Integration of 2D material-based electronic devices on flexible substrates for millimeter wave applications

Research on thin-film technology-based radio frequency (RF) circuits is increasing to address the demand for transparent, wireless, and wearable consumer electronics applications. Owing to their excellent electronic and mechanical properties, two-dimensional materials (2DMs) are candidates with high potential for such applications. The 2DMs graphene and molybdenum disulfide (MoS ₂ ) have the highest maturity in terms of material synthesis and fabrication technology. Graphene is of interest because of its high electron and hole mobility, although the lack of a bandgap limits the current saturation and the ratio of current between the ON and the OFF-states of graphene field-effect transistors (FETs). Therefore, we chose metal-insulator-graphene (MIG) diodes with high asymmetry as RF devices and semiconducting MoS ₂ as the channel material for FETs. We thus combine the strengths of graphene and MoS ₂ by integrating MIG diodes and MoS ₂ -FETs on 8 µm-thick polyimide substrates, complemented with high-quality passive components. The MIG diodes have asymmetries over 100 A/A and peak responsivities of approximately 20 V ^-1 , whereas the MoS ₂ FETs have transconductance mobilities averaging 7 cm²/V∙s, with peaks at 17 cm²/V∙s. Furthermore, the technology was developed with standard microfabrication techniques and 2DMs grown with wafer-scalable chemical vapor deposition processes. It was verified by realizing two on-chip wideband power detectors operating up to 30 GHz. Our technology explores new applications of 2D materials in integrated RF circuits and paves the way for full-fledged integrated transceivers on flexible substrates.