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Tunable microwave filters using ferroelectric thin films

Wang, Xu (2009)
Ph.D. thesis, University of Birmingham.

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Frequency agile microwave devices based on Barium Strontium Titanate (BST) thin films have gained a lot of interest in recent years. The frequency agility of the ferroelectric devices is based on the external DC electric field controlled permittivity of BST thin film. In this research work, several tunable microwave filters incorporating BST thin film varactors operating in a frequency range between 1 GHz and 25 GHz are designed, tested and analysed. A lumped element lowpass filter incorporating integrated meander line inductors and BST parallel plate capacitors is implemented on a high resistivity silicon substrate and demonstrates 32.1 % tuning of the cut-off frequency at 15 V. A combline bandpass filter employing integrated BST parallel plate varactors as tuning elements is implemented on a MgO substrate and shows a reasonable tuning from about 8 GHz to 12 GHz with 10 V bias of only one resonator. Two pole and four pole coupled resonator bandpass filters with discrete BST or GaAs varactors as tuning elements are implemented in a frequency range of 1 - 3 GHz. The filters based on BST parallel plate capacitors show an insertion loss in line with the GaAs filters, which is also the lowest insertion loss of BST filters ever reported. Future work on improving the BST film and metal film loss at tens of gigahertz range is also discussed.

Type of Work:Ph.D. thesis.
Supervisor(s):Lancaster, M.J.
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Electrical, Electronic and Computer Engineering
Subjects:TK Electrical engineering. Electronics Nuclear engineering
Institution:University of Birmingham
Library Catalogue:Check for printed version of this thesis
ID Code:1227
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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