Abstract
Gallium Nitride (GaN) is considered as the second most popular semiconductor material in industry after silicon. This is due to its wide applications encompassing Light Emitting Diode (LED) and power electronics. In addition, its piezoelectric properties are fascinating to be explored as electromechanical material for the development of diverse microelectromechanical systems (MEMS) application. In this article, we conducted a theoretical study concerning surface mode propagation, especially Rayleigh and Sezawa mode in the layered GaN/sapphire structure with the presence of various guiding layers. It is demonstrated that the increase in thickness of guiding layer will decrease the phase velocities of surface mode depending on the material properties of the layer. In addition, the Q-factor value indicating the resonance properties of surface mode appeared to be affected with the presence of fluid domain, particularly in the Rayleigh mode. Meanwhile, the peak for Sezawa mode shows the highest Q factor and is not altered by the presence of fluid. Based on these theoretical results using the finite element method, it could contribute to the development of a GaN-based device to generate surface acoustic wave, especially in Sezawa mode which could be useful in acoustophoresis, lab on-chip and microfluidics applications.
Highlights
The demand for surface acoustic wave (SAW) technology, especially in signal processing and filtering has increased significantly due to its robustness, simplicity, inexpensive cost for mass production and good compatibility with CMOS processes [1]
With a further increase of Gallium Nitride (GaN)’s thickness making it superior to the wavelength λ, Sezawa mode could disappear to produce a SAW with the propagation mainly determined by GaN layer
We can observe that both Sezawa modes generate the highest phase velocity compared to Rayleigh and shear modes
Summary
The demand for surface acoustic wave (SAW) technology, especially in signal processing and filtering has increased significantly due to its robustness, simplicity, inexpensive cost for mass production and good compatibility with CMOS processes [1]. GaN/Si [15], GaN/Sapphire [18] and GaN/SiC [2], it is possible to exploit the Sezawa mode which appears on “slow on fast” structures if the acoustic velocity of the thin layer is smaller compared to the bulk substrate This particular mode produces a higher velocity than the fundamental Rayleigh mode as demonstrated by several previous studies [19,20]. They demonstrated experimentally the possibility to obtain 15 percent higher phase velocities compared to Rayleigh SAW by using Sezawa mode with Q factor below 1000 [15] Sezawa mode has been used in the biosensor application for the detection of human immunoglobulin-E (IgE) by using ZnO-Si-layered structures with a maximum sensitivity of 4.44.106 cm2 /g This configuration excited a resonance frequency of Sezawa mode at 1.497 GHz with a wavelength of 32 μm [22]. The effect of various guiding layers on surface mode propagation was demonstrated in order to elucidate the potential of Sezawa mode by using GaN-based SAW devices
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