Research On MEMS Vapor Cell Fabrication Technology Applied To CPT Chip-Scale Atomic Clock

The combination of the Micro-PNT system and satellite navigation and inertial navigation technology can build an autonomous,real-time,continuous PNT network which is not limited by time,area and space,and realizes a wide range of applications in the national economy,military fields and national security.The chip-scale atomic clock,which is the core module of the system,pays more attention to low power consumption,small size and high stability while realizing the positioning,navigation,and timing functions.The CPT atomic clock is a chip-level device that can be realized only by using the CPT principle.The light and atoms interact to make the two superfine energy levels of the alkali atomic state coupled to a common excited state to prepare the CPT state.It has very high stability and overcomes the disadvantage that the quartz crystal oscillator is easily affected by external conditions such as temperature and humidity under severe conditions.The physical part of the chip-scale atomic clock mainly includes the circuit system,the optical path system and the magnetic shielding system.The reduction of the physical part volume is the key to the miniaturization of the chip-scale atomic clock.This paper takes the physical part of the passive CPT atomic clock as the main research object.Detailed research has been carried out on the MEMS vapor cell packaging process.The work done in this article is briefly described as follows:Firstly,the current status of chip-scale atomic clocks at home and abroad is reviewed,and the implementation methods of chip-scale atomic clocks are summarized in various countries,regions and laboratories.The atomic frequency standard and the principle of CPT are explained in detail.The shifted buffer gas was simulated and analyzed.Secondly,a combination of chemical reaction method and photodecomposition method was used to avoid interference caused by the introduction of impurities.The inductively coupled plasma deep silicon etching technology and double-sided anodic bonding process were used to design and prepare a dual-cavity MEMS vapor cell,which can be integrated and batched production.Deep silicon etching technology and anodic bonding technology are the key technologies in the preparation process of the vapoe cell.This article describes the experimental steps in detail.Finally,the leak rate of the prepared vapor cell was checked by fine leak detection of tracer gas helium(He)and coarse leak detection by weight gain.An experimental platform for absorption spectrum of MEMS vapor cell was built to test the absorption spectrum at different temperatures.