Second generation GaN takes on SiC in electric vehicles
Nexperia has launched its second generation gallium nitride (GaN) technology, taking on silicon carbide in mid-range electric vehicle applications.
The H2 650V GaN FET is a cascode device, combining a high mobility HEMT GaN-on-silicon transistor with a low voltage silicon MOSFET in a single package. This reduces the complexity of designs by allowing a simple silicon driver to be used, says Michael LeGoff, general manager for GaN at Nexperia and the former managing director of Plessey Semiconductor. “This means it is very simple to drive with a 15 percent improvement, it’s a big improvement,” he said.
Packaging is a key element for automotive designs and the H2 is initially packaged in a TO-247 with an on resistance RDS(on) of 41 mΩ (max 35 mΩ typ. at 25 °C). However a version in the company’s proprietary CCPAK copper clip surface mount packaging is planned which gives an RDS(on) of 39 mΩ (max 33 mΩ typ. at 25 °C). Replacing the internal bond wires with copper clips reduces parasitic losses, optimizes electrical and thermal performance and improves reliability. The CCPAK GaN FETs are available in top- or bottom-cooled configurations to improve heat dissipation.
Future optimisations of the process and package will see RDS(on) falling to under 20mΩ for 100kW designs, says LeGoff. The third generation will cut that in half to 10mΩ.
The device is aimed at on-board chargers and DC-DC converters, taking 400V from the battery pack in mid-range electric vehicle designs direct to a 12V rail without intermediate steps. The company is looking at 900V and 1200V GaN devices that can be used with 800V systems in the future, says LeGoff.
The first generation H1 GaN parts were used in a demonstrator inverter design with Ricardo: NEXPERIA TEAMS WITH RICARDO ON INVERTER DEMONSTRATOR
The new GaN technology at Nexperia uses through-epi vias to make a connection to the back of the silicon substrate.
This reduces defects and shrinks the die size by around 24 percent compared to the first generation. Using the through-epi via also allows a bottom connection on the device. This eliminates the ceramic shim that was needed in the first generation part, improving the thermal performance.
Reliability is a key question for GaN devices, but both versions meet the demands of AEC-Q101 for automotive applications, says LeGoff. “Being an automotive supplier, everything we do is AECQ and even with that, with 90bn components shipped a year and 50 percent in automotive, showing the reliability of GaN since we started in 2012, it’s still a fight,” he said. “We continue to do all the long term and life tests, we have been working with the research teams in the OEMs and Tier One suppliers. I think working with the corporate research teams in automotive is putting the device into their tests and we continue to develop various applications, and they are becoming more and more comfortable – we have another 85kW e-mobility application and we are seeing progress across the board. It’s still a fight, but I think the solution is so compelling with the efficiency with GaN is driving the industry.
The parts will be fully qualified for reliability, he says. “We expect AECQ101 qualification in early to mid 2021, and our customers are starting to work with the product now with qualification later,” he said. “It will be JEDEC approved by the end of year for industrial designs in 2021.”
It is the power density that is the driver rather than higher frequency switching that is of interest to the automotive designers, he says. “We test to 500kHz – we have seen some applications for chargers up to 1MHz, and GaN is very comfortable in those ranges at higher power. The traction inverters are 20 to 30kHz because of the EMI, some are pushing to 40kHz.”
The thrid generation will focus on driving down the on resistance at 650V. “H3 will deliver 150kW in a 2litre inverter with 10mΩ and 100A switching. That matches anything coming from SiC,” he said. “900V and 1200V devices are the roadmap but the focus into the market is 650V.”
The parts will be built on a 8in silicon line in Hamburg with GaN reactors providing the epi layer on top of the silicon wafers, although there is also a pilot 6in line at the Hazel Grove fab in manchester, UK.
As well as electric vehicle designs, the H2 parts can be used for industrial power supplies in the 1.5-5 kW range for titanium-grade rack mounted telecoms, 5G and datacentres.
The 650 V GAN041-650WSB in TO-247 and GAN039-650NBB in CCPAK are sampling now.
More information including product specs and datasheets is available at www.nexperia.com.