arXiv subjects

Johannes Mohr

Publications and source records attributed to Johannes Mohr.

5 recordsLinked to original sources

arXiv2026

Improved selector behavior in ultrathin chromium-doped V$_2$O$_3$ films

Devices based on the negative differential resistance effect in chromium doped V$_2$O$_3$ are considered to be promising as selector elements for use in emerging memory technologies, as well as for neuromorphic applications. It is shown by electrical measurements, that the switching effect is maintained for very thin films down to 5 nm, and even improved properties such as a low leakage current and an abrupt transition are observed. For these thicknesses, the behavior of crystalline and amorphous films becomes very similar; most strikingly, a forming step is required in both. Transmission electron microscopy reveals this to be likely due to a thin amorphous layer that forms at the interface to the TiN electrode. Elemental mapping further shows a complex distribution of the chromium dopants, as well as a diffusion of Ti into the layer from the electrode, which might be responsible for the improved properties.

cond-mat.str-el↗

arXiv2024

Electronic vs. phononic thermal transport in Cr-doped V2O3 thin films across the Mott transition

Understanding the thermal conductivity of chromium doped V2O3 is crucial for optimizing the design of selectors for memory and neuromorphic devices. We utilized the time-domain thermoreflectance technique to measure the thermal conductivity of chromium doped V2O3 across varying concentrations, spanning the doping induced metal-insulator transition. In addition, different oxygen stoichiometries and film thicknesses were investigated in their crystalline and amorphous phases. Chromium doping concentration (0%-30%) and the degree of crystallinity emerged as the predominant factors influencing the thermal properties, while the effect of oxygen flow (600-1400 ppm) during deposition proved to be negligible. Our observations indicate that even in the metallic phase of V2O3, the lattice contribution is the dominant factor in thermal transport with no observable impact from the electrons on heat transport. Finally, the thermal conductivity of both amorphous and crystalline V2O3 was measured at cryogenic temperatures (80-450 K). Our thermal conductivity measurements as a function of temperature reveal that both phases exhibit behavior similar to amorphous materials, indicating pronounced phonon scattering effects in the crystalline phase of V2O3.

cond-mat.str-el↗

arXiv2024

Bulk-like Mott-Transition in ultrathin Cr-doped V2O3 films and the influence of its variability on scaled devices

The pressure driven Mott-transition in Chromium doped V2O3 films is investigated by direct electrical measurements on polycrystalline films with thicknesses down to 10 nm, and doping concentrations of 2%, 5% and 15%. A change in resistivity of nearly two orders of magnitude is found for 2% doping. A simulation model based on a scaling law description of the phase transition and percolative behavior in a resistor lattice is developed. This is used to show that despite significant deviations in the film structure from single crystals, the transition behavior is very similar. Finally, the influence of the variability between grains on the characteristics of scaled devices is investigated and found to allow for scaling down to at least 50 nm device width.

cond-mat.str-el↗

arXiv2022

Fabrication of highly resistive NiO thin films for nanoelectronic applications

Thin films of the prototypical charge transfer insulator NiO appear to be a promising material for novel nanoelectronic devices. The fabrication of the material is challenging however, and mostly a p-type semiconducting phase is reported. Here, the results of a factorial experiment are presented that allow optimization of the film properties of thin films deposited using sputtering. A cluster analysis is performed, and four main types of films are found. Among them, the desired insulating phase is identified. From this material, nanoscale devices are fabricated, which demonstrate that the results carry over to relevant length scales. Initial switching results are reported.

cond-mat.mtrl-sci↗

arXiv2019

Design of materials properties and device performance in memristive systems

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.

cond-mat.mtrl-sci↗