Effects of trap-state density reduction by plasma hydrogenation inlow-temperature polysilicon TFT |
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Authors: | Wu I.-W. Lewis A.G. Huang T.-Y. Chiang A. |
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Affiliation: | Xerox Corp., Palo Alto, CA; |
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Abstract: | The reduction of trap-state densities by plasma hydrogenation in n-channel polysilicon thin-film transistors (poly-TFTs) fabricated using a maximum temperature of 600°C has been studied. Hydrogenated devices have a mobility of ~40 cm2/V×5, a threshold voltage of ~2 V, an inverse subthreshold of ~ 0.55 V/decade, and a maximum on/off current ratio of 5×108. The effective channel length decreases by ~0.85 μm after a short hydrogenation which may be attributed to the activation of donors at trap states near the source/drain junctions. Trap-state densities decrease from 1.6×1012 to 3.5×1011 cm-2 after hydrogenation, concomitant with the reduction of threshold voltage. Using the gate lengths at which the trap-state densities deviate from the long-channel values as markets for the leading edge of passivation, the apparent hydrogen diffusivity is found to be 1.2×10-11 cm2/s at 350°C in the TFT structure |
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