Influence of high pressure annealing conditions on ferroelectric and interfacial properties of Zr rich MFM capacitors

Abstract

Ferroelectric $HfO_2$ films have drawn significant attention in recent times due to its potential applications in ferroelectric random access memory (FeRAM), negative capacitance field effect transistors (NCFET), ferroelectric tunnel junction (FTJ), synaptic devices. Ferroelectricity in $HfO_2$ depends on various factors such as composition, post metallization process, process conditions, etc. In this research report, an in-depth analysis is carried out to understand the role of high-pressure annealing (HPA) conditions on ferroelectricity as well as interfacial non-ferroelectric film in $Hf_xZr_{1-x}O_2$ (HZO) capacitors in metal-ferroelectric-metal (MFM) structure. HZO demonstrates highest ferroelectricity at 1:3 Hf:Zr ratio in HPA and a maximum remanent polarization (Pr) of 31 ${\mu C cm^{-2}}$ was achieved as compared to 19 ${\mu C cm^{-2}}$ obtained in RTA (1:1 HZO). To understand the influence of HPA conditions, HZO 1:3 capacitors are annealed at various temperatures (300 °C, 400 °C, 500 °C, 600 °C) and pressures (1 atm, 50 atm, 200 atm). Ferroelectricity in HZO is found to enhance with increasing HPA temperature or pressure due to higher ferroelectric phase formation as revealed by GIXRD analysis. Transient pulse switching measurement suggests reduction in the effective thickness of the interfacial non-ferroelectric film at a high HPA temperature and pressure which was also validated by impedance analysis. Further, impedance analysis reveals a reduction in the number of oxygen vacancy defects with increasing annealing temperature and pressure implying a phase transition from the tetragonal phase of non-ferroelectric layer to ferroelectric orthorhombic phase. Additionally, excellent endurance property till $10^{9}$ cycles with reduced wake-up effect was observed in 1:3 HZO capacitors with increasing the HPA temperature, while higher annealing pressure is found to increase Pr without affecting its endurance property. The results obtained herein, can be of significant scientific importance, especially to achieve enhanced ferroelectric property with reduced wake-up effect in HZO ferroelectrics, which is beneficial for FeRAM applications.