Retention of intermediate polarization states in ferroelectric materials enabling memories for multi-bit data storage

Abstract

A homogeneous ferroelectric single crystal exhibits only two remanent polarization states that are stable over time, whereas intermediate, or unsaturated, polarization states are thermodynamically instable. Commonly used ferroelectric materials however, are inhomogeneous polycrystalline thin films or ceramics. To investigate the stability of intermediate polarization states, formed upon incomplete, or partial, switching, we have systematically studied their retention in capacitors comprising two classic ferroelectric materials, viz. random copolymer of vinylidene fluoride with trifluoroethylene, P(VDF-TrFE), and Pb(Zr,Ti)O3. Each experiment started from a discharged and electrically depolarized ferroelectric capacitor. Voltage pulses were applied to set the given polarization states. The retention was measured as a function of time at various temperatures. The intermediate polarization states are stable over time, up to the Curie temperature. We argue that the remarkable stability originates from the coexistence of effectively independent domains, with different values of polarization and coercive field. A domain growth model is derived quantitatively describing deterministic switching between the intermediate polarization states. We show that by using well-defined voltage pulses, the polarization can be set to any arbitrary value, allowing arithmetic programming. The feasibility of arithmetic programming along with the inherent stability of intermediate polarization states makes ferroelectric materials ideal candidates for multibit data storage.

Physical reality of the Preisach model for organic ferroelectrics

“…It has been recently demonstrated by Katsouras et al that these intermediate states are of remarkable stability, in contrast to the conventional theory which assumes the local energy minima to be fundamentally thermodynamically unstable 19 . This counterintuitive observation can now be rationalized by the electrostatic decoupling of the ferroelectric domains in P(VDF-TrFE) due to its semi-crystalline structure.…”

“…In contrast to BTA, the narrow E i distribution would be consistent with weaker interactions between crystallites due to relatively large inter-crystallite distances filled with amorphous material. A similar “effectively independent domains” argument has been used when explaining the stability of the intermediate polarization states in P(VDF-TrFE) capacitors 19 .…”

“…Most research on the Preisach model for ferroelectrics has been on inorganics, and focused on macroscopic 2 , 3 or local measurements 6 , 7 of the hysteron distribution, as well as on using the model to predict hysteresis loop behavior 4 , 8 – 10 . There are few applications of the model on organic ferroelectrics 11 – 15 , and these have been limited to the polymer PVDF and its copolymers 10 , 16 – 19 . However, the physical reasons behind the shape and width of the distribution and especially the implications of the broadening of the Preisach distribution (PD) for other ferroelectric properties such as the switching kinetics are rarely discussed.…”

Structure and Electrical Properties of Na0.5Bi0.5TiO3 Epitaxial Films with (110) Orientation

“…The mainstay ferroelectric materials for applications have traditionally been the Pb(Zr,Ti)O 3 (PZT) films due to their excellent performance (large remnant polarization P r and small coercive field E C ). However, the use of lead gives rise to environmental concerns, which is the driving force for the development of alternative lead-free ferroelectric materials [6][7][8]. Na 0.5 Bi 0.5 TiO 3 (NBT) with good ferroelectric properties and high Curie temperature has been considered to be an excellent candidate to replace lead-based ferroelectric materials [9][10][11].…”

Switching properties of epitaxial La0.5Sr0.5CoO3/Na0.5Bi0.5TiO3/La0.5Sr0.5CoO3 ferroelectric capacitor

“…[4][5][6] However, PZT lms are not environmentally friendly materials, thus many efforts have been made to develop lead-free new type ferroelectric materials. 7,8 Sodium bismuth titanate, Na 0.5 Bi 0.5 TiO 3 (NBT), with A-site composite perovskite structure is considered as an excellent candidate to replace lead based ferroelectric materials. 9,10 Recently, we have successfully prepared a single-phase high quality NBT bulk material by solid state reaction method, and investigated the optical properties and ferroelectric properties.…”