The influence of thin film fabrication process on ferroelectric properties and ferroelectric random access memories

由于铁电存储器的应用，铁电薄膜已成为人们感兴趣的材料。因此，铁电薄膜的制备方法多种多样。然而，所得到的铁电薄膜具有极化疲劳、压痕等特殊性质。我们对这些现象进行了研究，获得了关于这些现象的知识，并测试了这些薄膜的热激电流。获得了疲劳样品的TSC峰，揭示了极化疲劳现象的主要原因是极化反转注入俘获载流子引起的磁畴钉扎。用脉冲测量的方法研究了薄膜中的内偏置场。采用化学溶液沉积工艺制备的PZT薄膜在D-E磁滞回线上向负偏压方向发生了明显的初始电压漂移。结果表明，产生电压漂移的原因是冷却过程中自发极化的自然取向所引起的空间电荷分布不对称引起的内偏场。内偏置场在零偏置场下引起非对称退极化。

Ferroelectric thin films have been interesting materials because of FeRAM application. Therefore, ferroelectric thin films are fabricated by various preparation methods. However, the ferroelectric thin films obtained shows the peculiar properties such as the polarization fatigue, imprint and so on. We studied these phenomena, and obtained the knowledge about them.The thermally stimulated current (TSC) of the this films were examined. The peak of TSC of fatigued sample are obtained, revealing that the main origin of the polarization fatigue phenomena was the domain pinning caused by trapped charge carriers injected by polarization reversal. The internal bias field in the films were also investigated by pulse measurement. The PZT thin films obtained by a chemical solution deposition process exhibited a conspicuous initial voltage shift in the D-E hysteresis loop toward the negative-bias field. It was concluded that the origin of the voltage shift was an internal bias field due to asymmetric space-charge distribution induced by the natural alignment of spontaneous polarization during the cooling process. The internal bias field caused asymmetric depolarization at the zero-bias field.