Modeling Leakage Currents in Metal Insulator Metal Structures with High K Materials

Various products such as personal computers, cellular phones and mobile devices require high speed and low power consumption. Such improvements have been attained by minimizing physical dimensions of electronic devices, leading to high density integration of transistors and capacitors on integrated chips (]Cs). However, as a consequence of down-scaling device dimensions, tunneling of electrons through thin gate oxides (SiO2) increases, leading to increased static power leakage. This constitutes wastage in power, and for the case of memory applications necessitates faster refresh cycles. In order to overcome such issues, high-k materials (such as HfO2 and ZrO2) that allow physically thicker films and reduce leakage current while maintaining gate capacitance have been proposed. Unfortunately, high-k materials have high defect densities that give rise to trap levels within the semiconductor band gap and open pathways for leakage currents. Such leakage currents are detrimental in Metal-Insulator-Metal capacitors that are the next generation capacitors for Radio Frequency (RF), DRAM (Dynamic Random Access Memory), and analog/mixed signal ICs applications. Hence, a detailed understanding of transport process is required to predict the dominant leakage current mechanism in high- k materials. In this research, a complete transport picture is presented by accounting for electron flow through the high- k oxides including trap-assisted transport. Other conduction mechanisms such as direct tunneling, Fowler-Nordheim (FN) tunneling and elastic trap assisted tunneling have also been considered to provide a complete model that can determine the leakage current density as a function of applied voltage or electric fields. For completeness, analyses for the material parameters (e.g., the optical permittivity) were carried out based on a commercial software package (CASTEP). This material analysis package uses density functional theory. The overall model has been validated with experimental data for Cr/HfO2/Cr and TiN/ZrO2/TiN structures. The leakage current densities in these materials agree well with the experimental data published.