Ordering of ferroelectric polarization1 and its trajectory in response to an electric field2 are essential for the operation of non-volatile memories3, transducers4 and electro-optic devices5. However, for voltage control of capacitance and frequency agility in telecommunication devices, domain walls have long been thought to be a hindrance because they lead to high dielectric loss and hysteresis in the device response to an applied electric field6. To avoid these effects, tunable dielectrics are often operated under piezoelectric resonance conditions, relying on operation well above the ferroelectric Curie temperature7, where tunability is compromised. Therefore, there is an unavoidable trade-off between the requirements of high tunability and low loss in tunable dielectric devices, which leads to severe limitations on their figure of merit. Here we show that domain structure can in fact be exploited to obtain ultralow loss and exceptional frequency selectivity without piezoelectric resonance. We use intrinsically tunable materials with properties that are defined not only by their chemical composition, but also by the proximity and accessibility of thermodynamically predicted strain-induced, ferroelectric domain-wall variants8. The resulting gigahertz microwave tunability and dielectric loss are better than those of the best film devices by one to two orders of magnitude and comparable to those of bulk single crystals. The measured quality factors exceed the theoretically predicted zero-field intrinsic limit owing to domain-wall fluctuations, rather than field-induced piezoelectric oscillations, which are usually associated with resonance. Resonant frequency tuning across the entire L, S and C microwave bands (1–8 gigahertz) is achieved in an individual device—a range about 100 times larger than that of the best intrinsically tunable material. These results point to a rich phase space of possible nanometre-scale domain structures that can be used to surmount current limitations, and demonstrate a promising strategy for obtaining ultrahigh frequency agility and low-loss microwave devices.
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Acknowledgements Work at Drexel University and the University of California at Berkeley was supported in part by the US National Science Foundation (NSF) and the Semiconductor Research Corporation under the ‘Nanoelectronics in 2020 and Beyond’ programme grant number DMR 1124696 and by the Materials Science Division of the US Army Research Office (ARO). Z.G. and G.X. acknowledge support from the ARO under grant number W911NF-14-1-0500. A.P. and A.A.P. acknowledge support from the NSF under grant number IIP 1549668. A.W.-C. acknowledges support from the NSF under grant number DMR 1608887. C.J.H. acknowledges support from the Office of Naval Research under grant number N00014-15-11-2170. J.E.S. acknowledges support from the Air Force Office of Scientific Research under grant number FA9550-13-1-012. I.G., A.S., H.B., J.E.S. and G.X. acknowledge support from the NSF–BSF (US–Israel Binational Science Foundation) joint programme under grant numbers BSF 2016637 and CBET 1705440. S.P. and A.R.D. acknowledge support from the ARO under grant number W911NF-14-1-0104. A.R.D. also acknowledges the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under award number DE-SC-0012375 for the development of the BST materials. A.D. acknowledges support from the NSF under grant number DMR 1708615. S.S. acknowledges support from the NSF under grant number DMR 1608938. L.W.M. acknowledges support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract number DE-AC02-05-CH11231: Materials Project programme KC23MP for the development of new functional materials. R.A.Y. and C.J.G.M. acknowledge support from ARO under grant number W911NF-14-1-0335. Numerical GLD and phase-field simulations were carried out on Proteus, a computer cluster supported by the Drexel University Research Computing Facility.