Public defence of doctoral thesis in the field of Advanced materials and photonics, M.Sc. Jennifer Ott

M.Sc. Jennifer Ott will defend the thesis "Application of atomic layer deposited thin films to silicon detectors" on 19 March 2021 at 12 in Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering.

Opponent: Dr. Kevin Lauer, CiS Forschungsinstitut für Mikrosensorik GmbH, Germany
Supervisor: Professor Hele Savin, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering

The public defense will be organized via remote technology. Follow defence: https://helsinki.zoom.us/j/68423621703
Zoom Quick Guide: https://www.aalto.fi/en/services/zoom-quick-guide

Thesis available for public display at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Press release:
Silicon is the most common substrate material in semiconductor radiation and particle detectors due to its reasonable cost, good availability and processability. Pixel detectors made of silicon are used for particle tracking at many high-energy physics experiments, including all large experiments at the Large Hadron Collider at CERN. These form a very challenging environment for silicon detectors, especially due to the extreme radiation levels. This doctoral thesis features the application of aluminium oxide (Al2O3) thin films grown by atomic layer deposition (ALD) as field insulation and surface passivation in silicon pixel detectors. This approach aims to mitigate some of the radiation-induced damage on detectors, as well as reduce the number of high-temperature fabrication steps, by using AC-coupled pixel sensors with Al2O3 as insulator, and titanium nitride (TiN) thin-film biasing resistors. Surface passivation and electrical properties of Al2O3 films deposited on detector-grade float-zone or magnetic Czochralski silicon are studied first with contactless characterization methods, and later in diode and MOS capacitor devices. Specifically, the impact of the oxygen precursor used for ALD on the properties of Al2O3 films is investigated. While water as oxidant provides the best recombination lifetimes, as well as the best breakdown properties in diodes, the negative oxide charge achieved with this ALD process is comparatively low and is compensated in gamma irradiation. Films deposited using ozone exhibit higher charge and better radiation hardness, and considering all experiments, a combination of water and ozone is identified as the best choice of ALD oxidant. In addition, the phenomenon of blistering in Al2O3 films deposited with water is investigated in more detail, and new observations on the influence of substrate doping and resistivity on blistering are shown. Processing of pixel detectors is described with an emphasis on the ALD steps, also noting on the post-anneal temperature and TiN bias resistor fabrication. Finally, pixel sensors are flip-chip bonded to an existing readout ASIC and tested with radioactive sources, confirming their functionality. It is concluded that ALD-grown Al2O3 films are a promising alternative to the conventionally used silicon oxide and insulating implants for small-pitch silicon pixel detectors, which are under development for a variety of future collider physics experiments.

Contact information of doctoral candidate: