ABSTRACT
Ever since the demonstration of the first Field-Effect Transistor (FET) in 1960 and Complementary Metal-Oxide-Semiconductor (CMOS) configuration in 1963, there has been continuous advancement in the CMOS technology [1-4]. These advancements are driven and sustained by uninterrupted CMOS scaling or miniaturization of transistors following an exponential trend that is commonly known as Moore’s law [5]. It is remarkable that despite several difficult technical challenges, the trend of reducing dimensions of transistors and the resultant exponential growth of the semiconductor industry have continued unabated for more than five decades. The obstacles associated with forthcoming miniaturization of transistors that looked unsurmountable at first, were finally overcome using ingenious techniques before the trend could be upset.
As the transistors are miniaturized below 10 nm, the continued scaling down of transistors faces a real threat due to the inability of the transistor to switch from the OFF-to the ON-state without leading to increased power dissipation [6-10]. With CMOS scaling, the architecture of transistors and the technology to realize them have undergone numerous changes over the years, though the basic mechanism of operation of the transistors has remained the same. The physics of current transport in a conventional transistor imposes certain restrictions that prohibit further lowering of supply voltages in an integrated circuit (IC). As a result, the current trend of miniaturizing transistors, while keeping the supply voltage constant does not allow improving the energy efficiency of the ICs, which could have been obtained by decreasing the supply voltage [11]. This necessitates exploring transistors based on new operating principles, improved architectures, and perhaps novel non-silicon-based material systems that can overcome the limitations of the conventional transistors [10]. In this respect, Tunnel Field-Effect Transistors (TFETs), operating on the basis of quantum mechanical tunneling, have been demonstrated to possess excellent switching properties which are beyond the theoretical capabilities of a conventional transistor [7, 10, 12]. As a result TFETs can be employed in ICs with low supply voltages, resulting in highly energy-efficient circuits.
This makes TFETs quite fascinating for researchers and has spurred intense experimental and theoretical exploration of TFETs during the last ten years.
In this chapter, the concepts of CMOS scaling will be discussed, highlighting the need for novel devices such as TFETs in the near future. This will help readers in understanding the context in which the current research on TFETs is being carried out and in appreciating the remaining chapters of this book.
This chapter starts by describing the fundamentals of Metal-OxideSemiconductor Field-Effect Transistors (MOSFETs), CMOS and CMOS scaling. This is followed by a description of the historical perspective and the current trends of CMOS scaling. Finally, major challenges to the continued scaling of CMOS are discussed. A short review of the emerging devices that can potentially improve the existing CMOS technology or replace conventional transistors is also presented.
