Thermoelectric infrared detectors with improved mechanical stability for the Composite Infrared Spectrometer (CIRS) far infrared focal plane

摘要

The Composite InfraRed Spectrometer (CIRS) instrument aboard the Cassini spacecraft en route to Saturn is a cryogenic spectrometer with far-infrared (FIR) and mid-infrared (MIR) channels. The CIRS FIR focal plane, which covers the spectral range of 10 - 600 cm↑(-1), consists of focusing optics and an output polarizer/analyzer that splits the output radiation according to polarization. The reflected and transmitted components are focused by concentrating cones onto thermoelectric detectors. These thermoelectric detectors consist of a gold black absorber on top of a gold foil that is welded to a thermoelement consisting of two semiconductor pyramids. After the detectors were integrated into the focal plane assembly and the CIRS instrument, the detectors proved to be extremely susceptible to two environmental survivability conditions: acoustics and airflow. Several changes were investigated to improve the integrity of the detectors including detector airflow geometry, structural changes to the detectors, and more intensive screening methods. The geometry of the air paths near the sensing elements was modified. Two structural modifications were implemented to improve the stability of the sensing elements. These were changes in the geometry of the thermoelectric pyramids by ion milling, and a change in the gold foil thickness. New screening methods, centrifuge and modulated force testing, were developed to select the most rugged detectors. Although several methods gave significant improvements to the detector's stability, the modification that allowed the detectors to meet the environmental survivability requirements was the change in the geometry of the air paths near the sensing elements.