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The characteristics and reliability of laser-activated polycrystalline silicon thin-film transistors (poly-Si TFTs) under the stress condition of drain voltage (V[sub d]) = 12V and gate voltage (V[sub g]) = 15 V have been investigated. In spite of reducing the source/drain resistivity by using laser activation method, the leakage current (V[sub g] < 0) is larger for laser-activated poly-Si TFTs in comparison with traditional furnace-activated counterparts. It is also found that the post-stress leakage and on/off current ratio degrade much faster for laser-activated poly-Si TFTs, while the degradation rates of threshold voltage and subthreshold swing are comparable to those of traditional furnace-activated TFTs. The laser activation modifies the grain structure between drain and channel region and causes grain discontinuity extending from the drain side to the channel region. The grain discontinuity near drain side in the polysilicon film has been investigated by transmission electron microscopy analysis. The effective trap state density calculated from typical I-V curve has been compared for laser-activated and furnace-activated TFTs. As a result, an inferior reliability with extra trap state density and larger leakage current was observed in the laser-activated poly-Si TFTs. [ABSTRACT FROM AUTHOR]

We have fabricated a polycrystalline silicon thin-film transistor with self-aligned SiGe raised source/ drain (SiGe-RSD TFT). The SiGe-RSD regions were grown selectively by ultrahigh vacuum chemical vapor deposition at 550 °C. It was observed that, with SiH[sub 4] and GeH[sub 4] gas flow rates of 5 and 2 sccm, respectively, the poly-SiGe could be selectively grown up to 100 nm for source/drain regions. The resultant transistor structure features an ultrathin active channel region (20 nm) and a self-aligned thick source/drain region (120 nm), which is ideally suited for optimum performance. The significant improvements in electrical characteristics, such as higher turn-on current, lower leakage current, and higher drain breakdown voltage have been observed in the SiGe-RSD TFT, compared to the conventional TFT counterpart. These results indicate that TFTs with SiGe raised source/drain structure would be highly promising for ultrathin TFTs applications. [ABSTRACT FROM AUTHOR]