Two-port tunable interdigital capacitors fabricated on low-loss MBE-grown Ba0.29Sr0.71TiO3

This paper describes the fabrication, measurement, and modelling of radio-frequency (RF), tunable interdigital capacitors (IDC). The devices utilize electric-field tunable BaxSr(1−x)TiO3 (BST) thin films grown by hybrid molecular beam epitaxy (MBE) on LaAlO3 (LAO) substrates, a first growth of its kind. A high-quality interface was achieved by hot-sputtering epitaxial platinum. S/L-band IDCs demonstrate high quality factors (200) combined with 47% tunability. The devices demonstrate a commutation quality factor averaging 6,000 across the L band. A phase shifter unit cell was simulated and implemented using the IDC equivalent circuit parameters.