Query: The demand for reliable and high-performance resistive memory devices has spurred intense research into the optimization of dielectric materials. Among these, multilayer hexagonal boron nitride (h-BN) has emerged as a promising candidate due to its exceptional dielectric properties and potential for resistive switching applications. In this context, this paper focuses on the deliberate engineering of resistive properties in multilayer h-BN films through the incorporation of ammonia during growth and subsequent ammonia annealing. The introduction of ammonia during the growth process is a deliberate strategy to modulate the structural and morphological characteristics of the multilayer h-BN. Our investigations reveal a correlation between the incorporation of ammonia, larger grain sizes, and accelerated growth rates. The resulting improvements in film quality are particularly advantageous for resistive memory applications, where reliable and robust electrical performance is paramount and dielectric applications.
Resistive Random Access Memory (RRAM) has been considered as one of the most promising devices for the artificial synapse. However, there are still several issues to be overcome: 1) low reliability due to the random diffusion of atoms or vacancies, 2) low endurance due to structural breakdown during the switching process, and 3) high off-current due to thermally activated hopping transport through the trap states. In CVD-grown samples, native lattice defects (e.g., vacancies, grain boundaries) promote the penetration of metallic ions originating from the electrodes to form conductive nanofilaments (CNFs). In fact, the formation and dissolution of CNFs in CVD-grown h-BN films is what enables its NVRS behavior, but a significant defect density can lead to many conductive paths within the active region of a single device. Thus, existing h-BN memristor demonstrations using planar MIM configurations have many paths which are difficult to control in number, location, and conductive state (on, off, or partial formed CNFs). Growth of larger grain sizes and seamless stitching of grains would reduce the paths for leakage. We found that incorporating ammonia gas during the growth of hexagonal boron nitride (h-BN) significantly enhances both crystal quality and growth rates. Ammonia serves as a nitrogen source that maintains the optimal boron to nitrogen ratio, promoting the formation of high-quality crystalline layers with fewer defects.
Ammonia annealing of the multilayer h-BN films introduces a novel avenue for defect engineering. The deliberate introduction of ammonia during the post growth annealing process of the grown multilayered films significantly modifies the defect configurations within the layers. This facilitates the formation of molecular bridges, adding a controlled variability to the resistive properties of the material. We focus on elucidating the role of nitrogen incorporation at boron sites in these molecular bridges, demonstrating how this process enhances resistivity and robustness against unintended electrical breakdown events. The synergy between growth conditions, defect engineering, and resistive properties explored in this study offers a nuanced understanding of how multilayer h-BN can be tailored for optimal performance. 

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Subject: engineering
Intent: Paper Understanding