Improvement in Characteristic Variability of TFTs Using Grain Growth Control by Micro Thermal Plasma Jet Irradiation on a-Si Strips

Grain growth from molten silicon during micro-thermal-plasma-jet ( μ-TPJ) irradiation has been controlled by applying amorphous-silicon (a-Si) strips. The grain boundaries (GBs) in strip pattern with the width of 1 μm are significantly reduced compared with the case without strip pattern. In strip pattern, random GBs were almost excluded and most of the strips consist of Σ3 coincidence site lattices (CSLs) GBs or in some cases single grains. TFTs with strip pattern showed threshold voltage (V_th), field effect mobility (μ_FE) and sub-threshold swing value (S) of 1.8 ±0.10 V, 303 ±24 cm²/V·s and 240±17 mV/dec, respectively. In the case of P-type TFTs, they were -1.8±0.22 V, 98±7 cm²/V·s, 285 ±17 mV/dec, respectively. TFTs fabricated with the proposed pattern showed high performance and the variability reduced to 1/3 compared with the case without strip pattern. These characteristics and small variation with proposed patterns enabled us to operate CMOS circuits. The 8-bits shift register fabricated with proposed pattern was operated at a supply voltage of 5 V clock frequency of 4 MHz.