Comparison of Chromium- and Aluminum-Gated Nanocrystalline Silicon TFTs

Three sets of bottom-gate (BG) nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) with amorphous silicon nitride (a-SiN
_x
:H) as the gate dielectric were produced under various nc-Si:H plasma deposition conditions. Chromium (Cr) and aluminum (Al) were used as the gate electrodes in each TFT set. The effects of the gate electrode on the nc-Si:H TFT performance, particularly on its electrical stability, were studied. For each TFT set, Al-gated TFTs resulted in the higher mobility, lower subthreshold slope, and better stability compared to the Cr-gated TFTs. The impact of the Cr- or Al-gate underlayer on the surface and bulk properties of a-SiN
_x
:H and nc-Si:H films was analyzed in detail considering back channel etching (BCE) characteristics, electrical, scanning electron microscope (SEM), Raman, grazing angle X-ray diffraction (GAXRD), and Fourier transform infrared-attenuated total reflection (FTIR-ATR) measurements. Structural differences were recognized in a-SiN
_x
:H and nc-Si:H films grown in the BG TFT sequence depending on the type of the gate electrode. Based on these findings, possible reasons were proposed to explain the superiority of the Al over Cr as the gate electrode for nc-Si:H TFTs.