Micro-fabricated vapor cells with sealed Rb atoms by distillation at wafer level and two-step bonding for miniature atomic clocks

This paper proposes a new method to fabricate and evaluate Rb vapor cells sealed by two-step bonding for miniature atomic clocks. The proposed method achieves miniaturization and long-term frequency stability by the wafer-level process. First, the vapor cells are fabricated to seal only Rb atoms in vacuum to confirm the absence of residual gases. Second, the vapor cell is fabricated to seal with buffer gases to confirm the stability. The Allan deviation at an averaging time of 3000 s is 1.7 × 10⁻¹¹. These results show that the proposed method has improved long-term stability compared to the vapor cell fabricated by the conventional method that uses an alkali-atom dispenser.