Japanese researchers develop ultra-high-temperature transistor for Venus exploration

Researchers in Japan have engineered a novel transistor designed to function reliably at temperatures exceeding 1,100 degrees Fahrenheit (600 degrees Celsius), marking a significant advancement for electronics intended for extreme environments. The device could potentially power surface probes for Venus, where atmospheric conditions routinely reach 860 degrees Fahrenheit (460 degrees Celsius).

Most contemporary electronics rely on transistors to regulate electrical current. However, the newly developed component is a junction field-effect transistor (JFET), which utilizes an electrical field to modify the conductivity of its channel. While JFETs are generally more challenging to miniaturize than the metal-oxide-semiconductor field-effect transistors (MOSFETs) prevalent in consumer technology, they offer reduced noise levels because their operation does not depend on an oxide layer that can generate interference. Details of the findings were published on August 17 in the journal APL Electronic Devices.

Since the early 2000s, silicon carbide (SiC) JFETs have been viewed as a promising solution for low-power integrated circuits targeting Venus missions. Previous landers equipped with conventional silicon-based electronics were limited to surviving only a few hours on the planet’s surface. The Soviet Union’s Venera 13 holds the longevity record, operating for 2 hours and 7 minutes.

The study’s authors noted that SiC-based integrated circuits are particularly suited for high-heat applications such as aerospace engine control, geothermal drilling, and deep-space exploration, where standard silicon chips fail. Despite this potential, recently developed SiC-JFETs have struggled with two primary issues: poor controllability and high leakage currents.

Controllability issues often stem from dopant atoms penetrating deeper than anticipated into the regular crystal structure of the SiC substrate. While negligible under normal conditions, this penetration at high temperatures causes significant variations in the voltage required to open the channel, disrupting reliable operation. In conventional designs, this can shift voltage thresholds by more than 2 volts. Additionally, at temperatures above 660 degrees Fahrenheit (350 degrees Celsius), the SiC substrate becomes less resistive, allowing current to bypass the switch when it is off, leading to incorrect signals and increased power consumption.

Even top-performing existing JFETs are generally restricted to long-term operation at 930 degrees Fahrenheit (500 degrees Celsius). The team from Kyoto University hypothesized that these persistent challenges arose because researchers were applying design principles from the silicon era to a fundamentally different material.

To address these limitations, the researchers designed a bottom-gate structure, positioning the gate beneath the SiC conducting channel. By heavily doping the gate region intentionally, any unintended dopant penetration into the channel does not alter the overall doping profile. This design minimizes the impact on threshold voltage, even under extreme heat.

The team also utilized dopants to form two semiconductor “wells” around the JFET within the SiC material. These wells create boundaries that act as barriers to current flow, preventing electricity from bypassing the channel when the transistor is deactivated, even if the substrate becomes more conductive at high temperatures.

In testing, the researchers measured the transistor’s ability to switch current on and off against theoretical threshold voltage predictions across a temperature range from room temperature to 1,110 degrees Fahrenheit. The devices demonstrated stable, normal operation above 873 Kelvin (1,110°F). Notably, at approximately 750 degrees Fahrenheit (400 degrees Celsius), the threshold-voltage error was reduced to less than 0.1 volts.

Beyond Venus exploration, the transistor could benefit jet engine technology. Currently, components near gas turbines require thermal shielding, lengthy wiring, and energy-intensive cooling systems, which constrain engine design. Before the device can be deployed in space or aviation applications, the team must integrate it into more complex circuits, scale production to the wafer level, and ensure the entire circuit package can withstand extreme temperatures and pressures.

Such goals may not be unrealistic. NASA has previously demonstrated that SiC-JFET integrated circuits could endure 860 degrees Fahrenheit (460 degrees Celsius) and 9.3 megapascals of pressure for 60 days, as well as 930 degrees Fahrenheit (500 degrees Celsius) in air for over a year. Furthermore, in 2024, scientists at Japan’s National Institute for Materials Science developed a diamond-based MOSFET capable of operating above 570 degrees Fahrenheit (300 degrees Celsius).