NTT Achieves World-First Breakthrough in AlN-Based High-Frequency Transistors for Post-5G Era

NTT Achieves World-First Breakthrough in AlN-Based High-Frequency Transistors for Post-5G Era

Japanese telecom giant demonstrates millimeter-wave signal amplification using aluminum nitride semiconductors, opening new pathways beyond power device applications

NTT Corporation announced on December 8, 2025, that it has successfully demonstrated the world’s first operational aluminum nitride (AlN)-based high-frequency transistor, marking a significant milestone in semiconductor technology.

The breakthrough overcomes longstanding challenges in achieving high-frequency performance with high aluminum composition materials through innovative low-resistance structural design.

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Breaking Through Technical Barriers

The achievement centers on enabling high-frequency operation in transistors with aluminum compositions exceeding 75%, a threshold previously considered prohibitively difficult. The technology demonstrates signal amplification capabilities in the millimeter-wave band, with potential applications in enhancing wireless communication services for the post-5G era.

NTT is presenting these findings at the 71st IEEE International Electron Devices Meeting (IEDM 2025) in San Francisco, California, scheduled for December 10, 2025.

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AlN’s Journey from Insulator to Semiconductor

Aluminum nitride was historically regarded as an insulator with no electrical conductivity. However, NTT’s development of high-quality AlN thin-film growth techniques led to the world’s first successful semiconductorization of AlN in 2022, fundamentally changing the material’s prospects.

As a semiconductor, AlN possesses exceptional physical properties. Its large breakdown electric field makes it particularly promising for power device applications, with projected power losses of less than 5% compared to silicon, 35% compared to silicon carbide (SiC), and 50% compared to gallium nitride (GaN).

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Innovative Low-Resistance Architecture

The key innovation lies in NTT’s approach to managing resistance in high aluminum composition devices. While aluminum gallium nitride (AlGaN) semiconductors show improved performance indices as aluminum composition increases, this traditionally came at the cost of increased contact resistance and channel resistance.

NTT addressed the contact resistance challenge by redesigning the conventional structure. Instead of forming electrodes directly on the AlGaN channel layer, engineers inserted an AlGaN contact layer between the electrode and channel, reducing the energy barrier and suppressing resistance increases.

For channel resistance, the team employed a polarization-doped AlGaN channel structure to generate high-concentration three-dimensional electron gas, increasing electron density in the channel layer and lowering overall resistance.

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Impressive Performance Metrics

The results demonstrate excellent drain current response relative to drain voltage. Even with high aluminum composition (85%), the transistors achieved substantial drain current and on-off current ratios, confirming effective resistance reduction.

Most notably, the devices achieved power amplification at frequencies exceeding 1 GHz—a world first for high aluminum composition transistors. The maximum operating frequency reached 79 GHz in the millimeter-wave band, representing the highest value reported for AlN-based transistors to date.

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Expanding Beyond Power Applications

This development significantly broadens AlN’s potential application domains beyond power devices. The performance index for high-output, high-frequency devices—proportional to the product of breakdown electric field and saturated electron velocity—is five times higher for AlN compared to GaN, making these results particularly significant for wireless communications infrastructure.

The technology promises contributions to post-5G wireless communication advances, including expanded coverage areas and increased transmission speeds. NTT plans to continue research and development toward device structures capable of handling larger currents and voltages, creating technology applicable across the spectrum from power devices to wireless communication systems.

This breakthrough follows NTT’s December 2024 announcement regarding the elucidation of current transport mechanisms in AlN-based Schottky barrier diodes, demonstrating the company’s sustained commitment to advancing AlN semiconductor technology across multiple device categories.

The successful demonstration of high-frequency operation in AlN-based transistors represents not just a technical achievement, but a potential paradigm shift in how the telecommunications industry approaches next-generation wireless infrastructure design and implementation.

NTT Achieves World-First Breakthrough in AlN-Based High-Frequency Transistors for Post-5G Era.