Conformal thin film patterning using sonication assisted cracking-lithography

Sammanfattning

The micro and nanoscale patterning of thin films on three-dimensional (3D) surfaces is pivotal for advancing electronic, photonic, and biomedical devices. Existing patterning methods face significant challenges, including limited material compatibility, suboptimal performance compared to conventional CMOS processes, and insufficient control over surface and thickness resolution. This thesis presents a novel sonication-assisted conformal patterning technique that integrates two-photon polymerization (2PP) with lift-off processes, enabling high-resolution patterning of a broad range of solid-state thin films, including dielectrics, metals, and semiconductors, on almost any 3D surface. Protocols were established to achieve sub-micrometer precision, focusing on highaccuracy alignment, adhesion control, and reliable fabrication. Feature sizes were demonstrated on scales as small as 100 nm, and pattern sizes were extended up to 100 μm, showcasing scalability and flexibility. The relationship between ultrasonic power required for scaffold lift-off and scaffold height-to-width aspect ratio was investigated, optimizing the sonication-assisted cracking process. The method was successfully applied to various 3D structures, including hemispheres, vertical surfaces, and stepped pyramids, as well as curved silicon surfaces. Multi-layer patterning with different thin-film materials was achieved on the same 3D surfaces, enabling increased complexity and functionality. The electrical performance of patterned nanowires demonstrated results comparable to conventional devices. The feasibility of a one-step lift-off method was explored. Challenges associated with metal coatings on high-reflectivity films, such as silver, were also addressed, expanding the material compatibility of the technique. The integrated 2PP and sonication-assisted conformal patterning technique provide a versatile, high-resolution, and scalable method for patterning thin films on complex 3D surfaces, effectively overcoming the limitations of existing approaches. This advancement lays the foundation for innovative manufacturing techniques and functional structures in micro- and nano-engineering. Future work may involve applying conformal patterning techniques to fiber end faces and developing innovative devices that leverage this method, thereby further expanding its application scope.