Epitaxial rare earth oxide (EOx) FinFET: A variability-resistant Ge FinFET architecture with multi VT

Band to band tunneling (BTBT) is a major challenge in Ge FinFETs due to its smaller band gap. Reduction in BTBT by quantum-confinement (QC) based increase in band-gap requires narrow Wfin. However, Line Edge Roughness (LER) on narrow fins causes large V_T variability. Improved fin-width process e.g. SADP [1], ALE [2] have been proposed to reduce LER. Alternatively, variability resistant transistor design has been recently proposed with thin Ge on Si highly retrograde doped fins by our group [3], which also provides multiple V_T capability - a major challenge in FinFETs. However, this has 2 challenges - (i) thickness limitation of <; 2nm of defect-free Ge on Si and (ii) RDF in the retrograde doped fins. In this study, we propose a dual-gate structure like FinFET by epitaxially growing undoped Ge /rare earth oxide (e.g. Gd₂O₃) [4] stack on highly doped Si fins. By statistical simulations, we show that this structure can reduce LER based variability by more than 90% in comparison to FinFETs at a similar performance. RDF is negligible due to the undoped Ge channel. Thicker (>2nm) defect-free Ge can be grown epitaxially on Gd₂O₃ [4]. We show the multi-V_T capability enabled by independent back-gate biasing, and hence provides a significant advantage over FinFETs. Experimental data from MOSCAP with epi Gd₂O₃ as gate dielectric (~ 4.5 nm) show lower leakage currents than LSTP specification.