Fabrication of Thin Composite Emission Filter for High-Performance Lens-Free Fluorescent Imager

摘要

The emission filter plays a key role in resolving a modest-quality image of the lens-free fluorescent imager. Thecomplementary structure of an interference filter and absorption filters exhibits a high-rejection ratio, corresponding tothe lens-based fluorescence device. However, existing fabrication methods are facing challenges to reach a reasonablefilter thickness for low invasiveness. It is difficult to deposit interference filters on the polymer-based absorption filter andCMOS die directly. Conversely, the interference is fragile and easy to crack so that transferring from its substrate to theimage sensor is a fatiguing task. Here we report composite filter fabrication using laser lift-off (LLO) and silicon plasmaetching. The LLO utilized high energy laser to separate the interference filter from the glass substrate, whereas the plasmaetching tailored SiF_6 gas to completely annihilate silicon-substrate whereby the filter was deposited beforehand. As aresult, a narrow-size filter is successfully fabricated by LLO, yet a crack issue for a larger sensor size remains unsolved.On the other hand, the plasma etching produced large-size and spotless filters with relatively high reproducibility.Additionally, this method offers multiple device fabrication in a single process, which, we expect, could intensify largescalelens-free fluorescent imager applications in the future.