Integrating biodegradable cellulose nanopaper into oxide thin-film transistors (TFTs) for next generation flexible and green flat panel displays has attracted great interest because it offers a viable solution to address the rapid increase of electronic waste that poses a growing ecological problem. However, a compromise between device performance and thermal annealing remains an obstacle for achieving high-performance nanopaper TFTs. In this study, a high-performance bottom-gate IGZO/Al2O3 TFT with a dual-layer channel structure was initially fabricated on a highly transparent, clear, and ultrasmooth nanopaper substrate via conventional physical vapor deposition approaches, without further thermal annealing processing. Purified nanofibrillated cellulose with a width of approximately 3.7 nm was used to prepare nanopaper with excellent optical properties (92% transparency, 0.85% transmission haze) and superior surface roughness (Rq is 1.8 nm over a 5 × 5 μm2 scanning area). More significantly, a bilayer channel structure (IGZO/Al2O3) was adopted to fabricate high performance TFT on this nanopaper substrate without thermal annealing and the device exhibits a saturation mobility of 15.8 cm2/(Vs), an Ion/Ioff ratio of 4.4 × 105, a threshold voltage (Vth) of −0.42 V, and a subthreshold swing (SS) of 0.66 V/dec. The room-temperature fabrication of high-performance IGZO/Al2O3 TFTs on such nanopaper substrate without thermal annealing treatment brings industry a step closer to realizing inexpensive, flexible, lightweight, and green paper displays.Keywords: cellulose nanofiber nanopaper; electrical properties; IGZO semiconductor; thin-film transistor; ultrasmooth;

The control of channel length is of great significance in the fabrication of thin film transistors (TFTs) with high-speed operation. However, achieving short channel on untreated glass by traditional piezoelectric inkjet printing is problematic due to the impacting and rebounding behaviors of droplet impinging on solid surface. Here a novel method was proposed to obtain short channel length on untreated glass by taking advantage of the difference in the retraction velocities on both sides of an ink droplet. In addition, droplets contact mechanism was first introduced in our work to explain the formation of short channel in the printing process. Through printing droplets array with optimized drop space and adjusting appropriate printing parameters, a 2.4 μm of channel length for TFT, to the best of our knowledge, which is the shortest channel on substrate without pre-patterning, was achieved using piezoelectric inkjet printing. This study sheds light on the fabrication of short channel TFT for large size and high-resolution displays using inkjet printing technology.

In this work, an innovative all-sputtered bottom-gate thin film transistor (TFT) using an amorphous InGaZnO (IGZO)/Al2O3 bi-layer channel was fabricated by fully room temperature processes on a flexible PEN substrate. A bi-layer channel consisting of 10 nm-thick IGZO and 3 nm-thick Al2O3 was clearly observed in high resolution TEM images. The chemical structure of IGZO was dependent on different sputtering modes (pulse-DC/DC/RF), which were investigated by XPS measurements. The ultrathin Al2O3 layer on IGZO showed a significant effect on enhancing the mobility, reducing the off-state current, and improving the gate-bias stability. As a result, the IGZO/Al2O3 bi-layer TFT eventually exhibited a saturation mobility of 18.5 cm2 V−1 s−1, an Ion/Ioff ratio of 107, an on-state voltage of 1.5 V and a subthreshold swing of 0.27 V decade−1, as well as good stability under NBS/PBS and bending strain. The fabrication of this TFT can be suitably transferred to large-size arrays or paper-like substrates, which is in line with the trend of display development.

Aluminum-doped zinc oxide (AZO) has been regarded as a potential and promising material for thin-film transistors (TFTs) owing to its low cost and nontoxicity. Generally, the high conductivity of AZO should be suitably reduced before using in TFTs as a semiconductor. Traditional ways to reduce the conductivity of AZO is by increasing doping content of aluminum (>5 at%). Herein, a novel approach is first reported to convert conductive AZO into a semiconductor by rationally designing a bilayer channel structure that consists of an AZO island film and a thin Al2O3 film, serving as “electron donor” and “electron bridge,” respectively. Consequently, TFTs with island-like AZO/Al2O3 channel material present the saturation mobility of 8.04 cm2 V−1 s−1, on/off current of 1.6 × 107, and subthreshold swing of 0.83 V dec−1. Moreover, the underlying mechanism for the excellent electrical properties of obtained TFTs is that the electron conduction in AZO/Al2O3-TFTs is proved to be dominated by the percolation conduction due to the effective control of carriers concentration. This method proposed in this report sheds light on the conversion of conductive oxide film to semiconductor layer for TFTs.

In this work, an innovative all-sputtered bottom-gate thin film transistor (TFT) using an amorphous InGaZnO (IGZO)/Al2O3 bi-layer channel was fabricated by fully room temperature processes on a flexible PEN substrate. A bi-layer channel consisting of 10 nm-thick IGZO and 3 nm-thick Al2O3 was clearly observed in high resolution TEM images. The chemical structure of IGZO was dependent on different sputtering modes (pulse-DC/DC/RF), which were investigated by XPS measurements. The ultrathin Al2O3 layer on IGZO showed a significant effect on enhancing the mobility, reducing the off-state current, and improving the gate-bias stability. As a result, the IGZO/Al2O3 bi-layer TFT eventually exhibited a saturation mobility of 18.5 cm2 V−1 s−1, an Ion/Ioff ratio of 107, an on-state voltage of 1.5 V and a subthreshold swing of 0.27 V decade−1, as well as good stability under NBS/PBS and bending strain. The fabrication of this TFT can be suitably transferred to large-size arrays or paper-like substrates, which is in line with the trend of display development.