Uncooled multimirror broad-band infrared microbolometers

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 flow 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 mum, a wide-band channel of 0.3 to 100 mum and a window channel from 8 to 12 pm each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 pm x 400 pm microbolometers in a 1 x 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 pin 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 10degrees V/W, detectivities above 10(8) cm Hz(1/2)/W, noise equivalent power less than 4 x 10(-10)W/Hz(1/2) and thermal time constant less than 15 ms.