Efficient Xe Filling of MEMS Vapor Cells Empowered by Customized Triple Stack Wafer Bond Processing

Abstract

Nuclear-magnetic-resonance (NMR) gyroscopes based on MEMS vapor cell technology are currently being investigated worldwide and show superior advantages over current MEMS gyroscopes. However, there are still challenges in the upscaling and further deployment of NMR gyroscopes, due to the extremely high cost of the required gases (i.e. 129Xe, 131Xe), size, and high power consumption. To tackle these bottlenecks, in this study, a miniaturized, chip-scale, and low-cost NMR gyroscope has been conceptualized and fabricated. Here, a cost-effective and scalable filling of MEMS vapor cells with isotropic Xe filling was developed via an innovative microfabrication and wafer stacking process flow. By utilizing ultra-thin glass wafers, Taiko-processed silicon wafers, and an external gas flow system integrated into the wafer bonders, a sequential anodic bonding technique was executed to create a hermetically sealed chamber through which Xe gas can flow in a minimal volume. Fig. 1 shows the configuration of the triple-stack bonded wafer featuring the sealed chamber, the gas inlet, and the outlet. The Xe mass flow rate during the efficient filling process was 3.2528 *10-7 kg/s with a total filling time of <100 sec, as verified by the two-way Fluid-Structure Interactions (FSI) simulation data. As a result, it was demonstrated that the consumption of Xe gas during device filling can be dramatically reduced, which has a substantial impact on the total cost of the MEMS vapor cell. Figure 1. A demonstration of the triple-stack bonded wafer (glass-Silicon-glass) with an efficient Xe gas-filling process Figure 1