Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Abstract

There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. V C 2013 AIP Publishing LLC.

Combining ferromagnetic resonator and digital image correlation to study the strain induced resonance tunability in magnetoelectric heterostructures

“…Many ME systems based on ferromagnetic/ferroelectric heterostructures have been developed, encompassing voltage-tunable microwave signal processing devices [3][4][5], magnetoelectric random access memory devices [6][7][8][9] and strain-control GMR devices [10][11][12]. For all these kinds of systems, the properties are controlled via the elastic voltage-induced strains transmitted from the ferroelectric medium to the ferromagnetic one.…”

Effects of oxygen vacancies on polarization stability of barium titanate

“…It is obvious that, whether isolated or not, OVs result in the increase of dielectric loss. To avoid such an unfavorable effect and save energy, a smart strategy is to treat a ferroelectric device with high-pressure oxygen annealing [10,11]. In this protocol, the OV sites can be occupied by oxygen and thus the dielectric loss is reduced [10].…”

“…Moreover this structure may be tuned by strain [8,9]. It has also been confirmed that dielectric loss increases with the increase of the OV concentration [10,11]. To the best of our knowledge, however, micromechanism of OV behind the exceptional dielectric loss remains largely unexplored due to lack of an effective protocol for experiments.…”

Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO3 tunable capacitors with high figures of merit

“…Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO 3 Parallel plate capacitors with quality factors exceeding 1000 were fabricated using Ba 0.3 Sr 0.7 TiO 3 (BST) thin films grown by hybrid molecular beam epitaxy on epitaxial Pt bottom electrodes. The influence of film stoichiometry was investigated by varying the (Ba þ Sr)/Ti ratio around the stoichiometric composition.…”

“…[1][2][3][4][5] A main focus of materials and device optimization is to simultaneously achieve high quality factors (Q ¼ 1/tand, where tand represents the dielectric loss tangent) while tuning the capacitance at least by a factor of two with an applied DC bias. 2,6 Q-factors exceeding 1000 and tunabilities up to 5:1 were reported in BST films that were grown by molecular beam epitaxy (MBE).…”