11.4 1650µm2 thermal-diffusivity sensors with inaccuracies down to ±0.75°C in 40nm CMOS

Abstract

Compact temperature sensors are widely used in SoCs to monitor on-chip temperature gradients and hot-spots, which are known to negatively impact reliability [1–4]. In this application, sensors must be able to accurately track fast thermal transients with little overhead in terms of their area and trimming. However, conventional MOS- and BJT-based sensors do not scale well in nanometer CMOS, as BJT-based sensors are incompatible with sub-1V supplies, while both require expensive multi-point trimming to achieve sub-1°C inaccuracy [1–4]. Recently, it has been shown that the well-defined thermal diffusivity of bulk silicon can be exploited to realize small, fast and accurate temperature sensors [5,6]. Such thermal-diffusivity (TD) sensors operate by measuring the temperature-dependent phase-shift of an electro-thermal filter (ETF), which consists of a resistive heater in close proximity to a thermopile. Moreover, unlike BJT-based sensors, TD sensors are compatible with sub-1V supplies, since their heaters can be operated from any supply voltage.