Properties Of LiNbO3 Thin Films Research Articles

Effect of the annealing treatment on the physical and structural properties of LiNbO3 thin films deposited by radio-frequency sputtering at room temperature

Reaching the full potential of the 5th Generation of mobile applications (5G) requires pushing the performances of acoustic radio-frequency (RF) filters beyond their current limits. Current high-performances RF filters (above 2.5 GHz) are based on aluminium nitride (AlN). Their bandwidth is however limited by the low electromechanical coupling coefficient of AlN. In this context, due to its higher electromechanical coupling coefficient, lithium niobate (LiNbO3) is a good candidate as an active piezoelectric material. For this application, LiNbO3 films need to be stoichiometric and to be either highly textured or monocrystalline. However, there seems to be no deposition process for high quality LiNbO3 thin films on silicon available at the moment, which could be mainly due to the difficulty to achieve a high crystalline quality and to the challenging control and of its stoichiometry. In the present work, the realization of highly textured films deposited directly on silicon substrate by RF sputtering at room temperature and after annealing was demonstrated. The effect of the annealing parameters (temperature and ramping rates) was studied. LiNbO3 layers with a strong degree of texture along the c-axis were obtained. The X-ray diffraction analysis showed that an optimum texture of 99% can be reached by a high temperature of annealing and a fast temperature ramping rate. The effect of annealing parameters on the presence of secondary phase LiNb3O8 and film density was also investigated.

Effect of light induced heat treatment on the structural and morphological properties of Linbo3 thin films

In this research, the spin coating technique has been used to achieve the deposition process of the lithium-niobate. A halogen lamp has used to maintain required heating during the deposition process. A Range of temperatures (60 - 120 °C) was applied on a substrate of a single crystal silicon wafer to maintain high quality deposition process. The deposited films were subsequently annealed to annealing temperature of 500 °C. Films were characterized and analyzed using X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscope (SEM), Raman spectroscopy. The results showed there is a significant impact that the substrate temperature can role over the structural and morphological properties of the prepared films. It also showed that there is a critical value of substrate temperature yields to the best combination of morphological and structural properties. Moreover, the higher values of the refractive index suggest that this material is more suitable for optical waveguides applications.

Optical investigations and optical constant of nano lithium niobate deposited by spray pyrolysis technique with injection of Li2CO3 and Nb2O5 as raw materials

This paper explored physical properties of LiNbO3 thin films that was deposited on quartz substrate employing spray pyrolysis technique. New raw materials were exploited as the precursor compounds. The films were annealed at different annealing temperatures, i.e. room temperature to 600 °C. The LiNbO3 are characterized and analyzed by the FESEM, AFM, X-ray diffraction and analyzed by UV–Visible and photoluminescence. The optical properties were analyzed by ultra violet- visible (UV–Visible) and photoluminescence measurements. The results indicated that the orientation of films crystallization and the grain size decreased with the increment of annealed temperatures. Energy band gap was recorded approximately 3.9 eV. The transmission efficiency was found to be in the range of 43–78%. Refractive index was observed from 2.02 to 2.43. Optical conductivity increased from 1.8 × 104 to 2.4 × 104 (s−1). The real and imaginary components of dielectric constants (er, ei), and Urbach energy decreased with higher annealing temperature.

Influence of target-substrate distance during pulsed laser deposition on properties of LiNbO3 thin films

This paper shows the results of studying the influence of target-substrate distance during pulsed laser deposition on electrical properties of LiNbO3 thin films. It has been shown that changing the target-substrate distance we can obtain thin films with a different composition. EDX spectra indicate that the LiNbO3 thin films fabricated under 120 mm target-substrate distance depleted Nb (0.7 atm. %) compare to LiNbO3 films fabricated under 20 mm target-substrate distance (11.0 atm. %). Varying target-substrate distance in the range from 20 mm to 120 mm charge carrier mobility increasing from 24 cm2/V·s to 395 cm2/V·s and concentration of charge carrier decreasing from 3·1013 cm-3 to 1·1012 cm-3. Obtained results can be used under development and fabrication of integral acousto-optic and surface acoustic wave (SAW) devices.

Structural, optical and femtosecond third-order nonlinear optical properties of LiNbO3 thin films

LiNbO3 thin films were deposited by means of Al:ZnO as intermediate layer using pulsed laser deposition and their structural, linear and nonlinear optical (NLO) properties were investigated. The films were found to be polycrystalline, (110) orientation for Al:ZnO/fused silica and (300) orientation for Al:ZnO/quartz substrates. The films demonstrated a transparency of >80% in the visible and near-infrared region. The NLO studies were performed with the Z-scan technique using ∼150fs, 80MHz pulses at 800nm. The studies revealed that the polycrystalline LiNbO3films and (300) LiNbO3films demonstrated reverse saturable absorption while a transition to saturable absorption was observed in the case of (110) LiNbO3. The presence of two-photon absorption is attributed to the indirect transition via intermediate defect levels which is related to the structural asymmetry. The large nonlinearity in refractive index could be a result of the strain induced ferroelectric polarization. The magnitude of the third order optical nonlinearity of all films was ∼10−11e.s.u. which is orders of magnitude higher than the value obtained for single crystal Z-cut LiNbO3.

Properties of LiNbO3 Thin Film Deposited by Chemical Vapor Deposition and Frequency Characteristics of Film Bulk Acoustic Wave Resonator

We have realized the fabrication of a film bulk acoustic wave resonator (FBAR) using a thin LiNbO3 film deposited by chemical vapor deposition (CVD) for the first time. As a result, a 2.9 GHz FBAR with an impedance ratio of 40 dB at resonant ( fr) and antiresonant ( fa) frequencies was realized. The LiNbO3 film has a mixed polarity. As a result of scanning nonlinear dielectric microscopy (SNDM), -c domains and +c domains occupy 82 and 18% of the LiNbO3 film, respectively. A shear mode was not excited on the fabricated FABR. According to a calculation, it is found that the shear wave mode can be suppressed by selecting the thickness of electrodes without any changes in the main responses of the longitudinal mode wave. It is important to deposit another oriented LiNbO3 film with a larger coupling factor to realize a wider-band device.

Preparation and Optical Waveguide Properties of LiNbO3 Thin Films by RF Magnetron Sputtering

C-axis-oriented LiNbO3 films were successfully obtained on ZnO/SiO2/Si, ZnO/glass and Pt/SiO2/Si substrates at substrate temperatures higher than 450°C by RF magnetron sputtering. LiNbO3 films were also grown epitaxially on α-Al2O3(001), (012) and (110) and LiTaO3(110) substrates at substrate temperatures higher than 650°C. The minimum optical propagation loss of the films was 6.47 dB/cm (TE0 mode) for the LiNbO3 film on LiTaO3. An improvement in the optical propagation loss after annealing treatment was observed.

Properties of LiNbO3 Thin Films Fabricated by RF Sputtering

Fabrication of LiNbO3 thin films by rf sputtering method and their properties have been studied. With substrate temperature above 400°C, single crystal films were deposited on LiTaO3 and sapphire substrates. Crystallographic relation between the grown films and the substrates are described. Measurements of refractive indices were carried out using Brewster angle method, and the data on the refractive indices of single and poly-crystalline films were obtained. Dielectric constants were measured for the samples deposited on Si substrates( The observed values were in the range of 40–50.