The main promise of tunnel FETs (TFETs) is to enable supply voltage ($V_{DD}$) scaling in conjunction with dimension scaling of transistors to reduce power consumption. However, reducing $V_{DD}$ and channel length ($L_{ch}$) typically deteriorates the ON- and OFF-state performance of TFETs, respectively. Accordingly, there is not yet any report of a high perfor]mance TFET with both low V$_{DD}$ ($sim$0.2V) and small $L_{ch}$ ($sim$6nm). In this work, it is shown that scaling TFETs in general requires scaling down the bandgap $E_g$ and scaling up the effective mass $m^*$ for high performance. Quantitatively, a channel material with an optimized bandgap ($E_gsim1.2qV_{DD} [eV]$) and an engineered effective mass ($m*^{-1}sim40 V_{DD}^{2.5} [m_0^{-1}]$) makes both $V_{DD}$ and $L_{ch}$ scaling feasible with the scaling rule of $L_{ch}/V_{DD}=30~nm/V$ for $L_{ch}$ from 15nm to 6nm and corresponding $V_{DD}$ from 0.5V to 0.2V.
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