Low temperature hermetically sealed, optically transparent miniature packages: from medical to space

Low temperature hermetic sealing has been a major challenge in many microsystem development efforts. Especially when miniaturization is involved, traditional methods of hermetic sealing are not easily applicable. This paper focuses on a beyond state-of-the-art, low-temperature, laser-based hermetic sealing technology. This sealing process is established using thin films, which are deposited using standard deposition methods like sputtering or evaporation, as the bonding layer. As no organic material like adhesive or flux is used in the bonding layer, this technique is a good alternative to fluxless eutectic solders like gold-tin (Au80Sn20) for hermetic sealing with the obvious advantage of much lower temperature of processing. Miniature packages with a volume as low as 1.2 mm
³
were demonstrated using sapphire as the housing material. Further, the technology was demonstrated with variety of housing materials like different glasses, silicon, alumina, and silicon carbide A temperature of less than 118 °C was measured 150 μm away from the sealing location. The seal showed a bond shear strength of 195 MPa for sapphire and 70 MPa for glass packages. The leak rate measurements showed that the packages were leak tight below the measurement equipment offset floor of 1×10
^-12
mbar * l/s. The reliability of the sealing method was also proven in space relevant conditions.