Question

Describe the challenges of GaN material. Explain why it can be applied in 5G communication.

Answer 1

1. Challenges of GaN material :

Since GaN has more and more appeal on the power electronics market and in the research community, topics related to PCB design, thermal loss extraction, and challenges related in how to control overvoltages due to fast switching and, consequently, gate oscillations .

1.1. PCB Layout/Design :

1.1.1. Device Package :

Available on the market, most of the GaNs are Surface-Mounted Devices (SMD). This trend relates primarily to decreasing the parasitic inductances between the device terminals, since this component can operate at high switching frequencies, and these parameters play a major role in switching performance.

The GaNs available have much smaller packages as compared to the TO family: 83-times smaller than TO-247-3 and 45-times smaller than TO-220 (considering only the package), which brings the benefit of space reduction, although the thermal cycle of the device should be addressed carefully. However, some off-the-shelf GaN devices are made in the TO-220 package. SMD components also bring the benefit of decreasing the power loop parasitics, since the drain-source-gate-kelvin pins are directly connected to the PCB and not via external pads, as for the TO family.

1.1.2. Internal Parasitics :

Since GaN semiconductors can operate at high switching frequencies due to their fast transient both to turn-on and turn-off, the internal and external parasitics due to, respectively, internal bond-wire connections and PCB layout need to be considered and minimized during device production and the PCB layout project in order to maximize device and system performance. As power electronics engineers, the only feature that can be controlled in this case is the PCB design parasitics, as the switches are off-the-shelf selected.

1.1.3. Signal and Power Loops :

The two critical loops that should be carefully projected in order to achieve the best performance of these devices are the signal and power loops. The parasitic inductances and capacitances influence the performance of these devices, but they are not the only ones. Copper-based planes and tracks interconnect the components on a PCB layout. These connections increase, primarily, the parasitic inductances of the loops, and consequently, these loops should be carefully routed and minimized in order to achieve a better circuit performance.

1.2. Thermal Management :

GaN devices cannot achieve their best performance if used in conventional TO packages, although some options are available on the market. Manufacturers are now developing new packages to overcome parasitic problems related to GaN devices, most of them SMD packages. These new packages introduce an extra challenge for power electronics engineers: thermal management. Thermal heat transfer proves to be correlated with the overall performance and reliability of the device, and some studies in the field have been realized. GaN components can survive much higher temperatures, in controllable environments, than the Si competitor.

For applications in power electronics, a major issue is related in how reliable these devices are to operate in harsh environments, for instance deserts (high ambient temperature) or space (difficult/impossible access to maintenance). Some discussions on this topic are found in the literature. Making these components as reliable as possible is a challenge faced by semiconductor researchers. Studies show that changes in the internal layer distribution/composition and gate overdrive protection improve the reliability of these devices. Additionally, the temperature-dependent thermal resistance and reliability of these devices are also an important point.

2. GaN in 5G Cellular :

5G is expected to offer significant advantages, including higher capacity and efficiency, lower latency, and ubiquitous connectivity. The new cellular network standard will enable the live transmission of high-quality video. 5G is currently being planned with a vision of greater than 10 Gbps transmission speeds for mobile broadband (phones/tablets/laptops) and ultra-fast low latency for Internet of Things (IoT) applications.

The base stations are an important component in the cellular network. They are the bottleneck through which all data must pass. The researchers are developing power amplifiers that are able to send more data more quickly and above all more efficiently through the cellular network. New power amplifiers provide the necessary radio frequencies over which the data is transmitted. As a first step, additional radio frequencies of up to 6 gigahertz are freed up for 5G. Currently, LTE is limited to 2.7 gigahertz.

In the RF field, in the near term, GaN will see the highest growth in cellular infrastructure applications. GaN’s bandwidth, power, and efficiency advantages provide compelling drivers for adoption in macro base stations and small cells. It will further penetrate cellular infrastructure, providing solutions for point-to-point communications. The largest potential market for commercial applications is power amplifier (PA) for base stations, and for new standards appearing at higher frequencies like WIMAX.

Higher frequencies mean faster data transmission, but unfortunately also less available power for the transmitters, For this reason, the scientists are manufacturing transistors and microchips that are only a few square millimeters in size out of the semiconductor material gallium nitride (GaN). Due to its special crystal structure, the same voltages can be applied at even higher frequencies, leading to a better power efficiency performance.

Today, GaN is slowly replacing silicon (Si) in the specific applications (i.e., RF amplifier front ends of 4G/LTE base stations). Next-generation 5G deployment will involve additional use of GaN technology. Pre-5G, there was increasing use of GaN- on-SiC in the macro cell. 5G will bring in GaN-onSi to rival GaN-on-SiC designs with inroads into the small cell space (micro/metro cells) before potentially overlapping into femtocells/home routers and even into handsets.

Furthermore, GaN technology will be well suited for 5G handsets. From a technology standpoint, 5G suffers from attenuation issues, requiring multiple antennas to improve signal quality using spatial multiplexing techniques. Each antenna requires dedicated RF front-end chipsets. Compared to gallium arsenide (GaAs) and Si, GaN has less antenna requirements for the same power levels. The resultant form factor advantages make GaN ideally suited for 5G handsets.