New Methodology Paves Way for Predicting the Lifetime of Electronic Devices Exposed to Radiation

A new methodology developed by the IAEA and its partners will enable measurement of radiation damage on electronic devices inside radiation detectors and other instruments relying on radioactive materials, such as a CT scanner or machine used for radiotherapy. (Photo: D. Calma/IAEA)

Solar technology and radiation therapy could benefit from a new methodology developed to better understand the effects of ionising radiation on electronic devices. The technique could help predict the lifetime of these devices with the aim of improving their performance. 

The methodology is the result of a four-year Coordinated Research Project (CRP) supported by the IAEA, which involved 14 research groups from 13 countries.

The problem

Despite years of research, there are still significant gaps in the ability to predict how radiation affects and damages electronic materials and the electrical properties and performance of semi-conductors.

“Because of the huge variety of devices with very different properties, it is hard to implement an effective general model to quantify the effects of radiation on electronic materials,” said Ettore Vittone, a researcher from the University of Torino. “The results of the CRP will help us better understand the effects of energetic radiation in electronic materials and improve their quality and durability for long-term use.”

The new methodology takes into account both the immediate and long-term effects of damage on electronic materials and devices working in harsh radiation environments, said Aliz Simon, a nuclear physicist at the IAEA and coordinator of the CRP. “The performance of a detector used to measure radiation from a radiotherapy device, for example, will deteriorate over time. Knowing when its performance starts to decline will help conduct safe irradiation for cancer therapy,” she said.

The new methodology is based on a model that groups existing techniques for investigating radiation effects on semi-conductor devices.

Experimenting on solar cells with ion accelerators

One area where the methodology could come in handy is working on solar cells in satellites, which are exposed to – and can be damaged by – cosmic radiation.

To know how much radiation a solar cell installed to power a satellite could endure, researchers would have to reproduce cosmic ray exposure in experiments on earth. This, however, would be a gargantuan and time consuming task, so they opted for a more practical approach: evaluating the key parameters of the device materials. To do so, they used ion accelerators—machines that convert atoms into ions and accelerate them into energies of the order of MeV (millions of electron volt), similar to the energies emitted by radioactive nuclei. The device materials are then irradiated with ions from these accelerators. The electric signal induced is analysed and the resulting damage calculated.

The highly energetic ions from accelerators play a dual role in the experiments: they induce damage by penetrating into the material and deteriorating the electronic properties of the device. In parallel to this effect, the ions are also used as probes to measure structural changes because when they interact with the material, an electrical signal is induced and analysed.

Calculating the damage

The electrical signal induced is due to the motion of charge carriers generated by the ions. If the material does not have defects, the charge carriers can cross the whole device and the signal is at maximum. However, if there are defects, they would act as traps along the way and reduce the number of charge carriers crossing the device. As the number of charge carriers reduces, the electric output signal decreases and the efficiency of the device degrades.

“Since we know where and how many traps the damaging ions generated, we can extract parameters that characterise the radiation hardness of the material and use the parameters to predict how the device will behave in a traditional environment without the need to conduct additional experiments,” Vittone said.

The CRP aimed to develop an experimental and theoretical methodology accessible to any laboratory equipped with ion accelerators. However, at the current, initial stage, the methodology has been established only for low-level damage — when the radiation slightly perturbs the order for the crystalline lattice. The methodology is published in the Journal of Nuclear Instruments & Methods in Physics Research (NIM B) and can be found here.

Additional relevant studies by the project members are published in a special section of NIM B and on Science Direct.