High-Performance, Highly Bendable MoS₂ Transistors with High-K Dielectrics for Flexible Low-Power Systems

TLDR

Studies of MoS₂ and other 2D semiconductors have focused on rigid substrates, leaving flexible substrate research largely unexplored despite the materials’ promise for flexible smart systems. The study investigates MoS₂ transistors fabricated on industrial plastic sheets. The authors fabricated the transistors on plastic, performed mechanical testing and dielectric crack analysis, and used rigorous mechanics modeling to guide design for sub‑mm bending reliability. The devices achieved more than 100‑fold improvement in ON/OFF ratio and 4‑fold higher mobility than previous flexible MoS₂ transistors, retained performance down to a 1 mm bending radius, and showed that while HfO₂ and Al₂O₃ dielectrics have similar crack‑onset strain, crack propagation is slower in HfO₂, indicating a subcritical fracture mechanism.

Abstract

While there has been increasing studies of MoS2 and other two-dimensional (2D) semiconducting dichalcogenides on hard conventional substrates, experimental or analytical studies on flexible substrates has been very limited so far, even though these 2D crystals are understood to have greater prospects for flexible smart systems. In this article, we report detailed studies of MoS2 transistors on industrial plastic sheets. Transistor characteristics afford more than 100x improvement in the ON/OFF current ratio and 4x enhancement in mobility compared to previous flexible MoS2 devices. Mechanical studies reveal robust electronic properties down to a bending radius of 1 mm which is comparable to previous reports for flexible graphene transistors. Experimental investigation identifies that crack formation in the dielectric is the responsible failure mechanism demonstrating that the mechanical properties of the dielectric layer is critical for realizing flexible electronics that can accommodate high strain. Our uniaxial tensile tests have revealed that atomic-layer-deposited HfO2 and Al2O3 films have very similar crack onset strain. However, crack propagation is slower in HfO2 dielectric compared to Al2O3 dielectric, suggesting a subcritical fracture mechanism in the thin oxide films. Rigorous mechanics modeling provides guidance for achieving flexible MoS2 transistors that are reliable at sub-mm bending radius.