Modeling interconnects for thermoelectrically cooled infrared detectors

We present a circuit and electromagnetic (EM) co-simulation approach to modeling interconnects of an infrared photodetector chip mounted on top of a thermoelectric cooler and cased in the TO-8 detector housing. Such models are needed to design high-speed circuitry for detector modules capable of acquiring pulses of duration in nano- and picosecond range. With the EM simulation, we establish an equivalent circuit of the interconnects and then apply it to fit differential-mode reflection coefficients of interconnects of specially prepared detector samples measured in a novel test fixture with a vector network analyzer. In this way, we determine parameters of the equivalent circuit for three types of thermoelectric coolers of different height. We verify our approach by comparing the modeled and measured reflection coefficients of different interconnects.