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In this paper, a novel vertically arranged double-electrodes A0 mode Lamb-wave AlN resonator on SOI substrate with a high electromechanical coupling coefficient and high figure of merit (FOM) is reported. The AlN resonator has a sandwich structure with aluminum and N-type doped silicon as electrode layers and a 500 nm thick AlN film as piezoelectric layer. The resonator has only two electrodes vertically arranged rather than horizontal interdigitated (IDT) electrodes which is common in conventional Lamb-wave resonators. The electrode gaps for the vertically arranged double-electrodes resonators are defined by AlN layer thickness rather than by photolithography for lateral field excitation resonators, which results in higher electric field strength and higher electromechanical coupling efficient ( k t 2 ). Compared with conventional thickness field excitation (TFE) resonators with floating bottom electrodes, the vertically arranged double-electrodes resonators have higher electric field strength as the potential difference is larger between the top electrode and bottom electrode than that between the IDT electrodes and floating electrode. As a result, a higher electromechanical coupling coefficient is achieved. Furthermore, the resonant frequency of the vertically arranged double-electrodes resonator presented in this work can be defined by photolithography by controlling the width of the silicon layer. The k t 2 of the vertically arranged double-electrodes resonator calculated from the measurement results of admittance versus frequency by numerically fitting with the Butterworth Van Dyke model shows an increase by 3.85 times, from 0.073% to 0.281% compared with conventional TFE resonators, and the FOM also increases by three times, from 2.66 to 7.99. This work provides a new structure to design future AlN Lamb-wave resonators on SOI substrate.

Mg-Zn-Mn (ZM) alloy shows great potential in biomedical applications due to its biocompatibility and bio-essential element composition, as well as its favourable mechanical and degradation properties. This paper aims to explore the effect of Zn on corrosion behaviour of ZM alloys via finite element (FE) prediction and in-vitro testing. Microstructure analysis showed that Zn had the grain refinement effect, and the second phase of Mg-Zn between grains increased with the increase of Zn content, which improved the mechanical properties of the alloy significantly at the cost of acceptable reduction in plasticity. After a continuum damage mechanics (CDM)-based degradation model was applied to the FE package, the corrosion process of the ZM alloys was predicted. The results indicated that the grain boundary had poor corrosion resistance while the second phase facilitated delaying corrosion expansion. Furthermore, in-vitro tests were carried out and consistent results were obtained, i.e., the grain refinement made the entire corrosion process more uniform and severe corrosion in local areas was avoided, and the intergranular second phase was beneficial to delay the corrosion process. This study suggested that Mg-Zn-Mn alloy has satisfactory mechanical strength and controllable corrosion rate, which should be a promising candidate for future biomedical applications.