imec and Qromis present high-performance p-GaN HEMTs

Leuven, Belgium. Today imec and fabless technology innovator Qromis announced the development of high-performance enhancement-mode p-GaN power devices on 200-mm engineered coefficient of thermal expansion (CTE)-matched substrates, processed in imec’s silicon pilot line. The substrates are offered by Qromis as commercial 200-mm QST substrates as part of its patented product portfolio. The results will be presented at the CS International Conference April 10-11 in Brussels.

Today, GaN-on-Si technology is the industry standard platform for commercial GaN power switching devices for wafer diameters up to 150 mm. imec has pioneered the development of GaN-on-Si power technology for 200-mm wafers and qualified enhancement-mode HEMT and Schottky-diode power devices for 100-V, 200-V and 650-V operating voltage ranges, paving the way to high-volume manufacturing applications. However, for applications beyond 650 V such as electric cars and renewable energy, it has become difficult to further increase the buffer thickness on 200-mm wafers to the levels required for higher breakdown and low leakage levels, because of the mismatch in coefficient of thermal expansion (CTE) between the GaN/AlGaN epitaxial layers and the silicon substrate. One can envisage to use thicker Si substrates to keep wafer warp and bow under control for 900-V and 1,200-V applications, but practice has learned that for these higher voltage ranges, the mechanical strength is a concern in high-volume manufacturing, and the ever thicker wafers can cause compatibility issues in wafer handling in some processing tools.

Carefully engineered and CMOS fab-friendly QST substrates with a CTE-matched core having a thermal expansion that very closely matches the thermal expansion of the GaN/AlGaN epitaxial layers are paving the way to 900-V to 1,200-V buffers and beyond, on a standard semi-spec-thickness 200-mm substrate. Moreover, QST substrates open perspectives for very thick GaN buffers, including realization of free-standing and very low dislocation density GaN substrates by >100-micron thick fast-growth epitaxial layers. These unique features will enable long awaited commercial vertical GaN power switches and rectifiers suitable for high-voltage and high-current applications presently dominated by Si IGBTs and SiC power FETs and diodes.

In this specific collaboration, imec and Qromis developed enhancement mode p-GaN power device specific GaN epitaxial layers on 200-mm QST substrates, with buffers grown in AIXTRON’s G5+ C 200-mm high-volume manufacturing MOCVD system.

imec then ported its p-GaN enhancement mode power device technology to the 200-mm GaN-on- QST substrates in their silicon pilotline and demonstrated high performance power devices with threshold voltage of 2.8 V. “The engineered QST substrates from Qromis facilitated a seamless porting of our process of reference from thick GaN-on-Si substrates to standard thickness GaN-on- QST substrates using the AIX G5+ C system, in a joint effort of imec, Qromis, and AIXTRON,” stated Stefaan Decoutere, program director for GaN power technology at imec. The careful selection of the material for the core of the substrates, and the development of the light-blocking wrapping layers resulted in fab-compatible standard thickness substrates and first-time-right processing of the power devices.

“QST is revolutionizing GaN technologies and businesses for 200-mm and 300-mm platforms,” stated Cem Basceri, president and CEO of Qromis. “I am very pleased to see the successful demonstration of high-performance GaN power devices by stacking leading edge technologies from Qromis, imec, and AIXTRON,” Basceri said.

imec acknowledged funding from the Electronic Component Systems for European Leadership Joint Undertaking under grant agreement No 662133, designated as PowerBase.