A Sub-cm3 Energy-Harvesting Stacked Wireless Sensor Node Featuring a Near-Threshold Voltage IA-32 Microcontroller in 14-nm Tri-Gate CMOS for Always-ON Always-Sensing Applications

Abstract

An energy-harvesting wireless sensor node (WSN) integrates a 14-nm, 0.79-mm2, 32-b Intel Architecture core-based near-threshold voltage (NTV) microcontroller (MCU) that provides 17- $\mu \text{W}$ /MHz always-ON, always-sensing (AOAS) capability. The MCU implements four independent voltage-frequency islands, managed by an integrated power management unit and features a subthreshold voltage capable on-die oscillator and 42-nm fin-pitch, 8.3-pA leakage-per-bit SRAM. The MCU operates across a wide frequency (voltage) range from 297 MHz (1 V) to 0.5 MHz (308 mV), dissipating 23.5 mW to 21 $\mu \text{W}$ , and achieves $4.8\times $ better energy efficiency at an optimum supply voltage ( $V_{\text {OPT}}$ ) of 370 mV, 3.5 MHz, and 17 pJ/cycle. A functional AOAS WSN incorporating the NTV MCU shows promise for sustained $\mu \text{W}$ operation.