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Abstract
Silicon quantum dot spin qubit research at UNSW tests a large volume of devices in order to find those that pass all preliminary requirements to perform extensive measurements at cryogenic temperature. Currently, only one device can be tested in one cooldown session for preliminary testing, and strain-induced quantum dots are found when cooling down devices.
This thesis consists of two projects: first, the Si-MOS multiplexer project aims to improve efficiency by testing a number of devices through the multiplexing technique in one cooldown session. Second, the depletion mode charge sensor project intends to verify whether this modified device architecture could reduce the chance of forming strain-induced quantum dots while operating the device as a normal Single Electron Transistor (SET) charge sensor. In the multiplexer study, device robustness was examined and n-finger leakages were found on all tested samples. 74% of n-fingers conducted current with resistances at the M? regime due to high channel resistances contributed by the addressing switches. The results of SIMS analysis showed that the p-type channel stoppers had a lower doping concentration and shallower profile than the design, which could cause leakages. On the other hand, the results of the depletion mode charge sensor demonstrated that the device could be operated as an SET charge sensor, since electron charge transitions at a nearby quantum dot could be detected by this sensor through capacitive coupling. The two measured devices did not create strain-induced quantum dots, but there was not yet sufficient evidence to justify that this device architecture could significantly reduce the chance of forming these unintentional dots.
The results of the Si-MOS multiplexer project suggested that the fabrication process should employ ion implantation for making p-type channel stoppers, and redesign the addressing switches structure. Also, the depletion mode charge sensor project required a large number of devices to be measured, so that a statistical analysis could be created to justify whether this device architecture could reduce the chance of forming strain-induced quantum dots.