High mobility poly-Ge thin-film transistors fabricated on flexible plastic substrates at temperatures below 130°C

Abstract

Depletion-mode poly-Ge thin-film transistors (TFTs) with an effective hole mobility of 110 cm 2 /Vs and an ON/OFF ratio of 10 4 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.

Interface-controlled layer exchange in metal-induced crystallization of germanium thin films

“…Shu Hu (胡澍͒, 1,a͒ Ann F. Marshall, 2 Low-temperature synthesis of polycrystalline germanium ͑poly-Ge͒ thin films is of great interest in thin-film photovoltaic and electronics applications. We demonstrate metal ͑Al͒-induced crystallization to form poly-Ge thin films on both glass and polymer substrates at temperatures as low as 200°C.…”

Mechanics of thin-film transistors and solar cells on flexible substrates

“…Among metallic materials, stainless steel and molybdenum foils have been utilized as substrates in the fabrication of thin-film transistors (Theiss and Wagner, 1996;Wu et al, 1997;Howell et al, 2000;Wu et al, 2002;Park et al, 2003) and solar cells (Yang et al, 2003). A number of plastic materials (organic polymers) also have been tested successfully in a variety of thin-film applications (Constant et al, 1994;Young et al, 1997;Burns et al, 1997;Burrows et al, 1997;Gleskova et al, 1998;Parsons et al, 1998;Lueder et al, 1998;Thomasson et al, 1998;Sandoe, 1998;Carey et al, 2000;Sazonov et al, 2000;Boucinha et al, 2000;Kane et al, 2001;Ichikawa et al, 2001;Hsu et al, 2002a;Brida et al, 2002;Takano et al, 2003;Cheng et al, 2004;Gelinck et al, 2004;Shahrjerdi et al, 2004;Nomura et al, 2004;Monacelli et al, 2004;Choi et al, 2004).…”

Evaporated tellurium thin films for p-type field-effect transistors and circuits

“…Widely explored lowtemperature processing p-type thin films are amorphous Si, metal oxides (e.g. CuO x , NiO x and SnO x ), organic compounds/polymers and polycrystalline germanium (Ge) 2,3,11,12 . Among them, amorphous Si, metal oxides and organic compounds/polymers normally exhibit low hole mobilities on the order of 1 cm 2 V -1 s -1 or even less 2,5,11,13,14 .…”