Performance evaluation and calibration issues of large format infrared hybrid active pixel sensors used for ground- and space-based astronomy

Abstract

Instruments for large 10-m class telescopes increasingly require high sensitivity large format focal planes. The high spatial resolution achieved with adaptive optics combined with multiple integral field units feeding high resolution spectrographs are driving the pixel performance and require large detector formats. In the infrared spectral range, the array formats have arrived at 2K×2K pixels with both LPE and MBE grown HgCdTe on CdZnTe substrates. In the optical, fully depleted Si-PIN diodes of the same format are used. The light-sensitive diode arrays are hybridized to CMOS FET switched multiplexers such as the Hawaii-2RG array, which has recently been installed in one of the infrared instruments of the Very Large Telescope (VLT). Basic performance characteristics of the Hawaii-2RG arrays will be discussed such as the noise performance when a special technique of using reference pixels is employed. Larger focal planes are realized as mosaics of 2K×2K arrays. In order to increase the format of single arrays to 4K×4K and larger, the limited substrate sizes make it necessary to reduce the pixel size. However, with smaller pixels the coupling between pixels becomes a limiting factor for the detector point spread function. Fundamental calibration issues relevant to photon transfer techniques of modern CMOS active pixel sensors with special regard to the influence of interpixel coupling capacitances will be analyzed in detail. A novel technique will be presented to directly measure the point spread function generated by the capacitive coupling between adjacent pixels.