Al₂O₃ and Al₂O₃/ZrO₂ multilayer coatings were deposited by the magnetron method by sputtering the corresponding metal targets in a mixture of oxygen and argon gases. The microstructure of the cross sections to determine the thickness and elemental composition of the obtained coatings was studied by transmission and scanning electron microscopy. The surface morphology of Al₂O₃ coating samples was studied by scanning probe microsco

Kolesnikov, D. A.

Krytsyna, E. V.

Kudryavtsev, E. A.

Novikov, V. Yu.

Sudzhanskaya, I. V.

DSpace at Belgorod State University

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 12 No 1, 01022(4pp) (2020) Том 12 № 1, 01022(4cc) (2020)   2077-6772/2020/12(1)01022(4) 01022-1  2020 Sumy State University Production, Structure and Properties of Coatings Based on Al2O3 Obtained by Magnetron Method  D.А. Kolesnikov1, I.V. Sudzhanskaya1, I.Yu. Goncharov1,2, S.V. Lytovchenko3, V.Yu. Novikov1, Е.А. Kudryavtsev1, B.O. Mazilin3, Е.V. Krytsyna1, V.M. Beresnev3, O.V. Glukhov4  1 Belgorod State National Research University, 85, Pobiedy St., 308015 Belgorod, Russia 2 Belgorod State Technological University named after V.G. Shukhov, Belgorod, Russia 3 V.N. Karazin Kharkiv National University, 4, Svoboby Sq., 61000 Kharkiv, Ukraine 4 National University of Radio Electronics, 14, Science Boulevard, 61166 Kharkiv, Ukraine  (Received 22 January 2020; revised manuscript received 15 February 2020; published online 25 February 2020)  Al2O3 and Al2O3/ZrO2 multilayer coatings were deposited by the magnetron method by sputtering the corresponding metal targets in a mixture of oxygen and argon gases. The microstructure of the cross sec-tions to determine the thickness and elemental composition of the obtained coatings was studied by trans-mission and scanning electron microscopy. The surface morphology of Al2O3 coating samples was studied by scanning probe microscopy. It is shown that the formed Al2O3 coating and the Al2O3/ZrO2 multilayer coating have a columnar structure with the columns oriented perpendicular to the surface. The columnar structure of multilayer coatings is not violated during the transition from layer to layer. The coating sur-face consists of globules with a diameter of about 20 nm. It was found that the Al2O3 coating has dielectric properties using the method of impedance spectrometry. Thus, it was shown that the magnetron method can be used to apply high-quality multilayer dielectric coatings, which can be used as thermal barrier coat-ings to protect the blades of high-temperature stages of aircraft engine turbines.  Keywords: Magnetron by sputtering, Multilayer oxide coatings, Structure.  DOI: 10.21272/jnep.12(1).01022 PACS numbers: 61.46. – w, 62.20.Qp, 62-65. – g   1. INTRODUCTION  Currently, Al2O3 coatings are widely used in the semiconductor industry in metal oxide semiconductor field effect transistors (MOSFETs) [1], buffer oxide layers in a metal-ferroelectric-insulator-semiconductor field-effect transistor [2], in solar cells [3], as protective layers in microelectromechanical systems [4]. High dielectric constant, good adhesive properties to many materials, high melting point and chemical compatibil-ity with semiconductor processes have made Al2O3 a technologically used material [5, 6]. It is known that the properties of coatings are de-termined by the method and parameters of the process of their formation. The production of coatings by the magnetron method is a well-established method for creating dense and uniform coatings with high adhe-sive strength and repeatability. Metal oxide layers are widely used as thermal barrier coatings to protect tur-bine blades in the aviation industry. The need to obtain coatings of large thickness (about 100-150 microns) forces the use of multilayer coatings to relieve stresses in them also. In addition, the need to obtain coatings that are resistant to tensile stresses occurring during bending of a turbine blade dictates the requirements for a needle or column structure oriented perpendicular to the surface of the turbine blade. The main advantage of magnetron systems is the high coating rate and low pressure of the working gas [7], which makes it possible to obtain complex multi-layer coatings. The formed structures have low internal stresses, which is a significant factor when coating thin substrates. The objective of this work is to develop a coating technology that, with sufficient thickness, can be used as thermal barrier coatings on the blades of a high-temperature stage of an airplane turbine. 2. METHODS OF PREPARATION AND  EXAMINATION OF THE SAMPLES  Al2O3 and Al2O3/ZrO2 coatings were obtained by the magnetron method using the “NIKA 2012” multifunc-tional vacuum unit on silicon substrates with a titani-um sublayer for microscopic studies and on aluminum substrate for dielectric studies to exclude the influence of the substrate. The fine structure of the coatings was studied by transmission electron microscopy (JEOL JEM 2100). To study the structure of transverse cleavages of coatings and their composition, a QUANTA 200 3D scanning electron microscope was used. Surface topography im-ages were examined using an NTEGRA Aura scanning probe microscope (SPM). The dielectric properties of the coatings were determined by impedance spectrometry using the “Novocontrol concept 43” installation.  3. OBTAINING Al2O3 COATINGS  The Al2O3 dielectric coating was applied only to one (outer) surface of the plate. The plate was mounted with the working surface to the surface of the cathode in the chamber. The rotation of the sample around its axis during the coating deposition process was disabled. After loading the sample and evacuating the vacuum to a pressure of 10 – 4 Pa, the samples were cleaned with a beam of medium-energy ions using a high-frequency ion source in an argon atmosphere. The argon pressure reached (5-6)10 – 2 Pa. After that, the ion source was turned off, the argon supply was shut off, and a residual pressure of about 10 – 4 Pa was established. Then oxygen was introduced into the chamber. The oxygen pressure was about (7-8)10 – 2 Pa. The radio frequency plasma generator (RPG) was turned on, a potential of – 100 V was  D.А. KOLESNIKOV, I.V. SUDZHANSKAYA ET AL. J. NANO- ELECTRON. PHYS. 12, 01022 (2020)   01022-2 applied to the sample. The surface of the sample was cleaned with oxygen, and then it was coated with an oxide film. RPG power was 500 W. The cleaning time by the ion source was 3 min, and by RPG – 2 min. The flow of oxygen into the chamber was 3-4 l/h. After cleaning the surface of the sample, the oxygen flow into the chamber increased to 6-7 l/h. Argon was passed through the jacket installed in the chamber surrounding the magnetron at a flow rate of 2-3 l/h, until the gas pressure in the chamber was about 0.4 Pa without turning off the RPG and without changing its power. The coating deposition time was 1 h.  4. RESULTS AND DISCUSSION  Bright field images of the coating microstructure ob-tained by transmission electron microscopy (TEM), as well as electron diffraction patterns of Al2O3 coatings, are shown in Fig. 1. As can be seen from Fig. 1, the coatings are glued globules of about 20 nm of size for Al2O3 films. Globules, in turn, are composed of smaller structural elements.    a    b  Fig. 1 – Images of microstructure (a) and electron diffraction (b) of Al2O3 coatings obtained using TEM  Studies of the structure of transverse cleaved coatings presented in Fig. 2 clearly demonstrate the columnar structure. SPM images of the topography of the coating based on aluminum oxide Al2O3 surface are shown in Fig. 3. The surface of the coating is the peaks of rounded pyramids projecting to a height of approximately 7-8 nm, the diameter of which is about 100 nm.    Fig. 2 – SEM cross section image of Al2O3 coating    a    b  Fig. 3 – Images of the surface topography of the Al2O3 coating obtained by scanning probe microscopy (a, b)  The elemental composition of the coatings was de-termined by analyzing the spectra of characteristic X-ray radiation (Fig. 4) arising from the interaction of elec-trons with the coating material. Two large peaks corresponding to oxygen and alumi-num are present in the spectrum. The ratio of oxygen and aluminum atoms in the coating is 40.94 to 59.06, which is very close to the stoichiometry of aluminum oxide Al2O3. The measured deviation of the material from stoichiome-try may be due to the error of the device, which for alumi-num is about 0.2÷0.3 %, but for oxygen it is about 3÷5 %.  PRODUCTION, STRUCTURE AND PROPERTIES OF COATINGS … J. NANO- ELECTRON. PHYS. 12, 01022 (2020)   01022-3    Fig. 4 – The spectrum of characteristic X-ray radiation and a table of the content of elements in the coating in terms of weight (Wt) and atomic (At) percentages  The dielectric properties of Al2O3 coatings were stud-ied. The results of measurements of the dielectric con-stant (ε) and the dielectric loss tangent (tanδ) of Al2O3 coating as a function of frequency are shown in Fig. 5.    Fig. 5 – The frequency dependence of the real part of the complex dielectric constant (ε) and the dielectric loss tangent (tanδ) at room temperature for coatings based on aluminum oxides  An analysis of the dielectric constant ε and the die-lectric loss tangent tanδ as a function of frequency for coatings deposited by magnetron sputtering shows that ε and tanδ monotonously decrease with increasing fre-quency. The nature of the curves indicates the absence of phase transitions and dielectric relaxation processes. The relatively high values of ε at all frequencies, as well as the high value of tanδ at low frequencies, indicate the dielectric properties of the Al2O3 coating obtained. 5. OBTAINING MULTILAYER AL2O3/ZRO2  COATINGS  The Al2O3/ZrO2 multilayer coating was applied from two cathodes. The deposition mode with stops at each magnetron was 2 min for each magnetron. Total amount of layers is 40 (20 of each type). The total coat-ing thickness is about 2 microns. Coating deposition time was 80 min. The first cathode was aluminum, the second one was zirconium with iron inserts, in order to obtain zirconia stabilized by iron oxide. The inserts are cylindrical with a diameter of 5 mm, so that in the erosion zone the percentage of the area occupied by the inserts relative to the area occupied by zirconium is about 6÷7 % (Fig. 6).    Fig. 6 – Schematic representation of a composite cathode for deposition of layers containing ZrO2    a    b  Fig. 7 – Cross section image of the Al2O3/ZrO2 multilayer coating in topographic (SE-a) and phase (BSE-b) contrast obtained by scanning electron microscopy (SEM)   D.А. KOLESNIKOV, I.V. SUDZHANSKAYA ET AL. J. NANO- ELECTRON. PHYS. 12, 01022 (2020)   01022-4 The substrate was cleaned at the same parameters as for the deposition of an alumina coating. In addition, a titanium buffer layer of about 150 nm thickness was deposited on the coating surface. Initially, cathodes of Al and Ti were installed in the chamber. After applying the titanium sublayer, a zirco-nium cathode with iron inserts was replaced. A sublayer was applied in order to check the adhesion of the coating to titanium. A single-crystal Si substrate was selected in order to easily cross-chip. After air was let into the chamber, a part of the titanium sublayer was etched off by an ion source with argon supply for 10 s. Next, the ion source was turned off, oxygen was introduced into the chamber, argon was passed into the magnetron region, and a multilayer coating was deposited at the parame-ters presented below: gas pressure 0.5 Pa; Ar supply of 1.1 l/h for each magnetron; O2 supply: flow directly into the chamber (3.2 l/h); magnetrons/aluminum target: voltage 770 V, current 5 A; zirconium composite target: voltage 930 V, current 5 A. The current stabilization was used in both cases. A columnar structure is clearly observed through the entire multilayer coating, which is associated with the dynamics of coating growth. It should be noted that, despite the change in the phase composition in the layers, columnar structure disturbances are not observed over the entire coating thick-ness (Fig. 7). Most likely, such a structure is determined by the growth dynamics of the coating and does not de-pend on the type of substrate. Column coatings grow on both polycrystalline and single crystal substrates. The direction of the axis of the texture and the de-gree of texturing of the coating material does not de-pend on the type of substrate, but on the growth rate and parameters of the coating process, which, in turn, affect the magnitude of micro and macrostresses in the films, and through them the structure and texture.  6. CONCLUSIONS  Dielectric coatings based on Al2O3 and a multilayer coating Al2O3/ZrO2 were obtained by the magnetron method using the “NIKA 2012” multifunctional vacuum unit. The thickness of Al2O3 coatings was about 1.6 μm and of Al2O3/ZrO2 multilayer coating was about 1.2 μm. Studies of the structure showed that the obtained Al2O3 coating and the Al2O3/ZrO2 multilayer coating have a columnar structure with a size of structural elements less than 100 nm, which is caused by the growth dynam-ics of the coatings and depends on the parameters of the formation process. It was found that the resulting Al2O3 coating has dielectric properties used on the analysis of the dielectric constant and dielectric loss tangent.   REFERENCES  1. H. Liu, P.D. Ye, IEEE Electron Device Lett. 33 No 4, 546, (2012). 2. H.S. Choi, G.-S. Lim, J.-H. Lee, Y.T. Kim, S.-I. Kim, D.C. Yoo, J.Y. Lee, I.-H. Choi, Thin Solid Films. 444, 276 (2003). 3. S. Bordihn, V. Mertens, J.W. Muller, W.M.M. (Erwin) Kessels, J. Vac. Sci. Technol. А32 01А128 (2014). 4. G. Seguini, E. Cianci, C. Wiemer, D. Saynova, J.A.M. van Roosmalen, M. Perego, Appl. Phys. Lett. 102, 131603 (2013). 5. K.J. Hubbard, D.G. Schlom, J. Mater. Res. 11, 2757 (1996). 6. J. Robertson, Eur. Phys. J. Appl. Phys. 28, 265 (2004). 7. I.V. Dermel, K.A. Shashkeev. Proceedings of VIAM. Protective and functional coatings 59 No.11.107 (2017). 8. P. Reimann, Phys. Rep. 361, 57 (2002).   Отримання, структура і властивості покриттів на основі Al2O3, отримані магнетронним методом   Д.А. Колесніков1, І.В. Суджанская1, В.Ю. Новіков1, C.В. Литовченко3, Е.А. Кудрявцев1, І.Ю. Гончаров1,2, Б.О. Мазілін3, Е.В. Крицина1. В.М. Береснєв3, О.В. Глухов4  1 Бєлгородський Державний Національний Дослідницький університет, вул. Перемоги, 85,  308015 Бєлгород, Російська Федерація 2 Бєлгородський Державний Технологічний Університет імені В.Г. Шухова, вул. Костюкова, 46,  308012 Бєлгород, Російська Федерація 3 Харківський національний університет імені В.Н. Каразіна, пл. Свободи, 4, 61000 Харків, Україна 4 Національний університет радіоелектроніки, бульвар Науки, 14, 61166 Харків, Україна  Нанесення покриттів Al2O3 та багатошарових покриттів Al2O3/ZrO2 здійснювали магнетронним ме-тодом шляхом розпилення відповідних металевих мішеней в середовищі суміші газів кисню та арго-ну. Мікроструктура поперечних зрізів, визначення товщини і елементний склад отриманих покриттів досліджували методом трансмісійної та растрової електронної мікроскопії. Морфологія поверхні зраз-ків покриттів Al2O3 вивчалася методом скануючої зондової мікроскопії. Показано, що сформовані пок-риття як Al2O3, так і багатошарове покриття Al2O3/ZrO2 мають стовпчасту структуру з орієнтацією сто-впців перпендикулярно поверхні. Стовпчаста структура багатошарових покриттів не порушується при переході від шару до шару. Поверхня покриттів складається з глобул діаметром близько 20 нм. Мето-дом імпедансної спектрометрії встановлено, що покриття Al2O3 має діелектричні властивості. Таким чином, було показано, що магнетронним методом можна наносити якісні багатошарові діелектричні покриття, які можуть бути використані в якості термобар’єрних покриттів для захисту лопаток висо-котемпературних щабель турбін авіаційних двигунів.  Ключові слова: Магнетроне осадження, Багатошарові оксидні покриття, Структура. 

Production, Structure and Properties of Coatings Based on Al₂O₃ Obtained by Magnetron Method

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Production, Structure and Properties of Coatings Based on Al₂O₃ Obtained by Magnetron Method

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