Features of structure and mechanical properties LiNbO₃

Kostritskii S.M., Korkishko Y.N., Fedorov V.A., Mitrokhin V.P., Sevostyanov O.G., Chirkova I.M., Stepanenko O., Micheli M.D.

Zhang Z., Yang S., Xu C., Wang B., Duan N.

The hardness of X-, Y- and Z-cut lithium niobate (LiNbO3 or LN) is 12.8, 9.1 and 10.6 GPa, respectively. The pop-in phenomenon was observed for all loading experimental data of nanoindentation, which was induced by the formation of twins, confirmed using sub-nanometer scale transmission electron microscopy. The maximum shear stresses at pop-in for X-, Y- and Z-cut LN wafers are 20.6, 13.3 and 18.4 GPa, respectively, and the corresponding stresses are 25.5, 21 and 20 GPa.

Jeong S., Lee H., Cho H., Lee S., Kim H., Kim S., Park J., Jeong H.

High roughness and a greater number of defects were created by lithium niobate (LN; LiNbO 3 ) processes such as traditional grinding and mechanical polishing (MP), should be decreased for manufacturing LN device. Therefore, an alternative process for gaining defect-free and smooth surface is needed. Chemical mechanical planarization (CMP) is suitable method in the LN process because it uses a combination approach consisting of chemical and mechanical effects. First of all, we investigated the LN CMP process using commercial slurry by changing various process conditions such as down pressure and relative velocity. However, the LN CMP process time using commercial slurry was long to gain a smooth surface because of lower material removal rate (MRR). So, to improve the material removal rate (MRR), the effects of additives such as oxidizer (hydrogen peroxide; H 2 O 2 ) and complexing agent (citric acid; C 6 H 8 O 7 ) in a potassium hydroxide (KOH) based slurry, were investigated. The manufactured slurry consisting of H 2 O 2 –citric acid in the KOH based slurry shows that the MRR of the H 2 O 2 at 2 wt% and the citric acid at 0.06 M was higher than the MRR for other conditions.

Zhong Z.W.

Basu S., Zhou A., Barsoum M.W.

The room temperature deformation behavior of a LiNbO3 single crystal loaded along [0001] was studied by spherical nanoindentation. The threefold symmetry of the indentation marks was attributed to the formation of (10¯12) twins that reorient the basal planes to allow for basal slip, which is manifested by the formation of fully reversible, hysteretic loops upon cyclic loading. The differences in energy dissipation, threshold stresses, and loop shapes for the three different radii tips are attributed to the different sized twins that form. The results are consistent with our model for the formation of incipient kink bands within the twins.

Galinetto P., Marinone M., Grando D., Samoggia G., Caccavale F., Morbiato A., Musolino M.

In this work we report on micro-Raman analysis on lithium niobate (LN) substrates in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals. The fact that the linewidth of some Raman modes scale with the composition of LN crystals, together with the use of a confocal microscope, allowed a three-dimensional determination of the sample stoichiometry and of the crystalline quality. This local tool can supply additional information, which can be complementary to the electro-optic coefficients, carefully measured as well in order to check functional parameters. Raman spectra from buried regions were obtained on as-grown, etched and polished crystals and wafers. The depth profile of the peak energy and the linewidth of the Raman mode at 872 cm −1 indicate that mechanical processing of surfaces causes, in some cases, structural modifications till a depth of 15 μm.

Nagata H., Yagang Li, Finch A., Voisine K.R.

Growth of a bias point thermal shift induced by dc bias in z-cut LiNbO/sub 3/ optical intensity modulators is quantitatively discussed from the standpoint of its impact on field service. During 20 years of device operation under a worst-case dc bias condition, the thermal shift slope grows almost symmetrically with respect to a bias polarity. An initial small thermal shift of around /spl plusmn/7 mV//spl deg/C (3/spl sigma/ distribution bounds) increases continuously over time with biased operation at 55/spl deg/C and approaches /spl plusmn/70 mV//spl deg/C after 20 years. This increased temperature sensitivity would generate approximately a 2-V bias point shift toward the bias rail when modulator is exposed to temperature variation from 55/spl deg/C to 25/spl deg/C.

Bhagavat S., Kao I.

Lithium niobate is a non-centrosymmetric crystal. Due to its non-centrosymmetric nature, the properties such as hardness and fracture toughness are likely to be different on opposite faces of the same wafer. In many wafer production processes such as wiresawing, lapping, and polishing, opposite faces of the wafer are processed simultaneously. Thus, it is important to understand the nature of anisotropy on the opposite faces of the same wafer. As a first step, hardness anisotropy of three common orientations of lithium niobate wafers is studied using nanoindentation technique. The hardness values on opposite faces for the same direction are found to be different for most cases. Lithium niobate exhibits a significant indentation size effect. Lithium niobate also exhibits pop-in phenomenon similar to the pop-in behavior of other materials. The pop-in phenomenon in lithium niobate is dictated by crystallographic orientation.

Nagata H., Li Y., Bosenberg W.R., Reiff G.L.

DC drift of unbuffered dc bias electrode port of x-cut LiNbO/sub 3/ (LN) modulators is investigated. Unlike buffered LN modulators, their dc drift is irreversible and relatively suppressed after biased aging. Additionally, they show rolling-over-type drift and do not drift divergently. Extended temperature-voltage accelerated drift tests find temperature activation energy of 1.2 eV and a proportional relationship between drift rates and initially applied bias voltages. Such drift behaviors characteristic of unbuffered x-LN can demonstrate their high reliability with respect to dc bias drift.

Arizmendi L.

In this paper the most important properties of lithium niobate crystals for photonic applications are reviewed. We will summarize how acting on the stoichiometry, sample structure, doping and domain structure of the crystals, these properties are governed, and can be taylored for each specific application. Finally we present a review of photonic applications in a wide spectrum of fields as lasers and non-linear optics, optical communications, optical memories, and diffractive optics.

Xue D., Kitamura K.

Malovichko G., Grachev V., Kokanyan E., Schirmer O.

The spectra of EPR, NMR, ENDOR of lithium niobate crystals with different compositions, diverse modifiers and various probe impurities have been analysed. Congruent crystals with a high concentration of intrinsic defects have strong structural disorder and a random distribution of crystal fields and their gradients. Crystals with small contents of intrinsic defects offer extraordinary informative opportunities for their investigation by means of different spectroscopic techniques. As an example of the resolution enhancement in Li-rich crystals the EPR spectra of Yb3+ were considered in detail. Two new low-symmetry centers were found and their parameters were determined. The investigated strong interrelation of the intrinsic and extrinsic defect subsystems becomes especially apparent when concentrations of both defect classes are comparable.

Wooten E.L., Kissa K.M., Yi-Yan A., Murphy E.J., Lafaw D.A., Hallemeier P.F., Maack D., Attanasio D.V., Fritz D.J., McBrien G.J., Bossi D.E.

The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device.

Townsend P.D.

Levinstein H.J., Capio C.D.

It has been found that dislocations in LiNbO3 and LiTaO3 single crystals can be decorated by electric-field-enhanced diffusion of platinum or gold into the crystals at temperatures in the order of 600°C with voltages in the range of 250 to 1000 V/cm. To demonstrate the use of the technique, examples of low-angle boundary networks in LiNbO3 and LiTaO3 are shown. The general characteristics of the as-grown dislocation network in a [101̄0]-growth-axis LiNbO3 crystal are described, and the effect of annealing on the dislocation array in LiTaO3 crystals is discussed.

Choudhury T.T., Masuk N.I., Deb P., Islam M.N., Islam M.A.

Zoubir O., Lallaoui A., Edfouf Z.

Muratov K., Ablyaz T., Gashev E., Goryacheva I.

The regularities of the formation of the resulting raster tool trajectories based on Lissajous figures for the lapping process of planes are established. This makes it possible to maximize the cutting ability of the tool, which contributes to its more uniform wear and increased productivity and processing quality. Optimal parameters of productivity and roughness of the treated surface during lapping of zirconium ceramics are achieved through the use of ASM paste 28/20 µm. Based on Preston’s hypothesis, an exponential dependence of the change in the contact area during the lapping of planes of different initial shape of the macrorelief is obtained. The obtained theoretical and practical results of the study of the process of flat lapping with constant and variable clamping force of the treated surface to the surface of the tool. The influence of the force factor on the formation of the surface in the process of abrasive lapping has been established. Studies have been carried out and the main technological recommendations of precision surface treatment of workpieces based on hard, brittle ceramic material and bronze samples on equipment with a raster trajectory of the tool movement are presented. The optimal pressure value when processing ceramics should be considered 203–270 kPa (2.1–2.8 kg/cm2).

Irzaman, Khomariah N N., Safutra H., Nur Aidi M., Alatas H., Hardhienata H.

Ponomarev R.S., Sosunov A.V., Semenova O.R., Prokhorov N.P., Kuneva M.

Abstract Using chemical etching it was shown that the density of dislocation in lithium niobate (LN) single crystal wafers is higher near the surface in depth about 20 um than in the depth of crystal. It caused to change of diffusion coefficient during the waveguide formation with proton exchange (PE) method and can increase DC-drift of intensity optical modulators based on PE-waveguides.

Masloboeva S.M., Efremov I.N., Biryukova I.V., Palatnikov M.N.

This paper reports a process for the growth of optically homogeneous lithium niobate single crystals containing boron as a dopant. A LiNbO3:B crystal has been grown by the Czochralski technique using a single-phase growth charge synthesized from a Nb2O5:B precursor and lithium carbonate. We have assessed the optical quality of the crystal by a high-speed method from the number of scattering centers, evaluated its single-domain state by piezoacoustic measurements, and calculated its d333 piezoelectric modulus component. The results demonstrate that the crystal has a high degree of optical uniformity and is single-domain. The proposed method for LiNbO3:B crystal growth can serve as a basis of a commercial-scale process for the preparation of doped lithium niobate single crystals for various engineering applications.

Banerjee A., Wang X., Fang C., Wu E.A., Meng Y.S.

All-solid-state batteries (ASSBs) have attracted enormous attention as one of the critical future technologies for safe and high energy batteries. With the emergence of several highly conductive solid electrolytes in recent years, the bottleneck is no longer Li-ion diffusion within the electrolyte. Instead, many ASSBs are limited by their low Coulombic efficiency, poor power performance, and short cycling life due to the high resistance at the interfaces within ASSBs. Because of the diverse chemical/physical/mechanical properties of various solid components in ASSBs as well as the nature of solid-solid contact, many types of interfaces are present in ASSBs. These include loose physical contact, grain boundaries, and chemical and electrochemical reactions to name a few. All of these contribute to increasing resistance at the interface. Here, we present the distinctive features of the typical interfaces and interphases in ASSBs and summarize the recent work on identifying, probing, understanding, and engineering them. We highlight the complicated, but important, characteristics of interphases, namely the composition, distribution, and electronic and ionic properties of the cathode-electrolyte and electrolyte-anode interfaces; understanding these properties is the key to designing a stable interface. In addition, conformal coatings to prevent side reactions and their selection criteria are reviewed. We emphasize the significant role of the mechanical behavior of the interfaces as well as the mechanical properties of all ASSB components, especially when the soft Li metal anode is used under constant stack pressure. Finally, we provide full-scale (energy, spatial, and temporal) characterization methods to explore, diagnose, and understand the dynamic and buried interfaces and interphases. Thorough and in-depth understanding on the complex interfaces and interphases is essential to make a practical high-energy ASSB.

Sugak D., Syvorotka I., Yakhnevych U., Buryy O., Levintant-Zayonts N., Savytskyy H., Bonchyk O., Ubizskii S.

Sosunov A., Ponomarev R., Semenova O., Petukhov I., Volyntsev A.

The influence of pre-annealing of lithium niobate in the range of 400–800 °C was studied at each step of formation of proton-exchange waveguides. Pre-annealing affects the structure and optical properties of lithium niobate. There is a relationship between the initial structure of lithium niobate and the optical characteristics of proton-exchange waveguides. The linear dependence between the deformations of the annealing proton exchange waveguides and the refractive index is established. Pre-annealing leads to an improvement in the structure of the subsurface layer of lithium niobate, as well as a slight decrease in the refractive index due to an increase in the homogeneity and a lower concentration of protons inside the crystal. The crystal structure becomes most uniform at a temperature of 500 °C. The results can be useful for different optical crystals used for applications.