Long-term Reliability Evaluation of Internal Atmosphere on Sealed Packaged MEMS Devices

In order to improve the performance stability, MEMS devices often adopt sealed packaging, and the long-term reliability is highly correlated with the atmosphere inside the packing cavity. However, during long-term use, MEMS devices are exposed to a variety of environmental stresses such as temperature stress. It would cause the atmosphere inside sealed cavity of MEMS devices to change gradually, that deteriorates the long-term reliability of MEMS devices. In this paper, the evolution of the atmosphere inside MEMS devices was studied. The acceleration experiments of high-temperature and thermal shock were implemented, and the measured results of internal atmosphere were obtained. The experimental results show that the moisture content and hydrogen content of the samples before the experiment have good consistency, and the maximum values are 925 ppm and 4525 ppm, respectively. However, after 500 hours of high temperature experiment, the contents of moisture and hydrogen in the cavity increased significantly by 455% and 158%, respectively, and their maximum values are 9711 ppm and 14400 ppm, respectively. On the other hand, the moisture content increased by 12% and the hydrogen content changed by 33% after 100 cycles thermal shock. The source of increased internal gas was discussed. In addition, the influence of hydrogen on vacuum-packaged MEMS devices was studied. This work is helpful for designers to understand the atmosphere evolution inside MEMS devices and improve the long-term reliability of MEMS devices.