Strain-induced back channel electron mobility enhancement in polycrystalline silicon thin-film transistors fabricatedby continuous-wave laser lateral crystallization

Four-terminal (4T) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) having both front and back gates were fabricated to investigate the effect of the internal tensile strain induced by continuous-wave (CW) laser lateral crystallization (CLC) on the carrier mobility. The tensile strain values at the surfaces and back interfaces were estimated to be approximately 0.3% and over 0.4%, respectively. In both front and back channel operations, the successful operation of a variable threshold voltage (V_th) scheme was confirmed. Front and back channel effective electron mobilities of 4T CLC poly-Si TFTs were evaluated under bias conditions so as not to form an inversion layer on the V_th-control gate side. Because of the larger tensile strain at the back interface, the back channel effective electron mobility was 1.2 times larger than the front channel effective mobility.