Lithium Niobate Materials Research Articles

Micromachining Lithium Niobate for Rapid Prototyping of Resonant Biosensors

Lithium niobate material is widely used in MEMS application due to its piezoelectric properties. This paper presents the micromachining process of lithium niobate to rapid prototype a resonant biosensor design. A high precision CNC machine was used to machine a sample of lithium niobate material at 5 different spindle speeds to find out the best conditions to machine this brittle material. A qualitative visual check of the surface was performed by using scanning electron microscopy, surface roughness was quantitatively investigated using an optical surface profiler and Raman spectroscopy to check the strain of the surface. Results show that the surface quality of the lithium niobate was significantly affected by the spindle speed with optimum conditions at 70k rpm giving a strained surface with 500 nm rms roughness.

Optical logic gates based on electro-optic modulation with Sagnac interferometer.

In this work, we present a new structure to realize optical logic operation in a Sagnac interferometer with electro-optical modulation. In the scheme, we divide two counterpropagation signals in a Sagnac loop to two different arms with the electro-optical crystal by using two circulators. Lithium niobate materials whose electro-optical coefficient can be as large as 32.2×10(-12) m/V make up the arms of the waveguides. Using the transfer matrix of the fiber coupler, we analyze the propagation of signals in this system and obtain the transmission characteristic curves and the extinction ratio. The results indicate that this optical switching has a high extinction ratio of about 60 dB and an ultrafast response time of 2.036 ns. In addition, the results reveal that the change of the dephasing between the two input signals and the modification of the modulation voltage added to the electro-optical crystal leads to the change of the extinction ratio. We also conclude that, in cases of the dephasing of two initial input signals Δφ=0, we can obtain the various logical operations, such as the logical operations D=A¯·B, D=A·B¯, C=A+B, and D=A⊕B in ports C and D of the system by adjusting the modulation voltage. When Δφ≠0, we obtain the arithmetic operations D=A+B, C=A⊕B, D=A·B¯, and C=A¯·B in ports C and D. This study is significant for the design of all optical networks by adjusting the modulation voltage.

High-field terahertz bulk photovoltaic effect in lithium niobate.

The terahertz (THz) response of the ferroelectric prototype material lithium niobate (LiNbO3) is studied in the nonperturbative regime of light-matter interaction. Applying two-dimensional THz spectroscopy with few-cycle pulses of an amplitude E≈100 kV/cm and a center frequency of 2THz, we dissect the overall nonlinear response into different orders in the electric field. The underlying nonlinear current is of interband character and consists of a strong low-frequency shift current (SC) and higher harmonics of the THz fundamental. The SC component originates from the lack of inversion symmetry and the strong interband decoherence for long electron trajectories in k space as shown by theoretical calculations.

Full spectrum millimeter-wave modulation

In recent years, the development of new lithium niobate electro-optic modulator designs and material processing techniques have contributed to support the increasing need for faster optical networks by considerably extending the operational bandwidth of modulators. In an effort to provide higher bandwidths for future generations of networks, we have developed a lithium niobate electro-optic phase modulator based on a coplanar waveguide ridged structure that operates up to 300 GHz. By thinning the lithium niobate substrate down to less than 39 µm, we are able to eliminate substrate modes and observe optical sidebands over the full millimeter-wave spectrum.

Holographic imaging and interferometry with non-Bragg diffraction orders on volume and surface-relief gratings in lithium niobate and photo-thermoplastic materials

The recording of holographic volume and surface-relief gratings in a photorefractive crystal using a photo-thermoplastic (PTP) holographic camera with an image-bearing signal beam leads to the appearance of two Bragg and two or more non-Bragg diffracted beams that show the transformed images in each beam (rotation and angular amplification of images). Using this real-time mode of interferometry, the hologram is retrieved with a deformed object beam, resulting in the appearance of fringes with a proper phase shift in each of four diffracted beams. This one-shot (one-exposure) phase-shifting interferometry results in clarification of the object wave-front information (for example, from surface deformation) and solution of the sign ambiguity problem. This procedure demonstrates that high-resolution holographic imaging of the PTP holographic camera static deformations in the order of ∼0.1 mm can be revealed on the diffusion reflection surface. In addition, it was demonstrated that using the PTP materials could achieve holographic recording and imaging through phase aberration, with the image appearing in the non-Bragg diffraction order.

Defect modes tuning of one-dimensional photonic crystals with lithium niobate and silver material defect

In this paper, a novel PCs defect mode is designed by inserting a Ag/LiNbO 3/Ag sandwich structure into periodically stacked TiO 2/MgF 2 dielectric superlattice. The band gap calculation is conducted using transfer matrix method. An emergence of defect mode around 525 nm is demonstrated. By applying an external voltage on this defect mode, remarkable wavelength tuning can be achieved. At normal incidence, a tuning bandwidth up to 70 nm is obtained by moderate change of external voltage from −250 to 250 V. This feature can be employed to fabricate practical tunable filters in visible region.

Self-trapped beams for fabricating 3D integrated optical components

Extreme integration represents a popular trend in the construction of a wide range of technical devices. Optoelectronic and photonic components are no exception, as evidenced by the amount of research work devoted to writing optical microstructures inside dielectric (transparent) media. Advances in this area make it possible to envision more compact devices, consisting of 3D waveguides (see Figure 1), capable of functionalities that are out of reach with conventional technology. Moreover, this approach offers an advantageous substitute to standard planar integrated optics, which locates waveguides at the surface of substrates. Photoinscription is essentially the only simple, low-cost way of locally modifying a refractive index inside a medium in a controlled manner. The most common use of the technique involves scanning a tightly focused beam, often in the femtosecond regime, which modifies the refractive index through a combination of nonlinear processes: see Figure 2(a). Both optical waveguides and more complex photonic circuits can be made in this way.1 An alternative approach to this point-by-point inscription process—and the basis for our work—is to employ self-trapped beams, which can form a waveguide in a single step: see Figure 2(b). Beam self-trapping occurs when natural light diffraction is compensated by an appropriate nonlinear change (increase) in the refractive index induced by the propagating beam. The basic science of this phenomenon, which can be seen as the beam forming its own single-mode waveguide, has been widely studied over the past decades. In recent years, we have induced waveguides inside the ferroelectric material lithium niobate (LiNbO3). We chose this crystal for its strategic Figure 1. Schematic of an integrated optical component consisting of 3D optical circuits.

Comparison of Aqueous and Non-aqueous Soft-Chemical Syntheses of Lithium Niobate and Lithium Tantalate Powders

Lithium niobates and tantalates have a number of characteristics exploitable for optical and electrical devices that include ion conductivity, self-activating or dopant luminescence, piezoelectricity, pyroelectricity and ferroelectricity. To form these materials as nanometric powders or thin-film coatings, soft-chemical processing is required, and a limited number of procedures have been reported. We have explored two soft-chemical routes to lithium niobate and lithium tantalate materials: a non-aqueous procedure and an aqueous procedure. The non-aqueous procedure, which utilizes 1,4-butanediol and simple chemical precursors produces pure phase rhombohedral LiTaO3 and LiNbO3. For aqueous synthesis, we utilize the single-source polyoxoniobate salt: Li8[M6O19]·xH2O (M = Nb, Ta) in a hydrothermal reaction. If LiOH is added, the product is rock-salt type Li3MO4. Without LiOH, other phases are observed. The products are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, compositional analysis, and thermogravimetry, and the two soft-chemical processes are compared.

Evaluation on mass sensitivity of SAW sensors for different piezoelectric materials using finite-element analysis

The mass sensitivity of the piezoelectric surface acoustic wave (SAW) sensors is an important factor in the selection of the best gravimetric sensors for different applications. To determine this value without facing the practical problems and the long theoretical calculation time, we have shown that the mass sensitivity of SAW sensors can be calculated by a simple three-dimensional (3-D) finite-element analysis (FEA) using a commercial finite-element platform. The FEA data are used to calculate the wave propagation speed, surface particle displacements, and wave energy distribution on different cuts of various piezoelectric materials. The results are used to provide a simple method for evaluation of their mass sensitivities. Meanwhile, to calculate more accurate results from FEA data, surface and bulk wave reflection problems are considered in the analyses. In this research, different cuts of lithium niobate, quartz, lithium tantalate, and langasite piezoelectric materials are applied to investigate their acoustic wave properties. Our analyses results for these materials have a good agreement with other researchers' results. Also, the mass sensitivity value for the novel cut of langasite was calculated through these analyses. It was found that its mass sensitivity is higher than that of the conventional Rayleigh mode quartz sensor.

III-Nitrides growth and AlGaN/GaN heterostructures on ferroelectric materials

The growth of III-nitrides on the ferroelectric materials lithium niobate (LN) and lithium tantalate (LT) via molecular beam epitaxy (MBE) using rf plasma source has been investigated. We have found that gallium nitride (GaN) epitaxial layers have a crystalline relationship with lithium niobate (tantalate) as follows: (0 0 0 1) GaN || (0 0 0 1) LN (LT) with [10−10] GaN || [11−20] LN (LT). The surface stability of LN and LT substrates has been monitored by in situ spectroscopic ellipsometry in the vacuum chamber. Three different temperature zones have been discerned; surface degas and loss of OH group (100–350 °C); surface segregation/accumulation of Li and O-species (400–700 °C); surface evaporation of O-species and Li desorption (over 750 °C). However, LT shows only surface degassing in the range of 100–800 °C. Therefore, congruent LN substrates were chemically unstable at the growth temperature of 550–650 °C, and therefore developed an additional phase of Li-deficient lithium niobate (LiNb 3O 8) along with lithium niobate (LiNbO 3), confirmed by X-ray diffraction. On the other hand, LT showed better chemical stability at these temperatures, with no additional phase development. The structural quality of GaN epitaxial layers has shown slight improvement on LT substrates over LN substrates, according to X-ray diffraction. Herein, we demonstrate AlGaN/GaN heterostructure devices on ferroelectric materials that will allow future development of multifunctional electrical and optical applications.

Modeling of ultrasonic wave propagation in integrated piezoelectric structures under residual stress

The objective of this study is to understand the role of residual stress in piezoelectric layers in order to predict the performance of integrated structures. This is of particular importance in thick or thin film technology. Considering a bulk piezoelectric material, the Christoffel equation for a piezoelectric material is modified to take into account a uniform residual stress on a given cross section. A numerical study of its influence is carried out on the slowness curves and coupling coefficients of a lithium niobate material. In a second part, modified Christoffel tensor is used to calculate the dispersion curves of Lamb waves in a piezoelectric plate. The Lamb modes are found to be sensitive to the residual stress. In particular, it is shown how the behavior of the first Lamb modes is modified with residual stress. In a third part, these results are extended to a piezoelectric film laid down on a substrate in order to model the importance of these phenomena on the behavior of an integrated structure. The numerical study of guided waves in a lithium niobate plate is performed first, then the case of a lithium niobate film laid down on a silicon substrate is considered.

High-frequency surface acoustic wave devices based on LiNbO3∕diamond multilayered structure

This research is focused on the development of a new technology for the fabrication of high-frequency surface acoustic wave (SAW) filters based on diamond and lithium niobate (LiNbO3) materials. LiNbO3 films are in situ deposited at 490 °C on polycrystalline diamond substrates by radio-frequency magnetron sputtering; a multistep growth process is proposed to deposit oriented LiNbO3 films with a smooth surface. Conventional interdigital transducers are fabricated on top of the piezoelectric LiNbO3 layer by standard optical lithography. We report experimental results for a SAW bandpass filter operating at a frequency above 2.30 GHz. We have observed that Rayleigh SAW modes are excited within this structure, with extremely high phase velocities (up to 12000m∕s). This latter result illustrates the greatest advantage of using diamond as an acoustic substrate. It allows the fabrication of SAW devices operating in the gigahertz frequency range using standard optical lithography.

III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy

Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000°C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN∕GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.

Minimisation of mechanical cross-talk in periodic piezoelectric composite arrays

This paper describes an investigation into mechanical cross-talk within 1-3 and 2-2 connectivity piezoelectric composite array configurations, comprising a matrix of active piezoelectric elements embedded within a passive, polymeric, material. One way to take full advantage of the reported sensitivity and bandwidth improvements from single-crystal materials is to configure them as a piezoelectric composite. For this work, piezoelectric ceramic, lithium niobate and single-crystal pmn-pt materials are investigated as the active component in the piezocomposite array designs. Within these piezoelectric configurations, the generation of ultrasonic inter-pillar modes, which arise due to the periodicity of the active piezoelectric elements within the piezocomposite lattice, can be detrimental to the array performance. Consequently, finite element (FE) modelling, using PZFlex, is utilised to provide design techniques for the removal of these inter-pillar modes from the frequency band of interest and the realisation of unimodal piezocomposite transducer structures. Further FE modelling is used to generate dispersion data for 2-2, and doubly periodic 1-3, composite substrates. This dispersion data is used to design the linear arrays, with the objective of minimising mechanical inter-element cross-talk. A comparison between the FE predicted mechanical cross-coupling between array elements, for each composite material operating in air, is supported by experimentally measured data. Subsequently, the validated FE models are extended to include both operation into a solid load and the introduction of a backing material to simulate the operation of a practical NDE array transducer. The design techniques obtained from PZFlex are shown to produce arrays with low cross-talk and the extent of the cross-talk in manufactured and modelled ceramic and pmn-pt single-crystal arrays is compared.

Polarization separation/combination based on self-imaging

An integrated optical device for the separation/combination of orthogonal polarizations is described. The device relies on simultaneous symmetric and antisymmetric 131 off-center self-imaging. Calculations show that 90% throughput and 0.1% crosstalk can often be attained, with device length less than or comparable to other integrated optical polar- ization separation devices. The device is passive, requires only a single mask, and is not restricted to a specific fabrication method or material system. Devices can even be made in isotropic material systems with a deep etch. Simulation results are presented for the lithium niobate and glass waveguide material systems. © 2001 Society of Photo-Optical Instrumen- tation Engineers. (DOI: 10.1117/1.1402623)

Progress toward Device-Quality Second-Order NLO Materials: 3. Electrooptic Activity of Polymers Containing E,E,E-[4-(N,N-Dialkylamino)- phenyl]pentadienylidene-3-phenyl- 5-isoxazolone Chromophores

The realization of electrooptic coefficients leading to digital drive voltage levels is an important objective if polymeric electrooptic materials are to achieve significant commercial application. Polymeric materials characterized by electrooptic coefficients somewhat greater than those of the dominant commercial material lithium niobate are obtained with chromophores based on polyene bridge and isoxazolone acceptor segments.

Cu(C(10)H(9)N(3))(2)MOF(5).2H(2)O (M = Nb, Ta): Aligned [MOF(5)](2)(-) Oxide Fluoride Anions.

Two new compounds are reported that contain a 1:1 complex of a cis-bis(2,2‘-dipyridylamine)Cu2+ cation and an oxide fluoride [MOF5]2- (M = Nb, Ta) anion in which the polar distortions of the anions are aligned within one-dimensional chains. The bonding and charge on the oxide and fluoride ions and the distortions of the [NbOF5]2- and [TaOF5]2- anions resemble the ferroelectric material lithium niobate.

Volatile Liquid Precursors for the Chemical Vapor Deposition (CVD) of Thin Films Containing Alkali Metals

AbstractThe first volatile, liquid compounds of alkali metals were synthesized and used for the CVD of materials containing alkali metals. Amides of the type MNR1(SiMe2R2) and MN(SiMe2R2)2 [M = Li, Na, K; R1= t-butyl, t-amyl; R2= ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-hexyl, n-octyl] were made and characterized. The lithium amides were prepared via the deprotonation of the parent amine using butyl lithium. The sodium and potassium amides were formed by transamination of sodium amide and potassium bis(trimethylsilyl)amide with the parent amines. For example, lithium bis(ethyldimethylsilyl)amide was prepared from butyl lithium and bis(ethyldimethylsilyl)amine and was distilled as a clear, colorless liquid at 122 °C (0.2 Torr) having a viscosity of 37 cP at 40 °C. These alkali metal amides can be used as convenient liquid sources for CVD of mixed metal oxides containing alkali metals, such as the non-linear optical material lithium niobate, lithium-containing materials for battery electrodes, electrochromic tungsten bronzes, and the pyroelectric and ferroelectric material potassium tantalate.

Numerical computation of heat flow, fluid flow and interface shapes in the float zone of lithium niobate during a melting process

Computer simulations were performed to study the temperature and velocity distributions and the interface shapes in the floating-zone melt for lithium niobate materials. The input power distribution generated by the heat source was assumed to be Gaussian. The variation of the interface shapes and the transport phenomena in the flow zone relative to the input power was investigated. The results show that the shapes of the gas-melt and melt-solid interfaces and the temperature and velocity fields are modified by the gravity force; the influence of gravity increases as the input power increases. The present results are consistent with the recent experimental observations.

Applied-voltage induced fatigue of lithium niobate waveguide

z-cut lithium niobate optical modulator devices were ac (Vp-p=20 V) operated at 130 °C with an accumulated dc bias voltage of 4 and 8 V. A consequent dc drift phenomenon was larger for the 8 V bias application. After the operation, inversed domains were found along the Mach–Zehnder waveguides, particularly on the waveguide placed under the hot electrode. The results suggested that the device operation at higher voltage and temperature led to an accelerated dc drift and a fatiguelike deterioration of the lithium niobate material.