GaN breaks down design barriers

An article written by Paige West for Electronic Specifier Design, in collaboration with Yole Group – The performance advantages of GaN are well understood and the challenges of driving GaN HEMTs have been overcome. Remaining concerns may be price, availability and reliability, says Dr Denis Marcon, General Manager, Innoscience Europe.

GaN offers application benefits for several reasons. Firstly, it does not have a reverse recovery current, permitting simpler architectures to be used (e.g., totem pole for PFC). Secondly, it can operate at a higher frequency than silicon, enabling smaller passives to be used. The specific on resistance of GaN is much higher than silicon, so GaN device can be smaller. Lastly, GaN’s figure of merit (Ron x Qg) is 10 times better, resulting in much higher efficiencies.

Innoscience introduced bi-directional GaN (VGaN), the over-voltage protection unit in a battery management system requires two back-to-back silicon MOSFETs to block the current in both directions. These can be replaced by one VGaN HEMT for a solution that is 50% smaller and more efficient.

A silicon device normally has a blocking oxide below the gate to block the gate leakage. In GaN, this oxide layer is not present, so a two-diode back-to-back architecture is used (see Figure 1). By optimising the epitaxy, the processing and the architecture, Innoscience has reduced the leakage characteristic by nearly 10x, to under 3μA at 85°C for the device’s lifetime, making VGaN HEMTs suitable for use as the load switch inside mobile handsets.

Regarding price and the availability, it becomes clear why GaN has not yet been present in the mobile phone market. Assuming a 10% market penetration of the one billion phones sold in 2022, equates to 100 million GaN devices per year, requiring approximately 3,000 eight-inch wafers per month. Today, the total worldwide capacity of GaN, without Innoscience, is around 9000 wafers per month, according to Yole Group, therefore, mobile phones would require 33% of the worldwide capacity. Innoscience is an IDM (integrated device manufacturer) 100% focused on GaN. It can optimise design and manufacturing technology in-house without legacy silicon products to divide investment and capacity. It can provide eight-inch GaN wafers, cost-effectively in high volumes using two fabs. By 2025 the company will produce70,000 eight-inch wafers per month.

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