Evaluation method of TiO/sub 2/-SiO/sub 2/ ultra-low-expansion glasses with periodic striae using the LFB ultrasonic material characterization system

Experimental procedures and standard specimens for characterizing and evaluating TiO/sub 2/-SiO/sub 2/ ultralow expansion glasses with periodic striae using the line-focus-beam (LFB) ultrasonic material characterization system are discussed. Two types of specimens were prepared, with specimen surfaces parallel and perpendicular to the striae plane using two different grades of glass ingots. The inhomogeneities of each of the specimens were evaluated at 225 MHz. It was clarified that parallel specimens are useful for accurately measuring velocity variations of leaky surface acoustic waves (LSAWs) excited on a water-loaded specimen surface associated with the striae. Perpendicular specimens are useful for obtaining periodicities in the striae for LSAW propagation perpendicular to the striae plane on a surface and for precisely measuring averaged velocities for LSAW propagation parallel to the striae plane. The standard velocity of Rayleigh-type LSAWs traveling parallel to the striae plane for the perpendicular specimens was numerically calculated using the measured velocities of longitudinal and shear waves and density. Consequently, a reliable standard specimen with an LSAW velocity of 3308.18 /spl plusmn/ 0.35 m/s at 23/spl deg/C and its temperature coefficient of 0.39 (m/s)//spl deg/C was obtained for a TiO/sub 2/-SiO/sub 2/ glass with a TiO/sub 2/ concentration of 7.09 wt%. A basis for the striae analysis using this ultrasonic method was established.     

Evaluation of mass-produced commercial LiTaO3 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.     

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.     

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 +0.346×10^-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 +0.046×10^-3 (Li ₂O-mol%)/mm and a compositional homogeneity of less than 0.012 Li₂O-mol% in a Z-cut area of 50 mm×50 mm used for device substrates     

Determination of the true congruent composition for LiTaO3 single crystals using the LFB ultrasonic material characterization system.

The true congruent composition for LiTaO3 single crystals was determined by measuring the velocities of leaky surface acoustic waves (LSAWs) with the line-focus-beam ultrasonic material characterization (LFB-UMC) system for two 42 degrees YX-LiTa3s crystal ingots. The congruent composition determined here was 48.460 Li2O-mol%, corresponding to the LSAW velocity (42 degrees YX-LiTaO3) of 3125.3 m/s, and the absolute relationship between the LSAW velocity and chemical composition was obtained. Simulations on the variation of the melt and crystal compositions in a mass production of 100 crystals were conducted as a function of the composition of the starting material around the congruent composition. The result showed that the distributions of the melt and crystal compositions within and among the crystals varied largely with the material composition, providing the relationship of the material composition with the maximum composition variation for the 100 crystals. Based on these results, we verified the relationships between the tolerance of the material composition variation and the tolerances for the SH-type SAW velocity, LSAW velocity, and Curie temperature. The material composition needs to be constrained to within +/- 0.007 Li2O-mol% around the congruent composition to mass-produce the crystals with reliable homogeneity, satisfying the tolerance of +/- 0.01% in the SAW velocity. Furthermore, a guideline for the specification of reliable piezoelectric SAW-device wafer substrates was presented with the accurate interrelationships among the chemical composition ratio, LSAW velocity, and Curie temperature.     

Standardized evaluation of chemical compositions of LiTaO3 single crystals for SAW devices using the LFB ultrasonic material characterization system

The line-focus-beam ultrasonic material characterization (LIFB-UMC) system is applied to compare and evaluate tolerances provided independently for the Curie temperature T/sub C/ and lattice constant /spl alpha/ to evaluate commercial LiTaO/sub 3/ single crystals by measuring the Rayleigh-type leaky surface acoustic wave (LSAW) velocities V/sub LSAW/. The relationships between VLSAW, and T/sub C/ and /spl alpha/ measured by individual manufacturers were obtained experimentally using 42/spl deg/YX-LiTaO/sub 3/ wafers as specimens from three crystal manufacturers. In addition, the relationship between VLSAW and SH-type SAW velocities V/sub 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 LiTaO/sub 3/ crystals reported previously. The result of a comparison between the T/sub C/ tolerance of /spl plusmn/3/spl deg/C and the /spl alpha/ tolerance of /spl plusmn/0.00002 nm through the common scale of VLSAW or VSAW demonstrated that the /spl alpha/ tolerance is 1.6 times larger than the T/sub C/ tolerance. Furthermore, we performed a standardized comparison of statistical data of T/sub C/ and /spl alpha/ for LiTaO/sub 3/ crystals grown by two manufacturers during 1999 and 2000, using VLSAW. 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.     

Determination of the true congruent composition for LiTaO/sub 3/ single crystals using the LFB ultrasonic material characterization system

The true congruent composition for LiTaO/sub 3/ single crystals was determined by measuring the velocities of leaky surface acoustic waves (LSAWs) with the line-focus-beam ultrasonic material characterization (LFB-UMC) system for two 42/spl deg/YX-LiTaO/sub 3/ crystal ingots. The congruent composition determined here was 48.460 Li/sub 2/O-mol%, corresponding to the LSAW velocity (42/spl deg/YX-LiTaO/sub 3/) of 3125.3 m/s, and the absolute relationship between the LSAW velocity and chemical composition was obtained. Simulations on the variation of the melt and crystal compositions in a mass production of 100 crystals were conducted as a function of the composition of the starting material around the congruent composition. The result showed that the distributions of the melt and crystal compositions within and among the crystals varied largely with the material composition, providing the relationship of the material composition with the maximum composition variation for the 100 crystals. Based on these results, we verified the relationships between the tolerance of the material composition variation and the tolerances for the SH-type SAW velocity, LSAW velocity, and Curie temperature. The material composition needs to be constrained to within /spl plusmn/0.007 Li/sub 2/O-mol% around the congruent composition to mass-produce the crystals with reliable homogeneity, satisfying the tolerance of /spl plusmn/0.01% in the SAW velocity. Furthermore, a guideline for the specification of reliable piezoelectric SAW-device wafer substrates was presented with the accurate interrelationships among the chemical composition ratio, LSAW velocity, and Curie temperature.     

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.     

Evaluation and selection of LiNbO(3) and LiTaO(3) substrates for SAW devices by the LFB ultrasonic material characterization system

This paper demonstrates the evaluation and selection of commercially available LiNbO(3) and LiTaO(3) single crystals and wafers for surface acoustic wave (SAW) devices using the line-focus-beam ultrasonic material characterization (LFB-UMC) system. This system enables measuring leaky-SAW (LSAW) propagation characteristics precisely and efficiently for a number of specimens. The wafers are prepared from the top, middle, and bottom parts of four 128 degrees YX LiNbO(3) and seven X-112 degrees Y LiTaO(3) single crystals. For both series of crystals, the measured LSAW velocities increase from top to bottom in the crystals and with the increasing crystal growth number. The velocity changes for all wafers are 0.036% for 128 degrees YX LiNbO(3) and 0.035% for X-112 degrees Y LiTaO(3), corresponding to changes of 0.038 mol% and 0.075 mol% in Li(2)O concentration, respectively. Moreover, the inhomogeneity in the first X-112 degrees Y LiTaO(3) single crystal caused by some undesirable wafer fabrication processes can be detected precisely, although it is difficult for the conventional methods to obtain such information.     

The vibrational spectra of MgO-Al2O3-SiO2 glasses containing TiO2

The infrared spectra from a series of MgO-Al₂O₃-SiO₂ glasses containing TiO₂ are consistent with the existence of a phase-separated structure consisting of a high silica phase and a high modifier phase of metasilicate composition. The invariance of the spectra throughout the range of pre-crystallization heat treatments and compositions precludes the possibility of significant changes in the average number of non-bridged oxygen ions per silica tetrahedron either during nucleation treatments or upon the addition of TiO₂ to the base glass. The Raman spectra from the same series of glasses consist of two main high-frequency bands, at 1000 and 910 cm^–1 which change markedly in relative intensity as TiO₂ is added to the base glass, and several subsidiary bands at lower frequencies. It is suggested that the high-frequency bands arise from two dissimilar metasilicate-type structures which are the pre-cursors of the major crystalline phases which precipitate upon devitrification of the glasses, namely cordierite in the low titania glasses (rings of [SiO₄]^2– tetrahedra), and a pyroxene similar to enstatite in the high titania glasses (chains of [SiO₄]^2– tetrahedra).     

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     

Preparation of porous glass-ceramics of the TiO2-SiO2 system

Porous glass-ceramics of the TiO₂-SiO₂ system of high titania content have been prepared by heat treatment and subsequent acid leaching of phase-separated glasses of the TiO₂-SiO₂-Al₂O₃-B₂O₃-CaO-MgO (or -Na₂O) system. The porous glass-ceramics obtained in the study had a surface area of 100 to 300 m²g^–1, with an average pore radius of 3 to 9 nm. The ceramics which contained a large amount of anatase and rutile were expected to be applied in the field of photocatalysts.     

Crystallisation in the SrO-MgO-ZrO2-SiO2 (SMZS) system glasses

The SrO-MgO-ZrO₂-SiO₂ quaternary system was first investigated in 1989. It was reported that the lowest liquidus temperature is as 1000°C and located near the SrO-SiO₂ edge of the composition tetrahedron. Since the system has a wide range of glass formation, it has been extensively examined with the present study. After melting, depending on viscosity, glass melts tend to crystallise on cooling if the cooling rate is too slow to prevent such phenomenon. It is this behaviour that initiated investigation into the crystallisation ability of this glass system. As SMZS glasses include zirconia, surface crystallisation is generally inhibited. Hereby, crystallisation mechanisms, identification of crystal phases and microstructure of glass ceramics produced are given.     

Structural and microstructural study of glasses in the Li2O-TiO2-SiO2 system

Glasses from the Li₂O-TiO₂-SiO₂ system with TiO₂ content ranging between 5 and 20 mol % were prepared. The glasses studied have an opal appearance and when their microstructure is studied through transmission electron microscopy, a strong phase separation in droplet form is observed, with the size of the droplets depending on the TiO₂ and the Li₂O content. X-ray diffraction showed that these glasses are non-crystalline and identified the crystalline phases which take place after the corresponding thermal treatment to enhance liquid immiscibility. A structural study of the samples prepared was carried out through infrared spectroscopy. Titanium oxide is incorporated into glasses as a network modifier, so that titanium atoms place themselves in octahedral positions [TiO₆]. This is attributed to the presence of Li₂O which breaks up the glass network, favouring the hexacoordination of titanium atoms.     

介孔/大孔TiO2-SiO2复合氧化物材料的制备与表征

采用正硅酸甲酯和钛酸丁酯作为硅和钛的前驱体,在溶胶一凝胶过程中添加非离子表面活性剂C16EO10.作为结构导向剂合成双孔结构硅钛复合氧化物材料.扫描电镜(SEM)以及N2吸附/脱附法分析表明,材料具有三维连续大孔和骨架介孔的双孔分布结构.通过骨架元素分析(EDS)和X射线衍射分析可知,制备过程中添加的钛可以全部进入凝胶骨架中,且钛在骨架中的分散性较好.采用Hammett指示剂法和吡啶吸附红外光谱法分析了材料表面固体酸性,结果显示,硅钛复合氧化物属于中强酸,酸强度Ho在-5.6～-3.0之间的酸中心数大约为0.30 mmol/g左右.硅钛材料表面含有较丰富的L酸位和相对较少的B酸位.     

新型PU-DR19-SiO2纳米复合材料的制备和表征

利用溶胶-凝胶法将硅烷染料、含硅氧烷的非线性聚氨酯与TEOS共水解-缩合首先制备了新型PU-DR19-SiO2纳米复合材料,并用IR、SEM、TEM、UV-vis和DSC-TGA对其结构和性能进行了表征.结果显示:材料中有机相与无机相以共价键相连,没有发生相分离,且其中非线性较好的DR19生色团含量和材料的Tg都较纯NLO/PU有显著增加,可以用来制备性能优良的二阶非线性光学器件.     

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 non piezoelectric 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°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