Low-Cost Precision Patterning of Transparent Conductors and Failure Mode Analysis for Liquid Crystal Meandered Delay Lines

This letter details an optimized, low-cost process for the photolithographic patterning of Indium Tin Oxide (ITO) on glass and polycarbonate (PC) substrates for applications in microwave devices, such as liquid crystal-embedded meandered delay lines. A comprehensive fabrication protocol for both substrate types is presented, utilizing positive photoresists (AZ4562 and AZ5214E) and hydrochloric acid (HCl) etching. While high-fidelity patterning with sub-micron accuracy was achieved on glass substrates, the implementation on PC substrates revealed a critical failure mode: film cracking induced by thermal expansion coefficient mismatch. This study investigates the root cause of this cracking, linking it to the significant difference in the Coefficients of Thermal Expansion (CTE) between ITO (8.5 ∙ 10⁻⁶ /K) and PC (70.2 ∙ 10⁻⁶ /K). We demonstrate that replacing conventional thermal processing with room-temperature dehydration in a vacuum desiccator successfully mitigates this failure, enabling the fabrication of uniform and accurate ITO patterns on thermally sensitive polymer substrates.