Development of flexible thin films using plasma sputtering and control of their magnetic properties via Substrate roughness

Abstract

Although relatively young in the history of technology, thin films are firmly established in modern life. They form an essential part of electronic devices for data applications, communication, energy harvesting or field of medicine. Initially developed on solid substrates they found a niche in flexible market, enabling more exotic functions such as smart wearable textiles or curved elastic displays.
This project is focused on flexible thin films in nanometre range and study of their structural and magnetic properties. Particular attention was placed on substrates which form the base for a film to grow. Industry well known Kapton® and piezoelectric polyvinylidene difluoride (PVDF) foils were chosen for this purpose to act as flexible support for a film of common ferromagnetic materials - Fe, Co and NiFe. Samples were fabricated by popular magnetron sputtering method. Our films demonstrated an outstanding physical durability and retention of their magnetic properties even after repeatable mechanical stress. In fact, magnetic properties of our samples were found to be as good or better when compared to reference samples constructed on a solid substrate.
We have discovered some unexpected results when depositing very thin films onto roughened substrate surface. Magnetic coercive field significantly increased in some materials, whilst effective anisotropy developed in others that not normally possess one. These effects were firmly linked to the substrates themselves. This thesis reports on the so-called Roughness Effect and investigates conditions in which it intensifies.
Our study extends to exchange bias phenomena and a novel way of its construction. This is based on a reduction of ferromagnetic layer in the system by its deposition on a diamagnetic substrate. This simple yet effective innovation could pave the way for easier and inexpensive fabrication of devices based on exchange bias.
Here explored Roughness Effect and Exchange Bias are scientifically interesting phenomena. But this work also provides deeper understanding for both, whilst suggesting a simpler modification of magnetic properties in ferromagnetic thin film, which are the key players on electronics market today.

Date of Award	14 Dec 2020
Original language	English
Awarding Institution	University of Portsmouth
Sponsors	Kurt J. Lesker Company Ltd
Supervisor	Melvin Vopson (Supervisor) & Hooshyar Assadullahi (Supervisor)