Fused silica microlenses for hermetic packages as part of implantable optrodes

The request for stable and reliable devices is tremendous in the field of optogenetics. So far, no device which is called optrode, encapsulating the needed light source hermetically, can be found. We therefore introduce a novel optrode concept consisting of polyimide, silicone as well as a silicon- and fused silica-based hermetic package. One of the main features of the hermetic package is the integration of custom-made microlenses. These microlenses are fabricated using thermal reflow of photoresist. Chosen parameters for remelting the photoresist AZ9260 are 2 min @ 160 °C. An additional dry etching step is introduced to transfer the resist pattern into a fused silica substrate. We were able to fabricate lenses in diameters ranging from 25 μm to 1300 μm. The focal lengths of the etched lenses vary from 630 μm to 5500 μm for lens diameter ranging from 200 μm to 900 μm. Deviations of the transferred pattern to an ideal sphere range from 0.055 % and -0.151 % to 0.040 % and -0.003 % (300 μm and 700 μm lens diameter) and can be neglected.