High sensitivity uncooled microcantilever infrared imaging arrays

The design and operation of an advanced bimorph microcantilever based infrared imaging detector are presented. This technology has the potential to achieve very high sensitivities due to its inherent high responsivity and low noise sensor and detection electronics. The sensor array is composed of bimaterial, thermally sensitive microcantilever structures that are the moving elements of variable plate capacitors. The heat sensing microcantilever structures are integrated with CMOS control and amplification electronics to produce a low cost imager that is compatible with standard silicon IC foundry processing, and materials. The bimorph sensor structure is fabricated using low thermal expansion, high thermal isolation silicon dioxide and oxynitride materials, and a high thermal expansion aluminum alloy bimetal. The microcantilever paddle is designed to move away from the substrate at elevated imaging temperatures, leading to large modeled sensor dynamic ranges (similar to 16 bits). A temperature coefficient of capacitance, Delta C/C, (equivalent to TCR for n-ticrobolometers) above 30% has been modeled and measured for these structures, leading to modeled NEDT < 20 mK and thermal time constants in the 5-10 msec range giving a figure-of-merit [1] NEDT.Tau = 100-200 mK.msec. The development efforts to date have focused on the fabrication of 160x120 pixel arrays with 50 micron pitch pixels. Results from detailed thermo-electro-opto-mechanical modeling of the operation of these sensors are compared with experimental measurements from various test and integrated sensor structures and arrays.