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，铁电薄膜已经成为令人感兴趣的材料。因此，铁电薄膜的制备方法多种多样。然而，所制备的铁电薄膜却表现出了诸如极化疲劳、压痕等特殊的性质，我们对这些现象进行了研究，获得了对这些现象的认识，并测试了这种薄膜的热激电流（TSC）。通过对疲劳样品的TSC峰值的分析，发现极化疲劳现象的主要原因是极化反转注入的陷阱载流子引起的畴钉扎。用脉冲测量法研究了薄膜的内部偏置场。通过化学溶液沉积工艺获得的PZT薄膜在D-E磁滞回线中表现出明显的初始电压向负偏压场的偏移。得出结论，电压漂移的起源是由于在冷却过程中自发极化的自然排列引起的不对称空间电荷分布引起的内部偏置场。内部偏置场在零偏置场引起非对称去极化。

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.