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 (Qm) as high as 4382 and 1633. The series resonant frequency (fs)·Qm 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.

Batch Fabrication of Silicon Nanometer Tip Using Isotropic Inductively Coupled Plasma Etching.

This work reports a batch fabrication process for silicon nanometer tip based on isotropic inductively coupled plasma (ICP) etching technology. The silicon tips with nanometer apex and small surface roughness are produced at wafer-level with good etching homogeneity and repeatability. An ICP etching routine is developed to make silicon tips with apex radius less than 5 nm, aspect ratio greater than 5 at a tip height of 200 nm, and tip height more than 10 µm, and high fabrication yield is achieved by mask compensation and precisely controlling lateral etch depth, which is significant for large-scale manufacturing.