Scandium aluminum oxide (ScₓAl₁₋ₓO₃) has emerged as a promising high-K gate dielectric for ultra-wide bandgap (UWBG) semiconductor devices, particularly in applications involving gallium oxide (Ga₂O₃). The material’s high dielectric constant, combined with its ability to form favorable band alignments with Ga₂O₃, makes it a strong candidate for next-generation power electronics and high-frequency devices. This article examines the role of ScₓAl₁₋ₓO₃ in band offset engineering, leakage current suppression, and reliability under high-field stress, while comparing its performance with conventional dielectrics like SiO₂ and HfO₂.

One of the critical challenges in UWBG devices is achieving sufficient band offsets to minimize carrier injection and leakage currents. Ga₂O₃ has an ultra-wide bandgap of approximately 4.8 eV, necessitating a gate dielectric with a large conduction band offset (CBO) and valence band offset (VBO) to prevent unwanted charge tunneling. ScₓAl₁₋ₓO₃ exhibits tunable band alignment properties depending on the Sc/Al ratio. Studies indicate that Sc incorporation increases the dielectric constant while maintaining a CBO of around 1.5–2.0 eV with Ga₂O₃, which is superior to HfO₂ (CBO ~1.0–1.5 eV) and significantly better than SiO₂ (CBO ~0.5 eV). The higher CBO directly correlates with improved leakage current suppression, particularly at elevated temperatures and high electric fields.

Leakage current mechanisms in gate dielectrics include Fowler-Nordheim tunneling and Poole-Frenkel emission, both of which are exacerbated by insufficient band offsets and high defect densities. ScₓAl₁₋ₓO₃ demonstrates lower leakage currents compared to HfO₂ at equivalent electric fields due to its wider bandgap and better interface quality. For instance, at an applied field of 3 MV/cm, ScₓAl₁₋ₓO₃ films exhibit leakage current densities below 10⁻⁸ A/cm², whereas HfO₂ typically shows currents in the range of 10⁻⁶–10⁻⁵ A/cm² under similar conditions. The reduced leakage is attributed to the suppression of trap-assisted tunneling pathways, which are more prevalent in HfO₂ due to its higher oxygen vacancy concentration.

Thermal stability is another crucial factor for UWBG devices, especially in high-power applications where self-heating can degrade dielectric performance. ScₓAl₁₋ₓO₃ exhibits superior thermal stability compared to HfO₂, with minimal crystallization and interdiffusion observed up to 900°C. In contrast, HfO₂ tends to crystallize at temperatures above 500°C, leading to grain boundary-assisted leakage and increased trap densities. SiO₂, while thermally stable, suffers from a low dielectric constant (K ~3.9), necessitating thicker layers that compromise device scalability. The higher-K value of ScₓAl₁₋ₓO₃ (K ~14–18, depending on composition) allows for equivalent oxide thickness (EOT) scaling without sacrificing leakage performance.

Interface trap density (Dₜₜ) is a key metric for evaluating gate dielectric quality, as high Dₜₜ values can degrade channel mobility and threshold voltage stability. ScₓAl₁₋ₓO₃ deposited via atomic layer deposition (ALD) on Ga₂O₃ has demonstrated Dₜₜ values in the range of 10¹¹–10¹² cm⁻² eV⁻¹, comparable to state-of-the-art HfO₂ interfaces but with better bias temperature instability (BTI) characteristics. The improved interface is attributed to the formation of a chemically stable Sc–O–Ga bonding configuration, which reduces dangling bonds and mid-gap states. In contrast, SiO₂ interfaces with Ga₂O₃ often exhibit higher Dₜₜ due to lattice mismatch and weaker bonding.

ALD growth optimization is essential for achieving high-quality ScₓAl₁₋ₓO₃ films. Precursor selection, temperature, and pulse timing significantly influence film stoichiometry and defect density. Trimethylaluminum (TMA) and scandium precursors (e.g., Sc(Cp)₃) are commonly used, with water or ozone as oxidants. Growth temperatures between 250–300°C have been shown to yield films with minimal carbon contamination and uniform thickness. Post-deposition annealing in oxygen further reduces defects and improves dielectric integrity. The self-limiting nature of ALD ensures precise thickness control, critical for EOT scaling in nanoscale devices.

Reliability testing under high-field stress is necessary to assess the long-term performance of ScₓAl₁₋ₓO₃ dielectrics. Time-dependent dielectric breakdown (TDDB) measurements reveal that ScₓAl₁₋ₓO₃ films exhibit breakdown fields exceeding 8 MV/cm, outperforming HfO₂ (~6 MV/cm) and SiO₂ (~10 MV/cm, but at much higher EOT). The enhanced breakdown strength is linked to the material’s amorphous structure and reduced defect density. Additionally, positive and negative BTI tests indicate minimal threshold voltage shifts (<50 mV) after prolonged stress, suggesting robust charge trapping immunity.

In summary, ScₓAl₁₋ₓO₃ offers a compelling solution for high-K gate dielectrics in Ga₂O₃-based UWBG devices. Its tunable band offsets, low leakage currents, and excellent thermal stability address the limitations of conventional dielectrics like SiO₂ and HfO₂. ALD optimization enables precise film engineering, while reliability testing confirms its suitability for high-field applications. As UWBG technology advances, ScₓAl₁₋ₓO₃ is poised to play a pivotal role in enabling next-generation power electronics, RF devices, and beyond.