Surface Engineering of ITO Substrates to Improve the Memory Performance of an Asymmetric Conjugated Molecule with a Side Chain

Hou, Xianghui; Cheng, Xue‐Feng; Xiao, Xin; He, Jinghui; Xu, Qingfeng; Li, Hua; Li, Najun; Chen, Dongyun; Lu, Jianmei

doi:10.1002/asia.201700706

Cited by 9 publications

(12 citation statements)

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“…We proved the existence of charge trap and filamentary conduction by means of plotting the I‐V curve with a log‐log scale. In the low bias voltage region (Figure b (I)), the current follows Ohmic conduction behavior (I≈V 1.08 , Figure b (I)), owing to the thermal excitation of the filled traps . When the bias voltage increases, the traps generated from the structure defects are gradually filled and the Fermi level is raised to approach the conductive band.…”

Section: Resultsmentioning

confidence: 97%

“…The reason comes from that the decrease of aromatic hydrogen leads to the association of the absorption bands as well as mutual interaction of absorption vibrations between indole structures formed in polydopamine. The absorption band in the range of 800–700 cm −1 arises from the substitution of H in aromatic . Benefited from the strong intermolecular interaction, PDA films are of good thermal stability.…”

Section: Resultsmentioning

confidence: 98%

“…The charge trapping‐induced conductive filament are most likely responsible to our ternary memory device of polydopamine because of the following evidence. We first investigated the relationship between the top electrode's (Al) areas with current level of the three resistance states based on a statistic on a sample size of 50 by varying the electrode area from 0.0078 mm 2 , 0.031 mm 2 to 0.071 mm 2 (Figure a) . Each current level has similar magnitude and insensitive to the electrode area.…”

Section: Resultsmentioning

confidence: 99%

“…When the bias voltage increases, the traps generated from the structure defects are gradually filled and the Fermi level is raised to approach the conductive band. The I‐V curve approximately obeys a square law (I≈V 2.30 , Figure b (II) ), called by trap‐filled limited current mode (TFLC) . When the voltage further increases to the first threshold voltage (III), all traps in polydopamine films are filled up and the conductivity of the film rapidly jumps to a higher level (“1” state, Figure b (II)) .…”

Section: Resultsmentioning

confidence: 99%

“…The I‐V curve approximately obeys a square law (I≈V 2.30 , Figure b (II) ), called by trap‐filled limited current mode (TFLC) . When the voltage further increases to the first threshold voltage (III), all traps in polydopamine films are filled up and the conductivity of the film rapidly jumps to a higher level (“1” state, Figure b (II)) . Approximately, the current is designated as space charge limited current (SCLC, Figure b (III)) region .…”

Section: Resultsmentioning

confidence: 99%

See 4 more Smart Citations

Mussel‐Inspired Polydopamine Coating for Flexible Ternary Resistive Memory

Zhao

Cheng

Qian

et al. 2018

Chemistry An Asian Journal

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In recent years, numerous organic molecules and polymers carrying various functional groups were synthesized and used in fabrication of wearable electronic devices. Compared to previous materials that suffer from poisonousness, stiffness and complex film fabrication, we circumvent above matters by taking advantage of mussel-inspired polydopamine as our active material to realize resistive random access memories (RRAMs). Polydopamine thin films were grown on indium tin oxide glass catalyzed by Cu SO /H O and characterized by Fourier infrared spectroscopy (FT-IR), UV/Vis spectroscopy and scanning electron microscopy. The Al/Polydopamine film/ITO devices possess ternary memory behavior with good ternary device yield with two threshold voltages around 1.50 V and 3.50 V, long data retention over 10 s of continuous reading or 10 pulse reading. The two resistance switchings are attributed to defects functioning as charge traps and the formation of conductive filaments. A flexible device based on Al/polydopamine film/ITO/polyethylene terephthalate retains its ternary memory behavior after being bent with a bending radius of 1.54 cm and bending cycles up to 5000, demonstrating good compatibility and flexibility of polydopamine.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 3 more Smart Citations

Mussel‐Inspired Polydopamine Coating for Flexible Ternary Resistive Memory

Zhao

Cheng

Qian

et al. 2018

Chemistry An Asian Journal

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

Zhao

Sun

et al. 2019

Adv Elect Materials

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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...

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Irreversible Resistive State Switching in Devices with a Homoleptic Cobalt(II) Complex Active Layer

Barman

Khatua

Goswami

et al. 2021

Chemistry An Asian Journal

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Molecules with bi‐stable electronic transport behaviour have been in upfront research topics of the molecular semiconductor devices in the past few decades due to the use of such materials in resistive data storage devices. Transition metal complexes (TMC) are expected to be potential candidates in regard to the tunable and manifold redox behaviour expecting multiple bulk transport states. Finding alternate mechanisms in such devices with TMC as the active layer materials would revoke the multifaceted approach to the functional gain. We have succeeded in demonstrating write once‐read many (WORM) type of resistive memory device using a homoleptic Cobalt(II) (Co(II)) complex with large on/off current ratio ensuring the easy readout process at lower voltage. The advantage of this device was the turn on voltage was found to be the low (<2.7 V) operational voltage and the success ratio of the devices were more than 83%. The durability of the stored data was found to be more than 35,000 seconds which ensures the stability of the bistable state in the fabricated devices. Such ambient stable, solution processable devices are important for the large‐scale printable devices. The manuscript describes the preparation, optical and electrochemical characterisation of the metal complex used along with a detailed mechanistic investigations and electrical characterisation of memory device obtained from a stable cobalt complex.

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Surface Engineering of ITO Substrates to Improve the Memory Performance of an Asymmetric Conjugated Molecule with a Side Chain

Cited by 9 publications

References 55 publications

Mussel‐Inspired Polydopamine Coating for Flexible Ternary Resistive Memory

Mussel‐Inspired Polydopamine Coating for Flexible Ternary Resistive Memory

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

Irreversible Resistive State Switching in Devices with a Homoleptic Cobalt(II) Complex Active Layer

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