Performance, Reliability, and Supply Voltage Reduction, with the Addition of Temperature as a Design Variable

In any technology design, there rarely are "absolute" decisions that must be made. Instead, a variety of variables and choices must be evaluated to arrive at the best possible decision. The supply voltage must be reduced to mitigate the large power dissipation of ULSI ICs. Additionally, reduction of the supply voltage eliminates the need for extensive additional processing to address hot carrier reliability. In this light, maintaining a large Vdd is more expensive, as the additional processing increases manufacturing costs. A less expensive approach is to scale the supply voltage and use a very simple CMOS process. This simplification of fabrication is only possible if the supply voltage is treated as a design variable. However, design considerations and physical limits make it impossible to also scale the threshold voltage; this problem is most simply addressed by reduction of the operating temperature. Thus, the operating temperature can be thought of as another design variable that can be employed to continue FET scaling.