Modellierung und Simulation des Transports und assoziierter Phänomene in High-k-Dielektrika
Zusammenfassung der Projektergebnisse
It was the goal of the project to go beyond the so far existing approaches and to establish a higher-level simulation framework for leakage current studies. Therefore, a modeling environment was set up, where microscopic models for every relevant physical transport process were united in a comprehensive simulation framework with a kinetic Monte Carlo algorithm at its heart. The unique properties of the kinetic Monte Carlo formalism were exploited, such as modeling at the microscopic scale, e.g. to resolve single charge carrier motions, straightforward coupling to finite elements based differential equation solvers allowing to take into account, e.g., carrier-carrier interactions, the study of phenomena spatially localized in all three dimensions (electrode roughness effects, structural relaxation of defects, defect-assisted transport), and the investigation of the statistical interplay of different microscopic processes, e.g. the concurrent simulation of multiple transport mechanisms which allows to investigate their mutual interdependence. Having such a modeling environment at hand, we have carried out elaborate studies on the TiN/ZrO2 and SrRuO3/SrTiO3 material systems, which are of outmost importance for the semiconductor industry, where they are employed in the DRAM storage capacitor. Microscopic transport models were developed, which shed light on the microscopic transport in high-performance capacitors. Again, making use of the kinetic Monte Carlo framework and its modular architecture, which allows to augment transport models with only little effort, we iteratively improved our transport models by taking more and more physical effects into account. At the end, we could provide a self-consistent transport model for the both material systems. The detailed modeling on the microscopic scale, in contrast to the compact models, enabled us to propose target-oriented strategies how to optimize the performance of the capacitor structures. Problems which may arise in the future due to further downscaling of the capacitors could be identified in advance, and viable approaches how to tackle these could be provided. The simulation framework developed in the project can in the future be used to the study of other high-k dielectrics in order to provide theoretical support for the experimental efforts by unraveling the dominant microscopic transport mechanisms. Besides DRAM applications, the developed simulation tool, due to the variety of the implemented models and the versatility of the kinetic Monte Carlo algorithm and the program architecture itself, is well-suited to investigate transport in other metal-insulator-metal structures. For example, tunneling diodes for the rectification of high-frequency ac currents, which consist of an aluminum and a gold electrode separated by an ultrathin Al2O3 film were investigated. Another field of rising interest, for which kinetic Monte Carlo transport simulations has been successfully extended is the optimization of organic solar cells. The simulation framework established in the project has been adapted in order to simulate the complex microscopic processes involved in the photocurrent generation in these devices, namely exciton generation, diffusion, separation, decay and charge carrier injection, transport, recombination, extraction.
Projektbezogene Publikationen (Auswahl)
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"Modeling of leakage currents in high-k dielectrics: Three-dimensional approach via kinetic Monte Carlo," Applied Physics Letters, vol. 96, no. 6, pp. 1063, Feb. 2010
G. Jegert, A. Kersch, W. Weinreich, U. Schroeder, P. Lugli
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"Reliability of Al2O3-doped ZrO2 high-k dielectrics in three-dimensional stacked metal-insulator-metal capacitors," Journal of Applied Physics, vol. 108, no. 12, pp. 124104, Dec. 2010
D. Zhou, U. Schroeder, J. Xu, J. Heitmann, G. Jegert, W. Weinreich, M. Kerber, S. Knebel, E. Erben, T. Mikolajick
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"Monte Carlo Simulation of Leakage Currents in TiN/ZrO2/TiN Capacitors," IEEE Transactions on Electron Devices, vol. 58, no. 2, pp. 327, Feb. 2011
G. Jegert, A. Kersch, W. Weinreich, P. Lugli
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"Ultimate scaling of TiN/ZrO2/TiN capacitors: Leakage currents and limitations due to electrode roughness," Journal of Applied Physics, vol. 109, no. 1, pp. 014504, Jan. 2011
G. Jegert, A. Kersch, W. Weinreich, P. Lugli
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"Role of defect relaxation for trap-assisted tunneling in high-k thin films: A first-principles kinetic Monte Carlo study,” Physical Review B, vol. 85, no. 4, pp. 045303, Jan. 2012
G. Jegert, D. Popescu, P. Lugli, M. J. Häufel, W. Weinreich, A. Kersch
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"Feasibility Study of SrRuO3/SrTiO3/SrRuO3 Thin Film Capacitors in DRAM Applications," Electron Devices, IEEE Transactions on, vol. 61, no. 6, pp. 2130, Jun. 2014
D. Popescu, B. Popescu, G. Jegert, S. Schmelzer, U. Boettger, P. Lugli
