Valley Oakes/Cincinnati Electronics 256 x 256 InSb array evaluation

This array was developed for use in future NASA space infrared instrumentation and was funded by Craig McCreight at NASA Ames Research Center. The multiplexer was designed at Valley Oakes Semiconductor and fabricated using TRW's radiation hard 1.2 micron CMOS process as a baseline. Several processing variants were explored as this effort was directed toward the development of a low temperature (< 10 K) multiplexer. The 8 to 256 CMOS address decoders allow for random access and subarray readouts. Cincinnati Electronics developed the 2-D array of photovoltaic InSb mesa diodes. Much of this paper presents an evaluation of the bare multiplexer to determine the optimal operating point of the hybrid array. At 10 K, the detector reset node must be operated at a minimum of 2.2 V with respect to the reset on control signal (multiplexer ground) to overcome the threshold drop of the PMOS reset transistor. A linear regression of the multiplexer response at 10 K indicates that for linear gain response the reset voltage must be between 2.4 to 2.8 V. The standard deviation of the pedestal values gives an indication of multiplexer uniformity and is 32.0 mV. Charge pumping through the reset transistor adds bias to the detector. Within the operating range of the multiplexer, this charge pumping was measured to be 70 to 100 mV. The multiplexer operates continuously from 77 to 10 K with no anomalies due to threshold crossover in the CMOS gates.