Coplanar Waveguide Using Ferroelectric Thin Oxide Film: Dielectric Constant

• Published in: Journal of electroceramics 2004-07, Vol.13 (1-3), p.245-249
• Main Authors: Kim, W J, Kim, S S, Song, T K, Moon, S E, Kim, E K, Lee, S J, Han, S K, Kwak, M H, Kim, H Y, Kim, Y T, Ryu, H C, Kim, C S, Hang, K Y
• Format: Article
• Language: English
• Subjects: Bias; Coplanar waveguides; Dielectric constant; Direct current; Ferroelectric materials; Ferroelectricity; Microwaves; Oxide coatings
• ISSN: 1385-3449; 1573-8663
• DOI: 10.1007/s10832-004-5106-y

Coplanar waveguide (CPW) transmission lines were fabricated on thin ferroelectric Ba1-xSrxTiO3 films for tunable microwave applications. The growth of the ferroelectric oxide films was accomplished by a pulsed laser deposition with a partial oxygen background. Microwave properties of the CPW phase shifter were measured using a HP 8510C vector network analyser from 0.045-20 GHz with -40-40 V of dc bias. A large phase shift angle of about 120 degrees at 10 GHz was seen from the CPW (gap = 4 micron, length = 3 mm) with a 40 V of dc bias change. The dielectric constant of the thin ferroelectric film was found from the dimension of the CPW (gap, width, length) and the measured S-parameter by a modified conformal mapping. However, the dielectric constant of the ferroelectric thin film exhibits a gap dependency; dielectric constant (990-830) decreases with increasing gap size (4-19 micron, respectively). By adjusting the filling factors of the film, a "constant" dielectric constant of BST film is found to be 810 plus or minus 5. 12 refs.