Power trends: Dialog enters the GaN market

Interviews |
By Nick Flaherty

“We started working on GaN about three years ago,” said Moreno. “It’s in the emerging technology group as it’s an up and coming technology – there’s been a lot of adoption that we are starting to see over the years and in 2018 we are going to see a lot more adoption as the GaN process has become more mature. There’s been a lot of yield issues and being able to supply GaN wafers has been a major problem as there is a shortage of Epitaxy capacity but here are now a lot more foundries offing GaN and investing in MOVCD tooling and we see that availability is becoming greater,” he said.

This is what has prompted the company to launch now.

“We expect to start shipping in H2 18,” said Tseng. “The segment we are focusing on first in consumer but you can’t compare that to server or automotive applications where the requirements are higher, so we will get going in the consumer business first.”

“There’s definitely a need to build the economies of scale, and to drive down the cost you need that from travel adaptors for smartphones and tablets as well as notebook PCs, but there are a lot more applications that can drive GaN with higher frequency and higher efficiency,” he said. “There’s opportunities in automotive with the adoption of 48V batteries and lidar [laser drivers] is another opportunity to handle the rapid data of 300,000 to 1m scans per second.”

Next: 6in or 8in

All of this capacity is on 6in wafers at the moment for some interesting reasons. The problem is that going from 6in to 8in doesn’t buy as much throughput as with CMOS scaling says Moreno. “In GaN the bottleneck is the epi layer and it comes down to the handler. Because you can put so many wafers on the handler going to 8in only buys you 10% more throughput as you get less 8in wafers in the chamber – that’s a challenge for 8in,” he said.

“There’s plenty of 6in capacity around and I think the technology will scale on 6in,” he said. “There are a lot of areas where we can drive down cost, such as reducing deposition time and using new substrates where you can have a lower deposition time and better uniformity and those will also drive costs down and there is lot of 6in capacity we can take advantage of,” he said.

But there will be move to 8in wafers as the market progresses. “We are definitely seeing more foundries investigate GaN and within a year more foundries will be offering 8in wafers for GaN based on our discussions. Right now we work with TSMC but also in discussions with other foundries. We have an NDA with TSMC,” said Tseng.

The challenge is getting developers to use new design topologies.

 “We are using GaN in a different way. Some are just replacing a 650V superjunction FET you are not getting much of a boost,” said Tseng. “To use GaN you have to change the topology and get new magnetic and look for areas where GaN enables the new conversion technologies. You have to deliver not only the GaN devices but also the controllers.”

This can be a challenge. “GaN devices can be hard to use as standalone with special gate drives and tune the circuit to avoid EMI problems and we are taking all of that and integrating it into the drivers with level shifting and that allows us to tune the power device to the gate drive and the level shifting with more noise immunity,” he said. “A rule of thumb is to cut power losses in half.”

The company is not looking at different packaging to achieve this.

“Our products are all QFN [packages],” said Tseng. “The GaN devices are efficient so we don’t see the need for exotic packing but for automotive we are going to need other package. 2018 will be all QFN but after that looking at flip chip and clip packages as we go to higher frequencies.”

Multichip modules are also in the plan, with multiple die on on lead frame and on substrates but definitely not making modules for the power supply, he says.

Part of this comes from the transistor design itself. “Because the GaN devices are lateral we can integrate more transistors for drivers, logic, latches, protection devices – we focus on using GaN wherever we can, for example also using them for current sensing schemes,” said Tseng.

“We looked at vertical GaN – that gets you a smaller FET by 30 to 40% but we are package and bond pad limited so it has advantages in the sub 10mO devices but for 50mO or 100mO power devices vertical GaN looses its competitive edge and there are no foundries for the vertical devices.”

But there is still a lot of education to do.

“Being able to change the customers mind from silicon to GaN takes more discussions, more reference designs and some of these markets are new to us so it takes more work to take out the incumbents,” said Moreno.

There are opportunities to work with suppliers of the magnetic components on new design approaches. “It is an emerging technology and we are going to use topologies that haven’t been used before in the MHz range,” said Tseng. “Convincing customers has been a critical point for us with GaN – nobody wants to be first and there are areas where GaN is being used, power amplifiers, inverters, some server designs, so we point to those areas and work with large customers on testing and reliability, that’s the way.”

The company also starting testing of full designs a year ago to demonstrate the reliability of the components in real world applications..

“We qualify the technology now with JEDEC and above and beyond with in-circuit HTLL (high test level language), building the end applications such as a 65W adaptor with a decent sample size and submitting these adaptors through the whole HTLL process. We started a bit over a year ago gathering data for over a year so far,” said Tseng.

“We are also doing a lot of corner lots to test the entire design process to see the flaws in the process with the foundry – we ran a lot of test chips, we have seen where it fails, understand where it fails so its an ongoing process”

The new technology also fits with the company focus on free space wireless charging. “In general on the transmitter side the amplifier can benefit from GaN with faster switching to project more energy, that’s one area and in the future that’s a potential big area,” said Moreno.

While other companies have come to market faster, often partnering with startups, Dialog has developed and tested the technology in-house. The challenge now is to persuade consumer equipment designers to adopt the reference designs that Dialog will supply, hence the long term testing of real designs.

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