Development of Selectively Actuatable Micromirror Arrays and Scalable Lithography Processes for Large-Area Applications as Smart Window

This thesis provides an extensive overview on the state-of-the-art daylighting systems for applications in buildings and subsequently addresses the implementation of subfield addressing in micromirror arrays and investigation of a potential scalable lithography process for the large-area fabrication, both have been identified as the research gap in achieving the envisioned application as smart window. The work is conducted in continuation of the optimized fabrication process and the successful fabrication of a lab demonstrator achieved in the earlier research stage. Restricted actuation state from a single micromirror arrays module is limiting the utilization potential and hindering the tailored ambient lighting envisaged in the smart window application. The current design can only be actuated in a single state—either open, closed, or any allowed state in between—and a segmentation of a single window module into independently actuatable subgroup is necessary to allow combined actuation states of a single module. Such requirement is addressed in this work via implementation of subfield addressing. Driving schemes from the display technologies, namely the direct, passive matrix, and active matrix addressing are discussed and evaluated for potential adaptation into the micromirror arrays. Concept, design, and technological fabrication of subfield addressing in 4 × 4 and 8 × 8 passive matrix arrangements are executed on a single module with dimension of 10 × 10 cm². In addition to the functionality, subfield addressing in micromirror arrays is designed in accordance with fabrication process stability, reproducibility, and integrability with the optimized bi-layered process from previous works. Structuring of the fluorine-doped tin oxide (FTO) layer into separated column electrodes is implemented by means of metal-acid etch. Correspondingly, the micromirror layer is designed into separated row electrodes. Process parameter and optimization to achieve maximum active area out of the single module of 10 × 10 cm² are investigated and detailed. Finally, a function demonstrator consisting of four 10 × 10 cm² modules is fabricated as a proof-of-concept for the implementation of subfield addressing in micromirror arrays. Investigation of a potentially scalable lithography process is substantiated by the limited availability of bi-layered photomask in larger size. Such limitation has halted the large-area fabrication potential and consequently the application of micromirror arrays as smart window. Therefore, a fabrication method utilizing inclined UV exposure based on roll-lithography process is proposed as an alternative to the bi-layered photomask. The required process parameters, particularly the exposure angle, UV dose, and development time, are investigated and evaluated by the resulting leading-edge and undercut structures in the sacrificial photoresist layer.