Shanghai Technology Institute made progress in the study of ferroelectric tunneling effects

Recently, researchers from the Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Academician of the Chinese Academy of Sciences Yanjun Hao and Researcher Meng Xiangjian have made new progress in the study of the tunneling effect of ferroelectricity. Dr. Wang Jianlu and Ph.D. students Tian Bobo and Zhao Xiaolin of the research group conducted systematic research on ferroelectric tunnel junctions, and prepared ferroelectric tunnel junction solid state devices of polyvinylidene fluoride polymer (PVDF) materials, and discovered iron electrodes. The manipulated direct quantum tunneling effect. The results were published online on Nature Communications 7, 11502 (2016) (DOI: 10.1038/ncomms11502) with the title Direct tunnelling through organic ferroelectrics. For the first time, a ferroelectric PVDF polymer ultrathin film with a thickness of only a few nanometers was used as the barrier structure of the tunnel junction, and the regulation ratio of the ferroelectric polarization to the tunneling current was found to exceed 1000% for the purpose of exploring tunneling electrons and polarization. Coupling characteristics and the development of new electronic devices based on ferroelectric tunnel junctions provide the basis. The research work was done in collaboration with Professor Duan Chung-gang of East China Normal University and Garcia, a professor at the University of Paris, France. Wang Jianlu is the author of the paper and Tian Bobo is the first author of the paper.

The quantum tunneling effect is a quantum property, which is the phenomenon that microscopic particles such as electrons can pass through the “wall” that they could not pass through. The tunneling effect of ferroelectric energy is to replace the ordinary “wall” layer (or “barrier” layer) with a ferroelectric material, and use the polarization reversal characteristics of the ferroelectric material to change the thickness and height of the “wall” to achieve Quantum tunneling characteristics, state manipulation.

The realization of the ferroelectric quantum effect requires very high sample quality. Previous reports have reported that the tunneling effect of ferroelectricity is only observed in the complex oxide material systems of a few perovskite structures, and the preparation process and control are complicated. The mechanism is not yet clear. PVDF is a ferroelectric polymer material with many unique properties, such as two-dimensional ferroelectric properties, polarization reversal due to molecular chain twist, a variety of molecular configurations, and flexibility for coilable electrons, optoelectronic devices, etc. . This makes the PVDF iron tunneling effect has important scientific significance and practical application value.

Since 2010, the research group has carried out research on the tunneling effect of PVDF polymer ferroelectric charge, repeatedly optimized the ultrathin film and device fabrication process, improved the device structure several times, and explored optimization methods for film and device test characterization. Among them, the preparation of high-quality nano-thickness PVDF ultrathin films is one of the difficulties in this research. The group explored the use of a Langmuir-Blakit (LB) film transfer method to transfer precisely controlled PVDF two-dimensional films with a molecular layer thickness (a single layer thickness of about 2 nanometers and containing 3-4 molecular layers). On the substrate, samples with a smooth surface and orderly arrangement of molecular chains were obtained. A suitable temperature and atmosphere heat treatment process was explored to obtain a PVDF ultrathin film with two-dimensional ferroelectric properties. The related thin film preparation process achieved a breakthrough in early 2014. The related work was published in Appl. Phys. Lett. 104, 182907 (2014) .

Ferroelectric tunnel junction devices have important application values ​​in future high-density, low-power, highly integrated logic and memory devices. Based on the tunneling effect of ferroelectric energy, it can also be used to construct novel infrared thermal detectors and high-sensitivity novel photoelectric detectors. In addition to the above potential applications, PVDF ferroelectric tunnel junction devices also have the outstanding advantages of easy integration with silicon-based circuits, large-area fabrication, and curlable characteristics, which will facilitate its application in the field of flexible optical/electronic devices.

In addition, the research group has accumulated nearly 10 years in the field of development of PVDF-based ferroelectric polymer film physics and related devices, and has developed PVDF uncooled infrared detection related devices with independent intellectual property rights. PVDF detectors are already in the engineering field. Implement the application. Related technologies have been granted 4 invention patents, and more than 30 academic papers have been published in this field, including Appl. Phys. Lett. more than 10 articles, Phys.Rev.B 1 article, and New J. Phys. 1 article. J. Appl. Phys. 2 articles, 1 Scientific Reports, etc.

At the same time, the research group is working hard to further improve the quality of PVDF samples. It is hoped that new structural and functional devices will be developed on the basis of this research, and new mechanisms and new effects will be thoroughly analyzed. The work was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Shanghai Municipal Science and Technology Commission.