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

Abstract

Photonic structures denoted as LNOI (LiNbO 3 -on-insulator) are of considerable interest for integrated optics due to a high refractive-index contrast provided by the interface LiNbO 3 /insulator. A topical problem for LNOI-based optical waveguides is optical-frequency conversion, in particular realized on ferroelectric domains on the basis of quasi phase-matching principle. This paper presents extended studies on the fabrication of domain patterns by atomic force microscopy (AFM) methods (raster lithography, piezo-force microscopy, conductive AFM) in single-crystal ion-sliced LiNbO 3 films forming LNOI sandwiches. A body of data obtained on writing characteristics of domains and specified 1D and 2D domain patterns permitted us to manipulate the domain sizes and shapes. Of special importance is the stability of created patterns, which persist with no degradation during observation times of months. The domain coalescence leading to the transformation of a discrete domain pattern to a continuous one was investigated. This specific effect-found in thin LiNbO 3 layers for the first time-was attributed to the grounding of space-charges accumulated on domain walls. Observations of an enhanced static conduction at domain walls exceeding that in surrounding areas by not less than by five orders of magnitude supports this assumption. AFM domain writing in ion-sliced films serves as a basis for studies in nonlinear photonic crystals in integrated optical schemes.

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

“…The exposure characteristics of the domain diameter D(Utip) and D(tp) were presented in [19]. In agreement with [19,20], the written domains are fully stable. The dependences of the domain sizes D(Utip) and D(tp) are not affected by the inter-domain spacing.…”

“…One can expect that an electrostatic repulsion should be suppressed by the DWs' grounding leading to the elimination of accumulated charge. This effect was actually observed when AFM domain writing in LNOI [20]. If the metal layer was grounded when writing, the written patterns were regular and stable.…”

“…In the LNOI samples under investigations, a thin metal layer serving as an electrode is inserted between LiNbO3 film and SiO2. Recently, we presented the AFM -tip domain writing in LiNbO3 films forming LNOI [19,20] and DWC measurements in the written patterns [13]. Later on, AFM domain writing in LNOI and DWC observations in the written patterns were reported in [15,21,22].…”

A Theoretical Study on Rib‐Type Photonic Wires Based on LiNbO3 Thin Film on Insulator

“…Nowadays, a full wafer-scale (3 in. [7,[37][38][39][40][41][42][43][44][45][46] These devices are highly efficient, possess great application prospect, and are expected to replace most conventional devices. [6][7][8][9] Based on the LNOI thin-film, researchers have made much effort to develop various ultra-compact micro-photonic devices over the past years.…”

“…Based on the LNOI thin‐film, researchers have made much effort to develop various ultra‐compact micro‐photonic devices over the past years. To date, many LNOI PW devices have been demonstrated, such as (CMOS‐compatible) electro‐optic modulator, (electro‐optically tunable) micro‐ring or micro‐disk resonator, LNOI heterogeneous photonic device, grating coupler, photonic crystal, transverse‐electric/magnetic (TE/TM)‐pass polarizer, quantum optics device, as well as some nonlinear devices based on periodically poled LNOI (PPLNOI) PWs . These devices are highly efficient, possess great application prospect, and are expected to replace most conventional devices.…”