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Atomic Layer Deposition (ALD) is a unique vapor-phase non-line-of-sight deposition process, it can provide excellent control over the wall thickness of nanostructures at the sub-angstrom scale and can be used to create highly conformal coatings of dense inorganic film even on the nano-sized templates with high aspect ratios. Due to these inherent merits, it has become an inevitable process in current semiconductor industries. Following the success of ALD in the semiconductor industries, ALD is recently focused because it can efficiently enhance the performance of energy conversion and storage devices. As a representative example, electrochemical supercapacitors, as one type of novel power device, have attracted universal research interest because of their great potential to be applied in many fields. In particular, pseudocapacitor is recently focused due to its larger capacitance. The electrochemical energy conversion and storage performance of pseudocapacitors depends strongly on the intrinsic properties of the active electrode materials and their surface area. To maximize these performance, various nano-morphologies and transition metal oxides/hydroxides, such as NiO, Co3O4, MnO2, Ni(OH)2 and etc., having a large theoretical capacitance has been extensively investigated. Those psuedocapacitor materials, however, generally showed a high electrical resistivity and it remain unable to achieve high theoretical capacitance in practical applications. To solve these drawbacks, ultrathin conductive ALD coatings can be considered. As a representative example, we design and fabricate a novel hybrid 3D Ni(OH)2@ZnO nanostructured electrode material with a high surface area and high conductivity using a hydrothermal method and ALD. ALD-ZnO thin films were deposited on the surface of a 3D porous Ni(OH)2 nanostructure. The optimization of ALD-ZnO was performed to achieve a high conductivity and electrochemical performance. And, it was exhibited that this hybrid 3D core-shell structure, which benefits from the synergistic effects of both Ni(OH)2 and ZnO, can result in a much improved supercapacitor performance.

Proton exchange membrane fuel cell (PEMFC) is an efficient electrochemical energy conversion device that directly generates electricity from the chemical energy of fuels without the emission of greenhouse gases. The most reliable catalyst in PEMFC is Platinum (Pt) metal nanoparticles (NPs) that exhibit excellent electrochemical activity and stability compared to other catalysts. However, using of Pt catalyst is limited due to its very high cost and low abundance on Earth. Therefore, it is important to use Pt catalyst efficiently for making the PEMFC economically viable. In this regard, several synthesis techniques have been developed to reduce the loading and uniform distribution of Pt NPs on carbon support with high electrochemically active surface area (ECSA). One of the most efficient techniques to uniformly deposit Pt NPs with a controllable size on carbon support is to use a fluidized bed reactor (FBR) atomic layer deposition (ALD). Our group recently demonstrated that FBR-ALD Pt/C catalysts can exhibit high fuel cell performance and high endurance even with low Pt NPs loading by optimizing the surface of carbon supports combined with proper ALD process parameters [1]. However, it is still challenging to further improve the fuel cell performance by rational designing the Pt NPs surfaces in order to make FBR-ALD into a viable commercial production. In this study, a unique way to improve the fuel cell performance was suggested to design and optimize atomic scale surface textures of Pt NPs. During the FBR-ALD of Pt NPs, in-situ surface modulation of Pt NPs was applied via a proper protective oxide deposition and etching. A careful surface studies was performed to analyze the surface morphology, distribution and uniformity of Pt NPs. Electrochemical performances were evaluated and optimized by measuring cyclic voltammetry (CV) and oxygen reduction reaction (ORR). Finally, a fuel cell performance was studied through membrane electrode assembly (MEA) characteristics. References W. J. Lee, S. Bera, H. C. Shin, W. P. Hong, S. J. Oh, Z. wan, S. H. Kwon, Adv. Mater. Interfaces 6, 1901210 (2019).

A high dielectric constant (k = 22.5) Al-doped HfO2 film was prepared on Si substrate by plasma-enhanced atomic layer deposition (PEALD) at a reduced thickness of ~ 30 nm by realizing a (200) preferentially oriented tetragonal structure. The realization of a (200) preferred orientation was able to be obtained by the interface control in PEALD. When using a conventional supercycle that consisted of the Al2O3 and HfO2 subcycles, the dielectric constants of tetragonal Al-doped HfO2 films rapidly decreased from 37 to 8.5 as the film thickness decreased from ~ 92 to ~ 9 nm due to the change of the preferred orientation from (200) to (111). To obtain (200) preferentially oriented tetragonal Al-doped HfO2 thin films at highly thin thickness, a modified supercycle that consisted of the Hf-Al-O subcycle and the HfO2 subcycle was designed to increase Al dopant distribution in HfO2 films. As a result, a (200) preferentially oriented tetragonal Al-doped HfO2 films with a high dielectric constant of 22.5 was obtained at a reduced thickness of ~ 30 nm. Also, the leakage current densities of the Pt/~ 30 nm-thick-tetragonal Al-doped HfO2 films/Si capacitor were about 10-5 A/cm2 for a field strength of -1 MV/cm due to the crystallization after N2 annealing process.

Ru films were produced by atomic layer deposition (ALD) with an alternating supply of bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) and ozone at deposition temperatures of 225‐275 ◦ C. Ozone acted as an effective reactant for Ru(EtCp)2 .T he Ru fi lm thicknesses formed during one cycle were saturated at relatively high values of 0.09‐0.12 nm/cycle depending on the deposition temperatures, and their resistivities were about 16 μ cm. Moreover, a reduced nucleation delay was found for Ru ALD using ozone when compared to Ru ALD using oxygen gas. The amount of oxygen impurity incorporated into the Ru films was less than 1 at%, as determined by Auger electron spectroscopy. The interfacial adhesion property between Ru films prepared via ALD using ozone (ozone-Ru) and ZrO2 was good and 80% step coverage was achieved on a 3-D structure with a very high aspect ratio of 16:1, making them suitable for use as a top electrode material.

Copper (Cu) is widely adopted as an interconnection metal in advanced ultralarge-scale integration (ULSI) microelectronic devices due to its low electrical resistivity (1.67 μΩcm) and good electromigration (EM) resistance.[1,2] However, Cu easily diffuses into Si or SiO2 quickly, even at temperatures below 200°C.[2] Therefore, an adequate Cu diffusion barrier layer should be placed between Si and Cu to prevent the degradation of microelectronics devices caused by the diffusion of Cu. Of various barrier materials, tantalum nitride (TaN) has been widely used as barriers to Cu diffusion due to its immiscibility with Cu, superior thermal stability.[3.4] However, it requires an additional glue layer such as ruthenium (Ru) to enhance the adhesion properties between TaN and Cu. From a point of view on the metallization process, the insertion of additional layers, such as Ru, is not preferred because the integration of multi-layer stacked structure gets more difficult as the dimension of devices shrinks. Therefore, the development of multifunctional diffusion barrier material, which possesses a sufficient diffusion barrier property and an adequate adhesion property to Cu, has been focused for many researchers.[5,6]

In past decades, the themal inkjet (TIJ) printer has been widely used as one of the most well-known digital printing technology due to its low cost, and high printing quality. Since the printing speed of TIJ printers are much slower than that of laser printers, however, there has been intensive efforts to raise the printing speed of TIJ printers. One of the most plausible methods to raise the printing speed of TIJ printers is to adopt a page-wide array TIJ printhead. To accomplish this goal, the high efficiency inkjet heating resistor should be developed to settle the high power consumption problem of a page-wide array TIJ printhead. Recently, it was reported that atomic layer deposited RuO2-TiO2 heating resistor has many attractive properties for using it as a heating resistor such as appropriate resistivity range with a sufficiently low temperature coefficient of resistance (TCR) values and high oxidation resistance even at high temperatures. In this study, we investigated IrO2-TiO2 thin film resistor prepared by atomic layer deposition method. Similar to RuO2, IrO2 also have low resistivity and good oxygen diffusion barrier properties. Compare to Ru, the volatile phases of Ir form at above 1000°C, and no phase transformations are known in the temperature range from 4.2 to 1000K, which means that IrO2 remain more stable than RuO2 at higher annealing temperatures. The six samples were prepared and labeled as A: (IrO2)0.33-(TiO2)0.67, B: (IrO2)0.56-(TiO2)0.44, C: (IrO2)0.64(TiO2)0.36, D: (IrO2)0.72-(TiO2)0.28, and E: (IrO2)0.78(TiO2)0.22, respectively. These samples were prepared by adopting an adequate super-cycle for IrO2-TiO2 ALD, which is composed of IrO2 and TiO2 subcycle. Figure 1 shows the resistivities of the IrO2-TiO2 thin films with respect to the IrO2 intermixing ratio. At IrO2 intermixing ratios less than 0.5, the film resistivity was increased drastically with decreases in the IrO2 intermixing ratio. At IrO2-TiO2 thin films with IrO2 intermixing ratios over 0.5, however, film resistivity did not undergo a steeper rate of change with increasing IrO2 intermixing ratio. For IrO2 intermixing ratios in the range 0.55 0.78, the resistivity of the films can be controlled from 1500 to 356.7 ·cm, corresponding to appropriate resistivities for heating resistor application. The behavior of film resistivities is very similar to that of RuO2-TiO2, in which the resistivities are initially very high due to the high contents of highly resistive TiO2 and decrease gradually as the intermixing ratio of conductive oxide, RuO2 increases. With appropriate intermixing ratios (Sample C and E), the IrO2-TiO2 thin films showed lower absolute values of TCR values than TaN0.8336.1ppm/K). Compared to other systems, IrO2-TiO2 system has very small solubility above 600°C . Since their resistivities can be changed by solid solutions, therefore, the effect of O2 annealing on the resistivities of IrO2-TiO2 films were investigated, as shown in Figure 2. Though some solubility of TiO2 in IrO2 exist, the change in resistivities of IrO2-TiO2 films was below 10%. Therefore, it can be concluded that IrO2-TiO2 films can be also used as a heating resistor material.

We report on the photovoltaic properties of air-stable inverted organic solar cells in which zinc oxide (ZnO) of varying thicknesses is formed as the electron-transport layer by an atomic layer deposition (ALD) method. The device performance was found to be dependent on the ZnO thickness. Air-stable inverted solar cells with an optimized ZnO thickness reached a power conversion efficiency of 2.91%. This efficiency was found to be comparable to those of conventional organic solar cells. The use of the ZnO electron-transportlayerledtoimprovedairstability:thepowerconversionefficienciesofunencapsulatedorganicsolarcellsremained above 80% of their original values even after storage in air for thirty days.

TCO (Transparent Conducting Oxide) on flat glass is used in thin-film photovoltaic cell, flat-panel display. Nowadays, Corning® Willow Glass®, known as flexible substrate, has attracted much attention due to its many advantages such as reliable roll-to-roll glass processing, high-quality flexible electronic devices, high temperature process. Also, it can be an alternative to flexible polymer substrates which have their poor stability and degradation of electrical and optical qualities. For application on willow glass, the flexibility, electrical, optical properties can be greatly influenced by the TCO thin film thickness due to the inherent characterization of thin film in nanoscale. It can be expected that while thick TCO layer causes poor transparency, its sheet resistance become low. Also, rarely reports were focusing on the influence of flexible properties by varying TCO thickness on flexible glass. Therefore, it is very important to optimize TCO thickness on flexible Willow glass. In this study, Ti-ZnO thin films, with different thickness varied from 0 nm to 50 nm, were deposited on the flexible willow glass by atomic layer deposition (ALD). The flexible, electrical and optical properties were investigated, respectively. Also, these properties of Ti-doped ZnO thin films were compared with un-doped ZnO thin film. Based on the results, when Ti-ZnO thin films thickness increased, resistivity decreased and then saturated; transmittance decreased. The Figure of Merit (FoM) and flexibility was the highest when Ti-ZnO thickness was 40nm. The flexible, electrical and optical properties of Ti-ZnO thin films were better than ZnO thin film at the same thickness.

Proton Exchange Membrane Fuel Cell (PEMFC) is an electrochemical device that convert the chemical energy of reactants directly to electrical energy. The water-based, acidic polymer membrane usually used as its electrolyte. Therefore, the bipolar plate, as one of the most important components in PEMFC system, is required to be high corrosion resistance in the acidic condition. Currently, researchers have tried to develop metallic bipolar plate using a stainless steel. In case of using stainless steel, a passivation or protective coatings layers should be applied to improve its stability in the harsh environment. However, the general intrinsic defects (columnar structures, pinholes, pores, discontinuities) in the protective films, which can greatly affect its high performance. Therefore, a passive thin film with low defects and stable property was needed to be developed. In this work, TiN thin films were deposited on 316L stainless steel as the protective layer by using plasma enhanced atomic layer deposition (PEALD). For comparison, tetrakis-dimethylamido-titanium (TDMAT) and titanium tetrachloride (TiCl4) were used as different Ti sources, respectively. The microstructure, chemical composition and the corrosion behavior of TiN protective layer deposited by different sources were investigated by 4-point probe, XRD, FESEM, AES and potentiodynamic polarization equipment. The SEM results showed that the uniform TiN protective layers were successfully deposited on the 316L stainless steel substrate by both two sources. and the FCC crystal structure was confirmed by the XRD analysis. In addition, the TDMAT-deposited TiN has lower the corrosion current density (Icorr) and higher corrosion potential (Ecorr) than those of TiCl4-deposited TiN, which could be inferred that the TDMAT-deposited TiN will have a higher corrosion resistance and protective efficiency during the fuel cell application.

Ta-doped TiO 2 inverse opals were obtained by selective etching of a silica template after atomic layer deposition (ALD) of Ta-doped TiO 2 films and were applied as an electrode for dye-sensitized solar cells (DSSCs). Ta content in the Ta-doped TiO 2 film was controlled by the Ta/(Ta+Ti) unitcycle ratios in the Ta―TiO 2 supercycle of ALD. Also, excellent step coverage of nearly 100% in the inverse opal structure was confirmed by field-emission scanning electron microscopy (FE-SEM). Maximum photo-conversion efficiency of 1.56% was achieved with the Ta (3.4 atom %)-doped TiO 2 inverse opal electrode due to increased photocurrent density. However, further Ta doping (> 4.9 atom %) decreased the J sc and photoconversion efficiency.

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A cubic δ-TaN thin film with an electrical resistivity of 400 μΩ cm was successfully obtained by suppressing the formation of Ta 3 N 5 using two-step atomic layer deposition independent of NH 3 dosage. The deposition cycle involved two chemical reaction steps: The formation of elemental tantalum (Ta) by reducing tantalum pentafluoride (TaF 5 ) with hydrogen plasma and the subsequent nitridation of the preformed Ta with NH 3 at 200―350°C. The microstructure of the preformed Ta was β-Ta phase with an electrical resistivity of 220 μΩ cm, which was formed without regard to the deposition temperature. At a deposition temperature of less than 250°C, cubic δ-TaN with a Ta/N ratio of I was achieved independent of the NH 3 dosage. However, at a deposition temperature of greater than 300°C, the resistivity of Ta―N-based thin film increased abruptly as the NH 3 dosage exceeded 16.08 × 10 19 molecules/cm 3 due to the formation of Ta 3 N 5 .

Ti-Si-N coatings were deposited on stainless steel substrates using a hybrid coating system consisting of arc ion plating for Ti and a dc magnetron sputtering technique for Si in a gaseous N 2 /Ar mixture. On increasing the Si content in the Ti-Si-N coating, the microstructure changed from columnar to a nanocomposite. The anodic polarization measurement performed in 3 wt % NaCl solutions at room temperature revealed that Ti-Si-N coatings with higher Si contents had better corrosion resistance due to the formation of a unique nanocomposite microstructure where the highly corrosion-resistive amorphous SiN x phases surrounded the TiN crystallites.

Iridium (Ir) has been studied as a dynamic random access memory (DRAM) capacitor electrode material due to its conductive oxide phase (iridium oxide, IrO2), low resistivity, and good oxygen barrier property. As the capacitor electrode material, Ir should remain stable after high temperature annealing process in ambient oxygen, a process to crystallize high dielectric constant (high-k) materials. However, when Ir was annealed in ambient oxygen, the surface roughening occurred as shown in Fig. 1. The surface roughening of the electrode materials could degrade the capacitor properties due to film delamination or local breakdown of the high-k materials. And thus, Ir should remain stable morphologically during the highly oxidizing process. In this study, 2-step annealing process was investigated to improve the morphological stability of Ir films at the high temperature annealing in ambient oxygen. Since atomic layer deposition (ALD) techniques are the most suitable process in the integration of the DRAM capacitor due to their excellent step coverage in the 3-dimenstional structures, Ir films were prepared by plasma-enhanced atomic layer deposition (PEALD) using (ethylcyclopentadienyl)(1,5-cyclooctadiene) iridium [Ir(EtCp)(COD)] and ammonia (NH3) plasma. Compared to Ir films prepared by ALD using oxygen gas, the Ir films prepared by NH3 plasma had smooth surface and preferred (111) orientation. Figure 1 shows the surface roughness change of Ir films before and after annealing. The root-mean-square (RMS) roughness was increased drastically after annealing in ambient oxygen, however, the RMS roughness was relatively preserved after annealing in ambient argon compared to the as-deposited Ir films. Figure 2 shows the XRD analysis of Ir films before and after annealing. When Ir films annealed in ambient oxygen, IrO2 peaks were detected at an annealing temperature above 550 °C, which means that Ir was oxidized to form IrO2. This indicates that the volume expansion from oxidation led to surface roughening. However, the IrO2 peaks were disappeared at as an annealing temperature increased up to 850 °C in ambient oxygen. This is because IrO2 was reduced to Ir at the high temperature. Ir is more stable phase than IrO2 at high temperatures at the same oxygen pressure. During annealing at 850 °C in ambient oxygen, Ir was oxidized to form IrO2 during temperature rising step above 550 °C and the oxidized IrO2 was reduced to Ir at 850 °C. This oxidation and reduction process of the films led the abrupt increment of the RMS roughness. And thus, simple annealing process in ambient oxygen is not suitable process for Ir films as the electrode material applications. To adopt the high temperature annealing in ambient oxygen, a 2-step annealing process was designated. The 2-step annealing process was consisted of a temperature rising step in ambient argon and a temperature maintenance step in ambient oxygen. During the temperature rising-step, the surfaces of Ir films remained smooth because oxygen was not supplied into the rapid thermal annealing (RTA) system. After the temperature reached at 850 °C, oxygen was supplied into the RTA system and annealing in ambient oxygen was proceeded where the Ir film exists in stable condition to prevent oxidation of Ir. As a result of the 2-step annealing process, the surface of Ir films was still remained smooth and oxidation of Ir was not occurred at an annealing temperature of 850 °C as shown in Fig. 1 and Fig. 2.

Plasma-enhanced atomic layer deposition PEALD of iridium Ir films was investigated using Ir EtCp COD and NH3 plasma. Deposited Ir films had smooth surface and preferred 111 orientation. After simple annealing in ambient oxygen, surface roughening occurred because Ir was oxidized above 550°C, and the oxidized IrO2 during temperature rising was reduced to Ir at 850°C. However, by adopting two-step annealing, Ir films showed excellent thermal and morphological stability at 850°C. During two-step annealing at 850°C, the oxidation during temperature rising was suppressed by supplying argon, and annealing in ambient oxygen progressed after the temperature reached 850°C. © 2008 The Electrochemical Society. DOI: 10.1149/1.2973336 All rights reserved.

Ru-incorporated TaN (Ru-TaN) films were investigated as a Cu diffusion barrier material. Ru-TaN films were prepared by sequential deposition of Ru and TaN using plasma-enhanced atomic layer deposition (PEALD). The film composition was controlled by the number of Ru unit cycles. While the resistivity of Ru-TaN films was increased abruptly at low Ru composition (∼0.06), the resistivity of Ru-TaN films was decreased gradually as the Ru composition increased after that composition. The crystal structures of Ru-TaN films were amorphous at the Ru composition range from 0.19 to 0.52 due to disturbance of grain growth. However, the Ru-TaN films had TaN-like structure below this range and Ru-like structure above this range. The amorphous Ru-TaN films had nanocrystallite embedded structure in an amorphous matrix. This amorphous Ru-TaN barrier showed a better Cu diffusion barrier property (∼700°C) than the TaN barrier (∼650°C) because the Cu diffusion through the grain boundary was suppressed by the amorphization. In addition, the Ru-TaN barrier exhibited good adhesion to both Cu and SiO 2 .

The initial stages of ruthenium film growth in plasma-enhanced atomic layer deposition (PEALD) on titanium nitride (TiN) substrate were investigated in detail. During the initial stages of ruthenium film growth, the influence of the substrate surface was significant and controlling thickness by counting the number of deposition cycles is no longer valid. The time required for saturated adsorption of Ru(EtCp) 2 as well as the amount of deposited ruthenium atoms per cycle changed during the initial stage. The time required for saturated adsorption of Ru(EtCp) 2 on homogeneous ruthenium surfaces was 7 s. However, it increased up to 25 s during the initial stage of the ruthenium film growth where the film growth on heterogeneous TiN substrate is dominant. By considering these changes during the initial stages of ruthenium PEALD growth, the full coverage of PEALD ruthenium can be obtained at a minimum thickness of 2.7 nm.

Stacked RuO 2 /Ru structures were produced by atomic layer deposition (ALD) using an alternating supply of his(ethylcyclopentadienyl)ruthenium [Ru(EtCp) 2 ] and O 2 gas at a deposition temperature of 270°C. The type of the deposited film, either Ru or RUO 2 , was controlled by the total pressure in the ALD system as well as the ratio of the adsorbed Ru(EtCp) 2 to the partial pressure of O 2 in the following O 2 gas pulse. The resistivity of the deposited Ru and RuO 2 thin films was about 15 and 70 μΩ cm, respectively. The surface morphology of Ru films annealed in O 2 ambient was seriously degraded by surface oxidation. Moreover, RUO 2 films were also agglomerated due to the residual stress releasing during the annealing process. However, a stacked RUO 2 /Ru structure produced using ALD maintained a smooth surface even at an annealing temperature of 800°C in ambient O 2 . Auger electron spectroscopy confirmed that the stacked RuO 2 /Ru structure successfully blocked oxygen and silicon diffusion. Therefore, the stacked RuO 2 /Ru structure produced by ALD is suitable for use as the bottom electrode material for high dielectric applications.

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Ruthenium-titanium nitride (Ru-TiN) thin films were grown by plasma-enhanced atomic layer deposition (PEALD) at a growth temperature of 200°C. For the Ru-TiN PEALD, Ru and TiN were sequentially deposited to intermix TiN with Ru. The composition of Ru-TiN films was controlled by changing the number of deposition cycles allocated to Ru, while the number of deposition cycles for TiN was fixed to one cycle. The microstructures of Ru-TiN films changed from polycrystalline to amorphous, as the intermixing ratio of Ru increased in the deposited Ru-TiN films. The resistivity of the Ru-TiN film was abruptly increased by adding Ru at the first stage, but after showing a peak resistivity, it decreased with the intermixing ratio of Ru in the films. Especially, the film of Ru 0.67 -(TiN) 0.33 showed an electrical resistivity of 190 μΩ cm. As a Cu diffusion barrier layer, amorphous Ru-TiN films showed a superior copper diffusion barrier property to TiN or Ru itself, which had a polycrystalline structure. Moreover, Ru-TiN films showed a good adhesion to both chemical vapor deposition copper and an underlayer of SiO 2 .

Ruthenium thin films were produced by plasma-enhanced atomic layer deposition (PEALD) using an alternating supply of bis(ethylcyclopentadienyl)ruthenium and plasma at a deposition temperature of 270°C. The film thickness per cycle was self-limited at 0.038 nm/cycle, which was thinner than the thickness obtained from the conventional ALD using oxygen instead of plasma. The ruthenium thin film prepared with PEALD had a preferential orientation toward (002), and it was progressively promoted with plasma power. The PEALD of ruthenium shows a merit in controlling ultrathin film thickness with less than 2 nm more precisely and more easily than the conventional ALD, due to the reduced transient period at the initial film growth stage. Also, ruthenium thin film improved the interfacial adhesion of metallorganic chemical vapor deposited copper to diffusion barrier metals by forming Cu-Ru chemical bonds at the interface without degrading the film resistivity of copper. © 2004 The Electrochemical Society. All rights reserved.