Effect of Large-Area Exfoliation and Etching on the Electrical Behavior of Transition-Metal Dichalcogenide Field-Effect Transistors

Large-area layer transfer was used to fabricate multilayer transition-metal dichalcogenide (TMDC) thin-film transistor (TFT) arrays with areas of (40 × 40 μm2) from single-crystal flakes. The effects of plasma etching of the TFT backchannel surface and bulk defects in the layers on the electrical performance and stability of the n-channel depletion-mode TFTs were investigated. Few-layer structures (∼3 monolayers) were fabricated using a dry etching process to thin multilayer (∼60–90 nm thick) TMDC structures. The etching improved the threshold voltage of the TFTs, resulting in a positive threshold voltage shift of +40 V after etching the backchannel, correlating to a bulk trap density of approximately 1 × 1016 cm–3 eV–1 per monolayer. Etching the MoS2 surface resulted in a threshold voltage shift of 0.2 V per nanometer of MoS2 removed (for MoS2 thicknesses >15 nm). For MoS2 layers etched to <15 nm, the threshold voltage changed to ∼1.8 V per nanometer. An observed degradation of the carrier transport and electrical stability of these samples were found to be due to the proximity of the etched surface approaching the active channel region of the device. The results reveal the performance trade-offs of fabricating large-area arrays of few-layer TMDC TFTs using a mechanical exfoliation and dry etching approach.