| With further investigation of the organic semiconductor materials and the resistive memory devices,the researches focus much on the reproducibility and stability of the organic electronics,which may be the greatest impediment on the way to industrialization.To meet the requirement for the future application,scientists proceed to develop novel materials,fabricate high-quality nano films,adjust the molecular packing in the film state,and explore high-performance memory devices structures.However,till now,most of the reported works still tried to synthesize fresh memory media,involving molecular structure engineering and surface topographies characterization.Few of them show interest on the compatibility between the packing patterns of the molecules and the sandwich top/bottom device structure.For the organic moelcules with defined structures,the stacking patterns of them are basic fixed after film-forming,and change a few even being processed by externals photothermal aftertreatment.Hence,investigation on the film morphology and the intermolecular packing styles show great meaning for the improvement of the devices properities,such as high device efficiency and yield,low device power consumption,etc.Based on the guidance of theory and experiment,in this paper,we study from the ionization of the materials,subsequently,combine the molecular design and the innovation of the electrophoretic deposition technology.The large-sacle and well-patterned thin-films were successfully fabricated with uniformity and controlable thickness through our stragety,which effectively improve the memory performance of the ionic-type devices:(1)Investigation the ionization Effect in organic semiconductor on multilevel resistive memory behaviors:Introducing ionization effect into organic small molecules might be a useful strategy to adjust their memory behaviors.Here,a neutral D/A conjugated small molecules molecule LD is prepared and further converted to its ionic form(LD-IOM)and zwitterionic form(LD-ZIOM).Compared to UV ultraviolet absorption of LD,an obvious blue shift of LD-IOM and LD-ZIOM in the absorption spectra are presented by 44 and 88 nm.Molecular dynamics results simulate the preferential molecular packing modes of LD,LD-IOM and LD-ZIOM,which reveals J-,Slide-H-and H-aggregations,respectively.LD-based memory devices exhibit binary WORM memory behavior,while LD-IOM and LD-ZIOM based devices reveal upgraded ternary memory behaviors.The counterions(OTF-)in LD-IOM manifest an induction effect on molecular packing orientations and cause two separated threshold voltage distributions attributed to ion fractionation and migration effect.(2)Investigation the application of the controllable electrophoretic deposition technology for monolithic organic memory devices:With the booming organic electronics,developing industrial scale organic nanofilm become an important challenge.Herein,a high-efficiency technology is proposed to deposit organic nanofilm,named as electrophoretic deposition(EPD).Combined with the ingenious molecular design that introducing pyridinium group and flexible substituents to form versatile solutionprocessable organic salts,we used EPD technology to fabricate scalable organic films.By adjusting different deposition conditions,an area of 104 mm2 and controllable film thickness(ranging from 50 nm to 1.55 μm)are obtained.Differernt from traditional spin-coated films,the EPD films show excellent mechanical and electrochemical properties,which can be attributed to their compact molecular stacking,and delicate morphology and purity.In a 104 mm2 film,2745 memory device cells can be integrated together,which are measured to be excellent binary data-storage behavior(yield 95%)with large ON/OFF ratio(>103),small reading bias(1.0 V),and high stability and reproducibility.Besides,the EPD-based films and devices can also be decoated by a reverse EPD process,demonstrating the promising application for environmental protection and information security.(3)Investigation the fabrication of one-dimensional reticular organic nanofibers via electrophoretic deposition selective technique for nonvolatile memory mevice:The synthetic methods and scalable fabrication technology of organic nanofibers(ONFs)film based on π-conjugated molecules with donor-acceptor(D/A)structure remain a crucial point for practical applications of organic electronic integrated devices,particularly organic memory devices(OMDs).Here,the combination of cathode electrophoretic deposition(C-EPD)and the positively-charged molecules was promoted to grow controllable ONFs film from a mixed organic solvent(MeCN/TOL).As expected,a well-organized network of one-dimensional(1D)ONFs film was formed with central assistance of the solvent effect and exterior electric field,while the natural π-πstacking interactions and electrostatic force play an instrumental role during the growing process.The reticular ONFs films exhibited compact molecular packing,together with superior optoelectronic and electrochemical properties.The prototype sandwich-structure memory devices based on ONFs film showed more stable binary nonvolatile memory(NVM)behavior with a yield of 90%and energy-efficient performance with lower the switching threshold voltage than that of the device made by the bulk material.This study is particularly intriguing to promote an efficient and scalable ONFs-fabrication technology,which is desirable for highperformance ONFs-based electronic devices in various potential applications.(4)Investigation the fabrication of delicate thin-film with grain-like nanostructure for multilevel data storage performance:Utilizing electrophoretic deposition technology(EPD)to fabricate delicate thin-film has been proved to be useful and efficient.In order to achieve multilevel data storage performance,rational molecular design and controllable EPD technology are combined to produce highquality memory device.The netural organic molecule ID-CzNO2Py and its organic salt ID-CzNO2Py-EtI composed of isoindigo and nitrocarbazole groups are synthesized.By the adjustment of the EPD parameters,a delicate thin-film with assembly grain-like nanostructure can be fabricated from mixed electrolyte.The first layer grown between the ITO substrate and the molecules(I/M)is totally different form the subsequent growth model among the molecular layers(M/M).Although all the devices based on ID-CzNO2Py film(SP),IDCzNO2Py-EtI(SP)and ID-CzNO2Py-EtI(EPD)reveal ternary WORM-type performance,the yields of them are measured to be 15%,30%,55%,respectively.This work demonstrates that the electrode interfacial bonding plays a key role to grow controllable organic thin-films.Furthermore,the EPD-assisted process is expected to assemble more well-patterned nanostructures,which can be used to scale down and integrate nano-electronic components... |
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