Device level vacuum packaged micromachined infrared detectors on flexible substrates

This paper presents progress made in making device-level vacuum-packaged microbolometers as infrared detectors on flexible substrates. Polyimide PI5878G serves as the flexible substrate and semiconducting yttrium barium copper oxide (YBCO) is used as the bolometric material. Finite element analysis is used to design a vacuum cavity housing a microbolometer. Suitable materials are selected for the microcavity fabrication based on results of the computer simulations. During fabrication, sacrificial polyimide around the detector facilitates the formation of a vacuum microcavity with an optical window. Micromachining is carried out through trenches in the microcavity wall. After isolating the microbolometer from the ambient, the trenches are sealed shut by sputtering in vacuum. The fabricated devices are characterized for responsivity and detectivity. At a bias voltage of 10 V, 40-40mu m² devices exhibited a current responsivity of 6.13 timesl0^-5 A/W to a broad-band infrared radiation modulated at 5 Hz. A maximum detectivity of 1.76times10⁵ cm-Hz^1/2/W was measured. A relatively low thermal conductance of 3.36times10^-6 W/K was measured implying good thermal isolation of the bolometers and therefore an intact vacuum cavity