A Wafer Level Packaged Fully Integrated Tunable Fabry-Pérot Filter With Extended Optical Range For Multispectral and Hyperspectral Imaging

Abstract

We report on the design, fabrication and characterization of a wafer level packaged, vacuum sealed, fully integrated and cell-phone compatible tunable micromachined Fabry-Perot filter ( $\mu $ FPF), operating within the visual and near-infrared (VIS-NIR) optical range. Implementation of a normally closed architecture combined with the electrostatic actuation enlarging, rather than closing, the optical cavity allows to achieve enhanced tunability of the optical gap. To evaluate the design and operational parameters, an electro-opto-mechanical model of the device was built and the resulting system of equations, coupling the structural, squeeze film, electrostatic and electric circuit domains, was solved numerically. The devices with an optical aperture of 1.85 mm and with robust elastic suspensions made of single crystal Si were fabricated and, consistently with the model prediction, the filter tunability within the range between 100 nm and 500 nm was demonstrated in the experiments. Vertically integrated design resulted in a small, 1 mm, thickness of a fully assembled device. Due to its compact size, manufacturability and short response time within the millisecond range, our tunable filter can be directly integrated into mobile phone camera modules, portable hyperspectral imagers, and remote sensors.