Low Helium Permeation Cells for Atomic Microsystems Technology
Argyrios Dellis, Shah Vishal, Elizabeth A. Donley, Svenja A. Knappe, John E. Kitching
The miniaturization of instruments and sensors based on laser-cooled atoms is hindered by the large pumps needed to maintain the vacuum requirements. A significant source of vacuum contamination is the permeation of gases through the walls of the chamber. Aluminosilicate glass (ASG) is a material with a permeation rate many orders of magnitude lower than borosilicate glass, which is commonly used for cell fabrication. We have identified a suitable source of ASG that is fabricated in wafer form and can be anodically bonded to silicon. We have fabricated chip-scale alkali vapor cells using this glass for the windows and we have measured the helium permeation rate using the pressure shift of the hyperfine clock transition. The permeation rate for the specific type of glass is at least three orders of magnitude lower than that of borosilicate glass at room temperature.