Transition-free indirect bonding towards 3D multi-layer glass stacking

Optical and photonic devices comprised of fused-silica glass portfolios play an important role in astronomical detections, which requires the bonding interfaces to own robust mechanical properties and less optical loss. Indirect bonding lowers the difficulty of the bonding process than direct bonding by introducing the non-negligible intermediate or transition layers but will inversely diminish the optical properties. In this study, a transition-free indirect bonding (TFB) strategy was developed to realize glass bonding with hard-to-distinguished interfacial boundary. In the process, the oxygen plasma activation was applied to reconstruct the glass surface. Owing to the produced chemical sites with the plasma surface activation, multiple paths could be provided for surface and interface reactions than conventional indirect bonding method hydroxide-catalyzed bonding (HCB). These adequate reactions constructed a whole and uniform Si-O network crossing the bonding interfaces, which was free of transition boundary between the interface and bulk substrates. The uniform and non-transition interface performed higher bonding strength and excellent optical transmittance with less loss than HCB. Based on the TFB strategy, multilayer chips were combined together enabling a 3D multi-layer chip stacking with low transmittance loss and stable mechanical structure for state-of-the-art optical applications in astronomical detection, laser instruments, and optical sensors.