Low-power temperature sensor could turn wearables into “unawareables”

The sensor, developed by a team led by Patrick Mercier of the Jacobs School of Engineering at the University of California San Diego, works by minimising power consumption in two domains: the current source of the device and the conversion of temperature to a digital readout. It takes advantage of a phenomenon generally seen as a disadvantage in electronics, known as gate leakage. The gate is the part of a semiconductor device that is capable of turning on or off the flow of electrons, but as electronics become smaller, the gate material has become so thin that electrons can pass through it even when it is closed, via the quantum tunnelling effect.

Rather than trying to eliminate leakage, the San Diego team has used the leaking electrons to power the sensor. To digitise the temperature, the team used another innovative approach: rather than passing the current through a resistor whose resistance changes with temperature, measuring the voltage across it, and converting that voltage to give a reading, they use the current to charge two capacitors. One capacitor charges in a fixed amount of time regardless of temperature, and the other charges faster at higher temperatures.