Abstract
Micro-electro-mechanical system (MEMS) vapor cells are key components for sensors such as chip-scale atomic clocks (CSACs) and magnetometers (CSAMs). Many approaches have been proposed to fabricate MEMS vapor cells. In this article, we propose a new method to fabricate wafer-level filling of MEMS vapor cells based on chemical reaction and evaporation. The Cs metals are firstly obtained through the chemical reaction between cesium chloride and barium azide in a reservoir baseplate. Then, the Cs metals are evaporated to the preform through the microchannel plate and condensed on the inner glass surface of the preform. Lastly, the MEMS vapor cells are filled with buffer gas, sealed by anodic bonding, and mechanically diced into three dimensions: 5 mm × 5 mm × 1.2 mm, 4 mm × 4 mm × 1.2 mm, and 3 mm × 3 mm × 1.2 mm. The full width at half maximum (FWHM) linewidth of the coherent population trapping (CPT) signal of the MEMS vapor cells is found to be 4.33 kHz. The intrinsic linewidth is about 1638 Hz. Based on the CPT signal, the frequency stability is 4.41 × 10−12@1000 s. The results demonstrate that the presented method of the wafer-level filling of MEMS vapor cells fulfills the requirements of sensors such as CSACs.
Highlights
Sensors such as chip-scale atomic clocks (CSACs) and magnetometers (CSAMs) are widely used in many fields, such as satellite navigation systems [1–3]; global positioning systems (GPS) receivers [4]; precise timing for seismic measurements on the ocean floor related to oil exploration, acoustic sensing, and earthquake detection [5]; and measurement of magnetic fields produced by the heart [6], brain [7], and in space [8]
The golden cesium can be seen from the holes in the micro-electro-mechanical system (MEMS) vapor cellswafer
An approach for the wafer-level filling of the MEMS vapor cells based on chemical reaction and Cs evaporation is proposed
Summary
Sensors such as chip-scale atomic clocks (CSACs) and magnetometers (CSAMs) are widely used in many fields, such as satellite navigation systems [1–3]; global positioning systems (GPS) receivers [4]; precise timing for seismic measurements on the ocean floor related to oil exploration, acoustic sensing, and earthquake detection [5]; and measurement of magnetic fields produced by the heart [6], brain [7], and in space [8]. CSACs and CSAMs consist of control circuits and physics packages. Traditional physics packages feature a glass-blown vapor cell. Glass-blown vapor cells have a large spherical shape with a long stem. Even the smallest glass-blown vapor cells reported until now have a diameter of 3 mm (14.1 mm3 ) except for the stem [9]. The spherical shape makes glass-blown vapor cells difficult to be assembled. With the growing demand for small-volume, low-power-consumption, and high-performance devices, sensors fabricated by micro-electro-mechanical system (MEMS) technologies are becoming more and more popular. As one of the most important components of physics packages, MEMS vapor cells have been pursued by scientists for many years. Compared to traditional glass-blown vapor cells, MEMS vapor cells have the advantages of smaller volume, easier assembly, and higher fabrication efficiency. The first MEMS vapor cell was presented by Liew et al
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