Flader, I.B., Chen, Y.H., Yang, Y.S., Ng, E.J., Shin, D.D., Heinz, D.B., Ortiz, L.C., Alter, A.L., Park, W., Goodson, K.E., Kenny, T.W., 2019, “Micro-Tethering for Fabrication of Encapsulated Inertial Sensors With High Sensitivity,” J. MicroElectroMechanical Systems, Vol. 28, pp. 372-381.
This paper demonstrates a post-fabrication technique for creating highly compliant structures inside a hermetic, wafer-scale encapsulation process. Single crystal silicon micro-tethers were fabricated alongside compliant structures to temporarily provide additional anchoring and increased device rigidity during the fabrication process. This technique mitigates in-process stiction for compliant devices by tethering the large, free-moving structures during fabrication. After successful fabrication, the micro-tethers can be selectively removed by two methods. The first method utilizes a potential voltage difference across the device. Joule heating can be concentrated in the microtether and the device separated after supplying requisite heat energy. The second method utilizes mechanical fracturing where a large external force is applied to separate the device from the tether. Micro-tethers in this paper were attached to differential resonant beam accelerometers, and were designed for detachment by each method: Joule heating and mechanical fracture. Our results show that the 40 mu m thick device can be successfully detached by both methods, indicated by the device sensitivity increase from similar to 100 Hz/g to similar to 400 Hz/g.