Poly-Crystalline Boron Nitride Memristor with Ultra-Low Set Voltage

This work focuses upon the growth of h-BN films through low pressure chemical vapor deposition (LPCVD) technique with a control over crystallinity and film thickness. The films undergo a phase transition from amorphous to polycrystalline as the growth temperature increases from 930 to 990 °C. Hereafter, thickness of the as-grown polycrystalline films is optimized by changing the duration of growth time. Following the growth process, memristor devices are fabricated on the hBN films using silver (Ag) as the active metal electrode, and effect of both the crystallinity and film thickness is explored. Memristor behavior in the amorphous film is explained through the de-localization of the electronic states under the influence of an external bias, while in polycrystalline films, it is attributed to the grain boundary (GB) and defect mediated migration of charge carriers via the electrochemical metallization (ECM) mechanism. Furthermore, the memristive characteristics of the polycrystalline hBN film exhibit a shift from non-volatile to volatile with the decrease in film thickness. Polycrystalline hBN film with a thickness of 3 nm demonstrated threshold switching behavior with an excellent I_ON/I_OFF ratio of 10^₃ at an ultra-low set voltage of 0.17 V. The transition from non-volatile to volatile behavior can be explained through the electric field-induced nucleation theory.