SIGE HETEROSTRUCTURE FETS
Over the past 20 years, the channel length of MOS transistors has halved at intervals of approximately three or four years. This continual shrinking of the size of MOS transistors has led to increasing performance in electronic systems and increasing packing density. The question that arises now is ‘how long can this trend continue?’ A number of factors are posing a threat to the evolution of CMOS technology. Firstly, the channel length of the MOS transistor is deﬁned using optical lithography, which is limited by the wavelength of the radiation used. The current thinking is that optical lithography can reach channel lengths of around 0.15 µm, but it is not clear that it can meet the challenge of smaller geometries. Other lithography techniques exist, such as electron beam and x-ray lithography, but these have associated problems that remain to be solved.