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Ruud Steenwelle (promotion date: 11 May 2012)

Strain and composition effect in epitaxial PZT thin films


Promotion date: 11. May 2012

Promotor: Prof. dr. ing. Guus Rijnders

Co-promotor: Prof. dr. ing. Dave Blank


The successful integration of high-quality perovskite thin films with silicon, opens a pathway to create perovskite thin film devices with a large range of new functionalities. In this way piezoelectricity, superconductivity, magnetism and dielectricity can be integrated in the silicon technology and mass-production.

The relations are demonstrated between crystallographic and functional properties of PZT (Pb,(Zr,Ti)O3) films with thicknesses often used in applications such as piezoelectric MEMS. The effects of strain and compositions, and their mutual interactions, show the freedom to tune the functional properties of PZT thin films and its applications.

In particular, we were able to image ferroelectric domains using advanced microscopes and imaging techniques. They were found to switch, to rotate and to shrink to atomic scales in certain special circumstances, and we showed how to use this for optimizing properties of the piezoelectric MEMS. These results have led to the introduction of a new phase diagram for PZT thin films.

Is your thesis work of a fundamental nature, or also application oriented?

I feel lucky that I have been able to gain experience on both fundamental research and application oriented research and development.

On the fundamental size, the origin of piezoelectricity and the morphotropic phase boundary in certain piezoelectric materials are still unknown. We contributed to the understanding using strain engineering the ferroelectric domain structures. The recently achieved high-quality films by pulsed laser deposition, offered a great opportunity to discover the boundaries of the functionalities within which devices can be properly designed.

On the application development, I worked to make improvements on piezoelectric MEMS as a platform technology, for example in inkjet print heads, ultrasound transducers and energy harvesters. In this project companies were involved like Solmates, Thermofisher and Océ.

Was there a special moment that you recall?

In the last part of the PhD project, I was really happy when all separate research topics that were initiated earlier, were coming together and form a consistent story. Using the Landau-Devonshire thermodynamic theory and the adaptive phase theory, I was able to match theory and experimental evidence convincingly, demonstrating the effects of composition and misfit strain on epitaxial polydomain PZT films. A nice cross-pollination of theory and experiment was shown here.

Did you succeed in having some nice articles published?

Some of them are still underway. We hope to finish them in a post-doc period after the promotion date. Applied Physics Letters and Sensors & Actuators, published our findings already. Also was I a speaker on conferences in for example Xiang, China and in Vancouver, Canada.

What are your future plans?

After the experience with fundamental research, I am interested in a business career. It would be nice if research and the high-tech sector are going to be part of that. On the other hand, I am very interested in all kinds of job perspectives. I keep open all possibilities, so to say.

What, in your opinion, is important for Mesa+ to stay successful in future?

As a PhD student, one is allowed to make use of all the equipment available at Mesa+. This was of vital importance for my research as well, leading to very nice results at the end. The input of technical experts is very important, as they possess a lot of expertise and are always willing to help.

The approach of Mesa+ I like very much so. The PhD’s are encouraged to perform complicated experiments on their own. They are even expected to do so. This is a great way of building up one’s skills and learning to perform research independently. It should be noted that Mesa+ can only provide the optimum boundary conditions. The students need to seize the opportunities that they are provided with.

In future, I guess, it is important for Mesa+ to continue the drive for fundamental research towards excellence. However, it would be fun and useful to intensify the efforts to commercialize the fundamental findings. A possibility is to put the entrepreneurial opportunities in the centre of attention more often, for example at the annual Mesa+ day. I am convinced this is important for the continuity of the Mesa+ institute as an important player in international and national research.