Reduction of Low-Frequency Noise in Flexible Carbon Nanotube Thin-Film Transistors with Inorganic Polymer Insulator

Carbon nanotube (CNT) thin-film transistors (TFTs) possess high mobility and mechanical flexibility, making them promising for flexible electronics applications. While there have been reports demonstrating analog circuits such as analog front-ends using CNT TFTs [1], reducing noise in the low-frequency region (&lt;1 kHz) is critical for the measurement of physiological signals from human body such as ECG and EEG. In this study, we report the fabrication of flexible CNT TFTs using inorganic polymer as the gate insulator, which is expected to have low trap density, and the evaluation results of low-frequency noise.<br/>We fabricated bottom-gate CNT TFTs on polyethylene naphthalate (PEN) substrates using a self-aligned process. The inorganic polymer gate insulator was formed from perhydropolysilazane [2] as a precursor, by spin-coating and low-temperature annealing at 90 degC. The thickness was 400 nm. After applying poly-L-lysine to the surface of the inorganic polymer, we immersed it in a semiconductor CNT dispersion solution (0.5% sodium cholate aqueous solution) to form a high-density and uniform CNT thin film. The channel length and width of the TFT were both 100 µm.<br/>The CNT TFTs with the inorganic polymer insulator exhibited a high on-current (0.2 mA/mm) and a steep subthreshold swing (130 mV/dec). The noise power density of low-frequency noise was approximately 50 % reduced compared to the devices with the conventional low-temperature ALD Al₂O₃ insulator. This suggests that the inorganic polymer insulator has a lower trap density, which is a noise source, compared to the Al₂O₃.<br/><br/>[1] T. Kashima et al., Research Square (2020) DOI: 10.21203/rs.3.rs-68702/v1.<br/>[2] Y. H. Kang et al., ACS Appl. Mater. Interfaces 12, 15396 (2020).