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Evaluation of High-Voltage Cascode GaN HEMT in Different Packages

Fig. 1. Bonding diagram and schematic for cascode GaN HEMT in stack-die package.
Advanced power semiconductor devices have consistently proven to be a major force in pushing the progressive development of power conversion technology. The emerging gallium-nitride-based power semiconductor device is considered a promising candidate to achieve high-frequency, high-efficiency, and high-power-density power conversion because it has a faster switching speed and lower switching-related loss than previous devices. Accompanied by the fast switching speed, inevitably there is high dv/dt and di/dt introduced at the same time, which can barely be observed in the comparatively slow Si MOSFET. As a result, package design is critical to enabling the promising high performance of GaN devices.

The limitations of the traditional packaging for high-voltage cascode GaN HEMT includes significant turn-on loss during hard-switching turn-on, and significant internal parasitic ringing in hard-switching turn-off due to the impact of common-source inductors.

In order to improve the package design, we propose a stack-die package, with all common-source inductors eliminated. According to previously developed loss models, the stack-die package is predicted to have significant improvement compared to traditional packages. Experiments with a prototype of this stack-die package that was fabricated in the lab show that around 30% of the turn-on energy is reduced during hard-switching turn-on, and the internal parasitic ringing is almost eliminated in hard-switching turn-off.

Fig. 2. Package impact in hard-switching turn-on and hard-switching turn-off.
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