Random networks of single-walled carbon nanotubes (SWCNTs) offer new-form-factor electronics such as transparent, flexible, and intrinsically stretchable devices. However, the long-standing trade-off between carrier mobility and on/off ratio due to the coexistence of metallic and semiconducting nanotubes has limited the performance of SWCNT-random-network-based thin-film transistors (SWCNT TFTs), hindering their practical circuit-level applications. Methods for high-purity separation between metallic and semiconducting nanotubes have been proposed, but they require high cost and energy and are vulnerable to contamination and nanotube shortening, leading to performance degradation. Alternatively, additional structures have been proposed to reduce the off-state current, but they still compromise carrier mobility and suffer from inevitable expansion in device dimensions. Here, we propose a density-modulated SWCNT network using an inkjet-printing method as a facile approach that can achieve superior carrier mobility and a high on/off ratio simultaneously. By exploiting picoliter-scale drops on demand, we form a low-density channel network near the source and drain junctions and a high-density network at the middle of the channel. The modulated density profile forms a large band gap near the source and drain junctions that efficiently blocks electron injection under the reverse bias and a narrow band gap at the high-density area that facilitates the hole transport under the on-state bias. As a result, the density-modulated SWCNT TFTs show both high carrier mobility (27.02 cm2 V–1 s–1) and a high on/off ratio (>106). We also demonstrate all-inkjet-printed flexible inverter circuits whose gain is doubled by the density-modulated SWCNT TFTs, highlighting the feasibility of our approach for realizing high-performance flexible and conformable electronics.

Single-walled carbon nanotube (SWCNT) random networks have become strong candidates for next-generation electronics due to their exceptional mechanical, electrical, and optical properties. However, metallic nanotubes in networks generally incur a trade-off between the charge carrier mobility and on/off ratio, limiting the performance of SWCNT-based devices. Therefore, various methods to increase the purity of semiconducting nanotubes in entire random networks have been reported, but this direction has faced other issues, such as nanotube shortening, higher cost, and higher energy. Here, we introduce SWCNT random network-based thin-film transistors (SWCNT TFTs) with a varying purity profile of semiconducting SWCNTs across the channel, exploiting the superior mobility of metallic SWCNTs by partially tuning the semiconducting SWCNT purity and developing a novel perspective on metallic nanotubes in semiconductor channels. Based on the high-precision drop-on-demand capability of inkjet printing and various concentrations of semiconducting SWCNT ink, we form selectively patterned channel regions with different semiconducting SWCNT purities. The metallic nanotube-dominant region drastically increases the carrier density with a minimized Schottky barrier, while high-purity semiconducting regions at the channel boundaries effectively block off-state leakage through carrier depletion. As a result, the SWCNT TFTs with selectively patterned metallic nanotube regions show superior carrier mobility (75.50 cm 2 V −1 s −1 ) and channel width normalized on-current (34.33 nA μm −1 ) without compromising the on/off ratio (1.62 × 10 7 ). To show the feasibility of our device in high-performance electronics, we demonstrate all-inkjet-printed flexible display driving circuits with two transistors that enable low-power, high-performance operation in display applications.