Integration of self-assembled redox molecules in flash memory devices

Jonathan Shaw*, Yu Wu Zhong, Kevin J. Hughes, Tuo-Hung Hou, Hassan Raza, Shantanu Rajwade, Julie Bellfy, James R. Engstrom, Héctor D. Abruña, Edwin Chihchuan Kan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

Self-assembled monolayers (SAMs) of either ferrocenecarboxylic acid or 5-(4-Carboxyphenyl)-10,15,20-triphenyl-porphyrin-Co(II) (CoP) with a high-κ dielectric were integrated into the Flash memory gate stack. The molecular reductionoxidation (redox) states are used as charge storage nodes to reduce charging energy and memory window variations. Through the program/erase operations over tunneling barriers, the device structure also provides a unique capability to measure the redox energy without strong orbital hybridization of metal electrodes in direct contact. Asymmetric charge injection behavior was observed, which can be attributed to the Fermi-level pinning between the molecules and the high-κ dielectric. With increasing redox molecule density in the SAM, the memory window exhibits a saturation trend. Three programmable molecular orbital states, i.e., CoP0, CoP1-, and CoP2-, can be experimentally observed through a charge-based nonvolatile memory structure at room temperature. The electrostatics is determined by the alignment between the highest occupied or the lowest unoccupied molecular orbital (HOMO or LUMO, respectively) energy levels and the charge neutrality level of the surrounding dielectric. Engineering the HOMO-LUMO gap with different redox molecules can potentially realize a multibit memory cell with less variation.

Original languageEnglish
Article number5676192
Pages (from-to)826-834
Number of pages9
JournalIEEE Transactions on Electron Devices
Volume58
Issue number3
DOIs
StatePublished - 1 Mar 2011

Keywords

  • Coulomb blockade effect
  • high-κ dielectric
  • nonvolatile memory devices
  • reductionoxidation (redox)-active molecules
  • self-assembled monolayer (SAM)

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