Study of Random Variation in Germanium-Source Vertical Tunnel FET

An optimally designed germanium-source vertical tunnel FET (V-TFET) is investigated using technology computer aided design simulation. Three consecutive band-to-band tunneling (BTBT) mechanisms (i.e., lateral, vertical, and additional vertical BTBT) are used in the V-TFET to enhance its performance as well as to maintain an average subthreshold slope below 60 mV/decade at 300 K. The impact of various V-TFET parameters on its performance is also investigated. Furthermore, the impact of threshold voltage variation (σ V_TH) due to random variability [e.g., line-edge roughness (LER) and random dopant fluctuation (RDF)] on the performance of the V-TFET is studied. The LER in the V-TFET is found that the electric field is increased by the LER in the source region, resulting in the generation of lucky paths, which can lead to increase σ V_TH. Without a gate-to-source overlap region in the V-TFET, RDF/LER-induced σ V_TH is considerably increased by a lateral tunneling mechanism. As a result, the gate-to-source overlap region in the V-TFET is critical to enhancing the performance and designing a variation-aware V-TFET. Last but not least, field-induced quantum confinement leads to delay the onset voltage of the vertical BTBT, so that the device performance and process-induced random variation (especially, RDF) are significantly deteriorated.