Candidate: Delaram Sadat Ghadri
Title: Theoretical and Experimental Analysis of Resistor Networks for Use in Superconducting Analog to Digital Applications.
Date: December 5, 2018
Time: 1:00 pm
Place: EIT 3145
Supervisor(s): Mansour, Raafat R.
Superconducting micro-electronics (SME) technology is capable of realizing extremely high speed digital receivers performing direct digitization of microwave signals with very low power consumption. SME technology uses integrated circuits based on Josephson junctions and rapid single flux quantum logic operating at 4K. The analogue to digital converter (ADC) is a basic building block of such receivers. Quantization and sampling are two fundamental parts of ADCs. Flash ADCs are the fastest converters, which consist of comparators and a resistor network.
This thesis investigates the use of a multi-layer niobium-based low temperature superconducting process to implement the resistor network. Several configurations for resistors are investigated both electrically and thermally . The resistors are designed to maintain their values over 50GHz Floating metals structures are added and optimized to minimize inductance of the structure in order to have a frequency independent resistors over 50GHz. Several resistors and 1-bit R-2R ladder network are fabricated in the same process and measured in an RF cryogenic probe station at the Center for Integrated RF Engineering (CIRFE) lab at the University of Waterloo. Thermal theoretical analysis, using COMSOL software is also carried-out for these resistors to investigate temperature variations through the structures when operating at different power levels. The investigation is important to make sure that the dissipated heat by the resistors do raise the local temperature above the transition temperature of the niobium.
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