Fabrication of micromachined devices on flexible substrates

This paper overviews the current state-of-the-art in electronics and MEMS devices on flexible substrates. the technical challenges ahead in the fabrication of electronic circuits and our work in progress on the development of infrared detectors on flexible substrates. A novel fabrication method has been developed for microbolometers on flexible polyimide substrates. Two methods are being employed. The first is to bond a Kapton sheet to a Si carrier wafer with an adhesive and the second is to spin a polyimide (Kapton-like) substrate film onto a Si wafer coated with a release layer. This research is the first known effort to build microsensors on a flexible substrate. Low temperature fabrication techniques are employed to minimize the thermal cycling of the polyimide substrate. In our preliminary work, microbolometers on flexible substrates displayed a temperature coefficient of resistance (TCR=(1/R)(dR/dT)) of -3.07%, at room temperature. The microbolometers achieved responsivity and detectivity as high as 6/spl times/10/sup 3/ V/W and 3/spl times/10/sup 7/ cm.Hz/sup 1/2//W, respectively, at 1.85 /spl mu/A of current bias. This detectivity is approximately 40% of the temperature fluctuation limit for these detectors. These results are comparable to the ones obtained with micromachined devices on silicon substrates.