MEMS THz sensors using metasurface structures
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We report on THz MEMS sensors suitable for large focal plane arrays and readout schemes compatible with real-time imaging. Terahertz absorption near 100 %, optimized to particular monochromatic quantum cascade laser (QCL) illumination sources, was achieved using metal-dielectric metasurfaces. MEMS devices were designed using metasurface absorbers as structural components, allowing for streamlined fabrication of very efficient detectors in two different configurations. In the first scheme, bi-material sensors were used, where the heat from the absorbers is converted into mechanical deformation. The angular displacement, proportional to the absorbed THz radiation, was then optically probed. In the second configuration, THz to IR conversion was achieved whereas the front side of the metasurface absorbs THz and the backside served as an efficient infrared emitter, allowing its temperature to be probed directly by a commercial, thermal (infrared) camera. The devices are comprised of ultrathin films of silicon-rich silicon oxide and aluminum, deposited on silicon substrates and were fabricated standard MEMS processes including Bosh deep reactive ion etching to remove the substrate. The sensors were fabricated in a matrix configuration and individually characterized. The main figures of merit, such as spectral response, thermal time constant and sensitivity are controlled by the geometry and can be modified by design according to the application demands.