Guru Subramanyam, Ph.D.
Electrical and Computer Engineering
Two passive, analog phase control circuit designs utilizing ferroelectric varactors are presented. The tuning capabilities of single layer and parallel plate varactors deposited on a Ba0.6Sr0.4TiO3 (BST) thin film are characterized. Phase control is demonstrated through cascading multiple shunt varactors along a coplanar waveguide (CPW) structure. Through the application of a 0V – 8V DC bias, the capacitance in the circuit is tuned to control the transmission phase shift (angle of S21). Simulations of both phase control device structures are performed in AWR Microwave Office and compared with measurement data. Both circuit and mathematical models are developed and compared to simulation results. Multiple phase shifter devices of a varying number of varactor segments are fabricated on a high resistivity Si or sapphire wafer. Standard microelectronic processing techniques are used for fabrication of the phase shifter circuit. BST thin film is deposited using a large area pulsed laser deposition (PLD) system available in our lab. All circuits are tested from 1 - 20 GHz using an on-wafer probe station and a vector network analyzer. The phase shifter design consisting of 20 parallel plate varactor segments achieved the highest figure of merit (FOM) of 27.54 degrees/dB at a frequency of 15 GHz.
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Electrical and Computer Engineering | Engineering
Spatz, Devin William, "Design and Fabrication of Passive Barium Strontium Titanate (BST) Thin Film Varactor Based Phase Shifters for Operation within a 5-15 GHz Bandwidth" (2016). Honors Theses. 135.