Transistors and NASA's Radiation Challenge

Transistors and NASA's Radiation Challenge
by Simon Mansfield
Sydney, Australia (SPX) Sep 25, 2024

The unique properties of Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) highlight a complex issue in space exploration. While these transistors are highly effective for radiation detection, they pose significant risks when used in space missions, as demonstrated by NASA's Europa Clipper mission. Despite their vulnerability in space, MOSFETs play a vital role in monitoring radiation exposure on Earth and in orbit.

MOSFETs have revolutionized many areas, from consumer electronics to scientific advancements. These versatile devices are found in everyday gadgets like radios and MP3 players and are also integral to satellite communications. Their capacity to measure radiation by detecting electrical changes when exposed to ionizing radiation makes them critical in both space missions and medical treatments, such as cancer therapy.

Australia has been at the forefront of developing MOSFET-based radiation detectors. Recent work from ANSTO and its collaborators demonstrated how a system of four MOSFETs can accurately measure radiation doses for patients undergoing Boron Neutron Capture Therapy (BNCT).

Ironically, the same radiation-sensitivity that makes MOSFETs invaluable in radiation measurement almost caused issues for NASA's Europa Clipper. The mission faced potential failure due to radiation damage to the spacecraft's MOSFET-based systems. This dual role in radiation detection and vulnerability underscores the need for innovative solutions in both space exploration and healthcare applications.

The Versatility of MOSFETs
As central components in modern electronics, MOSFETs follow Moore's Law, with transistor numbers increasing exponentially, enabling more powerful and efficient technologies. Companies such as NVIDIA use billions of these transistors in their GPUs to power AI systems, thanks to their ability to manage power efficiently and handle complex tasks.

Research from ANSTO and the University of Wollongong (UOW) recently highlighted the capabilities of a Quad-MOSFET array in accurately measuring radiation during BNCT. Each transistor in the array interacts with different materials to assess various radiation energy levels, ensuring precise monitoring during treatments.

In another instance, the MOSkin dosimeter, developed at UOW's Centre for Medical Radiation Physics, uses MOSFET technology to provide real-time radiation dose measurements during radiotherapy. This innovation enhances the safety and accuracy of cancer treatments.

MOSFETs in Space Exploration
MOSFETs are essential to spacecraft systems due to their low power consumption and efficiency. However, in harsh space environments, such as around Jupiter, these devices are exposed to high levels of ionizing radiation. NASA faced this challenge with the Europa Clipper mission, where MOSFETs were at risk of malfunction due to radiation-induced effects. Single event effects (SEE) can cause a MOSFET's state to switch unexpectedly, while total ionizing dose (TID) effects slowly degrade performance over time.

Radiation Hardness and Testing
Radiation hardness defines a device's resilience against ionizing radiation. MOSFETs not specifically designed for space are vulnerable to radiation damage. To mitigate this, engineers use thicker oxide layers or employ radiation shielding, though these measures may still be inadequate in extreme environments like Jupiter's radiation belts.

At ANSTO's Centre for Accelerator Science and the Australian Synchrotron, aerospace companies test their instruments for radiation hardness to evaluate their performance in space. NASA engineers applied a process called annealing to repair radiation damage in MOSFETs on the Europa Clipper spacecraft, a method also used to restore MOSFETs after medical treatments, allowing them to be reused.

The Impact of Mission-Based Research
The story of MOSFETs is an example of how mission-driven research can lead to unexpected innovations. While initially designed for specific tasks, the technology developed often has applications far beyond its original scope. For instance, memory foam, initially created to improve aircraft cushion safety, is now used in everyday products like running shoes.

Conversely, everyday inventions can solve critical problems in space exploration, as demonstrated by Velcro, which became indispensable for securing items during space missions after being inspired by the simple design of burrs sticking to fabric.

With modifications in place, NASA's Europa Clipper spacecraft is set to launch on October 10th.