Design, assembly and reliability of a hermetic package for a 600°C wireless temperature sensor

This paper describes the development process and reliability testing results of a high-temperature stable, hermetically sealed ceramic package. The assembly of a passive, wireless 600°C temperature sensor in Surface Acoustic Wave (SAW) technology, that does not require any cables or power supply, is demonstrated. The sensor is developed for applications supporting enhanced equipment safety and process control. The device comprises a langasite (La₃Ga₅SiO₁₄) piezo-electric chip equipped with high-temperature stable metal layers, deposited and structured using common photolithography techniques. The chip is then flip-chip bonded into the high-temperature stable ceramic package. To reduce the enormous mechanical stress caused by the different coefficients of thermal expansion (CTEs) of chip and package, various design- and process-related approaches were implemented. Finally, a technology was developed to hermetically seal the package in a high-temperature process.