Niobium Oxide and Tantalum Capacitors: M-I-S Model Parameters Comparison

摘要

An analysis of charge carrier transport and charge storage in NbO and Ta capacitors was performed. The aim of this paper is to characterize the active region quality of NbO and Ta capacitors. Our method for assessment of defects in active region of NbO and Ta capacitors is based on evaluation of VA, CV, noise and nonlinearity characteristics and theirs temperature dependencies. VA characteristics in normal and reverse mode at room and elevated temperatures have been measured and MIS structure characteristics have been obtained. The charge storage in these MIS structures depends on applied voltage. The charge is stored not only on electrodes, but also in the insulating layer. Capacitance is given by a charge stored on both electrodes and also in Nb_2O_5 and Ta_2O_5 layers. The kinetics of charging and discharging processes of localized states in the insulating layers are different from electrodes charging and discharging kinetics. An additional capacitance given by charge localized in Nb_2O_5 and Ta_2O_5 layers depends on frequency and temperature. The capacitance increases due to the fact that more localized states are involved in the charge storage process. Charge stored in Nb_2O_5 and Ta_2O_5 layers is changed with relaxation constant, which is continually varying from 10 to 1000 s. Sources of this electric charge are deep localized states as oxygen vacancies, donors, polarones and electrical dipoles orientation. The VA characteristic in reverse mode for NbO and Ta capacitors reveals "threshold" reverse voltage U_N in the range of 1.0 to 1.2 V for NbO technology and U_N in the range of 1.8 to 2.2 V for Ta technology.