Ultralow Acoustic Loss Micromachined Butterfly Lamb Wave Resonators on AlN Plates

High-Q Resonator-Inductor Using LiNbO₃ Plate for Frequency Tuning in 1-5 GHz

In this article, a new high quality factor ( Q ) inductor with piezoacoustic plate acoustic wave (PAW) resonators is presented. As indicated by the investigation of the acoustic wave propagation characteristics and transducer materials, the coupling coefficient ( k² ) of the shear-horizontal plate (SH₀) mode that propagates in the LiNbO₃ plate increases to 55.7%, which leads to a wide inductive bandwidth of 29%. The longitudinal and transversal spurious modes are inhibited through novel edge reflector design and transducer engineering. The peak inductor quality factor ( [Formula: see text]) of the acoustic resonator-inductor is obtained as 347, and a large range of inductance values are achieved to be up to 49 nH by regulating the interdigital transducer (IDT) number of fingers (NF). It is noteworthy that a larger inductance is realized in a more miniaturized device. Furthermore, the wavelength-scaling-induced physics is investigated for frequency tuning in 1-5 GHz, which reveals the multifrequency ability on a single chip of the SH₀ acoustic resonator-inductor.

High Quality-Factor and Spectrum-Clean AlN Lamb-Wave Resonators with Optimized Lateral Reflection Boundary Conditions and Transducer Design

This paper presents a high quality-factor (Q) and spectrum-clean AlN Lamb-wave resonator (LWR). The width of its lateral reflection boundary was optimized to weaken the transverse modes' coupling and wave guiding, and then to improve the LWR's Q value and spectral purity, which was verified by finite element analysis and experimental characterization. In addition, the series resonance quality factor (Qs) value of the interdigitated (IDT)-Ground LWR is similar to that of the IDT-Floating LWR, but its parallel resonance quality factor (Qp) is nearly doubled, due to the reduction of the electrical loss induced by its static capacitance (C0). The measured results show that the designed LWR with optimized boundary reflection conditions and IDT-Ground structure exhibit Qs and Qp values as high as 4019.8 and 839.5 at 401.2 MHz and 402.9 MHz, respectively, meanwhile, it has good spectral purity. Moreover, the influence of the metal ratio and material of the LWR's IDT electrodes on the device's performance was also studied by theoretical analysis and experimental verification.

A MEMS Fabrication Process with Thermal-Oxide Releasing Barriers and Polysilicon Sacrificial Layers for AlN Lamb-Wave Resonators to Achieve fs·Qm > 3.42 × 1012

This paper presents a micro-electro-mechanical systems (MEMS) processing technology for Aluminum Nitride (AlN) Lamb-wave resonators (LWRs). Two LWRs with different frequencies of 402.1 MHz and 2.097 GHz by varying the top interdigitated (IDT) periods were designed and fabricated. To avoid the shortcomings of the uncontrollable etching of inactive areas during the releasing process and to improve the fabrication yield, a thermal oxide layer was employed below the platted polysilicon sacrificial layer, which could define the miniaturized release cavities well. In addition, the bottom Mo electrode that was manufactured had a gentle inclination angle, which could contribute to the growth of the high-quality AlN piezoelectric layer above the Mo layer and effectively prevent the device from breaking. The measured results show that the IDT-floating resonators with 12 μm and 2 μm electrode periods exhibit a motional quality factor (Q_m) as high as 4382 and 1633. The series resonant frequency (f_s)·Q_m values can reach as high as 1.76 × 10¹² and 3.42 × 10¹², respectively. Furthermore, Al is more suitable as the top IDT material of the AlN LWRs than Au, and can contribute to achieving an excellent electrical performances due to the smaller density, smaller thermo-elastic damping (TED), and larger acoustic impedance difference between Al and AlN.

Dissipation Analysis Methods and Q-Enhancement Strategies in Piezoelectric MEMS Laterally Vibrating Resonators: A Review

Over the last two decades, piezoelectric resonant sensors based on micro-electromechanical systems (MEMS) technologies have been extensively studied as such sensors offer several unique benefits, such as small form factor, high sensitivity, low noise performance and fabrication compatibility with mainstream integrated circuit technologies. One key challenge for piezoelectric MEMS resonant sensors is enhancing their quality factors (Qs) to improve the resolution of these resonant sensors. Apart from sensing applications, large values of Qs are also demanded when using piezoelectric MEMS resonators to build high-frequency oscillators and radio frequency (RF) filters due to the fact that high-Q MEMS resonators favor lowering close-to-carrier phase noise in oscillators and sharpening roll-off characteristics in RF filters. Pursuant to boosting Q, it is essential to elucidate the dominant dissipation mechanisms that set the Q of the resonator. Based upon these insights on dissipation, Q-enhancement strategies can then be designed to target and suppress the identified dominant losses. This paper provides a comprehensive review of the substantial progress that has been made during the last two decades for dissipation analysis methods and Q-enhancement strategies of piezoelectric MEMS laterally vibrating resonators.