Microbolometers on a flexible substrate for infrared detection

Uncooled semiconducting YBaCuO infrared microbolometers have been fabricated on a flexible polyimide substrate formed by spin-coating a silicon wafer with a release layer. The wafer was used as a carrier for the flexible substrate during fabrication. The finished microbolometers on the flexible substrate showed a temperature coefficient of resistance (TCR) TCR =(1/R)(dR/dT) of -3.03% K^-1, at room temperature, which is comparable to the TCR values observed for semiconducting YBaCuO microbolometers fabricated directly on Si. In order to provide protection and better mechanical integrity, some of the devices were encapsulated. The microbolometers attained a responsivity and detectivity as high as 3.5×10³ V/W and 1×10⁷ cm·Hz¹2//W, respectively, at 2.88 μA of current bias. The responsivity and detectivity of the encapsulated microbolometers, on the other hand, were 1.6×10³ V/W and 4.9×10⁶ cm·Hz¹2//W, respectively at 1 μA of current bias. Spin-coated liquid polyimide solved two major problems previously encountered with the solid polyimide sheets when used as a flexible substrate. First, flatness of the flexible substrate was maintained with no air bubbles. Second, the thermal expansion of the flexible substrate during the fabrication process due to thermal cycling was minimal. All measurements reported in this paper, were taken prior to releasing the flexible substrate from the Si wafer containing the finished microbolometers.