Crystals

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11 pages, 8075 KiB

Open AccessArticle

Growth of Thin AlN Films on Si Wafers by Reactive Magnetron Sputtering: Role of Processing Pressure, Magnetron Power and Nitrogen/Argon Gas Flow Ratio

by Matilde Kammer Sandager, Christian Kjelde and Vladimir Popok

Crystals 2022, 12(10), 1379; https://doi.org/10.3390/cryst12101379 - 28 Sep 2022

Cited by 4 | Viewed by 2119

Abstract

AlN is a wide band gap semiconductor that is of growing industrial interest due to its piezoelectric properties, high breakdown voltage and thermal conductivity. Using magnetron sputtering to grow AlN thin films allows for high deposition rates and uniform coverage of large substrates. [...] Read more.

AlN is a wide band gap semiconductor that is of growing industrial interest due to its piezoelectric properties, high breakdown voltage and thermal conductivity. Using magnetron sputtering to grow AlN thin films allows for high deposition rates and uniform coverage of large substrates. One can also produce films at low substrate temperatures, which is required for many production processes. However, current models are inadequate in predicting the resulting structure of a thin film when different sputter parameters are varied. In this work, the growth of wurtzite AlN thin films has been carried out on Si(111) substrates using reactive direct current magnetron sputtering. The influence of the processing pressure, magnetron power and N

_{2}

/Ar ratio on the structure of the grown films has been analyzed by investigating crystallinity, residual film stress and surface morphology using X-ray diffraction, profilometry, atomic force microscopy and scanning electron microscopy. In every case, the films were found to exhibit c-axis orientation and tensile stress. It was found that high-quality AlN films can be achieved at an N

_{2}

/Ar ratio of 50% and a low pressure of 0.2 Pa. High magnetron powers (900–1200 W) were necessary for achieving high deposition rates, but they led to larger film stress. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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12 pages, 3079 KiB

Open AccessArticle

Fast, Accurate and Full Extraction of Coupling-of-Modes Parameters by Finite Element Method

by Xueping Sun, Rui Ma, Shun Zhou, Xiuting Shao, Jin Cheng, Dabin Lin, Wen Wang and Weiguo Liu

Crystals 2022, 12(5), 706; https://doi.org/10.3390/cryst12050706 - 16 May 2022

Cited by 3 | Viewed by 1768

Abstract

This paper presents a new numerical approach for the full extraction of the coupling-of-modes (COM) parameters by stationary and eigenfrequency analyses in the finite element method (FEM). This is a fast method extracting from the results of static analysis and eigenfrequency analysis. It [...] Read more.

This paper presents a new numerical approach for the full extraction of the coupling-of-modes (COM) parameters by stationary and eigenfrequency analyses in the finite element method (FEM). This is a fast method extracting from the results of static analysis and eigenfrequency analysis. It avoids the long calculation time of admittance frequency response analysis, which is commonly used in extracting COM parameters. In addition to the usual COM parameters (velocity, reflection coefficient, transduction coefficient and capacitance), the phases of reflection and transduction coefficient can be also extracted with this method. The proposed method was applied to different cutting types LiNbO₃ with different types of thicknesses in a varying interdigital transducer (IDT). These examples show that our approach has great potential in extracting all the COM parameters of the Rayleigh SAW for all kinds of IDT structures. Therefore, it is a fast, accurate, general and full extraction approach of COM parameters. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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7 pages, 1986 KiB

Open AccessArticle

Dielectric and Piezoelectric Properties of Mn-Doped Bi(Mg_1/2Ti_1/2)O₃-PbTiO₃ Piezoelectric Single Crystals with MPB Composition

by Jinfeng Liu, Guisheng Xu, Xiu Zhu and Meilin Chen

Crystals 2022, 12(5), 567; https://doi.org/10.3390/cryst12050567 - 19 Apr 2022

Viewed by 1614

Abstract

Mn-doped BMT-PT single crystals were grown using a flux method. The crystals were irregular and 4–10 mm in size. The EPMA and XRD results showed that the composition of the crystals was in the range of MPB. The room temperature dielectric permittivity ε [...] Read more.

Mn-doped BMT-PT single crystals were grown using a flux method. The crystals were irregular and 4–10 mm in size. The EPMA and XRD results showed that the composition of the crystals was in the range of MPB. The room temperature dielectric permittivity ε_r and dielectric loss tanδ were 806 and 3.4% at 1 KHz. As the temperature increased, the rhombohedral phase did not first transform into the tetragonal phase, but transformed into the cubic phase directly. Owing to the Mn-doping, the ferroelectric hysteresis loops of the sample were quite narrow. The Curie temperature T_c, piezoelectric coefficient d₃₃ and thickness electromechanical coupling factor k_t of the single crystals along the <001> direction were 464 °C, 392 pC/N and 0.51, respectively. The piezoelectric properties are much better than the values of the ceramics and the undoped BMT-PT single crystals with a MPB composition. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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13 pages, 3701 KiB

Open AccessArticle

Electrocaloric Effect in (1−x)(0.8Na_0.5Bi_0.5TiO₃-0.2BaTiO₃)−xCaTiO₃ Solid Solutions at High Electric Fields

by Ojars Martins Eberlins, Eriks Birks, Maija Antonova, Maris Kundzins, Maris Livins and Andris Sternberg

Crystals 2022, 12(2), 134; https://doi.org/10.3390/cryst12020134 - 19 Jan 2022

Cited by 1 | Viewed by 1672

Abstract

Recently, promising results were obtained in studies of the electrocaloric effect in thin films. Therefore, research into this effect at high applied electric field values in bulk ferroelectrics is an important task for those scoping out materials that could be appropriate for cooling [...] Read more.

Recently, promising results were obtained in studies of the electrocaloric effect in thin films. Therefore, research into this effect at high applied electric field values in bulk ferroelectrics is an important task for those scoping out materials that could be appropriate for cooling devices based on the electrocaloric effect. The present study addresses electrocaloric effect in (1−x)(0.8Na_1/2Bi_1/2TiO₃-0.2BaTiO₃)−xCaTiO₃ solid solutions by the direct method in electric fields ranging from 0 up to 100 kV/cm and at temperatures of up to 150 °C. The choice of 0.8Na_1/2Bi_1/2TiO₃-0.2BaTiO₃ as the starting composition is motivated by high spontaneous polarization within the studied range of electric fields, while CaTiO₃ is added to reduce depolarization temperature at, and below, room temperature. In the studied temperature range, the maximal value of electrocaloric effect with temperature change of ΔT = 1.0 °C was found in the composition with x = 0.050 at 100 °C, having significant contribution from the entropy jump at the first-order phase transition induced by an electric field. At increasing CaTiO₃ concentration, the attainable ΔT decreases. Measurements of polarization current, which were taken simultaneously with ΔT measurements, allowed us to study differences between ΔT obtained by the direct and the indirect methods. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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9 pages, 5247 KiB

Open AccessArticle

On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb₁₈W₁₆O₉₃

by Frank Krumeich

Crystals 2021, 11(12), 1514; https://doi.org/10.3390/cryst11121514 - 5 Dec 2021

Cited by 3 | Viewed by 2308

Abstract

The evaluation of HAADF-STEM images of a sample with the composition Nb₁₈W₁₆O₉₃ provided new insights into its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of [...] Read more.

The evaluation of HAADF-STEM images of a sample with the composition Nb₁₈W₁₆O₉₃ provided new insights into its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal–oxygen strings determines the oxygen-to-metal ratio (O/ΣM with M = Nb,W). For a large area, the O/ΣM was determined to be 2.755, which is bigger than the value of Nb₁₈W₁₆O₉₃, which is O/ΣM = 2.735. To a large extent, the three-fold TTB superstructure of Nb₈W₉O₄₇ with a high oxygen content is present (O/ΣM = 2.765). In addition, a new four-fold TTB superstructure was found in small domains. Nb₁₂W₁₁O₆₃ with an O/ΣM = 2.739 obviously accommodates part of the sample’s metal excess compared to the stable phase Nb₈W₉O₄₇. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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11 pages, 9496 KiB

Open AccessArticle

Thermodynamic Study of Adsorption Capacity between Metal Film and Optical Crystal: Adsorption Energy of Ni Films on LiNbO₃ Substrates

by Yuhang Xu, Fei Lu, Kaijing Liu and Changdong Ma

Crystals 2021, 11(11), 1273; https://doi.org/10.3390/cryst11111273 - 20 Oct 2021

Viewed by 1447

Abstract

The growth of large areas of two-dimensional homogeneous graphene depends on the bond between the metal film, which acts as a catalyst, and the substrate material. The structural differences between the metal and the various anisotropic crystals make this growth method a challenge [...] Read more.

The growth of large areas of two-dimensional homogeneous graphene depends on the bond between the metal film, which acts as a catalyst, and the substrate material. The structural differences between the metal and the various anisotropic crystals make this growth method a challenge for the feasibility of growing graphene on optical crystals. In this paper, the evolution of the adsorption energy between nickel (Ni) films and Lithium Niobate (LiNbO₃, LN) crystals is modelled under different thermal treatment environments by constructing a physical model of the temperature dependence of the adsorption energy between the two materials. With the aid of a series of simulated full annealing processes, the changes in adsorption energy at different temperatures were calculated. The results show that there are two “temperature windows” with target annealing temperatures of 700–800 K and 950–1050 K that prove to have high adsorption energies. This is of great guiding and practical significance for the direct transfer-free synthesis of graphene on LiNbO₃ substrates. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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13 pages, 5929 KiB

Open AccessArticle

Non-Invasive Visualization of Ferroelectric Domain Structures on the Non-Polar y-Surface of KTiOPO₄ via Raman Imaging

by Julian Brockmeier, Peter Walter Martin Mackwitz, Michael Rüsing, Christof Eigner, Laura Padberg, Matteo Santandrea, Christine Silberhorn, Artur Zrenner and Gerhard Berth

Crystals 2021, 11(9), 1086; https://doi.org/10.3390/cryst11091086 - 7 Sep 2021

Cited by 2 | Viewed by 2712

Abstract

Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of [...] Read more.

Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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12 pages, 2687 KiB

Open AccessEditor’s ChoiceArticle

Scanning Electron Microscopy Investigation of Surface Acoustic Wave Propagation in a 41° YX-Cut of a LiNbO₃ Crystal/Si Layered Structure

by Dmitry Roshchupkin, Evgenii Emelin, Olga Plotitcina, Anatoly Mololkin and Oleg Telminov

Crystals 2021, 11(9), 1082; https://doi.org/10.3390/cryst11091082 - 6 Sep 2021

Cited by 4 | Viewed by 2500

Abstract

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO₃ crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration [...] Read more.

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO₃ crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration mode, made it possible to visualize the SAW and PSAW in the LiNbO₃/Si layered structure. The process of the SAW and PSAW propagation in a LiNbO₃/Si layered structure and in a bulk 41° YX-cut of a LiNbO₃ crystal were compared. It was demonstrated that the SAW velocities in the layered LiNbO₃/Si structure exceed the typical SAW velocities for LiNbO₃ and Si single crystals. In the layered structure, the SAW and PSAW velocities were 4062 m/s, 4731 m/s, and 5871 m/s. It was also demonstrated that the PSAW velocities are the same in the LiNbO₃/Si layered structure and in the bulk 41° YX-cut of a LiNbO₃ crystal. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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10 pages, 2817 KiB

Open AccessArticle

Bridgman Growth and Photoelectronic Property of Relaxor-Based Ferroelectric Single Crystal Pb(Sm_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃

by Fan Liao, Yan Zhao, Ziyun Chen, Yanqing Zheng and Hongbing Chen

Crystals 2021, 11(4), 402; https://doi.org/10.3390/cryst11040402 - 10 Apr 2021

Cited by 8 | Viewed by 2238

Abstract

A relaxor-based ferroelectric single crystal with the nominal composition of xPb(Sm_0.5Nb_0.5)O₃-(0.7‒x) Pb(Mg_1/3Nb_1/3)O₃-0.3PbTiO₃ (x = 0.01, 0.02, and 0.03) was grown by the vertical Bridgman process. The electrical properties and the [...] Read more.

A relaxor-based ferroelectric single crystal with the nominal composition of xPb(Sm_0.5Nb_0.5)O₃-(0.7‒x) Pb(Mg_1/3Nb_1/3)O₃-0.3PbTiO₃ (x = 0.01, 0.02, and 0.03) was grown by the vertical Bridgman process. The electrical properties and the ferroelectric domains, as well as the luminescent characteristics of the single crystals, were investigated systematically. The piezoelectric coefficient d₃₃ of the single crystals are slightly higher than that of the undoped PMN-PT single crystal under direct current polarization, while the crystal wafers gain a much higher d₃₃ value upon being polarized with alternating current voltage. The single crystals possess a decreased phase transition temperature of around 60 °C and a decreased Curie temperature of 92~116 °C compared with the undoped PMN-PT single crystal. The crystal wafers polarized with alternating current voltage exhibited a desirable optical transmittance, which is associated with the domain structure changes inside the crystal medium. The domain density of the crystal wafers under alternating current polarization was significantly decreased compared with the direct current polarized crystal wafers. The luminescent spectra of the crystal wafers exhibit the typical emission peaks corresponding to the characteristic transition of Sm³⁺ ions in the crystal lattice. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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