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

由于FeRAM的应用，铁电薄膜已成为一种有趣的材料。因此，铁电薄膜的制备方法多种多样。但得到的铁电薄膜表现出极化疲劳、压印等特殊性能。我们研究了这些现象，并获得了有关它们的知识。测试了薄膜的热激发电流（TSC）。疲劳试样的TSC峰表明极化疲劳现象的主要原因是极化反转注入的被困载流子引起的畴钉住。用脉冲测量法研究了膜内的偏置场。化学溶液沉积法制备的PZT薄膜在D-E迟滞回路中出现了明显的初始电压向负偏置场偏移。结果表明，在冷却过程中，由于自发极化的自然排列而引起的空间电荷分布不对称导致了内部偏置场。内偏置场在零偏置场处引起非对称退极化。

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.