Correlation between Imprint and Long-Time Polarization Reversal under Low Fields in Ferroelectric Thin Films

Time interval of slow polarization reversal in ferroelectric thin films is broadened over more than two decades to disobey the classical Kolmogorov-A vrami-Ishibashi （KAI） equation as the applied field approaches the coercive field of domain switching. The assumption of a Lorentzian distribution of logarithmic waiting times of reversed domain nucleation in this equation can resolve this dilemma. In our work, we explain this equation from the coercive-voltage distribution in thin films, and derive a similar function to describe slow polarization reversal from the consideration of a long-time imprint effect rather than the KAI model.     

Thickness Effect on (La_(0.26)Bi_(0.74))_2Ti_4O_(11) Thin-Film Composition and Electrical Properties

Highly oriented(00l)(La_(0.26)Bi_(0.74))_2Ti_4O_(11 )thin films are deposited on(100) SrTiO_(3 )substrates using the pulsed laser deposition technique.The grains form a texture of bar-like arrays along Sr Ti O_3110directions for the film thickness above 350 nm,in contrast to spherical grains for the reduced film thickness below 220 nm.X-ray diffraction patterns show that the highly ordered bar-like grains are the ensemble of two lattice-matched monoclinic(La,Bi)_4Ti_3O_(12 )and TiO_(2 )components above a critical film thickness.Otherwise,the phase decomposes into the random mixture of Bi_2Ti_2O_(7 )and Bi_4Ti_3O_(4 )spherical grains in thinner films.The critical thickness can increase up to 440 nm as the films are deposited on LaNiO_3-buffered SrTiO_(3 )substrates.The electrical measurements show the dielectric enhancement of the multi-components,and comprehensive charge injection into interfacial traps between(La,Bi)_4Ti_3O_(12 )and TiO_(2 )components occurs under the application of a threshold voltage for the realization of high-charge storage.     

Erasable Ferroelectric Domain Wall Diodes

The unipolar diode-like domain wall currents in LiNbO3 single-crystal nanodevices are not only attractive in terms of their applications in nonvolatile ferroelectric domain wall memory,but also useful in half-wave and full-wave rectifier systems,as well as detector,power protection,and steady voltage circuits.Unlike traditional diodes,where the rectification functionality arises from the contact between n-type and p-type conductors,which are unchanged after off-line production,ferroelectric domain wall diodes can be reversibly created,erased,positioned,and shaped,using electric fields.We demonstrate such functionality using ferroelectric mesa-like cells,formed at the surface of an insulating X-cut LiNbO₃ single crystal.Under the application of an in-plane electric field above a coercive field along the polar Z axis,the domain within the cell is reversed to be antiparallel to the unswitched bottom domain via the formation of a conducting domain wall.The wall current was rectified using two interfacial volatile domains in contact with two side Pt electrodes.Unlike the nonvolatile inner domain wall,the interfacial domain walls disappear to turn off the wall current path after the removal of the applied electric field,or under a negative applied voltage,due to the built-in interfacial imprint fields.These novel devices have the potential to facilitate the random definition of diode-like elements in modern large-scale integrated circuits.     

Artificial Modulation of Ferroelectric Thin Films into Antiferroelectric through H+ Implantation for High-Density Charge Storage

Hydrogen ions are implanted into Pb（Zro.3Tio.7）03 1014 ions/cm^2. Pseudo-antiferroelectric behaviour in thin films at the energy of 40keV with a flux of 5 x the implanted thin films is observed, as confirmed by the measurements of polarization versus electric hysteresis loops and capacitance versus voltage curves. X-ray diffrac- tion patterns show the film structures before and after H＋ implantation both to be perovskite of a tetragonal symmetry. These findings indicate that hydrogen ions exist as stable dopants within the films. It is believed that the dopants change domain-switching behaviour via the boundary charge compensation. Meanwhile, time dependence of leakage current density after time longer than lOs indicates the enhancement of the leakage cur- rent nearly in one order for the implanted film, but the current at time shorter than i s is mostly the same as that of the original film without the ionic implantation. The artificial tailoring of the antiferroelectric behaviour through H＋ implantation in ferroelectric thin films is finally proven to be achievable for the device application of high-density charge storage.     

A Ferroelectric Domain-Wall Transistor

On the basis of novel properties of ferroelectric conducting domain walls, the domain wall nanoelectronics emerges and provides a brand-new dimension for the development of high-density, high-speed and energy-efficient nanodevices. For in-memory computing, three-terminal devices with both logic and memory functions such as transistors purely based on ferroelectric domain walls are urgently required. Here, a prototype ferroelectric domain-wall transistor with a well-designed coplanar electrode ge...