Self-supporting uncooled infrared microbolometers with low-thermal mass

A new micromachined microbolometer array structure is presented that utiliz es a self-supporting semiconducting yttrium barium copper oxide (Y-Ba-Cu-O) thin film thermometer. The Y-Ba-Cu-O thermometer is held above the substra te only by the electrode arms without the need of any underlying supporting membrane. This represents a significant improvement in the state-of-the-ar t for microbolometers by eliminating the thermal mass associated with the s upporting membrane. The reduced thermal mass permits lowering the thermal c onductance to the substrate to obtain increased responsivity or having a sh orter thermal time constant to allow for higher frame rate camera. The simp le structure does not suffer from warping problems associated with stress i mbalances in multilayer microbolometer structures that utilize a supporting membrane such as Si3N4. Devices were fabricated by growing Y-Ba-Cu-O films on a conventional polyimide sacrificial layer mesa. Subsequent etching of the sacrificial layer provides the air gap that thermally isolates the micr obolometer. Y-Ba-Cu-O possesses a relatively high temperature coefficient o f resistance of 3.1%/K at room temperature. The 400-mn-thick Y-Ba-Cu-O film exhibited absorptivity of about 30%. The responsivity and detectivity appr oached 10(4) V/W and 10(8) cm Hz(1/2)/W to filtered blackbody infrared (IR) radiation covering the 2.5 to 13.5 mum band. This extrapolates to noise eq uivalent temperature difference (NETD) less than 100 mK. The micromachining techniques employed are post-complementary metal-oxide-semiconductor (CMOS ) compatible, allowing for the fabrication of focal plane arrays for IR cam eras.