MEMS-based Tunable Metasurface for Reflective Display Applications

In an era where portable electronic devices are indispensable for a wide range of activities, the need for displays that provide both long-lasting battery life and excellent visibility in different lighting conditions is increasingly important. Emissive displays, which are widely used in current technologies, face challenges in adapting to changing environmental lighting. Unlike the human visual system that naturally sustains a consistent perception of visual elements in varying lighting conditions, emissive displays struggle to adapt their brightness effectively to diverse ambient settings. This inefficiency leads to greater power consumption to keep the screen visible, especially in well-lit areas, which in turn shortens the device's battery life. The issue can further lead to eye strain, caused by the disparity in luminosity between the display and its immediate surroundings.Reflective displays emerge as a promising alternative that leverages, rather than tries to match, ambient light. This thesis focuses on the development and investigation of Micro-Electro Mechanical Systems (MEMS)-based tunable metasurface technology for potential use in reflective displays for mobile devices. This tunable metasurface alters the reflectivity by dynamically switching the surface morphology between flat (reflective) and nano-structured (absorption). The research progresses through several stages, beginning with the development of a static prototype that uses amorphous silicon (aSi) nanopillars and flat areas to achieve a contrast ratio of 1:50 between reflective and absorptive states. Building on this initial work, a dynamic prototype featuring electrostatic actuation is successfully developed. The device achieves a notable contrast ratio of 1:3 and demonstrates a switching time of 54 ms. While the optical and mechanical performance present opportunities for further optimization due to strain-induced deformations affecting the geometry and high electric resistivity, they nevertheless showcase the prototype's capability to alter the optical response.Furthermore, the thesis delves into scalable manufacturing processes, with a strong emphasis on self-alignment methodologies. Various deposition techniques are scrutinized, and the feasibility of this self-aligned, scalable manufacturing process is experimentally validated, despite some unresolved actuation failures.Additionally, the thesis incorporates a computational aspect, involving the development of a Python wrapper for commercial Rigorous Coupled-Wave Analysis software. This computational framework facilitates advanced geometric definitions, input configurations, and a wide range of post-simulation visualizations, from spectral data to near-field electromagnetic plots.In summary, this thesis provides a comprehensive investigation into the technological feasibility and scalability of MEMS-based tunable metasurfaces as a promising avenue for future reflective displays, while also highlighting areas that require further research.