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Atomic layer deposition (ALD) is a thin-film fabrication method that can be used to deposit films with precise thickness controllability and uniformity. The low deposition temperature of ALD, however, often interrupts the facile crystallization of films, resulting in inferior optical and electrical properties. In this study, the extremely localized crystallization of TiO2 thin films was demonstrated by per-cycle plasma treatment during the plasma-enhanced ALD process. By layering crystalline and amorphous films, a phase-gradient TiO2 film with precisely modulated optical and electrical properties was fabricated. Moreover, the ratio between the amorphous and crystalline layer thicknesses for a high dielectric constant and low leakage current density was optimized.

In this study, we demonstrated the seed layer mediated growth of high-quality BaTiO3 (BTO) thin films using a two-step radio frequency (RF) magnetron sputtering process. Since the as-grown BTO thin films obtained by RF magnetron sputtering at the deposition temperatures of 300–500 °C were amorphous with a low dielectric constant of 20, it is necessary to develop a fabrication process for obtaining crystalline high-k BTO thin films without sacrificing other film properties such as morphology and leakage current. First, it was revealed that ex-situ post-deposition annealing (PDA) at high temperatures in the 700–800 °C range led to the crystallization of BTO films and a high dielectric constant of 121. However, the film morphology deteriorated significantly during PDA, and consequently, a high leakage current was observed due to the rough and discontinuous surface containing voids and micro-cracks. To achieve an excellent leakage current characteristic as well as a high dielectric constant for a crystalline BTO thin film, in-situ crystallization was carried out through local epitaxial growth using a crystalline seed layer. The crystalline BTO seed layer was formed by annealing a 5-nm-thick amorphous BTO film at 700 °C on which the in-situ crystallized BTO main layer was deposited at 500 °C. The in-situ crystallization method resulted in a smooth and uniform surface and a high dielectric constant of 113. In addition, the in-situ crystallized BTO film exhibited a low leakage current density of 10−6 A/cm2 (at 0.8 V) displaying an improvement by a factor of 103 compared to the ex-situ crystallized BTO film.

The continuous device scaling of dynamic random access memories has been increasing demands for the development of dielectric materials with high dielectric constants and low leakage currents. In this study, we developed MgO thin films through atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)magnesium combined with two different reactants, H2O or O2 plasma, and compared the physical and chemical characteristics of MgO thin films produced by thermal ALD (Th-ALD) and plasma-enhanced ALD (PEALD). The films were deposited in a temperature range of 200–400 °C, and self-limited surface reactions were observed for both ALD processes. Th-ALD MgO films showed the oxygen deficient composition, while more stoichiometric MgO films were achieved by PEALD process. To evaluate the electrical characteristics of the MgO films, the metal–insulator–metal capacitors were fabricated. The electrical characteristics of the MgO film, such as the dielectric constant and leakage current, were compared according to the reactant type. The bulk-limited leakage current conduction mechanisms of the Th-ALD and PEALD MgO thin films were also investigated.

The synthesis of a continuous and high-quality large-area layer is a key research area in the field of two-dimensional (2D) metal chalcogenides. To date, several techniques, including chemical vapo...

In2O3 films were deposited by atomic layer deposition (ALD) using a newly synthesized heteroleptic In precursor, In(DMAMP)2(OiPr), and O3 at 150–300 °C. Self-limiting growth characteristics were exhibited for a wide ALD temperature range of 200–300 °C and growth rate of 0.029–0.033 nm/cycle. At a low temperature of 150 °C, the amorphous In2O3 film was deposited, while polycrystalline In2O3 films were achieved at 200–300 °C. The In2O3 films grown in this ALD temperature range had high densities of 7.0–7.2 g/cm3, which are comparable to those of bulk In2O3. At all growth temperatures (150–300 °C), no carbon or nitrogen impurities were detected, suggesting high reactivity of the In(DMAMP)2(OiPr) precursor. The ALD In2O3 films showed n-type electronic property with high electron concentrations of 1.6 × 1020–3.6 × 1020/cm3 and a Hall mobility of 31–39 cm2/V·s.

Atomic layer deposition (ALD) of SnO and SnO 2 thin films was successfully demonstrated over a wide temperature range of 70–300 °C using a divalent Sn-precursor, bis( N- ethoxy-2,2-dimethyl propanamido)tin (Sn(edpa) 2 ). The regulated growth of the SnO 2 and SnO films was realized by employing O 2 -plasma and H 2 O, respectively. Pure SnO 2 and SnO films were deposited with negligible C and N contents at all the growth temperatures, and the films exhibited polycrystalline and amorphous structures, respectively. The SnO 2 films presented a high transmittance of > 85% in the wavelength range of 400–700 nm and an indirect band gap of 3.6–4.0 eV; meanwhile, the SnO films exhibited a lower transmittance of > 60% and an indirect band gap of 2.9–3.0 eV. The SnO 2 films exhibited n-type semiconducting characteristics with carrier concentrations of 8.5 × 10 16 –1.2 × 10 20 cm −3 and Hall mobilities of 2–26 cm 2 /V s. By employing an alternate ALD growth of SnO and SnO 2 films, SnO 2 /SnO multilayer structures were successfully fabricated at 120 °C. The in-situ quadrupole mass spectrometry analysis performed during ALD revealed that the oxidation of chemisorbed Sn-precursor occurs dominantly during the Sn(edpa) 2 /O 2 -plasma ALD process, resulting in the production of combustion by-products, whereas the Sn(edpa) 2 /H 2 O ALD process was governed by a ligand exchange reaction with the maintenance of the original oxidation state of Sn 2+ .

Herein, we performed a comparative study of plasma-enhanced atomic layer deposition (PEALD) of SnO2 films using Sn(dmamp)2 as the Sn source and either H2O plasma or O2 plasma as the oxygen source in a wide temperature range of 100&ndash, 300 &deg, C. Since the type of oxygen source employed in PEALD determines the growth behavior and resultant film properties, we investigated the growth feature of both SnO2 PEALD processes and the various chemical, structural, morphological, optical, and electrical properties of SnO2 films, depending on the oxygen source. SnO2 films from Sn(dmamp)2/H2O plasma (SH-SnO2) and Sn(dmamp)2/O2 plasma (SO-SnO2) showed self-limiting atomic layer deposition (ALD) growth behavior with growth rates of ~0.21 and 0.07&ndash, 0.13 nm/cycle, respectively. SO-SnO2 films showed relatively larger grain structures than SH-SnO2 films at all temperatures. Interestingly, SH-SnO2 films grown at high temperatures of 250 and 300 &deg, C presented porous rod-shaped surface morphology. SO-SnO2 films showed good electrical properties, such as high mobility up to 27 cm2 V&minus, 1&middot, s&minus, 1 and high carrier concentration of ~1019 cm&minus, 3, whereas SH-SnO2 films exhibited poor Hall mobility of 0.3&ndash, 1.4 cm2 V&minus, 1 and moderate carrier concentration of 1 &times, 1017&ndash, 30 &times, 1017 cm&minus, 3. This may be attributed to the significant grain boundary and hydrogen impurity scattering.

Carbon nanofibers (CNFs) are used as active materials for electrodes in various energy devices, such as lithium ion secondary batteries, supercapacitors, and fuel cells. Recent studies have shown that nanoscale coatings on carbon nanotubes increase the output and lifespan of these devices owing to the improvement of their mechanical and chemical properties. Among various coating methods, atomic layer deposition (ALD) can adjust the thickness of the coating layer conformally without any directional growth. Therefore, ALD can coat particles with high aspect ratios, such as CNFs, even at nanometer levels of thickness. In this work, we grew two different morphologies of a SnO2 layer on CNF. We used two types of ALD equipment: flow-type ALD (static ALD), and fluidized bed reactor-type ALD (dynamic ALD). Static ALD could form a discontinuous SnO2, while a uniform SnO2 layer was formed by pre-inserting a layer of Al2O3. On the other hand, dynamic ALD formed a uniform SnO2 layer without pre-insertion of an Al2O3 layer. X-ray photoelectron spectroscopy analysis revealed that both Sn4+ and Sn2+ were present in SnO2 on the CNF deposited by static ALD, probably due to the formation of an interfacial layer between the SnO2 and CNF. When the dynamic ALD method was used, only Sn4+ was present in the SnO2 on CNF. Cyclic voltammetry analysis was performed to characterize the electrochemical properties of the SnO2-coated CNF as an electrode on a direct methanol fuel cell. It was revealed that the discontinuous SnO2 on CNF deposited by static ALD showed the highest current efficiency as well as enhanced electrocatalytic stability.

Inhomogeneous superconductivity in rare-earth (RE)-doped CaFe2As2 (Ca122) compounds leads to a novel state of matter in which the superconducting and magnetic states can be simultaneously controlled by using an electric current (I). Both La- and Ce-doped Ca122 single crystals show a very broad superconducting transition width (ΔTc) due to their non-bulk nature. Surprisingly, ΔTc becomes sharper or broader after an electric current larger than a threshold value (It) is applied, with a concomitant change in the normal-state magnetism. The sharpened (broadened) ΔTc is accompanied by a decrease (an increase) in the amplitude of the ferromagnetic signals. The sensitive changes in the superconductivity and magnetism that occur when an external current is applied are related to the inhomogeneous electronic states that originate from the Fe magnetic state and/or self-organized superconducting/magnetic composites in Ca122 compounds. These discoveries shed new light on the role of Fe in Fe-based superconductors and will provide new ideas for the design of novel superconducting devices. Clues to the superconducting behavior of a complex, iron-based substance can be revealed with a technique based on electric current. When rare-earth atoms are incorporated into calcium–iron–arsenic (CaFe2As2) crystals, simultaneous magnetic and superconductive properties emerge after cooling below 50 K. Soon-Gil Jung and Tuson Park from South Korea’s Sungkyunkwan University, Suwon, and colleagues report that passing milliamp-level electric currents through rare-earth-doped CaFe2As2 causes unexpected shifts in superconducting transition temperatures and magnetic field responses. In some samples, a sharpening of the superconductivity onset point was accompanied by a loss of magnetic signals, while in others magnetism improved at the expense of well-defined superconducting temperatures. The researchers conclude that these changes arise from inhomogeneities within doped CaFe2As2, possibly from iron magnetic states or tiny self-assembled nanocomposites that become unstable past a current threshold. Large inhomogeneous electronic states in rare-earth-doped CaFe2As2 produce striking results of manipulating the superconducting phases via current-driven magnetic state. Magnetization hysteresis loops at superconducting state (2 K) and normal state (50 K) for La-doped CaFe2As2 are largely changed by the electric current because their high-Tc regions are localized. Current path between high-Tc regions is considered as a long wire, thus current-induced large magnetic field around the path can modulate the magnetic state in normal/weak superconducting regions. These observations provide new insights into the role of Fe in the Fe-based superconductors and ideas for the design of new superconducting devices.

The fabrication of high-k BaTiO3 (BTO) films for applications such as multilayer ceramic capacitors or dynamic random access memory has been achieved via the ex-situ crystallization of amorphous BTO into perovskite structure through post-deposition annealing (PDA). However, high-temperature PDA at temperatures exceeding 700 °C results in the severe degradation of BTO properties. In other words, ex-situ crystallization via PDA results in an increased dielectric constant but is accompanied by inferior leakage current characteristics caused by rough surface morphologies and defects such as voids and cracks. In this study, we demonstrate the in-situ crystallization of BTO films by introducing a high-quality SrRuO3 (SRO) film as a seed layer. The SRO film is deposited using rf magnetron sputtering at 270 °C–500 °C, and stoichiometric SRO films are obtained on SiO2, Al2O3, and TiN substrates by controlling the growth temperature; subsequently, rapid thermal annealing at 700 °C is conducted to crystallize the SRO film. The polycrystalline SRO film on the TiN substrate exhibits excellent morphology with uniform grains as well as a continuous and smooth surface, whereas the SRO films on the SiO2 and Al2O3 substrates exhibit rough and discontinuous surfaces. The SRO seed layer on TiN permits the in-situ growth of crystalline BTO films at a relatively low temperature of 500 °C featuring a high dielectric constant of 160 and a low leakage current density of 9.5 × 10-7 A/cm2 at 0.8 V, which are 2.2 and 3.3 × 107 times improved compared with those of the ex-situ crystallized BTO film on bare TiN, respectively.

Aluminum oxide (AlO x ) thin films were synthesized by mist-chemical vapor deposition (mist-CVD) using aluminum acetylacetonate (Al(acac) 3 ) dissolved in an aqueous solvent mixture of acetone and water. Nitrogen gas was used to purge the precursor solution and growth rates between 7.5–13.3 nm/min were achieved at substrate temperatures of 250–350 °C. The AlO x layers deposited at temperatures below 350 °C exhibit 3–5 at% residual carbon levels, however those grown at 350 °C exhibit only 1–2 at% carbon impurity. Reasonable dielectric properties were obtained in the latter, with a dielectric constant (κ) of ~ 7.0, breakdown field of ~ 9 MV/cm and relatively low leakage current density of ~ 8.3×10 −10 A/cm 2 .

Novel indium complexes [(CH3)2In(OR)]2 (1–7) were synthesized using a series of donor-functionalized alkoxide ligands as potential precursors for thin-film applications. These complexes showed dimeric configurations with two μ2-O bridging between the metal centers. Moreover, the indium metal centers in these complexes exhibited pentacoordinated states with distorted trigonal-bipyramidal geometry. The complexes were characterized by Fourier transform (FT)-infrared, and FT-nuclear magnetic resonance spectroscopies, elemental analyses, and thermogravimetric analyses (TGA). The TGA curves of complexes 4 and 7 exhibited a single-step mass loss at 100–275 °C, indicating good volatility and thermal stability.

A sneak path current—a current passing through a neighboring memory cell—is an inherent and inevitable problem in a crossbar array consisting of memristor memory cells. This serious problem can be alleviated by serially connecting the selector device to each memristor cell. Among the various types of selector device concepts, the diffusive selector has garnered considerable attention because of its excellent performance. This selector features volatile threshold switching (TS) using the dynamics of active metals such as Ag or Cu, which act as an electrode or dopant in the solid electrolyte. In this study, a diffusive selector based on Ag-doped HfOx is fabricated using a co-sputtering system. As the Ag concentration in the HfOx layer varies, different electrical properties and thereby TS characteristics are observed. The necessity of the electroforming (EF) process for the TS characteristic is determined by the proper Ag concentration in the HfOx layer. This difference in the EF process can significantly affect the parameters of the TS characteristics. Therefore, an optimized doping condition is required for a diffusive selector to attain excellent selector device behavior and avoid an EF process that can eventually degrade device performance.

As the device scaling of dynamic random access memory continues, the demand for the development of new dielectric film with high permittivity and low leakage current that may replace the currently used ZrO2/Al2O3-based dielectric film has increased drastically. In this aspect, MgO thin film has been spotlighted due to its high band gap (7-8 eV) and moderate dielectric constant (9-10). In this study, we investigated the growth behavior and film properties of the MgO ALD film using Mg(EtCp)2 precursor and the different reactants of H2O and O2 plasma. MgO thin films were deposited at the temperature range of 200-400°C, and the self-limited surface reaction was observed to secure optimal growth conditions. Glancing angle X-ray diffraction and X-ray photoelectron spectroscopy were used to examine crystalline structure and chemical properties, respectively. To evaluate the electrical characteristics of the MgO films, the Pt/MgO/TiN capacitor was fabricated with different MgO thicknesses at various deposition temperatures. The electrical characteristics such as dielectric constant and leakage current density of the MgO film were examined depending on the reactants, and the leakage current conduction mechanism of the MgO thin films was elucidated. Figure 1

The clinching process has been shown to be able to join dissimilar material sheets as an alternative to spot welding. In this study, monotonic and fatigue tests were conducted using tensile-shear specimens for an evaluation of the strengths of a joint. In the fatigue tests, an interface failure occurred. The fatigue ratio of the joint is 0.29, assuming a fatigue endurance limit at 2 x106 cycles. The maximum von-Mises stress of the joint at the load amplitude corresponding to the fatigue endurance limit is slightly higher than the yield strength of Al-5052 alloy. This indicates that the strength of the neck region is increased partially due to work hardening.

Although perovskite tin titanate (SnTiO3, STO) has been predicted to have ferroelectricity with a large spontaneous polarization, the implementation of metastable perovskite STO remains a great challenge. In this study, the atomic layer deposition of STO films was attempted using bis(1-dimethylamino-2-methyl-2-propoxy)tin(II) as the Sn source, titanium-tetrakis-isopropoxide as the Ti source, and water as the oxygen source. It was found that during the process, adsorption of both the precursors was enhanced on the heterogeneous reaction surface because of the correlation growth behavior. STO films remained amorphous below 250 °C. Furthermore, although the film was crystallized at 270 °C, the perovskite phase was not identified. Despite the use of the Sn precursor with Sn2+, Sn ions in all the films transformed into Sn4+. Although the postdeposition annealing process in a forming gas atmosphere was conducted for the perovskite conversion, the STO film transformed into Ti5Sn3, an intermetallic compound, at 500 °C.

The strain states of [111]-, [110]-, and [002]-oriented grains in poly-crystalline sputtered (Ba,Sr)TiO(3) thin films on highly [111]-oriented Pt electrode/Si substrates were carefully examined by X-ray diffraction techniques. Remarkably, [002]-oriented grains respond more while [110]- and [111]-oriented grains do less than the theoretically estimated responses, which is understandable from the arrangement of the TiO(6) octahedra with respect to the stress direction. Furthermore, such mechanical responses are completely independent of the degree of crystallization and film thickness. The transition growth temperature between the positive and negative strains was also different depending on the grain orientation. The unstrained lattice parameter for each type of grain was different suggesting that the oxygen vacancy concentration for each type of grain is different, too. The results reveal that polycrystalline (Ba,Sr)TiO(3) thin films are not an aggregation of differently oriented grains which simply follow the mechanical behavior of single crystal with different orientations.

Ruthenium (Ru) has attractive material properties due to its promising characteristics such as a low resistivity (7.1 μΩ·cm in the bulk), a high work function (4.7 eV), and feasibility for the dry etch process. These properties make Ru films appropriate for various applications in the state-of-art semiconductor device technologies. Thus, it has been widely investigated as an electrode for capacitor in the dynamic random access memory (DRAM), a metal gate for metal-oxide semiconductor field effect transistor (MOSFET), and a seed layer for Cu metallization. Due to the continuous shrinkage of microelectronic devices, better deposition processes for Ru thin films are critically required with excellent step coverages in high aspect ratio (AR) structures. In these respects, atomic layer deposition (ALD) is a viable solution for preparing Ru thin films because it enables atomic-scale control of the film thickness with excellent conformality. A recent investigation reported that the nucleation of ALD-Ru film was enhanced considerably by using a zero-valent metallorganic precursor, compared to the utilization of precursors with higher metal valences. In this presentation study, we will display our research results on the synthesis and characterization of novel ruthenium complexes. The ruthenium compounds were easy synthesized by the reaction of ruthenium halide with appropriate organic ligands in protic solvent, and characterized by NMR, elemental analysis and thermogravimetric analysis. ALD of Ru film was demonstrated using the new (zero-valent) Ru metallorganic precursor and O2 as the Ru source and reactant, respectively, at the deposition temperatures of 300-350oC. Self-limited reaction behavior was observed as increasing Ru precursor and O2 pulse time, suggesting that newly developed Ru precursor is applicable for ALD process. Detailed discussions on the chemical and structural properties of Ru thin films as well as its growth behavior using new Ru precursor will be also presented.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

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Dynamic random access memory (DRAM) is used as the main memory of every modern computer, due to its high density, high speed and efficient memory function. For successful operation of DRAM, a large cell capacitance (~ 25 fF) and low leakage current (10 A/cm or 1 fA/cell) are required. In a traditional Si-based capacitor, the target cell capacitance has been achieved by increasing the surface area of the capacitor. More recently, innovations have been made in the component materials. A metal electrode, TiN or Ru, and a dielectric material with a higher-k value (k is the relative dielectric constant), such as HfO2 (k ~ 25) and ZrO2 (k ~ 40), are being explored in giga-bit scale DRAMs. The minimum achievable tox is ~ 0.7 nm for ZrO2 which are currently being used in the DRAM industry. However, the technology road map for memory devices states that tox less than 0.5 nm is necessary for the DRAMs with a design rule of < 40 nm. Perovskite-based dielectric films such as SrTiO3 and (Ba,Sr)TiO3 were reported to exhibit k values of several hundreds. However, growth of these films is extremely difficult with the atomic-layerdeposition (ALD) which is a method of choice for the growth of the dielectric films in microelectronic devices. In this presentation, the authors will report rutile TiO2 (k value ~100) based capacitor technology. The possible leakage current by the small energy gap of 3.1 eV rutile TiO2 was tweaked by the elaborate doping of TiO2 films with Al atoms. A minimum tox ~ 0.4 nm was achieved with the safe leakage current density. A crucial problem related with the high cost of Ru material was alleviated by adopting ultra-thin Ru/TiN electrode. Some specific Ru electrode material that offers a superior dielectric performance of the capacitor was also introduced. The merit of oxide electrode (ex. RuO2) over its metal counterpart is also discussed. Figure 1 shows the summary of the leakage current vs. tox data from the TiO2 and Al-doped TiO2 thin films on Ru (30 nm) and Ru (3 nm)/TiN electrode. The growth of thinner Ru films on TiN electrode are influenced by the TiN layer and show a even improved dielectric performance of TiO2 film grown on top.

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TiO2 thin films with high dielectric constants (83 - 100) were grown on sputtered and atomic-layer-deposited (ALD) Ru electrode at a growth temperature of 250oC using the atomic- layer-deposition method. The as-deposited films were crystallized with rutile structure. Further improvements in the leakage current characteristics are achieved by proper doping of Al and Hf, thereby an equivalent oxide thickness (tox) ~ 0.6 nm with small enough leakage current density (1 x 10-7 A/cm2 at 0.8V) was achieved. These good properties are also realized from 3D structured hole-type capacitors. The rutile structured TiO2 films were also obtained from Ru electrode which is deposited by an ALD process using a newly developed noble precursor. In addition, it was confirmed that the Ru metal film step coverage on the capacitor hole structure with an aspect ratio of 17 is > 90 %. The thermal stability of the Ru electrode on severe 3D holes was improved with the adoption of hydrogen plasma process.