Wafer scale fabrication of highly integrated rubidium vapor cells

This paper reports on wafer scale fabrication of MEMS rubidium (Rb) vapor cells used for spectroscopic measurements in miniaturized atomic clocks. The cell filling process is based on pipetting minute amounts of dissolved rubidium azide (RbN₃) into cavities etched in a silicon wafer, hermetic sealing of the cavities by anodic bonding of glass caps, and in situ UV decomposition of the RbN₃ into Rb and N₂. All relevant elements required for operation such as resistive heaters, temperature sensors, and coils are integrated onto the vapor cell using planar technology. Experiments showed short term frequency stability below 10^-10 at 1 second integration time.