Commentary: JWST near-infrared detector degradation— finding the problem, fixing the problem, and moving forward

Abstract

The James Webb Space Telescope (JWST) is the successor to the Hubble Space Telescope. JWST will be an infrared-optimized telescope, with an approximately 6.5 m diameter primary mirror, that is located at the Sun-Earth L2 Lagrange point. Three of JWST’s four science instruments use Teledyne HgCdTe HAWAII-2RG (H2RG) near infrared detector arrays. During 2010, the JWST Project noticed that a few of its 5 μm cutoff H2RG detectors were degrading during room temperature storage, and NASA chartered a “Detector Degradation Failure Review Board” (DD-FRB) to investigate. The DD-FRB determined that the root cause was a design flaw that allowed indium to interdiffuse with the gold contacts and migrate into the HgCdTe detector layer. Fortunately, Teledyne already had an improved design that eliminated this degradation mechanism. During early 2012, the improved H2RG design was qualified for flight and JWST began making additional H2RGs. In this article, we present the two public DD-FRB “Executive Summaries” that: (1) determined the root cause of the detector degradation and (2) defined tests to determine whether the existing detectors are qualified for flight. We supplement these with a brief introduction to H2RG detector arrays, some recent measurements showing that the performance of the improved design meets JWST requirements, and a discussion of how the JWST Project is using cryogenic storage to retard the degradation rate of the existing flight spare H2RGs.

The on-orbit performance of the Orbiting Carbon Observatory-2 (OCO-2) instrument and its radiometrically calibrated products

“…The rate of bad-pixel formation in all three FPAs has been much slower since the observatory was launched and the FPAs were cooled to their operating temperatures. This experience is consistent with the experience of the James Webb Space Telescope (JWST) Detector Degradation Failure Review Board (Rauscher et al, 2012), which documented rapid degradation of this class of HgCdTe FPAs at room temperature and much slower degradation at cryogenic temperatures.…”

Development of sensitive long-wave infrared detector arrays for passively cooled space missions

“…The 2012 LWIR detector arrays delivered by TIS also benefited from process improvements that were made after detector degradation was noticed by the JWST program. 20 The failure mode has been identified by TIS and has been fully eliminated through process modifications. The improved approach has already been implemented in most Teledyne FPA products for several years, with no reports of similar failures.…”

The integration and test program of the James Webb Space Telescope

“…Testing of prototype units with the revised design indicates that the root cause has been addressed successfully and that the new detectors will be appropriately robust. 12 Replacement detector assemblies incorporating the new focal plane arrays are not expected to be available for installation into the NIR SI's until 2014.…”