An 8.75mm3 microsystem targeting temperature sensing achieves zero-net-energy operation using energy harvesting and ultra-low-power circuit techniques. A 28pJ/cycle, 0.4V, 72kHz ARM Cortex-M3 microcontroller processes temperature data. A custom 3.3fW leakage per bit SRAM stores microprocessor results. Two 1mm2 solar cells and a thin-film Li battery power the microsystem through an integrated power management unit. The complete microsystem consumes 7.7µW when active. Between sensor measurements it enters a 550pW data-retentive standby mode. The microsystem can process hourly temperature data for 5 years using only energy stored in the battery. This lifetime is extended indefinitely using energy harvesting to recharge the battery, enabling energy-autonomous operation.
Gregory Chen, Matthew Fojtik, Daeyeon Kim, David Fick, Junsun Park, Mingoo Seok, Mao-Ter Chen, Zhiyoong Foo, Dennis Sylvester, David Blaauw, “A Millimeter-Scale Nearly-Perpetual Sensor System with Stacked Battery and Solar Cells,” IEEE International Solid-State Circuits Conference (ISSCC), February 2010 ©IEEE