A.E. Komlev1, V.A. Volpyas2, R.A. Platonov3, A.G. Altynnikov4, A.B. Kozyrev5

St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia
 

Nowadays, ion-plasma sputtering is one of the widely used methods for obtaining multilayer multicomponent structures. In ion-plasma sputtering, the film stoichiometry is determined by the composition of the sputtered target, and several different targets are usually required to create a structure with a variable stoichiometric composition over the thickness. This leads to the need to interrupt the deposition processes and the formation of sharp edges in the stoichiometric composition of the growing structure, and to undesirable interface defects between layers with different stoichiometry.

In this paper, we propose a new technique for the formation of thin films of a composite material with a given distribution of the stoichiometric composition over the thickness. The technique is based on the dynamic change in the pressure of the working gas during the technological process of ion-plasma sputtering of the target. In this paper, as an example, we consider the use of the developed method for creating polycrystalline thin films of a ferroelectric with a perovskite structure based on a solid solution of barium-strontium titanate BaxSr1-xTiO3 (BSTO). Experimental samples of films have been obtained, and their stoichiometric composition has been studied. The obtained results were analyzed and compared with the simulation results. The influence of the pressure of the working gas on the stoichiometric composition and the deposition rate of thin films is described. It is shown that the optimal range of operating gas pressures, in which the most effective change in the stoichiometric composition parameter x is possible, lies in the region of low pressures up to ~20 Pa, at which the depth of the thermalization zone of sputtered target atoms is comparable to the depth of the thermalization zone of sputtered target atoms. value of drift space target–substrate. An increase in the target-substrate distance leads to the suppression of the stoichiometric change with a change in the pressure of the working gas.

Note that the presented method allows one to deposit multicomponent films of a large class of oxides with a given continuous change in stoichiometry over the film thickness (gradient films) using only one target with a given initial stoichiometry. The considered method is most efficient in the deposition of multicomponent materials with a greater difference in the atomic masses of the components. The absence of transitional interlayer regions during the formation of the structure of multilayer oxide films makes it possible to control their electrophysical properties, providing high ordering of the structures in a wide range of their thicknesses. The developed method can be widely used in the electronics industry due to the wide use of multicomponent gradient films, which, depending on the composition, can have unique characteristics and properties such as high strength, controlled transparency, and temperature stability.

Komlev A.E., Volpyas V.A., Platonov R.A., Altynnikov A.G., Kozyrev A.B. Method for the formation of thin films with a given stoichiometric distribution of the composition over the thickness. Nanotechnology: development and applications – XXI century. 2023. V. 15. № 1. P. 32–40. DOI: https://doi.org/10.18127/ j22250980-202301-03 (in Russian)

1. Gao W., Zhu Y., Wang Y., Yuan G., Liu J.M. A review of flexible perovskite oxide ferroelectric ƍlms and their application. Journal of Materiomics. 2020. № 6. P. 1–16.
2. Won S.S., Seo H., Kawahara M., Glinsek S., Lee J., Kim Y., Jeong C.K., Kingon A.I., Kim S.H. Flexible vibrational energy harvesting devices using strain-engineered perovskite piezoelectric thin ƍlms. Nano Energy 2019. № 55. P. 182–192.
3. Sharma A.P., Behera M.K., Pradhan D.K., Pradhan S.K., Bonner C.E., Bahoura M. Lead-free relaxor-ferroelectric thin ƍlms for energy harvesting from low-grade waste-heat. Scientific Reports. 2021. № 11, P. 1–10.
4. Mikolajick T., Schroeder U., Slesazeck S. The past, the present, and the future of ferroelectric memories. IEEE Transactions on Electron Devices. 2020. № 67. P. 1434–1443.
5. Park M.H., Lee Y.H., Kim H.J., Kim Y.J., Moon T., Kim K.D., Hyun S.D., Hwang, C.S. Morphotropic Phase Boundary of Hf1–xZrxO2 Thin Films for Dynamic Random Access Memories. ACS applied materials & interfaces. 2018. № 10. P. 42666–42673.
6. Crunteanu A., Muzzupapa V., Ghalem A. Huitema L., Passerieux D. Borderon C., Renoud R., Gundel H.W. Characterization and performance analysis of BST-based ferroelectric varactors in the millimeter-wave domain. Crystals. 2021. № 11. P. 277.
7. Gu Z., Pandya S., Samanta, A.; Liu, S.; Xiao, G.; Meyers, C.J.; Damodaran, A.R.; Barak, H.; Dasgupta, A.; Saremi, S.; et al. Resonant domain-wall-enhanced tunable microwave ferroelectrics. Nature 2018, 560, 622–627.
8. Liu G., Wolfman J., Autret-Lambert C., Sakai J., Roger S., Gervais M., Gervais F. Microstructural and dielectric properties of Ba0.6Sr0.4Ti1-xZrxO3 based combinatorial thin film capacitors library. Journal of Applied Physics. 2010. № 108. P. 114108.
9. Zhang N., Wang D., Wang J., Fang H., He B., Guo J., Han Y., Zhang P., Shi C., Chen Y. et al. Enhanced Piezoresponse and Dielectric Properties for Ba1-XSrXTiO3 Composition Ultrathin Films by the High-Throughput Method. Coatings. 2021. № 11. P. 1491.
10. Tumarkin A., Volpyas V., Zlygostov M., Odinets A., Sapego E. Varying the Composition of Ferroelectric Films during Ion-Plasma Sputtering: Simulation and Experiment. Bulletin of the Russian Academy of Sciences: Physics. 2018. № 82. P. 346–351.
11. Yudin P., Duchon J., Pacherova O., Klementova M., Kocourek T., Dejneka A., Tyunina M. Ferroelectric phase transitions induced by a strain gradient. Phys. Rev. Research. 2021. № 3. P. 033213.
12. Tian H.Y., Chan H.L.W., Choy C.L., No K. The effects of composition gradients of BaxSr1-xTiO3 thin ƍlms on their microstructures, dielectric and optical properties. Materials Science and Engineering: B. 2003. № 103. P. 246–252.
13. Petraru A., Droopad R., Kohlstedt H. Characterization of VO2/ferroelectric thin ƍlm heterostructures deposited on various complex oxide single crystal substrates. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. 2019. № 37. P. 021514.
14. Tumarkin A., Gaidukov M., Gagarin A., Samoilova T., Kozyrev A. Ferroelectric strontium titanate thin ƍlms for microwave applications. Ferroelectrics. 2012. № 439. P. 49–55.
15. Hollmann E., Vol‘pyas V., Wordenweber R. Monte–Carlo simulation of the particle transport during physical vapor deposition of ceramic superconductors. Physica C: Superconductivity. 2005. № 425. P. 101–110.
16. Volpyas V., Kozyrev A. Thermalization of atomic particles in gases. Journal of Experimental and Theoretical Physics. 2011. № 113. P. 172–179.
17. Depla D., Leroy W. Magnetron sputter deposition as visualized by Monte Carlo modeling. Thin Solid Films. 2012. № 520. P. 6337–6354.
18. Kozak T., Vlcek J., Šimon Kos. Transport and ionization of sputtered atoms in high-power impulse magnetron sputtering discharges. Journal of Physics D: Applied Physics. 2013. № 46. P. 105203. URL: https://doi.org/10.1088/0022-3727/46/10/105203.
19. Volpyas V.A., Komlev A.Y., Platonov R.A., Kozyrev A.B. Thermalization of the flow of sputtered target atoms during ion-plasma deposition of films. Physics Letters A. 2014. № 378. P. 3182–3184.
20. Tumarkin A.V. et al. Thermostable ferroelectric capacitors based on graded films of barium strontium titanate. Technical Physics 2017. № 62.10. P. 1592–1598.
21. Behrisch R. (Ed.): Sputtering by Particle Bombardment I. V. 47 aus: Topics in Applied Physics. Springer-Verlag, Berlin-Heidelberg-New York 1981. 280 Seiten, Preis: DM 85. Berichte der Bunsengesellschaft for physikalische Chemie. 1982. № 86. P. 340–340.
22. Lu S.G., Zhu X.H., Mak C.L., Wong K.H., Chan H.L.W., Choy C.L. High tunability in compositionally graded epitaxial barium strontium titanate thin films by pulsed-laser deposition. Applied Physics Letters. 2003. № 82. P. 2877–2879.
23. Vorobiev A., Gevorgian S. Intrinsically switchable thin film bulk acoustic wave resonators. Applied Physics Letters. 2014. № 104.
    P. 222905.
24. Afrosimov V., Il’in R., Karmanenko S., Melkov A., Sakharov V., Serenkov I. Evidence of multiphase nucleation in perovskite film growth on MgO substrate from medium energy ion scattering analysis: Example of YBaCuO and (Ba,Sr)TiO3. Thin Solid Films. 2005. № 492. P. 146–152.