In this chapter we consider both evolutionary and revolutionary advances that go beyond current CMOS technology. By evolutionary we mean advances that retain the standard CMOS paradigm, i.e., the devices are still FETs, consist of similar materials to that used for CMOS, and can be fabricated using current techniques. Revolutionary advances, on the other hand, break out of the standard CMOS paradigm. In these approaches novel substances are used, radically different devices take the place of CMOS FETs, and even the nature of computation is different. The revolutionary approaches to replacing CMOS may or may not prove successful. It is the purpose of this chapter to introduce the student to potential replacements to CMOS keeping in mind that all, some, or none of these approaches may supplant CMOS for computing applications. Finally, the list of revolutionary approaches that we will address is not exhaustive. Specifically, most of the quantum effect methods will not be discussed here, in particular, single electron transistors, spin based devices (spintronics), resonant tunneling devices, and quantum computing. The interested reader is referred to the book by Brennan and Brown (2002) for a discussion of these topics. We will restrict ourselves to discussion of devices that do not require knowledge of quantum mechanics.
Evolutionary advances beyond CMOS
In this section we examine three different evolutionary approaches that go beyond standard CMOS devices. These are Si on insulator, SOI, dual gate FETs, and silicon–germanium, SiGe, structures. Let us first examine SOI.