IMPROVEMENT OF FATIGUE PROPERTIES IN FERROELECTRIC NONVOLATILE MEMORY PREPARED BY PULSED LASER ABLATION

采用ArF脉冲激光烧蚀（PLA）技术，在氧化硅（100）上制备了铁电铅-锆-钛酸铅(Pb (Zr_<0.52>Ti_<0.48>) O_3: PZT薄膜电容器。疲劳试验结果表明，加速频率和开关脉冲测量频率的增加增加了极化反转的寿命，但降低了开关电荷密度Q_<SW>。在50 kHz时，Q_W即使在超过10^<10>周期后也保持初始值。Q_<SW>的测量频率依赖性表明，无论快慢域都发生了均匀疲劳，并且在铁电-金属界面上可能形成了低介电常数的附加层。本文还介绍了不同电极通过薄膜结构对PZT薄膜铁电性能的影响。这些实验表明，薄膜结构与疲劳抗力之间没有简单的相关性。抗疲劳性能的提高主要是通过降低Q_<SW>来实现的，但两者之间的相关性存在一定的模糊性。为了研究PZT薄膜电容器的疲劳性能，提出了氮化钛铝（Ti-Al-N； TAN）电极薄膜。在TAN/(100) Si上具有随机取向PZT薄膜的电容器没有表现出铁电磁滞回线，但在TAN/(100) MgO上具有优先[100]取向PZT薄膜的电容器却表现出了铁电磁滞回线。这表明在制备铁电氧化物时，在（100）MgO表面生长了具有高抗氧化性的tan电极膜。对于金属铁电体/绝缘体/半导体-(MFIS-)场效应晶体管存储器，提出了PZT/MgO/(100) Si结构。所制得的PZT薄膜为高取向钙钛矿型PZT薄膜，具有铁电P-E滞回。

For metal/ferroelectrics/metal (MFM) memory, ferroelectric lead-zirconate-titanate (Pb (Zr_<0.52>Ti_<0.48>) O_3 : PZT) thin-film capacitors were fabricated by ArF pulsed laser ablation (PLA) using Ni-alloy electrodes on oxidized (100) silicon. The fatigue test revealed that the increase in the frequency both for acceleration and measurement of switching pulse increases the life of polarization reversal while it decreases the switched charge density Q_<SW>. At 50 kHz, Q_W keeps the initial value even after switching above 10^<10> cycles. The measurement frequency dependence of Q_<SW> suggests that a homogeneous fatigue takes place irrespective of fast and slow domains and additional layrs of a low dielectric constant are probably formed in the ferroelectric-metal interface.The effect of various electrodes on the ferroelectric properties of PZT films through the film structure is also presented. These experiments revealed that there is no simple correlation between the film structure and the fatigue resistance. The fatigue resistance is, however, found to be improved primarily by decreasing Q_<SW>, although the correlation shows some ambiguity. For examining the fatigue properties, titanium-aluminum-nitride (Ti-Al-N ; TAN) electrode films were proposed for PZT thin-film capacitors. Capacitors with rather randomly oriented PZT films on the TAN/(100) Si did not show a ferroelectric hysteresis loop, but the capacitor with preferentially [100] -oriented PZT film on the TAN/(100) MgO did. This suggests that a TAN-electrode film was grown on (100) MgO with a high oxidation resistance at the high temperature employed for ferroelectric oxide preparation.For metal ferroelectrics/insulator/semiconductors-(MFIS-) FET memory, PZT/MgO/(100) Si structure was proposed. The PZT film obtained was found to be highly oriented perovskite PZT film with a ferroelectric P-E hysteresis.