The Dawn of 1200 V Gallium Nitride Transistors

The market for power semiconductor devices at ~650 V is fiercely competitive with silicon (Si), silicon carbide (SiC) and gallium nitride (GaN) all staking their claim as being best suited to the plethora of applications in this space.

That range of applications is vast – still low enough power to include consumer electronics and data centres while also encompassing some renewable energy and even light industrial products. But most importantly, from a growth point of view over the next decade is the automotive market, namely electric vehicles (EV). The UK is banning the sale of new non-electric cars from 2030 with many nations globally to follow suit over the following decade. This will lead to a huge demand for power semiconductor devices in EV inverters. Not to mention the associated EV charging infrastructure and the vehicle’s on-board charger(OBC).

Broadly speaking Si is seen to have an edge in terms of cost and reliability. SiC leads in terms of conduction loss, thermal management and device footprint reduction while GaN is unmatched in terms of switching loss and is offering ever more competitive pricing.

Higher voltages applications have to date been seen as a shootout between Si IGBTs and SiC MOSFETs. GaN devices being lateral in structure simply couldn’t compete. This is about to change, 1200 V GaN transistors are no longer an academic novelty, they are not even on the horizon they are already here.

Why 1200 V?

Why is there an impetus for 1200 V GaN? Firstly, it opens up the industrial market in terms of applications like motor drives. But even in a decade this is only estimated to be a small portion of the power semiconductor market. Is it worth the research and development to bring GaN into this space? The real market driving force again looks to be EVs. There is an increasing shift to 800 V systems, the Porsche Taycan was the first production model car to make this shift in 2019. The benefits being a faster charging time and reduced size and weight of cabling. The car is still compatible with standard 400 V infrastructure, think of it like a phone with a ‘fast-charge option’.

Often new product innovation start in this manner, as a premium products before hitting the mainstream. Take the original Tesla model S for example, or even GaN based USB-C chargers with early entrants being third-party boutique accessories followed today by OEMs to the point where now both Apple and Samsung offer GaN based chargers.

In terms of 800 V EVs, General Motors have announced their ‘Ultium’ 800 V battery will power it’s future vehicles while Hitachi has also developed an 800 V EV inverter.

1200 V in the market, more on its way

Just last month Transphorm announced a 1200 V GaN FET with sampling beginning in 2023. We have already analysed our first 1200 V GaN device at TechInsights, produced by Vancouver based GaN Power International, the GPIHV30DFN.. Both GaN power floorplan and power essentials reports have now been completed on this device.

Figure 1 shows a lateral HEMT structure with source-drain pitch measuring 26 µm. This is only 4 µm longer than the 22 µm source-drain pitch found in their GPI65060DFN part as analysed in a separate GaN power floorplan report.

Figure 2 shows the epitaxial structure of the GaN epitaxy for the GPIHV30DFN device as measured by scanning transmission electron microscopy (STEM). These devices are thought to be manufactured at TSMC. If we compare these layers to another recent product also thought to be manufactured at TSMC – the Navitas NV6128 they seem identical with a total thickness of 5.2 µm.

In 2021 Imec announced GaN epitaxy on 200 mm wafers qualified to 1200 V with a hard breakdown of 1800 V and leakage below 10 µA/mm2 up to 150° C. This stands to be a defining moment for 1200 V GaN, historically it has been a significant challenge to grow thick enough defect free GaN material on 200 mm substrates rated up to 1200 V with sustainable product yield.

So how will these 1200 V GaN devices of the future stand up to their SiC counterparts? It still seems unlikely they will be able to match SiC purely in terms of its conduction performance. Figure 4 shows a plot of breakdown voltage (V) vs. specific on-resistance (RDS(ON) * A ) for various power semiconductor materials. The solid lines represent theoretical maximum performance with the dots representing commercial devices analysed by TechInsights over recent years.

We can see GaN’s performance from this standpoint is competitive with the GPIHV30DFN sitting amongst leading SiC 1200 V counterparts. In fact GaN’s theoretical maximum performance is better than 4H-SiC. However, while theses transistors remain lateral structures they will not be able to better the leading SiC devices in this regard.

As with GaN at lower voltages it is likely to be switching performance and relative low cost compared to SiC where they can compete.

Summary

The future of GaN devices is exciting with this new frontier promising to extend competition in the exponentially growing power semiconductor device market. With initial 1200 V GaN offerings already being competitive we can only expect even more optimised performance over the coming years. Coupled with the fact these devices can be made from 200 mm GaN-on-Si material the relative cost is also appealing. Automotive manufacturers will have no shortage of options when designing their EVs in the coming years!

References

• UK plans to bring forward ban on fossil fuel vehicles to 2030 (The Guardian) 2020.
• The battery: Sophisticated thermal management, 800-volt system voltage (Porsche Website) 2019.
• GM Reveals New Ultium Batteries and a Flexible Global Platform to Rapidly Grow its EV Portfolio (GM Website) 2020
• Will 800 V charging become the EV industry norm? (Electronics 360) 2021.
• Transphorm to Demonstrate 99% Efficiency Power Switching with a 1200 Volt GaN Power Transistor at ISPSD 2022 (Transphorm Website) 2022
• GPIHV30DFN Datasheet (GaN Power International Website) 2022.
• GaN Power International Inc. GPIHV30DFN 1200 V Enhancement-Mode GaN Power FET Power Floorplan Analysis (PFR-2110-801) TechInsights, 2021.
• GaN Power International Inc. GPIHV30DFN 1200 V Enhancement-Mode GaN Power FET Power Essentials Summary (PEF-2110-801) TechInsights, 2021.
• GPI65060DFN Datasheet (GaN Power International Website) 2022.
• GaN Power International Inc. GPI65060DFN 650 V Enhancement-Mode GaN Power FET Power Floorplan Analysis (PFR-2110-802) TechInsights, 2021.
• Imec and AIXTRON Demonstrate 200 mm GaN Epitaxy on AIX G5+ C for 1200V Applications with Breakdown in Excess of 1800V (Imec Website) 2021