Hermetic sealing of MEMS sensors for high temperature electronics applications

Abstract

In this study, 100 μm sealing width of both Al-Ge eutectic bonds and Pt-In Transient Liquid Phase bonds were fabricated and evaluated. The experiments were conducted to determine the feasibility of the bonding for usage in high temperature applications.

The samples underwent shear testing to gauge their shear strength at room temperature and at 250°C. Thermal aging was done to determine the effects it has on the respective bondings. The microstructure was also analyzed using SEM and SEM-EDX in which defects such as voids can and are being detected. C-SAM was ultimately done to observe the sample’s hermeticity.

Results obtained for Pt-In TLP bonding were encouraging as it recorded an average shear strength value of 60.39 MPa at room temperatures. However tests under hot shear (250°C) substantially lowers the shear strength value. The drop in shear strength concludes that this sealing method was unstable at high temperatures, though it is still capable for lower temperature applications.

Al-Ge eutectic bonding on the other hand shows promise with high shear strength recorded. Degradation at high temperatures and with thermal aging was very minimal and this was partly contributed by a voidless bond formation of Al and Ge at the interface. The stability of the bonding at high temperatures was determined to be safe and suitable for high temperature applications.