Electrochemical Synthesis and Nonvolatile Resistance Switching of Mn3O4 Thin Films

An electrodeposition method is introduced to produce crystalline films of Mn3O4 from aqueous solution. The films are electrodeposited potentiostatically from a solution of 0.2 M Mn(II) acetate at a pH of 6 and a deposition temperature of 80 degrees C. The anodic deposition is performed in the potential range of 0.275-0.350 V vs Ag/AgCl/KCl(sat.). In this potential range the current efficiency is 100%. Both the stoichiometry and the morphology of the films can be controlled through the applied potential. Films deposited at a low overpotential grow with a [001] preferred orientation, columnar microstructure, and near-stoichiometric Mn(III)/Mn(II) ratio of 1.99. Films deposited at higher overpotential deposit with a near-random orientation, porous or powdery microstructure, and Mn(III)/Mn(II) ratio of 2.62. At potentials greater than 0.38 V, amorphous films of MnO2 are produced. The as-deposited Mn3O4 has a very high resistivity of 4.4 x 10(8) Omega cm. The electrodeposited Mn3O4 films undergo unipolar, nonvolatile resistance switching. An Au/Mn3O4/AuPd cell can be reversibly switched between a high resistance state (30 M Omega) and a low resistance state (14.8 Omega) by applying SET and RESET voltages of the same polarity. SET and RESET times of approximately 2 and 50 ns were observed. Because of the large resistance contrast between the two states and the persistence of each state, Mn3O4 is a candidate for future resistive random access memory (RRAM) devices.