Retention of resistance states in ferroelectric tunnel memristors

Resistive properties of Co/BaTiO3/La2/3Sr1/3MnO3 ferroelectric tunnel junctions on (110) NdGaO3 substrates are investigated. A notable characteristic of these junctions is the memristive behavior—a dependence of resistance on amplitude and duration of a writing pulse, which is attributed to field-induced charge accumulation at the Co/BaTiO3 interface. It is found that retention of the resistance states depends on the thickness of the ferroelectric barrier: the junctions with the thinnest 4-unit-cell-thick BaTiO3 barrier exhibit significant relaxation of the low resistance state while the junctions with thicker barriers exhibit stable resistance. It is proposed that, in a thinner barrier, a larger depolarizing field triggers a faster dissipation of the accumulated charges, resulting in a recovery of interfacial tunnel barrier height and gradual transition from a low to a high resistance state.