A micromachined ZnO/Si3N4 Lamb wave device for ultraviloet sensing application

Acoustoelectric (AE) effect, which arises from the interaction of acoustic waves and mobile carriers, is one of important sensing mechanisms of acoustic wave sensors. Nevertheless, investigations about the influences of AE effect on Lamb wave sensors in the literatures remain little thus far. In this regard, a micormachined 1.5 mm ZnO/Si
₃
N
₄
Lamb wave device employing the AE effect for ultraviolet (UV) sensing application is studied both theoretically and experimentally. By introducing dispersion relations, a model associated with the acoustoelectric effect is modified to deal with the interactions of Lamb waves and mobile carriers. As numerical examples, Lamb wave propagation associated with the AE effect in ZnO/Si
₃
N
₄
/Si and ZnO/Si
₃
N
₄
layered structures are discussed. Numerical results show attenuation of a ZnO/Si
₃
N
₄
membrane due to the AE effect can be much more obvious than that of a ZnO/Si
₃
N
₄
/Si layered plate. On the experimental side, two types of Lamb wave devices, based on a ZnO/Si
₃
N
₄
/Si plate and an ultra-thin ZnO/Si
₃
N
₄
membrane respectively, were realized and discussed. Under a 0.06 mWcm
^-2
370 nm-UV illumination, a 1.8 dB insertion loss (IL) drop on the 1.5 mm ZnO/Si
₃
N
₄
membrane and a 0.8 dB drop on the ZnO/Si
₃
N
₄
/Si layered plate were observed respectively. The experimental findings indicate that through proper designs, a micromachined ZnO/Si
₃
N
₄
Lamb wave device can be a promising candidate for sensing applications using the acoustoelectric effect.