Dielectric properties and spectroscopy of large-aspect-ratio ferroelectric thin-film heterostructures

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High energy density and breakdown/operating voltages with lower dielectric film thickness and manufacturing cost are the necessary traits in futuristic capacitors for a variety of applications. Prior studies have reported the successful fabrication of high-k, thin-film ferroelectrics with aspect ratios (diameter/thickness) <1000; however, devices with aspect ratios >104–105 are necessary to meet the large-capacitive requirements in pulsed-power applications such as the inverters in hybrid electric vehicles (HEVs). It is also widely accepted that the breakdown field of thin films decreases logarithmically with an increase in the aspect ratio (area) due to the increased probability of producing a defect spot. These observations raise an important question: can we fabricate ferroelectric high-k film capacitors that have large aspect ratio and can sustain high fields? Here we report the fabrication and characterization of Pb0.92La0.08Zr0.52Ti0.48O3 thin-film capacitors with aspect ratios >104 that can be operated at ∼1 MV cm−1 and are suitable for embedded passives in HEVs. Dielectric spectroscopy showed a low-frequency anomalous relaxation behaviour in large-aspect-ratio heterostructure, which was analysed and interpreted using an equivalent circuit model. The measured anomalous relaxation behaviour was de-convoluted using the model to obtain the actual material response. High capacitances (1–5 µF) and energy densities of (∼9 J cm−3) were routinely measured in these high-aspect-ratio films.