Polarization dynamics in ferroelectric thin films

Abstract

The remanent polarization at zero electric field and the capability of being switched between multiple stable states make ferroelectric materials good candidates for non-volatile memories. Practically, ferroelectric materials are commercially available and have been applied to ferroelectric random-access memories (FeRAM) for computers and radio frequency identification (RFID) cards. For application in data storage, three factors are crucial: (i) a fast writing/reading speed, (ii) a reliable data retention, and (iii) a slow degradation during a large number of writing/reading cycles. These challenges have attracted a wide research interest from both industry and academia, since they are not only of practical interests but trigger intriguing fundamental questions related to the ferroelectric materials as well. It is the major scope of this thesis to study the polarization-related device physics motivated by the aforementioned practical requirements. We focus on thin films of the ferroelectric polymer poly-vinylidene-fluoride (PVDF) and its random copolymers with trifluoroethylene [P(VDF-TrFE)]. We shall show that the conclusions derived also apply to inorganic ferroelectric materials such as Pb(Zr,Ti)O3, and BaTiO3. Our investigation is based on macroscopic electrical measurements and nanoscale scanning probe measurements. Modeling at mesoscopic level is involved.