Resistive Memory Based On Supramolecular Organic Semiconductors

With the advent of the big data era,how to boost the storage density of information,improve the reliability of stored information,and quicken the processing speed of information have become urgent issues for scientific researchers.Resistive memory is considered as the most promising memory device for the next-generation information storage due to its simple structure,high switching ratio,low production cost,fast responsing speed,low power consumption and easy integration.Compared with inorganic resistive memory,organic resistive memory has the advantages of favourable processability,excellent mass production potential,flexibility and easy three-dimensional stacking.It can be widely used in flexible wearable and three-dimensional integrated electronic devices.Many studies have confirmed that the conductivity of polyaniline,polypyrrole,and polyindole can increase exponentially under proton acid doping.Therefore,we can say they have two stable states and have the potential for resistive memory which is based on the switching of different conductive states.However,researchs based on resistive memory devices using polyaniline,polypyrrole and polyindole as resistive switching layers are still rare.In the application of resistive memory,two key issues need to be solved:the dispersion of polymers and how to achieve their doping and dedoping under external applied electric field.Polypseudorotaxanes or Inclusion Complexes are supramolecular systems formed by host-guest interactions.Due to host-guest interactions,the physicochemical properties of the guest molecules will be changed.Cyclodextrin containing many hydroxyl groups is often used as the host molecule of the polypseudorotaxane or inclusion complex.And after the formation of polypseudorotaxane or inclusion complex,the dispersibility of the guest will be improved;Meanwhile,cyclodextrin can form hydrogen bonds with the guest.Those hydrogen bonds can hop under the applied electric field,therefore,there exist the possibility to realize the H+ doping of the guest.When a reverse electric field is applied,H+can hop back to the cyclodextrin and the guest return the undoping state.Based on the analysis above,a series of polypseudorotaxanes or inclusion complexes were prepared in this paper.They are applied to resistive memory device for the first time,and their resistive properties and resistive mechanisms were also studied.At the same time,FeC-rGO composite was prepared by the π-π interaction of the organometallic ferrocene and reduced graphene oxide.The resistive performance and resistive mechanism of the composite were systematically studied,and its application in artificial synapses was explored.Detailed research contents are as follows:1.β-CD-PANI polypseudorotaxane was synthesized through two-step:prepare the includion complex of monomer firstly and then polymerize all under ice bath.The structure of β-CD-PANI polypseudorotaxane was characterized by UV-Vis-NIR,IR,NMR and XRD spectra.And Al/β-CD-PANI polypseudorotaxane/ITO resistive memory device with sandwich structure was prepared and the resistive performance of the device was tested.The memory device exhibit excellent nonvolatile resistive switching behavior with the SET voltage of-1.27 V and RESET voltage of+1.61 V,also with high ON/OFF ratio of 108,short response time of 29 ns,long retention time of over 105 s.It can be rewritten for 500 times,revealing its superior memory function for write-read-erase-read(WERE)cycles and also the device yield is high.The states of included PANI after SET and RESET were characterized by the in-situ UV-Vis-NIR,in-situ ATR-FTIR,and in-situ XPS spectra,proving that the resistive switching is attributed to the H+ doping and dedoping of polyaniline which is induced by the breaking and forming of hydrogen bonding under an external applied electric field.The Au/β-CD-PANI polypseudorotaxane/Au/PET device was prepared by using the all-printing technology.The device shows the similar resistive behavior as Al/β-CD-PANI polypseudorotaxane/ITO and has excellent flexibility.The device still has superior resistive performance when bent to a curvature radius of 3 mm,and the device with a curvature radius of 3 mm can even bend for 100 times without significant resistive performance degradation.2.β-CD-PPy polypseudorotaxane was synthesized under ice-bath assisted by ultrasonic and the preperation includes the inclusion of pyrrole monomer and then polymerize under the addition of oxidant.UV-Vis-NIR,IR,NMR and XRD spectra characterizations confirm the formation of β-CD-PPy polypseudorotaxane structure.Also,resistive memory device with Al/β-CD-PPy polypseudorotaxane/ITO structure was prepared and the resistive performance of the device was measured.Th e SET voltage of the device is+0.79 V and the RESET voltage is-0.93 V and the ON/OFF ratio can reach to 2.3×107.The response time of the device is 90 ns and the retention time is over 105 s.It can be repeatedly erased and rewritten for 500 times and the device yield is high.And through in-situ XPS analysis,it is proved that the resistance mechanism of the device is the redox of PPy and H+ doping and dedoping of polypyrrole induced by hydrogen bonding under the application of external electric field.3.The β-CD-Indole trimer inclusion complex was prepared by the method of inclusion of monomer firstly and then oxidation at room temperature.The structure of the inclusion complex was characterized by UV-Vis-NIR,IR,NMR and XRD spectra.An Al/β-CD-Indole trimer inclusion compound/ITO device was prepared.The SET voltage of the device is+2.87 V and the RESET voltage is-2.11 V.The ION/IOFF of the device can reach 1.6×105,with the responsing time of the device of 280 ns,also with favorable WE performance and excellent device yield.The switching mechanism of Al/β-CD-Indole trimer inclusion complex/ITO device was determined as the redox of indole trimer under the action of electric field and β-CD doping and dedoping ofindole trimer.4.Calixarene TBC[6]was prepared by traditional methods.TBC[6]-PANI polypseudorotaxane was synthesized through the includion of monomer firstly and then polymerize under ice bath.The structures of TBC[6]-PANI polypseudorotaxane were characterized by UV-Vis-NIR,IR,NMR and XRD spectra.Al/TBC[6]-PANI polypseudorotaxane/ITO device was prepared through spin-coating.The device show multi-level resistance switching with VSET1 of-0.10 V and VSET2 of-0.6 V.The ON/OFF ratio of HRS→LRS1 is 2.2×104 and LRS1→LRS2 is about 4.Meanwhile,when scanning forward,the ON/OFF ratio of LRS2→LRS1 is about 3000 with VRESET1 of+1.10 V,and LRS1→HRS is about 10 with VRESET2 of+2.00 V.Through in-situ UV-Vis-NIR spectra,it was found that doping/de-doping of polyaniline induced by hydrogen bond between TBC[6]and redox of TBC[6]under applied electric field result in the conductivity changes of the device,thus showing multi-level resistance switching behavior.5.GO was fabricated through modified Hummers.FeC-rGO composite was obtained through π-π stacking interaction of GO and FeC,followed with in-situ reduction.The structure of the composite was charactered by XRD,FTIR,Raman,UV-Vis,PL spectra and C-V test.Meanwhile,the morgraphy was observed by SEM and AFM.A sandwiched Al/FeC-rGO/ITO device was prepared with VSET of-1.70 V and VRESET of 2.10 V.And ION/IOFF ratio can reach up to 1.1×108,which shows good WERE performance and stability.Through XPS and Raman Maping analysis,the resistance behavior of the device was derived from the redox of ferrocene and the orbital hybridization mode transformation of rGO.Based on the grain sizes differential of FeC nanocrystallines,Al/FeC-rGO/ITO device for simulating artificial synapse can achieve potentiation and depression by applying pulse voltage,also be used for image pattern recognition.