Imec and Aixtron pave the way for GaN to enter SiC high voltage domain
Demonstration of epitaxial growth of GaN buffer layers qualified for 1200V applications on 200mm QST substrates, with a hard breakdown exceeding 1800V
Imec, a research and innovation hub in nanoelectronics and digital technologies, and Aixtron, a provider of deposition equipment for compound semiconductor materials, have demonstrated epitaxial growth of GaN buffer layers qualified for 1200V applications on 200mm QST substrates, with a hard breakdown exceeding 1800V.
The manufacturability of 1200V-qualified buffer layers opens doors to highest voltage GaN-based power applications such as electric cars, previously only with feasible SiC-based technology. The result comes after the successful qualification of Aixtron’s G5+ C fully automated MOCVD reactor at Imec, Belgium, for integrating the optimised material epi-stack.
Over the years tremendous progress has been made with GaN-based technology grown on for example 200mm Si wafers. At Imec, qualified enhancement mode HEMTs and Schottky diode power devices have been demonstrated for 100V, 200V and 650V operating voltage ranges, paving the way for high-volume manufacturing applications. However, achieving operating voltages higher than 650V has been challenged by the difficulty of growing thick-enough GaN buffer layers on 200mm wafers. Therefore, SiC so far remains the semiconductor of choice for 650-1200V applications – including for example electric cars and renewable energy.
For the first time, Imec and Aixtron have demonstrated epitaxial growth of GaN buffer layers qualified for 1200V applications on 200mm QST (in SEMI standard thickness) substrates at 25degC and 150degC, with a hard breakdown exceeding 1800V.
The image above shows vertical forward buffer leakage current measured on 1200V GaN-on-QST at two different temperatures: (left) 25degC and (right) 150degC. Imec’s 1200V buffer shows vertical leakage current below 1µA/mm2 at 25degC and below 10µA/mm2 at 150degC up to 1200V with a breakdown in excess of 1800V both at 25degC and 150degC, which makes it suitable for the processing of 1200V devices.
Denis Marcon, senior business development manager at Imec: “GaN can now become the technology of choice for a whole range of operating voltages from 20V to 1200V. Being processable on larger wafers in high-throughput CMOS fabs, power technology based on GaN offers a significant cost advantage compared to the intrinsically expensive SiC-based technology.”
Key to achieving the high breakdown voltage is the careful engineering of the complex epitaxial material stack in combination with the use of 200mm QST substrates, executed in scope of the IIAP program The CMOS-fab friendly QST substrates from Qromis have a thermal expansion that closely matches the thermal expansion of the GaN/AlGaN epitaxial layers, paving the way for thicker buffer layers – and hence higher voltage operation.
Felix Grawert, CEO and president of Aixtron said: “The successful development of Imec’s 1200V GaN-on-QST epi-technology into Aixtron’s MOCVD reactor is a next step in our collaboration with Imec.
"Earlier, after having installed Aixtron G5+C at Imec’s facilities, Imec’s proprietary 200mm GaN-on-Si materials technology was qualified on our G5+ C high-volume manufacturing platform, targeting for example high-voltage power switching and RF applications and enabling our customer to achieve a rapid production ramp-up by pre-validated available epi-recipes.
"With this new achievement, we will be able to jointly tap into new markets.” Currently, lateral e-mode devices are being processed to prove device performance at 1200V, and efforts are ongoing to extend the technology towards even higher voltage applications. Next to this, Imec is also exploring 8-inch GaN-on-QST vertical GaN devices to further extend the voltage and current range of GaN-based technology.