Solution-processed metal-oxide thin-film transistors: a review of recent developments

Abstract

Driven by the rapid development of novel active-matrix displays, thin-film transistors (TFTs) based on metal-oxide (MO) semiconductors have drawn great attention during recent years. N-type MO TFTs manufactured through vacuum-based processes have the advantages of higher mobility compared to the amorphous silicon TFTs, better uniformity and lower processing temperature compared to the polysilicon TFTs, and visible light transparency which is suitable for transparent electronic devices, etc. However, the fabrication cost is high owing to the expensive and complicated vacuum-based systems. In contrast, solution process has the advantages of low cost, high throughput, and easy chemical composition control. In the first part of this review, a brief introduction of solution-processed MO TFTs is given, and the main issues and challenges encountered in this field are discussed. The recent advances in channel layer engineering to obtain the state-of-the-art solution-processed MO TFTs are reviewed and summarized. Afterward, a detailed discussion of the direct patterning methods is presented, including the direct photopatterning and printing techniques. Next, the effect of gate dielectric materials and their interfaces on the performance of the resulting TFTs are surveyed. The last topic is the various applications of solution-processed MO TFTs, from novel displays to sensing, memory devices, etc. Finally, conclusions are drawn and future expectations for solution-processed MO TFTs and their applications are described.

Printable Semiconductors for Backplane TFTs of Flexible OLED Displays

“…Here, we introduce the possible opportunities and challenges based on each semiconductor material. 1)Metal oxides. Beginning with the exploitation of new materials, along with the optimization of device structures and low‐temperature annealing methods, solution‐processed metal oxide TFT technology has made great progress in a short time, and is considered the most promising material for flexible AMOLED display applications . However, the resultant TFTs generally exhibited inferior electrical performance with relatively large deviation compared to vacuum‐deposited ones, which might originate from the residual impurities and the imperfect lattice framework.…”

Stepped Annealed Inkjet-Printed InGaZnO Thin-Film Transistors

“…For other TFTs with different element molar ratios, the increase of V SD produced a reverse inhibition current and caused the I SD to decrease in the saturation region. Figure 2e exhibits the typical transfer curves I SD -V G at V SD = 30 V; it can be seen that the I on /I off was significantly enhanced along with a gradual decrease of the molar proportion of indium because a smaller percentage of Indium in InGaZnO resulted in a decrease of the off current [38]. Although the increase of the proportion of indium enhances the mobility of the channel layer, the I off of the TFT still retains a relatively high value in the off state, which will affect the stability and the ability to resist noise signal interference of the TFT devices.…”

“…Furthermore, the VT of 12.3 V and the saturation mobility of 0.323 cm 2 •V −1 •s −1 of the TFT with the 30-nm-thick InGaZnO channel layer and that of the TFT with the 120-nm-thick channel layer (~11.2 V and 0.012 cm 2 •V −1 •s −1 ) at VSD = 30 V were derived from Figure 5d. Gallium serves as the suppressor and the stabilizer to suppress the generation of oxygen vacancies because Ga-O bonds are much stronger than In-O and Zn-O bonds in InGaZnO films [38]. However, the increasing film thickness will consequently introduce a large number of defects, such as Next, the printed patterned InGaZnO channel layers needed to be annealed to remove organic impurities.…”

“…The carrier concentration of InGaZnO can be controlled at a low level, which is important for TFTs to operate. Moreover, Ga serves as the suppressor and stabilizer to suppress the generation of oxygen vacancies and decreases the free electron concentration, because Ga-O bonds are much stronger than In-O and Zn-O bonds [38].…”

Inkjet-Printed Top-Gate Thin-Film Transistors Based on InGaSnO Semiconductor Layer with Improved Etching Resistance

“…In contrary, MO-TFTs fabricated by solution-based techniques are more attractive for their low fabrication costs and high throughput [1][2][3][4]. Among all of the solution-based techniques, inkjet printing, as the state-of-the-art drop-on-demand technique, is widely used in a variety of materials such as organic compounds, graphene, carbon nanotubes and oxides [5][6][7][8] and is particularly attracted in MO-TFT fabrication for its low material waste and high efficiency [9][10][11].…”