Nanoshape Imprint Lithography for Fabrication of Nanowire Ultracapacitors


A. Cherala, Chopra, M., Yin, B., Mallavarapu, A., Singhal, S., Abed, O., Bonnecaze, R., and Sreenivasan, S. V., “Nanoshape Imprint Lithography for Fabrication of Nanowire Ultracapacitors,” IEEE Transactions on Nanotechnology, vol. 15, no. 3, 2016.


Emerging nanoscale applications in energy, electronics, and medicine require high throughput patterning with complex shape control at the nanoscale that is beyond the capabilities of optical lithography and block copolymer-based self-assembly. We introduce a technique for creating precise two-dimensional nanoshapes with sharp corners by imprint lithography, and apply it to enable shaped silicon nanowire capacitors that significantly exceed standard nanowire capacitor performance due to relative increase in surface area per unit projected area. The patterning technique employs atomic layer deposition to fabricate a template with diamond-like shapes consisting of corners with 2 nm radii of curvature. Template materials and chemical staining of the imprint polymer enable precise imaging of the template and replicated resist. Continuum mechanics appears no longer applicable at the length scale of similar to 3 nm. A systematic increase in the radius of the imprinted corner is observed contrary to predictions by a linear elastic continuum model shedding new light on shape relaxation of polymers, and on the limits of nanoshape replicability by imprint lithography. Novel diamond-shaped silicon nanowires (100-nm half-pitch) have been fabricated using nanoshape imprint followed by metal-assisted chemical etching, and have been incorporated into shaped nanowire capacitors that exceed standard nanowire capacitors performance by similar to 90%. The 3-nm resolution limit does not degrade the performance of the shaped capacitor. This increased capacitance validates the ability to preserve nanoshape cross section during patterning and deep etching over large areas. Lithographic scaling to 10-nm half-pitch has the potential to further increase capacitance by a factor of 10.


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