Soutenance de thèse : Francesco PEDROLI le 12/03/2020

« Dielectric  strength  and  leakage  current:  from  synthesis  to
processing optimization »

12/03/2020 - 14h00 - Amphithéâtre Clémence Royer - Bâtiment Jacqueline Ferrand de l’INSA Lyon

Doctorant : Francesco PEDROLI

Laboratoire INSA : LGEF

Thèse CIFRE : Sté Solvay

Ecole doctorale : ED 162  MEGA

Electro-active  polymers  (EAPs)  such  as  P(VDF-TrFE-CTFE)  was  demonstrated  to  be greatly promising in the field of flexible sensors and actuators. The advantages of using EAPs for smart electrical devices are due to their low cost, elastic properties, low density and  ability  to  be  manufactured  into  various  shapes  and  thicknesses.  In  earlier  years, P(VDF-TrFE-CTFE) terpolymer attracted many researchers due to its relaxor-ferroelectric
property that exhibits high electrostriction phenomena. Although their attractiveness, this class  of  materials  still  owns  two  main  technological  limitations:  low  breakdown  voltage and  the  high  level  of  leakage  current  when  high  voltages  are  applied.  The  quadratic dependence of the strain response and mechanical energy density on the applied electric field highlights the relevance of EAP breakdown electric field, while reducing the dielectric losses.  The  low  dielectric  strength  of  P(VDF-TrFE-CTFE)  terpolymer  turns  out  to  be  a main concern for achieving high actuation performances. Moreover, the large of electric field required to attain satisfactory levels of deformation (≥ 40 V/µm, about) inevitably lead  to  high  level  of  leakage  current  and  thus  short  life-time.  This  work  demonstrates that  it  is  possible  to  dramatically  increase  the  electrical  breakdown  and  decrease  the dielectric  losses  by  controlling  processing  parameters  of  the  polymer  synthesis  and fabrication procedures. Enhancement of intrinsic dielectric strength is obtained by tuning the  terpolymer  molecular  weight  and  by  improving  the  purity  of  polymeric  dissolution used  for  fabrication  of  terpolymer  films.  The  reduction  of  dielectric  losses,  and  with particular  attention  at  the  high-voltage  conduction  losses  (or  leakage  current)  are achieved by the introduction of a novel thermal treatment in the film fabrication process, called electro-thermal annealing.