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Design, Simulation, Fabrication, and Characterization of MEMS-based, Tunable FABRY-PEROT Interferometer Filter in the Long Wavelength Infrared Region

  • Author(s): Kim, Tae Sung
  • Advisor(s): Kubby, Joel
  • et al.
Abstract

Demand for a small, portable IR spectrometer has been growing steadily for many years. A monochromator is one of the essential parts that comprises any spectroscopy system. A MEMS-based, tunable Fabry-Perot interferometer filter (FPI), that is proposed to be a monochromator with a broadband IR detector array in an improvised explosive device detection system, is designed, simulated, fabricated and characterized in this dissertation. With the operational wavelength range in the long wavelength IR region, from 8 to 11 µm, a distributed Bragg reflector with germanium and zinc sulfide is used to implement the mirror that covers the target spectrum. One of the mirrors is fabricated with four beam springs in an X-shape to tune the passing wavelength of the FPI filter by adjusting the gap distance between two membranes using electrostatic attraction.

Designed device is simulated to confirm it meeting the required device specification. Taking advantage of SOI wafer, the FPI filter is fabricated with simple fabrication process with only four lithography masks, one deposition, and three etch steps. The scaffold structure is fabricated with both surface micromachining and bulk micromachining process. The DBR mirror is deposited using EBPVD on two membranes, and then assembled into the FPI filter. The fabrication process is performed at the Stanford Nanofabrication Facility (SNF). Fabricated device is characterized at the UCSC and the SNF. Completed FPI filter showed the necessary filtering and tuning behavior with 30% transmittance peak and 2 µm FWHM. With expected performance of 100% peak and 0.15 µm FWHM, however, a need for significant performance improvement is observed. The cause of transmission peak degradation is attributed to the loss due to reflection and absorption of Si membrane and of passband broadening to the plate defeats of the DBR. The direction of study for further process improvement is suggested.

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