Solution-processed InGaZnO Thin-film Transistors Research Articles

Influence of metallization process on solution-processed InGaZnO thin film transistors

Low-temperature solution-processed InGaZnO (IGZO) thin film transistors (TFTs) have recently attracted significant attention as the next-generation flexible display TFTs, owing to their high transparency, high electrical performance, low-cost fabrication, and large-area scalability. However, solution-processed amorphous IGZO TFTs have several drawbacks, such as poor film quality or low stability, and have been studied with view to improving the device performance. One of the critical components determining device characteristics is the metallization process, which we systematically studied using aluminum (Al) source and drain electrodes. The electrical properties were measured for different channel lengths and evaluated using the threshold voltage (V th) and subthreshold swing (SS). Al electrodes directly affect the channel region, enhancing the electron density because of the doping effect from Al and oxygen vacancy-related oxidation of Al and causing an abnormal negative shift of V th, which is confirmed by the component analysis via various spectroscopies. To understand and improve the TFT characteristics, we conducted a low-temperature post-annealing process and polymer passivation and succeeded in moving V th from over 150 V to near 0 V and remarkably improved SS. This study discovered that the influence of source-drain metallization on the channel region determines the device characteristics through the close relation between metal oxidation and the number of oxygen vacancies.

Low-temperature solution-processed InGaZnO thin film transistors by using lightwave-derived annealing

In this paper, a lightwave-derived low-temperature annealing method is demonstrated on solution-processed InGaZnO (IGZO) films for the flexible thin film transistors (TFTs) applications. It is demonstrated that lightwave-derived low-temperature annealing (~230 °C) enhances the IGZO TFTs performance. Compared with the conventional furnace annealing process, lightwave annealing can effectively facilitate the decomposition of the IGZO precursors and form a smooth and dense IGZO film. With AlOx used as a dielectric layer, the optimal IGZO TFTs exhibit the carrier mobility of 13.4 cm2/Vs and a high on-current to off-current ratio (Ion/Ioff) of > 105. This work indicates that lightwave annealing is a practical approach to fabricate the oxide semiconductors at a low annealing temperature and show great potential for the next-generation low-cost wearable device fabrication.

Enhanced electrical properties in solution-processed InGaZnO thin-film transistors by viable hydroxyl group transfer process

We propose a simple hydroxyl group transfer method to improve the electrical characteristics of solution-processed amorphous InGaZnO (IGZO) thin-film transistors (TFTs). Tuned poly(dimethylsiloxane) elastomer, which has a hydroxyl group as a terminal chemical group, was adhered temporarily to an IGZO thin-film during the solidification step to transfer and supply sufficient hydroxyl groups to the IGZO thin-film. The transferred hydroxyl groups led to efficient hydrolysis and condensation reactions, resulting in a denser metal–oxygen–metal network being achieved in the IGZO thin-film compared to the conventional IGZO thin-film. In addition, it was confirmed that there was no morphological deformation, including to the film thickness and surface roughness. The hydroxyl group transferred IGZO based TFTs exhibited enhanced electrical properties (field-effect mobility of 2.21 cm2 V−1 s−1, and on/off current ratio of 106) compared to conventional IGZO TFTs (field-effect mobility of 0.73 cm2 V−1 s−1 and on/off current ratio of 105).

Reduction of hysteresis in solution-processed InGaZnO thin-film transistors through uni-directional pre-annealing

The hysteresis of the solution-processed oxide thin-film transistors (TFTs) is fatal issue to interrupt stable operation. So, we came up with uni-directional pre-annealing to solve the problem. There are inevitable defects when solution-processed oxide TFTs are fabricated, due to the porosities by the solvent volatilization. Also oxygen vacancies needed for carrier generation in metal oxide semiconductor can be trap states inducing charge carrier trapping. Uni-directional pre-annealing improved the hysteresis, preventing randomly solvent evaporation and decreased the defects of the film. We can result in advanced stability of the solution-processed oxide TFTs, at the same time showing that the field effect mobility was enhanced from 3.35 cm2/Vs to 4.78 cm2/Vs simultaneously, and exhibiting better subthreshold swing from 0.89 V/dec to 0.23 V/dec.

Low-Cost Label-Free Electrical Detection of Artificial DNA Nanostructures Using Solution-Processed Oxide Thin-Film Transistors

A high-sensitivity, label-free method for detecting deoxyribonucleic acid (DNA) using solution-processed oxide thin-film transistors (TFTs) was developed. Double-crossover (DX) DNA nanostructures with different concentrations of divalent Cu ion (Cu(2+)) were immobilized on an In-Ga-Zn-O (IGZO) back-channel surface, which changed the electrical performance of the IGZO TFTs. The detection mechanism of the IGZO TFT-based DNA biosensor is attributed to electron trapping and electrostatic interactions caused by negatively charged phosphate groups on the DNA backbone. Furthermore, Cu(2+) in DX DNA nanostructures generates a current path when a gate bias is applied. The direct effect on the electrical response implies that solution-processed IGZO TFTs could be used to realize low-cost and high-sensitivity DNA biosensors.

Effects of Mg doping on the gate bias and thermal stability of solution-processed InGaZnO thin-film transistors

Mg-doped IGZO TFTs showed improved TFT performance and thermal stability due to fewer oxygen deficiencies and less interface electron trapping. • We fabricated Mg-doped IGZO TFTs with improved performance using solution-process. • Mg doping reduced the oxygen deficiencies and less interface electron trapping of a-IGZO films. • Mg dope-TFT showed high mobility of 2.35 cm 2 /V s and an on–off current ratio over 10 6 . • For better device stability (gate-bias and thermal stability) was proved. The effects of magnesium (Mg) doping (molar ratio Mg/Zn = (0–10 at.%)) on solution-processed amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) grown using the sol–gel method are investigated. TFT devices fabricated with Mg-doped films showed an improved field-effect mobility of 2.35 cm 2 /V s and a subthreshold slope (S) of 0.42 V/dec compared to those of an undoped a-IGZO TFT (0.73 cm 2 /V s and 0.74 V/dec, respectively), and an on–off current ratio of over 10 6 . Moreover, the 5 at.% Mg-doped TFT device showed improved gate bias and thermal stability due to fewer oxygen deficiencies, smaller carrier concentration, and less interface electron trapping in the a-IGZO films.

Effect of annealing temperature on the electrical performances of solution-processed InGaZnO thin film transistors

We fabricated bottom gate thin-film-transistors (TFTs) with solution processed InGaZnO (IGZO) channel layers thermal-annealed at various temperatures. The solution based process inherently requires heat treatment at high temperatures to complete the chemical reaction of the thin films; therefore, thermal annealing is an important process to adjust the electrical characteristics of the thin films and TFTs. The IGZO channel layers retained structurally amorphous phase and high optical transparency at annealing temperatures of up to 600 °C. On the other hand, the electrical performances of the IGZO TFTs were highly sensitive to the annealing temperature. Thermal annealing at higher temperatures induced a negative shift of the threshold voltage (V TH) and an increase in the saturation mobility and on–off current ratio. The IGZO TFT annealed at 400 °C showed an appropriate V TH and on–off current ratio, but its saturation mobility was inadequate. Annealing at temperatures of more than 500 °C led to an excessive negative shift of V TH, despite the high saturation mobility.

Electrical characteristics of solution‐processed InGaZnO thin film transistors depending on Ga concentration

AbstractWe investigated the role of Ga in solution‐processed InGaZnO thin film transistors (TFTs). The incorporation of Ga into a InZnO compound system results in a decrease in the carrier concentration of the films and an off‐current of TFTs. This is a result of the Ga ions forming stronger chemical bonds with oxygen, as compared to the Zn and In ions, acting as a carrier suppressor. It was verified, using X‐ray photoelectron spectroscopy (XPS), that the vacancy‐related oxygen 1s peak was decreased when the Ga content increased.