OKI has developed a technique that can build vertical gallium nitride (GaN) transistors with high currents up to 1800V.
OKI developed the GaN lifting technique with the QST (Qromis Substrate Technology) wafer technology licensed to Shin Etsu Chemical in 2019. Shin Etsu started shipping the wafers in September.
OKI’s CFB (crystal film bonding) technology is used to lift off only the GaN functional layer from the QST substrate which can be as large as 300mm and bond it to a different material substrate. While such techniques have been used for microLED displays, this combination enables the vertical conduction of GaN and is expected to contribute to the realization and commercialization of vertical GaN power devices capable of controlling large currents and voltages up to 1880V says OKI.
The two companies are working on vertical GaN power devices by partnering with companies that manufacture these devices.
- Shin-Etsu licenses Qromis GaN technology
- Mass production starts for 650V GaN on 200mm ceramic wafers
GaN devices are attracting attention as next-generation devices that combine high device characteristics with low power consumption, such as power devices that require high breakdown voltages of 1800 volts or more, high-frequency devices for Beyond5G, and high-brightness micro-LED displays.
In particular, vertical GaN power devices are expected to achieve significant demand growth as devices that can improve the basic performance of electric vehicles by endowing them with extended driving ranges and shortened power supply times. However, two major challenges hinder the implementation of vertical GaN power devices: the diameter of the wafers must be increased to improve productivity and vertical conductivity must be realized to enable large current control.
The coefficient of thermal expansion of Shin-Etsu Chemical’s QST substrate is equivalent to that of GaN and so can suppress warpage and cracking. This characteristic enables the crystal growth of thick GaN films with high breakdown voltages even on wafers larger than 8 inches, thereby enabling the production of wafers with larger diameters.
On the other hand, OKI’s CFB technology can lift off only the GaN functional layer from the QST substrate while maintaining high device characteristics. The insulating buffer layer required for GaN crystal growth can be removed and bonded to various substrates via metal electrodes that allow ohmic contact.
Bonding of these functional layers to a conductive substrate with high heat dissipation will enable both high heat dissipation and vertical conductivity. Through this, the combined technologies of Shin-Etsu Chemical and OKI solve the above two major challenges, paving the way for the social implementation of vertical GaN power devices.