Proceedings Article | 21 May 2014
Proc. SPIE. 9100, Image Sensing Technologies: Materials, Devices, Systems, and Applications
KEYWORDS: Staring arrays, Long wavelength infrared, Infrared imaging, Spectroscopy, Interfaces, Reflectivity, Spectral resolution, Infrared radiation, Electronic filtering, Semiconducting wafers
Imaging spectrometry can be utilized in the midwave infrared (MWIR) and long wave infrared
(LWIR) bands to detect, identify and map complex chemical agents based on their rotational and
vibrational emission spectra. Hyperspectral datasets are typically obtained using grating or
Fourier transform spectrometers to separate the incoming light into spectral bands. At present,
these spectrometers are large, cumbersome, slow and expensive, and their resolution is limited
by bulky mechanical components such as mirrors and gratings. As such, low-cost, miniaturized
imaging spectrometers are of great interest. Microfabrication of micro-electro-mechanicalsystems
(MEMS)-based components opens the door for producing low-cost, reliable optical
systems. We present here our work on developing a miniaturized IR imaging spectrometer by
coupling a mercury cadmium telluride (HgCdTe)-based infrared focal plane array (FPA) with a
MEMS-based Fabry-Perot filter (FPF). The two membranes are fabricated from silicon-oninsulator
(SOI) wafers using bulk micromachining technology. The fixed membrane is a standard
silicon membrane, fabricated using back etching processes. The movable membrane is
implemented as an X-beam structure to improve mechanical stability. The geometries of the
distributed Bragg reflector (DBR)-based tunable FPFs are modeled to achieve the desired
spectral resolution and wavelength range. Additionally, acceptable fabrication tolerances are
determined by modeling the spectral performance of the FPFs as a function of DBR surface
roughness and membrane curvature. These fabrication non-idealities are then mitigated by
developing an optimized DBR process flow yielding high-performance FPF cavities. Zinc
Sulfide (ZnS) and Germanium (Ge) are chosen as the low and the high index materials,
respectively, and are deposited using an electron beam process. Simulations are presented
showing the impact of these changes and non-idealities in both a device and systems level.
