SAW device

Parameter Quartz BaTiO, PbTiO, Sm PZT 4 PZT5H LF4T PVDF 

The comparison of piezoelectric properties of several of the major piezoelectric ceramics discussed above is given in Table 13.3. hi this table, PZT 4 is hard PZT (PZT doped with acceptor ions, such as K or Na at the A site, or Fe % Al % or Mn at the B site), PZT 5H is soft PZT (PZT doped with donor ions, such as La at the A site, or Nb or Sb at the B site), LF4T is (K Na Li, ) (Nbj j Ta, jSbj f )Oy and PVDF is piezoelectric polymer synthesized using copolymerization of vini-lydene difluoride with trifluoroethylene (TrFE). 

The fundamental parameters controlling operating characteristics of SAW-based sensors are the SAW velocity, the temperature coefficients of delay (TCD), the electromechanical coupling factor, and the propagation loss. In SAW applications, the coupling factor relates to the maximum bandwidth obtainable and the amount of signal loss between input and output that determines the fractional 

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A chemical microsensor can be defined as an extremely small device that detects components in gases or Hquids (52—55). Ideally, such a sensor generates a response which either varies with the nature or concentration of the material or is reversible for repeated cycles of exposure. Of the many types of microsensors that have been described (56), three are the most prominent the chemiresistor, the bulk-wave piezoelectric quartz crystal sensor, and the surface acoustic wave (saw) device (57). 

A SAW device is configured as a delay line and fed by a radio frequency signal. Any change in the velocity Av is detected as a change AT in the phase delay of the wave, thanks to a phase detector that gives a voltage proportional to the difference of phase between signal input and output. 

Kushibiki, J., Asano, H., Ueda, T., and Chubachi, N. (1986). Application of line-focus-beam acoustic microscope to inhomogeneity detection on SAW device materials. IEEE 1986 Ultrasonics Symposium, pp. 749-53. IEEE, New York. [244]... 

Barrier layers for Cu metallization in surface acoustic wave (SAW) devices, which are increasingly used in the information technique and telecommunications industry, have been investigated by SIMS depth profiling in comparison to AES (Auger Electron Spectrometry).125 Development trends in SAW devices focus on smaller structures, higher input power or higher frequency. Two Cu metallization systems (of 150 nm thickness) on a LiNb03 substrate with different barrier layers ... 

Fig. 21. A surface acoustic wave dual-delay line oscillator. The sensitise layer is placed in the propagation path of one of the two SAW devices. The differenee in Ireqnency (At) between the two channels provides a dtrecl result of the mass loading and electric field effects associated w ith the sensor layer...

The packaging (i.e., electrical insulation for operation in electrolytes) is more difficult with SAWs due to their rectangular geometry. SAWs are easier to fabricate with lithographic microfabrication techniques and therefore are more suitable for use in an array (Ricco et al., 1998). The choice of electrode materials is critical for QCM, where acoustic impedance mismatch can result in substantial lowering of the Q factor of the device. On the other hand, it does not play any role in the SAW devices. The energy losses to the condensed medium are higher in SAWs and this fact makes them even less suitable for operation in liquids. Nevertheless, SAW biosensors have been reported (Marx, 2003). 

There are certain aspects of performance that make the Apm oscillators potentially attractive as chemical sensors. First of all, the fact that both surfaces contribute to the signal means that the sensitivity is higher than for the corresponding SAW device. The most important advantage follows from the fact that velocity of the lowest order of the antisymmetric mode is much slower than the compressional velocity of sound in most liquids (900-1,500 m s-1), which means that the energy... 

The interaction of the acrylamldoxime polymer coatings with the MSF and DMMP simulant vapors was investigated by infrared spectroscopy and by the SAW device response. 

Fig. 4 SAW Device (7% Acrylamidoxime Terpolymer coating) Response to 1000 ppm MSF and DMMP.

Fig. 5 MSF and DMMP Vapor Concentration Dependence of SAW Device Coated with 3,7 and 45% Acrylamidoxime Terpolymers and Correlation with Terpolymer Glass Transition Temperature and Solubility Parameter.

Mercury binding leads to an increase of mass of the gold layer which can be detected by electro-acoustic transducers based on quartz microbalance (QMB the abbreviation QCM = quartz crystal microbalance is also widely used), surface acoustic waves (SAW)—devices [20] or microcantilevers [21,22], Adsorption of mercury vapour increases resonance frequency of shear vibrations of piezoelectric quartz crystals (Fig. 12.2). This process can be described by Sauerbrey equation [23]. For typical AT-cut quartz, this equation is... 

Fig. 5. A The designed pattern used in microCE and B, C optical micrographs of two selected areas of the pattern that was transferred into a glass slide. D The designed pattern used in SAW device and E an SEM image of a portion of the pattern generated in silver on Si/Si02...

Acknowledgements. The work in our laboratory was supported in part by ONR, DARPA and NSF (Grant PHY 9312572), and made use of MRSEC shared facilities supported by the NSF under Grant DMR-9400396. The authors thank Dr. J. Michael Ramsey for design of the CE in Fig. 5 A and Professor Michael Grunze for the design of the SAW device in Fig. 5 D. JAR gratefully... 

Integrated systems of pressure and temperature are also on the market [5]. For analytical purposes only SAW devices are used for antibody and gas detection which are in an early stage of research [6]. 

The simple piezoelectric mass detection systems and the more sensitive surface acoustic wave (SAW) devices operate well in a dry or constant humidity gaseous environment (26,27), but they suffer from loss of signal in aqueous media. In the former case, this is largely a non specific response to water at the surface, and in the latter case it is associated with serious loss of the surface Rayleigh wave to the bulk solution. 

There are several applications of ZnO that are due to its excellent piezoelectric properties [28,164]. Examples are surface-acoustic wave (SAW) devices and piezoelectric sensors [28,165-167]. Typically, SAW devices are used as band pass filters in the tele-communications industry, primarily in mobile phones and base stations. Emerging field for SAW devices are sensors in automotive applications (torque and pressure sensors), medical applications (chemical sensors), and other industrial applications (vapor, humidity, temperature, and mass sensors). Advantages of acoustic wave sensors are low costs, ruggedness, and a high sensitivity. Some sensors can even be interrogated wirelessly, i.e., such sensors do not require a power source. 

Fig. 1.21. Frequency spectrum of a 10 j.m wavelength SAW device on a 1.5 pm thick ZnO film on an r-sapphire substrate. The ZnO film was deposited by MOCVD using diethyl-zinc and oxygen. The inset shows the geometry of the device with the interdigitated contact fingers. Reprinted with permission from [168]...

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