Characteristics of Planar Junctionless Poly-Si Thin-Film Transistors With Various Channel Thickness

Abstract

N-type junctionless (JL) planar poly-Si thin-film transistors (TFTs), which contain an in situ heavily phosphorous-doped channel with thickness ranging from 8 to 12 nm, were fabricated and characterized. The devices exhibit superior current drive and good control over performance variability. From C-V characterization, the ionized dopant concentration in the channel is determined to be around 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and the fixed charge density to be around -6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The negative fixed charge density is probably related to the segregation of phosphorous species at the oxide/channel interface. We also observed a reverse short-channel effect from the relationship between the threshold voltage and the channel length. One mechanism considering enhanced phosphorous segregation is proposed to explain this finding.