Domain Patterning in Ion-Sliced LiNbO3 Films by Atomic Force Microscopy

Omni-functional crystal: Advanced methods to characterize the composition and homogeneity of lithium niobate melts and crystals

Lithium niobate (LN) is a type of multifunctional dielectric and ferroelectric crystal that is widely used in acoustic, optical, and optoelectronic devices. The performance of pure and doped LN strongly depends on various factors, including its composition, microstructure, defects, domain, and homogeneity. The structure and composition homogeneity can affect both the chemical and physical properties of LN crystals, including their density, Curie temperature, refractive index, and piezoelectric and mechanical properties. In terms of practical demands, both the composition and microstructure characterizations these crystals must range from the nanometer scale up to the millimeter and wafer scales. Therefore, LN crystals require different characterization technologies when verifying their quality for various device applications. Optical, electrical, and acoustic technologies have been developed, including x-ray diffraction, Raman spectroscopy, electron microscopy, and interferometry. To obtain detailed structural information, advanced sub-nanometer technologies are required. For general industrial demands, fast and non-destructive technologies are preferable. This review outlines the advanced methods used to characterize both the composition and homogeneity of LN melts and crystals from the micro- to wafer scale.

Evolution of Nanodomains and Formation of Self-Organized Structures during Local Switching in X-Cut LNOI

The features of nanodomain growth during local switching in X-cut lithium niobate on insulator (LNOI) were comprehensively studied using the biased tip of a scanning probe microscope. The obtained results were discussed in terms of the kinetic approach. The revealed differences in domain growth in bulk LN and LNOI were attributed to the higher bulk conductivity of LNOI. The obtained influence of humidity on the shape and growth of isolated domains was attributed to the water meniscus. Analysis of the transition between the “forward growth” and “sideways growth” stages was performed by switching to the stripe electrode. A sand-glass-shaped domain was formed due to growth in the opposite direction after the domain touched the electrode. Stable periodical domain structures down to 300 nm were created and characterized in LNOI. Highly ordered comb-like domains of various alternating lengths, including four- and eight-fold increase periods, were produced by performing biased tip scanning along the Y axis. The obtained knowledge is important for the future development of nanodomain engineering methods in monocrystalline ferroelectric thin films on insulators.

Domain modulation in LiNbO3 films using litho piezoresponse force microscopy

Domain engineering plays a pivotal role in the development of ferroelectric non-volatile memory devices. In this work, we mainly focus on the domain kinetic in ion-sliced single crystal LiNbO₃ thin films under tip-induced electric fields using piezoresponse force microscope (PFM). Polarization reversal takes place when the electric fields are above threshold value (coercive voltage V _c) of films. Besides, the dependence of domain dynamic on pulse duration and amplitude were investigated in detail, and specific local domain reversal (5 μm) was completed by the optimized poling condition. All the results reveal that tip-induced polarization reversal could be an effective way to domain engineering, which gives much more promising prospects regarding to the high density non-volatile ferroelectric memory devices.

Effects of the Domain Wall Conductivity on the Domain Formation under AFM-Tip Voltages in Ion-Sliced LiNbO3 Films

The specified domain patterns were written by AFM-tip voltages in LiNbO3 films composing LNOI (LiNbO3-on-insulator). The domain wall conductivity (DWC) was estimated in the written patterns. This estimate was based on the effects of load resistors RL inserted between DWs and the ground, on the features of occurring domains. In this case, the domain formation is controlled by the ratio between RL and the DWs’ resistance RDW. Starting from the comparison of patterns appearing at different RL, the value of RDW in a specified pattern was estimated. The corresponding DWC is of σDW ≈ 10−3 (Ohm cm)−1 which exceeds the tabular bulk conductivity of LiNbO3 by no less than twelve orders of magnitude. A small DW inclination angle of (10−4)0 responsible for this DWC is not caused by any external action and characterizes the domain frontal growth under an AFM-tip voltage.