Publication: Resistive Switching and Current Conduction Mechanisms in Hexagonal Boron Nitride Threshold Memristors with Nickel Electrodes
Researchers from RWTH Aachen University, AMO GmbH and Forschungszentrum Jülich have conducted a detailed study of the current conduction mechanisms and resistive switching mechanism of volatile memristors based on two-dimensional hexagonal boron nitride between two nickel electrodes. The work was recently published in the journal Advanced Functional Materials.
Memristors - short for "memory resistor" - are promising devices for next-generation memory and bioinspired computing systems. The unique property of these passive circuit elements is that their resistance can be "programmed" (either volatile or nonvolatile) by applying an external voltage. Memristive phenomena have been observed in various materials such as metal oxides, chalcogenides, amorphous silicon, and two-dimensional (2D) materials, each with different advantages and disadvantages. Recently, the 2D material hexagonal boron nitride (h-BN) has become the focus of many researchers since it has several advantageous physical properties such as high in-plane thermal conductivity, thermal and chemical stability, and mechanical flexibility. Last but not least, a wide band gap enables a large switching window. Moreover, its layered van der Waals structure allows integration on arbitrary substrates leading to pristine interfaces.
In the recently published work, Völkel and colleagues were able to point out the crucial role that defects in the h-BN play in the device behavior by using temperature-dependent current-voltage measurements in the different resistive states of the devices and by comparing the measured data with different theoretical models: Current conduction in the high-resistive state occurs through defect-supported jumping of electrons through the material. Switching to the low-resistance state can be understood by the formation and re-dissolution of nickel filaments along boron defect sites in the h-BN - a conclusion supported by high-resolution transmission electron microscopy (TEM) images.
Thus, the analytical method presented by Völkel and colleagues represents an alternative way to analyze the switching mechanism of memristors, in addition to already established methods such as TEM or conductive atomic force microscopy.
The research work was funded by the German Federal Ministry of Education and Research through the projects NEUROTEC (16ES1134, 16ES1133K), NEUROTEC 2 (16ME0399, 16ME0398K, 16ME0400) and NeuroSys (03ZU1106AA, 03ZU1106BA).