Fabrication of adaptive microbolometers

In this paper, the fabrication of microbolometers with electronically controllable responsivity is presented. The first generation devices are built in a standard polysilicon-based micromachining process with HF etch-release and demonstrated with a responsivity that can be tuned over a factor of 50. The responsivity is controlled by applying a voltage between the microbolometer and the substrate. The resulting electrostatic force causes a small portion of the support beam to contact the substrate, which thermally shorts the device at that point. The thermal contact points are defined using curved support beams with residual-stress from a Cr/Au metallization. The lowest portion of the beams contacts the substrate, and the curvature protects the device from full "snap-down,μ which might induce stiction. The fabrication of the second generation microbolometers based on VO_x and silicon nitride materials with a polyimide etch-release is also described. The thermal contact points for these devices are defined by beam mechanics rather than by beam curvature induced by stress, and they actuate at 17 volts. The test array has a fill-factor of 91% for a pixel period of 140μm limited by our photolithography equipment.