Enhanced electrical stability of nitrate ligand-based hexaaqua complexes solution-processed ultrathin a-IGZO transistors

Abstract

We report solution-processed, amorphous indium-gallium-zinc-oxide-based (a-IGZO-based) thin-film transistors (TFTs). Our proposed solution-processed a-IGZO films, using a simple spin-coating method, were formed through nitrate ligand-based metal complexes, and they were annealed at low temperature (250 °C) to achieve high-quality oxide films and devices. We investigated solution-processed a-IGZO TFTs with various thicknesses, ranging from 4 to 16 nm. The 4 nm-thick TFT films had smooth morphology and high-density, and they exhibited excellent performance, i.e. a high saturation mobility of 7.73 ± 0.44 cm 2 V −1 s −1 , a sub-threshold swing of 0.27 V dec −1 , an on/off ratio of ~10 8 , and a low threshold voltage of 3.10 ± 0.30 V. However, the performance of the TFTs degraded as the film thickness was increased. We further performed positive and negative bias stress tests to examine their electrical stability, and it was noted that the operating behavior of the devices was highly stable. Despite a small number of free charges, the high performance of the ultrathin a-IGZO TFTs was attributed to the small effect of the thickness of the channel, low bulk resistance, the quality of the a-IGZO/SiO 2 interface, and high film density.

Numerical Simulation on Thickness Dependency and Bias Stress Test of Ultrathin IGZO Thin‐Film Transistors Via a Solution Process

“…To validate the simulation results, we compared them to measurement of ref. . The experimental data were measured for a‐IGZO TFT with inverted‐staggered structure.…”

“…The simulation of NBIS and PBS agreed very well with what have been reported for solution‐processed ultrathin a‐IGZO TFT in ref. in which it was found that the thinner 4 nm show high stability compared with thicker 16 nm TFT for PBS and NIBS.…”

“…The inverted‐staggered a‐IGZO TFT structure used for numerical simulation is shown in Figure and it is the same as in ref. . The structure consists of a 4/16 nm thick a‐IGZO active layer and a 100 nm SiO 2 as a gate insulator layer.…”

“…It has been observed that the a‐IGZO TFT stability improved with increasing channel thickness . By contrast other work showed that a decrease in the TFT channel thickness enhanced its stability . Therefore, it seems that the experimental investigation of the effect of thickness on the stability is not conclusive due to many factors: in case of contamination issues during the TFT fabrication, density of defects in the channel films, morphology of these films, or absorption of ambient gas during or after fabrication.…”

Optimizing the Properties of InGaZnOx Thin Film Transistors by Adjusting the Adsorbed Degree of Cs+ Ions

“…In recent years, solution process and magnetron sputtering have been commonly used to achieve low temperature prepared a-IGZO TFTs. However, a-IGZO prepared by the solution process shows disadvantages such as lots of film defects, large roughness, and poor uniformity of large areas—inducing low carrier mobility of a-IGZO TFTs (generally < 10 cm 2 V −1 s −1 ), which cannot satisfy the requirements of high-definition flexible display applications [13,14,15,16]. The studies also showed that most of the sputtered a-IGZO TFTs always need an annealing process to guarantee their high performance, since unannealed a-IGZO fabricated by magnetron sputtering still have many defects inside [17,18,19].…”