9 results on '"von Witzleben, Moritz"'
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2. Switching kinetics of valence change memory devices on a sub-100 ps timescale
- Author
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von Witzleben, Moritz Alexander, Waser, Rainer, and Negra, Renato
- Subjects
LRS ,Aufladezeit ,Impedanzanpassung ,HRS ,VCM ,ddc:621.3 - Abstract
Dissertation, Rheinisch-Westf��lische Technische Hochschule Aachen, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2021). = Dissertation, Rheinisch-Westf��lische Technische Hochschule Aachen, 2021, The further development of today's memory technologies faces several technological barriers, which yields the demand for new approaches. One emerging memory type that has the potential to overcome these barriers is the valence change memory (VCM), which may also be usable for neuromorphic applications or in-memory computations. In VCM devices, the information is stored within different resistive states, namely a high resistive state (HRS) and a low resistive state (LRS), which can be programmed with electrical stimuli. The transition from the HRS to the LRS is referred to as SET and the opposite transition as RESET. In this thesis, the SET and RESET times of TaOx-, ZrOx-, and HfOx/TiOx-based VCM devices were studied in the time regime from 50 ps to 100 ns. Signals in this time regime contain high frequency components in the gigahertz regime. The signals require proper impedance matching up to the VCM device, which are, therefore, integrated into coplanar waveguide (CPW) structures. Nevertheless, an integrated VCM device constitutes a parallel plate capacitor with a considerable electrical charging time, which delays the measured SET and RESET times. To estimate the electrical charging time, an experimental approach was used, with which the time-dependent effective voltage at the VCM device could be determined. This approach used the Fourier transformation of the applied voltage pulse and the VCM device's scattering parameters. From the resulting effective voltage at the VCM device, the electrical charging time of all tested VCM devices was determined. The results indicate that conducted optimizations of the CPW structure decreased the electrical charging time significantly and allowed fast measurements on a sub-100 ps time scale. By employing dedicated hardware and integrating this hardware into a software, the measurements could be automated. This allowed collecting comprehensive data sets on the SET and RESET kinetics of the tested VCM devices and, thereby, allowed resolving their transient resistance on a picosecond time scale. The measured SET kinetics revealed that all studied devices can switch within 50 ps from the HRS to the LRS. To the author's knowledge, this is the fastest switching time reported for VCM devices. By comparing the SET kinetics of differently sized TaOx-based VCM devices and using the determined electrical charging times, it could be shown that the SET kinetics of VCM devices in the subnanosecond regime are mainly limited by the electrical charging time. The migration of mobile donors (e.g. oxygen vacancies), which limits the SET kinetics on slower time scales, and the heating time of the VCM device have only a minor influence. Achieving similar fast RESET times proved to be more difficult. In all studied VCM devices, the coexistence of a unipolar switching mode could be shown. This unipolar switching mode is triggered at higher voltages, which would be required for faster RESET times. Nevertheless, on some HfOx/TiOx-based VCM devices 50 ps fast RESET times could be measured repeatedly. From these kinetics measurements, RESET programming windows could be determined and, finally, approaches were derived to achieve faster RESET times., Published by RWTH Aachen University, Aachen
- Published
- 2021
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3. Intrinsic RESET Speed Limit of Valence Change Memories.
- Author
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von Witzleben, Moritz, Wiefels, Stefan, Kindsmüller, Andreas, Stasner, Pascal, Berg, Fenja, Cüppers, Felix, Hoffmann-Eifert, Susanne, Waser, Rainer, Menzel, Stephan, and Böttger, Ulrich
- Published
- 2021
- Full Text
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4. Design of materials properties and device performance in memristive systems
- Author
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L��bben, Michael, C��ppers, Felix, Mohr, Johannes, von Witzleben, Moritz, Breuer, Uwe, Waser, Rainer, Neumann, Christian, and Valov, Ilia
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Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Future development of the modern nanoelectronics and its flagships internet of things and artificial intelligence as well as many related applications is largely associated with memristive elements. This technology offers a broad spectrum of functionalities, however, it follows predominantly a phenomenological approach and crucial challenge/limit for further development remains variability and lack of fundamental materials' design strategy. Here we demonstrate the vital importance of materials' purity for determining memristors' functionalities, showing that part per million foreign elements significantly change the performance. By appropriate choice of chemistry and amount of doping material we can selectively enhance desired operation mode. We highlight how dopant dependent structure and charge/potential distribution in the space charge layers and the cell capacitance determine the device kinetics and functions. We evidence for first time experimentally the relation between materials properties and switching/neuromorphic performance, thus providing rules and directions for a rational design of memristive devices.
- Published
- 2019
5. Exploiting the switching dynamics of HfO 2 -based ReRAM devices for reliable analog memristive behavior
- Author
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Cüppers, Stefan, Menzel, S., Bengel, C., Hardtdegen, Alexander, Von Witzleben, Moritz Alexander, Böttger, Ulrich, Waser, R., and Hoffmann-Eifert, S.
- Subjects
ddc:600 - Abstract
APL materials 7(9), 091105 (2019). doi:10.1063/1.5108654, Published by AIP Publ., Melville, NY
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- 2019
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6. The ultimate switching speed limit of redox-based resistive switching devices
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Menzel, Stephan, Von Witzleben, Moritz Alexander, Havel, Viktor, and Böttger, Ulrich
- Subjects
ddc:540 - Abstract
Faraday discussions 213, 197-213 (2019). doi:10.1039/C8FD00117K, Published by Royal Society of Chemistry, London, Cambridge [u.a.]
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- 2019
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7. Impact of the Ohmic Electrode on the Endurance of Oxide-Based Resistive Switching Memory.
- Author
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Wiefels, Stefan, Von Witzleben, Moritz, Huttemann, Michael, Bottger, Ulrich, Waser, Rainer, and Menzel, Stephan
- Subjects
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OXIDE electrodes , *ELECTRODES , *MEMORY , *TIME measurements , *VALENCE fluctuations , *METALLIC oxides , *ANNEALING of metals - Abstract
As one of the key aspects in the reliability of redox-based resistive switching memories (ReRAMs), maximizing their endurance is of high relevance for industrial applications. The major limitation regarding endurance is considered the excessive generation of oxygen vacancies during cycling, which eventually leads to irreversible RESET failures. Thus, the endurance could be increased by using combinations of switching oxide and ohmic electrode (OE) metal that provides a high barrier for the generation of oxygen vacancies [defect formation energy (DFE)]. In this work, we present a sophisticated programming algorithm that aims to maximize the endurance within reasonable measurement time. Using this algorithm, we compare ReRAM devices with four different OE metals and confirm the theoretically predicted trend. Thus, our work provides valuable information for device engineering toward higher endurance. [ABSTRACT FROM AUTHOR]
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- 2021
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8. Variability-Aware Modeling of Filamentary Oxide-Based Bipolar Resistive Switching Cells Using SPICE Level Compact Models.
- Author
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Bengel, Christopher, Siemon, Anne, Cuppers, Felix, Hoffmann-Eifert, Susanne, Hardtdegen, Alexander, von Witzleben, Moritz, Hellmich, Lena, Waser, Rainer, and Menzel, Stephan
- Subjects
LOGIC circuits ,COMPACTING ,VALENCE fluctuations ,EXPECTATION (Psychology) - Abstract
Bipolar resistive switching (BRS) cells based on the valence change mechanism show great potential to enable the design of future non-volatile memory, logic and neuromorphic circuits and architectures. To study these circuits and architectures, accurate compact models are needed, which showcase the most important physical characteristics and lead to their specific experimental behavior. If BRS cells are to be used for computation-in-memory or for neuromorphic computing, their dynamical behavior has to be modeled with special consideration of switching times in SET and RESET. For any realistic assessment, variability has to be considered additionally. This study shows that by extending an existing compact model, which by itself is able to reproduce many different experiments on device behavior critical for the anticipated device purposes, variability found in experimental measurements can be reproduced for important device characteristics such as I-V characteristics, endurance behavior and most significantly the SET and RESET kinetics. Furthermore, this enables the study of spatial and temporal variability and its impact on the circuit and system level. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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9. The ultimate switching speed limit of redox-based resistive switching devices.
- Author
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Menzel S, von Witzleben M, Havel V, and Böttger U
- Abstract
In contrast to classical charge-based memories, the binary information in redox-based resistive switching devices is decoded by a change of the atomic configuration rather than changing the amount of stored electrons. This offers in principle a higher scaling potential as ions are not prone to tunneling and the information is not lost by tunneling. The switching speed, however, is potentially smaller since the ionic mass is much higher than the electron mass. In this work, the ultimate switching speed limit of redox-based resistive switching devices is discussed. Based on a theoretical analysis of the underlying physical processes, it is derived that the switching speed is limited by the phonon frequency. This limit is identical when considering the acceleration of the underlying processes by local Joule heating or by high electric fields. Electro-thermal simulations show that a small filamentary volume can be heated up in picoseconds. Likewise, the characteristic charging time of a nanocrossbar device can be even below ps. In principle, temperature and voltage can be brought fast enough to the device to reach the ultimate switching limit. In addition, the experimental route and the challenges towards reaching the ultimate switching speed limit are discussed. So far, the experimental switching speed is limited by the measurement setup.
- Published
- 2019
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