Solution processable amorphous hafnium silicate dielectrics and their application in oxide thin film transistors

Abstract

Novel solution-processed amorphous high-k dielectrics for thin film transistors (TFTs) have been systemically studied with the objective of achieving high performance and reducing costs for the next generation displays. In this research, amorphous hafnium silicon multiple oxide (HfSiOx) was fabricated by a simple spin-coating method. Here, we have demonstrated that the incorporation of a silicon oxide has significant effects on the properties of HfO₂. The HfSiOx dielectrics had no obvious crystallization peaks even when the annealing temperature reached up to 800 °C while the HfO₂ films were crystallized at 400 °C. The HfSiOx films had an energy band gap of 6.05 eV, which was wider than HfO₂ films (5.69 eV), the breakdown voltage increased from 2.4 MV cm⁻¹ (HfO₂) to 2.9 MV cm⁻¹ (HfSiOx) and the leakage current decreased from 4.4 × 10⁻⁷ A cm⁻² to 3.7 × 10⁻⁷ A cm⁻² at an electric field of 2 MV cm⁻¹. To achieve optimized device performance, the influence of annealing temperature on the characteristics (including the surface and interface, the chemical and structural evolution) of the solution processed HfSiOx dielectrics was emphasized in this research. To demonstrate the HfSiOx application in oxide TFTs, we fabricated HfInZnO (HIZO) and ZnSnO (ZTO) TFTs with HfSiOx dielectrics, and both of them showed low off-state current indicating HfSiOx is an attractive candidate used in TFTs. The ZTO TFTs with amorphous HfSiOx dielectrics operated well under a gate voltage of −0.53 V, exhibiting a high saturation mobility of 153 cm² V⁻¹ s⁻¹, a small subthreshold swing of 0.17 V dec⁻¹, and a large on–off current ratio 3.4 × 10⁷.