Flexible printed three dimensional (3D) integrated carbon nanotube complementary metal oxide semiconductor (CMOS) thin film transistors and circuits

The threshold voltage modulation of carbon nanotube thin-film transistors (TFTs) and flexible three-dimensional (3D) integration circuits has become hot research topics for carbon-based electronics. In this paper, a doping-free gate electrode technology is introduced to significantly modulate the threshold voltage of polymer-sorted semiconducting single-walled carbon nanotube (sc-SWCNT) TFTs in combination with the highly effective gate-controlling ability of solid-state electrolyte thin films as the dielectrics. A systematic investigation was conducted on the impact of printed silver, evaporated silver, and evaporated aluminum (Al) gate electrodes on the threshold voltage of flexible printed bottom-gate and top-gate SWCNT TFTs. The results indicate that the SWCNT TFTs with Al gate electrodes exhibit enhancement-mode characteristics with excellent electrical properties, such as the negative threshold voltages (−0.6 V), high I_on/I_off (up to 10⁶), low subthreshold swing (61.4 mV · dec⁻¹), and small hysteresis. It is attributed to either the formation of lower work function thin films (Al₂O₃) at the electrode/dielectric layer interfaces through the natural oxidation of the Al bottom-gate electrodes or the dipole reaction of the Al top-gate electrodes from X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) data. In addition, 3D complementary metal-oxide-semiconductor (CMOS) inverters with common gate electrodes were constructed using the resulting enhancement-mode P-type SWCNT TFTs and matched N-type SWCNT TFTs, which shows high voltage gain (34), rail-to-rail output and high noise margins (80.04%, V_DD = −1 V) as well good mechanical flexibility at low operation voltages. It demonstrates that SWCNT TFTs have great advantages for building large-scale 3D flexible integrated circuits.