Study On Hf_xZr_1-xO₂ Nano-films Prepared By Sol-Gel Method And Their Properties

As representative high-permittivity (high-k) dielectrics, HfO2 and ZrO2 based materials have been intensively studied and practically implemented in microelectronics and already widely replaced SiO2 as the transistor gate dielectric material and dynamic random access memory (DRAM) capacitor medium. Recently, the discovery of ferroelectricity in HfO2 based thin films was reported. If using this new type of ferroelectric materials instead of popular perovskite-type ferroelectrics, e.g., Pb(Zr,Ti)O3 (PZT), SrBi2Ta209 (SBT), and (Bi1-xLax)4Ti3O12 (BLT) may lead to a significant breakthrough on the storage density and performance in development of integrated ferroelectric-semiconductor devices such as non-volatile ferroelectric memories.Under the guide of phase transformation theory of the nanometer thin film ma-terial, we choose the sol-gel method with inorganic aqueous precursor to prepare HfxZr1-xO2thin films for the equipment requirements is not high, and the operation is simple. Nano-HfxZr1-xO2 thin films were prepared by modified sol-gel processes to reveal their surface, structural and chemical properties. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the precursor were performed. The surface morphology of the thin films was characterized by atomic force micro-scopy (AFM) and scanning electron microscope(SEM). Grazing incidence X-ray dif-fraction (GIXRD) and X-ray reflectivity (XRR) data of HfxZr1-xO2 thin films were measured. X-ray photoelectron spectroscopy (XPS) detected the content of different elements at the surface of the film and reflected the situations of the surface bonds. Multiferroic 100 V Test System was applied to measure the electrical properties of the films.The experiments proves using the sol-gel method with aqueous precursor can get thin film with the thickness less than 2 nm to over 200 nm, the film thickness was proportional to the number of spin coating cycles. AFM images revealed the film surfaces were smooth and flat, no pores and micro-cracks were discernable. The 60.0 nm ZrO2 thin film is crystallized at the annealing temperature between 550℃ to 600℃ with the tetragonal phase. The 60.0 nm HfO2 thin film is crystallized at the annealing temperature between 600℃ to 700℃ with the monoclinic phase. Addition of helped to partially stabilize the tetragonal structure of HfO2, and the tetragonal phase stability depends strongly on film thickness. The stabilization of the tetragonal phase in Hf0.5Zr0.5O2 films could be maintained only when the thickness was below 12.9 nm. A further increase in the thickness led to the Hf0.5Zr0.5O2 films consisting of a mixture of tetragonal and monoclinic phases, which should be attributed to a reduction of the surface energy contribution. According to the results of P-E and I-E, the dielectric constant of HfO2 was increased when doped with ZrO2. The dielectric constant of the 14.7-nm-thick HfO2 film,12.9-nm-thick Hf0.5Zr0.5O2 films and 29.5-nm-thick ZrO2 films were 13.6,27.8 and 42.1. The leakage current density of the films were ap-proximately 2.4×10-6,3.5×10-6 and 2.2×10-6A/cm2 at an applied electric field of 1 MV/cm.