Low-frequency charge trapping and bistable domain switching in Mg-doped LiNbO3 single crystal films

Abstract

Lithium niobate single-crystal films are interesting for the integration of optoelectronic and surface acoustic wave devices. However, the domains have the preferred orientations, which limit their application in non-volatile memory devices. Here, we fabricated 5% Mg-doped LiNbO3 single-crystal films by ion-slicing of surface layers of bulk lithium niobate single-crystals. The Mg doping can improve the electrical performance of the films with the appearance of a definitive coercive voltage irrespective of applied voltages in polarization-voltage (P-V) hysteresis loops, unlike the undoped films where the apparent coercive voltages in P-V hysteresis loops equal the maximum applied voltages. Subsequent unipolar pulse stressing shows comprehensive charge injection into the films to occur at repetitive periodicities below 0.5 s that can symmetrize P-V hysteresis loops along the voltage axis. The injected charge in contradiction to an internal imprint field can change domain switching dynamics that can be described by the model of a non-ferroelectric passive layer in series with an ideal ferroelectric layer. The dielectric permittivities at low frequencies show the Maxwell-Wager relaxation of the injected charge with the broad distribution of relaxation times. As the periodicity is above 2 s, the injected charge within each cycle can be driven out of the film during intermittent time by the imprint field. This study shows the possibility of charge injection in stabilization of bipolar domain orientations in LiNbO3 single-crystal films.