Inkjet-Printing-Based Density Profile Engineering of Single-Walled Carbon Nanotube Networks for Conformable High-On/Off-Performance Thin-Film Transistors

Abstract

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.

Selective Purity Modulation of Semiconducting Single-Walled Carbon Nanotube Networks for High-Performance Thin-Film Transistors

“…These values correspond to a more than 11 times higher I on , a 10 times higher mobility, and a 70 times higher on/off ratio compared to the 99-RTFT. Figure d compares the mobilities and on/off ratios of SWCNT TFTs in the literature. ,,,,− Previously reported TFTs based on SWCNT random networks exhibit a strong negative correlation between the mobility and on/off ratio. In contrast, our SPM-TFTs are located completely away from the trade-off trend area, simultaneously exhibiting the highest mobility and on/off ratio.…”

“…Furthermore, homogeneous, isotropic random networks of even highly purified semiconducting SWCNTs (S-CNTs) still cannot enhance the performance due to the limited carrier density of S-CNTs themselves and junction-induced mobility degradation. To alleviate these issues, anisotropic or additional geometries have been employed in channel regions, such as network density profiles, nanotube alignment, and double-gate structures . However, they are still uncompetitive compared to industrial transistors in terms of both performance and fabrication complexity, limiting a window of performance engineering around the previous trade-off curve.…”

Stretchable conductors for stretchable field-effect transistors and functional circuits

“…To get an FET with high carrier mobility and on/off ratio, using an inkjet printing technique, Oh et al produced a channel network with high density in the centre of the channel and a channel network with low density around the source/drain junctions. 457 Therefore, the densitymodulated SWCNT TFTs exhibited high carrier mobility and on/off ratio of up to 27.02 cm 2 V À1 s À1 and 10 6 , respectively.…”

Enhanced current path by circularly and periodically-aligned semiconducting single-walled carbon nanotubes for logic circuit device

“…Semiconducting single-walled carbon nanotubes (SWCNTs) have been considered one of the promising materials for future deformable highperformance thin-film transistors (TFTs) because of its excellent electrical, mechanical, and optical properties [1][2][3][4][5][6]. One of the most effective methods to fabricate SWCNT film is solution process, such as inkjet-printing and soaking using well-dispersed SWCNT ink due to the advantages of low-cost fabrication, large-area, and low temperature processing [7][8][9][10][11][12][13][14][15][16]. Although the soaking method has the advantage in density control of SWCNT network, additional processes such as surface treatment and patterning are needed for removing unnecessary SWCNT [17,18].…”