On-chip microcapacitors

Scientists from Lawrence Berkeley National Laboratory and University of California Berkeley developed microcapacitors with ultrahigh energy and power density that could be used for on-chip energy storage.

The microcapacitors were made with thin films of hafnium oxide (HfO₂) and zirconium oxide (ZrO₂) engineered to achieve a negative capacitance effect, which increased overall capacitance and enabled it to store greater amounts of charge.

“We’ve shown that it’s possible to store a lot of energy in microcapacitors made from engineered thin films, much more than what is possible with ordinary dielectrics,” said Sayeef Salahuddin, a Berkeley Lab faculty senior scientist and UC Berkeley professor, in a release. “What’s more, we’re doing this with a material that can be processed directly on top of microprocessors.”

The films were grown with atomic layer deposition. The ratio of HfO₂ and ZrO₂ leads the films to be either ferroelectric or antiferroelectric. Balancing the composition at the tipping point between the two gives rise to the negative capacitance effect where the material can be very easily polarized by even a small electric field.

By interspersing atomically thin layers of aluminum oxide after every few layers of HfO₂-ZrO₂, they could grow the films up to 100 nm thick and integrate them into 3D trench capacitor structures. The researchers claim the microcapacitor shows 9x higher energy density and 170x higher power density compared to today’s electrostatic capacitors. They are working on scaling up the technology and integrating it into full-size microchips. [1]

Deformable micro-supercapacitor

Researchers from Pohang University of Science and Technology (POSTECH) and Korea Institute of Industrial Technology (KITECH) built a micro-supercapacitor (MSC) capable of stretching, twisting, folding, and wrinkling.

The team used laser ablation for fine patterning of both eutectic gallium-indium liquid metal (EGaIn) and graphene layers on a stretchable polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene copolymer (SEBS) substrate.

The MSC retailed its areal capacitance after stretching up to 1,000 cycles and operated stably while being mechanically deformed. [2]

Oriented 2D nanofillers

Researchers from the University of Houston, Jackson State University, and Howard University have developed a flexible high-energy-density capacitor created using layered polymers with mechanically exfoliated flakes of 2D materials as nanofillers.

By arranging materials like mica and hexagonal boron nitride (hBN) in specific layers, they created a thin sandwich-like structure with higher energy density and efficiency than capacitors with randomly blended-in nanofillers.

“Our work demonstrates the development of high energy and high-power density capacitors by blocking electrical breakdown pathways in polymeric materials using the oriented 2D nanofillers,” said Maninderjeet Singh, a University of Houston chemical engineering PhD graduate and now a postdoctoral research scientist at Columbia University, in a release. “We achieved an ultra-high energy density of approximately 75 J/cm³, the highest reported for a polymeric dielectric capacitor to date.” [3]

References

[1] Cheema, S.S., Shanker, N., Hsu, SL. et al. Giant energy storage and power density negative capacitance superlattices. Nature (2024). https://doi.org/10.1038/s41586-024-07365-5

[2] Kim, KW., Park, S.J., Park, SJ. et al. Deformable micro-supercapacitor fabricated via laser ablation patterning of Graphene/liquid metal. npj Flex Electron 8, 18 (2024). https://doi.org/10.1038/s41528-024-00306-2

[3] Singh, M., Das, P., Samanta, P. N., et al. Ultrahigh Capacitive Energy Density in Stratified 2D Nanofiller-Based Polymer Dielectric Films. ACS Nano 2023 17 (20), 20262-20272. https://doi.org/10.1021/acsnano.3c06249

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