We are currently developing a magnesium diboride (MgB2) detector array for use
in future space-based spectrometers. This 2-D array is intended for use in high-resolution
investigations of the outer planets and their icy moons. The state of the array processing,
the current pixel design as well as signal-to-noise considerations is briefly discussed.
Expected pixel sensitivities and comparison to current state-of-the-art infrared (IR)
detectors will be briefly discussed.
Noise was studied in an MgB2 thin film grown on a SiN substrate, with a superconducting transition
temperature, Tc, near 39K. At the mid-point of the transition and at 10Hz a noise spectral density
Sv = 0.34nVHz1/2 was measured. The temperature noise, Kn , of the MgB2 film at different frequencies is
compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used
currently in transition-edge devices. Kn values predict that 2-D arrays of high performance infrared devices
can be developed using MgB2.
KEYWORDS: Thin films, Superconductors, Bolometers, Silicon, Infrared detectors, Resistance, Temperature metrology, Signal to noise ratio, Sensors, Silicon films
An MgB2 thin film was grown on a SiN-Si substrate, with a superconducting transition temperature, Tc, near 39K. At the mid-point of the transition (T= 38.24K) and at 10Hz a noise spectral density SV = 0.34nV/ √Hz was measured. The temperature noise, Kn, of the MgB2 film at different frequencies is compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used currently in transition-edge bolometers. Κn values predict that high performance far-IR thermal detectors (i.e bolometers) can be developed using MgB2 as a thermistor.
The performance of a high Tc (~90 K) transition-edge superconducting (TES) bolometer on a monolithic sapphire membrane is presented and discussed. It is compared to the performance of a previous TES bolometer on non-monolithic sapphire substrate. The development and optimization of monolithic sapphire membranes is critical for the fabrication of 1 and 2-D arrays of TES bolometers. Moderately cooled and optimized TES bolometers are expected to be the replacements of choice for thermopiles and other room temperature thermal sensors on far IR instruments on future planetary missions.
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 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.
Virgil Kunde, Peter Ade, Richard Barney, D. Bergman, Jean-Francois Bonnal, R. Borelli, David Boyd, John Brasunas, Gregory Brown, Simon Calcutt, F. Carroll, R. Courtin, Jacky Cretolle, Julie Crooke, Martin Davis, S. Edberg, Rainer Fettig, M. Flasar, David Glenar, S. Graham, John Hagopian, Claef Hakun, Patricia Hayes, L. Herath, Linda Spilker, Donald Jennings, Gabriel Karpati, C. Kellebenz, Brook Lakew, J. Lindsay, J. Lohr, James Lyons, Robert Martineau, Anthony Martino, Mack Matsumura, J. McCloskey, T. Melak, Guy Michel, Armando Morrell, C. Mosier, LaTunia Pack, M. Plants, D. Robinson, Louis Rodriguez, Paul Romani, Bill Schaefer, Stephen Schmidt, Carlos Trujillo, Tim Vellacott, K. Wagner, D. Yun
The composite infrared spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. CIRS will retrieve vertical profiles of temperature and gas composition for the atmospheres of Titan and Saturn, from deep in their tropospheres to high in their stratospheres. CIRS will also retrieve information on the thermal properties and composition of Saturn's rings and Saturnian satellites. CIRS consists of a pair of Fourier Transform Spectrometers (FTSs) which together cover the spectral range from 10-1400 cm-1 with a spectral resolution up to 0.5 cm-1. The two interferometers share a 50 cm beryllium Cassegrain telescope. The far-infrared FTS is a polarizing interferometer covering the 10-600 cm-1 range with a pair of thermopile detectors, and a 3.9 mrad field of view. The mid-infrared FTS is a conventional Michelson interferometer covering 200-1400 cm-1 in two spectral bandpasses: 600-1100 cm- 1100-1400 cm(superscript -1 with a 1 by 10 photovoltaic HgCdTe array. Each pixel of the arrays has an approximate 0.3 mrad field of view. The HgCdTe arrays are cooled to approximately 80K with a passive radiative cooler.
A simple polishing technique was developed for thinning the LaAlO3 substrates for high-quality Tc bolometer films, and thus reducing their heat capacity. A 150-ms bolometer was made on a LaAlO3 substrate with a 5-Hz D* value of 1.5 x 10 exp 8. It is shown that passive temperature stabilization is adequate for operation at the transition. There remained excess noise at the transition, but this noise appears to be of nonbolometric origin.
Past and present planetary exploration is briefly reviewed, and the planned 1996 Cassini mission to Saturn and Titan is examined. The CIRS experiment aboard Cassini, which will retrieve information on the atmospheres of Titan and Saturn, is discussed. Ongoing efforts to build a high-sensitivity, high-Tc bolometer that would greatly improve detection in Titan's atmosphere are addressed.
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