Abstract
I-V characterization of Ta-Ta2O5-MnO2 capacitors was investigated at different temperatures, and Poole–Frenkel (PF) emission saturation was experimentally observed. Under the saturation voltage, the I-V curves at different temperature converged, and the temperature dependency was vanished. Above the saturation voltage, the leakage current was decreasing as the temperature increased. In order to evaluate the effects of saturation voltages (VS) on time-to-failure (TTF) of the capacitors, VS were first determined at +2°C and +25°C, then voltage accelerating tests were conducted at 85°C under 1.6 times of rated voltage. The distribution of VS and TTF of the samples were plotted and compared. It was shown that samples with lower saturation voltage failed earlier in the distribution of time-dependent dielectric breakdown. Comparing conventional methods for evaluating the quality of tantalum capacitors by measuring the leakage current at elevated temperature, the nondestructive measurement of saturation voltage at +2°C and +25°C may provide a novel and practicing approach tool to screening out capacitors with defected Ta2O5 layers.
Highlights
Because of its wide applications in electronics sciences, tantalum pentoxide (Ta2O5) has been extensively investigated both experimentally and theoretically over the past decades [1]
In order to reduce the influence from other conduction mechanisms, higher temperature ranges such as +85°C are not suggested for the measurement of PF saturation voltage
Previous study by Teverovsky [16] shows that the degradation of leakage currents of tantalum capacitors is caused the migration of oxygen vacancies to the cathodes, lowering the Schottky barrier at the MnO2-Ta2O5 interface
Summary
Because of its wide applications in electronics sciences, tantalum pentoxide (Ta2O5) has been extensively investigated both experimentally and theoretically over the past decades [1]. 2. PF Emission Saturation e classical PF effect is the thermal emission of charge carriers from Coulombic (i.e., charged) traps in the bulk of a dielectric, enhanced by the applied electric field [9]. Considering an electron in a trapping center, the Coulomb potential energy of the electron can be reduced by the application of an electric field across the dielectric film. Where J is the current density, μ is the electronic drift mobility, Nc is the density of states in the conduction band, qΦ ( Φ) is the trap energy level, T is the absolute temperature, q is the electronic charge, E is the electric field across the dielectric, k is the Boltzmann’s constant, and β, the PF constant, which is given by Hill [11] as . Zednicek et al reported that the dominant conduction mechanism through Ta2O5 is the PF emission at high temperature and high electric field [12]
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