RF GaN-on-Si transistor sets new performance benchmark

Imec claims a new benchmark for mobile RF transistor performance. The approach, based on a gallium nitride (GaN) metal-oxide semiconductor high-electron-mobility transistor (MOSHEMT) on silicon (Si), delivers record efficiency and output power for an enhancement-mode (E-mode) device operating at low supply voltage, marking a critical step toward high-efficiency 6G power amplifiers.

Imec also demonstrated a record-low contact resistance of 0.024 Ω· mm, necessary to further boost output power in future designs. The combination is crucial to integrating GaN technology into next-generation mobile devices, especially when targeting the 6G FR3 band between 7 and 24 GHz, imec said.

Gate structure of imec's RF GaN-on-Si transistor.

Cross-sectional TEM image of the gate structure in imec’s GaN-on-silicon transistor, showing the finely etched gate region enabling the device’s E-mode operation. (Source: imec)

Mobile networks today based on gallium arsenide (GaAs) heterojunction bipolar transistors (HBTs) struggle to maintain performance as efficiency and gain degrade significantly above 10 to 15 GHz, causing rapid battery drain and poor energy use in equipment, imec said. While GaN transistors on silicon carbide (SiC) demonstrate strong RF performance in high-frequency base station applications, the cost and limited wafer scalability of SiC remain barriers for mobile applications, the research hub explained.

In comparison, silicon offers a scalable and cost-effective platform; however, building high-efficiency GaN transistors on it has been challenging due to the lattice and thermal mismatch between the two materials, with the challenge even greater for E-mode designs as they typically require thinning the transistor barrier and channel under the gate, limiting on-current and increasing the off-state leakage, imec said.

Imec’s GaN-on-Si E-mode MOSHEMT reaches a record 27.8 dBm (1 W/mm) output power and 66% power-added efficiency (PAE) at 13 GHz and 5 V. The performance was enabled by combining a gate recess technique to shift the device into E-mode, with an InAlN barrier layer offsetting the performance loss from the thinned channel.

Imec also demonstrated a record-low contact resistance of 0.024 Ω· mm using a regrown n⁺(In)GaN layer, which maximized current flow and minimized power loss. Imec said the result was obtained in a separate module, but it is fully compatible with the E-mode transistor architecture. Simulations showed that integrating this contact module could improve the output power density by 70%, meeting the performance target for 6G user equipment.

Imec’s next step is to integrate the contact module into the E-mode transistor and validate the power and efficiency gains. The results were recently presented at the 2025 Symposium on VLSI Technology and Circuits in Kyoto, Japan. Visit imec for more information.

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