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
This Brief includes a Technical Support Package (TSP).
Rapid Infrared Pixel Grating Response Testbed
(reference NPO47823) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the Rapid Infrared Pixel Grating Response Testbed (NPO-47823). It addresses the challenges associated with the fabrication and testing of custom infrared arrays, particularly Quantum Well Infrared Photodetectors (QWIPs), which are essential for various NASA and Department of Defense (DoD) projects, including the next Landsat mission.
The primary focus of the testbed is to provide a low-cost, efficient method for verifying the performance of large area infrared arrays before committing to full-scale fabrication. The testbed utilizes a reusable maskset that operates across a wavelength range of 3-13 micrometers. This approach significantly reduces the costs and resources required for testing new detector array concepts, as it only necessitates a single device wafer and an inexpensive 320x256 read-out integrated circuit.
The document emphasizes the limitations of standard QWIP arrays, particularly their low quantum efficiency (QE). Despite this drawback, QWIPs are favored for their uniformity and ability to be manufactured into large format arrays. The development of a fast-turnaround, reliable QWIP testbed is expected to enhance JPL's capabilities in technology insertion for upcoming missions.
Figures included in the document illustrate the performance of various grating designs and their spectral responses, showcasing how the testbed can identify the best-performing configurations for specific applications. The results from the testbed allow for the optimization of array parameters, addressing uncertainties related to cavity effects and array thinning, which are critical in new array designs.
The document also acknowledges the contributions of various team members involved in the project, including those responsible for grating response calculations, detector fabrication, and lithographic mask design. It highlights the collaborative effort within JPL to advance infrared technology for aerospace applications.
Overall, the Technical Support Package outlines a significant advancement in infrared detector testing, providing a framework that could lead to improved performance and reliability in future space missions, while also addressing budgetary constraints faced by research and development projects.
