Theoretical current-voltage characteristics of ferroelectric tunnel junctions
Theoretical current-voltage characteristics of ferroelectric tunnel junctions
复制标题
DOI：
10.1103/physrevb.72.125341
复制
发表时间：
2005-09-01
影响因子：
3.7
通讯作者：
Waser, R
中科院分区：
文献类型：
--
作者：
Kohlstedt, H;Pertsev, NA;Waser, R
我们提出了铁电隧道结（FTJ）的概念。这些结由两个由纳米厚的铁电势垒隔开的金属电极组成。在直接电子隧道效应代表主要传导机制的假设下，分析了 FTJ 的电流-电压特性。首先，描述了铁电材料固有的逆压电效应对隧道电流的影响。计算表明，由于应变引起的势垒厚度、电子有效质量和导带边缘位置的变化，压电源的晶格应变改变了电流-电压关系。值得注意的是，由于压电效应，电导最小值从零电压偏移，并且在铁电势垒中极化反转后发生与应变相关的电阻切换。其次，我们分析了由于金属电极中电子对极化电荷的不完美屏蔽而产生的内部电场的影响。结果表明，对于非对称 FTJ，这种去极化场效应也会导致极化反转后势垒电阻发生相当大的变化。然而，所产生的电流-电压环路的对称性与应变相关的电阻开关的特征不同。考虑到应变和去极化场效应，描述了伴随 FTJ 不对称性增加而从一种类型到另一种类型的滞后曲线的交叉。值得注意的是，具有不同顶部和底部电极的非对称 FTJ 由于较大的电阻开/关比而更适合非易失性存储器应用。
We present the concept of ferroelectric tunnel junctions (FTJs). These junctions consist of two metal electrodes separated by a nanometer-thick ferroelectric barrier. The current-voltage characteristics of FTJs are analyzed under the assumption that the direct electron tunneling represents the dominant conduction mechanism. First, the influence of converse piezoelectric effect inherent in ferroelectric materials on the tunnel current is described. The calculations show that the lattice strains of piezoelectric origin modify the current-voltage relationship owing to strain-induced changes of the barrier thickness, electron effective mass, and position of the conduction-band edge. Remarkably, the conductance minimum becomes shifted from zero voltage due to the piezoelectric effect, and a strain-related resistive switching takes place after the polarization reversal in a ferroelectric barrier. Second, we analyze the influence of an internal electric field arising due to imperfect screening of polarization charges by electrons in metal electrodes. It is shown that, for asymmetric FTJs, this depolarizing-field effect also leads to a considerable change of the barrier resistance after the polarization reversal. However, the symmetry of the resulting current-voltage loop is different from that characteristic of the strain-related resistive switching. The crossover from one to another type of the hysteretic curve, which accompanies the increase of FTJ asymmetry, is described taking into account both the strain and depolarizing-field effects. It is noted that asymmetric FTJs with dissimilar top and bottom electrodes are preferable for the nonvolatile memory applications because of a larger resistance on/off ratio.