Observation of electron velocity overshoot in sub-100-nm-channel MOSFET's in Silicon

Abstract

n-channel MOSFET's with channel lengths from 75 nm to 5 µm were fabricated in Si using combined X-ray and optical lithographies, and were characterized at 300, 77, and 4.2 K. Average channel electron velocities υ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> were extracted according to the equation <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\upsilon_{e}=g_{mi}/C_{ox}</tex> , where g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mi</inf> is the intrinsic transconductance and C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ox</inf> is the capacitance of the gate oxide. We found that at 4.2 K the average electron velocity of a 75-nm-channel MOSFET is 1.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s, which is 1.8 times higher than the inversion layer saturation velocity reported in the literature, and 1.3 times higher than the saturation velocity in bulk Si at 4.2 K. As channel length increases, the average electron velocity drops sharply below the saturation velocity in bulk Si. These experimental results strongly suggest velocity overshoot in a 75-nm-channel MOSFET.