GaN is a semiconductor material that can amplify high power radio frequency signals efficiently at microwave frequencies to enhance a system’s range. Therefore it has become the technology of choice for high-RF power applications that require the transmission of signals over long distances such as EW, radar, base stations and satellite communications. The advantages of GaN-based devices stems largely from the attractive intrinsic physical properties of the material. The material exhibits wide bandgap, high breakdown voltage, extremely high power density and high gain at microwave frequencies. The raw materials for GaN are available in large quantities. Nitrogen can be taken from the air, and gallium is a waste product in metal working.
Compared to Silicon (Si) and Gallium Arsenide (GaAs), gallium nitride is a robust technology and possesses better performance characteristics. GaN semiconductor devices offer high breakdown voltages, saturation velocity, high electron mobility and high thermal conductivity among others. This has enabled the implementation of GaN on a wide basis high frequency RF devices and LEDs. These factors in combination are expected to positively impact the growth of the GaN semiconductor devices globally.
These properties, make GaN devices well suited for high power, high frequency and wide bandwidth applications in extreme environments. GaN transistors can operate at higher temperatures, and higher current densities than their SiC counterparts. The switching speed of a GaN power transistor may reach an unbelievable 100V/ns.
GaN based components are commonly used in blue and white LEDs. In power electronics applications, GaN diodes and transistors, in particular, have received interest, for example in frequency converters or electric cars. It is believed that in radio applications, 5G network base stations will use GaN based power amplifiers in the future. In electronics applications, a GaN transistor offers low resistance and enables high frequencies and power densities. However, the exploitation of higher frequencies necessitates the development of high-speed information communication technologies that use high-frequency-operation transistors such as high-electron-mobility transistors (HEMTs).
The GaN semiconductors devices market is primarily being driven by factors such as advancement in technology coupled with the expansion in the application areas for GaN based devices. There has been a rapid advancement in the GaN technology as a result of which various companies are coming up with new innovative products that are cost-effective and have better design and performance. Moreover, in order to address the growing demand for high power and high temperature applications there has been an increase in the usage of GaN semiconductor devices, according to report by ReportLinker.
In recent years, GaN HEMTs have been widely used as high-frequency power amplifiers in long-distance radio wave applications, such as radars and wireless communications. It is also expected that they will be used for weather radars to accurately observe localized torrential rainfall, as well as in millimeter-waveband wireless communications for fifth-generation mobile communications (5G). The outreach of microwaves from the microwave and millimeter-wave bands used for radar and wireless communications can be extended by increasing the output power of the high-frequency GaN HEMT power amplifiers used for transmitter. This allows for expanded radar observation range as well as longer distance and higher capacity communications.
GaN Market Rise to Fore
Transparency Market Research states that the global GaN semiconductor devices market will expand at a high 17.0 percent CAGR over the period between 2016 and 2024. With such exponential growth, the market, which had a valuation of US$870.9 million in 2015, is projected to rise to US$3,438.4 million by 2024. Of the key end-use industries utilizing GaN semiconductors, the aerospace and defence sector dominates, accounting for a share of over 42 percent of the global market in 2015.
The increased usage of GaN semiconductor devices in the defense sector has also emerged as a key driver of the global GaN semiconductor devices market. The continuous rise in defense budgets of developing and developed countries as well as the demand for inclusion of the technologically most advanced products in the arsenal of national and international armies will propel the global GaN semiconductor devices market in the near future, says TMR.
The global market for gallium nitride (GaN) semiconductor devices is largely consolidated, with the top four companies commanding a share of over 65 percent of the overall market in 2015, states Transparency Market Research (TMR) in a new report. The dominant company among these four top vendors, Efficient Power Conversion Corporation, accounted for a 19.2 percent share of the global market in the said year. The other three topmost companies of the global market, which collectively enjoyed a considerably large share in the overall global market in the said year, are NXP Semiconductors N.V., GaN Systems, and Cree. Other companies are Triquint/RF Micro Devices, Sumitomo, RFHIC, MACOM/Nitronex, Mitsubishi, and Microsemi have GaN device portfolios covering a wide range of application.
The opportunity in the global GaN semiconductor devices market was pegged at US$870.9 mn in 2015 and is poised to reach US$3,483.4 bn by 2024, expanding at a significant CAGR of 17.0% from 2016 to 2024. On the basis of wafer size, the 4 inch segment will continue to be at the forefront of growth until 2024, accounting for 53.95% of the overall market revenue. The 8 inch segment is expected to progress at a phenomenal CAGR of 33.6% during the forecast period. The rising demand for 8 inch based GaN semiconductor devices can be attributed to their excellent switching characteristics and small parasitic capacitance, says Transparency Market Research (TMR).
North America was the leading revenue contributor in 2015. However, Asia Pacific is estimated to surpass the region by the end of the review period. China, India, Korea, and Japan will be sights of high growth rate in the region. The flourishing growth of the electronics sector is one of the primary factors driving the growth of the region. Moreover, the lower production and labor costs in the region are attracting international companies to set up their production facilities, which in turn is propelling the growth of the region. The valuation of the regional market is anticipated to rise to more than US$1 bn by the end of 2024.
Gallium-Nitride Transistors: GaN-HEMT
A typical GaN-HEMT utilizes the two-dimensional electron gas (2DEG) formed at the GaN/AlGaN interface as the conducting channel. GaN-HEMTs are promising next-generation high-frequency devices because they provide the advantages of both high-frequency operation (due to the 2D nature of the channel electrons) and large output power due to a large bandgap.
In this context, GaN-HEMTs have been developed for application in high-frequency power amplifiers of satellite base stations and radar sensors. As regards their commercial use, GaN-HEMTs operating in the X-band (~10 GHz) have been commercialized by Eudyna (now acquired by Sumitomo Electric Industries). However, GaN-HEMTs are still not a mature technology since they have not fully replaced existing technologies in the millimeter-wave frequency (>60 GHz) domain.
Fujitsu Successfully Triples the Output Power of Gallium-Nitride Transistors
Fujitsu Limited and Fujitsu Laboratories Ltd. today announced that they have developed a crystal structure that both increases current and voltage in gallium-nitride (GaN) high electron mobility transistors (HEMT), effectively tripling the output power of transistors used for transmitters in the microwave band.
The GaN HEMT technology can serve as a power amplifier for equipment such as weather radar – by applying the developed technology to this area, it is expected that the observation range of the radar will be expanded by 2.3 times, enabling early detection of cumulonimbus clouds that can develop into torrential rainstorms. To expand the observation range of equipment like radar, it is essential to increase the output power of the transistors used in power amplifiers. With conventional technology, however, applying high voltage could easily damage the crystals that compose a transistor. Therefore, it was technically difficult to increase current and voltage simultaneously, which is required to realize high-output power GaN HEMTs.
Research is ongoing for indium-aluminum-gallium nitride (InAlGaN) HEMTs for the next generation GaN HEMT that would contribute to increased current, as InAlGaN HEMTs can increase electron density within the transistor. When high voltage is applied, however, an excessive amount of voltage becomes concentrated on a part of the electron supply layer, damaging the crystals within transistors. Consequently, these transistors had a serious issue whereby their operating voltage could not be increased
Fujitsu and Fujitsu Laboratories have now developed a crystal structure that improves operating voltage by dispersing the applied voltage to the transistor, and thereby prevents crystal damage (patent pending). This technology has enabled Fujitsu to successfully achieve the world’s highest power density at 19.9 watts per millimeter of gate width for GaN HEMT employing indium-aluminum-gallium nitride (InAlGaN) barrier layer. This research was partially supported by Innovative Science and Technology Initiative for Security, established by the Acquisition, Technology & Logistics Agency (ATLA) of the Japanese Ministry of Defense.
For conventional InAlGaN HEMTs, all of the applied voltage between the gate and drain electrodes were applied to the electron supply layer, and numerous electrons having high kinetic energy were generated in the electron supply layer. Subsequently, these electrons would violently strike the atoms which compose the crystal structure, causing damage. As a result of this phenomenon, there was a limit to the maximum operating voltage of the transistor.
By inserting the newly developed high-resistant AlGaN spacer layer, the voltage within the transistor can be dispersed across both the electron supply layer and the AlGaN spacer layer. By mitigating the concentration of voltage, the kinetic energy increase of the electrons within the crystal is suppressed and damage to the electron supply layer can be prevented, leading to an improved operating voltage of up to 100 volts. This operation voltage corresponds to over 300,000 volts if the distance between the source electrode and gate electrode is one centimeter.
Fujitsu and Fujitsu Laboratories have succeeded in developing a transistor that can provide both high current and high voltage by inserting a high-resistance AlGaN spacer layer between the electron supply layer and the electron channel layer. Furthermore, by applying the single-crystal diamond substrate bonding technology Fujitsu developed in 2017, the heat generation within the transistor can be efficiently dissipated through diamond substrate, enabling stable operations.
Challenges being overcome
The major challenges to more widespread GaN adoption have been reliability and price. Many of the early reliability challenges of GaN have been solved and GaN today demonstrates, via RF life test, a mean time to failure (MTTF) of greater than 1 million hours at a junction temperature above 200°C.
However in applications below 3.5GHz, GaN-on-SiC is not cost-effective enough versus Si-LDMOS. The Low volumes, the cost of the SiC wafers, coupled with wafer diameters in the 2″ – 4″ range all contribute to GaN devices being many times more expensive than competitive technologies like GaAs and LDMOS.
The various costs involved in the production of GaN devices include cost of substrate, fabrication, packaging, support electronics and development. Thus, high cost is one of the major challenges in the commercialization of GaN based devices. Though producing GaN in large volumes can help overcome these issues, currently, there is no widespread adopted method for growing GaN in bulk due to high operating pressures and temperatures, low material quality and limited scalability.
In 2013, RFMD introduced the first 6-inch GaN-on-SiC wafers for RF power transistors and M/A-COM technology introduced a line of GaN devices in plastic packaging. Companies like TriQuint, Cree and UMS continue to expand their GaN product and process portfolios. Developments like these and ongoing process improvements will continue to reduce the cost of GaN devices.
A SOI wafer is a suitable substrate for gallium nitride crystals
GaN based components are becoming more common in power electronics and radio applications. The performance of GaN based devices can be improved by using a SOI wafer as the substrate’, says Academy Research Fellow Sami Suihkonen.
In cooperation with Okmetic Oy and the Polish ITME, researchers at Aalto University have studied the application of SOI (Silicon On Insulator) wafers, which are used as a platform for manufacturing different microelectronics components, as a substrate for producing gallium nitride crystals. The researchers compared the characteristics of gallium nitride (GaN) layers grown on SOI wafers to those grown on silicon substrates more commonly used for the process.
“We used a standardised manufacturing process for comparing the wafer characteristics. GaN growth on SOI wafers produced a higher crystalline quality layer than on silicon wafers. In addition, the insulating layer in the SOI wafer improves breakdown characteristics, enabling the use of clearly higher voltages in power electronics. Similarly, in high frequency applications, the losses and crosstalk can be reduced,” explains Jori Lemettinen, a doctoral candidate from the Department of Electronics and Nanoengineering.
Growth of GaN on a silicon substrate is challenging. GaN layers and devices can be grown on substrate material using metalorganic vapor phase epitaxy (MOVPE). When using silicon as a substrate the grown compound semiconductor materials have different coefficients of thermal expansion and lattice constants than a silicon wafer. These differences in their characteristics limit the crystalline quality that can be achieved and the maximum possible thickness of the produced layer.
‘The research showed that the layered structure of an SOI wafer can act as a compliant substrate during gallium nitride layer growth and thus reduce defects and strain in the grown layers,” Lemettinen notes.
IQE’s GaN on SiC achieves breakthrough power and frequency results for Satellite Communications and 5G Applications
High frequency microwave capabilities of up to 40GHz (also known as Ka-band) are essential for satellite communications and will become increasingly important for next generation (5G) wireless communications. However, until now, designers have faced compromises between frequency and power.
The breakthrough results are published in IEEE Electron Device Letters, Vol 36, No. 10, October 2015 in an article by Fitch et al. entitled: Implementation of High-Power-Density X-Band AlGaN/GaN High Electron Mobility Transistors in a Millimeter-Wave Monolithic Microwave Integrated Circuit Process.
The authors demonstrated 7.7 W/mm at 35 GHz and VDS = 30 V on a standard 4 × 65-μm T-gated FET and then 12.5 W/mm at 10 GHz and VDS = 60 V on a 4 × 75-μm T-gated FET by adding a field plate. These are the highest reported power densities achieved simultaneously at X-band and Ka-band in a single wideband GaN MMIC process.
Freescale Introduces Breakthrough Ultra-Wideband RF Power GaN Transistors in Advanced Plastic Packages
Freescale Semiconductor, the global leader in radio frequency (RF) power transistors, has introduced two ultra-wideband RF power gallium nitride (GaN) transistors in new advanced plastic packages.
“We have innovated the capability to metalurgically bond our GaN-on-SiC chips to copper flanges, and over-mold them to enable unprecedented thermal performance,” said Mali Mahalingam, Freescale Fellow and head of RF package development. “In addition, this new package platform supports complex internal matching schemes that enable superior broadband performance.”
“The industry-leading bandwidth of these two products will enable our customers to replace two or even three separate RF PA’s with a single RF lineup, vastly reducing system cost,” said Paul Hart, senior vice president and general manager of Freescale’s RF business. “In addition, the devices’ ultra-low thermal resistance will allow customers to reduce the cost of their cooling systems, or run at full CW-rated power to much higher case temperatures.”