Imec presented a GaN-on-Si double heterostructure field-effect transistor (FET) architecture for GaN-on-Si power switching devices at the recent International Electron Devices Meeting. The architecture meets the normally off requirements of power switching circuits and is characterised by low leakage and a high breakdown voltage, which are said to be essential parameters in reducing the power loss of high-power switching applications. High-voltage power devices are traditionally based on Si-Mosfet structures. However, for a number of applications, Si power devices have reached the intrinsic material limits.
GaN compounds are described as the best candidates to replace Si power devices thanks to their high band gap (transport properties) and their high electrical breakdown field. However, the cost of GaN power devices is high. GaN epilayers grown on large-diameter Si wafers, potentially measuring up to 200mm, offer a lower-cost technology compared to other substrates. Imec obtained a high breakdown voltage of almost 1,000V combined with low on-resistance by growing a SiN/AlGaN/GaN/AlGaN double heterostructure FET structure on a Si substrate.
By combining its double heterostructure FET architecture with in-situ SiN grown in the same epitaxial sequence as the III-nitride layers, the company obtained e-mode device operation. This is typically required in applications for safety reasons. The fabrication is based on an optimised process for the selective removal of in-situ SiN. The resulting SiN/AlGaN/GaN/AlGaN double heterostructure FET is characterised by a breakdown voltage of 980V, an excellent uniformity and a low dynamic specific on-resistance.
Within Imec's industrial affiliation programme (IIAP) on GaN-on-Si technology, the company and its partners focus on the development of GaN technology for both power conversion and solid-state lighting applications. A goal of the programme is to lower GaN technology cost by using large-diameter GaN-on-Si and by leveraging on the scale of economics. Imec is inviting both integrated device manufacturers and compound semiconductor industry members to join the programme.
