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(a) Schematic of a polycrystalline PZT oxide. (b) Experimental data show a wide distribution of breakdown time. (c) Cell-based model for TDDB. The GB regions have higher pre-existing defects (darker cells) and thus the required number of defects for a breakdown is smaller than that in grain regions. (d) The simulation results of Weibull distribution for the polycrystalline oxide.
Top view (x-z plane) of the PZT oxide using conductive AFM technique. (a) Topography of the oxide shows the grain (lighter) and grain boundary (darker) regions. (b) Leakage map on the same area shows that the grain boundaries have higher leakage current due to larger pre-existing traps. Moreover, some grain boundary locations have even higher leakage current (hot spots), indicating a distribution of defect density along the grain boundaries. (c) The leakage current values, along a horizontal line located in the region as highlighted in (b), is shown along with the topographical background in the same region. The current peaks clearly correlate with the topographic valleys due to the grain boundaries.
The topography (a), and the leakage current before (b) and after (c) voltage stress clearly show (circled) that the breakdown happens on region coincides with a grain boundary. The stress has been applied using the conductive AFM tip by repeated scanning with a stress bias.
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