Reactive Sputtering Process Research Articles

(Invited) Influence of Target-Sample Distance on Residual Stress for Sputter-Deposited Ferroelectric AlScN

Ferroelectric Al1-x Sc x N films have been extensively studied as a material for next-generation non-volatile ferroelectric memories. A high remnant polarization (P r) of over 100 µC/cm2 is attractive even under 10 nm thin films [1,2]. As the role of Sc atoms in the AlN crystal to apply tensile stress, the elongation in the lattice constant eases the displacement of N atoms by an electric field. Besides, one of the issues of ferroelectric AlScN films is the increase in E C while thinning the thickness. The source of the change is explained by the stress applied from the bottom electrode. We have made a Raman spectroscopy study to measure the stress in AlScN films with different thicknesses, and find that higher compressive stress is presented for thinner film, especially for higher Sc composition films [3]. However, the physical source of the stress is yet to be known. In this presentation, a Raman spectroscopy measurement was conducted on AlScN films with different target-sample (T/S) distance, which can strongly affect the stress in the film, as reported in TiN case [4]. Al0.7Sc0.3N films were deposited on (0001) sapphier substrates by reactive sputtering process. Film thickness were varied from 5 to 50 nm to confirm the thickness dependence stress in the films. The T/S distance was set to 100, 130, and 150 mm. Differetial Raman spectra obtained by subtracting the signal of sappire substrate is shown in fig. 1. We can confirm two broad and weak peaks indicated with doted line around 580 (E2 H) and 850 /cm (A1LO). The two Raman peaks show a slight blue shift with longer T/S distance. The obtained Raman shifts on thickness are summarized in fig. 2. A blue shift is observed for both peaks while thinning the thickness. With longer T/S distance, the shift in E2 H was fully relaxed even with a thickness of 5 nm. On the other hand, only a limited relaxation was obtained with A1LO. In conclusion, we have confirmed that longer T/S distance can relax the thickness-dependent compressive stress in AlScN films. The stress relaxation can contribute to stabilize the coercive field for thin ferroelectric AlScN films. Acknowledgement This study was supported by MEXT Initiative to Establish Next-generation Novel Integrated Circuits Centers (X-NICS) JPJ011438 Reference [1] S. Fichtner, N. Wolff, F. Lofink, L. Kienle, and B. Wagner, “AlScN: A III-V semiconductor based ferroelectric,” J. Appl. Phys. 125, 114103 (2019). [2] G. Schönweger, N. Wolff, M. R. Islam, M. Gremmel, A. Petraru, Kienle, H. Kohlstedt, S. Fichtner” In-Grain Ferroelectric Switching in Sub-5 nm Thin Al0.74Sc0.26N Films at 1 V” Adv. Sci. 10, 2302296 (2023) [3] Y. Tokita, T. Hoshii, H. Wakabayashi, K. Tsutsui, K. Kuniyuki “Identification of cpmpressive strain in thin ferroelectric Al1-xScxN filns by Raman spectrascopy” Jpn. J. Appl. Phys. 63 04SP31 (2024) [4] A. Neidhardt, U. Reinhold, E. schroeter, W. Wuttke ” Position dependence in planar magnetron sputtering of TiN films” Thin Solid Films, 173109 127 (1989) Figure 1

Semiconductor WO3 thin films deposited by pulsed reactive magnetron sputtering

A pulsed reactive magnetron sputtering system with a tungsten target and a gas mixture of argon and oxygen was investigated as a source for the deposition of semiconductor WO3 thin films on soda lime glass substrates and on the glass with transparent conductive SnO2:F (FTO) electrode. The reactive sputtering process was performed in HiPIMS mode with low pulse repetition frequency fp ≈ 50–100 Hz and short pulse duration in HiPIMS discharge Ton = 100 μs. The second mode investigated was the mid-frequency (MF) magnetron discharge with pulse frequency fp = 40 kHz and pulse length Ton = 15 μs. The plasma parameters were investigated for both HiPIMS and MF modes using the planar RF probe operating at the frequency fprobe = 350 kHz and the grid QCM with biased collector electrode. Ion density ni and tail electron temperature (Te) were determined in both pulsed reactive magnetron sputtering discharge modes with time resolution. The maximum value ni ≈ 5 · 1017 m−3 was found in the reactive HiPIMS mode, and the maximum value ni ≈ 7 · 1016 m−3 was found in the reactive MF (40 kHz) mode. The degree of ionization of sputtered particles in reactive HiPIMS was determined for different values of (QO2) and was found to be in the range of ri ≈ 0.1–0.3. The deposition rate determined by QCM in reactive HiPIMS was practically independent on (QO2), but in the case of reactive MF, the measured deposition rate decreased significantly with increasing (QO2). The WO3 films deposited in both modes have a predominantly monoclinic crystal structure. The light and dark conductivity and the light/dark conductivity ratio (Ld) were measured under dark conditions and UV light illumination. At higher (QO2), the maximum value of Ld ≈ 300 was found for MF deposited WO3 and the maximum value of Ld ≈ 30 was found for HiPIMS deposited WO3. The photoelectrochemical measurement of WO3 deposited on FTO electrodes confirmed the n-type conductivity, and these films functioned as photoanodes in photoelectrochemical cells. MF deposited WO3 films systematically exhibited slightly higher photocurrents than HiPIMS deposited WO3. It was shown that these optimum photocurrents for HiPIMS and MF were found at QO2 ≈ 80 sccm and could not be improved by further increasing of (QO2).

Compositional changes between metastable SnO and stable SnO2 in a sputtered film for p-type thin-film transistors

p-Type tin(II) oxide (SnO (Sn2+)) formation using radiofrequency (RF) reactive magnetron sputtering and post-deposition annealing (PDA) processes was investigated. The as-grown SnOx film deposited from an SnOx (SnO:Sn = 60:40) target by RF sputtering at an oxygen partial pressure (PO2) of 0 Pa consisted of 2 % Sn (Sn0), 42 % Sn2+, and 56 % SnO2 (Sn4+). However, compared with the Sn2+ fraction observed after PDA under N2 and low-vacuum (∼1 Pa) conditions, that after PDA at 300 °C under high vacuum (< 5 × 10−4 Pa) (HVPDA) increased substantially to greater than 62 %. This result was attributed to the transformation from SnO2 to SnO during HVPDA. A staggered bottom-gate thin-film transistor with an SnO channel (10 nm), which was fabricated by HVPDA at 300 °C, exhibited p-type properties, including a relatively high on-current/off-current (Ion/Ioff) ratio of 5.1 × 104 and a hole field-effect mobility (µFE) of 1.8 cm2/(V·s).

Structural, linear/nonlinear optical characteristics and radiation shielding effectiveness of Cu4O3/Cu2O dual-phase thin films: Influence of oxygen flow rate in reactive sputtering process

In the present work, we investigated the impact of oxygen flow rate on the structural, linear, and nonlinear optical characteristics while also evaluating the radiation shielding effectiveness during reactive radio frequency (rf) sputtering in the deposition of Cu4O3/Cu2O dual-phase thin films. Microstructural analysis revealed distinct changes with increased OFRs, switching from a Cu2O cubic structure phase to a Cu4O3 tetragonal structure phase. The XRD patterns revealed good crystallinity, and the crystallite size of the film reduced from 28 nm to 22 nm, and the microstrain exhibited an opposing trend as the oxygen flow rate increased. In contrast, investigating the optical properties of dual-phase Cu4O3 and Cu2O thin films using UV–Vis–NIR spectroscopy revealed intriguing trends in the absorbance spectra, absorption coefficient, and extension index. The apparent bandgap increases from 2.0 eV to 2.62 eV with increasing oxygen flow rates. In addition, nonlinear optical parameters, including the nonlinear refractive index n2 linear, nonlinear sensitivity (χ1 and χ3), and nonlinear absorption coefficient βc were calculated to demonstrate the applicability of these materials. The dual-phase structure of the films enhances their potential for effective radiation shielding. Our findings provide valuable insights into the design of properties of Cu4O3/Cu2O dual-phase thin films for applications ranging from photoelectric and nonlinear optical devices to radiation shielding effectiveness.

Oxygen plasma treatment WO3 nanorods for Improvement H2S gas sensing

Herein, the oxygen (O2) plasma has been used to post-treat tungsten oxide (WO3) nanorods to improve the sensing performance of the H2S gas sensor. The reactive DC magnetron sputtering process with the glancing-angle deposition (GLAD) technique was used to prepare the WO3 nanorods. After deposition, the WO3 nanorod thin films were treated with O2 plasma at different treatment power from 100 – 200 W. The physical structure of as-deposition and treated WO3 nanorod thin films was investigated crystal structure and morphology by grazing incident X-ray diffraction (GIXRD), field-emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscope (HRTEM). The result indicated that the WO3 nanorod structure transformed to the monoclinic polycrystalline phase. FE-SEM and HRTEM observed slight changes in the shape of the WO3 nanorods. The H2S sensing properties were measured at 10 ppm at 150 – 350°C operating temperatures. At an operating temperature of 200 °C, the response to H2S of O2 plasma treated WO3 nanorods is increased by a factor of 5 – 15, and the maximum response to H2S is 15. The results showed that the O2 plasma treatment process improved the sensing response of the WO3 nanorods.

Basic principles of modeling reactive sputtering

This work describes a number of principles, which are proved to be effective in modeling various physical and chemical processes. In the article, a process model is defined as its representation using another similar (or identical) process built on a number of simplifying assumptions. This model is called physicochemical. The main phenomena on the surfaces and in the gas environment of the sputtering system, used for modeling, are identified. A scheme for deriving a system of equations describing the process is given. An example of modeling based on a non-isothermal surface chemical reaction is described. It shows the possibility of studying experimentally immeasurable dependencies characterizing the process of reactive sputtering. The article is addressed mainly to aspiring researchers who have dared to try to understand the features of reactive sputtering models proposed by different authors.

Titanium oxynitride thin films by the reactive sputtering process with an independent pulsing of O2 and N2 gases

Titanium oxynitride thin films are deposited by DC reactive magnetron sputtering. A pure titanium target is sputtered in a reactive atmosphere composed of argon, oxygen and nitrogen gases. The oxygen mass flow rate as well as that of the nitrogen gas are both pulsed during the deposition time using an independent and rectangular signal for each reactive gas. A constant pulsing period T = 45 s is applied for both reactive gases and a delay time δ of 34 s between N2 and O2 injection times is set for all depositions. Oxygen and nitrogen duty cycles are systematically and independently changed from 0 to 100 % of their pulsing period. From real time measurements of the Ti target potential and total sputtering pressure, it is shown that the reactive process alternates between oxidized, nitrided and elemental sputtering modes as a function of the oxygen and nitrogen injection times. The full poisoning of the Ti target surface by oxygen and/or nitrogen can be avoided for some given ranges of O2 and N2 duty cycles. Deposition rates of titanium oxynitride films are substantially enhanced and can be adjusted between that of pure Ti and TiN films with a gradual transition of their electrical conductivity and optical transmittance in the visible range. These results support that titanium oxynitride compounds exhibiting absorbent to transparent behaviors can be precisely sputter-deposited by means of a two reactive gases pulsing process.

In-situ hydrogenated V2O5 thin films: Study of the structural dynamics and their behavior as Li-ion batteries cathode

This investigation focuses on a one-step preparation method to produce hydrogenated V2O5 thin films by controlling the atmosphere of the DC reactive magnetron sputtering process. An increasing hydrogen flux during the film deposition promotes the formation of defects such as oxygen vacancies and hydroxyl sites in the oxide matrix. The hydrogenated samples were tested as cathodes in Li-ion batteries and exhibited lower charge capacities but superior stability to cycling compared to pristine V2O5 film. These results pave the way to prepare hydrogenated transition metal oxide thin films by a simple route without further thermal procedures and affordable conditions.

Enhancing sputtered GaN/Si film quality by adding AlGaN buffer layer in a continuous deposition process

In this work we demonstrate the achievement of significative improvements in the structural and morphological quality of wurtzite GaN films (approximately 250 nm thick) by introducing an initial growth step involving an AlGaN buffer layer on p-type Si (100) substrates through a continuous reactive sputtering process. We investigated the influence of using single and multiple AlxGa1-xN buffer layers with varying Al content (x ranging from 0.07 to 0.37) and different thicknesses (from 166 nm to 1 µm). The obtained samples underwent characterization through X-ray diffraction and scanning electron microscopy. The results reveal a slight increase in the c-axis preferred growth direction and grain sizes even with a single and thin (250 nm) Al0.07Ga0.93N buffer layer. Conversely, the use of a single Al0.37Ga0.63N buffer layer led to significant morphological changes and a remarkable improvement in the c-axis preferred orientation. The most favorable outcomes were observed with the implementation of a triple AlGaN buffer layer, featuring decreasing Al content from the substrate, indicating the attainment of a high-quality GaN top layer comparable to epitaxial GaN.

Tuning Surface Defect States in Sputtered Titanium Oxide Electron Transport Layers for Enhanced Stability of Organic Photovoltaics.

Nonfullerene acceptors (NFAs) have dramatically improved the power conversion efficiency (PCE) of organic photovoltaics (OPV) in recent years; however, their device stability currently remains a bottleneck for further technological progress. Photocatalytic decomposition of nonfullerene acceptor molecules at metal oxide electron transport layer (ETL) interfaces has in several recent reports been demonstrated as one of the main degradation mechanisms for these high-performing OPV devices. While some routes for mitigating such degradation effects have been proposed, e.g., through a second layer integrated on the ETL surface, no clear strategy that complies with device scale-up and application requirements has been presented to date. In this work, it is demonstrated that the development of sputtered titanium oxide layers as ETLs in nonfullerene acceptor based OPV can lead to significantly enhanced device lifetimes. This is achieved by tuning the concentration of defect states at the oxide surface, via the reactive sputtering process, to mitigate the photocatalytic decomposition of NFA molecules at the metal oxide interlayers. Reduced defect state formation at the oxide surface is confirmed through X-ray photoelectron spectroscopy (XPS) studies, while the reduced photocatalytic decomposition of nonfullerene acceptor molecules is confirmed via optical spectroscopy investigations. The PBDB-T:ITIC organic solar cells show power conversion efficiencies of around 10% and significantly enhanced photostability. This is achieved through a reactive sputtering process that is fully scalable and industry compatible.

Analysis of the Inhomogeneous Growth of Sputtered Black TiO2 Thin Films.

Black titanium dioxide (B-TiO2) is a highly active photoelectrochemical material compared to pure titanium dioxide due to its increased light absorption properties. Recently, we presented the deposition of thin-film B-TiO2 using an asymmetric bipolar reactive magnetron sputter process. The resulting samples exhibit excellent photoelectrochemical properties, which can be fine-tuned by varying the process parameters. In this article, results of morphological, electrical, and photoelectrochemical measurements are discussed to better understand the surprisingly high electrochemical activity of the films. In order to study the influence of the dynamic process on film formation, we use static sputtering with a fixed substrate covering the entire chamber area in front of the two targets. This allows the material composition of the sputtered film to be analyzed depending on its relative position to the targets. The results lead to the conclusion that the asymmetric bipolar sputtering mainly produces two phases, a transparent, nonconductive crystalline phase and a black, conductive amorphous phase. As a consequence, the dynamically sputtered samples are multilayers of these two materials. We discuss that the significantly better electrical and photoelectrochemical properties emerge from the inhomogeneous nature of the laminates, like also found in core-shell nanoparticles of B-TiO2.

Reactive sputtering of ferroelectric AlScN films with H2 gas flow for endurance improvement

The impact of H2 gas flow in the reactive sputtering process to 60 nm-thick ferroelectric Al1−x Sc x N films is investigated with x of 0.26 (high-Sc) and 0.12 (low-Sc). Al1−x Sc x N films exhibit clear ferroelectric switching, confirming the robustness against reducing ambient. The dielectric constants (ε i) as well as the leakage current decrease, and the breakdown field (E BD) increases with H2 flow. Although the remanent polarization (P r) decreases with H2 flow, the wake-up effect is suppressed for the high-Sc film, and the fatigue effect is weakened for the low-Sc film. By probing the change in the coercive field (E c) after the switching cycle test, we anticipate oxygen impurities bonded to Sc and Al atoms are the source of wake-up and fatigue effects, respectively. As a result, a high endurance cycle of 2 × 107 times was achieved for low-Sc films with H2 flow.

Моделирование реактивного распыления. Основные принципы

This work aims to describe the fundamental principles whose application for the purposes of modelling various physical and chemical processes has proven to be effective. The model of a process is defined as its representation using another similar (or identical) process, constructed based on a number of simplifying assumptions. Such a representation is referred to as a physicochemical model. The main phenomena occurring on the surfaces and in the gaseous environment of a spray system, which are used in developing reactive sputtering models, are identified. A scheme for deriving a system of equations describing the model in an analytical form is given. An example of modelling based on a non-isothermal surface chemical reaction is given, which demonstrates the possibility of studying immeasurable dependencies characterizing the process of reactive sputtering experimentally.

Evaluation of low-loss alumina material for high-power RF windows

Conventional RF vacuum windows are made of metalized ceramics, hermetically brazed to a pillbox cavity. High-power windows, operating in ultra-high frequency (UHF) band, require the fabrication of ceramic disks with diameters on the order of 9”. Furthermore, a Titanium Nitride (TiN) multipactor suppression coating must be applied to the ceramic surfaces. The large size and complex internal geometry of these windows create challenges in validating the coating in the fully fabricated assembly. This study evaluates a novel low-loss alumina AO479U, provided by Kyocera, and a reactive sputtering process suitable to deposit a 10-20 nm thick TiN coating on a large diameter window. The paper will report the changes in the TiN coating through chemical cleaning and vacuum braze processes using stylus profilometry, optical microscopy, Scanning Electron Microscopy (SEM), and Rutherford Backscattering Spectroscopy (RBS).

Hollow Cathode Gas Flow Sputtering of Nickel Oxide Thin Films for Hole‐Transport Layer Application in Perovskite Solar Cells

Nickel oxide (NiO1+δ) is a versatile material used in various fields such as optoelectronics, spintronics, electrochemistry, and catalysis which is prepared with a wide range of deposition methods. Herein, for the deposition of NiO1+δ films, the reactive gas flow sputtering (GFS) process using a metallic Ni hollow cathode is developed. This technique is distinct and has numerous advantages compared to conventional sputtering methods. The NiO1+δ films are sputtered at low temperatures (100 ºC) for various oxygen partial pressures during the GFS process. Additionally, Cu‐incorporated NiO1+δ (Cu x Ni1−x O1+δ) films are obtained with 5 and 8 at% Cu. The thin films of NiO1+δ are characterized and evaluated as a hole‐transporting layer (HTL) in perovskite solar cells (PSCs). The NiO1+δ devices are benchmarked against state‐of‐the‐art self‐assembled monolayers (SAM) ([2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (also known as MeO2PACz)‐based PSCs. The best‐performing NiO1+δ PSC achieves an efficiency (η) of ≈16% without a passivation layer at the HTL interface and demonstrates better operational stability compared to the SAM device. The findings suggest that further optimization of GFS NiO1+δ devices can lead to higher‐performing and more stable PSCs.

Zirconium (Oxy)Nitrides for (Photo)Electrochemical Applications

Transition metal (TM) nitrides are an emerging class of (photo)electrocatalytic materials that have recently received growing research interest.1,2 In general, nitrogen-poor TM nitrides are usually refractory materials with metallic character while nitrogen-rich nitrides often possess semiconducting character.3 Hence, while the former are potential electrocatalyst candidates, the latter may qualify as photoelectrode absorber materials. For example, ZrN has recently been proposed as an electrocatalyst for both the electrochemical nitrogen4 and oxygen5 reduction reactions (ORR and NRR), while Zr3N4 and also Zr2N2O have been suggested as potential photoanode materials in photoelectrochemical water oxidation.2 In this contribution, we test these hypotheses regarding the (photo)electrochemical characteristics of Zr-based (oxy)nitrides by experiment. To this end, we investigate reactively sputtered thin films for the electrochemical NRR/ORR and the photoelectrochemical oxygen evolution reaction (OER). Previous experiments on Ta-based nitrides have shown that addition of oxygen during the reactive sputter process is necessary to access higher metal oxidation states.6 As we introduce controlled amounts of oxygen at otherwise fixed deposition conditions, we observe a transition from metallic ZrN to a disordered nitrogen-rich ZrxNy to a crystalline bixbyite-type Zr2N2O to nitrogen-doped cubic ZrO2. Crystalline Zr3N4 was not accessible under the used experimental conditions. In our experiments, we observe a lack of electrocatalytic activity for ZrN in NRR and ORR and instabilities of the disordered nitrogen-rich ZrxNy in the photoelectrochemical OER. Introducing more oxygen into the structure, however, leads to a more stable crystalline structure (Zr2N2O), the opening of a band gap in the visible range, and the emergence of photoelectrochemical activity for oxidation reactions. Based on chopped linear sweep voltammetry measurements, we show that Zr2N2O films are photoactive for the OER in alkaline electrolyte with low onset potentials, indicating an overall favorable band alignment of the material with respect to the water oxidation and reduction potentials. While the observed photocurrents are still about one order of magnitude lower than for the benchmark oxynitride photoanode TaON, further material optimization could potentially close this gap and provide a materials system functioning as sustainable photoanode.References 1 W. Sun, C.J. Bartel, E. Arca, S.R. Bauers, B. Matthews, B. Orvañanos, B.R. Chen, M.F. Toney, L.T. Schelhas, W. Tumas, J. Tate, A. Zakutayev, S. Lany, A.M. Holder, and G. Ceder, Nat. Mater. 18, 732 (2019). 2 Y. Wu, P. Lazic, G. Hautier, K. Persson, and G. Ceder, Energy Environ. Sci. 6, 157 (2013). 3 A. Salamat, A.L. Hector, P. Kroll, and P.F. McMillan, Coord. Chem. Rev. 257, 2063 (2013). 4 Y. Abghoui, A.L. Garden, J.G. Howalt, T. Vegge, and E. Skúlason, ACS Catal. 6, 635 (2016). 5 Y. Yuan, J. Wang, S. Adimi, H. Shen, T. Thomas, R. Ma, J.P. Attfield, and M. Yang, Nat. Mater. 19, (2019). 6 C.M. Jiang, L.I. Wagner, M.K. Horton, J. Eichhorn, T. Rieth, V.F. Kunzelmann, M. Kraut, Y. Li, K.A. Persson, and I.D. Sharp, Mater. Horizons 8, 1744 (2021).

NO2 gas sensing performance of Ag−WO3−x thin films prepared by reactive magnetron sputtering process

NO2 gas sensing performance of Ag−WO3−x thin films prepared by reactive magnetron sputtering process

Photocatalytical and corrosion behavior of sputtered zirconium oxynitride thin films doped with titanium

ZrTiON coatings were deposited by reactive magnetron sputtering process of a single Zr target, while Ti was added by placing Ti ribbons on the erosion track of the Zr sputtering target. The variation of parameters such as the number of Ti ribbons, the applied sputtering current, and the reactive gas flow led to obtaining different sample configurations. The coatings were analyzed in terms of chemistry (chemical composition and chemical states) by X-ray Photoelectron Spectroscopy, morphology by Atomic Force Microscopy, surface energy, photodegradation tests, electrochemical studies, and accelerated corrosion tests. It was found that the coatings show features of oxides, nitrides, and oxynitrides, depending on the deposition conditions applied. The photodegradation efficiency regarding methylene blue solutions under visible light varies between 58% and 96%, depending on the type of illuminant and the sample characteristics, while the lowest corrosion rate was exhibited by the reference samples deposited without the addition of Ti. The samples doped with Ti and deposited with 1.5 A sputtering current exhibited a more efficient photodegradation effect, compared to the reference ZrON sample. The accelerated corrosion tests showed that the coatings deposited with an applied current of 2 A behaved significantly better than the ones deposited with 1.5 A sputtering current after 8 h of exposure to the water vapor and sulfur dioxide gas atmosphere.

Nanocrystal Engineering of Thin-Film Yttria-Stabilized Zirconia Electrolytes for Low-Temperature Solid-Oxide Fuel Cells.

To overcome significantly sluggish oxygen-ion conduction in the electrolytes of low-temperature solid-oxide fuel cells (SOFCs), numerous researchers have devoted considerable effort to fabricating the electrolytes as thin as possible. However, thickness is not the only factor that affects the electrolyte performance; roughness, grain size, and internal film stress also play a role. In this study, yttria-stabilized zirconia (YSZ) was deposited via a reactive sputtering process to fabricate high-performance thin-film electrolytes. Various sputtering chamber pressures (5, 10, and 15 mTorr) were investigated to improve the electrolytes. As a result, high surface area, large grain size, and residual tensile stress were successfully obtained by increasing the sputtering pressure. To clarify the correlation between the microstructure and electrolyte performance, a YSZ thin-film electrolyte was applied to anodized aluminum oxide-supported SOFCs composed of conventional electrode materials which are Ni and Pt as the anode and the cathode, respectively. The thin-film SOFC with YSZ deposited at 15 mTorr exhibited the lowest ohmic resistance and, consequently, the highest maximum power density (493 mW/cm2) at 500 °C whose performance is more than five times higher than that of the cell with YSZ deposited at 5 mTorr (94.1 mW/cm2). Despite the basic electrode materials, exceptionally high performance at low operating temperature was achieved via controlling the single fabrication condition for the electrolyte.

A Ferroelectric Property Tailoring Method of Al0.7Sc0.3n Films by Sputter-Deposition Pressure

New ferroelectric materials have been extensively studied for scaled non-volatile memory [1]. Among materials, Al1-x Sc x N (ASN) films are attracting attention owing to their high remnant polarization (Pr ) of over 100 µC/cm2 [2]. Although the material is started to be characterized, a high coercive field (E c) with a relatively high leakage current has been an issue. As reactive sputtering used to deposit nitrides is known to be influenced by the condition, in this study, we have changed the sputtering pressure for ASN deposition and characterized the ferroelectric properties. The composition of the ASN films is Al0.7Sc0.3N.Metal-insulator-metal (MIM) capacitors with 50-nm-thick ASN film capacitors with TiN electrodes were fabricated by a reactive sputtering process. We varied the sputtering pressure from 0.76 to 1.1 Pa. Figure 1 shows the leakage current (J-V) of the capacitors. The capacitor with a low-pressure ASN film shows a relatively low leakage current and a breakdown field (E BD) of 8 MV/cm which is high considering the bandgap of the ASN film to be 3.2 eV. On the other hand, the capacitor with a high-pressure ASN film showed a high leakage current with a reduced E BD of 5.2 MV/cm. As the leakage current is determined by the interface, stacking the ASN layers may result in reducing the leakage current while maintaining a high E BD. The leakage current of a capacitor with a 5-nm-thick low-pressure ASN at each interface and a 40-nm-thick high-pressure ASN film is also shown in fig. 1. We see a slight suppression in the leakage current and improvement in the E BD to be 6.2 MV/cm. P r of the capacitors were obtained by positive-up-negative-down (PUND) measurements. The pulse-height dependent P r is shown in fig. 2. The capacitor with a low-pressure ASN film revealed a high E c of 3.8 MV/cm, while the one with a high-pressure ASN film was 3.4 MV/cm. The capacitor with stacked ASN films showed the same E c of 3.4 MV/cm. The capacitors with single film showed a gradual change in the P r on the electric field. In the stacked one, in contrast, a sharp change in the electric field with a constant P r of 100 μC/cm2 was obtained.In conclusion, stacked ASN films deposited by different sputter pressures show reduced leakage current with a high breakdown field. Although the physical change by the pressure is still unknown, tailoring the interface and bulk regions has a possibility to further improve the ferroelectric properties.