorientation on the resulting TFT characteristics. Specifically, using low-temperature SLS processes, we have fabricated and analyzed n-channel and p-channel devices (40 μm width × 8 μm length) with three different orientations of the channel with respect to the grain boundaries: parallel, 45° inclined, and perpendicular on Corning 1737 glass substrates.The results reveal that the TFTs with the best (worst) characteristics were obtained for the devices with parallel (perpendicular) alignment. In general, for both n- and p-channel devices, the most prominent orientation-dependent effects were observed in the values of the field effect mobilities, which were 340, 227, and 141 cm2/Vsec for n-channel devices and 145, 105, and 80 cm2/Vsec for p-channel devices, in the order of increasing orientation mismatch. In contrast, no notable effect was manifested in the leakage currents, while small effects were seen for the sub-threshold slopes and threshold voltages. The degradation of device performance under hot-carrier stress was found to decrease with increasing orientation mismatch.