Recent progress of (Ba,Sr)TiO3 thin films for tunable microwave devices

Abstract

The (Ba 1-x Sr x )TiO 3 (BST) ferroelectric thin films exhibit outstanding dielectric properties, even at high frequencies (Ͼ1 GHz), and large, electric-field dielectric tunability. This feature makes them suitable for developing a new class of tunable microwave devices. The dielectric properties and dielectric tuning property of BST thin films are closely related to the film compositions, substrate types, and post-deposition process. The successful implementation of BST films as high-frequency dielectrics in electrically tunable microwave devices requires a detailed understanding of both their processing and material properties. This paper will review the recent progress of BST thin films as active dielectrics for tunable microwave devices. The technical aspects of BST thin films, such as processing methods, post-annealing process, film compositions, film stress, oxygen defects, and interfacial structures between film and substrate, are briefly reviewed and discussed with specific samples from the recent literature. The major issues requiring additional investigations to improve the dielectric properties of BST thin films for tunable microwave applications are also discussed.

Microwave loss mechanisms in Ba0.25Sr0.75TiO3 films

“…This observation is in agreement with thermodynamic predictions [26]. The reduction of oxygen vacancy concentration in the BST films is possible by optimization of the deposition conditions (deposition temperature [27], pressure [27,28], laser spot size on the target [29], etc), and/or by post-deposition annealing in oxygen atmosphere [30,31].…”

Systematic investigation of the annealing temperature and composition effects on the dielectric properties of sol–gel BaxSr1−xTiO3 thin films

“…Many studies have been carried out concerning the Ba/Sr ratio effect, on the optical properties [5][6][7][8], on nanomechanical characteristics [9], on the electrical properties [10][11] or dielectric properties at low frequencies [12] and microwave frequencies [13][14][15].…”

Novel Integration of Metal–Insulator–Metal (MIM) Capacitors Comprising Perovskite-type Dielectric and Cu Bottom Electrode on Low-Temperature Packaging Substrates

“…However, crystallization and densification of these dielectric films are largely dependent on the postdeposition high-temperature annealing in oxygen-rich ambient [2], which is incompatible with those low-temperature packaging substrates, and the low-cost base metal with high electrical conductivity such as Cu, which is commonly found on printed circuit boards.…”