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Title: Ferroelectric microwave circuits
Author: Cheng, Leong Ching
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2009
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Ferroelectric materials have been found to be particularly attractive materials for the development of tunable microwave devices over the past few decades due to their distinctive characteristic that is the variation of dielectric constant as a function of electric field. In this research project, the work on how the finite difference method (FDM), a computational technique, is modified to suit the evaluation of the cross-sectional field distribution of a ferroelectric-based transmission line is presented and the results are verified. The modified FDM was employed for determining the effective dielectric constant (Ɛeff) and the characteristic impedance (Zc) of ferroelectric-based structures where the spatial variation of dielectric constant was taken into consideration. A significant portion of this research is focused on the application of ferroelectric materials in designing tunable microwave devices. Two optimised phase shifters incorporating Barium Strontium Titanate (Ba0.5Sr0.5TiO3 or BST) ferroelectric thin-films are designed, fabricated and measured. One is based on simple coplanar waveguide (CPW) transmission line, and another is based on tapered CPW structure. To date, no work on tunable attenuator using ferroelectric materials has ever been reported, as contrary to other extensively studied ferroelectric-based tunable microwave devices, namely tunable resonators, filters, and phase shifters. In this work, a novel design of tunable attenuator integrating BST thin-films is presented and verified with experimental results from a similar design of tunable attenuator based on Roger/Duroid 6010LM substrate of dielectric constant 10.2. The application of ferroelectric thin-films enables continuous variation of attenuation under controlled bias voltages with significant size and weight reduction in the overall device.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering