Pensala Tuomas, Ylilammi Markku
VTT Technical Research Centre of Finland, Micro- and Nanoelectronics, Espoo, Finland.
IEEE Trans Ultrason Ferroelectr Freq Control. 2009 Aug;56(8):1731-44. doi: 10.1109/TUFFC.2009.1238.
Zinc-oxide-based thin-film bulk acoustic wave (BAW) resonators operating at 932 MHz are investigated with respect to variation of dimensions of a boundary frame spurious mode suppression structure. A plate wave dispersion-based semi-2-D model and a 2-D finite element method are used to predict the eigenmode spectrum of the resonators to explain the detailed behavior. The models show how the boundary frame method changes the eigenmodes and their coupling to the driving electrical field via the modification of the mechanical boundary condition and leads to emergence of a flat-amplitude piston mode and suppression of spurious modes. Narrow band suppression of a single mode with a nonoptimal boundary frame is observed. Reduction of the effective electromechanical coupling coefficient k2eff as a function of the boundary width is observed and predicted by both models. The simple semi-2-D plate model is shown to predict the device behavior very well, and the 2-D finite element method results are shown to coincide with them with some additional effects. Breaking the resonator behavior down to eigenmodes, which are not directly observable in measurements, by the models, yields insight into the physics of the device operation.
研究了基于氧化锌的、工作在932MHz的薄膜体声波（BAW）谐振器，考察了边界框架杂散模式抑制结构尺寸的变化。基于板波色散的半二维模型和二维有限元方法被用于预测谐振器的本征模式频谱，以解释其详细行为。模型展示了边界框架方法如何通过改变机械边界条件来改变本征模式及其与驱动电场的耦合，并导致出现平幅活塞模式和抑制杂散模式。观察到使用非最优边界框架时对单模式的窄带抑制。两个模型都观察到并预测了有效机电耦合系数k2eff随边界宽度的减小。结果表明，简单的半二维板模型能很好地预测器件行为，二维有限元方法的结果在一些额外效应下与前者相符。通过模型将谐振器行为分解为在测量中无法直接观察到的本征模式，有助于深入了解器件工作的物理原理。
