Advanced IR detector technology development at CEA/LETI

Abstract

The Infrared laboratory at LETI is collaborating with the French MoD and SOFADIR to develop and exploit cooled and uncooled infrared imaging devices. The technologies being developed include mercury cadmium telluride (MCT) and amorphous silicon microbolometers. Long linear and large two-dimensional array formats are being developed. Wavelengths of interest include 1.5–2.5, 3–5 and 8–14 μm. Devices have also been produced using Si:Ga to image in the 17–25 μm range for space observation. The primary material employed for cooled detectors is MCT. A hybrid structure is employed using indium flip-chip bonding to interconnect MCT detector chip to readout chip. Two-dimensional focal plane arrays of 640×480 have been demonstrated with reported NETDs of 15 mK. Two colors infrared focal plane arrays are being developed using molecular beam epitaxy (MBE) which is also used for developing MCT epitaxy on heterosubstrate. The uncooled detectors are aimed primarily at providing lower cost imaging systems and silicon resistive bolometer technology is being employed. The devices comprise of fine scale surface micromachined bridges designed to provide thermal isolation from the substrate. Arrays 256×64 and 320×240 have been built with state-of-the-art reported NETD. The approach being adopted uses amorphous silicon provides a process that is not only CMOS compatible but may be fabricated in standard silicon foundry.