Mode-switchable ferroelectric thin-film bulk acoustic resonators (FBARs) are presented. Such resonators operate based on a dynamic nonuniform effective piezoelectricity in composite multilayer ferroelectrics with large electrostriction coefficients, like barium strontium titanate (BST). Harmonic resonance modes ( $\textit {nf}_{o}$ ) of a multilayer ferroelectric bulk acoustic wave (BAW) resonator can be selectively excited with an electromechanical coupling coefficient ( ${K}_{\mathrm {eff}}^{{{2}}}$ ) equal to the fundament mode, which is contrary to the trend ${K}_{\mathrm {eff}}^{{{2}}}\propto {1}/{n}^{{{2}}}$ exhibited by conventional piezoelectric BAW resonators. Such a device can selectively be set to resonate at its different resonance harmonics by generating a pattern of nonuniform piezoelectric coefficient proportional to the stress field of each mode with an application of a proper set of dc control voltages applied across the ferroelectric layers. Such a resonator allows for the design of a new class of band-switching filters. As an experimental validation, a mode-switchable FBAR and a band-switching ladder-type filter based on a bilayer ferroelectric BST structure are designed and fabricated for the first time. The bilayer BST FBARs not only can be switched ON or OFF but also by choosing different bias configurations, two resonance modes at 2 and 3.6 GHz can be selectively excited having ${K}_{\mathrm {eff}}^{{{2}}}$ of 8% and 7%, respectively.

中文翻译：

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基于负压电的电场驱动模式可切换多层铁电FBAR，可在不降低性能的情况下选择性控制谐波 ķ_EFF ²

提出了模式可切换的铁电薄膜体声波谐振器（FBAR）。这样的谐振器基于具有大电致伸缩系数的复合多层铁电体（如钛酸锶锶（BST））中的动态非均匀有效压电来工作。谐波共振模式（ $ \ textit {nf} _ {o} $ 多层铁电体声波（BAW）谐振器可以通过机电耦合系数（ $ {K} _ {\ mathrm {eff}} ^ {{{{2}}} $ ）等于基本模式，与趋势相反 $ {K} _ {\ mathrm {eff}} ^ {{{{2}}} \ proto {1} / {n} ^ {{{{2}}} $ 由常规的压电BAW谐振器展示。通过在铁电层上施加一组适当的直流控制电压，可以生成与每种模式的应力场成比例的非均匀压电系数模式，从而有选择地将这种设备设置为在其不同的谐振谐波下谐振。这种谐振器允许设计新型的频带切换滤波器。作为实验验证，首次设计和制造了基于双层铁电BST结构的可模式切换FBAR和带切换梯型滤波器。双层BST FBAR不仅可以打开或关闭，还可以通过选择不同的偏置配置来选择性地激发2 GHz和3.6 GHz的两个谐振模式 $ {K} _ {\ mathrm {eff}} ^ {{{{2}}} $ 分别为8％和7％。