Wafer-Level Hermetic All-Glass Packaging for Microalkali Vapor Cells of Chip-Scale Atomic Devices

Abstract

To maintain a controllable environment for microalkali vapor cells of high-performance chip-scale atomic devices, a novel wafer-level hermetic all-glass packaging technology for microalkali vapor cells of atomic devices was investigated. A glass wafer with metal vias was used as the substrate to host the miroalkali vapor cells. Wafer-level hemispherical glass bubbles prepared by a chemical foaming process were used as transparent packaging caps. The performance of the rubidium vapor cell in the all-glass hermetic package was characterized by a laser frequency locking system and an ultraviolet spectrophotometer. The results show that hermetic all-glass packaging at a wafer level was demonstrated successfully. The results also indicate that after the hermetic all-glass packaging, the temperature variation of the microalkali vapor cells was controllably below 0.2°C at different working temperatures of atomic devices. A chip-scale atomic magnetometer using the hermetic all-glass micro vapor cell was demonstrated eventually. IndexTerms-Atomic devices, chemical foaming process (CFP), hot forming process, microrubidium vapor cell, optically pumped atomic magnetometer, ultraviolet spectrophotometer, wafer-level hermetic package.

Recent Progress on Micro-Fabricated Alkali Metal Vapor Cells

“…In 2015, Ji et al of Southeast University proposed a chip-scale magnetometer spherical glass hermetic structure, as shown in Figure 23 [110], where the upper part of the package is a wafer-level hemispherical glass cell array prepared by a controlled process combining thermoforming and chemical foaming, and the lower part is a glass wafer with conductive metal holes, with a package radius of 10 mm. The feasibility of the hermetic package was verified by measuring the average 0.2 °C internal temperature change with In 2018, researchers at the University of Nottingham, UK, integrated a novel mobile magnetoencephalography device by utilizing a commercial SERF atomic magnetometer [108], as shown in Figure 22.…”

“…In 2015, Ji et al of Southeast University proposed a chip-scale magnetometer spherical glass hermetic structure, as shown in Figure 23 [110], where the upper part of the package is a wafer-level hemispherical glass cell array prepared by a controlled process combining thermoforming and chemical foaming, and the lower part is a glass wafer with In 2011, Shang et al of Southeast University proposed a spherical alkali vapor cell prepared by utilizing a chemical foaming process [109], which is prepared by first forming multiple cavities on the silicon wafer by etching, putting a foaming agent in the cavities, and then finally packaging them by covering the glass to the top of the foaming agentfilled silicon wafer cavities for anodic bonding. The average temperature is approximately 830-900 • C. The Pyrex glass softens at a high temperature and expands into a sphere under the action of the foaming agent, and finally, the whole body is cooled and annealed to form the cavity.…”