Study on warpage and filling behavior of glass in non-isothermal hot embossing.

Non-isothermal hot embossing has great potential in the mass production of glass micro optical components due to the relatively short heating-cooling cycle time. However, warpage was induced by the temperature gradient inside the glass replica during hot embossing, resulting in a deteriorated optical performance. Therefore, it is non-trivial to investigate the effects of process parameters on warping and filling behaviors of glass in non-isothermal hot embossing. Firstly, a high-quality microhole was fabricated on monocrystalline silicon carbide (SiC) mold by focused ion beam (FIB) lithography. By using a novel home-made gravity-assisted hot embossing machine, the geometric information (i.e., warpage and microstructures) on SiC mold was transferred into the surface of N-BK7 glass replica. The experimental results indicate that high embossing temperature enables not only the minimization of warpage but also the enhancement of microstructure replication accuracy. Furthermore, increasing embossing force enhances filling capacity but increases warpage amplitude. Interestingly, fast heating/cooling rates and short embossing time enable a small warpage as well as a high embossing efficiency. By optimizing the process parameters, especially the embossing temperature, a small warpage amplitude of 3 μm and a high transfer ratio of 99.11% were achieved, which can meet the high requirement of precision optical components. [ABSTRACT FROM AUTHOR]