Performance and Reliability Assessment of a Dielectric Charging Guard in MEMS Optical Switch Systems

Optical MEMS switching technology has attracted attention in managing data flow due to its compactness and robustness. It allows hundreds of optical channels to be switched by micro-mirrors with very low power consumption. Furthermore, the ability to switch signals independent of data rates, formats, wavelengths and protocols is advantageous in many real world environments such as internet peering exchanges, undersea cable landing locations and data centers. All of these applications require a highly reliable and stable switching system. Dielectric isolation has a huge impact on major failure modes of capacitive MEMS devices such as breakdown and charging. This issue becomes more challenging in electrostatic MEMS optical switches since they usually operate at relatively high voltages. The charges trapped in this dielectric layer could cause interference in the electric field, resulting in erratic responses of the steering mirrors and instability of pointing accuracy over temperature and time, which greatly degrades the system performance. Aiming at reducing charging and preventing high voltage breakdown, a dielectric charging guard has been developed by using an oxide "fence" with extended breakdown path length that is shielded by conductive sidewalls of the silicon interposer. In this paper, the reliability tests as well as the performance impact to the optical switch will be presented, including characterizations of breakdown voltage, leakage current, and charging verses temperature. The test results demonstrate highly repeatable switching accuracy of micro-mirrors with very low drift at varied temperature. Failures induced by fabrication will also be discussed.