Short Wavelength 128 By 128 Focal Plane Arrays For Remote Sensing Applications

Short wavelength (1-2.5 μm) 128 by 128 focal plane arrays have been fabricated and demonstrated with high pixel yields and dark current limited performance. Smaller arrays (32 by 32 and 64 by 64) have already been used successfully in the Airborne Imaging Spectrometer (AIS) instrument in the United States, Australia, and Western Europe. Ground-track swath width is enhanced by the development of 128 by 128 arrays. The long-term goal is to develop a 150 by 1000 mosaicked focal plane for use in the High Resolution Imaging Spectrometer (HIRIS) instrument, a facility instrument on the Earth Observing System (Eos). This instrument will map the earth with from 5 to 10 nm spectral resolution and 30 m spatial resolution for flux levels of 1010 to 1012 ph/cm2-s with An f/3.8 optical system. The detector material is HgCdTe grown by liquid phase epitaxy on a sapphire substrate which yields high-performance uniform detectors. The detectors are ion implanted photodiodes with ZnS passivation. They are mated to a silicon multiplexer through indium columns to fabricate the hybrid. Operational pixel yields of greater than 99 percent have been obtained. Reliability tests on 128 by 128 hybrids show that the device is mechanically durable to more than 50 thermal cycles. The detector arrays have been characterized at temperatures of 80-150 K. Mean RoA values of 4 x 106 ohms-cm2 and leakage currents below 5 x 10-13 A have been measured at 150 K. The peak quantum efficiency at 2.4 μm is 80 percent. These results indicate that the detectors have sufficient performance for dark current limited operation at low scene albedos. The multiplexer is an EG&G Reticon FET switch imager with two output amplifiers. It is a standard visible imager that has been modified for indium column growth and detector substrate bias control. The internal circuitry has not been changed. The charge is integrated in the detector capacitance under reverse bias and then transferred through common video lines into odd and even bucket brigades and clocked out through the output amplifiers. The read noise of the multiplexer is 950 electrons, and the maximum readout rate is 10 MHz. The maximum charge storage capacity is 5 x 106 electrons.