DESIGN CONSIDERATIONS FOR A NOVEL COPLANAR WAVEGUIDE BASED FERROELECTRIC VARACTOR SHUNT SWITCH

ABSTRACT

Novel ferroelectric variable capacitor (varactor) shunt switches have been designed, and experimentally verified recently. The varactor shunt switches are designed for microwave and millimeterwave switching applications, based on the nonlinear dielectric tunability of the Ba_0.6Sr_0.4TiO₃ (BST) thin-films. Nanostructured BST thin-films with dielectric tunability as high as 350% were used in this study. The device consists of a coplanar waveguide line loaded by a ferroelectric varactor. The large capacitance of the varactor at zero bias shunts the input signal to ground, thus isolating the output port, resulting in the OFF state of the device. When one applies a bias voltage corresponding of approximately 10 V (a dc electric field of ∼ 250 kV/cm), the varactor's capacitance is reduced to a minimum, allowing maximum transmission to the output, thus resulting in the ON state of the device. The microwave switching performance of the varactor shunt switch is compared with the RF MEMS switches for potential applications at microwave and millimeterwave frequencies.

Keywords:

• Tunable microwave dielectrics
• ferroelectric thin-film
• varactors
• varactor shunt switch

ACKNOWLEDGMENTS

The authors thank Mr. Keith Stamper, Mr. Mark Calcatera, and Ms. Becky Cortez for their technical assistance, as well as Mr. Robert Neidhard and Mr. Edward Nykiel for their assistance in the measurements. The authors also acknowledge useful discussions with Prof. Spartak Gevorgian at Chalmers University of Technology, Sweden.