Technical Insight
GaN gets set for mainstream adoption into RF energy markets
Products made from GaAs and LDMOS will be superseded by GaN variants that will penetrate new markets such as heating systems for microwave ovens, power sources for plasma lighting and automotive ignition
BY MARK MURPHY FROM MACOM
A narrow subset of semiconductor technologies has always serviced the RF and microwave domain. This approach allows the most appropriate technology to meet the unique requirements of a host of complex applications, ranging from consumer wireless handsets to military radar infrastructure.
As with any technology, different candidates must be assessed in terms of performance, reliability and cost. Do this, and it is clear that there is an absence of a one-size-fits-all solution for adequately addressing the needs of every RF application. Instead, a spectrum of semiconductor solutions has evolved for meeting specific technology challenges while fulfilling cost requirements.
Two of the most established technologies for serving many commercial applications are GaAs and silicon LDMOS. But they are now under threat from a new challenger, GaN, that is poised to deliver a ground-breaking transformation. Products based on this wide bandgap semiconductor are now commercially available from several companies, including ourselves "“ MACOM of Lowell, MA.
To fully appreciate this wide bandgap technology, and its supply chain dynamics that are propelling its industrial uptake, it is helpful to consider the evolution of GaAs from an esoteric technology to high-volume market mainstay "“ a trajectory that parallels what we are seeing with GaN.
And in addition, it is worthwhile to consider the role that LDMOS has played in the evolving RF market.
Back in the 1990s, GaAs was in a formative stage, similar to where GaN has been positioned in recent times. It was an emerging technology, underpinned by strong government funding and targeting applications that could pay a premium for high performance.
This state of affairs turned on its head with an explosion in demand for wireless handsets. GaAs had found its "˜killer application', and economies of scale were soon at play. Compound semiconductor companies drove the industry towards establishing robust, reliable and scalable GaAs supply chains, through investment of hundreds of millions of dollars in large-scale GaAs fabs. Thanks to this, GaAs chip manufacture shifted from boutique production to high-volume production in just a few years.
Now, GaAs is under threat from silicon-based technologies such as CMOS and SOI, which are both gaining market share in handsets. Several leading silicon industry vendors have announced initiatives to supplant most GaAs production, leveraging economies of scale that dwarf even the largest GaAs factories.
Like GaAs, LDMOS has undergone incremental growth and multi-decade longevity in the RF market, particularly in wireless infrastructure. Thanks to the maturity of the LDMOS supply chain and attendant manufacturing efficiencies, costs have been kept relatively low.
Up until very recently, the performance of GaAs and LDMOS products "“ evaluated in terms of power, efficiency, bandwidth and thermal stability "“ have been sufficient for their target applications. But both technologies have their flaws. GaAs is limited to a power output below 50 W, while LDMOS is incapable of operating above 3 GHz.
GaN compares extremely favourably to both incumbents, combining high output powers with a very wide frequency range. It also offers several other attractive attributes, but despite all its virtues, it has been held back by high prices. Devices can be as much as ten times more expensive than products based on GaAs or LDMOS.
GaN at the tipping point
Today, the performance advantages of GaN are well known to everyone involved in the RF and microwave industry. This wide bandgap semiconductor delivers a raw power density that is considerably higher than that of GaAs and LDMOS, and devices can be scaled to high frequency. Armed with these attributes, device designers can realise broad bandwidths while maintaining high efficiency.
Our team at MACOM has been developing and commercialising GaN technologies and devices for several years. Our latest technology, fourth generation GaN-on-silicon (Gen4 GaN), can be used to manufacture products that combine a peak efficiency in excess of 70 percent with a gain of 19 dB, for modulated 2.7 GHz signals. This level of efficiency exceeds that of LDMOS by more than 10 percentage points, and if properly exploited, it can have a tremendous impact at the system level in military, commercial and industrial applications.
The high power densities and great efficiencies of GaN make it a great source for RF basestation transmitters.
Historically, the sticking point for GaN has been its high price. But this should change, given the very high power densities and scalability to 8-inch substrates. With our Gen4 GaN, we are planning to produce GaN-based devices in volume production levels that undercut the cost per watt of comparable LDMOS products, and are significantly less than that of GaN-on-SiC variants, which are far more expensive. Working with partners, we are leaders of 6-inch silicon wafer production, and we intend to move to 8-inch production in 2017. The growing capacities, allied to lower cost structures, should break barriers to widespread GaN adoption in mainstream commercial markets.
Delivering GaN performance at a cost that's far closer to that of silicon will drive innovation within the RF domain and ultimately open massive market opportunities. Chief among them will be RF energy applications. Here, controlled electromagnetic radiation will heat items and drive all kinds of processes. Today, magnetron tubes tend to generate this energy, but they are set to be displaced by an all solid-state RF semiconductor chain.
There are several compelling reasons behind a switch to solid-state RF energy. They include a low-voltage drive, semiconductor-type reliability, a smaller form factor, and an "˜all-solid-state electronics' footprint. But perhaps the greatest attributes are fast frequency, phase and power-agility, and hyper-precision. Taken together, these strengths result in an unprecedented process control range, even energy distribution, and fast adaption to changing load conditions.
Benefits of switching the RF source in a microwave oven from a magnetron to a GaN RF unit include a longer system life, a constant output power and zone controllable heating.
Microwaves and lighting
One common consumer product that will be transformed by the arrival of Gen4 GaN is the microwave oven. Prototype magnetron replacements have already been produced using LDMOS technology, but they fall significantly short of the minimum performance level. Our GaN devices bridge that gap, providing an additional 10 percent efficiency. HEMTs can deliver 70 percent efficiency at 2.45 GHz, and do so at a cost that is competitive with a tube-based legacy technology that launched in the 1940s and has undergone manufacturing optimization over many decades. The strengths of GaN ensure a longer system life, constant output power and zone-controllable heating.
Another sector that will be transformed by the arrival of affordable, high-performance GaN products is plasma lighting. It is slowly making inroads in the overall lighting market, with the greatest success coming in grow lighting applications. Here it makes an ideal lighting source, thanks to a colour-rendering index that provides a very close match to that of natural sunlight.
Today, LDMOS technology is widely used to provide RF power excitation at frequencies of hundreds of megahertz. However, developments are underway to increase the frequencies of RF excitation towards 6 GHz. This must be accompanied by efficiencies in excess of 70 percent "“ requirements that are very tough to meet with LDMOS technology, but a given for GaN. Turning to this wide bandgap technology also enables a trimming of transistor dimensions. This helps the vendors of plasma lighting produce competitive products that will battle with LED lighting for the indoor light bulb replacement market.
Further opportunities for GaN exist in automotive ignition, heating and drying, and industrial, scientific and medical markets. In all these, the strengths of GaN make it a highly compelling alternative to LDMOS. In conventional vehicles, RF-based ignition systems are poised to replace spark plug technology. Channelling RF energy into a vehicle's combustion chamber provides a more even ignition distribution, and in turn produces a considerable boost in fuel efficiency and a cut in carbon dioxide emissions. When it comes to heating and drying, using RF energy enables uniform heating and drying of materials. Undesirable temperature gradients resulting from conventional approaches are then avoided "“ these can be particularly severe in materials with poor heat transfer characteristics. Benefits that follow include accelerated production processes for manufacturing applications, improved medical procedures and processes that involve blood and/or organ warming, and enhanced chemical processing techniques in scientific applications.
Massive markets
The total addressable market for RF energy applications is enormous. Just consider the microwave oven market, where annual sales exceed 70 million units, each of which requires a transmit power ranging from 0.6-1.5 kW. That equates to a total power demand of 42 GW to 105 GW. At current mainstream semiconductor price structures, that is a market opportunity of $10 billion to $25 billion.
The RF devices underpinning these systems have to strike an optimal balance between performance, power efficiency, small size and reliability "“ and they must do this at a price point that promotes mainstream commercial adoption. Championing the full potential of GaN for RF energy is a non-profit technical association, the RF Energy Alliance. It anticipates that the market can take off with the introduction of 300 W power amplifier modules that combine 70 percent efficiency with a price of just 4 cents per watt.
We are addressing this challenge with our recently released MAGe-102425-300. This is a rugged 300 W, GaN-on-silicon power transistor housed in a cost-effective plastic package optimized for use in commercial-scale solid-state RF energy applications. Incorporating Gen4 GaN technology, our MAGe-102425-300 delivers a performance that defies the inherent power efficiency and density limitations of LDMOS, while retailing at an equivalent price profile at scaled volume production levels. The MAGe-102425-300, which provides a 300 W output power at 2.45GHz, at an efficiency of 70 percent, leads the industry in meeting the core technical requirements for next-generation power amplifiers proposed by the RF Energy Alliance.
The total addressable market for RF energy applications is enormous. Just consider the microwave oven market, where annual sales exceed 70 million units, each of which requires a transmit power ranging from 0.6-1.5 kW. That equates to a total power demand of 42 GW to 105 GW. At current mainstream semiconductor price structures, that is a market opportunity of $10 billion to $25 billion.
MACOM's MAGe-102425-300 can deliver a 300 W output at 70 percent efficiency.
The RF devices underpinning these systems have to strike an optimal balance between performance, power efficiency, small size and reliability "“ and they must do this at a price point that promotes mainstream commercial adoption. Championing the full potential of GaN for RF energy is a non-profit technical association, the RF Energy Alliance. It anticipates that the market can take off with the introduction of 300 W power amplifier modules that combine 70 percent efficiency with a price of just 4 cents per watt.
We are addressing this challenge with our recently released MAGe-102425-300. This is a rugged 300 W, GaN-on-silicon power transistor housed in a cost-effective plastic package optimized for use in commercial-scale solid-state RF energy applications. Incorporating Gen4 GaN technology, our MAGe-102425-300 delivers a performance that defies the inherent power efficiency and density limitations of LDMOS, while retailing at an equivalent price profile at scaled volume production levels. The MAGe-102425-300, which provides a 300 W output power at 2.45GHz, at an efficiency of 70 percent, leads the industry in meeting the core technical requirements for next-generation power amplifiers proposed by the RF Energy Alliance.
As a member of the Alliance, we are committed to advancing the organization's charter to standardize solid-state RF energy technology and its associated components and sub-module roadmaps "“ an effort that will reduce complexity, cost, and the development time associated with bringing related products to market. The mainstream adoption of solid-state RF energy hinges in part on the cooperation and collaboration of Alliance member companies and the industry at large.
Advances in the technology of GaN and its supply chain have taken us to a position where we can deliver breakthroughs in manufacturing scale and cost structures. This will spur the mass market adoption of this technology. Its great performance at a competitive price will open up many new markets, ranging from heaters for microwave ovens and large-scale drying to new units for automotive ignition systems and horticultural lighting. There is no doubt that GaN-on-silicon RF transistors have a bright future ahead of them.
