LiNbO3 die-attach with Au-Ge eutectic solders

Lithium niobate (LiNbO3) single crystals are used as a promising piezoelectric material for high temperature sensors owing to its superior electromechanical coefficients and high frequency operation. The selection of materials and techniques for LiNbO3 die-Attach aiming for the service temperature up to 300 °C encounters many objectives and practical considerations, where the processing temperature should be kept below 450 °C due to the decomposition of the die. Among the few candidates of lead-free solders exist in this temperature range, gold-germanium (Au-12 wt. % Ge) eutectic solder has shown promising characteristics. Therefore, in the current study, LiNbO3 die-Attach to Hastelloy substrate with this solder was investigated. The mechanical properties of the corresponding assemblies were examined by a die-shear tester and the reliability of the joints has been assessed after thermal aging and thermal shock treatments at 300 °C.