Bench Talk

Gallium Nitride HEMTs: Next-Generation Semiconductors for Power Electronics

(Source: Edelweiss / stock.adobe.com)

Silicon-based metal oxide semiconductor field effect transistors (MOSFETs) have been the standard in power electronics applications since the 1960s. Still, the evolution of various technologies—particularly in the automotive and consumer electronics sectors—have created new challenges for developers seeking to provide higher efficiency and greater power density in increasingly smaller form factors. Power supplies for everything from large data centers and wall outlet AC adapters to onboard charging stations in automobiles require high voltages while taking up as little valuable board space as possible. Self-driving cars also require more efficient energy distribution to operate the growing number of imaging devices and sensors used to navigate and detect potential obstacles. And while silicon-based semiconductors have essentially already been maxed out in higher-demand implementations, GaN-based (gallium nitride) semiconductors are increasingly proving to be an optimal solution for these types of design challenges.

Understanding GaN HEMTs

GaN HEMTs (High Electron Mobility Transistors) aren’t necessarily a better option than Si MOSFETs, silicon carbide (SiC) MOSFETs, or IGBTs (insulated-gate bipolar transistors) in every design scenario. However, they are particularly well-suited for applications requiring high-frequency performance in the medium voltage range. 600V GaN FETs are most commonly used in traditional power supplies for everything from personal computers and consumer electronic devices to base station power supplies and wireless charging devices. In contrast, SiC MOSFETs can provide up to 1200V, making them a better fit for applications with higher current requirements like automotive traction inverters and large-scale solar farms. Despite providing less power than SiC MOSFETs, GaN HEMTs operate at higher frequencies—greater than 200kHz—delivering faster switching speeds with reduced transmission loss. And although GaN HEMTs feature a power density similar to traditional Si MOSFETs, their capacity to operate at higher frequencies makes them ideal for wireless charging applications. SiC MOSFETs and IGBTs are better suited for sets that require more power but less efficiency (i.e., electrically powered vehicles, large industrial machinery) or enormous power consumers like server farms.

What ‘s more, GaN HEMTs are offered in smaller form factors than conventional MOSFETs while being less costly to manufacture and operate. The raw materials used in GaN technology are also significantly less expensive than those in SiC devices. For example, GaN requires less heat than SiC to produce, resulting in significant energy savings for manufacturers. Additionally, GaN devices are developed on silicon substrates, as are most integrated circuits, allowing developers to use pre-existing production methods and facilities to produce GaN HEMTs with very little retrofitting. Finally, post-production operation of GaN HEMTs consumes less power and requires less cooling and, therefore, less energy to operate than SiC MOSFETs, providing additional cost savings to the consumer. 

One drawback of GaN HEMTs is the need to be used in conjunction with gate drivers in certain implementations due to their narrow optimal drive voltage. If the drive voltage is too low—less than two volts—the device may malfunction and turn on by itself, and if the gate withstand voltage is too low, the gate itself might break down. The optimal drive voltage for GaN implementation is between 4.5V and 6V—any less may mean it won't turn on, and any more might fry the circuit. Incorporating an external gate driver helps maximize transistor performance but takes up additional space on the board, which is a factor developers must consider. However, GaN devices produce less heat and require less cooling than their silicon-based counterparts, potentially lowering energy and maintenance costs for the customer even further.

The many benefits of using discrete GaN HEMTs may seem to be significantly restricted by the issues described above, but overcoming these limitations is possible. One advantage of GaN HEMTs is that they can be built on the same substrate as other integrated circuits, enabling additional circuitry to be included in the same device. For example, circuits for controlling the drive voltage to within the desired range to prevent a low voltage from turning on the device unexpectedly or driving the gate voltage too high and potentially damaging the device. At the same time, an integrated solution typically costs less than a discrete configuration, takes up less board space, reduces parasitic effects, and simplifies board layout. And from a performance standpoint, an integrated solution can maintain and even improve the high operating frequency advantage of the GaN HEMT compared to a multiple-device implementation. Reliability is also increased—a benefit that is very important for many power delivery applications.

ROHM Semiconductor’s Nano Cap™ 650V GaN HEMT Power Stage ICs combine the high-power density and efficiency of GaN technology with a silicon driver to form a fully integrated IC solution. GaN ICs are not only an optimal fit for medium voltage applications like base station chargers and power adapters—they can be implemented in industrial applications and high-density power supplies as well. The lower cooling requirements of ROHM’s GaN ICs minimize the need for heat sinks and other cooling mechanisms, further reducing physical board space. In fact, it wouldn’t be surprising to see GaN’s smaller form factor (and superior efficiency) eventually overtake silicon-based ICs as technologies continue to evolve, especially when implemented in tandem with gate drivers. For mobile applications that require ultra-high frequency operation and loss minimization, ROHM’s Nano Cap 650V GaN HEMT Power Stage ICs provide a complete and efficient solution.

Conclusion

Gallium Nitride HEMTs represent a promising frontier in power semiconductor technology, offering efficiency improvements and cost advantages for various applications, from consumer electronics to power delivery systems. With ongoing advancements and integration possibilities, GaN HEMTs, like those from ROHM Semiconductor, are poised to reshape the landscape of power electronics.

Author

Alex Pluemer is a senior technical writer for Wavefront Marketing, specializing in advanced electronics, emerging technologies and responsible technology development.