Temperature stable BaSrTiO3 thin films suitable for microwave applications

Abstract

In this paper, the properties of an optimized BaSrTiO 3 thin film, deposited on an alumina substrate using a sol-gel process, are presented. The real and imaginary parts of the permittivity and the tunability have been measured over 7 decades of frequency and in a temperature interval of 320• C, which provides a good knowledge of the material properties for microwave applications. The dielectric properties of the films show a good stability in frequency and in temperature. From −80• C to 20• C, the permittivity changes less than 2% and from −75 • C to 100• C, the tunability stays higher than 90% of its maximum value.The frequency dependence of the relative permittivity of the thin film is rather small since it only varies from 375 at 1 kHz to 350 at 5 GHz. As a main consequence, the tunability which attains almost 60% under a bias field of 400 kV/cm, is very stable in frequency up to 5 GHz. The dielectric losses tan δ, measured up to 1 GHz, stay below 0.02 for the complete frequency range. Although the material is in the ferroelectric phase, the hysteresis effect is quite negligible, which results in a well-determined permittivity value for a given electric bias field. The characterized thin film has been integrated into a reflectarray cell allowing a dynamic control of the reflected phase. The measured phase-shift value is close to the simulated one, showing the performance of the material.

Decomposition of the different contributions to permittivity, losses, and tunability in BaSrTiO3 thin films using the hyperbolic law

“…7,9 The solution has been deposited on platinum coated alumina substrates at 4000 rpm during 20 s, and the samples have been annealed during 15 min in a pre-heated open air furnace at 750 C. Deposition of fourteen layers results in an overall film thickness of typically 0.85 lm. The BST thin films have been doped with 1% of manganese corresponding to a Ba 0.80 Sr 0.20 Ti 0.99 Mn 0.01 O 3 composition.…”

A reconfigurable miniaturized planar inverted‐F antenna with integrated BaSrTiO3 capacitor

“…The BST thin films were synthesized on alumina substrates by chemical solution deposition (CSD) using a modified sol‐gel process . Intergration with the DC and RF electrodes allows realization of MIM type capacitor components, compatible with the proposed antenna topology, which hence can directly be integrated in the antenna for experimental verification of the obtained simulation results.…”

Design and Development of a Tunable Ferroelectric Microwave Surface Mounted Device

“…The precursor solution was composed of barium and strontium acetates to which titanium n-propoxide and an organic stabilizer were mixed in appropriate proportions. Details of the solution preparation are given in [8,11]. The solution has been deposited on an alumina substrate at 4000 rpm during 20 s and the sample has been annealed during 15 min in a pre-heated open air furnace at 750 °C in order to evaporate the organic material and crystallize the BST film in the ferroelectric perovskite structure (Fig 3a).…”

“…The BST film does not have a preferential orientation as it can be seen from the X-ray diffraction (XRD) pattern performed with a Brucker D8 diffractometer using the CuKα radiation but it is well crystallized and no parasitic peak is visible. Successive deposition of eight layers results in an overall film thickness of typically 500 nm and in a polycrystalline structure (Fig 3b) [11,12]. The BST thin film covers the entire surface of the substrate.…”