Resistance random access memories (RRAMs) are considered as promising candidates for the next generation non-volatile information storage techniques with simple structure, low-power consumption, high storage density and fast speed characteristics. With the ever increasing concerns about the wearable electronic equipments in recent years, the development of flexible resistance-switchable materials and flexible RRAMs should also be well addressed.
The research team led by Prof. Run-Wei Li at the Key Laboratory of Magnetic Materials and Devices (Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences) have devoted great efforts to the investigation of the resistive switching effect and its underlying mechanism in organic and inorganic materials over the past few years.The research team demonstrate that by controlling the physiochemical processes of transport of metal or oxygen ions, adsorption/desorption of functioning groups, doping of organic ions and etc with electric fields, it is possible to receive stable resistive switching effect in various thin film materials of BiFeO3, HfO2, graphene oxide, and PA-TsOH.It is also found that the organic materials usually shows uniform resistive switching, promising mechanical flexibility but poor thermal stability, while the inorganic counterparts on the contrary carry good thermal stability but relatively smaller ON/OFF ratio and poor mechanical flexibility. Recently, Prof Li’s team has made an excellent trade-off in the performance of resistive switching by using organic-inorganic hybrid systems.

Metal-organic frameworks, or MOFs, which are formed by association of metal cations or clusters of cations (“nodes”) and multitopic organic bridging ligands (“linkers”), are a fascinating class of crystalline hybrid materials, offering a well-defined and repeating three-dimensional structures, unique chemical versatility and an extraordinary degree of variability in their functionalities. Through co-operation with Ningbo University, Institute of Physics of Chinese Academy of Sciences, Stockholm University and University of Michigan, Mr. Liang Pan and Dr. Gang Liu observed stable resistive and ferroelectric switching behaviors in an indium MOF material, denoted as RSMOF-1 (RSMOF = resistance switchable metal−organic framework), with the chemical formula [InC16H11N2O8]•1.5H2O and a twofold-interpenetrated three-dimensional (3D) β-quartz topology (Figure 1). The resistive and ferroelectric switching behaviors of RSMOF-1 occur at room temperature with excellent reproducibility and low power consumption characteristics, which are important for electronic device applications. Experimental observations and a molecular dynamics simulation suggest that the resistive and ferroelectric switching properties are strongly regulated by the presence of guest water molecules in the nanochannels through electric field-controlled hydrogen-bonding interactions with the amino-tethered RSMOF-1, and demonstrate the in-principle possibility of using MOF materials to fabricate RRAM devices. The results have been published on J. Am. Chem. Soc. 136, 17477-17483 (2014), as well as filed a Chinese patent (201210177625.6).

It is worth nothing that the micron-sized RSMOF-1 single crystal, can not be fabricated into real memory chips, and its mechnical flexibility is much worse than that of the nanofilm materials. To solve these problems, Li‘s group has developed an improved liquid-phase epitaxy approach to directly deposit high quality MOF nanofilm of HKUST-1 on flexible gold-coated PET susbtrates (Figure 2). As such, uniform and reproducible resistive switching effect, which can be sustained under the strain of as high as 2.8%, and over the wide temperature range of -70 °C to +70 °C, has been observed for the first time in the all solid-state Au/HKUST-1/Au/PET thin film devices. The mechanical flexibility and environmental stability well meet the requirements for wearable application under earth surface conditions, thus providing promising material candidates for the development of flexible or even wearable information storage teqechniques. These results have been published on Adv. Funct. Mater. 25, 2677-2685 (2015) as an inside cover article, as well as files a Chinese patent (201510106614.2).

Prof. Runwei Li: runweili@nimte.ac.cn Mr. Liang Pan: pl8848@nimte.ac.cn
Research Staff Url:
http://english.nimte.cas.cn/rh/rd/newmaterials/mmd/mmd_research_interests/

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