Dispensing and hermetic sealing Rb in a miniature reference cell for integrated atomic clocks

An innovative method for filling and sealing the reference cell for a Rubidium (Rb) integrated atomic clock is presented. We used a simple, low-temperature solder sealing technique for producing mini-cells of the size of 12 x 10 x 2 mm, suitable for Rb miniature atomic clocks. The cell is made by two glass slides acting as the top and bottom walls, joined by a solder ring acting as the sidewall. In the frame of this research, we also developed a safe and convenient method for easily handling Rb: the alkali metal is stored inside a ‘pool’ of dodecane, which protects it from oxidation. Pure liquid Rb is then dispensed inside the cell using a glass micropipette; finally, the cell is heated in vacuum, in order to realize the sealing. The hermeticity achieved by the cell was tested by sealing N2O gas and monitoring its pressure through absorbance measurements using FTIR spectroscopy. The presented method allows easy handling and long-term storage of Rb, and finally led to the production of functional hermetic mini-cells. Keywords: Rubidium, atomic clock, reference cell, solder.