The ferroelectric tunnel junction has a simple metal ultra-thin ferroelectric metal layered device structure. The ferroelectric tunneling junction utilizes ferroelectric polarization flipping to regulate the quantum tunneling effect and obtain different resistance states, thereby achieving data storage functionality. Due to the sub nanosecond scale ultrafast flipping and compact cross array structure of ferroelectric polarization, ferroelectric tunnel junctions have attracted much attention in the field of information storage in recent years due to their advantages of high-speed read and write, low power consumption, and high storage capacity. The tunneling resistance (or switching ratio) is the core indicator for measuring the performance of tunnel junctions. In 2005, a theoretical model was proposed that tunneling electroresistance is related to interface charge shielding effect, ferroelectric polarization intensity, and other factors. At present, diversified electrode engineering is generally used, such as using the phase transition characteristics of intercalation to regulate tunneling barriers, introducing additional Schottky barriers using semiconductor electrode materials, or using emerging two-dimensional metal electrode materials to introduce carrier concentration control, to modulate charge shielding effects and improve tunneling electroresistance. The influence of ferroelectric polarization intensity on electroresistance is equally crucial. However, due to limitations in preparation techniques and quantitative research methods, there is currently no experimental verification on how the polarization strength of the ferroelectric layer quantitatively affects the tunneling electroresistance.

Hu Weijin and Yang Teng, researchers in the Functional Materials and Devices Research Department of Shenyang National Research Center for Materials Science, Institute of Metals, Chinese Academy of Sciences, and Tang Yunlong, researchers in the Joint Materials Structure and Defect Research Department, proposed the strategy of using buffer layers to quantitatively regulate epitaxial strain, delay ferroelectric lattice relaxation, and thus enhance polarization intensity, revealing the internal relationship between polarization intensity and ferroelectric tunnel junction switching ratio. On March 4th, the related research results were published in ACS Nano under the title of Epitaxial Strong Enhanced Ferroelectric Polarization Towards a Giant Tunneling Electricity. This achievement provides a new approach for designing high-performance ferroelectric tunnel junction memory with high switching ratio.

This study used Sr3Al2O6/La0.67Sr0.33MnO3/BaTiO3 as the model system and achieved atomic level layer by layer growth of multilayer films using laser molecular beam epitaxy technology. By combining high-resolution X-ray diffraction technology, macroscopic ferroelectric polarization performance testing, aberration corrected transmission electron microscopy and other research methods, it was found that the strain of BaTiO3 single crystal thin films can be continuously controlled by changing the thickness of the Sr3Al2O6 buffer layer, resulting in a linearly increasing ferroelectric polarization intensity with increasing in-plane compressive strain. The experimental results are consistent with first principles calculations. Research has found that the strain sensitivity coefficient is the highest among typical perovskite ferroelectric materials, reaching 28 μ C/cm2/%. Based on this, researchers were able to achieve up to 80% at the BaTiO3/La0.67Sr0.33MnO3 interface under -2.1% compressive strain μ The C/cm2 ferroelectric polarization intensity has broken the highest reported value so far. Thanks to this ferroelectric polarization intensity, a huge tunneling resistance of 105 was achieved in the La0.67Sr0.33MnO3/BaTiO3 (3.2 nm)/Pt ferroelectric tunnel junction, which is 100 times higher than the ferroelectric tunnel junction without a buffer layer.

The research work has received support from the National Key R&D Program, the National Natural Science Foundation of China, and the Liaoning Provincial Central Leading Local Science and Technology Development Special Project.

Paper link：

论文链接