Low pressure Au–Au bonding using flat-topped micro-bump Au arrays fabricated by Au film transfer and coining methods

The fabrication of highly functional optical devices requires solid-state, low-pressure bonding techniques. In this study, we developed micro-bump Au arrays that come into close contact at low pressure and facilitate low-temperature bonding. The micro-bumps were fabricated by Au film transfer and coining methods. A high die shear strength was achieved between the Si chip with the micro-bumps and the Si substrate with an Au film under a low bonding pressure of 10 MPa in ambient air at 150 °C after Ar fast-atom beam irradiation. The close contact between the micro-bumps and Au film was confirmed via cross-sectional scanning electron microscopy. Using the micro-bumps, a GaAs laser diode chip with an active layer near the bonding interface was junction-down mounted without degradation. The study findings confirm that the proposed methods can bond dissimilar materials at low bonding pressures, thereby contributing to the integration of optical components.