Miniaturized Pumps and Gauges for Ultra-High Vacuum Microsystems

vacuum gauge;vacuum pump;electron trap;Electrical Engineering;Engineering;Electrical Engineering

Deng, ShiyangKushner, Mark ;

University of Michigan

关键词: vacuum gauge;    vacuum pump;    electron trap;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/140796/kevindsy_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

For devices such as chip-scale atomic clocks (CSACs) and capacitance diaphragm gauges (CDGs) that require compact vacuum environments at sub-µTorr or even nTorr vacuum levels, the stability of the vacuum is generally of great importance.Miniaturized pumps and gauges can play critical roles in actively maintaining and monitoring chip-scale vacuum environments.Toward this end, this thesis describes two types of elements: (i) miniaturized radio frequency (RF) electron traps for magnet-less ion pumps, and (ii) miniaturized cold cathode gauges to measure vacuum levels.In traditional ion pumps, electrons are confined by crossed electric and magnetic fields in a Penning electron trap in order to extend electron lifetime and promote ionizing electron-gas collisions.However, CSACs are sensitive to magnetic fields.This thesis describes a magnet-less RF electron trap to replace the Penning electron trap for CSAC applications.The RF electron trap was investigated in two generations.The first-generation formed a 0.7 cm3 electron active volume.An RF signal of various power levels and at 143.6 MHz was applied across two RF electrodes spaced 0.7 cm apart to trap electrons that were supplied by an electron gun.It was shown experimentally that the steady state electrode potentials (SSEPs) on electrodes near the trap became more negative after applying certain RF power levels, which indicated higher electron density within the trap.The measured trends aligned well with the modeled trends.The electron density within the trap was estimated to be 3 x 105 cm-3, which was ~1000x the electron density in the electron beam as it exited the electron gun.The second-generation RF electron trap was refined in structure to have 10x finer perforated RF electrodes, a higher trap-to-device volume ratio, simplified electrode composition and RF characteristics, and a tunable operating frequency.The experimental results showed that the electron density was 2.24 x 106 cm-3 in the center of the RF electron trap when the trap was operated at 96.9 MHz with a transmitted RF power of 0.273 W.Both RF electron traps represent successful demonstrations of compact new structures for trapping electrons without using a magnetic field.Miniaturized vacuum gauges allow monitoring of pressure levels in compact systems without introducing significant performance-degrading dead volume.This thesis describes new designs for miniature cold cathode gauges (CCGs).Seven preliminary CCG designs with an internal volume of less than 1 cm3 were developed.Four of these preliminary CCG designs were shown via analysis to be capable of spiraling electrons with a direct current (DC) operating voltage lower than 1000 V.Four CCG designs were further refined to analytically demonstrate better electron spiraling capability while also fulfilling manufacturability requirements.A magnetron design (Design M.S) was fabricated with three-dimensional (3D) printing techniques for performance characterization.The Design M.S could start at a pressure as low as 10.5 µTorr when the power supply VS to the cathode was biased at –750 V, and the gauge current was repeatable from 10-3 Torr to 10-5 Torr at various VS from –750 V to –3000 V.The estimated average magnetic flux density was 0.2 T in Design M.S.The miniaturized CCGs are at least 10x smaller than commercially available CCGs, e.g., the MKS Series 903 inverted magnetron transducer, which has an internal volume of 15 cm3.