Integration of Self-Assembled Redox Molecules in Flash Memory Devices

Abstract

Abstract-Self-assembled monolayers (SAMs) of either ferrocenecarboxylic acid or 5-(4-Carboxyphenyl)-10,15,20-triphenylporphyrin-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., CoP 0 , CoP 1− , and CoP 2− , 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. Index Terms-Coulomb blockade effect, high-κ dielectric, nonvolatile memory devices, reduction-oxidation (redox)-active molecules, self-assembled monolayer (SAM).

Multi-scale Computational Framework for Evaluating of the Performance of Molecular Based Flash Cells

“…POMs have attractive properties for potential NVM application due to their ability to undergo stable multiple and reversible oxidation/reduction processes. Also, incorporation of regular arrays of numerous POMs into SiO 2 has already been experimentally reported (Shaw 2011). As a result, we decided to concentrate our attention on possible integration of POMs with the floating gate (FG) of the current BULK flash cell architecture Fig.…”

Multi-scale computational framework for the evaluation of variability in the programing window of a flash cell with molecular storage

“…2) is 15.6 nm. The tunneling oxide thickness T tun , similarly to [6] 4 N + (tetrapropyl-ammonium -TPA), forming an insulating barrier of permittivity very close to that of SiO 2 [14]. The POMs are oriented parallel relative to the SiO 2 surfaces.…”

“…2) could offer several very important advantages over the conventional polysilicon FG [5], [6]. For example, the charge storage is very localized, thus minimising cross-cell capacitive coupling (arising from charge redistribution on the sides of a poly-Si FG and being one of the most critical issues with flash memories).…”

“…Although this benefit is present in floating gates realised by charge-trapping dielectric or by a metallic nano-cluster array, both technologies exhibit very large variability -charge-trap memories suffer variation in trap-density and trap-energy and the size and density of nano-clusters is difficult to control (this precludes their ultimate miniaturization). In fact, the concept of using molecules as storage centers has already been demonstrated for organic redox-active molecules [6], [12].…”

FDSOI molecular flash cell with reduced variability for low power flash applications

“…1) to form the storage media in flash memory cells (see Fig. 2) could offer several very important advantages over the conventional polysilicon floating gate (FG) flash cells [1], [2]. It is believed that the POMS are more compatible with existing CMOS processes than organic molecules as by their nature they consist of oxygen atoms similar to SiO 2 .…”