Reliability studies on Ta_2O_5 high-κ dielectric metal-insulator-metal capacitors prepared by wet anodization

摘要

The temperature dependence of leakage current for tantalum oxide metal-insulator-metal capacitors has been investigated over the temperature range 20-160 ℃. The leakage current shows an increase with temperature and the conduction mechanism at medium to high electric fields is in agreement with the modified Poole-Frenkel model. The activation energy of the dominant deep trapping center in the oxide is calculated using this model. Constant voltage and constant current stress have been applied to the devices and the effect of stress conditions on leakage current, breakdown voltage, and high frequency capacitance-voltage have been investigated. Early oxide breakdown or time-dependent dielectric breakdown was observed during constant voltage and constant current stress, in which the former is a function of stress time and applied voltage or current. There is an increase in leakage current with time during the constant voltage stress, presumably due to generation of positive defect states. This is also apparent from the decrease in voltage with time during constant current stress. Degradation of the oxides by constant current stress and its effect on the oxide leakage current (or stress induced leakage current) at various constant current values and stress times has also been investigated and is discussed in this article.