Metal-insulator-metal ferroelectric switchable diodes based on zirconium oxide and their application in electromagnetic energy harvesting

In this work we report the design, fabrication, and full electrical characterization of metal-insulator-metal (MIM) diodes made of a 7 nm-thick layer of ferroelectric zirconium oxide (ZrO₂) in between a bottom electrode of platinum and a top electrode of titanium/gold, and with micrometre-scale dimensions of the contact area from 2×2 μm² to 4×4 μm². The experiments show that the fabricated ZrO₂-based MIM diodes are ferroelectric switchable diodes, the physical origin of the ferroelectricity of the ZrO₂ thin film being intrinsic size effects and internal mechanical stresses induced during film growth. This ferroelectricity was confirmed through measurements of the polarization-voltage dependence and of the current-voltage loops, with a remanent polarization of about 8 μC cm⁻² and an average coercive voltage of about 2.4 V for an as-deposited ZrO₂ layer on silicon, whereas the dc current-voltage characteristics give the proof of the ultrafast transport mechanism inside the devices and of their switching behaviour, with an on-off ratio of maximum 7 orders of magnitude. Finally, we have demonstrated the electromagnetic energy-harvesting capabilities of the proposed ZrO₂-based MIM diodes by applying a microwave signal at various frequencies up to 27 GHz and with different input power levels, attaining dc voltage outputs up to 1.5 V in unbiased conditions and a maximum dc output power of 2.25 μW.