Kaya Onurcan, Zhao Xuanyi, Cassella Cristian
IEEE Trans Ultrason Ferroelectr Freq Control. 2024 Sep;71(9):1063-1073. doi: 10.1109/TUFFC.2024.3432849. Epub 2024 Sep 4.
We present the first microacoustic metamaterial filters (MMFs). The bandpass of the reported MMFs is not generated by coupling, electrically or mechanically, various acoustic resonances; instead, it originates from the passbands and stopbands of a chain of three acoustic metamaterial (AM) structures. These structures form an AM transmission line (AMTL) and two AM reflectors (AMRs), respectively. Two single metal strips serve as input and output transducers with a wideband frequency response. Since MMFs do not rely on resonators, they do not require high-resolution trimming or mass-loading steps to accurately tune the resonance frequency difference between various microacoustic resonant devices. These steps often involve finely controlling the thickness of a device layer, with resolutions that can be as low as a few Angstroms when building GHz filters. The acoustic bandwidth of MMFs is mostly determined by geometrical and mechanical parameters of their AM structures. MMFs necessitate external circuit components for impedance matching, in contrast to the existing microacoustic filters that often employ circuit components only to eliminate ripples within their passband. We have designed and constructed the first MMFs from a 400-nm-thick scandium-doped aluminum nitride (AlScN) film using a 30% scandium-doping concentration. These devices operate in the radio frequency (RF) range. We validated these devices' performance through finite-element modeling (FEM) simulations and through measurements of a set of fabricated devices. When matched with ideal circuit components, the built MMFs exhibit filter responses with a center frequency in the ultrahigh-frequency range, a fractional bandwidth (FBW) of ~2.54%, a loss of ~4.9 dB, an in-band group delay between 70 ± 25 ns, and a temperature coefficient of frequency (TCF) of ~22.2 ppm/° C.
我们展示了首个微声学超材料滤波器（MMF）。所报道的MMF的带通并非通过电耦合或机械耦合各种声学共振产生；相反，它源自由三个声学超材料（AM）结构组成的链的通带和阻带。这些结构分别形成一条AM传输线（AMTL）和两个AM反射器（AMR）。两条单金属条用作具有宽带频率响应的输入和输出换能器。由于MMF不依赖于谐振器，它们不需要高分辨率微调或质量加载步骤来精确调谐各种微声学谐振器件之间的共振频率差。这些步骤通常涉及精细控制器件层的厚度，在构建GHz滤波器时分辨率可低至几埃。MMF的声学带宽主要由其AM结构的几何和机械参数决定。与现有的通常仅使用电路元件来消除其通带内纹波的微声学滤波器相比，MMF需要外部电路元件进行阻抗匹配。我们使用30%的钪掺杂浓度，从400纳米厚的钪掺杂氮化铝（AlScN）薄膜设计并构建了首个MMF。这些器件在射频（RF）范围内工作。我们通过有限元建模（FEM）模拟以及对一组制造器件的测量来验证这些器件的性能。当与理想电路元件匹配时，所构建的MMF呈现出具有以下特性的滤波器响应：中心频率在超高频范围内，分数带宽（FBW）约为2.54%，损耗约为4.9 dB，带内群延迟在70±25纳秒之间，频率温度系数（TCF）约为22.2 ppm/°C。
