Transistors for VLSI, for wireless: A view forwards through fog

Summary form only given. For VLSI, transistors are made small, making them plentiful (cheap) and the wires connecting them short, with low delay (CVDD/I), and low switching energy (CVDD2/2); small-area electronics is key. Low power demands low VDD yet low Ioff . Below threshold, we seek characteristics steeper than thermal; above it, dI/dV should be large. Tunnel FETs [1] are the most studied steep transistors. Yet, in nm TFETs, quantization increases barrier energies and nonparabolicy increases carrier mass. WKB hand calculations predict only 10% tunneling probability for a 2nm barrier, 1% for 4nm. The barrier thickness is not easily reduced, being set by the source doping and channel and dielectric thicknesses, hence on-current and logic speed will be low. Adding a second barrier [2] introduces a bound state, and dI/dV peaks as the state aligns with the source. A multi-layer electron anti-reflection coating (fig.1) [3], increases transmission over a broad energy range; design parallels microwave impedance-matching.