Monolithic Integration of Crack-Free 2D Bi₂O₂Se via Stress Modulation

The monolithic integration of 2D materials into silicon-based wafers is crucial for next-generation electronics and optoelectronics. Reliable transfer methods for wafer-scale 2D materials are a key prerequisite. As one of the most promising 2D semiconductors, bismuth oxygen selenide (Bi₂O₂Se) films show significant promise as high-performance photodetectors and advanced-architecture transistors. Although considerable efforts have been devoted to transfer methods for 2D Bi₂O₂Se, challenges such as limited film size, transfer-induced defects, cracks, and contamination remain. Herein, we report a novel transfer method for wafer-scale 2D Bi₂O₂Se single-crystal films based on the stress modulation of metal films. A composite transfer medium comprising tensile-stressed Ni and stress-free Cu was developed to enable intact and crack-free exfoliation of 2D Bi₂O₂Se films. By modulating the strain and fracture energies of the composite metal film, the transferred 4-inch 2D Bi₂O₂Se film exhibited a crack-free, intact, and uniform morphology, and two-layer and three-layer-stacked 2D Bi₂O₂Se films with clean interfaces were fabricated. Integrated 2D Bi₂O₂Se transistors exhibit high carrier mobility reaching up to ∼150 cm² V^-1 s^-1 with an on/off ratio ∼10⁶, which is better than other transferred wafer-scale 2D semiconductors. Overall, our findings are promising for the future integration of 2D materials into advanced electronics and optoelectronics.