Conductivity Modulation of Solution-Processed Two-Dimensional Materials for Printed Electronics Development

Printing of two-dimensional (2D) materials is emerging as a promising approach for scalable electronics manufacturing. The state-of-art advances, however, show inferior device performance due to poor electrical conductivity as a result of the discrete nature of the printed 2D material networks. Methods such as modifying the connections and alignments between the 2D material nanoflakes show limited enhancements. Here we introduce a ferroelectric polarization effect to overcome the conductivity limitation of printed 2D material networks and exploit this mechanism in printed electronics developments.<br/><br/>We start printed electronics fabrication with solution processing of 2D materials. The yield 2D materials are in an irregular, nanoscale dimension. Using MoS₂ as the example, we show that printed thin films from such nanoflakes give an extensively high electrical resistance due to the poor inter-flake contacts and the carrier transport of the nanoflakes. This makes it impractical to fabricate functional printed electronics. To address this issue, we couple the printed MoS₂ with ferroelectrics and show significant electrical resistance tunning from a high resistive state to a low resistive state, with a ratio of &gt;10³. We assume this arises from a complex mechanism of printed MoS₂ under the electric field. Our detailed density-functional theory calculations and spectroscopic characterisations suggest MoS₂ transition from a semiconducting state to a metallic state, driven by the localized electric field exerted by the nonlinear electric polarization of the ferroelectrics. The localized electric field can cause the electron cloud of MoS₂ to redistribute and form conductive electron gases on the surface or between the atomic planes. Such distortion in the electron cloud may deform the atomic structure of MoS₂, leading to a phase transition that can further promote the conductivity. Exploiting this transition, we demonstrate printed memristive electronics, for instance, ferroelectric tunnelling junctions, and show the possibility of implementing neuromorphic computing. Besides MoS₂, this transition mechanism may also be viable for other 2D materials (e.g. MoTe₂) and low-dimensional materials (e.g. CNTs).<br/><br/>Our approach to tune conductivity may serve as a universal strategy for modulating the properties of solution-processed low-dimensional material networks, and through printing, the approach can lead to scaled-up and even wafer-scale manufacturing of electronics that can find applications in, for instance, integrated and intelligent circuits, in-memory neuromorphic computing, and human-machine interfaces.