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

Abstract

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.

Bulky side chain effect of poly(N‐vinylcarbazole)‐based stacked polymer electrets on device performance parameters of transistor memories

“…Thermal properties of these polymers were evaluated by DSC and TGA (Supporting Information Figure S3‐S7). The commercial PVK showed a glass transition temperature ( T g ) at 216 °C, which was in agreement with the reported data . Other polymers exhibited a higher T g than PVK, which were attributed to the introduction of steric hindrance groups, resulting in difficulty of conformational changes.…”

“…However, the operation of OFET memories with charge storage electret has yet to be explored from the view of π‐stacked structure. As we all know, poly( N ‐vinylcarbazole) (PVK) is one of the most typical π‐stacked polymers, whose conformational changes under external electric field due to uniquely stacked structures have been studied extensively . Therefore, PVK was also expected to work in OFET memory as polymer electret.…”

Polymer‐Based Resistive Memory Materials and Devices

“…Most recently, in order to further investigate the conformation‐induced conductance switching of polymers containing carbazole groups, Chen et al synthesized a π‐stacked nonconjugated polymer poly(9,9′‐(4,4′‐(2‐(4′‐sec‐butylbiphenyl‐4‐yl)‐ethene‐1,1‐diyl)bis‐4,1‐phenylene)bis‐9 H ‐carbazole) ( P26 , Scheme ) via interposing several aromatic benzene ring on the side‐chain to tend to form π‐π interaction and increase steric effect . The device based on P26 in ITO/polymer/Al exhibits nonvolatile WORM memory behavior with an ON/OFF current ratio up to 10 4 .…”

“…Chen et al also investigated the steric effect of aromatic pendant groups on the memory behaviors of PVK derivative . For π‐stacked nonconjugated polymer P63 (Scheme ), it exhibits flash memory behavior with an ON/OFF current ratio of approximately 10 5 and is different from polymer P26 discussed in section , which exhibits WORM memory behavior.…”

A low onset voltage WORM type polymer memory based on functional PES

“…And as shown in the DTG curves, the polymers have two main unstable points of 391°C and 446°C because of the degradation of the side chain and the backbone of the polymer respectively, while a tiny weight loss (1%) at a temperature around 150°C was caused by the evaporation of water absorbed on the polymer surface. From all above, the thermal property of CN‐Azo‐PES is comparable with that of polyimides and better than the other polymer materials that have been reported for electrical memory usage . And to the best of our knowledge, in the memory storage processes, the outstanding thermal stabilities will make contributions to the performance of the devices for the absence of thermal decomposition.…”