Evaluation of Warpage and Residual Stress of Precision Glass Micro-Optics Heated by Carbide-Bonded Graphene Coating in Hot Embossing Process

Abstract

A newly developed hot embossing technique which uses the localized rapid heating of a thin carbide-bonded graphene (CBG) coating, greatly reduces the energy consumption and promotes the fabrication efficiency. However, because of the non-isothermal heat transfer process, significant geometric deviation and residual stress could be introduced. In this paper, we successfully facilitate the CBG-heating-based hot embossing into the fabrication of microlens array on inorganic glass N-BK7 substrate, where the forming temperature is as high as 800 °C. The embossed microlens array has high replication fidelity, but an obvious geometric warpage along the glass substrate also arises. Thermo-mechanical coupled finite element modelling of the embossing process is conducted and verified by the experimental results. Based on trial and error simulations, an appropriate compensation curvature is determined and adopted to modify the geometrical design of the silicon wafer mold. The warpage of the re-embossed microlens array is significantly decreased using the compensated mold, which demonstrates the feasibility of the simulation-oriented compensation scheme. Our work would contribute to improving the quality of optics embossed by this innovative CBG-heating-based hot embossing technique.

A Comprehensive Review of Micro/Nano Precision Glass Molding Molds and Their Fabrication Methods

“…Finally, the glass and the mold are cooled to room temperature before the glass is released from the molds. Typically, the cooling cycle is carefully controlled because cooling may lead to internal thermal stress, which can change a number of important properties, including the refractive index and Abbe number [ 17 , 18 , 19 , 20 ]. Based on the glass transition temperature ( T g ), above which the glass material becomes viscous fluid [ 21 ], optical glass materials can be categorized as (i) ultra-low T g glass ( T g ˂ 400 °C), (ii) low T g glass (400 °C ˂ T g ˂ 620 °C), or (iii) high T g glass ( T g ˃ 620 °C) [ 13 ].…”