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A new generation of microbolometers were designed, fabricated and tested for the NASA CERES (Clouds and the Earth's Radiant Energy System) instrument to measure the radiation flux at the Earth's surface and the radiant energy now within the atmosphere. These detectors are designed to measure the earth radiances in three spectral channels consisting of a short wave channel of 0.3 to 5 μm, a wide-band channel of 0.3 to 100 μm and a window channel from 8 to 12 μm each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 μm x 400 mm microbolometers in a 1 × 4 array of detectors in each of the three wavelength bands, thus yielding a total of 12 channels. The microbolometers were fabricated by radio frequency (RF) magnetron sputtering at ambient temperature, using polyimide sacrificial layers and standard micromachining techniques. A semiconducting YBaCuO thermometer was employed. A double micromirror structure with multiple resonance cavities was designed to achieve a relatively uniform absorption from 0.3 to 100 μm wavelength. Surface micromachining techniques in conjunction with a polyimide sacrificial layer were utilized to create a gap underneath the detector and the Si3N4 bridge layer. The temperature coefficient of resistance was measured to be -2.8%/K. The voltage responsivities were over 103 V/W, detectivities above 108 cm Hz12//W, noise equivalent power less than 4 × 10-10W/Hz12/ and thermal time constant less than 15 ms.
Date of Publication: Oct 2002