Microwave properties of tetragonally distorted (Ba0.5Sr0.5)TiO3 thin films

Abstract

A strong correlation is observed between the structure and the microwave dielectric properties of epitaxial Ba0.5Sr0.5TiO3 (BST) thin films deposited onto (001) MgO by pulsed laser deposition. Films were deposited at 750 °C in an oxygen pressure that was varied from 3 to 1000 mTorr. The tetragonal distortion (ratio of in-plane and surface normal lattice parameters, D=a/c) of the films depends on the oxygen deposition pressure. D varied from 0.996 at 3 mTorr to 1.003 at 800 mTorr. At microwave frequencies (1–20 GHz), BST films with low distortion have higher dielectric constants (ε∼500), and lower dielectric loss (tan δ∼0.02) compared to films with higher distortion. The correlation of the microwave properties with the film structure can be attributed to stresses and polarizability in the film. The BST film grown at the oxygen deposition pressure of 50 mTorr exhibits a large dielectric constant change and a low dielectric loss at the same time, which corresponds to the film in low stress (D=1.0004). For tunable microwave applications, BST films with low stress are desirable in order to achieve both low dielectric loss and large tunability.

Dielectric properties of BaMg1∕3Nb2∕3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

“…3 Numerous studies have shown that incorporating small amount of aliovalent (e.g., Mg 2þ 4 , La 3þ 5 , Al 3þ 6 , Ce 3þ 7 , Nb 5þ 6,8 ) or isovalent (e.g., Zr 4þ , Sn 4þ , Ge 4þ 9 ) ions into a BST lattice effectively modifies the dielectric properties (tunability, dielectric loss, and leakage current (LC)) of the BST film. 10 Mg 2þ and Nb 5þ , which are acting as an electron accepter and donor, respectively, by replacing the B site of the (A 2þ B 4þ O 2þ 3 ) perovskite, have received the most attention because of their drastic effect in altering the dielectric properties of the BST film.…”

Films minces ferroélectriques Ba2/3Sr1/3TiO3par ablation laser pour applications hyperfréquences

“…10'bar), la constante diélectrique mesurée à 12, 5 GHz est de 1114. Cette valeur est à comparer à E = 500 à 10 GHz obtenu par Kim et al [4] pour des films de BaSrTiO, de 300 nm seulement.…”

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

“…In the recent past, BST-based thin films for RF/microwave applications have been deposited on ceramic (MgO, LaAlO 3 , SrTiO 3 ) and a variety of other designer substrates. [141][142][143][144][145][146][147][148] Major drawbacks of these substrates are the high cost of the ceramic substrates and the fact that ceramic substrates, such as MgO, LaAlO 3 , and SrTiO 3 , are only available in small size geometries (2 in. wafers) which are not suitable for large-area film deposition.…”