Jury Members

Mme Céline LICHTENSTIGER    UNIVERSITÉ DE GENÈVE, Rapporteure
M. Guillaume NATAF  Université de Tours  Rapporteur
M. Jean François DAYEN Université de Strasbourg Examinateur
M. Pavlo ZUBKO University College London Examinateur
M. Stéphane FUSIL Laboratoire Albert Fert - CNRS Invité

This thesis investigates the fabrication and controllable manipulation of freestanding ferroelectric oxide membranes, with a particular focus on strain and flexoelectricity as levers for tuning polarization. In contrast to conventional substrate-clamped thin films, released membranes possess enhanced mechanical freedom, providing a direct platform to probe how strain gradients influence ferroelectric behavior.
Using a sacrificial-layer release method, we fabricated freestanding membranes of archetypal ferroelectrics such as PbZrTiO₃ (PZT) and BaTiO₃ (BTO). We first explored their response under passive, uncontrolled bending conditions. These deformations induced polarization reorientation within the membranes, revealing bending as a functional route for engineering ferroelectric polarization.
To achieve deterministic control, we then developed an on-demand method to shape the membrane and prescribe strain with precision. This approach employs photoactive azobenzene polymers (PAZO), where UV illumination generates periodic surface relief patterns that mechanically deform the membrane. A spatial light modulator sculpts the illumination profile, and thus the strain field, with high fidelity. Through this light-written strain, we realize 90° polarization rotations in PZT via piezoelectric coupling and full 180° reversals in BTO driven by flexoelectricity, all in a periodic and programmable manner
Together, these results illuminate the intertwined roles of strain and flexoelectricity in ferroelectric materials and establish a versatile platform for probing and harnessing these effects with unprecedented control.

Figure : Photosensitive polymer platform for advanced ferroelectric strain engineering