An 8b subthreshold hybrid thermal sensor with ±1.07°C inaccuracy and single-element remote-sensing technique in 22nm FinFET

Abstract

Thermal sensors are commonly used in modern highly dense systems-on-chip (SoC) to provide information about die temperature for thermal protection or performance optimization. To enable the deployment of multiple sensors in an SoC, the power and size of such sensors has been steadily reduced. Although most solutions are PNP-based [1-4], recently a low-power NPN-based current-mode thermal sensor [5] was implemented to meet the power and form-factor requirement with a robust architecture. However, since NPN devices are only available in a triple-well process, its use in low-cost dual-well processes is limited. This paper demonstrates a current-mode hybrid thermal sensor in an advanced 22nm FinFET process [6] based on subthreshold NMOS transistors and a parasitic PNP [7]. A simple voltage-based single-point soft-trimming was implemented to mitigate the sensitivity of the sensor to the subthreshold factor variability during manufacturing. Instead of placing the whole sensor system in multiple locations in a system, the hybrid architecture also supports single-element remote sensing. Only a 0.00021mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PNP device placed in the area of interest and a signal connection to the main sensor are then needed for temperature sensing. The sensor system achieves +/−1.07°C (±3σ) precision with 0.0043mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> silicon area and 50uA current consumption from a 1V supply.