Radiation Effects Of Carbon Nanotube Materials And Their Field-effect Devices

With the development of the nuclear industry and space exploration,the demand for radiation-resistant devices is increasing.Single-walled carbon nanotubes are a new type of semiconductor material with strong C-C bonds,nanoscale cross-sections,and low atomic numbers.Carbon nanotube field-effect transistors(CNT FETs)and integrated circuits based on them have been predicted and proven to be one of the most promising radiation-hardened electronic devices,with important application prospects in space and nuclear environments.At present,the irradiation research progress of CNT FETs mainly focuses on total ionizing dose effects,with less research on displacement damage.In this theis,fast neutrons and low-energy heavy ions with different doses were used to study the displacement damage of CNT FETs through theoretical and experimental methods,and the physical mechanisms of fast neutron and low-energy heavy ion irradiation effects were obtained by analyzing the changes in device electrical performance.Firstly,this theis carried out research on the preparation technology of CNT FETs.It was found that the high-quality functionalized monolayer and carbon nanotube film density control in the preparation process are key factors affecting device performance.By optimizing the film deposition process,high-consistency devices were prepared,and the key parameters of the devices were characterized and tested,laying the foundation for subsequent irradiation experiments.Since there is currently a lack of understanding of the fast neutron irradiation effect mechanism on CNT FETs,this theis used nuclear reactors to carry out fast neutron irradiation research.By analyzing the changes in the key electrical parameters of P-type and N-type devices before and after irradiation at different doses,the statistical change law was obtained to reveal the physical mechanism of fast neutron irradiation effects.This research found that fast neutron irradiation introduces negatively charged acceptor-like interface states;the ionization process of secondary particles generated by irradiation produces oxide trap charges in the gate oxide layer;and the increased charge traps and oxide trap charges cause trap-assisted tunneling effects(TAT).This work shows that due to the strong penetration ability of fast neutrons,the performance changes of devices do not directly originate from lattice damage of carbon nanotubes themselves,but are related to the interaction between carbon nanotubes and the environment,as well as the radiation sensitivity of device structures such as gate oxide layers and passivation layers.Previous ion irradiation studies mainly focused on the high-energy heavy ion irradiation effects on CNT FETs,lacking evaluation of low-energy heavy ion irradiation effects.Therefore,this theis used a 5 ke V gallium focused ion beam(FIB)to carry out low-energy heavy ion irradiation experiments on CNT FETs.Combined with TRIM simulation,the changes in device performance before and after irradiation at different doses were analyzed to evaluate the irradiation response of CNT FETs under low-energy heavy ions and reveal the change laws between displacement damage and device electrical parameters.This study found that compared with the good stability of devices under high-energy heavy ions in previous studies,CNT FETs are quite intolerant to low-energy heavy ion irradiation due to the larger Coulomb scattering cross-section.The current carrying capacity of the device gradually decreases with the amorphization process of the channel carbon nanotube network,and due to the percolation characteristics of the carbon nanotube network,the current can be redistributed between damaged and undamaged carbon nanotubes;a large amount of displacement damage in the gate oxide layer causes trap-assisted tunneling effects,significantly reducing the gate control ability of the device;and the accumulated static charge effect of low-energy gallium ion implantation causes electrostatic doping of carbon nanotubes.This research enriches the comprehensive understanding of displacement damage in CNT FETs,promotes a comprehensive evaluation of radiation resistance in CNT FETs,and lays an important technical foundation for improving CNT FETs radiation resistance and its application in special radiation-hardened devices and integrated circuits.