MESA+ University of Twente
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Minh Duc Nguyen (promotion date: 30 June 2010)

Ferroelectric and piezoelectric properties of epitaxial PZT films and devices on silicon

Promotion date: 30. June 2010

Promotors: Prof. Dr. Ing. Dave Blank

Assistant Promotor: Prof. Dr. Ing. Guus Rijnders

Main goal was to integrate Pb(Zr,Ti)O3 (PZT) thin films into microelectromechanical systems (MEMS), using the pulsed laser deposition (PLD) technique. By using conductive-oxide electrodes, the accumulation of oxygen vacancies and the formation of an interfacial layer can be prevented; therefore, the decrease of remnant polarization is prevented with an increase in the switching cycles. Effects of the interfacial layer near the ferroelectric film-electrode interface, on the ferroelectric and piezoelectric properties of PZT films, have been discussed. Furthermore, the integration of epitaxial PZT thin films onto silicon cantilever beams is investigated.

Were the investigations performed new?

PZT thin films used in MEMS is not very new. However, the epitaxial thin films to optimize high polarization and high piezoelectric properties are. Here, the investigations were aimed towards optimizing the technique. We build and studied two devices: a cantilever and a membrane, and checked the properties involved. Here, collaboration within MESA+ was rewarding. Together with the TST-group, I was able to measure the displacement of piezo-capacitors and piezo-cantilevers, using a laser-Doppler vibrometer.

Was your thesis project fundamental or more application-oriented?

Changing thin film compositions and thicknesses, for example, can lead to surprising changes of properties in devices. Then, fundamental questions arise as to why this happens and what underlying mechanisms play an important role.

In experiments, of course, one needs theoretical knowledge to build successful set-ups. This I found the most challenging part. Results can depend strongly on details during the etching process, the electrodes used and the etchants, and also performing very active or more kind etching procedures.

Did some nice publications appear?

Two are already published, in Applied Physics Letters and the Journal of Micromechanics and Microengineering. Two other publications are submitted.

What are your future plans?

At the moment, I am working for SolMateS, a spin-off company of the University of Twente. Academic research is helpful for SolMateS to build all kinds of small devices, using large-area PLD. My research is relevant for devices using cantilevers to catch and detect DNA fragments.
After that, I hope to return to my native country, Vietnam. Perhaps in the more far future an own research group would be possible, starting a new field, new thinking and building new useful systems. I hope to give new incentives to nanotechnology in Vietnam, and to attract new talent to find a career in this field.