Pumping silicon-based cavities to ultra-high vacuum (UHV) pressure levels is challenging using microfabricated pumps. Among the various technologies that achieve UHV at macroscale, ion-sorption pumps are currently the most promising for miniaturization because of the improved surface to volume ratio. Although they reach and maintain 7E-7 Torr, miniature ion-pumps that have been published use permanent magnets to trap electrons into 100s meter long mean free path to improve the probability of ionizing gas particles at the UHV levels. However, these magnets are cumbersome, bulky and heavy and can also interfere with sensitive circuits and sensors. This problem is compounded by the lack of absolute pressure sensors that do not require a calibration curve to measure the internal pressure. Drift due to real or virtual leaks after bonding can only be accurately measured using both a MEMS Pirani pressure gauge and a cold atom pressure gauge. The former can measure pressure variations down to ~1E-6 Torr while the latter, below 1E-7 Torr, such that the fusion of both technologies benefit from an ultra-wide dynamic measurement range. This proposal will develop a microfabricated ion-sorption ring-Orbitron pump based on previous theoretical work. This device uses a ring-shaped anode to electrostatically trap electrons and increase their mean free path to favor gas ionization without using magnets. The ionized gas particles, including N2 and other noble gas, are then trapped into the getter-coated sidewalls. This pump will be accompanied by a gas discharge pump that can operate across a broader pressure range. Neither the ring-Orbitron nor the gas-discharge pump require magnets nor moving parts to function; instead, they rely on electrical biasing which can be easily achieved without complex electronics. The proposed device also includes a cold atom cavity to measure pressure in the target UHV range as well as a graphite specimen to avoid loading the pump with Rubidium gas. The proposed device will be fabricated in phase II using silicon microfabrication technology, such that it will be highly compatible with silicon-based cavities.
Benefit: Benefits or technical enhancements include: 1. UHV microfabricated noble gas pump 2. High dynamic range pressure gauges 3. Low SWaP-C, MEMS fabricated pump
Keywords: MEMS ion pump, MEMS ion pump, Utra-high vacuum, Microfabrication
