Chemical‐Resistant, Highly‐Impermeable Integration of Large Differential Semiconductor and Oxide by Spatial‐Confined Plasma Assisted Ultrafast Laser Microwelding for Optofluidic Microsystem

Abstract Large‐differential semiconductor and oxide interconnect are widely used in high‐performance multi‐function integrated microsystems. In this work, spatial‐confined plasma‐assisted ultrafast laser microwelding has been developed to activate the inert surface and improve mass transportation for robust semiconductor‐oxide integration. The inherent stress concentration within the weld of semiconductor (Si) and oxide (Sapphire) can be compensated by inserting hundreds‐of‐nanometer‐thick intermediate oxide layer (SiO ₂ ). Amorphous silicate with embedded Si nanocrystals is generated to facilitate the bond between Si and Sapphire. While, SiO ₂ jet with extremely high energy can expand into the interior of Sapphire, bringing in numerous bonding sites. The shear strength of welded Si and Sapphire structures can be up to 10.7 ± 0.8 MPa. As‐received heterostructures also show high chemical resistance to acid (pH 2) and alkaline (pH 12) solutions, where the corrosive liquid is well preserved in the welded cavity after a long time. Developed Si‐based SERS optofluidic sensor by ultrafast laser microwleding of Si substrate and Sapphire window shows the reliable ability for high‐sensitive detection of low‐concentration chemicals (down to 10 ⁻¹² mol L ⁻¹ ). This method can be also applicable for large‐differential materials integration with broad combinations (e.g., Si/Ga ₂ O ₃ and SiC/Sapphire), which is promising for high‐performance multi‐function micro devices development.