The Effect Of Ordered Stacking In The Active Film On Resistive Memory Performance

With the coming of data era and industrial 4.0,lots of useful information come into human being’s vision,thus it is very important to design novel data-storage technologies and devices.Currently,the traditional “0” and “1” based binary memory devices that fabricated with silicon material have reached their limitation and cannot meet the requirement of data-storage strategically.In this case,many new storage technologies arises spontaneously,such as organic electric memory device which can increase the storage capacity through downscaling or multilevel memory device that can improve the memory density exponentially.In 2010,a small molecule based organic ternary memory device was first reported,which is a breakthrough in binary system and opens a new way for the research of small molecule based multilevel memory device.After years of research,the memory device showed a big improvement in multilevel behavior,threshold voltage,reproducibility and stability,rendering organic memory device more superiority.However,the previous reported small molecules only focused on the design of molecular structure,such as molecular backbone changing,donor-acceptor adjusting,molecular planarity tuning and etc.The tuning of the molecular structure also changed the molecular stacking in film state,and there is no systematical investigation on the memory properties and the molecular structures.This research investigated the molecular stacking on the behaviors of the memory devices:(1)Design two small molecules with different bridge spacers,ZIPGA with the spacer of benzene while ZIPCAD with the spacer of TPA.The sandwich-structured devices Al/ZIPGA/ITO and Al/ZIPCAD/ITO were achieved through spin-coating to form active layers with thickness of 100 nm.Electric measurements showed that Al/ZIPCAD/ITO device had no obvious memory behaviors,while Al/ZIPGA/ITO device exhibited typical ternary memory performance.Density-functional-theory and molecular stacking measurements indicated that TPA decreased the ordered intramolecular stacking in film state,blocked the mobility of the charge carriers thus device showed no memory behaviors.While ZIPGA formed an ordered molecular stacking in film state,which is beneficial for the mobility of the charge carriers through the film,thus exhibited the ternary memory property.(2)Based on the change of the molecular bridge bond in the first system,the molecular skeleton and the electronic structure are changed at the same time,so that the research is complicated.In the new system,we have chosen a pair of chiral enantiomers of the unequal and its racemic mixture as the organic layer,thus ensuring the same molecular skeleton and electronic structure of the same molecule.In this work,we demonstrate for the first time that racemic effect could be utilized to single out the intermolecular contribution from identical intramolecular properties of enantiomers and to effectively improve the performances of organic multilevel RRAM.Enantiomers are of identical electronic and geometrical topology despite of a spatially chiral discrepancy.Two enantiomers and their mixture were fabricated as the active organic layer to prepare organic multilevel RRAMs.Through a series of tests,it was found that the weak force of the spinous molecules is stronger than that of the unipolar molecules under the condition of constant molecular,resulting in a significant change in the stacking,thus exhibiting a better ternary performance.This also shows that changing the stacking has a significant effect on the device.(3)According to the above two researches,the memory performance can be affected by the stacking distance.Thus,this research system investigated the stacking distance in perovskite on multilevel memory behaviors.Since perovskite can form excellent layer-by-layer stacking and possess outstanding optoelectronic properties,the alkyl chains with different length were introduced to alter the distance between the neighbor perovskites.Electric measurements confirmed the different memory properties of the perovskite with various alkyl chains.The results show that the control of the interlayer spacing can effectively optimize the opening voltage of each gate,thus further saving energy consumption and developing a device with low power consumption.