Breaking symmetry to create a parallel-plate varactor dielectric with unparalleled microwave performance

Abstract

Voltage-tunable capacitors (varactors) are key to microwave circuits. Tunable dielectric varactors outperform competing technologies in almost every relevant metric but usually suffer from high dielectric loss. In contrast, Ruddlesden-Popper (RPs) dielectric thin films have remarkably low microwave loss. Unfortunately, their crystallographic symmetry has until recently dictated an in-plane device structure, precluding the favorable out-of-plane parallel-plate varactor design for minimized size and maximized electric field in the tunable dielectric. Guided by theory, we report RPs akin to the widely studied tunable microwave dielectric BaxSr1-xTiO3. Assembling these same atoms into the first RP phase with broken out-of-plane symmetry, we achieve a low-loss, out-of-plane tunable dielectric thin film. The highest performing film, (ATiO3)nAO film with A = Ba0.45Sr0.55 and n = 8, unlocks a tenfold improvement in the figure of merit for out-of-plane tunable dielectrics at 10 GHz, paving the way for a new generation of tunable monolithic microwave integrated circuits.

63 pages with 34 main manuscript pages and supplementary

References in corpus (5)

• Experimental demonstration of hybrid improper ferroelectricity and presence of abundant charged walls in (Ca,Sr)${}_3$Ti${}_2$O${}_7$ crystals
• Polar octahedral rotations: a path to new multifunctional materials
• Atomically precise interfaces from non-stoichiometric deposition
• Interface control of emergent ferroic order in Ruddlesden-Popper Sr${}_{n+1}$Ti${}_n$O${}_{3n+1}$
• Infrared nano-spectroscopy of ferroelastic domain walls in hybrid improper ferroelectric Ca${}_3$Ti${}_2$O${}_7$