Design and optimization of barium strontium titanate ferroelectric varactors

Date of Award


Degree Name

M.S. in Electrical Engineering


Department of Electrical and Computer Engineering


Advisor: Guru Subramanyam


Barium-Strontium-Titanate (BST) thin film based varactors are designed at specific capacitances under 0V dc bias on CMOS compatible low-resistivity silicon substrate. The BST varactor device operation is based on the nonlinear dielectric tunability of BST thin film sandwiched between two metal layers in a revised conductor-backed coplanar waveguide (CBCPW) transmission line configuration. The varactor capacitance at 0V dc bias is determined by the overlap area between the CPW signal line in the top metal electrode and a tapered shunt line in the bottom electrode. Therefore a series of devices with fixed 0 V capacitances ranging were designed and fabricated based on changing their corresponding overlap areas according to the original parallel plate capacitance equation. A schematic model is also utilized to extract the designed and measured capacitances. The relationship between the sizes of overlap areas and the extracted capacitances from the electromagnetic and schematic models is demonstrated by a reasonable agreement with the experimental measurements from fabricated devices.


Varactors Design and construction, Ferroelectric thin films, Electric engineering; ferroelectric; varactors; tunability; thin fim BST

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Copyright © 2012, author