RADIATION-HARDENED ELECTRONICS

Repairable integrated circuits for space

Field-effect transistors that use carbon nanotubes as the channel material and an ion gel as the gate exhibit a high tolerance to radiation and can be recovered following radiation damage using a simple annealing process.

Whether travelling to the Moon, Mars or beyond, the exploration of space requires complex electronic circuits that are resistant to high-energy solar and cosmic radiation. Radiation damage or glitching of critical electronics can cause mission failure, and an important factor in determining the lifetime of space electronics is the amount of radiation that can be withstood before destructive errors occur. Back here on Earth, radiation-immune electronics are also of value in the high-radiation environments of nuclear reactors, particle accelerators, and radioactive exclusion zones. Writing in Nature Electronics, Lian-Mao Peng, Zhiyong Zhang, Jianwen Zhao and colleagues at Peking University, Suzhou Institute of Nanotech and Nano-bionics, Shanghai Tech University and the Institute of Microelectronics in Beijing now report integrated circuits that can withstand much higher doses of total ionizing irradiation than silicon electronics and, due to a thermal annealing process that repairs devices, could potentially withstand an unlimited dose over their lifetime1.

Radiation damage to field-effect transistors (FETs) can be divided into three categories: total ionizing dose, displacement damage, and single-event effects. Total ionizing dose is mainly related to a cumulative ionization effect in the gate oxide region. For example, radiation tolerance of silicon-based logic transistors has been improved (up to around 5 Mrad (Si)) by thinning the gate oxide during scaling2, as this reduces the charge build-up in the oxide, and silicon-based power and hybrid integrated circuits suffer more from total ionizing dose effects than digital integrated circuits because their gate oxides are thicker. The oxide layer used for inter-device isolation is also vulnerable to total ionizing dose. High-k dielectrics can be used to improve the anti-radiation ability3, while a vacuum dielectric layer has been used in radiation-immune FETs, but with low performance4,5.

Peng, Zhang, Zhao and colleagues increased the total ionizing dose tolerance of their FETs by hardening all of the vulnerable parts. In particular, they use carbon nanotubes as the channel material, an ion gel as the gate, and polyimide as the substrate (Fig. 1). Carbon nanotubes are a compelling candidate to replace silicon in radiation-hardened devices6,7 since, in addition to excellent electronic properties, their strong carbon–carbon bonds and small cross-section reduce displacement damage from irradiation. The ion gel — a type of electrolyte consisting of ionic liquids — forms an electrical double layer serving as the effective dielectric between the electrolyte and the carbon nanotubes. The electron double layer is nanometre-thick, suppressing total ionizing dose effects, while providing a high gate efficiency. Finally, the thinness of the polyimide substrate significantly decreases the harmful effects of back-scattered and reflected high-energy particles. The resulting FETs and integrated circuits can withstand a radiation dose of up to 15 Mrad (Si) at a dose rate of 66.7 rad s–1, which is a record for top-gated transistors.

Fig. 1: Radiation-immune carbon nanotube field-effect transistors.
figure1

The transistors use semiconducting carbon nanotubes as the channel material, a printed ion gel as the gate and polyimide as the substrate. After irradiation, the transistors can be repaired with low-temperature annealing of the ion gel, or in extreme cases, dissolving and reprinting of the ion gel. The process restores the devices to their original performance capabilities, allowing them to undergo multiple radiation cycles.

Furthermore, irradiated FETs and integrated circuits can be fully recovered due to the excellent reparability of the ion gel (Fig. 1). The damaged devices are recovered by annealing at 100 °C for 10 minutes, leading to threshold voltages and transition voltages shifting back to their previous values; similar recovery of silicon-based integrated circuits would require thermal annealing at 400 °C for 1 hour. In the most extreme cases of radiation damage, the irradiated ion gel can be dissolved and a new gate reprinted, allowing multiple cycles of irradiation and recovery.

The work of Peng, Zhang, Zhao and colleagues is an important step in the development of electronics that are immune to radiation damage for application in extreme radiation environments. However, the technology is still at a relatively low technology readiness level — probably around level 3 on NASA’s Technology Readiness Level assessment of technological maturity8. To make integrated circuits based on electrolyte-gated carbon nanotube FETs fully deployable, the radiation tolerance to displacement damage and single-event effects needs to first be calibrated. The FETs also then need to be scaled down to submicrometre or even tens-of-nanometres sizes to achieve the level of performance and density practical applications will require. The researchers do though suggest that a thinner solid-state electrolyte could potentially be used as a substitute for the ion gel gate in order to scale down the devices, while maintaining a strong radiation tolerance. Finally, the success of such radiation-immune electronics will depend on the maturity of electrolyte-gated electronics, and while the technology is developing rapidly9,10, it still has a long way to travel.

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Correspondence to Lin Xiao.

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Wang, Y., Xiao, L. Repairable integrated circuits for space. Nat Electron 3, 586–587 (2020). https://doi.org/10.1038/s41928-020-00491-8

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