What Is a GaN Power Device?
A GaN power device is the next-generation semiconductor power device formed on gallium nitride crystals.
GaN power devices have attracted much attention in recent years because they can handle higher power with lower power loss than conventional power devices made on silicon using semiconductor processes. However, recent technological innovations related to compound semiconductors are resolving these issues.
Higher efficiency in GaN power devices also allows for simplification of heat removal mechanisms, which can contribute to significantly smaller products and lower power consumption.
Uses of GaN Power Devices
GaN power devices are widely used in chargers that enable rapid charging of smartphones and PCs and in amplifiers for cell phone base stations. Because they can handle more power than silicon-based power devices, they are often used in PC chargers and amplifiers for base stations as a replacement for them.
In addition, GaN power devices with high efficiency are beginning to be used in power conditioners for photovoltaic power generation systems, which require extremely high conversion efficiency. Furthermore, because of their ability to operate at high switching speeds, GaN power devices are also used in switching power supplies for server equipment, where power supply stability is required.
Principle of GaN Power Devices
The principle of GaN power devices lies in the fact that the semiconductor property called band gap of GaN is about three times larger than that of Si. This makes GaN devices resistant to high electric fields.
GaN power devices generally consist of a high electron mobility transistor circuit called a HEMT structure. The HEMT structure is normally ON, which means that the current always flows, and is turned OFF by applying a negative voltage to the gate. Therefore, if negative voltage cannot be applied to the gate electrode due to some problem, it cannot be turned off and becomes very unstable.
GaN power devices have such reliability problems, and stable normally OFF has been a challenge from the viewpoint of ease of use. Therefore, we have realized normally OFF by incorporating normally OFF Si-MOSFETs in the gate electrode.
Another challenge is a physical phenomenon called current collapses. This is a phenomenon in which ON resistance increases, and current concentration occurs during high-voltage switching, which is caused by defects in the GaN crystal fabrication process. However, thanks to innovations in crystalline thin-film deposition technology, high-quality deposition is now possible.
Other Information on GaN Power Devices
1. Segregation between GaN and SiC
GaN and SiC have large dielectric breakdown strength due to their large band gap, which makes it easy to increase device breakdown voltage. This makes them suitable for high-current, high-voltage applications. In particular, SiC is often used in high-current applications such as motor drives for EV vehicles and power generation systems and is expected to replace IGBTs shortly due to its device breakdown voltage.
On the other hand, GaN power devices are widely used in applications that require high switching speeds and high-frequency operation because of their high cut-off frequency (fT). This indicates high frequency characteristics, and high electron mobility, although it is difficult to achieve the same level of breakdown voltage as SiC.
In other words, GaN and SiC are divided into GaN devices for high-speed switching charging high-frequency applications for 5G base stations, and SiC devices for high-voltage and high-current applications.
2. Trends in GaN-based Power Semiconductors
GaN power semiconductors are now being used in two major applications: one targeting on-board charging of electric vehicles at relatively high 650 V or higher, and the other targeting voltage conversion in DC-DC converters from 48 V to 12 V in hybrid electric vehicles. Both of these applications, as GaN power semiconductors, along with SiC devices, are expected to drive the wide bandgap (WBG) device market in the future.
The challenges to the commercialization of these new applications are reliability, manufacturing yield, and cost. However, thanks to the efforts of semiconductor companies around the world, the potential for commercialization is making great strides.
3. Applications of GaN Devices
Other applications of GaN devices include light source applications: There are great expectations for GaN as a material for LED light sources and laser diodes with high luminous efficacy because GaN is a direct transition semiconductor among compound semiconductors.
As an electronic device, GaN is also expected to be used in high-power, high-frequency amplifier transistors for millimeter wave and sub-THz applications.