A test array has been developed to measure the response of pixel-integrated infrared gratings over a wavelength range from 3 to 13 μm for multiple grating geometries. This array allows for testing and for determining the performance of an infrared focal plane array camera before resources have been committed to the design and fabrication of the final array.

The 320×256 array of 25-μm test pixels comprises five types of grating geometries with theoretical peak response varying in 0.25-μm steps from 3 to 13 μm. The array has been designed to be hybridized to a FLIR-Indigo 9705 read out integrated circuit (ROIC). On the same lithographic mask as this array, large-area (200 μm) pixels have been designed with the same grating parameter sweep. Together the small and large area pixel comprise the rapid infrared pixel grating response testbed. This test- bed pattern is typically fabricated on one of JPL’s long wavelength infrared (LWIR) quantum well infrared photodetector (QWIP) wafers. The 320×256 detector array is then bonded to the FLIR/Indigo 320×256 ROIC, and used as the electronic backbone of the test-bed. The array is then thinned to replicate the characteristics of a standard deliverable camera array. Response of the test pixels is then measured and compared to the expected response. Shifts due to cavity and lithographic fidelity effects can be compensated for, and the final imaging array design can be made with confidence.

This work was done by Cory J. Hill, Jason M. Mumolo, and Daniel W. Wilson of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47823

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Rapid Infrared Pixel Grating Response Testbed

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This article first appeared in the February, 2014 issue of NASA Tech Briefs Magazine.

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