Performance of 320x240 uncooled bolometer-type infrared focal plane arrays

Abstract

The performance of a 320 x 240 bolometer-type uncooled infrared (IR) Focal Plane Array (FPA) is described. Vanadium oxide thin film is adopted for the bolometer material, having a sheet resistance of approximately 10 kohms/square. It is patterned such that the bolometer resistance is by a factor of 10 larger than the sheet resistance. On-chip readout integrated circuit (ROIC) is designed to reduce signal drift, extend dynamic range for object temperature and extend ambient temperature range in which operates non-uniformity correction is carried out with about 1/10 fewer frequency than the former ROIC.The 320 x 240 FPA consists of pixels sensitive to IR radiation and optical black (OB) pixels covered with plate which shuts out IR radiation. Drift is reduced by current mirror circuit, using the OB pixels and digital compensation circuit based on voltage change of OB pixels resulting from change in operation temperature. Both the dynamic range and the ambient temperature range are extended by decreasing integration gain and developing low-noise, low-power and large swing operational amplifier(OP-AMP). Since decrease in integration gain degrades noise equivalent temperature difference (NETD), bias voltage for bolometer is increased by factor of 2 and bandwidth is reduced by route half. Finally, IR image was obtained with prototype camera and NETD value was found to be smaller than 0.1K for F/1 optics at 60Hz frame rate and thermal time constant was measured to be 12 msec.