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Ferroelectric thin films

The aim of this work package was to develop effective methods for depositing ferroelectric thin films by pulsed laser deposition (PLD).

Our key interest was to deposit Ba Sr Ti O films (BSTO). These films were deposited on LAO and MgO substrates using single- and multi-target methods. The main objective was to broaden considerably the Curie transition in order to extend the temperature range of operation. This was achieved by depositing different stoichiometriy layers of BSTO that possessed different Curie transitions.

Two routes of thin BaxSr1-xTiO3 (where x = 0.25, 0.50 and 0.75) films deposition have been explored:
- Using a single target with corresponding stoichiometry and
- From two targets as a periodic structure of BaTiO3 (BTO) and SrTiO3 (STO) layers. It was found that both methods produce samples with stoichiometry close to that expected.

Raman spectroscopy showed that the transitional period in the thin films made by multi-target method was wider in the temperature range. The thin film made by the single target method becomes completely cubic at about 360 to 380K range whereas the thin film made from the two target film still shows the tetragonal and cubic phase at the same temperature range.

This broadening of phase transition is also evident in the preliminary electrical measurements made. The results prove the possibility of using the multi-target pulse laser deposition as a more flexible method for engineering thin film stoichometry.

Reported by

Imperial College London
Exhibition Road
SW7 2AZ London
United Kingdom
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