Research On MEMS Fabrication Technology Applied To Chip-scale Alkali Metal Atomic Clock System

In recent years,with the development of electronic information technology,atomic clock,the core component of time and frequency system,has been widely used.It can serve as the clock source in navigation equipment such as micro-compact UAV,satellite timing navigation receiver,unmanned submarine aircraft,tactical missiles,etc.It can also be combined with gyroscope and accelerometer to play an important role in the Micro-PNT system..According to the needs of economic construction and national defense construction,this work exerts a study on the CSAC system based on MEMS process and CPT principle,which can meet the development trend of miniaturization,low power consumption and high accuracy.As the passive CPT atomic clock based on the CPT principle is no longer constrained by the microwave resonant cavity volume in the physical system composition,it can meet the trend of micro-miniaturization and build a firm foundation for further miniaturization of CSAC.The paper reviews the research status of atomic clocks at home and abroad,briefly introduces the Rb /Cs alkali metal energy level theory and the interaction between light and atoms;introduces the CPT principle and the EIT phenomenon in detail;analyzes the parameters affecting the clock stability,and determines the appropriate gas ratio components through simulation analysis;introduces the overall architecture of the CPT chip-level atomic clock system,which mainly includes the physical system part,the optical system part and the peripheral circuit part,and the peripheral circuit part in detail.The MEMS alkali metal vapor cell is the "heart" of the CPT atomic clock,and is also the core component of the optical system.Therefore,the performance of the vapor cell has a direct impact on the atomic clock.The substrate materials of this paper are Si and BF33 glass,which are widely used in MEMS process.The structure is designed as a "double-cavity" glass-Si-glass sandwich structure,which combines photolysis and chemical reaction method to avoid the introduction of impurities and ensure the passage rate of light.The pre-fabrication processes including photolithography,DRIE etching,double-sided low-temperature anode bonding is used,the process flow is determined,the parameters are optimized,and the trend of large-tonnage scale and integration is met.At the same time,finite element simulation analysis of this anode bonding process is carried out to optimize the structural dimensions;gas-tightness testing of the vapor cell samples is carried out with the yield of 96.8%;SEM characterization and EDS analysis of the bonding surface are carried out,and an optical platform test is built,the absorption spectra of Cs and Rb at different temperatures are obtained.