Comparison of device structures for the dielectric breakdown measurement of hexagonal boron nitride

Abstract

Improving the film quality in the synthesis of large-area hexagonal boron nitride films (h-BN) for two-dimensional material devices remains a great challenge. The measurement of electrical breakdown dielectric strength (EBD) is one of the most important methods to elucidate the insulating quality of h-BN. In this work, the EBD of high quality exfoliated singlecrystal h-BN was investigated using three different electrode structures under different environmental conditions to determine the ideal electrode structure and environment for EBD measurement. A systematic investigation revealed that EBD is not sensitive to contact force or electrode area but strongly depends on the relative humidity during measurement. Once the measurement environment is properly managed, it was found that the EBD values are consistent within experimental error regardless of the electrode structure, which enables the evaluation of the crystallinity of synthesized h-BN at the microscopic and macroscopic level by utilizing the three different electrode structures properly for different purposes.Following the many advances in the science and application of graphene and other two-dimensional (2D) materials, van der Waals (vdW) heterostructure devices formed by stacking atomically thin layered 2D crystals have attracted significant interest because of their fascinating electrical, optical and mechanical properties. The atoms connect to each other in a unit layer with strong covalent bonds, while each layer is stabilized by weak vdW forces, which enables a wide variety of stacking without the limitation of lattice mismatch at the interface.1 Hexagonal boron nitride (h-BN) with its wide band gap (5.2 -5.9 eV 2 ) has been commonly used as an ideal insulating material in vdW heterostructure devices. Because insulating properties are important in electrical device applications, especially for gate insulators in field-effect transistors, fundamental research on the electrical breakdown strength (EBD) in the out-of-plane direction has been conducted using small flakes that were mechanically exfoliated from high quality single crystals, and the EBD has been reported as ~10 -12 MV/cm. [3][4][5][6] Recently, the in-plane EBD has also been determined to be ~3 MV/cm, 4 suggesting strong anisotropy in EBD.For practical applications, the large-area synthesis of h-BN has been intensively studied using various methods.7-14 However, the out-of-plane EBD values for scalable h-BN are largely scattered and limited to ~4 MV/cm, which is lower than that of the exfoliated sample.7-10 It is evident that there are common problems with impurities, and the presence of wrinkles and grain boundaries and the non-uniform thickness, which largely originate from the high nucleation density. 15 However, the out-of-plane EBD has been measured under different environmental conditions and by various electrode structures, such as the crossed electrode structure, 6-10 conductive atomic-force microscopy (C-AFM) 3, 5, 11 and probing systems. 12 To fairly compare the film quality, com...

Dielectric Properties of Ultrathin CaF2 Ionic Crystals

“…Note that this value is higher than those previously reported for TiO 2 (≈3 MV cm −1 ) [25] and mechanically exfoliated h-BN (≈12.0 MV cm −1 ) via CAFM. [26][27][28] Additional discussion about the calculation and meaning of dielectric strength can be found in Note S3 (Supporting Information). This observation further indicates the extraordinary potential of ultrathin CaF 2 films to serve as dielectric in nanoelectronic devices.…”

Localized Probing of Dielectric Breakdown in Multilayer Hexagonal Boron Nitride

“…25 The structural damage is due to the release of enormous amounts of energy at the instant of breakdown. The catastrophic HBD failure in very thick h-BN (20−30 nm), as used by Hattori et al, 58 is qualitatively similar to the structural damages suffered by capacitors in the early generations of CMOS technology when physically thicker (typically 10−100 nm) gate dielectrics were used. 59 A novel finding is that partial removal of h-BN material can still be observed even for breakdown at PBD hardness (I comp < 100 nA) and for considerably thinner (2−5 nm) h-BN films as compared to those reported by Hattori et al 25 What is notable is that some pitting is observed in h-BN even under very low current compliance in PBD (I comp = 1−5 nA), in sharp contrast to measurements on conventional SiO 2 60,61 and HfO 2 62 gate dielectrics.…”

Dielectric Breakdown in Single-Crystal Hexagonal Boron Nitride

“…7 Furthermore, h-BN is an insulator with a bandgap 8 of ∼6 eV, and thus one can use h-BN as a gate dielectric material and seamlessly integrate with a wide range of 2D semiconductors to create 2D heterostructure electronic devices, such as transistors 9 and resistive switching memories. 10 The utility of h-BN as a gate dielectric is shown by the measurement of the tunneling current 11−13 and breakdown field strength 14,15 in both chemical vapor deposited polycrystalline h-BN and high-pressure/high-temperature singlecrystal h-BN. Notable here are the pioneering works of Hattori et al showing that (a) dielectric breakdown field strength in single-crystal h-BN is higher along out-of-plane directions compared to in-plane directions 15 and (b) physical removal of h-BN occurs at the breakdown spot under hard breakdown conditions.…”

“…The utility of h-BN as a gate dielectric is shown by the measurement of the tunneling current − and breakdown field strength , in both chemical vapor deposited polycrystalline h-BN and high-pressure/high-temperature single-crystal h-BN. Notable here are the pioneering works of Hattori et al showing that (a) dielectric breakdown field strength in single-crystal h-BN is higher along out-of-plane directions compared to in-plane directions and (b) physical removal of h-BN occurs at the breakdown spot under hard breakdown conditions .…”