X-ray irradiation effects of carbon nanotube field-effect transistors

To further understand the patterns and mechanisms of total ionizing dose (TID) radiation damage in carbon nanotube field-effect transistor (CNTFET), the total dose effects of 10 keV X-ray irradiation on N-type and P-type CNTFETs are investigated in this work. The irradiation dose rate is 200 rad(Si)/s, with a cumulative dose of 100 krad(Si) for N-type devices and 90 krad(Si) for P-type devices. The differences in TID effect between N-type and P-type CNTFETs under the conditions of floating gate bias and on-state bias, the influence of irradiation on the hysteresis characteristics of N-type CNTFETs, and the influence of channel sizes on the TID effects of N-type CNTFETs are also explored. The results indicate that both types of transistors, after being irradiated, exhibit the threshold voltage shift, transconductance degradation, increase in subthreshold swing, and decrease in saturation current. In the irradiation process, N-type devices under floating gate bias suffer more severe damage than those under on-state bias, while P-type devices under on-state bias experience more significant damage than those under floating gate bias. The hysteresis widths of N-type devices decrease after being irradiated, and the TID damage becomes more severe with the increase of channel dimensions. The main reason for the degradation of device parameters is the trap charges generated in the irradiated process. The gate bias applied during irradiation affects the capture of electrons or holes by traps in the gate dielectric, resulting in different radiation damage characteristics for different types of devices. The reduction in the hysteresis width of N-type devices after being irradiated may be attributed to the negatively charged trap charges generated during irradiation, which hinders the capture of electrons by water molecules, OH groups, and traps in the gate dielectric. Moreover, the channel dimensions of the transistors also influence their radiation response: larger channel dimensions result in more trap charges generated in the gate dielectric and at the interface during irradiation, leading to more severe transistor damage.