Anisotropic Dielectric Breakdown Strength of Single Crystal Hexagonal Boron Nitride

Abstract

Dielectric breakdown has historically been of great interest from the perspectives of fundamental physics and electrical reliability. However, to date, the anisotropy in the dielectric breakdown has not been discussed. Here, we report an anisotropic dielectric breakdown strength (E) for h-BN, which is used as an ideal substrate for two-dimensional (2D) material devices. Under a well-controlled relative humidity, E values in the directions both normal and parallel to the c axis (E and E) were measured to be 3 and 12 MV/cm, respectively. When the crystal structure is changed from sp of cubic-BN (c-BN) to sp of h-BN, E for h-BN becomes smaller than that for c-BN, while E for h-BN drastically increases. Therefore, h-BN can possess a relatively high E concentrated only in the direction parallel to the c axis by conceding a weak bonding direction in the highly anisotropic crystal structure. This explains why the E for h-BN is higher than that for diamond. Moreover, the presented E value obtained from the high quality bulk h-BN crystal can be regarded as the standard for qualifying the crystallinity of h-BN layers grown via chemical vapor deposition for future electronic applications.

Dielectric Dispersion and High Field Response of Multilayer Hexagonal Boron Nitride

“…The physical breakdown mechanism of layered hBN is different from that in bulk materials because it exhibits weak van der Waals interactions in the out‐of‐plane direction between its constituent elements, unlike conventional dielectric materials. It has been reported that the degradation is mostly initiated in bulk insulating materials by trap charges induced perturbations in accordance with percolation theory, whereas in 2D hBN a unique layer‐by‐layer deformation occurred under electrical stress . When a high field is applied to a bulk dielectric material, the electron traps form conductive clusters that are piled up to form a conductive path from one electrode to the other, and eventually, dielectric breakdown is realized.…”

“…At a very high electrical field, the top layers of hBN start to melt, resulting in the increase of effective electric field due to thickness reduction ( F = V / t ). This process proceeds layer‐by‐layer toward the opposite electrode, and eventually, catastrophic failure of hBN occurs . For further details, see Figure S12 of the Supporting Information.…”

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

“…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.…”

Propagative plasmons in graphene investigated by simulation method and infrared spectroscopy

“…For a good thin film of SiO 2 , it is possible to have 500MV/m. H-BN dielectric breakdown has been recorded as high as 1GV/m [60,74]. Diamond can theoretically reach higher value [51,156].…”

“…Soon after, studies on encapsulated graphene in h-BN, a substrate known to be suitable for graphene [145,53], showed promising results [34,114]. h-BN high dielectric strength property (up to 1.2GV/m when exfoliated) [60], as well as its good lattice matching with graphene [162], make it a good candidate. Moreover, thin films of h-BN have been synthesis through CVD process conserving good dielectric properties (0.4 GV/m) [74].…”