Enhancing Tunability and Decreasing Temperature Sensitivity
- PDF / 5,380,852 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 179 Views
C8.20.1
Enhancing Tunability and Decreasing Temperature Sensitivity S.C. Tidrow, A. Tauber,1 D.M. Potrepka, F. Crowne, B. Rod Sensors Electron Devices, Directorate, Army Research Laboratory, Adelphi, MD 20783-1197, U.S. A. 1 Geo-Centers, Inc., New Upper Falls, MA 02164 ABSTRACT The employment of judicious substitution on B-sites in the perovskite oxide, BaTiO3, has yielded materials suitable for relatively temperature insensitive electric field tunable microwave devices. The properties, single-phase cubic perovskites with tunabilities as large as 30% at 1 V/µm and room temperature that possess low temperature coefficient of dielectric constant and tunability over the majority of the military specified temperature range, -55 to 125 ºC, have been achieved in the charge compensated system Ba1-xSrxTi1-2yCyDyO3 where C is Ho, Er, Tm, Lu, Sc, Y, In and D is Ta, Sb with 0 ≤ x ≤ 0.2, and 0 < y ≤ 0.10. INTRODUCTION Over the past decade there has been increasing interest in ferroelectric materials for electricfield tunable RF devices[1-9]. Of particular interest is the development of low cost, high performance phase shifters and variable true time delay devices for electronic scanning antennas[1-9]. New materials and device structures have been investigated in an effort to improve device performance[1-13]. Much of the early material efforts focused on investigating room temperature properties and reducing the loss tangent of the materials that is also typically associated with a resultant reduction in tuning of the material. While the figure of merit of the material, the tunability divided by the loss tangent of the material, has been used as the measure for improving materials, it has been shown that tuning of the material is the more important parameter for improving phase shifter device performance[13]. While more tunable materials usually have higher dielectric constants and higher losses that result in higher losses per unit length in both the material and metal of the device structure, it was shown that the length of the device can be significantly decreased in comparison to lower dielectric constant, less tunable, lower loss materials such that total losses, in order to provide 360 degrees of phase shift, are lower for the devices using highly tunable, higher loss materials. Bulk material phase shifters have been demonstrated with figures of merit of roughly 55 and 60 degrees/dB at 2.4 and 10 GHz, respectively[4,9]. Our group has been working to provide highly tunable, temperature insensitive, microwave compatible materials in an effort to provide the Army with broadband electric-field tunable devices such as variable true time delay devices[7] that operate consistently over the entire military specified temperature range for multi-function rf applications. The discussion in this paper will now focus on reporting that judicious charge compensated (dipole-like) substitution on B-sites in the perovskite oxide, BaTiO3, provides materials suitable for relatively temperature insensitive electric field tunable microwave dev
Data Loading...
