The ability of gallium nitride (GaN) semiconductors to handle high power levels, operate at higher frequencies and deliver superior linearity make this wide bandgap (WBG) technology highly suitable for RF applications in aerospace and defense, automotive, industrial, and telecommunications. GaN owes its potential in RF applications to its high current density, high electron mobility and high breakdown voltage.

Take high mobility, for example, which enables GaN to handle switching frequencies higher than silicon-based RF devices. Next, GaN’s higher power handling capabilities compared to silicon-based solutions translate into a higher transmission range and smaller component count to drive the antennas.

Not surprisingly, the adoption of 5G networks is fueling demand for RF GaN devices because of their ability to ensure higher data rates and spectral efficiency at higher radio frequencies. The GaN-based RF devices are now widely used in 5G base stations, radar systems and satellite communications.

In RF applications, one crucial design building block is the power amplifier (PA), which resides in RF front-end modules that send and receive RF signals to and from antennas. Here, laterally diffused metal-oxide semiconductor (LDMOS), an incumbent RF power technology, has been dominating PA designs. However, GaN’s superior RF characteristics and significantly higher output power make it a viable alternative to LDMOS in PAs for RF designs.

So, while GaN’s place in high-power RF designs is imminent, there’s a duel between GaN-on-silicon carbide (SiC) and GaN-on-silicon (Si) platforms for the RF design riches.

GaN-on-SiC vs. GaN-on-Si

While PAs for RF applications can be manufactured on either silicon or SiC wafers, GaN-on-SiC devices can be more expensive because of the competition for SiC wafers from high-power applications, as well as SiC’s non-mainstream semiconductor manufacturing processes. Conversely, GaN-on-Si technology is expected to offer competitive performance paired with silicon manufacturing’s large economies of scale.

STMicroelectronics (STMicro) has recently produced GaN-on-Si prototypes for RF designs in collaboration with MACOM, a supplier of semiconductor products for data center, defense, industrial and telecommunication applications. These prototype wafers and devices are aimed at challenging the established LDMOS and GaN-on-SiC technologies currently serving RF designs.

“We believe that the technology has now reached performance levels and process maturity where it can offer attractive cost and supply chain advantages for high-volume applications, including wireless Infrastructure,” said Edoardo Merli, GM and executive VP of the Power Transistor Sub-Group at STMicro. He added that prototype wafers and devices manufactured by STMicro have achieved cost and performance targets.

It’s worth mentioning that the RF GaN industry began with GaN-on-SiC wafers, and this technology has been around for more than a decade. The broadband GaN-on-SiC high electron mobility transistor (HEMT) devices are now a staple in defense and aerospace electronics because they can handle multi-mode communication waveforms via high linearity features. Besides military radars, it has become a technology of choice for telecom products like 5G massive MIMO infrastructure.

“For GaN RF market, GaN-on-SiC is the main technology platform,” said Ezgi Dogmus, lead analyst at Yole Intelligence. “Owning to their high bandwidth and efficiency, GaN-on-SiC devices keep taking share from LDMOS in the 5G market and are starting to benefit from the 6-inch wafer platform transition.”

Microchip, for example, has been offering discrete transistors, as well as HEMTs fabricated on GaN-on-SiC technology. These RF GaN devices span 2-20 GHz and are designed to meet the linearity and efficiency challenges posed by the higher-order modulation techniques employed in 5G, satellite communications and defense applications. Even MACOM, now collaborating with STMicro on GaN-on-Si wafers, has been producing PAs based on GaN-on-SiC technology.

However, RF GaN devices manufactured on silicon substrates are cheaper, and their compatibility with CMOS processes facilitates large-scale manufacturing. Researchers at the Leuven, Belgium-based imec have recently used a CMOS-compatible platform to fabricate GaN HEMTs. Its GaN-on-Si process flow for RF begins with the metal-organic vapor deposition growth of an epitaxial structure on 200-mm silicon wafers.

The European semiconductor research outfit has also picked GaN-on-Si technology for its advanced RF program. It’s currently working on issues like parasitics within the device structures and optimization of devices for higher operating frequencies. Researchers at imec are devising new tools to improve GaN-on-Si device characteristics.

GaN-on-Si making headway

The GaN-on-Si technology is rapidly maturing due to the development of technology initially intended for power electronics applications. GaN-on-Si technology was initially developed for power electronics applications to facilitate more efficient power conversion in battery chargers, lighting systems, photovoltaics, and power supplies for computers, servers, and automotive.

While the market share of RF components based on GaN-on-Si technology is still tiny, it’s making headway as a cost-efficient and scalable solution. For instance, PAs based on this technology could find a place in smartphones for their ability to facilitate large bandwidth and small form factor.

For now, it’s competing with established LDMOS and GaN-on-SiC technologies, while steadily progressing toward commercialization and high-volume production. Having allies like imec and STMicro is significant and will be critical in advancing toward future milestones like product.

By: DocMemory
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