title: The combined effect of mechanical strain and electric field cycling on the ferroelectric performance of P(VDF-TrFE) thin films on flexible substrates and underlying mechanisms.
abstract: In this manuscript, we study the combined effect of mechanical strain and electric field cycling on the ferroelectric properties and polarization fatigue of P(VDF-TrFE) based flexible thin film capacitors from the perspective of flexible memory applications. The devices show nearly 80% retention of ferroelectric polarization after 30 000 bending cycles at mechanical strains of up to ca. 0.8%, mimicking a typical number of bending cycles a product is expected to go through. On the other hand, electric field cycling of the unstrained as well as mechanically strained devices results in over 50% drop in the ferroelectric polarization of the capacitors within 105bipolar switching cycles. We find that 20% reduction in the polarization upon mechanical cycling is due to the formation of cracks in P(VDF-TrFE) thin films whilst ca. 50% polarization reduction during purely electrical or mechano-electrical fatigue is concomitant with the development of bubbles in the top electrode of the devices which eventually coalesce to give rise to bursting and eventual delamination of the electrode. A detailed investigation into the electrical fatigue mechanisms shows that the fatigue is primarily driven by the degradation of the P(VDF-TrFE) thin films due to HF elimination triggered by a high enough electric field, also manifested by reduced crystallinity and a reduced number of total dipoles of P(VDF-TrFE) films. The results clearly suggest that polarization reduction upon electric field cycling i.e. electrical fatigue is a greater bottleneck in the use of flexible memory devices than the mechanical cycling.
authors.affiliation: Department of Materials Science & Engineering, Samtel Centre for Display Technologies, Indian Institute of Technology Kanpur, Kanpur 208016, India. deepas@iitk.ac.in.
authors.forename: Deepa
authors.initials: D
authors.lastname: Singh
authors.affiliation: Department of Materials Science & Engineering, Samtel Centre for Display Technologies, Indian Institute of Technology Kanpur, Kanpur 208016, India. deepas@iitk.ac.in.
authors.lastname: Deepak
authors.affiliation: Department of Materials Science & Engineering, Samtel Centre for Display Technologies, Indian Institute of Technology Kanpur, Kanpur 208016, India. deepas@iitk.ac.in.
authors.forename: Ashish
authors.initials: A
authors.lastname: Garg