Automated Vacuum Stacking for Additive Assembly of 2D van der Waals Heterostructures

Wafer-scale synthesis of monolayer 2D materials (2DMs) address the stochastic, small-area limitations of micromechanical exfoliation. Using wafer-scale synthesized 2D semiconductors along with large-area patterning and multi-functional polymer stamps, we demonstrate a highly automated, dry-transfer, additive assembly process. Our high-vacuum system can assemble 2D heterostructures at the precision of actuator limits (few micron lateral/0.2° rotational). Identical structures have been assembled in parallel and stacks of high layer counts (25+) have been achieved, all without active user control of the system. Fabricated heterostructures include a range of 2DMs (MoS₂, WS₂, WSe₂, graphene) and metal electrodes (Au, Ti), and can be deposited onto a variety of substrates (SiO₂, Al₂O₃, 2DMs). We also demonstrate controlled twisted n-layer heterostructure assembly, where number of layers depends on area limits of single-crystal 2DMs growth.