Short-Channel Features and Channel Length Guideline in High-Resolution Display Panel Oxide Transistors

초록

Scaling of accumulation-mode amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) is increasingly important but seems not easy with a decreased cell size. It is because oxygen-vacancy donors may uncontrollably shorten channel length (L ch) by a lateral extension (2 Delta L) during an n + source/drain (S/D) forming process, causing short-channel effects (SCE). A minimum L ch guideline is thus necessary based on Delta L estimation. Here, industry-fabricated a-IGZO TFTs with nominal channel lengths of 2.5 to 10 mu m were analyzed to extract an effective length, L eff (equivalent to L ch-2 Delta L). The threshold voltage (V th) of our a-IGZO TFTs has rarely shifted until L ch is reduced to similar to 3 mu m; however, further scaling to L ch = 2.5 mu m, the V th appears to drastically shift to a negative voltage. Concomitantly, serious drain-induced barrier lowering (DIBL) is observed for devices with an L ch of 2.5 mu m. We attribute such SCE features to 2 Delta L-reduced channel length, L eff, because an estimated 2 Delta L appears over 1.5 mu m. Finally, through experiments and Poisson's equation treatment for incipient accumulation, we first suggest a practical L eff guideline that enables reliable device operations: minimum L eff = similar to 0.96 mu m and a nominal L ch >= 3 mu m.

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