Transistor That Operates At 600°C

Researchers

Overview

Kyoto, Japan — For more than two decades, silicon carbide — SiC — has been promoted as the key to developing extreme-environment electronics. Yet despite its promise, the field has remained stuck at the stage of basic research, so far failing to result in the development of practical devices. Now, a team of researchers at Kyoto University has set about to change that.

“We believe the lack of development is because the research community has been trying to apply silicon-era thinking to a fundamentally different material,” says first author Mitsuaki Kaneko.

The team focused on junction field-effect transistors, also known as JFETs. Previous research has suggested that complementary JFETs, based on SiC JFETs, can be applied to low-power integrated circuits for operation in extreme environments. However, the JFETs that the researchers created previously — which had conventional top-gate structures fabricated in semi-insulating SiC substrates — suffered from low controllability and large leakage currents at high temperatures. This motivated the team to set their sights on solving these two issues, which they knew would be essential for practical use.

“Our goal is to open a new path forward with complementary JFETs designed to harness the intrinsic properties of SiC itself,” says Kaneko.

Rather than developing everything from scratch, the team deliberately employed industry-standard manufacturing methods to build their new JFET structure, adopting a bottom-gate design to improve the threshold voltage controllability. They also employed well-based isolation instead of a semi-insulating substrate to suppress the high-temperature leakage current.

The result was a new SiC transistor structure that succeeded on the very first attempt. Upon completion of the new design, the team was able to demonstrate that their device can operate successfully at 600°C. The adoption of the bottom-gate structure significantly improved the transistor’s threshold voltage controllability and drastically reduced the leakage current, which is now very close to the theoretical limit predicted from the material properties of SiC.

This study proves that SiC is already a mature power device technology in itself, and demonstrates the immense potential of the newly developed bottom-gate structure for implementing reliable, extreme-temperature SiC-based integrated circuits.

However, many challenges still lie ahead on the path to practical implementation. One by one, the team intends to address these by creating more complex circuits, scaling up to wafer-level production, and ensuring the entire package remains robust in extreme environments.