Novel approaches to ferroelectric and gallium nitride varactors

Date of Award


Degree Name

Ph.D. in Electrical Engineering


Department of Electrical and Computer Engineering


Advisor: Guru Subramanyam


This dissertation addresses the implementation of high-electron-mobility transistor (HEMT) based gallium nitride (GaN) varactors and compares them to barium strontium titanate (BST) parallel plate varactors in terms of tunability, quality factor, power handling capability, and size. New designs of multilayered BST varactor devices that utilize three-dimensional packaging of high dielectric ferroelectric materials are described. These structures are designed to improve device quality, while also generating new geometries that explore device physics that have not been previously explored with barium strontium titanate.A GaN foundry process was used to fabricate two varactor topologies, and devices have measured tunability exceeding 40%. Capacitance voltage relationships of the varactors are compared to intrinsic capacitances of transistors of the same gate periphery and bias voltages. Correlations between measurements are described with findings that will support design success of future GaN based varactors.A 1-Port BST varactor device was also generated, and the resulting capacitance has more than 60% tunability in a 0.135 mm² total device size. The resulting device geometry is similar to those of previous designs and allows for a direct comparison to the measured performance of 1-Port GaN varactor devices.Nonlinear device models are generated for each varactor technology and used in the design of a radio frequency filter implemented on a printed circuit board. The same filter is used with both GaN and BST varactors so tests of the RF signal power handling capability as well as bias power consumption are compared.


Varactors Design and construction, Gallium nitride, Ferroelectric devices, Electrical Engineering, varactor, capacitor, barium strontium titanate, gallium nitride, BST, GaN

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Copyright © 2014, author