Facile Route to Inkjet Printed Carbon Nanotube-Based Inverters with High Gain for Biosignal Monitoring

Single-walled carbon nanotubes (SWCNTs) have gained much attention as a promising semiconducting nanomaterial in the field of electronic, optical, and photonic applications. In order to implement such applications in the form of wearable devices, inkjet printing technology has shown great promise for cost-effective, large-area device fabrication. In designing electrical circuits, however, dissimilar n-type semiconductors are often required because SWCNTs typically exhibit p-type behavior. This may result in the addition of complex fabrication steps and more areal footprint to match the performance imbalance between two dissimilar semiconductors. Herein, we report a facile route to the fabrication of inkjet-printed p-type SWCNT transistor-based inverters, in which their transistor modes can be simply tuned from enhancement mode to depletion mode by increasing the number of printed SWCNT layers. The threshold voltage shift was systematically obtained by increasing the printing counts of SWCNTs in the channel area. With this transistor-mode-change strategy, a high gain inverter-based amplifier circuit is realized to monitor real-time biosignals, including the chest movement during breathing and muscular movement by a hand gesture.