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Targeted chemical pressure yields tuneable millimetre-wave dielectric



Natalie M. Dawley, Eric J. Marksz, Aaron Hagerstrom, Gerhard H. Olsen, Megan E. Holtz, Jingshu Zhang, Chris Long, Craig Fennie, David A. Muller, Darrell G. Schlom, James Booth, Nate Orloff


Tunable dielectrics are key constituents for emerging high-frequency devices in telecommunications—including tunable filters, phase shifters, and baluns—and for miniaturizing frequency-agile microwave and millimeter-wave components. Today, strained films of (SrTiO3)6SrO have the highest room-temperature figure of merit (FOM), which combines measures of loss and available tuning, of any tunable dielectric material at millimeter-wave frequencies . The low loss at frequencies up to 125 GHz results from the defect mitigating nature of the (SrTiO3)nSrO Ruddlesden-Popper structure; the tunability arises from a ferroelectric instability induced by epitaxial strain. Unfortunately, the necessity for epitaxial strain limits the film thickness to 50 nm or less, which results in insufficient total device tuning for many practical applications. Here, we employ a chemical alternative to provide local strain to help induce a ferroelectric instability, by strategically introducing barium into this Ruddlesden-Popper titanate. No natural barium-containing Ruddlesden-Popper titanates are known, but this atomically-engineered superlattice material enables low-loss, tunable dielectric properties to be achieved with lower epitaxial strain, creating a path to thicker materials and higher device tuning. This combination of local, chemical strain with epitaxial strain results in new low-loss (SrTiO3)n−m(BaTiO3)mSrO tunable dielectric materials with a 200% improvement in the FOM at commercially-relevant millimeter-wave frequencies.
Nature Communications


Tunable Dielectric, epitaxial, ferroelectric, millimeter-wave frequencies


Dawley, N. , Marksz, E. , Hagerstrom, A. , Olsen, G. , Holtz, M. , Zhang, J. , Long, C. , Fennie, C. , Muller, D. , Schlom, D. , Booth, J. and Orloff, N. (2019), Targeted chemical pressure yields tuneable millimetre-wave dielectric, Nature Communications, [online],, (Accessed April 18, 2024)
Created December 22, 2019, Updated October 12, 2021