Source-Coupled HgCdTe Staring Hybrid Focal Planes For Tactical Applications

AbstractStaring infrared focal plane arrays with epitaxial HgCdTe photovoltaic detectors coupled to surface channel CCD multiplexers have been fabricated and characterized. A source-coupled input circuit with background suppression is utilized. The HgCdTe backside- illuminated detector arrays have bandgaps suitable for operation in either the 3 - 5 or 8 - 12 ym region. Performance characterization of the multiplexer will be given at cryo­ genic temperatures. Charge transfer efficiency, subthreshold transconductance, threshold voltage temperature dependence, and 1/f noise measurements will be presented. These mea­ surements will be compared with ideal models. Characteristics of the hybrid focal plane have been measured in a wide variety of backgrounds. Data will be presented on the noise characteristics, detectivity and noise equivalent temperature difference in backgrounds temperatures suitable for passive thermal imaging.I. IntroductionThe demand for high performance second generation thermal imaging systems has stimulated the development of focal plane arrays with a large number of detectors interfaced with charge transfer devices. There are basically two types of infrared focal planes, monolithic and hybrid. For monolithic focal planes, the multiplexer is fabricated as an integral part of the structure. For hybrid focal planes, photodetector arrays and the silicon CCD multiplexer are two separate entities joined together by using an array bonding technology. In this paper we report the characterization of one type hybrid focal plane using backside-illuminated HgCdTe photovoltaic detectors coupled with a silicon CCD multiplexer. The emphasis will be on its performance in a high background flux tactical environment. In such a structure, as shown in Figure 1, the detector senses incomingincoming radiation, while the multiplexer is used for both low noise integration and read- SC8011208 out of the signal. In Section II, the HgCdTe photodetector array is briefly discussed, while the operation and characterization of the CCD multiplexer are described in Sec­ tion III. Section IV deals with the mechani­ cal interface between the detector array and the multiplexer. Finally, in Section V we present a detailed characterization of the hybrid focal plane including noise, D* and NEAT measurements. Focal planes operating both in the 3 - 5 ym and 8 - 12 ym regions will be discussed.