On the temperature dependence of subthreshold currents in MOS electron inversion layers, revisited

The drain current of a transistor in subthreshold operation exhibits a temperature dependence due to the thermal voltage, kT/q. The magnitude of this temperature dependence, as measured in 1979, was reported to be greater than the expected kT/q due to increased interface state densities; however, thirty years later, we saw little dependence. This behavior is of interest because subthreshold-enabled asynchronous circuits allow for operation below threshold with optimal power performance at threshold, but the original work suggests that static current will increase with temperature at a rate greater than predicted by the thermal voltage alone. Furthermore, the previously recorded behavior was very similar to what would be expected from ESD diodes. We revisit the work by Card et al., and present data from a commercially available 350nm process over temperature.