- Penn State researchers built a monolithic 3D chip that runs solely on ambient light without using a battery
- The chip stacks silicon photovoltaics, MoS₂/WSe₂ complementary logic and graphene chemical sensors within ~50 nm of each other
- The development also opens the door to larger 2D circuits incorporating some of the same design philosophy in the future
Research at Penn State University has found an interesting breakthrough in engineering, building a compact integrated circuit that runs entirely on solar energy.
The IC, which skips batteries altogether, aims to run calculations and be able to sense chemicals in its vicinity by harvesting solar energy available to it, aiming to do so by stacking everything monolithically rather than splitting things up across different dies.
The move comes as engineers continue to grapple with the need for long-lasting and versatile IoT and edge computing systems, many of which are installed in remote or hard-to-reach locations, making replacing batteries a difficult, if not impossible, proposition at times.
A vertically stacked solution centered around solar energy
Battery-free electronics that rely on renewable energy are in greater focus as engineers, stakeholders and consumers seek such devices to meet growing market demand.
What makes the research team at Penn State’s development so unique is that it has attempted to address what conventional electronics have so far failed to do: reduce losses by investing in a structure that effectively bypasses a significant portion of the board-area, wire-loss power and latency requirements of such devices.
The chip does this by utilizing two types of semiconductor materials (MoS₂ and WSe₂), a photovoltaic silicon module and graphene-based sensors and stacking all three layers vertically.
The graphene-based sensors at the top react to liquids placed on them and send electrical signals that are processed in the middle logic layer where the semiconductor layer resides, while the silicon solar cell module at the bottom generates power by converting ambient light into electricity.
“We showed that heterogeneous materials – silicon, graphene, MoS2 and WS2-can be monolithically integrated in three dimensions to create a self-powered sensing and computing system. This is different from simply placing separate chips next to each other or connecting them externally. We show that sensing, computation and energy harvesting can be brought into nanoscale proximity, which can reduce footprint, interconnect length and energy loss,” said Saptarshi Das, one of the authors of the paper documenting this approach.
While the move itself documents a small custom-built chip, it has interesting implications for the future, where larger circuits could use the design as a building block for IoT needs, especially in remote environments where batteries can be difficult to replace, even though efficiency is at the heart of lower-power nanoscale circuits.
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