Thermally isolated focal plane readout

Abstract

A focal plane array having an interconnect bump that has high thermal resistivity, and which may be used to interconnect the detector and readout of the array. The detector and readout each have separate heat sinks with separate temperature controls. The readout may thus be operated at a higher temperature than the detector. A high thermal resistance interconnect bump is employed to limit heat leakage from the readout to the detector to an acceptable level, and to enable a thermal gradient to be maintained simultaneously with a net savings in refrigerator power. The heat sink for the detector is made in such a way as to not obscure the active area of the detector, that is, it is annular in shape so as to surround the active area of the detector. The interconnect bump comprises a thermally insulating pedestal comprising a material such as polyimide, for example, with an over-the-edge metallization employed as an electrical contact. The pedestal employs perforating vias in order to increase the thermal resistance. Disposed on top of the pedestal is an indium bump which mates with a corresponding bump on the detector. A similar interconnect having a polyimide pedestal may also be provided on the detector to provide for even greater thermal resistance. The high thermal resistivity of the interconnect allows the detector and readout to operate at distinct optimal temperatures.