Analysis of Abnormal Upturns in Capacitance–Voltage Characteristics for MOS Devices With High-$k$ Dielectrics

Abstract

In this letter, we analyze the nonsaturating upturns of capacitance under strong accumulation bias in MOS capacitors with high-k dielectrics. By comparing the electrical properties of dielectric samples with and without HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and by varying the ambient temperature, it is found that the conduction through the shallow trap levels in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk produces not only a steady-state current but also a dynamic current, which, in turn, causes the upturn in capacitance. The addition of RC shunts to the conventional small-signal model is proposed to consider the dynamic leakage effect. The model's effectiveness is verified by fitting the measured impedance spectrum and the measured capacitance. We suggest that measuring at a high frequency of hundreds of megahertz eliminates the dynamic interaction by shallow trap levels, allowing gate capacitance to be successfully reconstructed.