A transition towards gallium nitride on silicon (GaN-on-Si) RF power devices is happening in the market, which is a trade-off between enhanced performance and moderate cost. GaN power amplifiers offer superior power capability, efficiency, bandwidth, and linearity compared with pure silicon or gallium arsenide (GaAs)-based technologies commonly used, enabling higher performance and lower overall system costs. GaN-based low-noise amplifiers tend to exhibit improved robustness, noise figure, and dynamic range compared with Si and GaAs devices.
In addition, GaN-based transistors can operate at high temperatures, reducing system cost, size, and weight, which are traits that have elevated its rank for defense applications. However, the growth of GaN-on-Si is advantageous in more cost-sensitive commercial applications where some performance metrics associated with silicon carbide can be compromised for the lower cost of silicon wafers. Silicon carbide is the more ideal substrate for growth of GaN from a crystal perspective, but processing methods can be applied to achieve an acceptable defect density for certain applications on a less ideal wafer, silicon, that possesses a higher lattice mismatch for epitaxy.
The developers and producers of GaN-on-Si power electronics are pursuing various business strategies. Some companies are selling their devices on the open market, while others are targeting the closed merchant market. In addition, there is a niche market of companies offering design or foundry services or just licensing their technology. The closed merchant strategy, which is common with a new technology, is often implemented within a partner business relationship, which limits access to a vendor's know-how and its intellectual property (IP) via a non-disclosure agreement.
Companies pursuing this strategy include International Rectifier (IRF) and Transphorm. RF Micro Devices is an example of a company offering manufacturing foundry services providing access to GaN-on-Si high-power device technology that is available to its merchant customers and business partners. All in all, there are nearly 25 vendors engaged in the commercialization of high voltage GaN-on-Si high-electron mobility transistors (HEMTs), ICs, and modules for power conversion applications.
IRF started commercial shipments of GaN-on-Si power devices in early May and says that its capital-efficient manufacturing model enables customers with improvements in key application-specific figures of merit of up to a factor of ten compared to state-of-the-art silicon-based technology. Its recently released products are the result of ten years of research and development focused on the company's proprietary GaN-on-Si epitaxial technology. This company believes that GaN has the potential to be incorporated into every business unit and product line over the long-term.
The companies that are developing GaN-on-Si technology have several technical challenges to overcome for increased commercialization including: containing the current collapse phenomenon (where current decreases and on-resistance increases during operation), developing the technologies for manufacturing enhancement-mode HEMTs, and validating device reliability. Reliability is still somewhat suspect.
What’s more, GaN HEMT selling prices must become more competitive for penetration into the commercial power electronic market, which could be accomplished via manufacturing on larger, 200mm diameter Si wafers. The industry is just transitioning to 150mm Si substrates, so it still has a learning curve to achieve, as wafer processing evolution cycles are not trivial. More traditional GaN-on-SiC based power devices will still reign supreme in less cost-sensitive military applications that utilize the full benefits of these material systems, where performance is more critical.