While the existing mobile networks use frequencies up to 2.5 GHz, the future mobile network of the 5th generation (5G) will work in the frequency range from 24 to 72 GHz. This will enable a data transfer speed up to 20 gbps (gbps – gigabits per second). The foundation of the 5G technology rests on high-frequency filters based on materials with high electrically tunable permittivity and low dielectric losses.
A research team led by Stanislav Kamba from the Institute of Physics of the Czech Academy of Sciences, in collaboration with American and German colleagues, succeeded in developing a new material with the required properties. This material consists of a succession of atomic layers of SrTiO3, BaTiO3 and SrO (see figure below).
The layers were deposited using molecular beam epitaxy on DyScO3 substrate, which induces a mechanical strain of about 1%. The growth resulted in layers with a supergrid structure and changeable thickness of the SrTiO3. The best microwave parameters were achieved in films of (SrTiO3)5(BaTiO3)SrO. These layers have the lowest dielectric losses and high electrically tunable permittivity – properties that have never been achieved before. These properties will enable a radical reduction of energy efficiency of mobile networks and a less frequent charging of mobile phones.
The Czech team participated mainly in the characterization of the thin films in the terahertz (1012 Hz) frequency range, in the explanation of the low dielectric losses and of the high tunability using an electrical field. Results were published on 23 December 2019 in Nature Materials.
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N.M. Dawley, E.J.Marksz, A.M. Hagerstrom, G.H. Olsen, M.E. Holtz, V. Goian, C. Kadlec, J. Zhang, X. Lu, J.A. Drisko, R. Uecker, S. Ganschow, C.J. Long, J.C. Booth, S. Kamba, C.J. Fennie, D.A. Muller, N.D. Orloff and D.G. Schlom, Nature Materials, https://doi.org/10.1038/s41563-019-0564-4