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Noise and Transport Analysis of the Niobium Oxide Layers
Sita, Zdeněk ; Hájek, Karel (oponent) ; Koktavý, Bohumil (oponent) ; Grmela, Lubomír (vedoucí práce)
Niobium oxide capacitor is a new type of passive components, which was developed to overcome basic disadvantages of Tantalum capacitors – limited ore source and burning failure mode. Similarly to Tantalum one, the niobium oxide capacitor can be described as a reverse MIS structure. V-A characteristics in normal and reverse mode at 77 and 300K, capacitance dependence of depleted layer on voltage and frequency, temperature and time dependence of leakage current and noise spectral density in frequency and time domains for different voltages were used to study charge carrier transport mechanisms in Nb2O5 dielectric and to define physical parameters, controlling the leakage current. Experimental data verified validity of proposed MIS structure band diagram and provided its key parameters. It was proven that the charge carrier transport in NbO capacitors is given by ohmic, Poole-Frenkel and tunnelling component in normal mode, and Schottky emission in reverse mode. Poole-Frenkel mechanism in normal mode and Schottky emission in reverse mode are dominant in the standard application voltage range. At high voltages, the tunnelling mechanism in normal mode determines breakdown voltage of the capacitor. In reverse mode, the barrier height between dielectric and anode determines resistance against thermal breakdown of the capacitor. It was found that NbO and Ta capacitors have identical conductivity mechanisms. Specifics of NbO anode material are reflected only in different values of the band diagram parameters, not in the principles of charge carrier transport mechanisms. This explains basic difference between both capacitors, which is in the quality of the dielectric layer at the anode - dielectric interface. Lower potential barriers and higher number of defects in the dielectric, caused by additional stable oxide, result in higher leakage current of NbO capacitor. This effect has however no effect on reliability of the component. Theoretical models and determined testing methods were used to select proper anode materials, to evaluate suitable dopants for NbO raw material improvement and to optimize the anodic oxidation technology. Charge carrier transport parameters were correlated with the reliability and on the basis of experimental data optimization of the capacitors manufacturing process was proposed. Better understanding of transport mechanisms in the NbO capacitors gave complete overview of the new Niobium oxide based component with highlighting strong and weak points of this new technology, and provided tools for better understanding of driving forces which improve efficiency and reliability of NbO capacitors.
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Noise and Transport Analysis of the Niobium Oxide Layers
Sita, Zdeněk ; Hájek, Karel (oponent) ; Koktavý, Bohumil (oponent) ; Grmela, Lubomír (vedoucí práce)
Niobium oxide capacitor is a new type of passive components, which was developed to overcome basic disadvantages of Tantalum capacitors – limited ore source and burning failure mode. Similarly to Tantalum one, the niobium oxide capacitor can be described as a reverse MIS structure. V-A characteristics in normal and reverse mode at 77 and 300K, capacitance dependence of depleted layer on voltage and frequency, temperature and time dependence of leakage current and noise spectral density in frequency and time domains for different voltages were used to study charge carrier transport mechanisms in Nb2O5 dielectric and to define physical parameters, controlling the leakage current. Experimental data verified validity of proposed MIS structure band diagram and provided its key parameters. It was proven that the charge carrier transport in NbO capacitors is given by ohmic, Poole-Frenkel and tunnelling component in normal mode, and Schottky emission in reverse mode. Poole-Frenkel mechanism in normal mode and Schottky emission in reverse mode are dominant in the standard application voltage range. At high voltages, the tunnelling mechanism in normal mode determines breakdown voltage of the capacitor. In reverse mode, the barrier height between dielectric and anode determines resistance against thermal breakdown of the capacitor. It was found that NbO and Ta capacitors have identical conductivity mechanisms. Specifics of NbO anode material are reflected only in different values of the band diagram parameters, not in the principles of charge carrier transport mechanisms. This explains basic difference between both capacitors, which is in the quality of the dielectric layer at the anode - dielectric interface. Lower potential barriers and higher number of defects in the dielectric, caused by additional stable oxide, result in higher leakage current of NbO capacitor. This effect has however no effect on reliability of the component. Theoretical models and determined testing methods were used to select proper anode materials, to evaluate suitable dopants for NbO raw material improvement and to optimize the anodic oxidation technology. Charge carrier transport parameters were correlated with the reliability and on the basis of experimental data optimization of the capacitors manufacturing process was proposed. Better understanding of transport mechanisms in the NbO capacitors gave complete overview of the new Niobium oxide based component with highlighting strong and weak points of this new technology, and provided tools for better understanding of driving forces which improve efficiency and reliability of NbO capacitors.
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