Characterization of a two-stage 30 K Joule-Thomson microcooler

Micromachined cryocoolers are attractive tools for cooling electronic chips and devices to cryogenic temperatures. A two-stage 30 K microcooler operating with nitrogen and hydrogen gas is fabricated using micromachining technology. The nitrogen and hydrogen stages cool down to about 94 and 30 K, respectively, using Joule-Thomson expansion in a restriction with a height of 1.10 mu m. The nitrogen stage is typically operated between 1.1 bar at the low-pressure side and 85.1 bar at the high-pressure side. The hydrogen stage has a low pressure of 5.7 bar, whereas the high pressure is varied between 45.5 and 60.4 bar. In changing the pressure settings, the cooling power can more or less be exchanged between the two stages. These typically range from 21 to 84 mW at 95 K at the nitrogen stage, corresponding to 30 to 5 mW at 31-32 K at the hydrogen stage. This paper discusses the characterization of this two-stage microcooler. Experimental results on cool down and cooling power are compared to dynamic modeling predictions.