Monolithic Integration of Multi-Spectral Optical Interference Filter Array on Thin Film Amorphous Silicon Photodiodes

Hydrogenated amorphous silicon thin film photodetectors combined with optical filters are routinely used for biological detection applications based on fluorescence. Monolithic integration of these filters to the photodetectors further enhances the portability and simplicity of the system. However, due to the multitude of fluorophores used in such applications, it is often necessary to combine multiple filters in a single chip for increased ease of application and portability of the system. In this work, we report a novel facile technique to integrate multiple filters in a chip with four photodiodes, in an innovative methodology that leverages the beneficial characteristics of different types of deposition techniques to fabricate precise multilayer interference filters. Ion beam deposited MgO layers with different thicknesses are successively patterned by lift-off and sandwiched between two standard dielectric mirrors deposited via plasma-enhanced chemical vapor deposition to produce the filter array. The successful integration of the devices is demonstrated through fluorescence measurements of grape fluorescence at two different wavelengths which are utilized in grape maturation monitoring in the viticulture sector.