Boron nitride (BN) exhibits exceptional thermal stability, making it a critical material for high-temperature electronic applications in aerospace and automotive industries. Its structural and electronic properties allow it to function reliably in extreme environments where conventional semiconductors fail. BN exists in multiple polymorphs, with hexagonal boron nitride (hBN) and cubic boron nitride (cBN) being the most relevant for electronic applications.

Thermal Stability and Electronic Properties
BN maintains structural integrity at temperatures exceeding 1000°C in inert atmospheres, with minimal degradation in electrical performance. Unlike silicon-based semiconductors, which experience significant leakage currents and dopant diffusion above 300°C, BN retains high resistivity and low dielectric losses even under thermal stress. Its wide bandgap (~6 eV for hBN and ~6.4 eV for cBN) ensures minimal intrinsic carrier generation at elevated temperatures, reducing unwanted conductivity shifts.

In oxidizing environments, hBN demonstrates stability up to 850°C before gradual oxidation occurs, while cBN resists oxidation until temperatures surpass 1200°C. This stability is crucial for aerospace applications, where components must endure rapid thermal cycling and prolonged exposure to extreme heat. BN’s thermal conductivity (~400 W/m·K for cBN, ~300 W/m·K for hBN in-plane) further enhances its suitability by efficiently dissipating heat from active electronic components.

High-Temperature Sensors
BN-based sensors leverage its thermal and chemical inertness for operation in harsh conditions. For example, BN-coated thermocouples exhibit minimal drift when measuring exhaust gas temperatures in jet engines or automotive systems, where temperatures often exceed 800°C. The material’s low thermal expansion coefficient (≈1–3 × 10⁻⁶ K⁻¹) prevents mechanical delamination or signal distortion under thermal cycling.

BN is also used in gas sensors for combustion monitoring. Its surface properties allow selective adsorption of gases like NOₓ and CO at high temperatures without catalytic degradation. Unlike metal-oxide sensors, BN-based devices do not suffer from baseline drift due to material oxidation, enabling long-term stability in automotive exhaust systems.

Transistors and High-Power Devices
BN serves as an ideal substrate or gate dielectric for high-temperature transistors. In metal-oxide-semiconductor field-effect transistors (MOSFETs), hBN’s atomically smooth surface and low defect density reduce interface scattering, maintaining high carrier mobility (>1000 cm²/V·s in graphene-hBN heterostructures) even at 500°C. This is critical for power electronics in electric vehicles, where junction temperatures can reach 200–300°C during operation.

Wide-bandgap transistors incorporating BN layers demonstrate reduced leakage currents compared to silicon carbide (SiC) or gallium nitride (GaN) devices at similar temperatures. Experimental BN-GaN heterostructures have shown stable operation at 600°C with minimal threshold voltage shift, making them viable for aerospace power systems requiring reliability under thermal extremes.

Integrated Circuits for Harsh Environments
BN’s dielectric properties enable its use in passive components for high-temperature integrated circuits (ICs). Capacitors with hBN dielectrics exhibit stable capacitance values (±2% variation) across a temperature range of -200°C to 400°C, outperforming conventional alumina or polymer-based components. This stability is essential for automotive control units exposed to underhood temperatures or avionics systems in supersonic aircraft.

In interconnect applications, BN’s electrical insulation prevents crosstalk and electromigration in densely packed circuits operating above 300°C. Its compatibility with chemical vapor deposition (CVD) allows seamless integration into back-end-of-line (BEOL) processes for high-temperature ICs.

Challenges and Material Optimization
Despite its advantages, BN faces challenges in doping and ohmic contact formation at high temperatures. Unlike silicon, BN lacks reliable p-type dopants with shallow activation energies, limiting its use in bipolar devices. Recent advances in fluorine-based plasma treatments have shown promise in achieving stable n-type conductivity in hBN up to 500°C.

For ohmic contacts, refractory metals like tungsten or molybdenum are used with BN interfaces to minimize interdiffusion. Annealing studies indicate that W-hBN contacts maintain specific contact resistances below 10⁻⁴ Ω·cm² after 100 hours at 600°C, meeting requirements for aerospace-grade electronics.

Industrial Adoption and Future Prospects
The aerospace sector increasingly adopts BN-based electronics for engine monitoring systems, where sensors and control circuits must endure temperatures above 500°C without cooling systems. In automotive applications, BN-enhanced power modules improve the efficiency of electric vehicle inverters by operating at higher junction temperatures than SiC devices.

Ongoing research focuses on optimizing BN heterostructures with 2D materials like graphene to exploit quantum confinement effects for ultra-high-frequency transistors. Such devices could enable next-generation radar and communication systems for hypersonic vehicles, where conventional electronics fail due to thermal and radiative extremes.

In summary, BN’s stability under extreme temperatures and its compatibility with high-performance electronic applications position it as a key material for advancing aerospace and automotive technologies. Continued development in doping techniques and integration processes will further expand its role in harsh-environment electronics.