Radiation effects in printed flexible single-walled carbon nanotube thin-film transistors

In this study, the gamma ray radiation effect on the characteristics of inkjet-printed semiconducting single-walled carbon nanotubes (sSWCNTs) thin-film transistors (TFTs) is investigated. The devices with top gate dielectrics consisted of BaTiO3 and poly(methyl methacrylate) (PMMA) were characterized before and after 150 krad 60Co gamma radiation in air. It reveals that the radiation results in a positive threshold voltage shift from -0.5 to 3.6 V (with a drain voltage biased at -1 V). The hysteresis decreases slightly from 1.2 to 0.5 V, indicating that the BaTiO3/PMMA dielectric layer effectively encapsulates the sSWCNTs TFTs from absorbing molecules in the environment. Furthermore, the charge pumping current ICP is measured with a gate voltage pulsed at 100 kHz. The maximum ICP increases from 90 to 140nA, which translates to an increase in the interface trap density from 4.5×1011 to 1.1×1012 cm-2eV-1. The charge pumping measurements at the frequency of 10∼250 kHz show that the increase of ICP induced by radiation is obvious when f>30 kHz but is little when f<30 kHz, which indicates that the radiation induced charge traps locate near sSWCNTs. The BaTiO3/PMMA gate dielectric remains to be a good insulator with a leakage current of less than 60 pA after radiation. Such printed flexible TFTs with the polymer gate dielectric possess similar radiation tolerant compared to convention devices on rigid substrates.