SloGaN

The SloGaN approach aimed to set up a complete value chain from GaN substrate fabrication right through to a DC/DC convertor demonstration. This full chain approach, including development of a process design kit (with compact models), GaN power device design based on 2D simulations, and validation of building-block improvements as well as GaN IC design and assembly, allowed the system to be optimized as a whole, rather than in sequential steps.

In particular, the project aimed to:

• develop an updated component roadmap for GaN integrated components (integrated switching poles), producing and validating prototype components
• develop a low loss driver set with built-in isolation fit for (integrated) GaN power components
• improve component-level models: reduced-order (equivalent circuits), thermal and reliability models
• demonstrate a substrate / package, bonding techniques and associated circuit mounting (soldering, sintering) for GaN power stages, aiming at improved thermal paths, thermal resilience, improved reliability and parasitic reduction
• validate the above building-block improvements in several complementary circuit categories representative of multiple applications such as power supplies in a wide voltage/power range, DC-DC interfaces for photovoltaics, batteries, DC-AC interfaces for drives and grid-coupling.

THE OUTCOMES

1. Successful integration

One of the primary goals of the project was to successfully develop and integrate various components on a single die. 

• High-side (HS) & low-side (LS) GaN transistors – many other companies and research centers have failed at this step. This is a key asset of imec’s GaN on SOI with DTI isolation between transistors.
• Gate driver - allows fast switching but also prevents parasitic turn on of the opposite side transistor when one (either HS or LS) turns on
• Gate driver voltage regulators - gate structure is known to be fragile with GaN transistors, so any overdrive should be avoided. However, in a fast transient switching system overshoots are difficult to avoid, hence gate voltage control is a key asset.

In addition, IMEC’s GaN-on-SOI process has been improved to avoid deep trench delamination, and a copper (Cu) redistribution layer was developed. Based on the design feedback, the threshold voltage has been reduced by 0.5 Volt.

2. Extending supply chain capabilities 

As part of the complete value chain approach, several specific learnings were achieved during the project. 

• Magwel’s ptmet tool capability was enhanced to achieve the SloGaN project goals while supporting design activities. 
• C-MAC has built tangible know-how of the sintering processes, based on the theoretical research, assembly and testing of demonstrator boards. 
• IMEC-EA contributed with modelling tools at die assembly level to provide support to power die assembly designs. 

3. Validation and demonstration 

The project resulted in the validation and demonstration of a series of power converters designed for different power levels. These were implemented in printed circuit boards (PCBs) which were used to characterize the performance of both the newly developed and reference components. The power efficiency results, demonstrated in a buck DC-DC converter, showed that the integrated half-bridge behaved as well as its discrete-based predecessor. This was a key result, confirming that the integration was successful and that it did not degrade efficiency – meaning that designers can now move away from using discrete components.