The mainstream development mode of modern integrated circuits (ICs) is the well-known Moore’s law. In addition to the general purpose ICs, many special types of ICs are also required for more specific applications, e.g. for those used in space and nuclear energy industries which raised demand for radiation-hardened transistors.
When a transistor is irradiated, failure can be caused by damage to the semiconducting channel, gate oxide, and surrounding insulators, such as an isolation or substrate oxide. Consequently, various radiation-hardening methods have been developed to protect transistors from damage and to prevent them from failure due to radiation damage.
In our recent work published in Nature electronics, we design a radiation-hardened FET by redesigning conventional FET with new channel, new gate and new substrate. We use carbon nanotube (CNT) as the channel, ion gel as the gate, and polyimide (PI) as the substrate. The new FET is shown to work well even after being subjected to 4 Mrad (Si) irradiation at a dose rate of 560 rad s-1.
Fig. 1 | Radiation-immune FET. a, Schematic diagram showing a radiation-immune CNT FET with printed ion gel on a polyimide substrate. b, SEM image showing solution-derived CNT film printed on a polyimide substrate. Inset: Optical image of a CNT FET using a finger structure and printed ion gel as the dielectric layer. c, Transfer characteristics of the radiation-hardened ion gel CNT FET before and after being subjected to irradiation.
Besides, we check the low dose rate effect of ion gel CNT ICs. In low dose rate irradiation experiments, the capture time of radiation-induced interface trap charge is prolonged, and then the parametric degradation at low rates can be more than 5-times greater than that at higher rates. Here, under a low dose rate irradiation environment (at a dose rate of 66.7 rad s-1), the printed ion gel gate CNT CMOS-like inverters can work well after TID irradiation of up to 15 Mrad (Si).
Fig. 2 | Radiation damage repairing of ion gel CNT FETs and CMOS-like inverters via annealing at moderate temperature. a, Schematic diagrams illustrating heating-induced radiation repairing processes of ion gel. b, Heating-induced VTC property recovery of CMOS-like inverters. c, Performance comparison of radiation-hardened ion gel CNT FETs and inverters achieved in this work and previous works.
Finally, we demonstrate rapid recovery of the new FET via annealing. By nature, ion gel is quasi-liquid, radiation damage on ion gel gate is thus reversible and repairable. Since the positive and negative ions flow easily, an annealing process can not only cause the radiation-induced trapped charges to drift away but also make the EDLs at the channel surface restore equilibrium. The combination of excellent radiation tolerance and reparability of the ion gel gate can promote radiation-damage-immune IC applications of CNT FETs, which will greatly extend the application field of future ICs.
Maguang Zhu†, Hongshan Xiao†, Gangping Yan, Pengkun Sun, Jianhua Jiang, Zheng Cui, Jianwen Zhao*, Zhiyong Zhang*& Lian-Mao Peng*. "Radiation-hardened and repairable integrated circuits based on carbon nanotube transistors with ion gel gates. " Nat Electron (2020). https://doi.org/10.1038/s41928-020-0465-1