PhD Defense of Francesco SERRA DI SANTA MARIA

This thesis investigates the behavior of Si and InGaAs FETs down to 10 K.
The study is born to answer impending question for the design of future quantum computers, particularly for what concerns processing electronics.
Within this framework, it is important to remember that processing electronics is needed to work as close as possible to the qubits, at an ambient temperature of a few Kelvin units.
Moreover, as this work shows, the noise generated in the device, either due to device-induced mechanism or to self-heating, needs to be maintained crucially low so not to distort the signals of the qubits.
Therefore, starting from the standard of an industrial 28nm Si technology, the thesis analyses the effects of deep cryogenic temperatures on this class sof MOSFETs and compares the results with what is already in literature or might still be under present study.
Furtheremore, in oreder to separate the effects that are induced by the material (Si in the first case) and the technology, the thesis proceeds to study devices relying on InGaAs.
As a first bridge to FDSOI, InGaAs MOSFETs with a buried oxide were studied, already highlighting both differences induced by the different quality of the oxide interface (higher Interface states) and new effects introduced by the new material under study (conduction in the satellite valleys).
Finally, with a particular interest for low-noise amplifiers, InGaAs-based high electron mobility transistors were studied.
The thesis has worked on both experimental and modelling topics.
For what concerns characterization of the studied devices, DC performances, flicker noise, capacitance behaviour, self-heating and conduction in the satellite valleys of InGaAs were the topics under study.
Starting from the data and knowledge collected throught the experimental analysis, the thesis also studied the applicabiulity of the Lambert W-function and of the Kubo-Greenwood integral on the 28nm Si FDSOI devices down to deep cryogenic temperature.
Finally, this work allowed to understand how each technology can be better suited for different purposes of processing electronics in quantum computers.
It moreover grants understanding on how MOSFETs and similar work when brought to cryogenic tenperature, according to both their structure and material.
The conduction in the satellite valleys of InGaAs has been a deeply investigated topic and, although the thesis produced very interesting results, it opened up the doors for further research in the future.
 

• M. Francis BALESTRA - Research Director CNRS : Supervisor
• M. Bogdan CRETU - Associate Professor HDR -National Higher School of Engineers of Caen  (ENSICAEN) : Reviewer
• M. Erik LIND- Full professor- Lund  University : Reviewer
• M. Christian ENZ - Professor of University - Federal Institute of Technology in Lausanne   (EPFL) :  Examiner
• M. Pascal XAVIER - Professor of University - Grenoble Alpes University : Examiner
• M. Gerard GHIBAUDO - Researcher - IMEP-LAHC : Guest
• M. Christoforos THEODOROU - Researcher - IMEP-LAHC : Guest