Achieving tunable memory performance from nonvolatile to volatile by altering the trap depth of charge trapping sites in functional imides containing carbazole moieties
“…The amorphous characteristic also made PIs as one of the ideal material for producing high quality thin films. 36,37 Meanwhile, the storage device could be prepared by conventional spin coating process. 12,32 Figure 5.The wide-angle X-ray diffraction patterns.…”
Three novel polyimides (PI(TPF-Br BPDA), PI(TPF-Ph BPDA), and PI(TPF-Ph-OMe BPDA)) with tetraphenyl fluorene (TPF) were synthesized and tested. The laboratorial results showed that the constructed electronic devices exhibited different memory behaviors due to the different steric hindrance substituents (bromine atom, phenyl, and 3,5-dimethoxyphenyl) in 2,7-position of TPF molecule. The memorizers based on PI(TPF-Br BPDA) and PI(TPF-Ph BPDA) presented volatile dynamic random access memory (DRAM) feature with turn-on voltages of −2.39 and +1.45 V, as same as −1.71 and +1.74 V, separately. However, the PI(TPF-Ph-OMe BPDA) based apparatus exhibited non-volatile write-once read-many-times memory (WORM) behavior with turn-on voltage of −1.13 V, due to the more charge traps of 3,5-dimethoxyphenyl moieties and higher dipole moment. The switching mechanism was verified by quantum simulation of energy level, electrostatic potential (ESP) surface and dipole moment. These results indicated that the electrical memory performance of the synthesized TPF-based PIs could be adjusted by modifying the electron donor structure.
“…The amorphous characteristic also made PIs as one of the ideal material for producing high quality thin films. 36,37 Meanwhile, the storage device could be prepared by conventional spin coating process. 12,32 Figure 5.The wide-angle X-ray diffraction patterns.…”
Three novel polyimides (PI(TPF-Br BPDA), PI(TPF-Ph BPDA), and PI(TPF-Ph-OMe BPDA)) with tetraphenyl fluorene (TPF) were synthesized and tested. The laboratorial results showed that the constructed electronic devices exhibited different memory behaviors due to the different steric hindrance substituents (bromine atom, phenyl, and 3,5-dimethoxyphenyl) in 2,7-position of TPF molecule. The memorizers based on PI(TPF-Br BPDA) and PI(TPF-Ph BPDA) presented volatile dynamic random access memory (DRAM) feature with turn-on voltages of −2.39 and +1.45 V, as same as −1.71 and +1.74 V, separately. However, the PI(TPF-Ph-OMe BPDA) based apparatus exhibited non-volatile write-once read-many-times memory (WORM) behavior with turn-on voltage of −1.13 V, due to the more charge traps of 3,5-dimethoxyphenyl moieties and higher dipole moment. The switching mechanism was verified by quantum simulation of energy level, electrostatic potential (ESP) surface and dipole moment. These results indicated that the electrical memory performance of the synthesized TPF-based PIs could be adjusted by modifying the electron donor structure.
“…This result is consistent with their excellent organo‐solubility. The amorphous characteristic also made PIs possess excellent film‐formation ability; thus, the memory device could be fabricated through convenient and conventional spin‐coating process …”
“…The electron-withdrawing group's strength matches with the traps' depth. 59 In compound 4d, the trap depths of the imidazole and nitro groups are 0.48 and 2.89 eV, respectively, including imidazole, −NO 2 , −F, and −CF 3 , which can act as a trap in negative ESP. These trapping centers can be stabilized in the excited state via intra/intermolecular charge transfer and impede the mobility of moving charge carriers.…”
Introducing a different acceptor into the same molecular
backbone
with a definite acceptor strength is the key to developing multilevel
memory devices. A series of Y-shaped imidazole- and triarylamine-based
compounds was designed and synthesized for multilevel data storage.
The influence of various donor and acceptor end-cap units on the photophysical,
electrochemical, and memory performance was evaluated. The electrochemical
analysis reveals a high highest occupied molecular orbital (HOMO)
level of around ∼5.0 eV and a low band gap with irreversible
anodic peaks (1.05–1.08 V), which indicates facile charge transport
in the donor/acceptor end-capped D–A systems. Switching the
memory behavior from binary to ternary was achieved by tuning the
acceptor strength in the molecular structure. The compounds with the
terminal electron-withdrawing groups displayed a ternary memory with
an ON/OFF ratio of 104 with a long-lasting retention time. tert-Butylphenyl and methoxyphenyl end-capped compounds
demonstrated binary memory with a low threshold voltage (−1.42
and −1.38 V) and an ON/OFF ratio of 105. The molecular
simulation confirms the charge transfer and trapping mechanism associated
with the compound binary/ternary memory behavior. This work demonstrates
that slight modification in the molecular structure can change the
memory behavior from binary to ternary and renders a new pathway for
updating the multilevel storage devices.
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