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It has recently been shown that bimaterial microcantilevers can be used as uncooled infrared detectors. Bimaterial microcantilevers deform as their temperature changes due to the absorption of infrared photons. Infrared imaging using uncooled cantilever arrays has already been achieved by a number of groups. In this paper, we examined the performance of microcantilevers as uncooled infrared detectors with optical readout. As in the case of other kinds of uncooled thermal infrared detectors, temperature fluctuation noise and background fluctuation noise are fundamental limits to the performance of microcantilever thermal detectors. Since microcantilevers are mechanical devices, thermo-mechanical noise will also influence their performance. We fabricated a SiN[sub x] microcantilever thermal detector with an Al layer in the bimaterial region. For the microcantilever geometry and materials used, the background fluctuation noise equivalent temperature difference, NETD[sub BF], calculated for f/1 optics and a 30 Hz frame rate was found to be 1.26 mK. The NETD[sub TF], limited by temperature fluctuation noise, was calculated to be 7.4 mK while the thermo-mechanical NETD[sub TM] was calculated to be 5.3 mK. The sum of all fundamental noise sources, including the intrinsic noise of the “optical lever” readout, results in a total NETD of 9.2 mK. Absence of the readout noise would improve this parameter by only 2%. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]