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Title: High-frequency electromagnetic characterisation and modelling of extreme impedance devices
Author: Votsi, Haris
ISNI:       0000 0004 7960 9184
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2019
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Nanoscale devices have an intrinsic impedance significantly different than the 50-Ω reference impedance of the measurement systems. This results in a high reflection coefficient, limiting the accuracy of the measurements leading in imprecise characterisation. In addition, the small dimensions of nanoscale devices forbid their physical access using conventional microwave probes. It is therefore essential to investigate new measurement techniques and to develop access structures, for nanoscale high-frequency characterisation. This thesis presents the fabrication of new access structures and calibration standards based on a co-planar waveguide design, for the microwave measurement of nanoscale devices. The calibration structures are used for the first time to move the measurement reference plane to a nanoscale device using a calibration algorithm. Furthermore, to mitigate for the impedance mismatch between the devices and the measurement systems, a new measurement technique based on active interferometry was developed. The method is based on a simplified measurement configuration and a custom calibration that mitigates for the finite directivity of the couplers used for the implementation of the technique, achieving a significantly higher measurement sensitivity for extreme impedances compared to conventional techniques. To showcase the potential usage of nanoscale devices within a microwave application, a prototype coplanar-waveguide switch has been developed that incorporates indium arsenide nanowires. The prototype device has shown encouraging high-frequency switching capabilities and an equivalent circuit model was developed that matches the high-frequency S-parameters of the device within an 8% error. Lastly, the electromagnetic coupling between calibration standards within an on-wafer environment has been successfully measured and investigated using an electro-optic on-wafer measurement system. The coupling can affect the accuracy of a calibration performed, and can have critical ramifications to the accurate characterisation of nanoscale devices.
Supervisor: Aaen, Peter Sponsor: University of Surrey
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral