Chip-level thermal management in GaN HEMT: Critical review on recent patents and inventions

The technological development of GaN high electron mobility transistor (HEMT) is on the right track to compete with Si and SiC-based power transistors for the market segment of >650 V. A proper thermal management strategy at the chip-level is capably alleviating the impact of self-heating two-dimensional electron gas (2DEG); hence increase the reliability, boosting the output power density, and widening the safe operating area of the GaN HEMT. This article compiles and discusses remarkable patents on chip-level thermal management in GaN HEMT to understand the available solutions disclosed beyond academia and the concept behind the inventions. These concepts, which are either proven or unproven, are critically being reviewed with support from relevant peer-reviewed research articles. The main strategies can be distinguished as four: A) top layer heat spreader, B) substrate heat spreader, C) buried heat spreader, and D) buried GaN in heat spreader. Strategies A and B using diamond are the most common and proven effective for cooling the 2DEG. The trend is moving towards adopting cheaper materials with high thermal conductivity, e.g. metals, 2D materials, and others. The strategies and patents are assessed to summarize their practicality, effectiveness, sophistication, and cost levels for the adoption of the proposed solutions.