AVS 50th International Symposium
    Electronic Materials and Devices Wednesday Sessions
       Session EM-WeM

Invited Paper EM-WeM5
Using Strain to Control Microwave Tunability and Loss in Barium Strontium Titanate Thin Films

Wednesday, November 5, 2003, 9:40 am, Room 321/322

Session: Multifunctional Electronic Materials
Presenter: S.W. Kirchoefer, Naval Research Laboratory
Authors: S.W. Kirchoefer, Naval Research Laboratory
W. Chang, Naval Research Laboratory
J.A. Bellotti, Naval Research Laboratory
J.M. Pond, Naval Research Laboratory
D.G. Schlom, Pennsylvania State University
Correspondent: Click to Email
Barium strontium titanate thin films exhibit an electric field dependent dielectric constant which can be exploited for tunable microwave devices. This technology has been of limited applicability due to the relatively high dielectric losses that typically accompany high tuning. The control of dielectric loss is of critical technological importance. Manipulation of deposition conditions and film impurities have been investigated widely as means for achieving improved films. Engineered film strain is an additional material parameter that can be controlled toward these ends, and this talk will report on experiments that demonstrate the advantages of both strain minimization and strain enhancement on the microwave properties of barium strontium titanate and strontium titanate thin films. It will be shown that the structural distortion caused by film strain results in decreased dielectric constant and tuning for compressive strain and increased corresponding values for tensional strain at room temperature. These results can be understood by examining the effects of lattice distortion on Curie temperature. A model based on thermodynamics and strain-induced polarization will be presented. The effects of strain on dielectric losses and device quality factor will also be discussed. Results from substrate mismatch strain and film annealing studies will be presented. Ongoing efforts to measure effects of extrinsic strain induced by externally-applied pressure will be discussed.