Ab-initio study of LD-HfO_2, Al_2O_3, La_2O_3 and h-BN for application as dielectrics in MTJ memory device

摘要

Low-dimensional (LD) forms of HfO_2, Al_2O_3, La_2O_3 and h-BN have been used as dielectric layer in the proposed MTJ memory device. Subsequently, DFT and NEGF model based atomistic computation were performed for the device using Quantum ESPRESSO. Self-consistent Field (SCF), Density of State (DOS) and Bandstructure calculations were carried out. The SCF converged uniquely for all LD materials used. Lowest energy was obtained for multilayer LD-La_2O_3 at -1760.7200095Ry and HfO_2 at -940.365Ry, thus predicting better accuracy in solving Schrodinger equation and wave functions. The DOS plots exhibited the valence band sharp peaks at -4.5eV, -0.5eV, -0.5eV and -4.25eV for multilayer LD-HfO_2, Al_2O_3, La_2O_3 and h-BN respectively. The energy band spacing manifested from DOS plots were found to be better for LD-HfO_2, La_2O_3 and h-BN. On inspecting the bandstructure plots, higher bandgap was observed for multilayer LD-HfO_2 (at 3.8eV), hence depicting it to have a better insulating property. Upon device computation, higher TMR was obtained for HfO_2 based MTJ memory device (i.e. 2.5 at 0 V), showcasing better readability of bits. While consistent boundary voltages were obtained from the DTMR calculations for h-BN and HfO_2 based devices, concluding them to have better stability of the memory states. The overall results obtained for different performance parameters of the MTJ memory device using LD-HfO_2 and h-BN were very impressive. Thus, predicting these materials as highly promising to be used as dielectrics in a MTJ memory device.