A monolithic polyimide micro cryogenic cooler

In this paper, we present the fabrication and testing of a monolithic polymer Joule-Thomson (J-T) micro cryogenic cooler (MCC) cold stage. The MCC cold stages are fabricated monolithically on a wafer all of polyimide. The fabrication is based on surface micro-machining technology using electroplated copper as the sacrificial layers and polyimide as the structural material. One of the techniques enabling this novel approach is the development of the wafer-level 3-D interconnect for making high pressure, e.g. 10 atm polymer fluid micro channels. To evaluate the performance of the MCC, a five-component fluid mixture designed for cooling from 300 K to 200 K was used as a refrigerant. The cold tip was able to reach to about 190 K under a refrigerant pressure ratio of only 5.5:1.1 bar. The heat-lift at 200 K was measured to be 5.2 mW.