Straining bismuth ferrite thin films provides current for mass data storage applications

                                            Mary Alexandra Agner

Bismuth ferrite thin films can be tuned using substrate strain to produce an on/off current ratio large enough for application to ultrahigh density memory.

Resistive computer memory, which stores data with resistance changes across a dielectric material, can be stacked in compact layers, making it a better solution for mass storage applications than conventional one-transistor-one-capacitor devices. The material chosen for these devices must have a sufficiently high on/off current ratio in order to be able to select memory elements.

Bismuth ferrite, BiFeO3, is a candidate material for resistive memory devices with room-temperature ferroelectric properties. Chen et al. demonstrate a method for tuning bismuth ferrite thin films using the strain from the film’s substrates to manipulate the material’s polarity and produce a high on/off current ratio.

The authors examined the natural domains which form in epitaxial multiferroic thin films as the film cools after deposition. They compared two substrates, gadolinium scandium (GdScO3) and strontium titanate (SrTiO3), which strained the bismuth ferrite film in tensile and compressive directions, respectively. They manipulated the film’s substrates in order to alter the polarization within the films. The change in polarization affected the free carriers within the film and thus changed the domain wall current.

The samples with gadolinium scandium substrate created higher on-current than those with strontium titanate substrates. The group concluded that in-plane ferroelectric polarization explained the higher domain wall current in the samples with gadolinium scandium substrates: More carriers accumulate at the domain walls, deepening the band bending at those walls, and creating the increased on-current, showing the film’s promise for mass storage applications.