Fabrication of wafer-level spherical Rb vapor cells for miniaturized atomic clocks by a chemical foaming process

In this paper, a novel low cost process for preparing wafer-level spherical Rb vapor cell for miniature atomic clocks is presented. The process is studied experimentally, which consists of the following steps: 1) small cavities A (for reactants) interconnected with large cavities B (working chamber) and channels are wet etched simultaneously on one side of a silicon wafer; 2) foaming agents and chemicals for preparing Rb with precisely controlled volume are distributed into cavities A; 3) bonding a Pyrex 7740 glass wafer to seal the cavities A, the cavities B and the channels under vacuum; 4) heating the bonded wafers in atmosphere to the softening point of the glass and the gas released by the foaming agents contained in cavities A will blow the glass covering on cavities B into spherical shells; 5) Rb flows into cavities B through channels in the form of vapor. The chemicals for preparing Rb is characterized by EDX before and after reaction. Results showed that the wafer-level Rb vapor cell is fabricated successfully. Results also indicate that Rb is formed after the reaction.