SILPAKORN UNIVERSITY SCIENCE AND TECHNOLOGY JOURNAL, Vol 6, NO 2 (2012)

Behavior of Ta2O5-Si Capacitors with Different Gate Electrode under Constant Current Stress

Margareta Pecovska-Gjorgjevich, Julijana Velevska, Elena Atanassova








Abstract


The electrical characteristics of MOS capacitors with Ta2O5 as oxide and with different gate electrodes (Al, Au, W, TiN) are investigated using high frequency capacitance-voltage (C-V) and current–voltage (I-V) measurements. The influence of deposition techniques of gate electrode (reactive sputtering and evaporation) and the type of electrode material (different work functions) are observed. Charged trapping properties were studied by measuring the gate voltage shift due to trapped charge generation in order to investigate the response to constant current stress (CCS) under various current/time conditions at room temperature. The results showed that the presence of pre-existing electron traps leads the changes of time dependent voltage during gate injected CCS in the initial stage, followed by the slow positive charge build-up, same for all the structures and characteristic for this oxide. Gate-induced defects due to ther rate of reaction of gate electrode with the oxide are responsible for different behavior of the structures with different gate electrodes, observed in the initial stage of CCS. The Au-gated devices appear to be the most susceptible to the constant current stress degradation. They also have highest values of capacitance and lowest leakage currents.

Key Words: Gate electrode; Dielectric properties; Oxides; Constant current stress

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