Shin-Etsu Taps QST Substrate for GaN Power Devices

Shin-Etsu Chemical Co., Ltd. has determined that QST® or Qromis Substrate Technology substrate*1 is an essential material for the implementation of high-performance, energy-efficient gallium nitride (GaN) power devices. Accordingly, the company will promote the development and launching on the market of these products.

Specifically, the design of QST® substrate is to have the same coefficient of thermal expansion (CTE) as GaN. Thus, it enables suppression of warpage and cracking of the GaN epitaxial layer and resultant large-diameter, high-quality thick GaN epitaxial growth. Taking advantage of these characteristics, it is expected to be applied to power devices and RF devices (5G and beyond 5G), which have been rapidly growing in recent years. Also, it suits MicroLED growth for MicroLED displays.

In addition to QST® substrates, Shin-Etsu Chemical will also make available GaN grown QST® substrates upon customer request. Specifically, the company offers 6-inch and 8-inch diameter substrates. At present, Shin-Etsu is working on 12-inch diameter substrates. Since 2021, the company provides sample evaluation and device development with numerous customers in Japan and globally. These apply for power devices, RF devices and LEDs. Especially for power devices, continuous evaluation is underway for devices in the wide range of 650V to 1800V.

So far, Shin-Etsu Chemical has repeatedly made many improvements to its QST® substrates. One example is lowering defects originating from the bonding process, which has enabled the supply of high-quality QST® substrates. In addition, for the heavily requested thicker GaN films, the company offers template substrates with optimized buffer layers. Specifically, these allowed its customers to realize stable epitaxial growth of more than 10μm thickness. Furthermore, various successful results have been reported. Among them include the thick-film GaN growth exceeding 20μm using QST® substrates and 1800V breakdown voltage*2 in power devices.

Crystal Film Bonding Technology

Moreover, Shin-Etsu Chemical and Oki Electric Industry Co., Ltd. have jointly succeeded in developing a technology to exfoliate GaN from QST® substrates and bond it to substrates made of different materials using Crystal Film Bonding (CFB)*3 technology. Until now, most GaN power devices have been lateral devices. However, CFB technology takes advantage of the characteristics of QST® substrates to realize vertical power devices, which control large currents by exfoliating a thick layer of high-quality GaN from an insulating QST® substrate.

To manufacturers of GaN devices, Shin-Etsu Chemical will provide QST® substrates or GaN grown QST® substrates. Meanwhile, Oki Electric Industry will provide its CFB technology through partnering or licensing. In this way, the two companies hope to contribute to the advancement of vertical power devices.

Based on these development results, and also based on business situation inquiries from customers, Shin-Etsu Chemical will continue to increase production to meet customer demand. It will contribute to a sustainable society that can use energy efficiently by further promoting the social implementation of GaN devices.

Shin-Etsu Chemical will make a presentation on the progress in the development of this product at SEMICON Taiwan, which will be held in Taiwan from September 6 to 8, 2023.

*1: A QST® substrate is a composite material substrate developed by Qromis, Inc. (Head Office: Santa Clara, California; CEO Cem Basceri) exclusively for GaN growth and was licensed to Shin-Etsu Chemical in 2019. QST® is a registered trademark held by Qromis, Inc. in the United States (registration number 5277631).

*2: Please refer to the following imec release (April 2021).

*3: CFB technology is a technology to exfoliate GaN epitaxial layers from substrates and is a registered trademark of Oki Electric Industry.