This paper introduces the first tunable ferroelectric capacitor (FeCAP)-based unreleased RF MEMS resonator, integrated seamlessly in Texas Instruments’ 130 nm Ferroelectric RAM (FeRAM) technology. The designs presented here are monolithically integrated in solid-state CMOS technology, with no post-processing or release step typical of other MEMS devices. An array of FeCAPs in this complementary metal-oxide-semiconductor (CMOS) technology’s back-end-of-line (BEOL) process were used to define the acoustic resonance cavity as well as the electromechanical transducers. To achieve high quality factor (Q) of the resonator, acoustic waveguiding for vertical confinement within the CMOS stack is studied and optimized. Additional design considerations are discussed to obtain lateral confinement and suppression of spurious modes. An FeCAP resonator is demonstrated with fundamental resonance at 703 MHz and Q of 1012. This gives a frequency-quality factor product \(f \cdot Q = 7.11 \times 10^{11}\) which is 1.6× higher than the most state-of-the-art Pb(Zr,Ti)O₃ (PZT) resonators. Due to the ferroelectric characteristics of the FeCAPs, transduction of the resonator can be switched on and off by adjusting the electric polarization. In this case, the resonance can be turned off completely at ±0.3 V corresponding to the coercive voltage of the constituent FeCAP transducers. These novel switchable resonators may have promising applications in on-chip timing, ad-hoc radio front ends, and chip-scale sensors.

本文介绍了第一个基于可调铁电电容器 (FeCAP) 的未发布 RF MEMS 谐振器，该谐振器无缝集成到德州仪器 (TI) 的 130 nm 铁电 RAM (FeRAM) 技术中。此处介绍的设计单片集成在固态 CMOS 技术中，没有其他 MEMS 器件典型的后处理或发布步骤。这种互补金属氧化物半导体 (CMOS) 技术的后端 (BEOL) 工艺中的一系列 FeCAP 用于定义声学谐振腔以及机电换能器。实现高品质因数（Q) 的谐振器，研究和优化了用于 CMOS 堆栈内垂直限制的声波波导。讨论了额外的设计考虑，以获得对杂散模式的横向限制和抑制。FeCAP 谐振器的基本谐振频率为 703 MHz，Q值为 1012。这给出了频率品质因数乘积\(f \cdot Q = 7.11 \times 10^{11}\)，比大多数状态高 1.6 倍最先进的 Pb(Zr,Ti)O ₃(PZT) 谐振器。由于 FeCAPs 的铁电特性，谐振器的转换可以通过调整电极化来打开和关闭。在这种情况下，谐振可以在 ±0.3 V 处完全关闭，对应于组成 FeCAP 换能器的矫顽电压。这些新颖的可切换谐振器可能在片上计时、ad-hoc 无线电前端和芯片级传感器中具有广阔的应用前景。