We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3).

The authors present a new method to determine film thicknesses and sticking coefficients (SC) of precursor molecules for atomic layer deposition (ALD) in high aspect ratio three dimensional (3D) geometries as they appear in microelectromechanical system manufacturing. The method combines a specifically designed experimental test structure with the theoretical predictions from a novel 3D Monte Carlo process simulation for large structures. The authors exemplify our method using Al2O3 and SiO2 ALD processes. SCs for trimethylaluminium and bis-diethyl aminosilane (BDEAS) are extracted. The SC for BDEAS is determined for the first time.

In this work, a process for the thermal activated atomic layer deposition (ALD) of ruthenium from the organometallic heteroleptic precursor [(ethylcyclopentadienyl)(pyrrolyl)ruthenium] with molecular oxygen was developed and characterized. Silicon substrates were precleaned in hydrofluoric acid and preheated to a specific temperature before coating with ruthenium. The corresponding cycle-by-cycle growth was monitored throughout the entire ALD process time, utilizing an in-situ real-time spectroscopic ellipsometer. Transmission electron microscopy and atomic force microscopy were applied at a reference sample to generate an appropriate optical model for the translation of the ellipsometric spectra into Ru film thicknesses. Given a representative set of process parameters the cycle-by-cycle growth was studied in detail, obtaining information about incubation, nucleation, linear growth and delamination. In order to determine the ALD characteristic dependencies, the following process parameters were varied while applying ellipsometry during the linear film growth regime on as-deposited ruthenium film surfaces; thus excluding effects from the initial foreign substrate material: both reactant doses and purging times, the substrate temperature and the total pressure. During the respective film growth experiments, one process parameter-setting was changed each 15 ALD cycles, which enabled a fast and extensive process development.

We demonstrate a top-down fabricated reconfigurable field effect transistor (RFET) based on a silicon nanowire that can be electrostatically programmed to pand n-configuration. The device unites a high symmetry of transfer characteristics, high on/off current ratios in both configurations and superior current densities in comparison to other top-down fabricated RFETs. Two NiSi2/Si Schottky junctions are formed inside the wire and gated individually. The narrow omega-gated channel is fabricated by a repeated SiO2 etch and growth sequence and a conformal TiN deposition. The gate and Schottky contact metal work functions and the oxide-induced compressive stress to the Schottky junction are adjusted to result in only factor 1.6 higher p-than n-current for in absolute terms identical gate voltages and identical drain voltages.