In this paper, new results are presented in the development of hybrid infrared focal-plane arrays. Attention is focused on hybrid focal-plane arrays using backside-illuminated InAsSb and HgCdTe photovoltaic detectors which are source-coupled into a charge-coupled device (CCD) multiplexer. Background suppression capabilities of the input circuit, charge skimming and partitioning, are experimentally demonstrated. Data on the uniformity and temperature dependence of the input MOSFET threshold voltage are presented. The temperature dependence of the threshold voltage agrees well with theoretically calculated values. Several aspects of the noise problems associated with the hybrid infrared focal-plane arrays are discussed. Noise of a source-coupled input circuit with a feedback amplifier is analyzed and it is shown that although two new noise sources are added, the circuit can operate with less noise than the simple source-coupled input circuit. To further understand focal-plane operation, a noise performance model has been constructed which gives excellent agreement with experimental data. Finally, the performance of hybrid focal-plane arrays is discussed.

Hybrid infrared focal-plane arrays

Apparatus for compressing an electrical input signal so as to accommodate a large dynamic range of the signal without loss of information represented by the signal, the apparatus comprising first, second and third (12, 14, 16) storage means for receiving the input signal; a gate (18) coupled between the second and third storage means so as to selectively inhibit the transfer of the signal from the second storage means to the third storage means; means (24. 28) coupling the third storage means to a receiving device; and means, including the gate (18), for enabling substantially all of the signal to be received by the receiving device for low levels of the signal, and for enabling only a portion of the signal to be received by the receiving device for other than low levels of the signal.

Electric signal compressing apparatus

Current research on infrared hybrid focal planes is directed toward devices in which detection occurs in a p-n junction formed in an intrinsic narrow energy bandgap semiconductor, and signal processing is accomplished in a Si CCD multiplexer which is electrically interfaced to the detector array. A hybrid array such as this, where the detector format is a 32 × 32 matrix, has been fabricated. The active material is backside-illuminated InAsSb which has been planar processed and fully passivated. The cutoff wavelength is 4.0 µm at the operating temperature of 77K. The CCD is four phase with a two level polysilicon gate structure. The signal input is via direct injection with an option for dc suppression. Operation of the focal plane in a staring mode that uses dc suppression is discussed. Data derived from the video output is presented; this includes responsivity and detectivity. Off focal plane non-uniformity compensation is also discussed. Displays of thermal images utilizing processed data from the hybrid focal plane array will be shown.

F.A. Cox

Papers

InAsSb hybrid imager evaluation