During the 20th century, the emergence of vacuum tubes marks the era of
electronics industry. To address the problems related to the vacuum tubes, solid state
switches were invented. The first Si/Sio2 based MOSFET (Metal Oxide
Semiconductor Field Effect Transistor) was illustrated by D. Kahng and M. Atalla in
1960 [1]. Since then, tremendous efforts are being carried out to scale the transistor
size and to improve density of Integrated Circuits (ICs) while keeping the fabrication
cost as low as possible. The device scaling also improves the operating frequency of
chips. It was observed that the static power became higher than the actual active
power because of the dimension scaling. This led the designers to change the device
scaling approach. After a certain point of time, the device scaling became one of the
reasons for the subthreshold degradation. This will be discussed in the following
sections.