Dielectric Breakdown in Chemical Vapor Deposited Hexagonal Boron Nitride

Insulating films are essential in multiple electronic devices because they can provide essential functionalities, such as capacitance effects and electrical fields. Two-dimensional (2D) layered materials have superb electronic, physical, chemical, thermal, and optical properties, and they can be effectively used to provide additional performances, such as flexibility and transparency. 2D layered insulators are called to be essential in future electronic devices, but their reliability, degradation kinetics, and dielectric breakdown (BD) process are still not understood. In this work, the dielectric breakdown process of multilayer hexagonal boron nitride (h-BN) is analyzed on the nanoscale and on the device level, and the experimental results are studied via theoretical models. It is found that under electrical stress, local charge accumulation and charge trapping/detrapping are the onset mechanisms for dielectric BD formation. By means of conductive atomic force microscopy, the BD event was triggered at several locations on the surface of different dielectrics (SiO2, HfO2, Al2O3, multilayer h-BN, and monolayer h-BN); BD-induced hillocks rapidly appeared on the surface of all of them when the BD was reached, except in monolayer h-BN. The high thermal conductivity of h-BN combined with the one-atom-thick nature are genuine factors contributing to heat dissipation at the BD spot, which avoids self-accelerated and thermally driven catastrophic BD. These results point to monolayer h-BN as a sublime dielectric in terms of reliability, which may have important implications in future digital electronic devices.Fil: Jiang, Lanlan. Soochow University; ChinaFil: Shi, Yuanyuan. Soochow University; China. University of Stanford; Estados UnidosFil: Hui, Fei. Soochow University; China. Massachusetts Institute of Technology; Estados UnidosFil: Tang, Kechao. University of Stanford; Estados UnidosFil: Wu, Qian. Soochow University; ChinaFil: Pan, Chengbin. Soochow University; ChinaFil: Jing, Xu. Soochow University; China. University of Texas at Austin; Estados UnidosFil: Uppal, Hasan. University of Manchester; Reino UnidoFil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lu, Guangyuan. Chinese Academy of Sciences; República de ChinaFil: Wu, Tianru. Chinese Academy of Sciences; República de ChinaFil: Wang, Haomin. Chinese Academy of Sciences; República de ChinaFil: Villena, Marco A.. Soochow University; ChinaFil: Xie, Xiaoming. Chinese Academy of Sciences; República de China. ShanghaiTech University; ChinaFil: McIntyre, Paul C.. University of Stanford; Estados UnidosFil: Lanza, Mario. Soochow University; Chin

Oriented Graphene Nanoribbons Embedded in Hexagonal Boron Nitride Trenches

Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs.Comment: 32 pages, 4 figures, Supplementary informatio

How Low Nucleation Density of Graphene on CuNi Alloy is Achieved

CuNi alloy foils are demonstrated to be one of the best substrates for synthesizing large area single-crystalline graphene because a very fast growth rate and low nucleation density can be simultaneously achieved. The fast growth rate is understood to be due the abundance of carbon precursor supply, as a result of the high catalytic activity of Ni atoms. However, a theoretical understanding of the low nucleation density remains controversial because it is known that a high carbon precursor concentration on the surface normally leads to a high nucleation density. Here, the graphene nucleation on the CuNi alloy surfaces is systematically explored and it is revealed that: i) carbon atom dissolution into the CuNi alloy passivates the alloy surface, thereby drastically increasing the graphene nucleation barrier; ii) carbon atom diffusion on the CuNi alloy surface is greatly suppressed by the inhomogeneous atomic structure of the surface; and iii) a prominent increase in the rate of carbon diffusion into the bulk occurs when the Ni composition is higher than the percolation threshold. This study reveals the key mechanism for graphene nucleation on CuNi alloy surfaces and provides a guideline for the catalyst design for the synthesis of graphene and other 2D materials

Minimizing the programming power of phase change memory by using graphene nanoribbon edge-contact

Nonvolatile phase change random access memory (PCRAM) is regarded as one of promising candidates for emerging mass storage in the era of Big Data. However, relatively high programming energy hurdles the further reduction of power consumption in PCRAM. Utilizing narrow edge-contact of graphene can effectively reduce the active volume of phase change material in each cell, and therefore realize low-power operation. Here, we demonstrate that a write energy can be reduced to about ~53.7 fJ in a cell with ~3 nm-wide graphene nanoribbon (GNR) as edge-contact, whose cross-sectional area is only ~1 nm2. It is found that the cycle endurance exhibits an obvious dependence on the bias polarity in the cell with structure asymmetry. If a positive bias was applied to graphene electrode, the endurance can be extended at least one order longer than the case with reversal of polarity. The work represents a great technological advance for the low power PCRAM and could benefit for in-memory computing in future.Comment: 14 pages, 4 figure

Advanced Data Encryption ​using 2D Materials

Advanced data encryption requires the use of true random number generators (TRNGs) to produce unpredictable sequences of bits. TRNG circuits with high degree of randomness and low power consumption may be fabricated by using the random telegraph noise (RTN) current signals produced by polarized metal/insulator/metal (MIM) devices as entropy source. However, the RTN signals produced by MIM devices made of traditional insulators, i.e., transition metal oxides like HfO and AlO, are not stable enough due to the formation and lateral expansion of defect clusters, resulting in undesired current fluctuations and the disappearance of the RTN effect. Here, the fabrication of highly stable TRNG circuits with low power consumption, high degree of randomness (even for a long string of 2 − 1 bits), and high throughput of 1 Mbit s by using MIM devices made of multilayer hexagonal boron nitride (h-BN) is shown. Their application is also demonstrated to produce one-time passwords, which is ideal for the internet-of-everything. The superior stability of the h-BN-based TRNG is related to the presence of few-atoms-wide defects embedded within the layered and crystalline structure of the h-BN stack, which produces a confinement effect that avoids their lateral expansion and results in stable operation.M.L. acknowledges generous support from the King Abdullah University of Science and Technology. This work was supported by the Ministry of Science and Technology of China (grants no. 2018YFE0100800, 2019YFE0124200), the National Natural Science Foundation of China (grants no. 61874075), the Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the 111 Project from the State Administration of Foreign Experts Affairs of China. A.A. and S.R. acknowledge the project: ModElling Charge and Heat trANsport in 2D-materIals based Composites—MECHANIC reference number: PCI2018-093120 funded by Ministerio de Ciencia, Innovación y Universidades. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). Y.S. acknowledges support from the European Union (Marie Sklodowska-Curie actions (grant no. 894840). The authors acknowledge technical advice from H.-S. Philip Wong from Stanford University and Xiaoming Xie from Chinese Academy of Sciences

How Low Nucleation Density of Graphene on CuNi Alloy is Achieved

CuNi alloy foils are demonstrated to be one of the best substrates for synthesizing large area single-crystalline graphene because a very fast growth rate and low nucleation density can be simultaneously achieved. The fast growth rate is understood to be due the abundance of carbon precursor supply, as a result of the high catalytic activity of Ni atoms. However, a theoretical understanding of the low nucleation density remains controversial because it is known that a high carbon precursor concentration on the surface normally leads to a high nucleation density. Here, the graphene nucleation on the CuNi alloy surfaces is systematically explored and it is revealed that: i) carbon atom dissolution into the CuNi alloy passivates the alloy surface, thereby drastically increasing the graphene nucleation barrier; ii) carbon atom diffusion on the CuNi alloy surface is greatly suppressed by the inhomogeneous atomic structure of the surface; and iii) a prominent increase in the rate of carbon diffusion into the bulk occurs when the Ni composition is higher than the percolation threshold. This study reveals the key mechanism for graphene nucleation on CuNi alloy surfaces and provides a guideline for the catalyst design for the synthesis of graphene and other 2D materials © 2018 The Authors

Vacancy-assisted growth mechanism of multilayer hexagonal boron nitride on a Fe2B substrate

The controllable synthesis of large-area and uniform hexagonal boron nitride (h-BN) films has been recently achieved on metal-boron alloy catalysts with the use of N feedstock, representing important progress in an economic and environmentally friendly process. However, the systematic investigation of the growth mechanism is still lacking, which impedes the further development of this method. In this work, on the basis of density functional theory (DFT) calculations and experiments, we reveal the vacancy-assisted growth mechanism of h-BN on FeB substrate. It is found that B vacancies created by the formation of BN dimers play important roles in the migration of B and N atoms near the catalyst surface. The diffusions of B and N atoms in the FeB substrate need to overcome energy barriers of only less than 1.5 eV, which enables abundant dissolution of N atoms near the catalytic surface. Moreover, we found the critical barrier for h-BN growth is in the nucleation stage, which is ∼2 eV. These advantages enable the synthesis of h-BN at a low temperature of 700 K in our experiments. This vacancy-assisted growth of h-BN films on FeB substrates is beneficial to the wafer-scale fabrication of multilayer materials, paving the way to potential applications in two-dimensional electronic and optoelectronic devices

Overview of Rational Design of Binary Alloy for the Synthesis of Two-Dimensional Materials

Two-dimensional (2D) materials attracted widespread interest as unique and novel properties different from their bulk crystals, providing great potential for semiconductor devices and applications. Recently, the family of 2D materials has been expanded including but not limited to graphene, hexagonal boron nitride (h-BN), transition metal carbides (TMCs), and transition metal dichalcogenides (TMDCs). Metal-catalyzed chemical vapor deposition (CVD) is an effective method to achieve precise synthesis of these 2D materials. In this review, we focus on designing various binary alloys to realize controllable synthesis of multiple CVD-grown 2D materials and their heterostructures for both fundamental research and practical applications. Further investigations indicated that the design of the catalytic substrate is an important issue, which determines the morphology, domain size, thickness and quality of 2D materials and their heterostructures