锆钛酸铅薄膜的铁电疲劳微观机理及其耐疲劳性增强

Micromechanism of ferroelectric fatigue and enhancement of fatigue resistance of lead zirconate titanate thin films

铁电随机存储器(ferroelectric random access memory,FeRAM)因其卓越的数据存储性能与非易失性存储特性等优势而备受关注,但其自身固有的铁电疲劳失效问题制约了FeRAM进一步的发展和商业化应用.FeRAM的疲劳失效与铁电薄膜的畴壁运动密切相关,但其内在疲劳机理仍有待深入研究.本文采用基于密度泛函理论(density functional theory,DFT)的第一性原理计算方法,研究了锆钛酸铅(Pb(Zr_(0.52)Ti_(0.48))O_(3),PZT)的疲劳失效机理并提出了增强其耐疲劳性能的方法.计算结果表明:PZT中氧空位与180°畴壁运动的耦合是其铁电疲劳的内在原因,PZT铁电薄膜中越靠近畴壁的地方越容易形成氧空位,畴壁处大量氧空位对畴壁运动的“钉扎”作用使畴壁迁移困难,抑制了其极化反转最终导致了铁电疲劳;Ba(Mg_(1/3)Nb_(2/3))O_(3)(BMN)缓冲层的存在可吸收PZT中的氧空位,降低畴壁处的氧空位浓度,提升其耐疲劳性能.实验结果表明,经过10^(10)次极化反转后,PZT铁电薄膜的剩余极化值降低了51%,而PZT/BMN薄膜的剩余极化值仅降低了18%;经过10^(12)次极化反转后,PZT/BMN薄膜的剩余极化值仍保持有82%并持续稳定.以上结果表明,BMN缓冲层引入确实能提高PZT铁电薄膜的耐疲劳性,有望满足FeRAM商业化应用的需求.

Ferroelectric random access memory(FeRAM)has been regarded as a promising technology for next-generation nonvolatile storage due to its excellent data storage performance and nonvolatile storage characteristics.However,fatigue degradation properties seriously impede the development and large-scale commercial use of FeRAM.In this paper,the interaction mechanism and enhancement of ferroelectric fatigue in lead zirconate titanate(PZT)thin film are investigated by the first-principles calculations(DFT).Theoretical calculations suggest that the coupling between oxygen vacancies and 180°domain walls in PZT is responsible for ferroelectric fatigue.Oxygen vacancies are more likely to be formed closer to domain wall,the“pinning”between oxygen vacancies and domain wall makes the migration of domain wall difficult,resulting in the suppression of polarization reversal and ultimately fatigue in ferroelectric thin film.The insertion of Ba(Mg_(1/3)Nb_(2/3))O_(3)(BMN)can absorb the oxygen vacancies in PZT and reduce the concentration of oxygen vacancies,and in doing so,the ferroelectric fatigue problem caused by the“pinning”effect of the oxygen vacancies can be eliminated.Moreover,the PZT thin films are deposited on Pt/Ti/SiO_(2)/Si(100)by the sol-gel method with using BMN buffer layer.The remnant polarization(Pr)of PZT film decreases by 51% and the PZT/BMN film remains 85%after 10^(10) cycles.Furthermore,it keeps stable even up to 10^(12) cycles.This paper demonstrates that the PZT/BMN film with excellent ferroelectric and fatigue endurance possesses the promising applications in FeRAM.