Molecular orbital calculation of the electronic structure of poly( N ‐vinylcarbazole)

Chen

Phys. Chem. Chem. Phys.

et al. 2012

In order to investigate the steric effect of aromatic pendant groups and the electrical bistability in nonconjugated polymers potentially for memory device applications, two π-stacked polymers with different steric structures are synthesized and characterized. They exhibit two conductivity states and can be switched from an initial low-conductivity (OFF) state to a high-conductivity (ON) state. Additionally, they demonstrate nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10(4), and flash memory behavior with an ON/OFF current ratio of approximately 10(5). Both steady-state and time-resolved fluorescence spectroscopies are used to examine the conformational change of the polymers responding to an applied external electrical voltage. The results provide useful information on different steric effects of pendant groups in polymer chains, resulting in various electrical behaviors. The possibility in realizing an "erasable" behavior through breaking π-stacked structures of pendant groups by a reversal of the electric field was also discussed on the basis of temperature-dependent fluorescence spectroscopy investigation. These results may thus offer a guideline for the design of practical polymer memory devices via tuning steric structure of π-stacked polymers.

Section: Electrical Switching Behavior Of the Polymersmentioning

confidence: 99%

The steric effect of aromatic pendant groups and electrical bistability in π-stacked polymers for memory devices

Chen

Phys. Chem. Chem. Phys.

et al. 2012

“…In the bulk polymer, carriers (holes) have a higher interchain mobility when the overlapping of related orbitals is large between two adjacent carbazole rings, and the disordered regions, in which carbazole rings do not stack regularly, act as trapping sites for carriers. 30 With the increases in spacer length and steric effect between the carbazole group and the polymer backbone, the electrical behavior observed upon application of an external bias to the device changes from that of a single conductivity state (for PVK) to that of the nonvolatile bistable states (for poly-(2-(N-carbazolyl)ethyl methacrylate, or PMCz) and then to that of the volatile bistable states (for poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole, or PVBCz). We have previously observed bistable electrical switching in the PMCz device.…”

Section: Introductionmentioning

confidence: 99%

Conformation-Induced Electrical Bistability in Non-conjugated Polymers with Pendant Carbazole Moieties

et al. 2007

Conformation-induced volatile and nonvolatile conductance switching effects were demonstrated in non-conjugated polymers containing the same electroactive pendant groups. Single-layer devices of the structure indium-tin-oxide/polymer/aluminum were fabricated from two non-conjugated polymers with pendant carbazole groups in different spacer units. The device based on poly(2-(N-carbazolyl)ethyl methacrylate) (PMCz) exhibited nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 106, while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 103. The formation of carbazole excimers resulting from conformation-induced conductance switching under an electric field was revealed in situ by fluorescence spectroscopy. The corresponding voltage-induced conformation ordering in the polymer film was captured by transmission electron microscopy. In the absence of a spacer unit between the pendant carbazole group and the main chain, regioregular poly(N-vinylcarbazole) (PVK) exhibited only one conductivity state (ON state). The differences in memory behavior among the three polymers were attributed to their inherent differences in the degree of regioregularity and ease of conformational relaxation of the field-induced regioregular carbazole groups. These conformational effects were in turn dictated by the chemical structure and steric effect of the spacer unit between the pendant carbazole group and the main chain.

“…In the thin films of polymer materials, the loosely packed supermolecular chains in the disordered regions, together with the chain ends and folding, usually act as trapping sites for charge carriers 225 and lead to low conductance of the material. If conformational ordering of the π conjugated moieties (which are effective carrier transport components) can be achieved under the application of external electric field or voltage, higher interchain mobility can be then obtained through the overlapping of related orbitals between two adjacent groups.…”

Section: Resistive Switching Mechanisms In Organic Materialsmentioning

confidence: 99%

Recent Advances in Resistive Switching Materials and Devices: From Memories to Memristors

Liu¹,

Chen²,

Gao³

et al. 2018

Eng. Sci.

Resistive switching devices have not only been considered as an emerging candidate for the next generation information storage technology, but also demonstrated great potential for in-memory computing systems with greatly enhanced computation capability. This review focuses on the recent advances in resistive materials and devices. We first describe the electric field-induced filamentary conduction model that accounts for the resistive switching behavior observed in inorganic materials, as well as the novel electric field-engineering strategy that is used to optimize the device structure and the memory performance. The alternative ways of using organic and hybrid materials to construct resistive switching devices are then illustrated. By tuning the charge transfer interaction and solid state electrochemical redox properties in small molecules, polymer, metal-organic framework and organic-inorganic hybrid perovskite materials, bistable and multibit memories, as well as the biomimicking memristors have been fabricated. Finally, we discuss the future development of the resistive switching materials and devices, aiming to clarifying the key issues that hinders its practical applications.