BiFe1–xCrxO3 Ferroelectric Tunnel Junctions for Neuromorphic Systems

We report on the fabrication of ferroelectric tunnel junctions of BiFe 0.45 Cr 0.55 O 3 as a tunneling barrier, Nb-doped (111) SrTiO 3 as a bottom electrode, and platinum as a top electrode. BiFeO 3 is a generic multiferroic material with perspectives for multiferroic tunnel junctions, with chromium being introduced to shift and enhance the magnetic ordering from canted magnetization to ferrimagnetism. We deposit the ferroelectric films by radio frequency magnetron sputtering, an industry-compatible synthesis method. After confirming the BiFe 1– x Cr x O 3 film composition and its partial crystallinity, we found possible indications of ferroelectricity through piezoresponse force microscopy. X-ray photoelectron spectroscopy together with optical band measurements provide the electronic band profile of the Nb:SrTiO 3 /BiFe 1– x Cr x O 3 /Pt structures. Pulsed electrical characterization reveals resistive switching with very high fatigue resistance (>10 6 cycles) consistent with direct tunneling across a trapezoidal barrier for a surface fraction of the film. These results make BiFe 1– x Cr x O 3 a promising candidate for ferroelectric tunnel junctions in particular, as they are able to operate as artificial synapses for neuromorphic circuit tiles as evidenced by spike-timing-dependent plasticity.