Microfabricated Bubble-in-Bubble Alkali Vapor Cell for 3-D Atomic Sensors

Abstract

This paper reports, for the first time, a novel microfabricated bubble-in-bubble alkali vapor cell. The wafer-level bubble-in-bubble structure is capable of simultaneous thermoforming within a foaming process, followed by approximate gas pressure filling between the two bubbles, which could eliminate the direct contact between the internal bubble and the external environment. The bubble-in-bubble structure will effectively reduce the leakage of the 3-D alkali vapor cell and improve thermal stability by maintaining different gas pressure in the outer bubble. A finite element model (FEM) is presented to simulate the fabrication process and various sizes (inner bubble height of 2.7 mm and outer bubble heights of 3.2 mm, 4.3 mm, and 5.2 mm) of bubble-in-bubble structures are demonstrated by experimental at a wafer level. The bubble-in-bubble vapor cells are potentially useful for highly reliable 3-D atomic sensors.