Comparison of two strategies to improve organic ternary memory performance: 3-Hexylthiophene linkage and fluorine substitution

• Two novel A-D-A type small organic conjugated molecules are synthesized.
• The incorporation of 3-hexylthiophene group greatly decreases the steric repulsion.
• The substitution of fluorine atom enhances crystallinity and molecular stacking.
• Both the fabricated devices show better nonvolatile ternary WORM memory behaviors.
• Both the two devices have higher ternary yield and lower threshold voltages.

In this paper, two acceptor-donor-acceptor (A-D-A) type organic small molecules, 4,4'-(5,5'-(benzo[c] [1,2,5]thiadiazole-4,7-diyl)bis(3-hexylthiophene-5,2-diyl))bis(N-(4-nitrophenyl)-N-phenylaniline) (NTPA2TBT) and 4,4'-(5,6-difluorobenzo[c] [1,2,5]thiadiazole-4,7-diyl)bis(N-(4-nitrophenyl)-N-phenylaniline) (NTPA2BTF2), were synthesized and fabricated into resistive random access memory devices. Compared with our previously reported molecule NTPA2BT, NTPA2TBT has 3-hexylthiophene linkages bridging its donor and acceptor, while there are two additional fluorine atoms in the benzothiadiazole moiety for NTPA2BTF2. Both the fabricated memory devices based on these two new molecules perform nonvolatile ternary memory characteristics with lower threshold voltages, higher reproducibility and better stability. The addition of 3-hexylthiophene bridges significantly promotes the planarity of the conjugation backbone and facilitates the molecular stacking, while the substitution hydrogen by fluorine improves the intermolecular interaction, and thus also induces an ordered molecular stacking. The insertion of 3-hexylthiophene bridges or fluorine atoms could be an effective strategy of tailoring organic molecules to improve data storage performance with lower power consumption.