Robust Tunability and Newly Emerged Q Resonance of Ba_0.8Sr_0.2TiO₃-Based Microwave Capacitors under Gamma Irradiations

The complex resonance of dielectric quality factor Q, combined with a capacitance tunability n higher than 3:1 without any dispersion, was achieved in the voltage-tunable interdigital capacitors (IDCs) based on epitaxial Ba_0.8Sr_0.2TiO₃ ferroelectric thin films across the microwave L (1-2 GHz), S (2-4 GHz), and C (4-8 GHz) bands at room temperature. The resonant Q and n features were driven by the microwave responses of the ferroelectric nanodomains engineered in the films. To promote their application in space radiation environments, the evolutions of Q and n both as functions of frequency f (1-8 GHz) and applied electric field E (0-240 kV/cm) were systematically investigated under a series of gamma-ray irradiations up to 100 kGy. The robust capacitance tunability was accompanied by the emergence of an additional Q resonance at 2.3 GHz in most post-irradiated devices, which is ascribed to extra polar nanoregions of expanded surface lattices associated with oxygen vacancies induced by irradiations.