Hexagonal boron nitride (hBN) is a van der Waals material with exceptional dielectric properties, making it a critical component in advanced electronics, particularly for 2D material-based devices. Its structural similarity to graphene, combined with its insulating nature, positions it as an ideal substrate or gate dielectric. The key dielectric characteristics of hBN include a high breakdown field, low dielectric loss, and a wide bandgap, all of which contribute to its superior performance in electronic applications.

One of the most notable properties of hBN is its high breakdown field, which exceeds 10 MV/cm. This value is significantly higher than that of conventional dielectrics like silicon dioxide (SiO2), which typically exhibits a breakdown field of around 10 MV/cm only under ideal conditions and often much lower in practical applications. The high breakdown field of hBN ensures that it can sustain large electric fields without undergoing dielectric failure, making it suitable for high-power and high-voltage applications. This property is particularly advantageous in field-effect transistors (FETs) where gate dielectrics must endure strong electric fields without leakage or degradation.

Another critical feature of hBN is its low dielectric loss, characterized by a loss tangent (tan δ) as low as 0.0005 at microwave frequencies. This minimal energy dissipation under alternating electric fields makes hBN an excellent candidate for high-frequency applications, including RF devices and resonators. The low dielectric loss stems from the absence of dangling bonds and minimal charge traps in its crystal structure, reducing energy absorption and heat generation. In contrast, SiO2 exhibits higher dielectric losses, especially at elevated frequencies, due to its more disordered amorphous structure and interfacial defects.

The wide bandgap of hBN, approximately 5.9 eV, further enhances its dielectric performance. This large bandgap ensures minimal charge carrier generation under normal operating conditions, resulting in low leakage currents. The insulating nature of hBN is crucial for maintaining high on-off ratios in 2D transistors, where minimizing unintended conduction paths is essential. Compared to SiO2, which has a bandgap of about 8.9 eV, hBN’s slightly smaller bandgap is offset by its superior crystalline quality and interfacial properties when paired with other 2D materials like graphene or transition metal dichalcogenides (TMDCs).

The frequency-dependent permittivity of hBN is another important aspect of its dielectric behavior. The relative permittivity (εr) of hBN is anisotropic, with in-plane (ε∥) and out-of-plane (ε⊥) values differing due to its layered structure. The in-plane permittivity is typically around 6.7, while the out-of-plane permittivity is lower, approximately 3.0. This anisotropy must be considered in device design, particularly in vertical heterostructures where electric fields may be applied perpendicular to the layers. In contrast, SiO2 has an isotropic permittivity of about 3.9, making it less versatile for applications requiring directional dielectric tuning.

Temperature effects on hBN’s dielectric properties are relatively mild compared to other materials. The permittivity of hBN remains stable across a broad temperature range, from cryogenic conditions up to several hundred degrees Celsius. This thermal stability is attributed to the strong covalent bonds within the boron-nitrogen layers and weak van der Waals interactions between them. At elevated temperatures, hBN maintains its insulating properties better than many oxides, which may experience increased leakage currents due to thermally activated defect states.

When compared to other dielectric materials, hBN offers distinct advantages beyond SiO2. For instance, aluminum oxide (Al2O3), another common high-k dielectric, has a higher permittivity (εr ≈ 9) but suffers from higher defect densities and interface states when deposited on 2D materials. HfO2, with an even higher permittivity (εr ≈ 20), is prone to charge trapping and reliability issues under high fields. In contrast, hBN provides a cleaner interface with 2D semiconductors due to its atomically smooth surface and lack of dangling bonds, reducing scattering and improving carrier mobility.

The combination of these properties makes hBN an indispensable material for 2D electronics. As a substrate, it provides an ultra-flat surface that minimizes charge impurities and phonon scattering, enhancing the performance of graphene and TMDC-based devices. As a gate dielectric, its high breakdown strength and low leakage ensure efficient electrostatic control without compromising device reliability. Furthermore, its optical transparency and compatibility with other van der Waals materials enable its use in flexible and transparent electronics.

In summary, the dielectric properties of hBN—high breakdown field, low dielectric loss, wide bandgap, and anisotropic permittivity—make it a superior choice for next-generation electronic applications. Its thermal stability and compatibility with 2D materials further solidify its role as a foundational component in advanced device architectures. While traditional dielectrics like SiO2 remain widely used, hBN’s unique advantages position it as a critical material for pushing the boundaries of performance in nanoscale and high-frequency electronics.