Monolayer FePt nanocrystal self-assembly embedded into atomic-layer-deposited Al2O3 films for nonvolatile memory applications

A simple approach is developed to fabricate oxide/FePt nanocrystals/oxide composite films by a combination of chemically-synthesized FePt nanocrystals' self-assembly and atomic layer deposition for ultrahigh-density nonvolatile memory applications. A hexagonally arranged monolayer of well-monodispersed FePt nanocrystals with a grain size of 4.5 nm has been assembled onto atomic-layer-deposited Al2O3 oxide by solution-based dip-coating. The lattice constant of this two-dimensional pattern is about 8 nm with the high density of 1.8 × 1012/cm2. A fraction of the Fe is oxidized during annealing at 500 °C for 5 min in O2 atmosphere, and the core-shell structure is formed with fcc-Fe0.75Pt nanocrystal core and amorphous Fe2O3 shell. The metal-oxide-Si capacitors with unannealed and annealed FePt nanocrystals embedded into Al2O3 films are electrically measured, and exhibit obvious memory effects with a hysteresis memory window of 4.1 and 8.1 V at the sweeping gate voltage of ±8 V, respectively. The enhanced memory window of samples with annealed FePt nanocrystals can be attributed to the existence of the Fe2O3 shell, which introduces additional interface and provides more trap sites for charge trapping storage.