Slow is the new fast (and other stories from the cutting edge of chip tech...)

Abstract

The power used by the CMOS (complementary metal-oxide semiconductor) logic that sits in practically all microprocessors is controlled by a formula that links the square of the voltage to the frequency at which the transistors switch. Because of the quadratic relationship, lowering the voltage has a dramatic effect on energy consumption. Intel is one of a group of companies investigating the potential of near-threshold and sub-threshold logic, where the supply voltage to each transistor is reduced to the point where it barely switches on. The technology takes advantage of the way in which small amounts of current pass through the transistor as it moves from the off state to the on. This is enough to charge the capacitances in downstream logic that help move from one state to another. However, with less current passing, the longer the entire process takes. A chip that happily operates at gigahertz frequencies at 1V has trouble switching at more than one megahertz when that voltage falls towards the threshold point, at around 0.25V for the latest process technologies; and yet, this is something that chip designers are willing to work with.