(Invited) Low-Frequency Noise in Flexible Carbon-Nanotube Analog Circuits

Since flexible devices can come into close contact with the human body, they are suitable for wearable sensor applications for long-term and non-invasive monitoring of biological and physiological signals in various fields such as medical/health care and sports, among others. In order to achieve a fully flexible sensor system, various electronic circuits need to be integrated on a flexible film, including the analog frontend (AFE) and radio-frequency (RF) frontend, as well as the sensors. Recently, we have demonstrated low-voltage CNT-based analog/digital mixed-signal circuits with excellent stability and robustness against variability, including the AFE. One remaining issue with CNT-based analog circuits is low-frequency noise, which directly impacts the sensitivity of the sensor system within the frequency range of physiological signals such as ECG and EEG. Here, we study the low-frequency noise of flexible carbon nanotube thin-film transistors and their influence on analog circuits. The low-frequency noise exhibits a typical 1/f spectrum. Inserting an interface layer between the CNT channel layer and gate insulator layer reduces Hooge's parameter of the 1/f noise. The results indicate that maintaining distance from the channel to traps in the gate oxide is important for reducing low-frequency noise.