Centre de Nanosciences
et de Nanotechnologies

Photostriction

 

Photo-induced response in ferroelectric-based thin films and micro-devices

 


Figure 1 : Photostriction project


Figure 2 : electrical characterization


Figure 3 : pump-probe measurement


Figure 4 : funding OxyMORE


Figure 5 : Argonne collaboration


Figure 6 : UCSD collaboration

Context

Complex ferroelectric oxides exhibit several functionalities (such as high piezoelectric coefficients and switchable polarization) which can be coupled and exploited in various types of devices (such as microactuators, sensors, energy harvesting structures or high-density memories). While electric fields are mostly applied to manipulate devices functionalities, using light could constitute an alternative and wireless approach with limited power consumption and noise in many potential applications. The generation of strain by light illumination is called photostriction. Up to now, previous works have been mainly focused on ferroelectric ceramics and single crystals but their too long response time prevents their integration in real devices. However, ultrafast photostriction effects are expected in ferroelectrics grown in thin films (thickness~10-100 nm).

Project

The general purpose is to investigate carefully the mechanisms of photostriction which remain not fully understood (including magnitude and time-scale) in ferroelectric thin films integrated in real capacitor geometries, to develop ultrafast light control of strain in functional devices. More precisely, this project aims at clarifying the physical mechanisms behind photostriction in PbZrTiO3 (PZT) thin films, by studying contributions from polarization state and interfaces, in order to optimize the photo-induced strain in devices geometries and develop photostrictive cantilevers. In particular, our work is focused on the effects of thin films chemical composition, thickness and interfaces with electrodes on the devices properties.
 

  • Ferroelectric materials design :
    - Thin films growth : PZT is known to show very high piezoelectric coefficients, so it is a promising material to achieve high photo-induced strain. PZT thin films are epitaxially grown by Pulsed-Laser Deposition (PLD) between two electrodes layers in capacitors structures and their structural quality is studied by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM).
    Equipments : PLD, XRD, AFM.
    - Patterning in micro-capacitors : The multilayers structures are patterned down to the micron scale, using several clean room processes, to define capacitors geometries optimized for photo-induced measurements.
    Equipments : lithography, sputtering, etching in clean room.

  • Lab electrical characterizations : As photostriction is described as a combination of voltage generation under illumination and converse piezoelectric effect, both physical mechanisms are studied using electrical characterization techniques.
    Equipments : I-V, polarization loops, piezoelectric measurements.

  • Pump-probe measurements (synchrotron) : The photostrictive effects at very short time scale (picoseconds range) are studied by pump-probe measurements at the synchrotron in Argonne National Lab (USA). The strain following optical excitation in our ferroelectric devices is investigated by time-resolved micro-focused X-ray diffraction.

Funding

Région Ile-de-France
DIM OXYMORE

Collaboration

University of California San Diego –UCSD
Argonne National Laboratory (Chicago, USA)
Laboratoire Structures, Propriétés et Modélisation des Solides (SPMS) de CentraleSupélec