Microwave dielectric properties of graded barium strontium titanate films

Abstract

Compositionally graded barium strontium titanate (BaxSr1−xTiO3 or BST) multilayers (5mol% MgO doped and undoped) were prepared via metallo-organic solution deposition on Pt–Si substrates and characterized electrically at 0.5, 5, and 10GHz. For the undoped BST multilayers, the small-signal dielectric response, tunability, and the loss tangent at 10GHz were 261, 25% at 1778kV∕cm, and 0.078, respectively. On the other hand, the Mg-doped BST multilayers displayed a significant improvement in the loss characteristics at 10GHz (0.039) but the dielectric response and its tunability were lower (189 and 15%, respectively, at 1778kV∕cm).

Understanding order in compositionally graded ferroelectrics: Flexoelectricity, gradient, and depolarization field effects

“…Their distinctive electric-field, thermal, and stress susceptibilities make such systems potentially important for a range of devices [2]. Compositionally graded ferroelectrics have been probed both experimentally [3,[5][6][7][8] and theoretically using Slater models [9], phenomenological Landau theory [10][11][12][13], transverse Ising models [14,15], and first-principles calculations [4] in an attempt to understand their internal crystal and polarization structure and the mechanisms underlying the manifestation of exotic properties. In this work, we focus on phenomenological approaches and thus narrow our discussion in this capacity.…”

Performance Enhanced Complex Oxide Thin Films for Temperature Stable Tunable Device Applications: A Materials Design and Process Science Prospective

“…On a positive note, due to the overlapping ''tails'' of the temperature dependencies of the permittivities of the top and bottom ferroelectric films, the tunability of such a varactor is expected to be larger than if the varactor was composed of only uniform composition BST 25/75 or BST 75/25 films. Although the quality factor of the varactor is highest over same temperature interval where the capacitance is temperature stable, the 1MHz Q-value is somewhat low, Q ~36,/ tan ~0.028, (Q~ 10/ tan ~0.1 at 10 GHz) with respect to the that obtained for the graded films and multilayer quasi graded films (Cole et al, 2008b). …”

“…The ARL-UConn group has also contributed to the body of knowledge focused on microwave performance of compositionally graded BST films. Specifically, the dielectric properties of their Mg-doped and undoped quasi-up-graded multilayer BST heterostructures at GHz frequencies were reported whereby they achieved high dielectric tunability (15%-25% at 1778 kV/cm) and low losses (0.04-0.08) (Cole et al, 2008b). The microwave characterization of both BST materials designs were carried out at frequencies ranging from 0.5 to 10 GHz using a coplanar inter-digitated capacitor (IDC) device configuration.…”

“…As with the studies discussed above there was no data reporting the temperature dependence of the dielectric response. Recently, the collaborative research activities between the U.S. Army Research Laboratory (ARL) and the University of Connecticut (UConn) has resulted in a series of publications focused on the dielectric response and temperature stability of MOSD fabricated compositionally stratified/multilayered BST (BST60/40 -BST75/25 -BST90/10) thin films on Pt-Si substrates , Cole et al, 2008a, Cole et al, 2008b. This series of papers evaluated the dielectric response for both RT material/device performance as well as temperature stability at 100 kHz and microwave (10 GHz) frequencies.…”

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

“…BST thin films with extreme temperature insensitivity have been demonstrated recently, [135][136][137][138][139][140][141][142] by conceiving a material design which controls the magnitude and the sign of the temperature coefficient of capacitance (TCC) of the BST thin film material in a parallel plate varactor device configuration. In particular, a very successful material design consisted of a compositionally stratified BST multi-layer heterostructure material design whereby the Ba/Sr ratios range from 60/40 to 90/10 within the thin film heterostructure.…”