RF GaN Gains Steam

Wide-bandgap semiconductors are hot topics these days.

One wide-bandgap semi type–silicon carbide (SiC)–is the talk of the town and is gaining steam in electric vehicles and other systems. But let’s not forget about gallium nitride (GaN). GaN, a binary III-V material, has 10 times the breakdown field strength with double the electron mobility than silicon.

GaN is used for LEDs, power electronics and RF. While GaN-based power semiconductors are heating up, the RF version of GaN is taking off. In 2018, sales of RF GaN-enabled devices grew by nearly 22%, according to Strategy Analytics. By 2023, the RF GaN device market will surpass $1.7 billion, according to the firm. Cree, Qorvo and Sumitomo are among the big suppliers of RF GaN.

For years, RF GaN was a niche-oriented technology used in the military/aerospace community, namely for radar.

Then, the technology quietly moved into the commercial market. “The first volume commercial application for GaN was in CATV amplifiers back in the early 2010s,” said Eric Higham, an analyst at Strategy Analytics. “This volume was not very high, so the first substantial commercial volume for GaN began in 2014 with base station applications. This was driven strongly by broad LTE deployments in China.”

For years, base stations have used RF power amplifiers (PAs) based on laterally-diffused metal-oxide semiconductor (LDMOS) devices, a planar double-diffused MOSFET technology.

In base stations, RF GaN is also used for power amplifiers. Over time, RF GaN has been displacing LDMOS in base stations. “LDMOS still represents the slight majority of base station PA revenue,” Higham said. “GaN has a much faster revenue growth rate. I expect that as 5G deployments go higher in frequency, RF GaN will become more prevalent. GaN base station power revenue will surpass LDMOS revenue within the next few years.”

What will 5G mean for RF GaN? “In the <6GHz range, silicon (SiGe and/or CMOS) will play an increasing role as the number of radiators in a massive MIMO antenna increases,” he said. “GaN will certainly offer advantages, but there will continue to be momentum for LDMOS from the standpoint of ‘if it’s not broken, don’t fix it.’ ”

As 5G heads higher in frequency (>6GHz), LDMOS will not be able to meet the requirements. “So this will mean more opportunity for GaN, with the competition being SiGe and CMOS. All of these factors will lead to GaN surpassing LDMOS, but LDMOS pricing will continue to make it the right technology for some base station PAs. So LDMOS share will decline, but I don’t think it will disappear anytime soon,” he said.

Here’s the big question: Is RF GaN being used for the power amps in the new 5G phones yet? In smartphones, the power amp is typically based on GaAs devices. Several OEMs are exploring RF GaN for the power amp in smartphones. “This idea of GaN in handsets won’t go away,” he said. “I remain unconvinced GaN will find its way into handsets in the near future. I hear that at lower power levels, GaN loses some of its efficiency advantages versus other technologies.”

Prices are also an issue. “GaAs is close to, if not a commodity, for handset PAs. And if you talk to device manufacturers that do both GaN and LDMOS technologies, you will hear anything from GaN is on par with LDMOS to GaN is still a multiple of LDMOS pricing.”

As 5G handsets move to higher in frequency, the GaN community wants a piece of the action. “Until the GaN unit price is much closer to GaAs and/or silicon, there are still too many hurdles for GaN in handsets,” he added.