This paper reports the first principle simulations of Fe/MgO/Fe, Fe/Y2O3/Fe, Fe/HfO 2/Fe, and Fe/Al2O3/Fe magnetic tunnel junctions (MTJs). From the device-level and circuit-level simulations carried out in this paper, the Fe/MgO/Fe configuration has been found to be the best. From the device-level simulations, all the four configurations of MTJs have been compared with regards to the bias dependence of tunnel magnetoresistance ratios (TMRs), insulator thickness dependence of TMR, and insulator thickness dependence of parallel and antiparallel state resistances. Finally, from the circuit-level simulations, the static and switching power dissipations have been computed along with the delay time estimation. [ABSTRACT FROM PUBLISHER]