Microwave tunable devices based on patterned ferroelectric thin film

Ferroelectric based varactors have been widely used in microwave tunable devices such as filters, phase shifters and impedance matching networks. Common used ferroelectric varactors are parallel plate structure and coplanar structure. In general, ferroelectric varactors have advantages of fast tuning speed, small size, low power consumption, and negligible current consumption. For the coplanar ferroelectric varactors, they need relatively higher bias voltage but can be easily fabricated. In fabricating coplanar ferroelectric varactors, we could further use patterned ferroelectric thin film for fabricating a planar tunable microwave device in order to reduce the device's insertion loss and unintentional tuning. Practical examples of phase shifter and tunable filters using high temperature superconductors (HTS) YBa
₂
Cu
₃
O
_7-δ
(YBCO) thin film and ferroelectric BST thin film will be presented. Other tunable devices using conventional conductor, gold as an example, such as phase shifters, impedance matching networks will also be discussed.