Targeted chemical pressure yields tuneable millimetre-wave dielectric


Epitaxial strain can unlock enhanced properties in oxide materials, but restricts substrate choice and maximum film thickness, above which lattice relaxation and property degradation occur. Here we employ a chemical alternative to epitaxial strain by providing targeted chemical pressure, distinct from random doping, to induce a ferroelectric instability with the strategic introduction of barium into today’s best millimetre-wave tuneable dielectric, the epitaxially strained 50-nm-thick n = 6 (SrTiO3)nSrO Ruddlesden–Popper dielectric grown on (110) DyScO3. The defect mitigating nature of (SrTiO3)nSrO results in unprecedented low loss at frequencies up to 125 GHz. No barium-containing Ruddlesden–Popper titanates are known, but the resulting atomically engineered superlattice material, (SrTiO3)nm(BaTiO3)mSrO, enables low-loss, tuneable dielectric properties to be achieved with lower epitaxial strain and a 200% improvement in the figure of merit at commercially relevant millimetre-wave frequencies. As tuneable dielectrics are key constituents of emerging millimetre-wave high-frequency devices in telecommunications, our findings could lead to higher performance adaptive and reconfigurable electronics at these frequencies.

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Fig. 1: The inequivalence of local chemical and global epitaxial strain in (SrTiO3)n−1(BaTiO3)1SrO phases.
Fig. 2: Structural characterization of ~50-nm-thick epitaxial (SrTiO3)n−1(BaTiO3)1SrO films with n = 2–6 grown on (110) DyScO3 substrates.
Fig. 3: Emergence of ferroelectricity in (SrTiO3)n−1(BaTiO3)1SrO films grown on (110) DyScO3.
Fig. 4: In-plane dielectric constant (K11) of 100-nm n = 6 (SrTiO3)n−1(BaTiO3)1SrO film on (110) DyScO3, and its tuneability at room temperature and high frequency.

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The synthesis, characterization and theoretical work at Cornell was supported by the US Department of Energy, Office of Basic Sciences, Division of Materials Sciences and Engineering (Award no. DE-SC0002334). Sample preparation was in part facilitated by the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (grant no. NNCI-1542081). Ferroelectric and dielectric measurements with temperature were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Infrared and terahertz studies were supported by the Czech Science Foundation (project no. 18–09265S) and by the MŠMT (project no. SOLID21-CZ.02.1.01/0.0/0.0/16 019/0000760). This work made use of Cornell Center for Materials Research Shared Facilities, which are supported through the NSF MRSEC program (no. DMR-1719875). Certain commercial equipment, instruments or materials are identified in this article to specify the experimental procedure adequately. Usage of commercial products herein is for information only; it does not imply recommendation or endorsement by NIST, and it is not intended to imply that the materials or equipment identified are necessarily the best available for the purpose.

Author information

N.M.D. and J.Z. synthesized the samples under the supervision of D.G.S. N.M.D. performed the ferroelectric and low frequency dielectric measurements versus temperature. G.H.O. performed the DFT calculations under the supervision of C.J.F. M.E.H. performed STEM measurements under the supervision of D.A.M. Millimetre-wave devices were fabricated and measured by E.J.M., A.M.H., X.L. and J.A.D. under the supervision of C.J.L., J.C.B. and N.D.O. R.U. and S.G. supplied the DyScO3 substrates. V.G. and C.K. performed the infrared and terahertz measurements under the supervision of S.K. N.M.D, D.G.S, E.J.M., A.M.H., N.D.O., G.H.O and M.E.H. wrote the manuscript. All authors discussed results and commented on the manuscript. The study was conceived and guided by D.G.S.

Correspondence to Darrell G. Schlom.

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Supplementary Discussion, Figs. 1–10, and Refs. 1–7.

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Dawley, N.M., Marksz, E.J., Hagerstrom, A.M. et al. Targeted chemical pressure yields tuneable millimetre-wave dielectric. Nat. Mater. 19, 176–181 (2020).

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