Conformal thin-film patterning via crack engineering

QC 20261009

Abstract

Many nanoscale devices depend on precisely patterned features.Conventional nanofabrication methods often define these featuresdirectly, imposing a trade-off between resolution, throughput, andcost. Crack-defined patterning offers an alternative: lithographyneed not define the final nanoscale feature itself, but can instead program a mechanical instability that creates it. Established crack-basedmethods typically load a film in its own plane, causing channel cracksto propagate laterally. This thesis develops a distinct crack-definedpatterning approach driven by out-of-plane stress. A lithographicallyplaced actuator peels the film away from the substrate, detaching andremoving material. Lithography defines the mechanical geometryand actuator location, whereas stored elastic energy and release determine the resulting feature. The approach spans zero-dimensional(0D) nanopores, one-dimensional (1D) nanoslits, and conformalpatterns on three-dimensional (3D) surfaces.The first part develops stress-induced ripping, which enablesscalable nanopore fabrication. Solid-state nanopores, mainly usedfor single-molecule sensing, need openings of a few nanometers thatare difficult to define directly at wafer scale. A pre-stressed beamdefined by i-line lithography pulls a fragment out of an ultrathinmembrane, forming sub-10 nm nanopores in parallel. Retaining thefragment as a self-aligned lid gives lidded nanopores down to 4 nm.Guided self-tearing extends this to programmed crack paths andsub-20 nm features in 0D, 1D, and curved 2D patterns.The second part extends the approach to 3D surfaces, where uniform resist coating and exposure are difficult. Scaffold-architectedlift-off (SALO) uses 3D-printed sacrificial scaffolds removed by sonication to pattern conformal films such as atomic-layer-depositedcoatings on slopes up to 90◦, while also enabling features as small as50 nm and sequential patterning of multiple materials.The final part evaluates the nanopores in devices. Rippednanopores detect DNA translocation through ionic current andprovide a SERS readout after metallization. Lidded plasmonicnanopores show an optical response that varies with pore–lid geometry. An integrated nanopore–cavity–electrode platform showstranslocation and temporary docking, but not direct molecularresidence; a fluidic memristor response is also compared with asimulated polymer-lidded concept.To summarize, these results establish a thin-film patterning strategy in which out-of-plane stress drives controlled fracture. Crackdefined patterning therefore complements lithography in applicationsthat require deterministic feature placement, sub-lithographic dimensions, nonplanar surface and large-scale parallel fabrication.

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