Study Of The Reliability Characteristics For Si-doped HfO₂ Ferroelectric Thin Films

Ferroelectric memory is being developed by taking the advantages of ferroelectric thin films and Si-based semiconductor integration technology. Compared to other types of memories, ferroelectric memory offers specific benefits including non-volatility, high write\read speed, low power consumption, and radioactive resistivity, and therefore has received great attentions over the last two decades.To date, perovskite ferroelectrics, like Pb(Zr,Ti)O3 (PZT), are the main materials used in volume production of ferroelectric memory. Due to the very poor compatibility of PZT with Si-based CMOS integration processes, the development of ferroelectric memory faces obstacles of high cost and low storage density. As a representative high-k dielectric material, HfO2 has been widely implemented in microelectronics owning to its excellent thermo-stability and lattice matching with Si. Recently, pronounced ferroelectricity was discovered in HfO2 thin films doped with Si, Zr, Y, Al, Gd, Sr and La. As HfO2 offers good compatibility with COMS integration process, it is reasonable to expect that the material related bottle neck of ferroelectric memories will be broken through by replacing PZT with HfO2 based novel ferroelectric thin films; both of the storage performance and density will be therefore improved significantly. For the sake of successful application in ferroelectric memories, considerable fundermental research, particularly, the decisive reliability study, needed to be done for the novel HfO2-based ferroelectric thin film, which was only treated as high-k dielectrics until 2011.This thesis mainly discussed the promising future and possible limitations of the representative Si-doped HfO2 ferroelectric thin films applied in non-volatile ferroelectric memories in the view of macroscopic electrical properties. It was found out that the temperature-dependent polarization reversal behavior could be indentified into three categories depending on the amplitude of the applied field (E0)-In the low field regime(E0<Ec), the dielectric permittivities showed a linear dependence on E0, thus for the first time demonstrating the applicability of the Rayleigh Law to 10nm ultra-thin films. In the medium field regime(Ec?E0?2Ec), the sub-switching hysteresis with increasing temperature was mainly attributed to thermally activated domain-wall motion and domain nucleation at increasing number of regions. In the high-field regime(E0>2Ec), a decrease in coercive field with increasing temperature was observed, which was consistent with the non-equilibrium nucleation-limited-switching model.At the alternating electric field, the remanent polarization Pr increased within limited cycles, which process was called wake-up, and then decreased due to fatigue. De-pinning of domains due to reduction of the defect concentration at bottom electrode interface was suggested as origin of the wake-up. The rate of wake-up was accelerated by reducing the frequency, increasing the amplitude of the cycling field or rising the temperature. Increasement in temperature or cycling frequency could reduce the resistance of fatigue, which behavior agreed well with the Local Phase Decomposition (LPD) theory. The trend to breakdown at high cycling field and poor endurance property were the main obstacles of the novel HfO2-based ferroelectric thin films to be applied in non-volatile ferroelectric memories.