Appropriate technology: a systems view

The concept of appropriate technology is considered using the systems approach. The concept of ‘small is beautiful’ is not always true. Smaller systems tend to grow and larger systems tend to break down into simpler ones. In a world with many boundaries and subsystems, appropriate technology may be an utopian ideal.</jats:p

Low Power Band to Band Tunnel Transistors

As scaling continues, the number of transistors per unit area and power density are both on the rise. A reduction in Vdd is highly desirable to reduce power consumption. For MOSFETs however, this would mean scaling the threshold voltage to maintain performance and thereby enhancing the off current and static power consumption since MOSFETs are limited to a swing of 60mV/decade at best. A low voltage transistor that allows Vdd scaling to 0.5V and below is highly desirable. In this thesis, gate induced band-to-band tunneling transistors are explored as a low voltage alternative because of their potential to achieve lower than 60mV/decade turn-off. Since BTBT is strongly dependant on the band gap of the semiconductor, moving from Silicon to Germanium to lower band gap materials can help scale ,Vdd. Biaxially strained Si1-xGex based heterostructures can provide ultra low effective band gaps. Strain is used to engineer complimentary Si1-xGex heterostructures with low effective band gap for both N and P type transistors. The design and fabrication of heterostructure based tunnel transistors is explored to help scale Vdd to 0.5V and below. Dopant engineering techniques to enhance the electric field are also explored both with simulations and experiments