This work reports on the first demonstration of the frequency tuning and intrinsic polarization switching of film bulk acoustic resonators (FBARs), based on sputtered AlScN piezoelectric thin films with Sc/(Al + Sc) ratio of approx. 30%. A box-like ferroelectric hysteresis behavior of 900 nm-thick Al_0.7Sc_0.3N sputtered films is obtained, showing a coercive electric field at ~3 MV/cm. The fundamental thickness-mode resonance of the bulk acoustic wave (BAW) resonator is measured at 3.17 GHz frequency with an excellent electromechanical coupling coefficient ( $k_{t}^{2}$ ) of 18.1%. The FBAR frequency response is studied, in both (i) the linear tuning regime, upon application of DC electric fields below the coercive field; as well as (ii) the polarization switching regime, upon application of electric fields above the coercive field. A large linear tuning range of 215 ppm $\times \,\,\mu \text{m}$ /V is obtained in case (i), resulting from the high scandium content. The series resonance frequency of the FBARs is switched ON and OFF in (ii) upon application of 350 V unipolar waveform across the Al_0.7Sc_0.3N thickness. This is the first demonstration of the intrinsically switchable AlN-based FBARs with a large tuning range; and record high $k_{t}^{2}$ reported for AlN-based FBARs to date. Furthermore, this work paves the way for realization of tunable and switchable wideband acoustic filters operating at super high frequency ranges (SHF). [2020-0203]

中文翻译：

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基于铁电氮化铝钪薄膜的薄膜体声波谐振器

这项工作报告了基于溅射 AlScN 压电薄膜的薄膜体声波谐振器 (FBAR) 的频率调谐和本征极化切换的首次演示，Sc/(Al + Sc) 比率约为 30%。获得了 900 nm 厚的 Al _0.7 Sc _0.3 N 溅射薄膜的盒状铁电滞后行为，显示出~3 MV/cm 的矫顽电场。体声波 (BAW) 谐振器的基本厚度模式谐振在 3.17 GHz 频率下测量，具有出色的机电耦合系数 ( $k_{t}^{2}$ ) 的 18.1%。在以下两种情况下研究 FBAR 频率响应：(i) 线性调谐机制，在矫顽场以下施加直流电场时；以及 (ii) 极化转换机制，在矫顽场上方施加电场时。215 ppm 的大线性调谐范围 $\times \,\,\mu \text{m}$ /V 在情况 (i) 中获得，这是由于钪含量高。FBAR 的串联谐振频率在 (ii) 中在跨越 Al _0.7 Sc _0.3 N 厚度应用 350 V 单极波形时打开和关闭。这是具有大调谐范围的本征可切换的基于 AlN 的 FBAR 的首次演示；并创历史新高 $k_{t}^{2}$ 迄今为止，报告了基于 AlN 的 FBAR。此外，这项工作为实现在超高频范围 (SHF) 下工作的可调谐和可切换宽带声学滤波器铺平了道路。[2020-0203]