You-Pin Gong

A TiAl2O5 nanocrystal charge trap memory device

A charge trapping memory device using Ti0.2Al0.8Ox film as charge trapping layer and amorphous Al2O3 as the tunneling and blocking layers was fabricated for nonvolatile memory application. TiAl2O5 nanocrystals are precipitated from the phase separation of Ti0.2Al0.8Ox film annealed at 900 °C. A memory window of 2.3 V and a stored electron density of 1×1013/cm2 were obtained. Good retention characteristics of the memory device at 80 °C were observed due to the deep charge trapping level as identified by the valence band offsets and electron energy loss spectrum measurements.

Interfacial structure and electrical properties of ultrathin HfO2 dielectric films on Si substrates by surface sol-gel method

Ultrathin HfO2 films with about ~3 nm thickness were deposited on n-type (1 0 0) silicon substrates using hafnium chloride (HfCl4) source by the surface sol–gel method and post-deposition annealing (PDA). The interfacial structure and electrical properties of ultrathin HfO2 films were investigated. The HfO2 films show amorphous structures and smooth surface morphologies with a very thin interfacial oxide layer of ~0.5 nm and small surface roughness (~0.45 nm). The 500 °C PDA treatment forms stronger Hf–O bonds, leading to passivated traps, and the interfacial layer is mainly Hf silicate (HfxSiyOz). Equivalent oxide thickness of around 0.84 nm of HfO2/Si has been obtained with a leakage current density of 0.7 A cm−2 at Vfb + 1 V after 500 °C PDA. It was found that the current conduction mechanism of HfO2/Si varied from Schottky–Richardson emission to Fowler–Nordheim tunnelling at an applied higher positive voltage due to the activated partial traps remaining in the ultrathin HfO2 films.

Magnetic properties of FePt nanoparticle assemblies embedded in atomic-layer-deposited Al2O3

Self-assembled face-centered cubic FePt nanoparticles on Si substrates were embedded into amorphous Al2O3 capping layers with various thicknesses in the range 5–20 nm using atomic layer deposition (ALD) technology. The effect of the Al2O3 layer thickness on the structure, mono-dispersibility, and magnetic properties of the FePt/Al2O3-matrix composite films was investigated. After annealing at 700 °C in a reducing atmosphere for 1 h, well-dispersed face-centered tetragonal (fct) FePt particles could be obtained for the samples with 10 nm-thick and greater Al2O3 layers. Experimental results suggest that the protection of the amorphous 10 nm-thick Al2O3 matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L10 ordering transition through annealing. The 5 nm fct FePt-nanoparticles/10 nm-thick Al2O3-matrix sample shows higher coercivity of 5.9 kOe. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a potential new approach to fabricate patterned magnetic recording media with ultrahigh areal density.

Impact of the Al/Hf ratio on the electrical properties and band alignments of atomic-layer-deposited HfO2/Al2O3 on S-passivated GaAs substrates

HfO2, Al2O3 and HfO2/Al2O3 (AHO) nanolaminates with various Al/Hf ratios (including 1:3.0, 1:2.1 and 1:1.3) were fabricated on S-passivated GaAs substrates by atomic layer deposition (ALD). The interface structure and band alignments of various dielectric/GaAs structures have been investigated systematically. The AHO films with the Al/Hf ratio of 1:1.3 suppress the formation of As oxides and elemental As overlayers around AHO/GaAs interfaces more effectively than other samples, showing higher accumulation capacitance, less hysteresis width (ΔVFB = 415 mV) and lower leakage current density. The band alignments of interfaces of HfO2/GaAs, Al2O3/GaAs and AHO/GaAs were established. The results indicate that ALD HfO2/Al2O3 nanolaminate structures could effectively tune the interface quality and band offset of gate dielectric films on n-GaAs.

Dense random packing formation of gold cluster‐based film characterized by scanning tunneling microscope

Gold films prepared by neutral gold cluster deposition on the HF‐treated Si(111) surface in a static argon atmosphere of 50 Pa have been characterized by scanning tunneling microscope in air at room temperature. Our studies demonstrate that the gold film is just the stacking up of clusters formed in the static argon atmosphere and shows dense random packing formation of clusters. The structure of the gold cluster‐based nanophase film is very compact and stable.

UV EMISSION OF TETRAGONAL ZrO2 NANOCRYSTALS EMBEDDED IN ZrSiO4 AMORPHOUS MATRIX

Amorphous films Zr0.8Si0.2O2 were deposited on quartz substrates at room temperature, by using pulsed laser deposition technique. After annealing at high temperature, Zr0.8Si0.2O2 films suffer a phase separation to precipitate tetragonal ZrO2 nanocrystals in ZrSiO4 amorphous matrix. Their crystal structure, microstructure, optical absorbance and photoluminescence have been systematically investigated. Tetragonal ZrO2 nanocrystals show intense UV emission around 392 nm under photonic excitation with a wavelength of 250 nm. The corresponding models of electronic excitation and transition related to UV emission also have been proposed.