September 30, 2020
TOKYO--Toshiba Electronic Devices & Storage Corporation (“Toshiba”) has developed a gallium nitride (GaN) cascode with a direct gate drive that realizes stable operation and simplification of system design. The device reduces risk of additional energy loss during switching due to false on, and like silicon its switching speed can be easily adjusted, an important consideration in the design of power electronics systems.
Details of the new discrete device were reported at the IEEE-sponsored International Symposium on Power Semiconductor Devices and ICs 2020 (ISPSD 2020), held online.
GaN power devices are candidates for achieving high efficiency and downsizing systems. They are currently used in quick chargers for smartphones and computers, and are expected to be adopted in the power supply of industrial equipment and servers.
Generally, power devices need to be normally-off, but GaN high-electron-mobility transistors (HEMTs) are normally-on. GaN transistors used for power conversion can be classified into cascode and p-GaN gate types. The cascode type is combined with a GaN HEMT and low voltage silicon MOSFET in a single package. The p-GaN gate type uses a p-GaN gate to make GaN HEMTs normally-off.
Toshiba’s new GaN cascode is less susceptible to noise, a source of malfunction, as it has a higher threshold voltage than p-GaN gate normally-off HEMT devices. It also does not require designated driver ICs.
It is normally difficult for this type of cascode to control its switching speed via an external gate resistor, because it uses a silicon MOSFET to drive the GaN HEMT. Toshiba solved this by developing a device with direct gate drive, where driver ICs directly drive the GaN HEMT. This supports changes to its switching speed, like silicon power devices, which helps to simplify the overall design of power electronics systems.
Another plus is that the new device contributes to stable operation by not showing false-on due to voltage changes in the silicon MOSFET from an external voltage change, because the GaN HEMT gate is controlled independently.
Toshiba confirmed that the new device has the reliability necessary for power supply applications.  As the new device is a discrete type, users can select driver ICs appropriate for the application.
 A predicted lifetime of more than 1000 years (Vds = 500 V at 150°C) was achieved.
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