OKI Develops GaN Lifting off/Bonding Technology on QST Substrates of Shin-Etsu Chemical

- Contributing to realization and wide spread of implementation in vertical GaN power devices -

TOKYO--(BUSINESS WIRE)--OKI (TOKYO: 6703), in collaboration with Shin-Etsu Chemical Co., Ltd. (Head Office: Tokyo; President: Yasuhiko Saitoh; "Shin-Etsu Chemical"), has announced the successful development of a technology that uses OKI's CFB (crystal film bonding) technology (Note 1) to lift off only the GaN (gallium nitride) functional layer from Shin-Etsu Chemical's uniquely improved QST^® (Qromis Substrate Technology) substrate (Note 2) and bond it to a different material substrate. This technology 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. The two companies will work further together to develop vertical GaN power devices that can be implemented in society by partnering with companies that manufacture these devices.

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 social 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. It 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 (Note 3). 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.

In the future, the two companies will contribute to the realization and widespread use of vertical GaN power devices through Shin-Etsu Chemical's provision of QST substrates or GaN grown QST substrates to companies manufacturing GaN devices and OKI's provision of CFB technology through partnering and licensing. Furthermore, OKI hopes to use CFB technology to provide added value to semiconductor devices that go beyond the framework of single materials and help realize the company's key message of "Delivering OK! to your life".

Explanation of terminology
*1:	CFB (crystal film bonding) technology
	A technology to lift off crystal films from growing substrates, and bond it to a different material substrate.
*2:	QST (Qromis Substrate Technology) substrate
	A composite material substrate developed by Qromis, Inc. (Head Office: California; CEO Cem Basceri) exclusively for GaN growth and was licensed to Shin-Etsu Chemical in 2019.
*3:	Ohmic contact
	An electrical bonding with a linear current-voltage curve according to Ohm’s law.

About Oki Electric Industry Co., Ltd. (OKI)

Founded in 1881, OKI is Japan's leading information and telecommunication manufacturer. Headquartered in Tokyo, Japan, OKI provides top-quality products, technologies, and solutions to customers through its Public Solutions, Enterprise Solutions, Component Products, and Electronics Manufacturing Services businesses. Its various business divisions function synergistically to bring to market exciting new products and technologies that meet a wide range of customer needs in various sectors. Visit OKI's global website at https://www.oki.com/.

Notes:

• Oki Electric Industry Co., Ltd. is commonly referred to as OKI.
• CFB is a registered trademark of Oki Electric Industry Co., Ltd. in Japan.
• QST is a registered trademark of Qromis, Inc. in the US.
• All other company names and product names in this document are the trademarks or registered trademarks of the respective companies.