Vertically Aligned MoS Films With Cu Achieve 85% Reliable Non-Volatile Resistive Switching

Memristors, circuit elements whose resistance depends on past electrical activity, hold great promise for next-generation electronics, and researchers are increasingly exploring low-dimensional materials to enhance their performance. Shuei-De Huang from Microelectronics Research, alongside Touko Lehenkari and Topias Järvinen, investigated the memristive properties of vertically aligned molybdenum disulfide (MoS₂) films using silver, copper, and gold electrodes. This work reveals that despite employing the same MoS₂ material, each metal exhibits remarkably different switching behaviour, a crucial finding for practical applications. Silver enables temporary, volatile switching, while copper delivers stable, non-volatile performance with resistance maintained for over 2500 seconds, and gold shows no switching at all. These results, alongside evidence of copper filament formation, demonstrate a pathway to fabricate versatile circuits by simply selecting different metals for deposition onto a single active material, offering a significant advance in memristor technology.

MoS2 Memristors, Fabrication and Retention Data

This supporting information details the fabrication and performance of memristors based on vertically aligned molybdenum disulfide (VA-MoS₂) films with varying metal electrodes. The research focuses on the fabrication process, electrical characteristics, and data retention capabilities of devices incorporating copper, silver, and gold electrodes. The fabrication process begins with a molybdenum seed layer, exhibiting a root mean square roughness of 0. 886nm, which influences the vertical alignment of the MoS₂ film. Precise control over metal deposition rates is crucial for achieving high-quality films.

Electrical characterization using current-voltage measurements reveals that the compliance current significantly impacts switching behaviour. Variability in switching voltages and currents is observed, suggesting sensitivity to local variations within the MoS₂ film. Data retention measurements demonstrate the stability of the high resistance state in silver devices, confirming the non-volatile nature of the memory. These findings highlight the importance of fabrication control and addressing device variability to create reliable memristor devices. The results confirm the potential of these devices for non-volatile memory applications.

Vertically Aligned Molybdenum Disulfide Film Fabrication

Scientists engineered vertically aligned molybdenum disulfide (VA-MoS₂) films to investigate memristive properties, employing a robust synthesis method confirmed through detailed structural characterization. Transmission electron microscopy confirmed the vertical alignment of MoS₂ layers, while atomic force microscopy revealed a smooth surface with an average roughness of 1. 49nm. Raman spectroscopy and X-ray diffraction further confirmed the layered structure and high quality of the synthesized films. To fabricate memristors, the team deposited silver, copper, and gold electrodes onto the VA-MoS₂ films.

Electrical characteristics were measured, revealing distinct switching behaviours dependent on the electrode material. Silver devices exhibited volatile switching, while copper devices demonstrated stable, non-volatile switching with retention exceeding 2500 seconds. Gold electrodes showed no memristive response. Approximately 85% of both silver and copper devices displayed reliable memristor behaviour, demonstrating the robustness of the fabrication process. These findings demonstrate that the choice of electrode material is a critical factor in controlling the switching characteristics of VA-MoS₂ memristors, opening avenues for simplified circuit fabrication.

Electrode Material Dictates Memristive Switching Behaviour

Scientists have achieved distinct memristive behaviours in vertically aligned molybdenum disulfide (VA-MoS₂) films by employing silver, copper, and gold as top electrodes. Investigations reveal that silver electrodes enable volatile switching, while copper electrodes demonstrate stable, non-volatile switching with retention exceeding 2500 seconds. Notably, gold electrodes exhibit no memristive response whatsoever. Structural characterization confirms a well-oriented layered crystal structure with a perpendicular alignment to the substrate. Raman spectroscopy shows characteristic vibration modes of MoS₂, indicating high film quality.

The team measured abrupt resistance changes in copper devices, coupled with a significant increase in copper content upon biasing, confirming a filament formation and rupture mechanism responsible for the stable non-volatile switching. Approximately 85% of both silver and copper devices exhibit reliable memristor behaviour, demonstrating the robustness of the fabrication process. These results demonstrate the potential for simplified fabrication of circuits by utilizing different metals on a single active material, opening avenues for advanced memory and neuromorphic computing applications.

Electrode Material Dictates MoS2 Memristive Behaviour

This research demonstrates that vertically aligned molybdenum disulfide (VA-MoS₂) films exhibit markedly different memristive behaviours depending on the choice of top electrode material. Scientists systematically investigated devices incorporating silver, copper, and gold electrodes, revealing a strong correlation between electrode composition and device functionality. Silver electrodes yielded volatile switching characteristics, while copper electrodes enabled stable, non-volatile switching with resistance retention exceeding 2500 seconds. Notably, gold electrodes did not induce any measurable memristive effect.

Detailed analysis indicates that the observed differences stem from variations in metal diffusion within the VA-MoS₂ film during operation. Copper devices exhibited a significant increase in copper concentration upon biasing, suggesting a filament-based switching mechanism involving the formation and rupture of conductive pathways. This is the first demonstration of a functional copper/VA-MoS₂ memristor. This work establishes a promising route towards simplified fabrication of integrated neuromorphic circuits, as a single active material can be tailored to exhibit diverse functionalities simply by selecting different electrode materials.