Film bulk acoustic resonator

On the transducer side, there have been more recent developments like the Lamb oscillator or the so-called film bulk acoustic resonators (FEAR). Lamb wave devices are related to SAW in terms of using interdigitated structures for transduction. The difference, however, is that in a Lamb wave resonator not only the surface, but the entire bulk of the device oscillates. This makes it much less sensitive against viscous damping. FEAR on the other hand consist of a metal/aluminium nitride/metal sandwich, where bulk waves (thickness oscillations) are induced in the AIN material. Eoth these devices have in com-... 

Fig. 13.1 Ditferent types of acoustic devices that can be used for sensing application FBAR film bulk acoustic resonators, TSM thickness shear mode, SMR solidly mounted resonators. Other designations are in the text...

Nirschl, M., Blither, A., Erler, C., Katzschner, B., Vikholm-Lundin, L, Auer, S., Voros, J., Pompe, W., Schreiter, M., Mertig, M., 2009. Film bulk acoustic resonators for DNA and protein detection and investigation of in vitro bacterial S-layer formation. Sens. Actuators A Phys. 156, 180—184. 

Zhang, M., et al., 2015a. Monolithic integrated system with an electrowetting-on-dielectric actuator and a film-bulk-acoustic-resonator sensor. J. Micromech. Microeng. 25 (2), 025002. Available at http //stacks.iop.org/0960-1317/25/i=2/ a=025002 key=crossref.98f635e91ff5ad9da80f30b3f46019cb. 

Qiu, X., et al., 2011. The effects of temperature, relative humidity and reducing gases on the ultraviolet response of ZnO based film bulk acoustic-wave resonator. Sens. Actuators B 151 (2), 360-364. Available at http //linkinghub.elsevier.eom/retrieve/pii/S0925400510006544. 

The key feature of all acoustic wave sensors for detecting vapors is that measurable characteristics of the acoustic wave is altered as a result of adsorption on the surface of a receptive layer or absorption into the bulk of a thin layer (Figure 3). After sorption of the vapor by a thin film on top of the acoustic resonator equilibrium conditions are established and as a consequence of the increased mass or more accurately the change in the phase velocity of the acoustic wave a signal is created. Surface coatings generally enhance the sorption of vapors with the key properties of selectivity and sensitivity while affording reversibility. Typically, rubbery polymers were used on SAW devices such as polyisobutylene or substituted polysiloxanes but also self-assembled... 

For measuring the mechanical characteristics of the aforementioned films such as coefficients of elasticity and viscosity, one can use the piezoelectric resonators of bulk acoustic waves [23]. It should be noted that this method may be used when the... 

TSM resonators possess lower mass sensitivity than most acoustic wave sensors that employ other mechanisms since they typically operate between only 5 and 30 MHz. Thinner devices can be used to increase frequencies that result in increased mass sensitivity, they are more fragile and harder to manufacture and handle [5]. Recent research on this topic has been on creating high-frequency TSM resonators with piezoelectric films and bulk silicon micromachining techniques. 

Operation of a SAW device as a chemical sensor normally involves the deposition of some chemically selective material onto the surface of the SAW device (2-5). In this work thin polymer films are coated over the entire surface of the SAW device. When a vapor is exposed to the polymer-coated SAW device, it distributes between the gas, bulk polymer phase, and interfaces, and comes to rapid thermodynamic equilibrium. Changes in mass and modulus that result from vapor absorption poturb the propagation of the surface acoustic wave (6), and ordinarily result in a r uction of the observ resonant frequency. The ratio between the concentration of the vapor in the gas phase, Cy, and the concentration of vapor in the polymer phase, Cp, is known as the partition coefficient, Kp, given by equation 1. The portion of the... 

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