Steep Sub-Threshold Swing Transistors
Abstract
Power consumption has been among the most important challenges for electronics industry and transistor scaling over the last decade. Scaling of the physical dimensions of silicon MOSFETs has not been accompanied by a similar scaling in the supply voltage (VDD). Consequently, the ICs have become more energy thirsty over the years. This has had a significant effect on the saturation of CPU frequency in the last decade as the power consumption of CPUs has already reached the limit of conventional cooling capability (≈ 100W/cm2). One of the main barriers in V DD scaling is that MOSFETs cannot be turned ON and OFF with a small change in gate voltage. It takes a change in gate voltage of 100s of millivolts in MOSFETs to make an ON/OFF transition. As a result, the supply voltage of MOSFETs cannot scaled down in conjunction with the channel length. To address this challenge, in this work, few novel transistors based on band to band tunneling (BTBT) are proposed. These tunneling devices offer a steep ON-OFF transition. Several novel tunnel-FET (TFET) designs have been proposed and their performances studied using state-of-the-art atomistic quantum transport simulations. Moreover, two simple analytic methods based on WKB and Fowler-Nordheim equations have been developed for analyzing the performance of TFETs. Despite of the steep ON-OFF transition, TFETs are known to suffer from low ON-current since the BTBT transmission probability is usually small. Different devices and techniques that boost the performance of TFETs are also proposed and analyzed in detail. The first chapter discusses the motivation for tunnel transistors and their operation. Chapter two provides a brief introduction on the modeling the tunneling mechanism. The following chapters present both numerical simulations and analytic modeling of the devices listed below: • Chemically doped tunnel FETs. • Electrically doped tunnel FETs. • Novel dielectric engineered tunnel FETs. • Dynamic bandgap FETs. • Novel L-gate tunnel FETs.
Degree
Ph.D.
Advisors
Klimeck, Purdue University.
Subject Area
Electrical engineering|Quantum physics|Nanotechnology
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