A Ferroelectric Thin-Film Transistor Based on Sputtered HfZrO and IGZO

Abstract

In recent years, because of increased demand in IoTs devices, wearable displays, circuits, sensors, and other high technology devices, the thin film transistors (TFTs) gated by ferroelectric film as memory devices are of considerable interest. Ferroelectric (FE) materials including Pb(Zr0.4Ti0.6)O3 (PZT), (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT), and polymer poly (vinylidenefluoride-trifluoroethylene) (P[VDF-TrFE]) have been used to realize ferroelectric transistors with nonvolatile memory. Particularly, HfO2-based materials have attracted a great deal of attention since the breakthrough in the ferroelectricity of Si-doped HfO2, which can overcome some of limitations of current ferroelectrics such as scalability, lead-free materials and suitable for high-temperature process. Moreover, HfO2-based materials exhibit better performance in terms of a switching characteristic than low-k gate insulator (SiO2) as well as high-k materials. In this study, the performance of sputter-deposited ferroelectric hafnium zirconium oxide (HfZrO)/high-k HfO2 gate dielectric for a-IGZO TFTs on glass substrates was investigated. The sputterd HfZrO film was crystallized with orthorhombic phases after rapid-thermal-annealing at temperature of 400 °C for 30 min in air and exhibited ferroelectricity. The performance of the FE-TFT based on HfZrO/HfO₂ (15 nm/185 nm) was compared to typical TFTs fabricated with PECVD-SiO₂ (200 nm) and sputtered HfO₂ only (200 nm) gate insulators. The transfer characteristics of the FE-TFTs were demonstrated with low operating voltage of 0.1 V, one order higher on-off ratio and drain current than the typical TFTs with the SiO₂ and HfO₂ gates, high field effect mobility 5.04 cm2V-1s-1 and small subthreshold slope (SS) about 117 mV/dec. The low operating voltage and small SS results of the HfZrO/HfO₂-based device indicates that the use of the HfZrO/HfO₂ could serve as a potential gate for the fabrication of high-performance FE-TFTs.