Microfabrication Of Alkali-metal Vapor Cells For Chip-scale Atomic Clock

The alkali metal vapor cell is the core component of the CPT atomic clock,has an important influence on the atomic clock.The processing technology combined with MEMS and anode bonding technology,can achieve mm³ cells and mass production.Due to the limitation of alkali metal filling technology,it is very necessary to realize high-hermeticity low-temperature anodic bonding.First,the cell structure,the processes including silicon hole forming,anode bonding and metal filling have been designed.The equipment has been introduced.Three methods for forming silicon holes have been tried.Laser drilling processed circular through holes with a diameter of 3mm on a 0.5/1mm thick silicon wafer.The chemical corrosion adopts KOH corrosion,The best corrosion condition is obtained by heating to 80℃in 30%KOH solution,which realizes square holes with the size in the range of 1.6mm-4mm on 0.5/1mm thick silicon wafers.The deep reactive ion etching method is used to realize the ideal dual-cell with narrow channels.The ANSYS software was used to simulate the bonding deformation at 300℃/1090N,which has a negligible effect on the bonding process.Change the bonding temperature from 200℃to 300℃at 800V/1090N.By measuring the bonding strength,gas leakage rates and peak current,bubbles on the substrate’s surface and cross-sectional electron microscope photos,concluded that samples all have great bonding effect.The bonding voltage is increased to obtain a better bonding effect.Finally achieved the bonding effect of 1.0×10^-13Pa·m³?s^-1 at 180℃/1200V/1090N.The filling part of alkali metal respectively tried the heating reaction of cesium chloride and calcium,cesium chromate and st101 to release alkali metals.A new type of paraffin sealing process is studied,which can theoretically achieve a more precise control of the size of the wax package,and can make reusable molds.The different silicon hole forming technologies,low-temperature anodic bonding technology,and alkali metal filling methods are helpful to achieve good cell hermeticity and high reliability of alkali metal vapor cell packaging.