Fabrication of modified lead titanate piezoceramics with zero temperature coefficient and its application on SAW devices

The Samarium-modified, lead titanate ceramics with a composition of (Pb0.67Ca0.15Sr0.06Sm0.08) (Ti0.98Mn0.02)O3 were prepared by conventional mixed-oxide method. By properly varying the sintering and poling conditions, the samples with zero temperature coefficient of resonant frequency were fabricated. The piezoelectric and dielectric properties were measured; it showed that the samples with zero temperature coefficient still keep high-thickness, electromechanical coupling coefficient, kt (>0.55), and small planar electromechanical coupling coefficient, kp. Surface acoustic wave (SAW) filters were fabricated; and the properties, including phase velocity and electromechanical coupling coefficient, were measured. Microstructural and compositional analyses have been carried out using scanning electron microscopy and x-ray diffraction.     

Surface acoustic wave characterization of PECVD films on galliumarsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given     

Optimization of SAW-type Surface Wave Ultrasonic Sensors for Ultrasonic SHM

Surface acoustic waves (SAW) are particularly suited for effectively monitoring and characterizing a structure’s surfaces (condition of the surface, coating, thin layer, micro-cracks, etc.), and in some cases it is necessary to permanently keep the sensors on the structures to enable continuous monitoring. This article focuses on the optimization of SAW-type interdigital sensors (or IDT sensors for InterDigital Transducer) because they can largely address this issue. Initially, the ability of piezoelectric materials (lead zirconate titanate [PZT] and Niobate de lithium) to generate SAW is studied by modeling. Then a design of an IDT sensor is defined and optimized for the generation of SAW on a substrate. Parameters such as electrode’s periodicity, thickness of piezoelectric plate, and type of contact between the plate and the substrate, are studied. Finally, experimental results are compared with those obtained by modeling.     

Surface acoustic wave characteristics and electromechanical coupling coefficient of lead zirconate titanate thin films

Lead zirconate titanate (PZT) thin films were created on ST-X quartz using radio frequency magnetron sputtering deposition. PZT films deposited on quartz are used as a new piezoelectric substrate for surface acoustic wave (SAW) devices. Microelectromechanical technique was used to fabricate interdigital transducers on the surface of the substrate to be used as a SAW delay line device. The results show that the PZT film was successfully deposited on ST-X quartz, and that the PZT film on ST-X quartz can enhance the electromechanical coupling coefficients of SAW.     

ZnO films on {001}-cut <110>-propagating GaAs substrates forsurface acoustic wave device applications

A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut 〈110〉-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 μm and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K² and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO₂ or Si₃N₄ on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the 〈110〉 propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the 〈100〉 direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values     

SAW COM-parameter extraction in AlN/diamond layered structures

Highly c-axis oriented aluminum nitride (AlN) thin piezoelectric films have been grown on polycrystalline diamond substrates by pulsed direct current (DC) magnetron reactive sputter-deposition. The films were deposited at a substrate temperature below 50/spl deg/C (room temperature) and had a typical full width half maximum (FWHM) value of the rocking curve of the AlN-002-peak of 2.1 degrees. A variety of one-port surface acoustic wave (SAW) resonators have been designed and fabricated on top of the AlN films. The measurements indicate that various SAW modes are excited. The SAW phase velocities of up to 11.800 m/s have been measured. These results are in agreement with calculated dispersion curves of the AlN/diamond structure. Finally, the coupling of modes parameters have been extracted from S/sub 11/ measurements using curve fitting for the first SAW mode, which indicate an effective coupling K/sup 2/ of 0.91% and a Q factor of about 600 at a frequency of 1050 MHz.     

钛酸铅和锆钛酸铅铁电薄膜的热释电效应的研究

本文测量了钛酸铅和锆钛酸铅铁电薄膜的热释电效应，在这些以钛薄片为衬底，用Ｓｏｌ－Ｇｅｌ方法制备的铁电薄膜上可测到明显的热释电响应，同时，对这些薄膜的牡民Ｉ－Ｖ特性也进行了测试，对敏感元工之间的热传导以及材料中发现的光效应对热释电响应的影响进行了分析和讨论。     

Influence of metal thickness on phase velocity and thermal sensitivity of SAW devices

Most surface acoustic wave (SAW) devices exhibit a very small sensitivity to thermal effects. However, even on intrinsically compensated crystal cuts, the deposition of metal strips at the surface (transducers or reflectors) induces important changes in the thermoelastic properties of the device. A theoretical approach based on the Sinha-Tiersten perturbation method is proposed to model the influence of metallization on SAW properties on (ST, X) quartz, namely the temperature stability of the phase velocity of Rayleigh waves. Because this perturbation method only gives access to the first-order temperature coefficient of frequency (TCF), it is combined with a conventional calculation of the second-order TCF to predict the evolution of the turnover temperature. The proposed calculation also requires temperature derivatives of the elastic constants of the metal, which can be calculated for different materials. Finally, theoretical results are compared with experimental data measured on SAW devices on (ST, X) quartz, using aluminum gratings     

Surface acoustic waves in thin films of barium strontium titanate on magnesium oxide substrates

It is established that, using a thin barium strontium titanate (BST) film as the active element in a surface acoustic wave (SAW) device, it possible to double the working frequency of the converter due to the formation of a periodic domain structure in the BST film. A thin ferroelectric film device with a standard electrode structure is capable of effectively exciting the SAW second harmonic. Variation of the external polarizing voltage applied to the electrodes ensures field-controlled electromechanical feedback in the converter.     

Deposition and characterization of thin ferroelectric lead lanthanum zirconate titanate (PLZT) films on sapphire for spatial light modulators applications

Ferroelectric lead lanthanum zirconate titanate (PLZT) films are deposited on R-plane sapphire using RF triode magnetron sputtering. Perovskite PLZT films with the desired composition (9/65/35) are obtained using compensated deposition techniques around 500 degrees C and postdeposition annealing at 650 degrees C. The deposited films exhibit good optical and electrooptical properties. The room temperature dielectric constant of the films was 1800 at 10 kHz. The refractive index of the films was in the range of 2.2-2.5. The films showed a quadratic electrooptic effect with R=0.6 x10(-16) m(2)/V(2). The development of PLZT on silicon-on-sapphire smart spatial light modulators using these films is also explored.     

The effects of ZnO films on surface acoustic wave properties of modified lead titanate ceramic substrates

Poly-crystal zinc oxide (ZnO) films with c-axis (002) orientation have been successfully grown on the strontium (Sr) modified lead titanate ceramic substrates with different Sr dopants by r.f. magnetron sputtering technique. Highly oriented ZnO films with c-axis normal to the substrates can be obtained under a total pressure of 10 mTorr containing 50% argon and 50% oxygen and r.f. power of 70 W for 3 hours. Crystalline structures of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The phase velocity, electromechanical coupling coefficient and temperature coefficient of frequency of surface acoustic wave (SAW) devices with ZnO/IDT/PT (IDT, inter-digital transducer; PT, PbTiO3 ceramics) structure were investigated. The devices with ZnO/IDT/PT structure shows that the ZnO film effectively raise the electromechanical coupling coefficient (kappa2) from 3.8% to 9.9% of the device with the concentrations of Sr dopants of 0.15. It also improves the temperature coefficient of frequency of SAW devices.     

Comparisons of polymer/gas partition coefficients calculated from responses of thickness shear mode and surface acoustic wave vapor sensors

Apparent partition coefficients, K, for the sorption of toluene by four different polymer thin films on thickness shear mode (TSM) and surface acoustic wave (SAW) devices are compared. The polymers examined were poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), poly(butadiene) (PBD), and poly(dimethylsiloxane) (PDMS). Independent data on partition coefficients for toluene in these polymers were compiled for comparison, and TSM sensor measurements were made using both oscillator and impedance analysis methods. K values from SAW sensor measurements were about twice those calculated from TSM sensor measurements when the polymers were PIB and PECH, and they were also at least twice the values of the independent partition coefficient data, which is interpreted as indicating that the SAW sensor responds to polymer modulus changes as well as to mass changes. K values from SAW and TSM measurements were in agreement with each other and with independent data when the polymer was PBD. Similarly, K values from the PDMS-coated SAW sensor were not much larger than values from independent measurements. These results indicate that modulus effects were not contributing to the SAW sensor responses in the cases of PBD and PDMS. However, K values from the PDMS-coated TSM device were larger than the values from the SAW device or independent measurements, and the impedance analyzer results indicated that this sensor using our sample of PDMS at the applied thickness did not behave as a simple mass sensor. Differences in behavior among the test polymers on SAW devices are interpreted in terms of their differing viscoelastic properties.     

A new triply rotated quartz cut for the fabrication of low loss IF SAW filters

Analysis of the quartz properties shows the existence of unexplored angular domains for which Rayleigh waves can be efficiently excited, exhibiting physical characteristics better than the ones of the (ST,X) cut. This paper presents a family of quartz cuts allowing significant improvements of surface acoustic wave (SAW) devices on quartz. A first set of experiments has been performed, confirming the theoretical predictions of the basic properties of SAW on these cuts. A second set of measurements then was achieved to refine the identification of coefficients needed to perform industrial SAW design. A demonstration of the improvements accessible using this new cut is presented. A low loss SAW filter working at 71 MHz has been fabricated using smaller aluminum thickness than that for standard quartz cuts, and exhibiting all the properties required for its industrial implementation.     

Effect of lead oxide on the dielectric characteristics of heterogeneous Pb(Zr, Ti)O3 + PbO films obtained by a two-stage method

We have studied changes in the dielectric properties of thin lead zirconate titanate Pb(Zr,Ti)O₃ (PZT) films, obtained using a two-stage ex-situ technology, as dependent on the microstructure of a perovskite phase and the content of microinclusions of excess lead oxide. The presence of these microinclusions leads to either anomalously low or high values of dielectric permittivity and anomalous pyroelectric response.     

State-dependent pyroelectric and thermal expansion coefficients in a PZT rectangular parallelepiped after compressive loading and unloading

A poled lead titanate zirconate rectangular parallelepiped was subject to compressive stress loading and unloading. After reaching a specific polarization, stress is removed and temperature is increased. Longitudinal polarization and longitudinal and transverse strains are measured during the temperature rise. A false contribution of leakage current to measured polarization is removed. From measured polarization and strains, pyroelectric and thermal expansion coefficients are evaluated. Dependence of the two thermal properties on remnant state variables is investigated. The evolution of remnant strains with relative remnant polarization is also discussed and compared with a previous work.     

PZT铁电薄膜Sol-Gel技术制备和电性能研究

以乙酸铅(Pb(CH₃COO)₂·3H₂O)、钛酸四丁酯(Ti(OC₄H₉)₄)、硝酸锆(Zr(NO₃)₄·5H₂O)替代锆醇盐为原料,通过在Pt/Ti/SiO₂/si基片与PZT薄膜之间引入PT种子层,采用改进的sol-gel工艺制备出无裂纹,致密性好,晶粒尺寸小且分布均匀的单一钙钛矿结构的Pb(Zr_0.53Ti_0.47)O₃铁电薄膜.实验结果表明,具有PT种子层的PZT铁电薄膜电性能较好.经600℃热处理的具有PT种子层的PZT薄膜,在1kHz测试频率下,其剩余极化强度和矫顽场分别为20μC/cm²和59kV/cm,介电常数和介电损耗分别为385和0.030.     

Elastic effects of polymer coatings on surface acoustic waves

Surface acoustic wave (SAW) devices are presently receiving careful scrutiny for applications in chemical sensing as well as in polymer characterization. Gas monitors based on SAW sensors have the potential for miniaturization and high sensitivity to a wide variety of substances. Polymer characterization is applicable to such diverse fields as protective coating design and decontamination of polymers. To better understand the physical mechanisms behind SAW response, the effects of the elastic properties in comparison to the mass loading of polymer coatings on SAW substrates were investigated. A theoretical basis for the effects of vapor-induced swelling or of thermal expansion was established. Compressive tension and its effect on SAW frequencies were found to be simple to describe, if there is no film slippage or polymer flow. The response of quartz substrate SAW crystals coated with polycarbonate and polyimide (glassy polymers) upon exposure to toluene and methanol was measured. Practical problems as to film uniformity, thickness measurement, and environmental control necessary in such measurements are described. Contrary to recent reports in the literature, no significant elastic tightening effect was observed with these vapor/polymer pairs.     

基于声表面波传感技术的微液滴检测方法

为了提高声表面波(SAW)技术用于微液滴体积测量的精度,提出了一种差分面积拟合法.根据声表面波信号的特点分析了差分面积拟合法的合理性,在自行研制的声表面波液滴体积检测系统上对该方法的应用进行了验证.采用两种黏性不同的微液滴,分别为5～9μL的微水滴和微油滴进行了测量.对测得的信号分别采用曲线峰值法和差分面积拟合法与微液滴大小进行回归.实验结果表明,采用差分面积拟合法进行回归得到的模型的相关系数相比采用峰值法提高了4%以上,同时对两种微液滴的预测均方根误差(RMSEP)减小了37%以上,从而证明了该方法的有效性.     

Theory and application of passive SAW radio transponders as sensors

Surface acoustic wave (SAW) radio transponders make it possible to read identification codes or measurement values from a remote location. The decisive advantage of these SAW transponders lies in their passive operation (i.e., no power-supply), and in the possibility of wireless installation at particularly inaccessible locations. The passive SAW transponders are maintenance free. Identification marks respond to an interrogation signal with their nonchanging identification pattern. In wireless SAW sensors the physical or chemical properties to be detected change the propagation characteristics of the SAW. SAW radio transponders are advantageously placed on moving or rotating parts and in hazardous environments such as contaminated or high voltage areas. They also can be used for contactless measurements in high vacuum process chambers, under concrete, extreme heat, or strong radioactive radiation, where the use of conventional sensors is complicated, dangerous, or expensive. In this paper we discuss the principles of wireless passive SAW transponders and present a radio frequency interrogation unit and several passive radio SAW sensors developed for noncontact measurements of temperatures, pressures, torques, and currents.     

Characterization and electrical properties of chemical vapor deposited ferroelectric lead titanate films on titanium

Lead titanate thin films were deposited on titanium substrates by a chemical vapor deposition (CVD) process involving the application of vapor mixtures of Pb, ethyl titanate (Ti(C(2)H(5)O) (4)), and oxygen. Auger electron spectroscopy (AES) analyses were performed to determine the chemical composition of lead titanate films. AES analysis revealed that TiO(2) and TiO interlayers formed between the PbTiO(3) and titanium substrate. AES also showed that stoichiometry was obtained in the lead titanate film deposited at 750 degrees C, Ti(C(2)H(2)O)(4) with 0.152, an O(2) partial pressure of 0.06 atm, and a gas flow rate of 800 sccm. The lead titanate with a stoichiometric composition has a DC conductivity of 3.2x10(-12) Omega(-1)-cm(-1) at room temperature. The nonsaturating loops observed in the present investigation may be caused by TiO(2) and TiO layers between the conductive substrate and the PbTiO(3) ferroelectric film. The ferroelectric properties of the stoichiometric PbTiO(3) film included a remanent polarization of 14.1 muC/cm(3) and a coercive field of 20.16 kV/cm.