Electrical Double Layer Force Enabled CMOS-compatible Transfer of van der Waals Materials

The integration and stacking of van der Waals (vdW) materials to target substrates or circuits is critical to their applications in high-end electronics, optics, moiré electronics, <i>etc</i>. Since high quality vdW materials are often grown with harsh conditions, the transfer of these vdW materials to target substrates is one of the key steps in the integration. However, the step of detaching nanomaterials from the growth substrate typically requires the use of either chemical etchants, electrochemical bubbling, or metal-assisted mechanical strain, which often leaves residue or introduces contamination, making the process CMOS-incompatible, low-yield and the quality of the vdW materials degraded. Furthermore, the substrate cannot be used again, adding significant cost to the manufacturing process (especially for single crystalline substrates). In this work, we present an electrical double layer (EDL) force enabled transfer method (termed as EFT, <u>E</u>DL <u>F</u>orce <u>T</u>ransfer) that is CMOS-compatible, with minimal damage to the vdW layer, widely applicable to different types of substrates and materials, and cost-effective. With the formation of the EDL, the vdW material is immediately repelled from the substrate by the strong EDL repulsion force. This method is suitable for various vdW materials (e.g., carbon nanotube, MoS₂, h-BN, etc.) and substrates (e.g., oxide, nitride, etc.). The as-transferred vdW materials show ultra-high nanoscale cleanliness, along with minimized wrinkles, cracks, metal contaminations and other transfer-induced defects. The MoS₂ transistors fabricated with this transfer method show higher ON current and reduced threshold voltage variation than devices made via chemical etching transfer. This EFT approach offers a facile and manufacturing-viable solution for vdW material integration, which will significantly advance the future development of atomically thin electronics.