This paper presents a batteryless system-on-chip (SoC) that operates off energy harvested from indoor solar cells and/or thermoelectric generators (TEGs) on the body. Fabricated in a commercial 0.13 μW process, this SoC sensing platform consists of an integrated energy harvesting and power management unit (EH-PMU) with maximum power point tracking, multiple sensing modalities, programmable core and a low power microcontroller with several hardware accelerators to enable energy-efficient digital signal processing, ultra-low-power (ULP) asymmetric radios for wireless transmission, and a 100 nW wake-up radio. The EH-PMU achieves a peak end-to-end efficiency of 75% delivering power to a 100 μA load. In an example motion detection application, the SoC reads data from an accelerometer through SPI, processes it, and sends it over the radio. The SPI and digital processing consume only 2.27 μW, while the integrated radio consumes 4.18 μW when transmitting at 187.5 kbps for a total of 6.45 μW.

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This paper compares six different 8T SRAM bitcells targeting different design space requirements -such as reliability and low power/energy -for Internet of Things (IoT) applications. Different bitcells leverage the varying characteristics of highthreshold (high-VT) and standard-threshold (standard-VT) devices to affect SRAM metrics like write margin (WM), Data Retention Voltage (DRV), Hold Static Noise Margin (HSNM), Read Static Noise Margin (RSNM), write and read energy, standby leakage power, and variability. The reliability for each bitcell over process (intra-and inter-die variation) and temperature variation is also evaluated. Measured results for a commercial 130nm test chip compare the most promising two 8T bitcell structures targeting low leakage and low energy.

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