Search Results (61)

The in situ electrochemical behaviors of Ti-39Nb-6Zr alloy were investigated in 2.3 ppm Li⁺ and 1500 ppm B³⁺ solution at 300 °C and 14 MPa. The activation energy is 12.84 kJ/mol, and the oxidation of titanium is controlled by oxygen ions diffusion in the liquid phases. The morphology, phase structure, and composition of the oxide film after 700 h exposure time in 300 °C and 14 MPa solution were characterized. The oxide film mainly included anatase TiO₂ phases, ZrO₂, Nb₂O₅, and a slight B₂O₃. The morphology of the film is shown by many nanocrystalline grains and the thickness is about 5 μm. The passivation film on the alloy substrate transforms from a single-layer film structure to a double-layer film structure. The impedance of the passivation decreases with the increase in temperature, which is related to the enhanced ion conductivity of the passivation film at high temperatures. The impedance of the dense layer inside the passivation film is much greater than that of the loose layer outside, and the dense layer inside plays a crucial role in the corrosion resistance of the Ti-39Nb-6Zr alloy. During the insulation process, the impedance of the dense layer inside the passivation film first increases and then slowly decreases, and the corrosion resistance of the passivation film first increases and decreases. Full article

LiNbO₃ plays a significant role in modern integrated photonics because of its unique properties. One of the challenges in modern integrated photonics is reducing chip production cost. Today, the most widespread yet expensive method to fabricate thin films of LiNbO₃ is the smart cut method. The high production cost of smart-cut chips is caused by the use of expensive equipment for helium implantation. A prospective method to reduce the cost of photonic integrated circuits is to use sputtered thin films of lithium niobite, since sputtering technology does not require helium implantation equipment. The purpose of this review is to assess the feasibility of applying sputtered LiNbO₃ thin films in integrated photonics. This work compares sputtered LiNbO₃ thin films and those fabricated by widespread methods, including the smart cut method, liquid-phase epitaxy, chemical vapor deposition, pulsed laser deposition, and molecular-beam epitaxy. Full article

With the development of piezoelectric-on-insulator (POI) substrates, X-cut LiNbO₃ thin-film resonators with interdigital transducers are widely investigated due to their adjustable resonant frequency (f_s) and effective electromechanical coupling coefficient ($K_{eff}^2$). This paper presents an in-depth study of simulations and measurements of laterally excited bulk acoustic wave resonators based on an X-cut LiNbO₃/SiO₂/Si substrate and a LiNbO₃ thin film to analyze the effects of electrode angle rotation ($\theta$) on the modes, f_s, and $K_{eff}^2$. The rotated $\theta$ leads to different electric field directions, causing mode changes, where the resonators without cavities are longitudinal leaky SAWs (LLSAWs, $\theta$ = 0$°$) and zero-order shear horizontal SAWs (SH₀-SAWs, $\theta$ = 90$°$) and the resonators with cavities are zero-order-symmetry (S₀) lateral vibrating resonators (LVRs, $\theta$ = 0$°$) and SH₀ plate wave resonators (PAW, $\theta$ = 90$°$). The resonators are fabricated based on a 400 nm X-cut LiNbO₃ thin-film substrate, and the measured results are consistent with those from the simulation. The fabricated LLSAW and SH₀-SAW without cavities show a $K_{eff}^2$ of 1.62% and 26.6% and a Bode-Q_max of 1309 and 228, respectively. Meanwhile, an S₀ LVR and an SH₀-PAW with cavities present a $K_{eff}^2$ of 4.82% and 27.66% and a Bode-Q_max of 3289 and 289, respectively. In addition, the TCF with a different rotated $\theta$ is also measured and analyzed. This paper systematically analyzes resonators on X-cut LiNbO₃ thin-film substrates and provides potential strategies for multi-band and multi-bandwidth filters. Full article

With the rapid development of fifth-generation (5G) mobile communication technology, the performance requirements for radio frequency front-end surface acoustic wave (SAW) devices have become increasingly stringent. Surface acoustic wave devices on piezoelectric thin film-based layered structures with high electromechanical coupling coefficients and low-frequency temperature compensation characteristics have emerged as a key solution. In this work, a SAW resonator based on an Al/41° Y-X LiNbO₃/SiO₂/poly-Si/Si multi-layered structure is proposed. FEM modeling of the proposed resonator and the influences of the thicknesses of the LiNbO₃, SiO₂, and Al electrodes on performances such as the parasitic noise, bandwidth, and electromechanical coupling coefficient are analyzed. Optimal parameters for the multi-layer piezoelectric structure are identified for offering large coupling up to 24%. Based on these findings, a single-port SAW resonator with an Al/41° Y-X LiNbO₃/SiO₂/poly-Si/Si substrate structure is fabricated. The experimental results align well with the simulation results; meanwhile, the SAW filter based on the proposed resonator demonstrates that a center frequency of 2.3 GHz, a 3-dB fractional bandwidth of 23.48%, and a minimum in-band insertion loss of only 0.343 dB are simultaneously achieved. This study provides guidance for the development of multi-layer film SAW resonator-based filters with high-performance. Full article

Lithium niobate (LiNbO₃) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO₃ (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits. Full article

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO₃ thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO₃ thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO₃ thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance. Full article

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the $YZ$-cut of a LiNbO₃ ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO₃ substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of $\Lambda =60$ μm was fabricated on the surface of the LiNbO₃ crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude–frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass. Full article

Al-Cu thin films were fabricated by RF magnetron sputtering from aluminum (Al) and copper (Cu) metal targets to improve the acoustic performance of SAW devices on LiNbO₃ substrates. To optimize the electrode material for SAW devices, Al-Cu films with various compositions were fabricated and their electrical, mechanical, and acoustic properties were comprehensively evaluated. The Al-Cu films exhibited a gradual decrease in resistivity with increasing Al content. The double-electrode SAW devices composed of Al-Cu films demonstrated a resonant frequency of 70 MHz and an average insertion loss of −16.1 dB, which was significantly lower than that of devices made with traditional Au or Al electrodes. Additionally, the SAW devices showed an increase in the FWHM values of the resonant frequency and a decrease in the insertion loss as the Al content in the IDT electrode decreased. These findings indicate that improving the performance of SAW devices can be achieved by reducing the density of the IDT electrodes, rather than focusing solely on their electrical characteristics. Full article

LiNbO₃ thin films are grown on a c-plane (0001) sapphire wafer at a relatively low substrate temperature by chemical beam vapor deposition (CBVD) in Sybilla equipment. Raman measurements only evidence the LiNbO₃ phase, while HR-XRD diffractograms demonstrate a c-axis-oriented growth with only (006) and (0012) planes measured. The rocking curve is symmetric, with a full width at half maximum (FWHM) of 0.04°. The morphology and topography observed by SEM and AFM show very low roughness, with rms equaling 2.0 nm. The optical properties are investigated by a guided-wave technique using prism coupling. The ordinary refractive index (n_o) and extraordinary refractive index (n_e) at different wavelengths totally match with the LiNbO₃ bulk, showing the high microstructural quality of the film. The film composition is estimated by Raman and bi-refringence and shows a congruent or near-stoichiometric LiNbO₃. Full article

Highly efficient surface acoustic wave (SAW) transducers offer significant advantages for microfluidic atomization. Aiming at highly efficient atomization, we innovatively accomplish dual-surface simultaneous atomization by strategically positioning the liquid supply outside the IDT aperture edge. Initially, we optimize Lamb wave transducers and specifically investigate their performance based on the ratio of substrate thickness to acoustic wavelength. When this ratio $h/\lambda$ is approximately 1.25, the electromechanical coupling coefficient of A₀-mode Lamb waves can reach around 5.5% for 128° Y-X LiNbO₃. We then study the mechanism of droplet atomization with the liquid supply positioned outside the IDT aperture edge. Experimental results demonstrate that optimized Lamb wave transducers exhibit clear dual-surface simultaneous atomization. These transducers provide equivalent amplitude acoustic wave vibrations on both surfaces, causing the liquid thin film to accumulate at the edges of the dual-surface and form a continuous mist. Full article

The study of the properties of ferroelectric materials against irradiation has a long history. However, anti−irradiation research on the ferroelectric domain has not been carried out. In this paper, the irradiation of switched domain structure is innovatively proposed. The switched domain of 700 nm lithium niobate (LiNbO₃, LN) thin film remains stable after gamma irradiation from 1 krad to 10 Mrad, which was prepared by piezoresponse force microscopy (PFM). In addition, the changing law of domain wall resistivity is explored through different sample voltages, and it is verified that the irradiated domain wall conductivity is still larger than the domain. This domain wall current (DWC) property can be applied to storage, logic, sensing, and other devices. Based on these, a ferroelectric domain irradiation resistance model is established, which explains the reason at an atomic level. The results open a possibility for exploiting ferroelectric materials as the foundation in the application of space and nuclear fields. Full article

In the present paper the humidity sensing properties of regioregular rr-P3HT (poly-3-hexylthiophene) polymer films is investigated by means of surface acoustic wave (SAW) based sensors implemented on LiNbO₃ (128⁰ Y-X) and ST-quartz piezoelectric substrates. The polymeric layers were deposited along the SAW propagation path by spray coating method and the layers thickness was measured by atomic force microscopy (AFM) technique. The response of the SAW devices to relative humidity (rh) changes in the range ~5–60% has been investigated by measuring the SAW phase and frequency changes induced by the (rh) absorption in the rr-P3HT layer. The SAW sensor implemented onto LiNbO₃ showed improved performance as the thickness of the membrane increases (from 40 to 240 nm): for 240 nm thick polymeric membrane a phase shift of about −1.2 deg and −8.2 deg was measured for the fundamental (~78 MHz operating frequency) and 3rd (~234 MHz) harmonic wave at (rh) = 60%. A thick rr-P3HT film (~600 nm) was deposited onto the quartz-based SAW sensor: the sensor showed a linear frequency shift of ~−20.5 Hz per unit (rh) changes in the ~5–~50% rh range, and a quite fast response (~5 s) even at low humidity level (~5% rh). The LiNbO₃ and quartz-based sensors response was assessed by using a dual delay line system to reduce unwanted common mode signals. The simple and cheap spray coating technology for the rr-P3HT polymer films deposition, complemented with fast low level humidity detection of the tested SAW sensors (much faster than the commercially available Michell SF-52 device), highlight their potential in a low-medium range humidity sensing application. Full article

In pressurized water reactors, LiOH may be concentrated in some areas, leading to the accelerated corrosion of fuel claddings. Injecting boric acid into primary coolants can mitigate the accelerated corrosion effect of LiOH on Zircaloys, but the effects of boron content on the corrosion behavior of the Zr-Sn-Nb alloy are still unknown. This work focused on the corrosion and hydrogen absorption behavior at 360 °C/18.6 MPa in 100 mg/kg LiOH solutions with 0 mg/kg, 50 mg/kg, and 200 mg/kg boron contents for up to 510 days, aiming to study the effect of boron content on corrosion resistance in LiOH solutions. Corrosion kinetics, microstructures of oxide films, hydrogen absorption concentrations and hydride morphology were obtained after the test. The results show that injecting boron in LiOH solutions can significantly reduce the corrosion weight gain, hydrogen concentration, and hydrogen length of Zr-Sn-Nb alloys, that is, improving corrosion resistance effectively. During the oxidation of the Zr-Sn-Nb alloy, B³⁺ and Li⁺ incorporate in oxide films. The incorporation of Li⁺ may lead to the generation of oxygen vacancies, which can carry oxygen from the solutions to O/M interface, accelerating corrosion. The incorporation of B³⁺ in oxide films will slow down the oxidation of Zr-Sn-Nb alloys by reducing the oxygen vacancies caused by Li⁺ aggregation. Full article

This article presents lithium niobate (LiNbO₃) based on shear horizontal (SH0) resonators, utilizing a suspended structure, for radio frequency (RF) applications. It demonstrates the design, analysis, and fabrication of SH0 resonators based on a 36Y-cut LiNbO₃ thin film. The spurious-free SH0 resonator achieves an electromechanical coupling coefficient ($k_t^2$) of 42.67% and a quality factor (Q_r) of 254 at the wave-propagating orientation of 0° in the 36Y-cut plane. Full article

Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol–gel/spin-coating approach of polycrystalline LiNbO₃ films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol–gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO₃ films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films. Full article