Impact of asymmetric electrodes on ferroelectricity of sub-10 nm HZO thin films.

In this study, platinum (Pt) and tungsten (W), two materials with dissimilar coefficients of thermal expansion (CTE) and work functions (WF), are used as the top electrode (TE) and the bottom electrode (BE) in metal/ferroelectric/metal (MFM) structures to explore the ferroelectricity of hafnium zirconium oxide (HZO) with a thickness less than 10 nm. The electrical measurements indicate that a higher CTE mismatch between HZO and TE/BE is beneficial for enhancing the ferroelectric properties of nanoscale HZO thin films. The different WFs of TE and BE generate a built-in electric field in the HZO layer, leading to shifts in the hysteresis loops and the capacitance-voltage characteristics. The structural characterizations reveal that the preferred formation of the orthorhombic phase in HZO is dominated by the W BE. The device in which W is used as the TE and BE (the W/HZO/W MFM structure) presents the optimal ferroelectric performance of a high remanent polarization (2Pr= 55.2µC cm-2). The presence of tungsten oxide (WOx) at the W/HZO interfaces, as revealed by high-resolution transmission microscopy, is also responsible for the enhancement of ferroelectric properties. This study demonstrates the significant effects of different CTEs and WFs of TE and BE on the properties of ferroelectric HZO thin films.

Effects of Electrical Parameters on Micro-Arc Oxidation Coatings on Pure Titanium.

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Study of Atomic Layer Deposition Nano-Oxide Films on Corrosion Protection of Al-SiC Composites.

In recent years, aluminum matrix composites (AMCs) have attracted attention due to their promising properties. However, the presence of ceramic particles in the aluminum matrix renders AMCs a high corrosion rate and makes it challenging to use traditional corrosion protection methods. In this study, atomic layer deposition (ALD) techniques were used to deposit HfO2, ZrO2, TiO2, and Al2O3 thin films on AMC reinforced with 20 vol.% SiC particles. Our results indicate that the presence of micro-cracks between the Al matrix and SiC particles leads to severe micro-crack-induced corrosion in Al-SiC composites. The ALD-deposited films effectively enhance the corrosion resistance of these composites by mitigating this micro-crack-induced corrosion. Among these four atomic-layer deposited films, the HfO2 film exhibits the most effective reduction in the corrosion current density of Al-SiC composites in a 1.5 wt% NaCl solution from 1.27 × 10-6 A/cm2 to 5.89 × 10-11 A/cm2. The electrochemical impedance spectroscopy (EIS) investigation shows that HfO2 deposited on Al-SiC composites has the largest Rp value of 2.0 × 1016. The HfO2 film on Al-SiC composites also exhibits effective inhibition of pitting corrosion, remaining at grade 10 even after 96 h of a salt spray test.

Improvement of Corrosion and Wear Resistance of CoCrNiSi0.3 Medium-Entropy Alloy by Sputtering CrN Film.

In this study, Co, Cr, and Ni were selected as the equal-atomic medium entropy alloy (MEA) systems, and Si was added to form CoCrNiSi0.3 MEA. In order to further improve its wear and corrosion properties, CrN film was sputtered on the surface. In addition, to enhance the adhesion between the soft CoCrNiSi0.3 substrate and the super-hard CrN film, a Cr buffer layer was pre-sputtered on the CoCrNiSi0.3 substrate. The experimental results show that the CrN film exhibits a columnar grain structure, and the film growth rate is about 2.022 µm/h. With the increase of sputtering time, the increase in CrN film thickness, and the refinement of columnar grains, the wear and corrosion resistance improves. Among all CoCrNiSi0.3 MEAs without and with CrN films prepared in this study, the CoCrNiSi0.3 MEA with 3 h-sputtered CrN film has the lowest wear rate of 2.249 × 10-5 mm3·m-1·N-1, and the best corrosion resistance of Icorr 19.37 µA·cm-2 and Rp 705.85 Ω·cm2.

Enhancement of the anticoagulant capacity of polyvinyl chloride tubing for cardiopulmonary bypass circuit using aluminum oxide nanoscale coating applied through atomic layer deposition.

For cardiopulmonary bypass, the polyvinyl chloride (PVC) circuit which can initiate the activation of platelets and the coagulation cascade after blood cell contacting is the possible detrimental effect. Surface coating of the PVC tubing system can be an effective approach to enhance circuit's hemocompatibility. In this study, aluminum oxide (Al2 O3 ) thin films were deposited through thermal atomic layer deposition (T-ALD) or plasma-enhanced ALD (PE-ALD) on PVC samples, and the anticoagulation of the Al2 O3 -coated PVC samples was demonstrated. The results revealed that Al2 O3 deposition through ALD increased surface roughness, whereas T-ALD had a relative hydrophilicity compared with blank PVC and PE-ALD. Whole blood immersion tests showed that blood clots formed on blank PVC and that a large amount of red blood cells was found on PE-ALD substrates, whereas less blood cells were noted in T-ALD samples. Both T-ALD and PE-ALD Al2 O3 films did not cause activation of blood cells, as evidenced in CD3+ /CD4+ /CD8+ , CD61+ /CD62P+ , and CD45+ /CD42b+ populations. Analysis of serum coagulation factors showed that a lower amount of prothrombin was absorbed on T-ALD Al2 O3 samples than that on blank PVC. For albumin and fibrinogen immersion tests, immunostaining and scanning electron microscopy further revealed that a thin albumin layer was absorbed on T-ALD Al2 O3 substrates but not on PVC samples. This study revealed that deposition of Al2 O3 films by T-ALD can improve anticoagulation of the PVC tubing system.

AlN epitaxy on SiC by low-temperature atomic layer deposition via layer-by-layer, in situ atomic layer annealing.

AlN thin films were epitaxially grown on a 4H-SiC substrate via atomic layer deposition (ALD) along with atomic layer annealing (ALA). By applying the layer-by-layer, in situ ALA treatment using helium/argon plasma in each ALD cycle, the as-deposited film gets crystallization energy from the plasma, which results in significant enhancement of the crystal quality to achieve a highly crystalline AlN epitaxial layer at a deposition temperature as low as 300 °C. In a nanoscale AlN epitaxial layer with a thickness of ∼30 nm, X-ray diffraction reveals a low full-width-at-half-maximum of the AlN (0002) peak of only 176.4 arcsec. Atomic force microscopy, high-resolution transmission electron microscopy, and Fourier diffractograms indicate a smooth surface and high-quality hetero-epitaxial growth of a nanoscale AlN layer on 4H-SiC. This research demonstrates the impact of the ALA treatment on the evolution of ALD techniques from conventional thin film deposition to low-temperature atomic layer epitaxy.

Suppression of GeO x interfacial layer and enhancement of the electrical performance of the high-K gate stack by the atomic-layer-deposited AlN buffer layer on Ge metal-oxide-semiconductor devices.

For high-performance nanoscale Ge-based transistors, one important point of focus is interfacial germanium oxide (GeO x ), which is thermodynamically unstable and easily desorbed. In this study, an atomic-layer-deposited AlN buffer layer was introduced between the crystalline ZrO2 high-K gate dielectrics and epitaxial Ge, in order to reduce the formation of interfacial GeO x . The results of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy demonstrate that the AlN buffer layer suppressed the formation of interfacial GeO x . Hence, significant enhancement of the electrical characteristics of Ge metal-oxide-semiconductor (MOS) capacitors was achieved with a two-orders-of-magnitude reduction in the gate leakage current, a 34% enhancement of the MOS capacitance, and a lower interfacial state density. The results indicate that the AlN buffer layer is effective in providing a high-quality interface to improve the electrical performance of advanced Ge MOS devices.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.