[synthos]

It's also, if not more so, a factor of transistor voltage. 1.1V transistors are less prone to upset events than 0.7V. It's possible (assumption, here) that some 3+ volt circuits are still used for critical components of the system

[adrian_b]

It would be possible to use much higher supply voltages if silicon were replaced with a semiconductor material having a higher band gap.

The main obstacle that has prevented this until now is that in all high-bandgap semiconductors it is easy to make only transistors of a single polarity, not transistors with both polarities, as required for CMOS logic. For high circuit densities it would be difficult to replace the CMOS logic, because all alternatives have higher idle power consumption.