In this thesis it is shown how multiple states can be created in a capacitor structure that comprises ferroelectric PZT (lead-zirconium-titanate). ‘We were able to control the local electric field at the ferroelectric-electrode interface,’ says Anirban Ghosh. ‘By utilizing the coupling between switchable polarization of PZT and non-switchable polarization of ZnO, the creation of multiple states was realized.’
This coupling is a first step in realizing human brain inspired computing devices which are not digital but analog in nature. ‘As human beings, we process data in a dynamic way,’ Anirban says. ‘In my work multiple switchable non-volatile states were realized, opening new ways towards brain inspired adaptive computing.’
The PhD project was performed within the Inorganic Materials Science Group, led by Professor Guus Rijnders. Anirban: ‘He showed great confidence in me and in my work, giving me complete freedom to pursue my own idea, and develop it from scratch.’
In June 2016 Anirban published his work in the high-impact journal Advanced Functional Materials. ‘Understanding the problem at the core, is the most important step in scientific research,’ he reckons. ‘From there I attacked the issue, combining fundamental research with well thought-out growth/deposition experiments and methods to characterize our model system.’
In the first chapters Anirban reports the growth of ZnO of different thicknesses, being able to manipulate the disorder (roughness) to order ratios. The thickness of the ZnO layers was utilized to manipulate the electric field at the ferroelectric-electrode interface. The manipulation of the switching dynamics for different thicknesses of ZnO was analyzed. ‘By enabling the ferroelectric-to-switch in a multi-valued manner, an important step towards neuron-like adaptive and multi-state memories is achieved,’ he concludes.
‘Knowing how to create and maintain multiple states, opens up a completely new paradigm,’ Anirban says. ‘It shows how materials science is capable of opening up a new dimension in the field of computation technology. The most memorable moment was to win the Best Student Award at a conference in Singapore. Also I was an invited speaker at the Mesa+ Day. Broad interest was shown in my work here at the University of Twente.’
Anirban will be working as a post-doc at the University of California Berkeley after his PhD Defence. ‘The work will be in a similar field. This is one of the best universities in the work to proceed my academic career. I love the freedom of doing research very much, broadening my knowledge base continuously.’
‘I enjoyed collaborating with Mesa+ colleagues, especially learning in depth about thin film structures. During my PhD I learned how theory and modelling can be utilised to design smart experiments which can lead to newer advances in the field. That serves as an inspiration for future research.’