Nanofabrication platforms for metasurface optics: From prototyping to mass-production

Abstract

Manipulating light using sub-wavelength scale structures (meta-atoms), once a purely theoretical concept for shorter electromagnetic wavelengths, has become achievable thanks to advances in high-end semiconductor manufacturing technology and their increased accessibility to research communities. This development has allowed metasurface optics to be born into the world, building upon a multitude of ideas and a solid understanding of physics. This dissertation focuses on four key aspects of metasurface research: the methods and intricacies of designing and prototyping, mass-manufacturing of metasurface optics, scaling up metasurfaces in size, and exploring other possibilities for expanding the research horizon, supported by proof-ofconcept examples. The feasibility of experimental proof-of-concept demonstrations for metasurfaces can be attributed to innovative fabrication processes. These processes demand understanding of how each manufacturing tool operates. Many metasurface devices were created using electron-beam lithography due to its versatility and adaptability. These prototypes offer a promising outlook for future devices, with the potential for increased efficiency, compactness, and lower consumer costs. The first chapter of this dissertation delves into the details of these fabrication processes and the associated meta-atom design process. Nevertheless, the transition from lab-scale prototypes to consumer-level mass manufacturing comes with its own set of constraints and challenges. For economic reasons, designing the manufacturing process based on conventional existing platforms often proves to be the more feasible approach. However, it introduces several restrictions, such as the choice of material, mechanical properties, and tool compatibilities. Chapter 2 of this dissertation discusses two primary methods for mass-producing metasurface optics while considering these constraints: the deep-ultraviolet (DUV) lithography process, the foundation of modern integrated circuit manufacturing, and rollto- roll (R2R) nanoimprint lithography, widely used for creating large-area functional films. Using existing semiconductor manufacturing tools as-is sometimes limits the size of the metasurface devices that can be produced. Chapter 3 explores strategies for working around these tool limitations through demonstrating a 100 mm diameter metasurface lens (metalens) capable of imaging celestial objects. Additionally, the chapter discusses the impact of potential fabrication errors on optical performance, offering insights on which errors are more or less critical to the final device quality. In the final part of the dissertation, other potential metasurface optics platforms are considered with proof-of-concept fabrication results. These include the metasurface-refractive hybrid lens platform, the multi-layer metasurface platform, metasurfaces directly fabricated on stretchable platforms, and scratch-resistant metasurface platforms. In summary, this dissertation aims to highlight the dynamic cycle between the theory and practical applications, emphasizing the crucial role of collaboration among researchers, engineers, and scientists in advancing the boundaries of our understanding and shaping of the future of optical technology and their practical applications.