Design and Implementation of Novel Optical Fabry-Pérot Arrays for Medical Applications

Optical sensing systems find a wide range of applications, especially in the medical field, for intelligent, patient-operated health monitoring and early diagnosis, facilitating immediate responses to warnings. Advances in technology have enabled sensors miniaturization with spectrometers using low-cost Fabry-Pérot filters, allowing integration into mobile phones and wearable devices without compromising their resolution. The challenge in filter fabrication is deforming supporting posts deformation during polymer cavity underetching to release the top membrane, because the polymer acts partly as supporting posts. This thesis proposes a solution by fabricating structured cavity filter, where the polymer acts only as a sacrificial layer. Different approaches were explored to structure the cavity polymer and support layer. The issue of falling the top Distributed Bragg Reflector DBR addressed and a solution proposed and implemented involving filters with larger top mesa diameter. Two photomasks were designed using CAD software for structured cavity and larger top mesa. The fabrication steps for realizing the entire filter structure were detailed, resulting in filters without supporting post deformation and avoiding top DBR falling. Electrostatic DC actuation was performed on structured cavity filters with various suspension geometries and membrane sizes working in the visible range. An example, a 3-straight-suspension filter with a 70 μm membrane diameter showed a tuning range of 58 nm for 20 V, with 45% transmittance and a 10 nm FWHM. In addition, a numerical simulation based on Finite Element Method FEM was conducted to investigate the initial displacement and electrostatic actuation of the top membrane. Results showed that increasing the top mesa diameter significantly reduced the initial displacement of the top membrane by more than half compared to the previous design. For example, a 3-straight-suspension filter with a 40 μm membrane and a 36 μm top mesa diameter showed initial displacement decrease by 333 nm (≈ 65%), from 506 nm to 173 nm, compared to a 30 μm top mesa diameter. During electrostatic actuation, displacement reduction in filters with larger top mesa diameters was minimal.