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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]

Oxidation of metal layer surfaces due to atomic layer deposition (ALD) of thin metal oxide films is studied. For this, dense and smooth metal films of Pt, Ta and Hf were grown by off-axis sputtering and were in-situ transferred into the ALD system. Oxide films like HfO2, TiO2 and Al2O3 with a thickness of about 2 to 3 nm were deposited between 250 and 300degC by means of plasma assisted ALD utilizing a remote oxygen plasma as oxygen source. The 'built-in' oxygen gradients formed at different metal/ALD metal oxide interfaces were analysed by angle resolved X-ray photoelectron spectroscopy. The Pt metal films show no evidence of oxidation due to the PE-ALD process, independent of the grown metal oxide. In contrast, the thickness of the metal oxide layers formed at the surfaces of the Hf and Ta metal films depends on the ALD surface reactions as well as on the differences in oxidation enthalpy of the substrate metal and the metal oxide. The results are important for the design of high-density memristor arrays based on OxRAM devices.

Ultrathin, dense, high purity, stoichiometric HfO2 films were grown by plasma-enhanced atomic layer deposition from TEMAH and O2 plasma at a substrate temperature of 300degC. Utilizing these high quality HfO2 thin films of precise thickness enabled an accurate study of the effect of the thickness of the oxide, i.e., 5 nm and 8 nm HfO2, and the oxygen exchange layer (OEL), i.e., 5 nm and 10 nm Ti, on the electroforming and resistive switching performance. A thinner oxide layer and a thicker OEL, respectively, resulted in a reduction of the electroforming voltage due to an easier formation of the conductive filament. In addition, differences in the bipolar type resistive switching behavior of various HfO2/Ti cells were observed and a transition into complementary switching was found for the stack built with 8 nm HfO2 and 5 nm Ti.

Ultrathin, dense, high purity, stoichiometric HfO2films were grown by plasma-enhanced atomic layer deposition from TEMAH and O2plasma at a substrate temperature of 300°C. Utilizing these high quality HfO2thin films of precise thickness enabled an accurate study of the effect of the thickness of the oxide, i.e., 5 nm and 8 nm HfO2, and the oxygen exchange layer (OEL), i.e., 5 nm and 10 nm Ti, on the electroforming and resistive switching performance. A thinner oxide layer and a thicker OEL, respectively, resulted in a reduction of the electroforming voltage due to an easier formation of the conductive filament. In addition, differences in the bipolar type resistive switching behavior of various HfO2/Ti cells were observed and a transition into complementary switching was found for the stack built with 8 nm HfO2and 5 nm Ti.