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The Direct Tunneling, Dielectric Breakdown Investigation, and RRAM Application in MBE Hexagonal Boron Nitride Monolayers Using Metal-Insulator-Metal Devices

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In today’s post-Morre era, low-dimensional materials and their potential electronic applications have attracted extensive attention, but high-quality material synthesis and complicated device physics investigation is still challenging. Our lab is able to use Molecular Beam Epitaxy (MBE) epitaxy to reliably grow high quality millimeter grain size continuous ultrathin 2D (two-dimensional) hexagonal boron-nitridefilm (h-BN ) on Cobalt (Co) and Nickle (Ni) catalytic transition metal substrates. This is highly advantage in 2D electronic and photonic device applications. In this thesis, we report our comprehensive electric tunneling, dielectric breakdown, and memory application of single-layer h-BN film by fabricating scalable Metal-insulator-metal (MIM) diodes.

Direct tunneling and dielectric breakdown in molecular beam epitaxial hexagonal boron nitride (h-BN) monolayers were studied based on Ni/h-BN/Ni device configuration in Chapter 2. Effective tunneling areas are orders of magnitude smaller than the physical areas of the devices. Statistical Weibull analysis of the breakdown characteristics shows that breakdown area-scaling law applies to the effective areas rather than physical areas of the devices. The h-BN based MIM devices can sustain repeated DC voltage sweeping stresses up to 85 times under an extremely high compliance current of 100 mA, and the critical electric field is determined to be at least 11.8 MV/cm, demonstrating high dielectric strength and reliability of these h-BN monolayers. The mechanism of the breakdown and recovery of the h-BN monolayer MIM devices is also discussed.

The second project (Chapter 3) is devoted to the evaluation of Resistive Random Access Memory (RRAM) devices and the mechanism discussion of monolayer h-BN in MIM structure. The memory performance of bipolar switching shows great endurance with 97 cycles at 100mA compliance current, and a high average of 10^3 on/off ratio, but the reliability is an issue. For this particular film, both non-volatile bipolar and unipolar resistive switching (RS) and volatile threshold (TH) switching phenomena were found to coexist and could be converted from one to the other by controlling the electrical power, which provides a better understanding of the switching models. In devices with Graphene bottom electrodes, bipolar resistive switching with self-compliance current is discovered, making h-BN potential in low-power device applications.

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