Reconfigurable RF/Microwave and Millimeterwave Circuits Using Thin Films of Barium Strontium Titanate and Phase Change Materials

Date of Award


Degree Name

Ph.D. in Electrical and Computer Engineering


Department of Electrical and Computer Engineering


Guru Subramanyam


Tunable passive rf/microwave devices are the building blocks of reconfigurable electronics. Barium Strontium Titanate (BST) based tunable devices are being studied over for two decades now and this technology is very mature. Researchers have tried different material compositions, substrates, and deposition techniques to increase the tunability of the BST thin films. Researchers have also demonstrated reconfigurable devices at rf/microwave frequencies, however with only limited applications. In this work a novel technique of integrating high tunable dielectric materials such as BST, in combination with a germanium telluride (GeTe) phase change material (PCM) is demonstrated. Integrating phase change material thin films with BST thin films gives additional tuning. The idea of integrating PCM with BST initiates a new era of reconfigurable electronics. These new devices can be implemented with very less fabrication constraints. A low loss rf switch with 0.23 dB insertion loss and more than 19.75 dB isolation at 15 GHz is presented. v An MIM varactor with increased tunability of about 6.3:1 (57%) is achieved, compared to 4:1 tuning of conventional varactor by integration of BST and GeTe thin films. Analog phase shifters with 360° phase shift in the frequency range of 24 GHz to 50 GHz has been demonstrated with good figure of merit (FOM) of 46.64 degrees/dB at 50 GHz and 19.07 degrees/dB at 24 GHz using MIM varactors with BST and GeTe thin films and 319° phase shift at 24 GHz with FOM 12.8 degrees/dB and more than 360° phase shift at 50 GHz with FOM(2V-10V) >21.5 degrees/dB using MIM varactor with only BST thin films. A defected ground structure (DGS) band stop filter with enhanced band-rejection behavior with a notch depth of -39.64 dB @ 27.75 GHz by cascading two-unit cells using BST thin films is achieved. Tunable DGS band stop filters were demonstrated by integration of BST and GeTe with 2.25 GHz tunability from 30.75 GHz to 33 GHz (7.32%) using a single filter and 3.25 GHz tuning from 27 GHz to 30.25 GHz (12.04%) by cascading two filters.


Electrical Engineering, 1.) Reconfigurable RF Switch 2.) Phase Shifter 3.) Tunable Band Stop Filter 4.) Phase Change Material (PCM)/ Germanium Telluride (GeTe) 5.) Barium Strontium Titanate (BST) 6.) Integration of BST with PCM

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