Amorphous Spiro‐OMeTAD Prepared Flexible Films with Surface Engineering Boost Ternary Resistive Memory Yield to 86%

Abstract

RRAMs) as a promising type have attracted considerable attention, due to its excellent miniaturization potential, high writing/reading speed, low energy consumption, and good endurance compared to traditional memory technology. [5][6][7] The resistances of an electrode/active layer/ electrode sandwich-like structure are multilevel adjustable, leading to n-nary memory. [8] However, the reproducibility of multilevel RRAMs heavily rely on the active materials with delicate design of inorganic oxide/nitrides, [9] organic molecules/polymers, [10][11][12][13][14] and biomaterials. [15,16] Organic molecules and polymers are intensively considered due to their structural tolerability, light weight, and large-scale stability. [6,[17][18][19][20][21][22] Numerous molecules were demonstrated their ternary memory behaviors. An intuitive principle usually obeyed is to design conjugated skeletons mounted by various electron acceptors/donors. However, recent statistical work indicated that the ternary device yield of these organic multilevel RRAMs remains as low as 30-50%, far away from the satisfaction considering the large scale production in industry after laboriously molecular innovation. [6,23] On the other hand, by surface engineering of the electrode, the device yield was improved to 82%, which was the highest among all reported values. [24,25] Breaking this record further remains extremely challenging and needs a comprehensive effort on both material selection and device fabrication techniques. Results and DiscussionIn this work, we employed 2,2′,7,7′-Tetrakis [N,N-di(4-methoxyphenyl) amino]-9,9′-spirobifluorene (Spiro-OMeTAD) (Figure 1a) as the active material and use solvent and surface engineering to boost the ternary device yield to 86%, which is the highest to date. Spiro-OMeTAD is conjugation-frustrated by its twisted Spiro structure, which leading to amorphous nature and glass forming tendency. It was selected inspired by its widely used in solar cells as hole-transporting layer because of proper energy levels with light absorbing material, easy processability, and thus promising charge extraction and collection ability. [26][27][28] In addition, Its electrical conductivity Organic ternary resistive memories can greatly improve the information density and thus are being extensively explored. However, the effective ternary device yield remains too low (usually <50%) for potential industrialization despite that laborious formula innovations have been attempted to improve molecular conjugation and crystallinity of the active materials. Here, it is demonstrated that using solvent and surface engineering, the devices based on amorphous 2,2′,7,7′-tetrakis[N,N-di(4methoxyphenyl) amino]-9,9′-spirobifluorene (Spiro-OMeTAD) achieve a ternary device yield of 86%, which is the highest among all reported to date. Spiro-OMeTAD is amorphous in the thin film and has a pristine device yield of 42%, challenging the concept that conjugated molecules or polymers should be employed in resistive memories. In addition, by optimizing th...

Switching the memory behaviour from binary to ternary by triggering S62− relaxation in polysulfide-bearing zinc–organic complex molecular memories

“…4d). 61 The better ternary memory performance of the FTO/4/Ag device is relative to its larger conjugated system and strong pÁ Á Áp stacking interactions, in which charged defects will be inhibited.…”

Recent advances in organic‐based materials for resistive memory applications

“…Extensive studies have revealed that organic small molecules could be applied as excellent resistive memory materials, attributing to their advantages of low cost, light weight, mechanical flexibility, and ease of processing 47,48,66,70,83‐104 . Many organic small molecules have been reported to exhibit resistive switching characteristics, including the binary and even higher multilevel nature 70,83‐96,105,106 .…”

“…Compared with the conventional spin‐coating method, we employed a dip‐coating technique to prepare small molecular thin films, which enabled high‐quality, homogeneous, and large‐area nanopatterns, and thus realized uniform resistive performances with high reproducibility up to 96%. Another efficient strategy was proposed by Zhao et al, which modified the bottom ITO electrode surfaces by octylphosphonic acid (OPA) monolayers, and succeeded in boosting the ternary resistive memory yield from pristine 42% to ultimate 86% 102 . Overall, the unique properties of single‐component organic small molecules make them promising candidates for next‐generation data storage devices.…”

Molecular-Shape-Controlled Binary to Ternary Resistive Random-Access Memory Switching of N-Containing Heteroaromatic Semiconductors

“…Especially, the resistances of some metal/organic/metal structured memory devices can be effectively adjustable through molecular engineering, leading to multilevel data storage. ,,− However, the probable instability of organic active compounds under high voltages often causes device degradation and/or failure during long-term operation. , Another challenge faced by organic-based ReRAM is the non-ideal resistive switching because of the inferior intrinsic conductivity of organic molecules . In fact, the recent studies suggest that the multilevel memory yield of organic-based ReRAM devices mostly remains relatively low (30–50%), which lags far behind the fundamental requirements of practical mass production after the laboratory development stage. ,, Therefore, it is crucial to design organic molecules with high intrinsic electrical stability and conductivity to develop high-performance multilevel ReRAM devices.…”

“…34 In fact, the recent studies suggest that the multilevel memory yield of organic-based ReRAM devices mostly remains relatively low (30−50%), which lags far behind the fundamental requirements of practical mass production after the laboratory development stage. 3,35,36 Therefore, it is crucial to design organic molecules with high intrinsic electrical stability and conductivity to develop high-performance multilevel ReRAM devices.…”