Sharp-Switching High-Current Tunneling Devices

Abstract

Tunneling FETs (TFETs) offer the possibility of overcoming the 60 mV/dec subthreshold slope limit of conventional transistors and thereby providing sharp-switching logic devices. We discuss two approaches to increasing the current drive of tunneling devices, both implemented in the silicon-germanium heterostructure system. First, the bipolar-enhanced TFET (BET-FET) multiplies the gate-controlled interband tunneling current by the Si/Ge heterojunction bipolar current gain. Both vertical and planar versions have been simulated, with high I ON > 1000 mA/mm accompanying low subthreshold swing over many decades of current. Second, the trigate Si/Ge heteronanowire TFET is based on shifting the tunneling junction from Ge in the on-state to Si in the off-state. Fabricated with a vapor-liquid-solid epitaxial Si/Ge hetero-nanowire channel and high-k dielectric trigate stack, the proof-of-concept prototype device exhibits reasonable I ON, sub-60 mV/dec slope, as well as surprising backgating properties.