Propagation Characteristics Of Surface Acoustic Waves Research Articles

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.

Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128° rotated Y-cut X-propagating lithium niobate (128° Y-XLiNbO3) single crystal has been studied. It is found that 0.042λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76ppm°C−1 to almost zero (∼1.4ppm°C−1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer.

Surface acoustic wave propagation characteristics of aluminum nitride thin films grown on polycrystalline diamond

Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus provides substantial advantages for the fabrication of high-frequency SAW devices when combined with a piezoelectric thin film. The properties of layered film structures consisting of a piezoelectric material layer, aluminum nitride (AlN), and a polycrystalline diamond layer grown on a silicon substrate have been examined. Highly textured AlN thin films have been sputter-deposited onto polycrystalline diamond substrates at room temperature. X-ray diffraction analysis of the multilayer structure as well as atomic force microscope images of the AlN surface indicate that the deposited AlN films were c-axis oriented with a full width at half maximum of the rocking curve of the AlN-002-peak of 2.1°. The thickness of the AlN layer was of 4.3 μm, whereas the diamond layer was 50 μm thick and resting on a 3-in Si wafer. Standard one-port SAW resonators with aluminum (Al) metallization have been subsequently fabricated and evaluated. Experimental results indicate that the fundamental as well as higher Rayleigh SAW modes are excited. Thus, the phase velocities of the first, second, third, and fourth mode are found to be 6.850, 10.000, 11.800, and 14.450 m/s respectively. A very good out-of-band rejection of −50 dB was obtained.

Research of Super-High Electromechanical Coupling Surface Acoustic Wave Substrates

The properties of surface acoustic wave (SAW) devices mainly depend on the choice of piezoelectric substrate materials. The important properties required for SAW substrates are a large electromechanical coupling coefficient (k2), small temperature coefficient of delay (TCD), and low propagation loss, etc. Especially, super-high coupling substrates are very important for obtaining wide-band SAW filters, wide-band voltage controll oscilater (VCO) and delay lines with small insertion loss. KNbO3 single crystal has an extremely large electromechanical coupling coefficient (k2=53%) and zero TCD at approximately room temperature. Large-scale single-crystal growth technologies are now under investigation. In this study, the propagation characteristics of SAW in PZNT and KTP substrates are investigated experimentally in order to obtain higher coupling substrates than those of KNbO3. The experimental results show that the substrates have large k2. Also, theoretical SAW propagation characteristics with a k2 of about 100% are analyzed and their physical phenomena are discussed.

Single crystal growth of KNbO3 and application to surface acoustic wave devices

Potassium niobate (KNbO 3 ) has large piezoelectric constants. The surface acoustic wave (SAW) substrates with high couplings are very important for wide-band SAW filters and SAW devices. Therefore, the large size KNbO 3 single crystals are required for SAW device applications. In this paper, the techniques of a large size of KNbO 3 using the top seeded solution growth techniques (TSSG) with large size of crucible of 60 mm φ platinum are described. The results show that 50×50×15 mm 3 single crystals are obtained. Also, the poling techniques of KNbO 3 crystal are investigated by using the nonlinear scanning dielectric microscope. The propagation characteristics of SAW and piezoelectric leaky surface waves in KNbO 3 single crystal were investigated theoretically. The results show that the electro-mechanical coupling coefficient of the surface wave propagating along the X -axis of the rotated Y -cut plane is extremely large: K 2 =0.53, compared to K 2 of 0.055 for LiNbO 3 . The experimental results of the above KNbO 3 substrates agree with the theoretical ones. Also the KNbO 3 substrates showed experimentally the zero temperature coefficients of frequency (TCF) around 20 °C.

Theoretical Analysis of Surface Acoustic Wave Propagation Characteristics under Strained Media and Applications for High Temperature Stable High Coupling Surface Acoustic Wave Substrates

Among the important properties required for surface acoustic waves (SAW) substrates are a large electromechanical coupling coefficient (k2), small temperature coefficient of frequency (TCF) and low propagation loss. The LiNbO3 and LiTaO3 have good properties as the SAW substrates with a large size. Unfortunately, these possess the defect of having large values of TCF. In this paper, SAW-bonded composite substrates with a large k2, small TCF, low propagation loss and no dispersion using conventional bonders are investigated theoretically and experimentally. The propagation characteristics of SAWs under strained piezoelectric crystals using the higher-order elasticity theory have been analyzed. The theoretical results show zero TCF on LiNbO3/SiO2 substrates. The experimental results for LiNbO3/glass substrates revealed a TCF of [-19 ppm/°C]. The propagation properties were almost the same as those of the single crystal.

Surface Acoustic Wave Propagation Characteristics under the Coded Electrodes of Surface Acoustic Wave Matched Filters

Surface acoustic wave (SAW) matched filters are advantageous for use as correlators with high data transmission rates and short spreading sequences. We have examined the second-order effect problem in the case of reducing the insertion loss of SAW matched filters, and proposed a new direct time response calculation analysis of the SAW matched filter. Using this method, we can directly calculate the signal time response, the directivity of the coded electrodes and the propagation and reflection properties of SS-modulated SAW signals. It is also possible to calculate the dynamic responses of the programmable SAW matched filters in the case of switching before the time duration of their impulse responses. We analyzed the decreasing slope of the impulse response, which is a problem of low-loss SAW matched filters, and found that the slope is caused by an electrical delay at the common bus bar, which can be corrected by connecting the coded electrodes to each other by capacitors.

Characteristics of interdigital transducers for mechanical sensing and non-destructive testing

An interdigital transducer (IDT) is one of the most essential components in surface acoustic wave (SAW) technology. The performance of the IDT is related to the propagation characteristics of SAWs on piezoelectric or non-piezoelectric substrates. In typical measurements of strain and acceleration, the construction of feedback loop delay-line oscillators is discussed for the use of SAWs on both a piezoelectric ceramic substrate and a layer structure consisting of a thin piezoelectric plate and fused quartz. The IDT can also operate as a transducer for radiating a longitudinal wave into water. The transducer performance for a solid—liquid boundary is discussed in terms of the real and imaginary velocities of leaky SAWs, the electromechanical coupling constant and the transducer efficiency for acoustic beam radiation into water. Practical C-mode acoustic imaging results are given for two types of transducer configurations.

A technique for measuring strain in layered structure media

Abstract A method for measuring strain in a non-piezoelectric substrate is described. The measurement utilizes the surface acoustic wave (SAW) propagating in layered media consisting of a non-piezoelectric substrate in acoustic contact with a thin piezoelectric plate. The SAW propagation characteristics in a PbZrO 3 -based piezoelectric medium on a fused quartz substrate are analyzed numerically. The phase velocities and electromechanical coupling constants of the Rayleigh and Sezawa modes are found as a function of the ceramic layer thickness. The measured phase velocity of the fundamental Sezawa mode propagating in a layered device is in good agreement with the numerical result. A delay line oscillator for the strain measurement is composed of an amplifier and the Sezawa mode delay device to which the bending stress is applied. An observed relationship between the oscillation frequency and bending strain applied to the device supports the validity of the present method for strain measurement.

Current Status of Piezoelectric Substrate and Propagation Characteristics for SAW Devices

This paper describes the current status of surface acoustic wave (SAW) materials and devices which are being manufactured or are under study in Japanese industries. This information are obtained from 31 companies to which the author sent a questionnaire. SAW propagation characteristics such as Rayleigh wave and leaky wave are also briefly summarized.

PC software for SAW propagation in anisotropic multilayers

A software package that provides an interactive and graphical environment for surface acoustic wave (SAW) and plate-mode propagation studies in arbitrarily oriented anisotropic and piezoelectric multilayers is described. The software, which runs on an IBM PC with math coprocessor, is based on a transfer-matrix formulation for calculating the characteristics of SAW propagation in multilayers that was originally written for a mainframe computer. The menu-driven software will calculate wave velocities and field variable variations with depth for any desired propagation direction: the graphics capability provides a simultaneous display of slowness or velocity and of SAW Deltav/v coupling constant curves, and their corresponding field profiles in either polar or Cartesian coordinates, for propagation in a selected plane or as a function of one of the Euler angles. The program generates a numerical data file containing the calculated velocities and field profile data. Examples illustrating the usefulness of the software in the study of various SAW and plate structures are presented.

Propagation Characteristics of SAW on a ZnO/SiO2/high-velocity-substrate Structure

The paper describes surface acoustic wave (SAW) propagation on a ZnO/SiO2/high-velocity-alumina-substrate multi-layered structure. It was shown that, quite independent of the elastic properties of the alumina substrate, the electromechanical coupling factor k2 and temperature coefficient of frequency (TCF) reflect those for Lamb waves in a ZnO/SiO2 composite membrane. This suggests a simple guiding principle to find multi-layered structures with moderate temperature stability and k2 for SAW, that is, TCF could be compensated without greatly reducing k2 by the proper choice of substrate materials.