PZT薄膜晶化动力学过程研究

【作者】 黄文；

【导师】 李言荣； 张鹰；

【作者基本信息】 电子科技大学 ， 微电子学与固体电子学， 2005， 硕士

【摘要】 锆钛酸铅(PZT)作为一种典型的钙钛矿结构铁电材料,具有突出的介电、压电和铁电性质。由于其在微传感器、微执行器等微电子机械系统(MEMS)和非易失性存储器(NVFRAM)中的广阔应用前景,硅基PZT 薄膜已经成为国内外微电子学和材料科学的研究热点。本论文基于薄膜成核生长的基本原理,围绕退火晶化工艺对PZT 薄膜结晶品质、微结构以及电性能的影响进行了深入系统的分析。首先, 采用磁控射频溅射在Pt/Ti/SiO2/Si 上制备了优质的非晶Pb(Zr0.48Ti0.52)O3薄膜,采用常规晶化(CFA)和快速晶化(RTA)两种晶化工艺,研究了退火温度、保温时间及升降温速率对薄膜结晶生长的影响。研究发现当升温速率低于10 ℃/s 为(100)面择优生长;升温速率在10 ℃/s-20 ℃/s 之间为(110)面择优生长;升温速率在20℃/s 以上则出现(111)面择优生长,且升温速率越快(111)面择优生长越强烈。针对晶化初期结晶行为表征困难的问题,首次提出用压电响应力显微镜(PFM)观察电畴来描述结晶过程。经过大量实验,确定了PZT 薄膜结晶临界温度为550 o C,晶核形成并开始成长的起始保温时间在20 秒到40 秒之间。一旦形核,晶粒将沿界面迅速生长并自发极化形成圆形的铁电畴。通过对电畴的面积积分得到经550 o C 60 秒退火的样品结晶率为4.6±0.2%。通过PFM对PZT薄膜电畴结构的观察发现薄膜电畴结构与薄膜的结构取向关系密切。在(100)取向的PZT 薄膜中首次观察到极化方向相反的电畴交界处出现了鱼骨状交错的复杂畴结构,这种鱼骨结构的电畴被认为是由于薄膜受较强的退极化场影响而形成的。而在(110)取向的PZT 薄膜中观察到大量明暗交错的90O电畴。由于90O电畴中畴壁处的“钉扎”效应会导致强烈的铁电疲劳性,(110)取向的PZT 薄膜不易用于铁电器件的制备。通过对Pt/PZT/Pt/Ti/SiO2/Si 结构铁电容电性能的测试发现经过650℃快速处理的(111)PZT 薄膜的剩余极化(2Pr)为40μc/cm2,矫顽电场约为70kv/cm;在10KHz 时介电常数约为235,介质损耗小于0.1。该性能指标完全可以满足铁电存储器件研制的要求。更多还原

【Abstract】 Owing to its excellent dielectric, piezoelectric and ferroelectric properties, PbZr1–xTixO3 (PZT) with perovskite structure is an attractive material for MEMS devices such as microsensor, microactor and NVFRAM. PZT thin film based on Si integration circuit has become a hot issue in microelectronics and material science. Aiming the annealing effects on the crystallization quality, microstructure and electric property, the dissertation had touched the following aspects: First, amorphous Pb(Zr0.48Ti0.52)O3 thin film was prepared on the Pt/Ti/SiO2/Si substrate by RF-magnetron sputtering method. Annealing by rapid thermal annealing (RTA) and conventional furnace annealing (CFA), the study focus on the effects of heating rate, duration time and annealing temperature on the crystallization and growth of PZT thin film. The results show that the thin film with (100)-texture occurred below the heating rate of 10 ℃/s; the (110)-texture occurred between the heating rate of 10 ℃/s and 20 ℃/s; the (111)-texture occurred when the heating rate was above 20 ℃/s. Furthermore, the heating rate was faster; the (111)-texture intensity was stronger. It was first time to investigate the crystallization behavior during the initial crystallization state by observing ferroelectric domain by means of PFM. Based on a series of experiments, the critical nucleation temperature of PZT thin film was determined at 550 o C. The initial duration time for nuclei growth was between 20 seconds and 40 seconds. Once the nuclei were formed, the crystal growth was very quick along the interface and spontaneously polarized to form round in shape ferroelectric domains. By calculation of the domain area of the thin film annealed at 550 o C for 60 seconds, the crystallization ratio was 4.6±0.2%. By means of PFM, it was found that the ferroelectric domain was in relation to the microstructure of thin film. It was first time to observe the occurance of the herringbonelike morphology ferrodomain in (100)-texture thin film at the interface between positive and negative polarization, which was due to the effect of strong depolarization field. While the (110)-texture PZT film with a large number of 90O ferroelectric domains occurance was believed not to meet the NVFRAM devices demands due to the ferroelectirc fatigue pinned by 90O domain wall. By investigating the ferroelectric and dielectric properties of the Pt/PZT/Pt/Ti/SiO2/Si structure capacitor, it was found that the film annealed by RTA at 650℃demonstrated prominent P-E curves and C-V character compared with the films annealed by CFA. The remnant polarization was as high as 40μc/cm2 and the coercive field was only 70kv/cm. The dielectric constant was 235 at 10kHz and the更多还原