High Mobility Poly-Ge Thin-Film Transistors Fabricated on Flexible Plastic Substrates at Temperatures below 130°C

Depletion-mode poly-Ge thin-film transistors (TFTs) with an effective hole mobility of 110 cm²/Vs and an ON/OFF ratio of 10⁴ have been fabricated on flexible polyethylene therephtalate (PET) substrates, taking advantage of a novel stress-assisted crystallization technique. Proper manipulation of an otherwise destructive mechanical stress leads to a drastic drop of crystallization temperature from 400°C to 130°C. External compressive stress is transferred to the Ge/PET interface by bending the flexible substrate inward, during the thermal post-treatment. Proper patterning of the a-Ge layer before thermomechanical post-treatment leads to a minimal crack density in the processed poly-Ge layer. Reduction in the crack density plays a crucial role in alleviating the stress-induced gate leakage current emanated from the crack traces propagating from the channel into the gate oxide.