Hybrid focal plane arrays for infrared imaging devices

Abstract

For high-performance thermal imaging systems in the 8-12 micron atmospheric window, hybrid two-dimensional detector arrays are the most promising of the presently developed techniques. These arrays use infrared photovoltaic detectors coupled to a silicon readout circuit. This paper gives some new experimental results obtained with arrays of Pb0.80Sn0.20Te detectors (10.6µm cutoff wavelength) coupled to a silicon CCD. For electrical coupling the direct injection mode is used, in which the photocurrent from each detector is injected into the CCD through an input diffusion. The signal efficiency is measured and the noise sources of the CCD readout are determined : detector noise, coupling noise and transfer noise in the CCD channel. The performances of this readout and its main limitations are analyzed. Experimental results are also given for a hybrid mosaic of 10 × 10 Pb0.80Sn0.20Te infrared detectors on a silicon CCD readout circuit. For this small staring array, batch technology is used to obtain an "island" structure that is compatible with the mismatch of the thermal-expansion coefficients of lead salt and silicon. The effects of threshold voltage dispersion and of the transconductance figure of the CCD are discussed in relation to the characteristics of the detectors. Signal and noise homogeneities measured on the array are also discussed.