Pumping capacity and reliability of cryogenic micro-pump for micro-satellite applications

In micro-satellites, delicate instruments are compacted into a limited space. This raises concerns of active cooling and remote cooling. Silicon based micro-pump arrays are employed thanks to manufacturing simplicity, a small cryogen charge, etc, and keep the instruments within a narrow cryogenic temperature range. The pumping capacity and reliability of the micro-pump are critical in terms of heat balance calculation and lifetime evaluation. The pumping capacity is associated with the diaphragm deflection while the reliability is associated with stress and fatigue. Both of them heavily depend on the silicon diaphragm, one of the key components. This paper examines the pumping capacity and reliability of the micro-pump under cryogenic temperature for micro-satellite applications. In this work, differential pressure was used for the actuation of a single-crystal silicon diaphragm. Diaphragm deflection and stress distribution were achieved using interferometry and micro-Raman spectroscopy, respectively. As a result, smaller pumping capacity was derived under cryogenic temperature, compared to that under room temperature, indicating a stiffer material. From stress mapping, the edge centers were believed to be the most vulnerable to fracture, which was further validated by analyzing the fracture diaphragm. Moreover, a fatigue testing was conducted for 1.8 million cycles with no damage found, verifying silicon as a viable material for long time operation in a cryogenic environment.