Most wireless electronics would not work without varactors. An international team that includes Czech physicists has now developed a material for them that lets electronics use less energy. The study appeared in the prestigious journal Nature Electronics.
What varactors do
High-frequency wireless electronics need components that use as little energy as possible. Varactors play a key role among them. A varactor is a capacitor whose capacitance can be changed smoothly by an applied voltage. This lets a circuit tune its frequency electronically, without any moving parts. Varactors are found, for example, in tunable filters or in antennas that can steer a signal.
The catch is that materials for varactors usually force a compromise. A material that tunes well tends to absorb a lot of energy and turn it into heat. And the other way round too. Yet having both at once, good tunability and low losses, would be ideal.
Exactly such a material has now been prepared. An international team that includes the group of Stanislav Kamba from the Institute of Physics of the Czech Academy of Sciences has developed a thin-film material that can be tuned unusually strongly by an electric field while keeping record-low losses in the microwave range. The results appeared in Nature Electronics, a journal published by Nature Portfolio since 2018 that covers both basic and applied research across the whole of electronics. It ranks among the most highly rated journals in its field.
Layers stacked atom by atom
The material has what is called a Ruddlesden-Popper crystal structure. It can be compared to a sandwich in which thin oxide layers with the composition (ATiO₃)ₙAO regularly alternate at the level of individual atoms. They were prepared by a team from Cornell University using molecular beam epitaxy (MBE), a method that builds the material layer by layer.
The Czech group contributed measurements in the terahertz and infrared range and, above all, explained why the material behaves this way. The cause is a so-called soft ferroelectric phonon, a peculiar vibration of the atoms that changes the material's structure and with it its electrical properties. This vibration responds sensitively to an electric field, so even a weak stimulus shifts it significantly and thereby tunes the permittivity, the quantity that determines a capacitor's capacitance.
"The main advance lies in how you tune them," says Stanislav Kamba, who took part in the research. "Earlier related materials could only be tuned along the layers. The new ones tune across their thickness, perpendicular to the surface, and that is exactly what makes it possible to build very small varactors from them."
The work is the result of a long-standing collaboration between Kamba's group and Professor Darrell Schlom of Cornell University. Stanislav Kamba is among the leading experts in high-frequency dielectric, terahertz, and infrared spectroscopy and in the behaviour of ferroelectric and multiferroic materials.
F. Bergmann, M.R. Barone, Z. Tian, A. Ross, G.H. Olsen, M.C. Papac, Samuel Freed, B.T. Bosworth, N.R. Jungwirth, E.J. Marksz, T.M. Karpisz, A.C. Stelson, N. Schnitzer, L. Bhatt, D. Sotir, A. Surampalli, V. Goian, C. Kadlec, A. Hansen, N. Rongitsch, D.A. Tenne, S. Kamba, D.A. Muller, I. Takeuchi, Long-Qing Chen, L.W. Martin, N.D. Orloff, and D.G. Schlom, Breaking symmetry yields a low-loss out-of-plane tunable microwave dielectric, Nature Electronics, (2026) https://doi.org/10.1038/s41928-026-01651-y
