A Monolithic Polyimide Micro Cryogenic Cooler: Design, Fabrication, and Test

In this paper, we present the design, fabrication, and testing of a monolithic polymer Joule-Thomson microcryogenic cooler (MCC) cold stage. The MCC cold stages were fabricated monolithically on a wafer out of polyimide. The fabrication was based on surface micromachining technologies using electroplated copper as the sacrificial layers and polyimide as the structural material. The process consisted of multilayers of metallization, coating of polyimide, and the patterning on each layer. One of the key techniques enabling this monolithic approach was the development of the wafer-level 3-D interconnect for making high pressure (e.g., 10 atm) polymer fluid microchannels. To evaluate the performance of the MCC, a five-component fluid mixture designed for cooling from 300 to 200 K was used as a refrigerant. The cold tip reached 190 K under a refrigerant pressure ratio of 6.2:1.1 bar. The heat-lift at 200 K was measured to be 5.2 mW.