Led by Mitsuaki Kaneko, Shunya Shibata, and Tsunenobu Kimoto, the Kyoto University team built a silicon carbide (SiC) junction field-effect transistor (JFET) using a bottom-gate layout with a double-well isolation structure. This design counters the channeling effect — where dopants scatter deeper than intended during ion implantation — that previously caused threshold voltages to shift by more than 2 V from design targets in top-gate JFETs. By placing the gate electrode beneath the channel, the researchers compensated for this channeling tail, reducing the threshold voltage discrepancy to less than 0.1 V at 400°C.
The double-well structure isolates each transistor using a pn junction, avoiding reliance on the semi-insulating SiC substrate, which loses its insulating properties as temperatures rise and allows leakage current to spread through the wafer. The team reports that the remaining leakage is close to the theoretical minimum set by SiC's material properties, leaving little room for further device-level improvement.
This approach stands out because ion implantation is already a standard step in commercial chip fabrication, making the production method compatible with existing manufacturing lines. In contrast, NASA Glenn Research Center has demonstrated SiC JFET integrated circuits with over 175 transistors running for more than a year at 500°C in air and 60 days on a simulated Venus surface at 460°C and 9.3 MPa, but those chips rely on epitaxial processes not widely adopted in industry.
SiC is already used in power electronics, but high-temperature logic remains a niche field. The Kyoto transistor is normally-on, meaning it conducts even without gate voltage, which draws standby power. Efficient complementary logic circuits require normally-off devices. The team previously demonstrated complementary SiC JFET logic gates at 350°C and plans to design normally-off devices in the new structure to enable low-power circuits. Long-term reliability and heat-tolerant packaging remain significant challenges before any commercial application in gas turbines or planetary probes becomes feasible.
Other researchers are exploring alternative wide-bandgap materials, such as beta-gallium oxide, which has shown stable operation from 500°C down to near absolute zero. The Kyoto work, however, offers a path using mainstream fabrication methods, potentially reducing barriers for industries seeking high-temperature sensors and electronics.