Research On Packaging Process Of Vapor Cell Applied Into Chip-scale Atomic Clock

Atomic clocks are currently the most stable and accurate time and frequency standards,and has a wide range of applications in the fields of positioning and navigation,aerospace,high-speed FM communication,punctuality and timing.However,the further applications of atomics are limited since the large volume and power dissipation.Based on the Coherent population trapping?CPT?principle and Micro-Electro-Mechanical-System?MEMS?technology,the CPT clock uses laser-excited alkali atomic transition to replace the traditional microwave excitation.Compared with the traditional atomic clock,CPT clock has the advantages of small size,low power consumption and high stability.It is the only atomic clock that can be realized in principle in the chip,and has broad application prospects in the field of high precision time standards.There are already mature chip atomic clock products in foreign countries.Due to the late start of the chip atomic clock in China,there have been some achievements,but there is no mature product at present.Therefore,it is very important to make breakthroughs in the field of chip atomic clock technology.The structure of CPT clock can be divided into two parts:the physical system and the circuit control system.This paper takes the chip atomic clock physical system as the research object,and studied key technologies of the physical system for chip-scale atomic clock.The main work is as follows:In this dissertation,it firstly makes brief review on the research situation about the CPT clock at home and abroad.Taking the super-level structural system of ⁸⁷Rb atom as an example,the basic principle of coherent population trapping is introduced.The main factors affecting the stability of CPT atomic clock are analyzed.Then,the vapor cell is the most crucial part in the physical system of atomic clock.This paper has summarized the main fabrication processes of MEMS vapor cell at home and abroad in the past few years,and analyzed the merits and drawbacks of various processes.Combining the advantages of simple operation of chemical reaction method and no impurity interference by photolysis method,the Rb alkali metal is formed by the Rb dispenser.Finally,the optical absorption spectrum is obtained in the test platform of vapor cell.At the same time,the deep silicon etching process and anodic bonding technology are the two most critical technologies in the vapor cell preparation process.DRIE etch rate is dependent on the aspect ratio.To know the aspect ratio dependence of DRIE,a test DRIE process is performed using the photo-maskwith different line width varying in order to control the etch depth of trenches.The quality of the anodic bonding directly determines the airtightness of the vapor cell.This paper summarizes a set of anodic bonding procedures for subsequent vapor cell batching through a large number of experiments,which can be used for a large number of production of vapor cell in the future.Finally,the traditional atomic clock physics system integration schemes are all discrete components,which are large in size and difficult to miniaturize.Based on the fabricated vapor cell and MEMS technology,this paper introduces the design process of light source system,optical path system,temperature control system,magnetic field and magnetic shielding system and detection system in detail,and gives the overall integration scheme of chip-scale atomic clock physical system.