Influences of Source/Drain Extension Region on Thermal Behavior of Stacked Nanosheet FET
Shobhit Srivastava, Sourabh Panwar, M. Shashidhara, Lomash Chandra, Neeraj Mishra, Abhishek Acharya
Abstract
A well-calibrated numerical-simulation-based study reveals that an elongated extension region can be a notable approach for the self-heating mitigation of nanosheet FETs. It is observed that a longer extension length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {EXT}}$ </tex-math></inline-formula> = 8 nm) reduces the ON current; however, it holds a smaller penalty in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {ON}}$ </tex-math></inline-formula> degradation (~10%) due to the self-heating effect (SHE). When the extension region is increased from 2 to 8 nm, a reduction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times $ </tex-math></inline-formula> in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {OFF}}$ </tex-math></inline-formula> is observed along with a reduction of ~9 mV/dec in the subthreshold swing. On the contrary, a change in ~15 mV in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> is observed when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {EXT}}$ </tex-math></inline-formula> is increased from 2 to 8 nm. Considering lattice heat due to SHE, intrinsic delay, unity-gain bandwidth, and the above-mentioned characteristic, the optimum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {EXT}}$ </tex-math></inline-formula> would be 5–6 nm. The longer extension lengths (2–8-nm increase) provide a lesser transconductance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${g}_{m}$ </tex-math></inline-formula> ) degradation (~15%) due to SHE. It is observed that intrinsic capacitance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}_{\text {gg}}$ </tex-math></inline-formula> reduces with an increment in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {EXT}}$ </tex-math></inline-formula> (2–8 nm), which eventually reduces the propagation delay (~20%) with an improvement in noise margin too. It is worth noting that for a common source amplifier, a longer extension region of 8 nm will also provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.87\times $ </tex-math></inline-formula> more voltage gain when compared with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {EXT}}$ </tex-math></inline-formula> of 2 nm, which increases to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.97\times $ </tex-math></inline-formula> in self-heating condition due to a smaller degradation “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {G}$ </tex-math></inline-formula> ” (from ~12.4% to ~6.6%) in gain with longer extension length.