Bulk acoustic wave devices, applications

Zinc oxide (ZnO) is a cheap but important material with many unique properties and potential applications [123-125]. Firstly, it is a gas/pressure-sensing ceramic and can be used as non-linear varistors and sensors [126]. Secondly, piezoelectric ZnO can find applications in surface and bulk acoustic wave devices [127-129]. Thirdly, it is a semiconducting oxide with a wide band gap of 3.37 eV at room temperature and a large exciton energy of 60 meV,... 

Piezoelectric-based or acoustic wave (AW) sensors such as surface acoustic wave (SAW), quartz crystal microbalance (QCM) or bulk acoustic wave (BAW), and cantilever-based devices create a specific class of gas sensors widely used in various applications (Ippolito et al. 2009 Korotcenkov 2011) (see Fig. 13.1). Virtually all acoustic wave-based devices use a piezoelectric material to generate the acoustic wave which propagates along the surface in SAW devices or throughout the bulk of the structure in BAW devices. Piezoelectricity involves the ability of certain crystals to couple mechanical strain to electrical polarization and will only occur in crystals that lack a center of inversion symmetry (Ballantine et al. 1996). 

Piezoelectric transducers have been applied to a wide variety of mass and chemical measurement applications. Bulk wave devices have been used for analytical measurements since the 1960s. Several reviews of their use have been published by Guilbault (33, 34), and a more recent and fairly comprehensive review has been written by Alder and McCallum (35). Applications involving SAW devices first appeared in 1979 (36, 37). Reviews of SAW sensor design have been published by Wohltjen (31) and Venema (25), and the surface chemistry of SAW chemical sensors has been discussed by Nieuwenhuizen (38). Most recently an issue of IEEE Transactions on Ultrasonics has been devoted to a review and discussion of acoustic sensor applications (84). 

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