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| This article provides the latest advances from the NSF Advanced Self-powered Systems of Integrated sensors and Technologies (ASSIST) center. The work in the center addresses the key challenges in wearable health and environmental systems by exploring technologies that enable ultra-long battery lifetime, user comfort and wearability, robust medically validated sensor data with value added from multimodal sensing, and access to open architecture data streams. The vison of the ASSIST center is to use nanotechnology to build miniature, selfpowered, wearable, and wireless sensing devices that can enable monitoring of personal health and personal environmental exposure and enable correlation of multimodal sensors. These devices can empower patients and doctors to transition from managing illness to managing wellness and create a paradigm shift in improving healthcare outcomes. This article presents the latest advances in high-efficiency nanostructured energy harvesters and storage capacitors, new sensing modalities that consume less power, low power computation, and communication strategies, and novel flexible materials that provide form, function, and comfort. These technologies span a spatial scale ranging from underlying materials at the nanoscale to body worn structures, and the challenge is to integrate them into a unified device designed to revolutionize wearable health applications.

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A 0.13μm CMOS low power wake-up radio is presented. The wake-up radio operates with -41dBm sensitivity at 915MHz using OOK modulation with a data rate of 100kbps while consuming 98nW active power, 11pW sleep power, and has an energy efficiency of 0.98pJ/bit. The wake-up radio occupies 0.03mm 2 and uses two off-chip components (an inductor and a capacitor). All biasing and calibration for process variation and mismatch is included on-chip. The entire radio operates from a single 1.2V supply.Index Terms -Wakeup radio, low power radio, body area networks, wireless sensor networks.

A boost converter for thermoelectric energy harvesting in 130 nm CMOS achieves energy harvesting from a 10 mV input, which allows wearable body sensors to continue operation with low thermal gradients. The design uses a peak inductor current control scheme and duty cycled, offset compensated comparators to maintain high efficiency across a broad range of input and output voltages. The measured efficiency ranges from 53% at mV to a peak efficiency of 83% at mV. A cold-start circuit starts the operation of the boost converter from 220 mV, and an RF kick-start circuits starts it from 14.5 dBm at 915 MHz RF power.

Most systems require a voltage reference independent of variation of power supply, process, or temperature, and a bandgap voltage reference (BGR) often serves this purpose. For ultra-low power (ULP) systems, the BGR may constitute a significant component of standby power, and the system start-up voltage is often determined by the voltage, V in , at which the BGR becomes operational. Lowering V in can also allow an ULP system to continue operation longer as its battery or energy harvested input voltage decreases. The minimum V in for state-of-the-art BGRs is restricted by V EB +V DS [1], where V EB is the emitter-base voltage of a pnp transistor, and V DS is the drain-source saturation voltage of a MOS transistor. Recent work brings the V in voltage down to 700mV [2]. There is a need to reduce the standby power and V in of a BGR to increase the lifetime of ULP systems. This paper presents a BGR circuit with measured minimum operating V in of 500mV, reducing the V in of [2] by 1.4×. Further, the power consumption of the proposed circuit is 32nW, which is 1.6× lower than the non-duty cycled BGR reported in [2]. A 2×-charge pump based bandgap core, a switched-capacitor network (SCN), and a current controlled oscillator and clock doubler circuit enable a BGR with a temperature variation of 75ppm/°C and power supply rejection (PSR) of up to -52dB at DC.