A new dimension of system architecture design is emerging where hundreds to thousands of ultralight (<10g) sensor nodes will collectively perform a spectrum of wireless sensor network missions in a distributed fashion. To support this architecture, the development of a technique is underway to design and fabricate self-powered wireless sensor nodes monolithically as a system-on-a-chip (SoC) with commercially available complementary metal-on-silicon (CMOS) technology. The goal is to realize a novel system-on-a-chip (SoC) component integration on a single silicon die.

Two essential technologies specifically targeted at non-benign environments are proposed: integrated solar cells in CMOS, and radiation hardening by design of asynchronous logic. Two prototype designs have been designed, fabricated, and tested. The average efficiency of the first prototype is 2.4%, compared to an estimated, but unverified, 1% from previous work. The actual efficiency of the junction is 8.3%, without considering the metallization overhead. An improved design demonstrates 3.44% efficiency, a 40% improvement. The junction efficiency alone is 11.3%. However, power from these first two prototypes cannot be harnessed properly in the current implementation.

This novel development has potential widespread application to a rapidly growing number of solar self-powered SoC designs of any type. The application of radiation hardening by design (RHBD) to asynchronous logic is suggested as a unique approach for bare-die SoC implementations in hostile environments. Starting with a common synchronous microcontroller design implemented with commercial logic gates, the application of RHBD results in an expected 200% core area increase and requires 160% more energy. The most significant result is that the application of asynchronous design reduced the energy penalty to 85% (from 160%) for a 6% area increase with no performance impact. Additionally, electromagnetic interference is greatly reduced.

This approach provides environmental tolerance to radiation and temperature extremes. A suggested next step would be the monolithic integration of the developed solar cells and microcontroller with a single-chip radio design and simple sensor. The focus of this work would be to minimize or eliminate the traditional external components and establish self-powered wireless interconnectivity.

The monolithic SoC approach has been challenged by various packaging alternatives, including traditional printed circuit board (PCB), multichip module (MCM), system-in-package (SiP), and now system-on-package (SOP); however, SoC’s attraction is its low cost and mass producibility. Related prototyping design activities have been undertaken, targeting a system mass less than one kilogram, leading to a 70-g satellite-on-a-PCB prototype.

This work was done by Dr. Tanya Vladimirova and Dr. David Barnhart of the University of Surrey, UK, for the Air Force Office of Scientific Research. AFRL-0126

This Brief includes a Technical Support Package (TSP).
Heterogeneous System-on-a-Chip for Self-Powered Wireless Sensor Networks

(reference AFRL-0126) is currently available for download from the TSP library.

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