Performance of 320 x 240 Uncooled IRFPA with SOI Diode Detectors

摘要

We reported a 320 x 240 uncooled IRFPA with 40 μm pitch having diode detectors fabricated on an SOI wafer. Since the fabrication process of the SOI diode detector is compatible with the silicon IC process, only a silicon IC fab is necessary for manufacture of the FPAs. This enables mass production of low cost uncooled FPAs. This paper focuses on the performance of the FPA. In the previous paper, we proposed a novel infrared absorbing structure which offers a very high fill factor. Although this structure exhibited a high infrared absorption because of interference absorbing components incorporated in the structure, large thermal capacitance was an issue. Thus we have improved the infrared absorbing structure in the newly developed FPA. The improved absorbing structure has been devised making use of reflection of metal interconnections including diode metal straps. A thermal time constant of 17 msec has been achieved without degrading the responsivity compared with the conventional absorbing structure. Nonuniformity of detector characteristics is much smaller than that of sputtered microbolometers. The nonuniformity of the detector voltage under bias current of 10 μA, which is a typical condition of the FPA, is less than 0.2% (sigma/mean) across an 8-inch SOI wafer. The output offset nonuniformity after on-chip amplification with a gain of 14 is less than 300 mV p-p without any offset correction. The uniformity of temperature coefficient is also good due to the excellent uniformity of the detector voltage. In order to achieve a low equivalent input noise, we have optimized an on-chip amplifier with a gate modulation circuit. Higher bias current of the detector is also effective in reducing the overall noise of the FPA because 1/f noise of the detector decreases with increase of the current. As a result, the NETD of the FPA is less than 0.12 K with ill optics.