Molecular Structure Adjust Film Stacking Morphology And Its Effect On Electrical Memon Device Performance

With the rapid development of electronic technique and mobile communication technology,the 5G era has quietly arrived.Various intelligent devices are interconnected to share information and humans have stepped into the era of big data.However,traditional information memorizers have approached their physical limits and cannot meet the ever-increasing demand for information storage due to the limitation of its own principles.In order to solve this problem,resistance random access memory(RRAM)was invented.Compared with traditional memories,RRAM has the advantages of higher storage density,stronger reliability,low cost,clear structure and so on.Since the organic small molecule-based RRAM was first reported in 2010,our group has designed and synthesized a large number of organic semiconductor materials with stable ternary storage capacity.However,most of these studies are limited to the adjustment of molecular structure and molecular skeleton,the stacking morphology of molecules in thin films and the orientation of molecules on bases have not been thoroughly researched.So,this dissertation designed and synthesized a series of small molecule compounds referring to previous work to systematically studied the relationship between the adjustment of the molecular structure,the intermolecular stacking state and the storage behavior of electrical storage devices by adjusting the electron cloud density distribution on the molecular backbone,the length of the alkyl chain in the molecule and the assembly between the molecules.This dissertation hopes to provide a theoretical basis for the design of high-performance organic memories in the future.This work includes the following three aspects.(1)Effect of different charge density distributions on the molecular skeleton on the intermolecular aggregation mode and device memory performance:Firstly,two D-A conjugated organic small molecules NI-Cz and NI-Cz-NO2 are synthesized with carbazole and naphthimide as the electron donor and acceptor,respectively.Compared to the molecule NI-Cz,the electron cloud density distribution in NI-Cz-N02 is more uniform after introducing a nitro group into the molecule skeleton.Then we study the effects of different charge density distributions on molecular aggregation and device switching behavior.The results show that the surface roughness of the NI-Cz molecular film is high and the surface of the NI-Cz-NO2 film tends to be flat.Both molecular films can form ordered intermolecular packing,but the stacking modes are different.NI-Cz appears as J-aggregation and NI-Cz-NO2 appears as H-aggregation.The memory performance test of "ITO/small molecule/Al" devices show that both molecules have stable ternary storage behavior.However,the turn-on voltage of NI-Cz-NO2 is lower since H-aggregation increases the overlap of the molecular conjugate plane and reduces the energy barrier of carrier migration inside the film.For NI-Cz molecules,although the J-aggregation makes the molecular packing regular,the rougher film surface hinders the stable contact between the molecules and the electrodes,thus showing a higher turn-on voltage.(2)The influence of flexible chain length on layered molecular stacking and the memory performance of device:two organic small molecular materials containing the same push-pull electronic group are designed and synthesized with different molecular flexible chain lengths.Carbazole,Azo bond and nitro group are introduced into the molecular skeleton to form the conjugate structure of D-A1-A2.X-ray diffraction and AFM results find that both molecules showed good layered stacking and the layers in the thin film state are smooth and flat.Theoretical calculations and experimental analysis show that two molecules are arranged on the substrate in a"standing" form,but molecules with longer alkyl chains are prone to entanglement during the stacking process,reducing the overlapping area of the molecular conjugate skeleton and making the device's turn-on voltage increases.Compared with the first work,which focused on the study of molecular-to-molecule stacking,this work further studies the effect of micro-nano structure morphology after the formation of intermolecular stacks on the memory performance of the device.(3)Application of organic Zn-based MOF material with clear stacking structure in electrical memory:Based on the previous two studies focusing on the intermolecular forces affecting the accumulation of molecules,this work proposes a new idea to synthesize organometallic frame materials connected with stable coordination bonds as electrical memory materials by using 1,4-Di(1H-pyrazol-4-yl)benzene as the ligand and metal Zn as the center atom.The powder XRD and crystal XRD results show that the N atoms in pyrazole can coordinate with Zn,and each metal node is bonded with four pyrazole molecules to form a regularly stacked MOF material.The material presents regular tetragonal three-dimensional stacking with regular holes distributed with side length of 12.8 A.I-V tests show that ITO/Zn-H2PyH/Al has a stable binary memory behavior and the binary ratio is more than 90%.Also,the turn-on voltage of Zn-H2PyH-based device stabilize at-2.8 V.