Research On Key Technologies Of MEMS Cell For CSAC Application

Passive atomic clock based on Coherent Population Trapping(CPT)principle which greatly reduces the volume of its structure compared to the active atomic clock,because it does not need the microwave cavity.At the same time,the Micro-Electro-Mechanical System(MEMS)technology has replaced the traditional glass-blowing process to produce alkali vapor cell,and reducing the size of the atomic vapor cell from centimeter to millimeter,which not only narrowing the physical system volume,but also greatly reducing the power consumption,including light source,detection,heating unit.Therefore,the atomic clock based on CPT principle is also called Chip Scale Atomic Clock(CSAC).The frequency stability of the CSAC is 3 to 4 orders of magnitude higher than that of a conventional crystal oscillator.In the positioning system,a 1 ?s clock error can cause a position error of nearly 300 m.Therefore,a high-precision clock in the navigation and positioning is particularly important.There are two key issues in CSAC,one is its dimension in chip,and the other is the frequency stability optimization.The key to minimize the clock is to reduce alkali vapor cell in chip scale.Therefore,it is the core technology to make a high-sealing,multi-atmosphere atomic cell.At the same time,the merits of atomic cell will also directly determine the frequency stability of the entire atomic clock system.In this paper,the fabrication scheme of miniaturized atomic cell is mainly studied,and the main work can be divided by the follows:First,the background and significance of the subject were explained in detail,and the development of research on the CPT atomic clock and research progress at home and abroad were combed;Second,the principle of CPT is studied,and focusing on the research on the influence of CPT resonant caused by collision,magnetic shift and light shift in chip scale alkali vapor cell;Third,the structure of CSAC is divided into two parts,which is contains the electrical system and the optical system.Then the two parts are introduced in detail.At the same time,the design of the scheme adopted in this project is introduced;Fourth,the manufacturing process of the MEMS alkali vapor cell was studied.Based on MEMS technology,an inductively coupled plasma(ICP)deep silicon etching machine was used to etching the silicon wafer.Combined with an anodic bonding machine,the vapor cell is packaged in two bonding processes,and two types of cell,buffer gas and non-buffer gas,are obtained.In the process of fabricating the vapor cell,the AZ4620 photoresist was used as the mask of the silicon wafer,and the surface morphology of the silicon wafer after the etching was researched.The etching rates of the silicon wafer in the etching process were calculated and the reasons for the difference of the etching rates under different sizes were analyzed;Fifth,the saturated absorption test was observed for the alkali vapor cell without buffer gas.The CPT resonance test was observed for the alkali vapor cell with buffer gas.The results showed that the cell,which was fabricated without the buffer gas,had the obvious saturated absorption phenomenon at the temperature of 80 centigrade,and the cell was filled with buffer gas,its CPT resonance spectrum was also observed.