Low-temperature direct bonding of flip-chip mountable VCSELs with Au-Au surface activation

This paper describes the result of low-temperature direct bonding of vertical-cavity surface-emitting lasers (VCSELs) by Au-Au surface-activated bonding (SAB). Flip-chip mountable VCSELs (250 μm × 250 μm × 100 μm thick) with anode and cathode on the same side of each chip were used for the experiments. After organic contaminants on the Au surfaces of the VCSELs and silicon substrates were removed by surface activation with argon radio-frequency plasma, Au-Au bonding was carried out by contact in ambient air with applied static pressure for 30 s. The die-shear strength and light intensity-current-voltage (L-I-V) curves were measured to evaluate the mechanical and optoelectronic characteristics of bonded VCSELs. The high die-shear strength of over 50 gf (54 MPa: shear force divided by the total electrode pad area) was achieved at a relatively low bonding temperature of 150°C and a contact load of 500 gf. The L-I-V measurements showed that the bonded VCSELs at the bonding temperature of 150°C functioned normally without degradation.