15.1 A Self-Powered SoC with Distributed Cooperative Energy Harvesting and Multi-Chip Power Management for System-in-Fiber

Rapid reductions in power and size of SoC have paved the way for mm-scale textile-based self-powered systems capable of sensing a variety of biological and environmental data such as sodium, glucose, temperature, and neural signals [1,3-6]. SoCs built for these applications need to be fully autonomous and miniaturized, capable of continuous sensing at nW-level to operate from scarce amounts of harvested energy, and able to communicate in a distributed sensing network. A prior smart E-textile system [1] enables self-powered Na+ sensing but is built with sm-scale commercial-off-the-shelf (COTS) components that consume >4mW. A mm-scale system-in-fiber in [2] with COTS components requires batteries for
$> 10\mu \mathrm{W}$
power. For systems using custom SoCs with nW power and mm-scale form factor [3–6], a base station is required to provide light (>3Klux [4], >60Klux [5]) to communicate and power the devices. This leads to reduced system autonomy and an inability for direct inter-SoC communication. We address these limitations with a fully autonomous self-powered system-on-chip (SoC) that can be distributed along a fiber strand, capable of simultaneously harvesting energy, cooperatively scaling performance, sharing power, and booting-up with other SoCs in-fiber. The SoC achieves 33nW power consumption for the whole chip under 92Lux light and can reduce control power down to 2.7nW for the energy harvesting and power management unit (EHPMU). With the proposed power sharing and cooperative dynamic voltage and frequency scaling (DVFS), the proposed SoC reduces the illuminance needed to stay alive by
$> 7\times$
down to 12Lux. We integrate the SoC into a
$2.2\times 1$
mm cross-section polymer fiber with an embedded electrical bus via a
$4.7\times 3.7\text{mm}$
interposer board, as shown in Fig. 15.1.1 (bottom). The timing waveform in Fig. 15.1.1 (right) shows how the SoCs can cooperatively scale their performance based on both the local [7–9] and adjacent SoCs' conditions. This allows the energy and performance of all the in-fiber SoCs to be flexibly and jointly balanced, thereby improving the system viability and adaptability.