Enhancing Glass-to-Glass Bonding at Room Temperatures Using Laser Surface Modification With Ti/Cu/Ti/TiO2 Thin Films

There are many applications for glass-to-glass bonding, such as manufacturing optical devices, electronic components, and microsystem applications. This article presents a simple and effective method for glass-to-glass bonding using laser modification with Ti/Cu/Ti/TiO2 thin films. Ti/Cu/Ti thin films were prepared on glass using magnetron sputtering and then exposed to the atmosphere for 30 min at room temperature for preoxidation to obtain Ti/Cu/Ti/TiO2 thin films. The TiO2 thin film was intentionally formed to improve the bonding quality. To analyze the bonding mechanism, the energy dispersive spectroscopy (EDS) and X-ray photoelectron spectra (XPS) analyses studied the microstructural evolution. The results show that Si diffuses from the glass to the thin films by laser irradiation. The laser beam penetrated the glass and was directly absorbed by the TiO2 thin films. Ti diffuses from the oxide thin film toward the glass, forming Ti–Si covalently structured silicate (the main component is TiSi2) in the bonded region. The formation of TiSi2 is the critical process for this laser bonding. Furthermore, the bonding strengths corresponding to different contact pressures applied during the bonding process were compared and analyzed. The results show that the method achieves more robust glass/TiSi2/Ti/Cu/TiSi2/glass bond pairs with tensile strengths up to 14 MPa and low bonding defect density (< 0.05%). Note that this laser bonding technology was processed at room temperature, allowing the use of thermally sensitive materials in device manufacturing. To verify the application potential of the laser bonding technique in 3-D glass packaging, a simple coplanar waveguide (CPW)–through-glass vias (TGVs)–CPW interconnect structure was developed on three-layer glass interposers in this article. The interconnection loss was successfully measured by constructing a three-layer interconnect structure with laser bonding. The results show that the insertion loss can meet the requirements of glass-based microsystem applications.