Study of Dielectric Breakdown Mechansim in Molecular Beam Epitaxial Ultrathin Hexagonal Boron nitride

Hexagonal boron nitride is promising as a dielectric layer for two-dimensional (2D) electronic devices. Nevertheless, the studies on failure mechanism and reliability of ultrathin h-BN are quite limited. In this presentation, we report detailed investigation of metal-insulator-metal devices based on our MBE grown h-BN ultrathin films (0.3-2 nm). Current- Voltage (IV) and Time Dependent Dielectric Breakdown (TDDB) measurements were carried out. The breakdown dielectric field of ultrathin h-BN can be as high as 12 MV/cm. Besides hard breakdown, soft breakdown is also responsible for the failure mechanism but can be self-healed after the stress is relieved. Under bias, the defects which are close to each other start trapping electrons and pile up, creating a path that leads to soft breakdown and prevents hard breakdown. As the bias is relieved, electrons detrap and the insulating property of the film recovers. Soft breakdown phenomenon can also occur many times before the h-BN film is totally worn out. Subsequent TDDB result under different stress voltages not only confirms soft breakdown mechanism, but also reveals the potential applications of untrathin h-BN for Resistive Random Access Memories (RRAM).