Material Characterization System Research Articles

Piezoelectric Properties of Ca3NbGa3Si2O14 Single Crystal

Langasite-type single crystal Ca3NbGa3Si2O14 (CNGS) was grown by the Czochralski technique. Dielectric, elastic and piezoelectric constants of CNGS were measured by the resonance-antiresonance method. At room temperature, dielectric constants ε11T/ε0 and ε33T/ε0 were 17.8 and 27.9, respectively. Electromechanical coupling coefficients k12, k25 and k26 were also determined as 10.9, 17.3 and 11.9%, respectively. The measurements were carried out in a temperature range from -30 to 80°C. Temperature coefficients of the dielectric, elastic and piezoelectric constants were obtained. The line-focus-beam and plane-wave ultrasonic material characterization system was employed for measuring bulk acoustic velocities, and longitudinal and transverse wave velocities of 7408.4 m/s and 3136.2 m/s, respectively, in the c-direction uncoupled with piezoelectricity at 23°C were obtained. This was in good agreement with the results determined by the resonance-antiresonance method. The density of CNGS was 4125 kg/m3. All the parameters of the CNGS crystal for bulk and surface acoustic wave applications were determined in this research.

A Simple and Low-Cost Measurement System for the Complex Permittivity Characterization of Materials

A microwave planar resonant sensor, its equivalent circuit, and the driving electronics for the measurement of the complex permittivity in compact areas of the material under test are presented. Compared to transmission or reflection sensors, the adoption of a scalar two-port measurement procedure reduces the cost of the system and improves its robustness. The measuring system requires only the calculation of two parameters, namely, the resonant frequency and the 3 dB bandwidth, thus achieving a substantial reduction of cost and computation time. Such a sensor can be adopted in moisture measurement systems, and its low cost is such as to allow its use even in a disposable manner.

Development of an improved calibration method for the LFB ultrasonic material characterization system

We investigated standard specimens for accurately calibrating the line-focus-beam ultrasonic material characterization (LFB-UMC) system without system dependencies. We evaluated several types of lithium tantalate (LiTaO3) substrates using two LFB-UMC systems with different device/system characteristics to measure and calibrate the propagation characteristics of the leaky surface acoustic waves (LSAWs), and analyzed the variations between the calibrated results. We concluded from this analysis that, by selecting materials with the cut surfaces and propagation directions of standard specimens that are identical to the objects to be calibrated, calibration errors resulting from different performance characteristics between the two systems could be nearly eliminated. Also, analytical errors caused by the effects of spectra with two close peaks (another propagation wave mode), one of the most common problems of characterization in the past, could be eliminated at the same time by this method.

Development of an improved calibration method for the LFB ultrasonic material characterization system

Development of an improved calibration method for the LFB ultrasonic material characterization system

Evaluation of mass-produced commercial LiTaO/sub 3/ single crystals using the LFB ultrasonic material characterization system

A mass-production line of lithium tantalate (LiTaO3) crystals with a maximum charge number of 60 for surface acoustic wave (SAW) devices was evaluated with the line-focus-beam (LFB) ultrasonic material characterization system. Some serious problems associated with chemical compositions were observed and resolved by measuring the velocities of Rayleigh-type leaky surface acoustic waves (LSAWs), VLSAW, for two groups of LiTaO3 wafers: 21 36 degrees Y X-LiTaO3 wafers selected randomly from crystal ingots grown with different charge numbers in different furnaces, and 14 42 degrees Y X-LiTaO3 wafers obtained at the top, middle, and bottom parts from 5 crystals selected from 39 crystals grown successively in the same furnace and crucible. Using the measured VLSAW and the predetermined relationship between VLSAW and Li2O concentrations, M(Li2O), we estimated the average M(Li2O) controlled in the current mass-production line to be about 48.77 mol% with a maximum difference of 0.75 mol%. The composition for each crystal ingot increased linearly about 0.04 mol% from the top to the bottom, and no dependence on the charge number was observed, as the melt composition used for the mass production was controlled through Curie temperature (TC) measurements. A nearly true congruent composition of 48.49 Li2O-mol% was obtained through the precise VLSAW data for the 42 degrees Y X-LiTaO3 wafers, that was about 0.3 mol% less than the melt composition in the production line. It was also pointed out that the TC measurement conditions, including room temperatures surrounding the measurement systems, should be re-examined for reliable production control. A guideline for more efficient mass production of the crystals has been established concerning the true congruent composition as the starting material.

Evaluation of mass-produced commercial LiTaO/sub 3/ single crystals using the LFB ultrasonic material characterization system

Evaluation of mass-produced commercial LiTaO/sub 3/ single crystals using the LFB ultrasonic material characterization system

F-2 A Super-Precision Evaluation Method of CTE for Ultra-Low Expansion Glasses Using the LFB Ultrasonic Material Characterization System(Measurement techniques, Imaging, Nondestructive testing)

F-2 A Super-Precision Evaluation Method of CTE for Ultra-Low Expansion Glasses Using the LFB Ultrasonic Material Characterization System(Measurement techniques, Imaging, Nondestructive testing)

Microanalysis of tool steel and glass with laser-induced breakdown spectroscopy.

A laser microscope system for the microanalytical characterization of complex materials is described. The universal measuring principle of laser-induced breakdown spectroscopy (LIBS) in combination with echelle optics permits a fast simultaneous multielement analysis with a possible spatial resolution below 10 pm. The developed system features completely UV-transparent optics for the laser-microscope coupling and the emission beam path and enables parallel signal detection within the wavelength range of 200-800 nm with a spectral resolution of a few picometers. Investigations of glass defects and tool steels were performed. The characterization of a glass defect in a tumbler by a micro-LIBS line scan, with use of a 266-nm diode-pumped Nd:YAG laser for excitation, is possible by simple comparison of plasma spectra of the defect and the surrounding area. Variations in the main elemental composition as well as impurities by trace elements are detected at the same time. Through measurement of the calibration samples with the known concentration of the corresponding element, a correlation between the intensity of spectral lines and the element concentration was also achieved. The change of elemental composition at the transient stellite solder of tool steels has been determined by an area scan. The two-dimensional pictures show abrupt changes of the element distribution along the solder edge and allow fundamental researches of dynamic modifications (e.g., diffusion) in steel.

Wide-aperture, line-focused ultrasonic material characterization system based on lateral scanning.

We present a new wide-aperture, line-focused ultrasonic material characterization system. The foci of the transmitting and receiving transducers are located in the specimen-immersion liquid interface; and the output voltage V(x,t) of the system is recorded as a function of the lateral position of the receiving transducer. The two-dimensional spectrum of V(x, t) can be expressed as a product of the transfer function of the system and the reflectance function of the interface. In comparison with a system based on scanning in the z direction, the angular resolution of the proposed technique increases with decreasing angle of incidence. There are no geometrical restrictions on the length of the recorded spatial data and the angle of incidence in the case of lateral scanning. The temperature coefficient of the measurement error is low because of the constancy of the propagation distance of ultrasound in the immersion fluid during data acquisition.

Comparison of acoustic properties between natural and synthetic α-quartz crystals

Accurate measurements of bulk and leaky surface acoustic wave (LSAW) velocities of natural α-quartz crystal were carried out using the line-focus-beam and plane-wave ultrasonic material characterization systems and then these measured velocities were compared with the velocities of synthetic α-quartz crystals. Longitudinal velocities of principal X-, Y-, and Z-cut specimens; shear velocities with X-axis polarized particle displacements of the Y- and Z-cut specimens; and LSAW velocities for these three specimens were precisely measured. We found all the velocities for the bulk waves and the LSAWs of natural quartz to be slightly smaller (within 1.00 m/s) than the velocities of synthetic quartz. Therefore, the acoustical physical constants of the natural quartz are very similar to those of synthetic quartz we reported recently.

Calibration of Curie temperatures for LiTaO/sub 3/ single crystals by the LFB ultrasonic material characterization system

The line-focus-beam ultrasonic material characterization (LFB-UMC) system is applied to a standardized comparison and evaluation of the Curie temperatures, T/sub C/, exclusively used in evaluating the chemical compositions of commercial LiTaO/sub 3/ crystals by measuring the velocities of Rayleigh-type leaky surface acoustic waves (LSAWs), V/sub LSAW/. We measured V/sub LSAW/ and T/sub C/ (standardized) under the same T/sub C/ measurement conditions for 36/spl deg/Y X-LiTaO/sub 3/ single-crystal wafers produced by four manufacturers and related the results to the T/sub C/ (individual) measured by the individual manufacturers. The relationships between V/sub LSAW/ and T/sub C/ (individual) varied from one company to another, and a single straight line of the proportional relationship between V/sub LSAW/ and T/sub C/ (standardized) was obtained for all wafers regardless of the manufacturer. These experimental results clarify that the problem associated with T/sub C/ measurements lies in the measurement conditions and the absolute accuracy of the measurement instruments. Measurements of the center frequencies of SH-type surface acoustic wave (SAW) filter devices are compared with V/sub LSAW/ measurements. A method of calibrating T/sub C/ using this ultrasonic system is proposed to establish standardized specifications of SAW-device crystal wafers.

Sensors for High-Throughput Materials Characterization: 24-channel Array of Quartz Crystal Microbalances

ABSTRACTWe have developed a multichannel materials characterization system based on thickness-shear mode (TSM) sensors, also known as quartz crystal microbalances (QCMs). The sensors are arranged as a 6 × 4 array that is compatible with available 24-well plates that can be manipulated with standard robotic equipment. Our sensor system can measure frequencies from 5 MHz to 20 MHz with a noise level of less than 0.1 Hz for a 1 sec acquisition interval. The sensors can be placed in a gas-flow-though cell for studies of vapor-sorption properties, or they can be immersed into a 24-well plate array for studies of materials solubility. The sensor array is connected to the measurement electronics through a multi-conductor cable, enabling the sensors to be operated in a temperature, pressure, or chemical environment, which would otherwise adversely affect the electronic stability. The 24-channel array has been applied to the screening of sensor materials for determination of chlorinated organic solvents at part per billion levels in groundwater wells. The primary screen is the discovery screen where materials are exposed to a single analyte concentration. The secondary screen is the focused evaluation where the best subset of these materials is exposed to analytes and interferences. The tertiary screen involves evaluation of material performance under conditions mimicking the long-term application. Six families of potential sensor materials were examined with rapid downselection by using this approach.

D-9 Longitudinal Acoustic Property Measurements of Solid Specimens by the Plane-Wave Ultrasonic Material Characterization System in the VHF/UHF Range

D-9 Longitudinal Acoustic Property Measurements of Solid Specimens by the Plane-Wave Ultrasonic Material Characterization System in the VHF/UHF Range

D-5 Evaluation of Glass Materials by the Line-Focus-Beam Ultrasonic Material Characterization System

D-5 Evaluation of Glass Materials by the Line-Focus-Beam Ultrasonic Material Characterization System

Quantitative characterization of the fabrication processes of domain-inverted layers in LiTaO3 by the line-focus-beam ultrasonic material characterization system

Application of the line-focus-beam ultrasonic material characterization system was extended to evaluate Z-cut LiTaO3 substrates with domain-inverted layers fabricated by proton exchange and quick heat treatment (QHT), and their fabrication processes and systems. Three Z-cut LiTaO3 substrates were proton-exchanged at 260 °C for 20 min; heat-treated for 30 s at 520, 540, and 560 °C, with a temperature increase rate of 80 °C/s; and annealed at 420 °C for 6 h. Slab-type domain-inverted layers with 0.50, 1.94, and 3.26-μm depths on the −Z surfaces and proton-exchanged layers on both the −Z and +Z surfaces were formed. Leaky surface acoustic wave (LSAW) velocities for both surfaces were measured in a frequency range of 100–300 MHz and found to exhibit different dispersion characteristics. Intrinsic LSAW velocity changes caused by the formation of domain-inverted layers were obtained from differences in the LSAW velocities for both surfaces. The velocity changes decreased with increases in the product fH of the ultrasonic frequency f and the domain-inverted layer thickness H. Relationships among the LSAW velocity changes, thicknesses of the domain-inverted layers, and process temperatures in QHT were experimentally obtained. An LSAW velocity variation of 2.6 m/s for the Y-axis propagation at 225 MHz was detected by a homogeneity evaluation on a specimen QHT-processed at 540 °C and annealed. This corresponded to a layer thickness variation of 0.20 μm and a QHT temperature variation of 2.9 °C.

Evaluation of the annealing effect of proton-exchanged LiTaO3 optical waveguides by the line-focus-beam ultrasonic material characterization system

We established an experimental procedure and collected basic data to evaluate the annealing process and effects for proton-exchanged LiTaO3 optical waveguides using the line-focus-beam ultrasonic material characterization (LFB-UMC) system in a frequency range of 100 to 300 MHz. Twelve Z-cut LiTaO3 substrates were proton-exchanged at 260 °C for 14 min in a pyrophosphoric acid solution and annealed at 420 °C for various periods from 10 sec to 24 h. The leaky surface acoustic wave (LSAW) velocities were decreased by the proton exchange, and were then increased and recovered by annealing in all propagation directions as the annealing time increased. The Y-axis propagation is most useful for an evaluation. The LSAW velocities decrease with an increase of the product fH, obtained from the frequency dependences and proton-diffused layer depths analyzed by secondary-ion mass spectrometry. Gradients of the fH dependences of the LSAW velocities become gentler with increases in the annealing time, corresponding to the concentrations and distributions of hydrogen and lithium ions in the proton-diffused layers. The relationships among the LSAW velocities, proton-diffused layer depths, relative concentrations of hydrogen ions at the specimen surfaces, and the annealing times were experimentally obtained. The measurement resolutions of the LFB-UMC system at 225 MHz to the proton-diffused layer depth, the relative concentration of hydrogen ions, and the typical annealing time for 1 min were estimated to be 4 nm, 0.2%, and 0.6 sec.

Evaluation and improvement of optical-grade LiTaO3 single crystals by the LFB ultrasonic material characterization system.

This paper describes the first demonstration for feeding back the results obtained by the line-focus-beam ultrasonic material characterization (LFB-UMC) system to the crystal growth conditions for optical-grade LiTaO3 crystals and for achieving much improved homogeneity of chemical composition. We evaluated a commercially available optical-grade LiTaO3 single crystal with a nominally congruent composition in detail, by measuring distributions of the velocities of leaky surface acoustic waves (LSAW) along the Y-axis direction for a Z-cut specimen plate prepared from the crystal grown in the Y-axis direction. We detected an increment of 0.66 m/s in LSAW velocity along the pulling axis direction corresponding to 0.024 mol% in Li2O content, and the compositional gradient was +0.346 x 10(-3) (Li2O-mol%)/mm. By experimentally obtaining the starting material composition dependence of the gradients, we developed a method of estimating the proper composition ratio that would lead to a more homogeneous crystal. We grew a new crystal with a Li2O content of 48.47 mol%, resulting in a very small compositional gradient of +0.046 x 10(-3) (Li2O-mol%)/mm and a compositional homogeneity of less than 0.012 Li2O-mol% in a Z-cut area of 50 mm x 50 mm used for device substrates.

High-accuracy standard specimens for the line-focus-beam ultrasonic material characterization system.

We prepared standard specimens for the line-focus-beam ultrasonic material characterization system to obtain absolute values of the propagation characteristics (phase velocity and attenuation) of leaky surface acoustic waves (LSAWs). The characterization system is very useful for evaluating and analyzing specimen surfaces. The calibration accuracy of these acoustic parameters depends on the accuracy of acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) determined for standard specimens. In this paper, we developed substrates of nonpiezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO2] glass) as standard specimens. These specimens can cover the phase velocity range of 2600 to 5100 m/s for Rayleigh-type LSAWs. To determine the elastic constants with high accuracy, we measured velocities by the complex-mode measurement method and corrected diffraction effects. Measurements of bulk acoustic properties (bulk wave velocity and density) were conducted around 23 degrees C, and bulk wave velocities were obtained with an accuracy of within +/-0.004%. We clearly detected differences in acoustic properties by comparing the obtained results with the previously published values; the differences were considered to be due to differences of the specimens used. We also detected differences in acoustic properties among four SiO2 substrates produced by different manufacturers.

Standardized evaluation of chemical compositions of LiTaO/sub 3/ single crystals for SAW devices using the LFB ultrasonic material characterization system

The line-focus-beam ultrasonic material characterization (LFB-UMC) system is applied to compare and evaluate tolerances provided independently for the Curie temperature T(C) and lattice constant a to evaluate commercial LiTaO3 single crystals by measuring the Rayleigh-type leaky surface acoustic wave (LSAW) velocities V(LSAW). The relationships between V(LSAW), and T(C) and a measured by individual manufacturers were obtained experimentally using 42 degrees Y X-LiTaO3 wafers as specimens from three crystal manufacturers. In addition, the relationship between V(LSAW) and SH-type SAW velocities V(SAW) that are actually used for the SAW device wafers was obtained through calculations, using the chemical composition dependences of the acoustical physical constants for LiTaO3 crystals reported previously. The result of a comparison between the T(C) tolerance of +/-3 degrees C and the a tolerance of +/-0.00002 nm through the common scale of V(LSAW) or V(SAW) demonstrated that the a tolerance is 1.6 times larger than the T(C) tolerance. Furthermore, we performed a standardized comparison of statistical data of T(C) and a for LiTaO3 crystals grown by two manufacturers during 1999 and 2000, using V(LSAW). The results clarified the differences of the average chemical compositions and of the chemical composition distributions among the crystal ingots between the two manufacturers. A guideline for the standardized evaluation procedure has been established for the SAW-device wafer specifications by the LFB-UMC system.

Development of the line-focus-beam ultrasonic material characterization system.

A line-focus-beam ultrasonic material characterization (LFB-UMC) system has been developed to evaluate large diameter crystals and wafers currently used in electronic devices. The system enables highly accurate detection of slight changes in the physical and chemical properties in and among specimens. Material characterization proceeds by measuring the propagation characteristics, viz., phase velocity and attenuation, of Rayleigh-type leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. The measurement accuracy depends mainly upon the translation accuracy of the mechanical stages used in the system and the stability of the temperature environment. New precision mechanical translation stages have been developed, and the mechanical system, including the ultrasonic device and the specimen, has been installed in a temperature-controlled chamber to reduce thermal convection and conduction at the specimen. A method for precisely measuring temperature and longitudinal velocity in the water couplant has been developed, and a measurement procedure for precisely measuring the LSAW velocities has been completed, achieving greater relative accuracy to better than +/- 0.002% at any single chosen point and +/- 0.004% for two-dimensional measurements over a scanning area of a 200-mm diameter silicon single-crystal substrate. The system was developed to address various problems arising in science and industry associated with the development of materials and device fabrication processes.