Structural and magnetic properties of micropolycrystalline cobalt thin films fabricated by direct current magnetron sputtering

Abstract

Pure cobalt (Co) thin films were fabricated by direct current magnetron sputtering, and the effects of sputtering power and pressure on the microstructure and electromagnetic properties of the films were investigated. As the sputtering power increases from 15 to 60 W, the Co thin films transition from an amorphous to a polycrystalline state, accompanied by an increase in the intercrystal pore width. Simultaneously, the resistivity decreases from 276 to 99 µΩ·cm, coercivity increases from 162 to 293 Oe, and in-plane magnetic anisotropy disappears. As the sputtering pressure decreases from 1.6 to 0.2 Pa, grain size significantly increases, resistivity significantly decreases, and the coercivity significantly increases (from 67 to 280 Oe), which can be attributed to the increase in defect width. Correspondingly, a quantitative model for the coercivity of Co thin films was formulated. The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy, which is primarily attributable to increased microstress.

Keywords

cobalt thin film / magnetron sputtering / microstructure / electromagnetic properties

References

[[1]] Kaloyeros AE, Pan YL, Goff J, Arkles B. Editors’ choice—Review—Cobalt thin films: Trends in processing technologies and emerging applications. ECS J. Solid State Sci. Technol., 2019, 8(2): 119,

[[2]] J. Mohapatra, M.Y. Xing, J. Elkins, and J.P. Liu, Hard and semi-hard magnetic materials based on cobalt and cobalt alloys, J. Alloys Compd., 824(2020), art. No. 153874.

[[3]] E. Abualgassem, M. Maarouf, A. Bake, D. Cortie, K. Alam, and M.B. Haider, Optical and magnetic properties of cobalt doped TiN thin films grown by RF/DC magnetron sputtering, J. Magn. Magn. Mater., 550(2022), art. No. 169023.

[[4]] G.D. Soria, K. Freindl, J.E. Prieto, et al., Growth and characterization of ultrathin cobalt ferrite films on Pt(111), Appl. Surf. Sci., 586(2022), art. No. 152672.

[[5]] Shukla V, Mukherjee C, Chari R, Rai S, Bindra KS, Banerjee A. Uniaxial magnetic anisotropy of cobalt thin films on different substrates using CW-MOKE technique. J. Magn. Magn. Mater., 2014, 370: 100,

[[6]] Y. Shiratsuchi, T. Murakami, Y. Endo, and M. Yamamoto, Evolution of magnetic state of ultrathin co films with volmer-weber growth, Jpn. J. Appl. Phys., 44(2005), No. 12R, art. No. 8456.

[[7]] Hsu CY, Chang CHT, Chen WH, Tsai JL, Tsay JS. Comparative studies of magnetic properties of Co films on annealed and unannealed rubrene/Si(100). J. Alloys Compd., 2013, 576: 393,

[[8]] S.D. Elliott, G. Dey, and Y. Maimaiti, Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations, J. Chem. Phys., 146(2017), No. 5, art. No. 052822.

[[9]] T. Kuschel, T. Becker, D. Bruns, et al., Uniaxial magnetic anisotropy for thin Co films on glass studied by magnetooptic Kerr effect, J. Appl. Phys., 109(2011), No. 9, art. No. 093907.

[[10]] Kumar D, Gupta A. Evolution of structural and magnetic properties of sputtered nanocrystalline Co thin films with thermal annealing. J. Magn. Magn. Mater., 2007, 308(2): 318,

[[11]] R. Gupta, A. Khandelwal, D.K. Avasthi, K.G.M. Nair, and A. Gupta, Phase transitions in Co thin film induced by low energy and high energy ion beam irradiation, J. Appl. Phys., 107(2010), No. 3, art. No. 033902.

[[12]] A. Jaiswal, S. Rai, M.K. Tiwari, V.R. Reddy, G.S. Lodha, and R.V. Nandedkar, Effect of Si layer thickness on the structural properties of a Co/Si multilayer system, J. Phys.: Condens. Matter, 19(2007), No. 1, art. No. 016001.

[[13]] Pandey N, Gupta M, Gupta R, Chakravarty S, Shukla N, Devishvili A. Structural and magnetic properties of Co-N thin films deposited using magnetron sputtering at 523 K. J. Alloys Compd., 2017, 694: 1209,

[[14]] Q.Y. Qian, F. Wang, X.K. Zhang, and Q.P. Zhao, Direct electro-phosphorization of nickel and cobalt films in hypophosphite solution for efficient hydrogen evolution, Inorg. Chem. Commun., 127(2021), art. No. 108555.

[[15]] R. Hippler, M. Cada, P. Ksirova, et al., Deposition of cobalt oxide films by reactive pulsed magnetron sputtering, Surf. Coat. Technol., 405(2021), art. No. 126590.

[[16]] Gao LB, Jiang SW, Li RG. Effect of sputtering pressure on structure and dielectric properties of bismuth magnesium niobate thin films prepared by RF magnetron sputtering. Thin Solid Films, 2016, 603: 391,

[[17]] J. Xu, M. Gao, L.L. Lu, Y.L. Wang, and X. Liu, Study on the resistivity and infrared emissivity of TiN_x films at different sputtering power, Infrared Phys. Technol., 119(2021), art. No. 103946.

[[18]] Sharma A, Mohan S, Suwas S. The effect of the deposition rate on the crystallographic texture, microstructure evolution and magnetic properties in sputter deposited Ni-Mn-Ga thin films. Thin Solid Films, 2016, 616: 530,

[[19]] Bose S, Mandal S, Barua AK, Mukhopadhyay S. Properties of boron doped ZnO films prepared by reactive sputtering method: Application to amorphous silicon thin film solar cells. J. Mater. Sci. Technol., 2020, 55: 136,

[[20]] Dai CD, Fu Y, Guo JX, Du CW. Effects of substrate temperature and deposition time on the morphology and corrosion resistance of FeCoCrNiMo_0.3 high-entropy alloy coating fabricated by magnetron sputtering. Int. J. Miner. Metall. Mater., 2020, 27(10): 1388,

[[21]] Liang FY, Yang JR, Wang HQ, Wu JW. Fabrication of Gd₂O₃-doped CeO₂ thin films through DC reactive sputtering and their application in solid oxide fuel cells. Int. J. Miner. Metall. Mater., 2023, 30(6): 1190,

[[22]] Zhang XZ, Xia YP, Liu X, Zhong YM, Zhao HB, Wang PH. Effect of annealing temperature on the microstructure and optoelectrical properties of ZnO thin films and their application in self-powered accelerometers. Int. J. Miner. Metall. Mater., 2019, 26(9): 1186,

[[23]] M.A. Basha, C.L. Prajapat, S. Singh, and S. Basu, Optimization and characterization of cobalt & gadolinium films using X-ray scattering, [in] AIP Conference Proceedings, Bhubaneswar, 2017.

[[24]] Wang Y. . Study on Microstructure and Properties of Co and CoTaZr Thin films by Magnetron Sputtering, 2012 Guangzhou Guangdong University of Technology [Dissertaion]

[[25]] K. Bukharia, P. Karmakar, D. Kumar, V.R. Reddy, and A. Gupta, Evolution of magnetic anisotropy in cobalt film on nanopatterned silicon substrate studied in situ using MOKE, J. Magn. Magn. Mater., 497(2020), art. No. 165934.

[[26]] M.O. Liedke, M. Körner, K. Lenz, et al., Crossover in the surface anisotropy contributions of ferromagnetic films on rippled Si surfaces, Phys. Rev. B, 87(2013), No. 2, art. No. 024424.

[[27]] Huang J W, Li Z. . X-ray Diffraction of Polycrystalline Materials: Experimental Principles, Methods and Applications, 2012 Beijing Metallurgical Industry Press 119

[[28]] Hoffman DW, Thornton JA. The compressive stress transition in Al, V, Zr, Nb and W metal films sputtered at low working pressures. Thin Solid Films, 1977, 45(2): 387,

[[29]] Cha JH, Ashok K, Suthan Kissinger NJ, et al.. Effect of thermal annealing on the structure, morphology, and electrical properties of Mo bottom electrodes for solar cell applications. J. Korean Phy. Soc., 2011, 59(3): 2280,

[[30]] Ahn H, Lee DC, Um Y. Substrate temperature effects on DC sputtered Mo thin film. Appl. Sci. Converg. Technol., 2017, 26(1): 11,

[[31]] Kumar M, Kumar A, Abhyankar AC. Influence of texture coefficient on surface morphology and sensing properties of W-doped nanocrystalline tin oxide thin films. ACS Appl. Mater. Interfaces, 2015, 7(6): 3571,

[[32]] Kajikawa Y, Noda S, Komiyama H. Comprehensive perspective on the mechanism of preferred orientation in reactive-sputter-deposited nitrides. J. Vac. Sci. Technol. A: Vac. Surf. Films, 2003, 21(6): 1943,

[[33]] Wang DD. . Theoretical Analysis About the Surface Structure and Energy Anisotropy of Crystal, 2007 Shanxi Shanxi Normal University [Dissertation]

[[34]] S. Mahieu and D. Depla, Reactive sputter deposition of TiN layers: Modelling the growth by characterization of particle fluxes towards the substrate, J. Phys. D: Appl. Phys., 42(2009), No. 5, art. No. 053002.

[[35]] G. Regmi and S. Velumani, Impact of target power on the properties of sputtered intrinsic zinc oxide (i-ZnO) thin films and its thickness dependence performance on CISe solar cells, Opt. Mater., 119(2021), art. No. 111350.

[[36]] Tian MB, Li ZC. . Material Technology and Thin Film Materials, 2018 5th Beijing Tsinghua University Press

[[37]] N. Daichakomphu, S. Abbas, T.L. Chou, et al., Understanding the effect of sputtering pressures on the thermoelectric properties of GeTe films, J. Alloys Compd., 893(2022), art. No. 162342.

[[38]] D.T.S. Perkins and R.A. Smith, Drude conductivity of a granular metal, Ann. Phys., 418(2020), art. No. 168170.

[[39]] Yoon JH, Cho S, Kim WM, et al.. Optical analysis of the microstructure of a Mo back contact for Cu(In, Ga)Se₂ solar cells and its effects on Mo film properties and Na diffusivity. Sol. Energy Mater. Sol. Cells, 2011, 95(11): 2959,

[[40]] Battu AK, Makeswaran N, Ramana CV. Fabrication, characterization and optimization of high conductivity and high quality nanocrystalline molybdenum thin films. J. Mater. Sci. Technol., 2019, 35(11): 2734,

[[41]] Liu XM, Zangari G. Easy axis dispersion and micromagnetic structure of electrodeposited, high moment Fe–Co–Ni films. J. Appl. Phys., 2001, 90(10): 5247,

[[42]] Durin G, Zapperi S. Bertotti G, Mayergoyz ID. The barkhausen effect. The Science of Hysteresis, 2006 Amsterdam Elsevier 181,

[[43]] Livingston J D, McConnell M D. Domain-wall energy in cobalt-rare-earth compounds. J. Appl. Phys., 1972, 43(11): 4756,

[[44]] Friedberg R, Paul DI. New theory of coercive force of ferromagnetic materials. Phys. Rev. Lett., 1975, 34(19): 1234,

[[45]] Ma B, Bao XQ, Sun AZ, Li JH, Gao XX. Microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination (HDDR) treated Nd–Fe–B strip cast alloys. J. Rare Earths, 2022, 40(5): 792,