Fused Silica Micro Birdbath Shell Resonators With 1.2 Million Q and 43 Second Decay Time Constant

Abstract

We report a micro-scale fused silica (FS) birdbath (BB) shell resonator with a high mechanical quality factor (Q = 1.2 million), long decay time constant (! = 43.6 s), a resonant frequency of 8.8 kHz for wineglass modes, and excellent symmetry resulting in a frequency split of only 6.7 Hz between two wineglass modes. The resonator has a volume of 41 mm 3 (radius = 2.5 mm, anchor radius = 0.5 mm, height ~ 2.1 mm). The resonator is useful in a wide range of applications, including inertial sensors, timing devices, and chemical and biological sensors.

Demonstration of 1 Million <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-Factor on Microglassblown Wineglass Resonators With Out-of-Plane Electrostatic Transduction

“…3-D side-walls of the wineglass geometry makes it challenging to fabricate radial electrodes with small capacitive gaps and to keep the gap uniform across the height of the structure. Even though post-fabrication assembly techniques have been successfully demonstrated [10], [11], these approaches create a bottle-neck in batch-fabrication of the devices at wafer level. In this paper, we explore an alternative transduction paradigm based on out-of-plane electrode architecture.…”

“…For thin film devices this is accomplished by defining electrode structures within the pre-etched cavity by placing a sacrificial layer in between the electrode and the device [4], [8]. For glassblown devices a wide variety architectures have been demonstrated, including deep glass dry etching of the capacitive gaps [9] (>30μm), utilization of thermal mismatch between the shell and the mold to create the capacitive gaps [6] (∼15μm), and various assembly techniques [10], [11] (∼15μm). Despite these advances, factors such as alignment errors between the shell and the electrodes, cross-talk between electrodes, relatively large gaps created by assembly based techniques and lack of scalability remain a challenge.…”

A high-q all-fused silica solid-stem wineglass hemispherical resonator formed using micro blow torching and welding

“…FS is an excellent material for 3D micro shell resonators, because 1) it has very low thermoelastic damping (TED) [1] due to its very low linear thermal expansion coefficient (α FS = 0.52 × 10 -6 K -1 ) and low thermal conductivity (k FS = 1.38 Wm -1 K -1 ), and 2) it has very low surface energy loss due to its very smooth surface (<1 nm) when reflow molded. We have recently reported a FS micro birdbath (BB) resonator with long τ = 43 s, Q = 1.2 million, frequency symmetry (Δf = 6 Hz), and a high angular gain (A g (calculated) ~ 0.25) [2]. To improve performance further, the Q of the resonator has to be increased.…”

“…To improve performance further, the Q of the resonator has to be increased. Several reasons have been identified as the source of lower Q in these small shell resonators [2]. Among these is energy loss through the anchor.…”

MEMS Micro-glassblowing Paradigm for Wafer-level Fabrication of Fused Silica Wineglass Gyroscopes

“…Q-factors up to 24k [4] were measured on poly-diamond wineglass shells. Blow molding was used to demonstrate Q-factors as high as 7.8k on bulk metallic glass shells [5] and above 1 million on fused silica shells [6]. We explore an alternative fabrication paradigm under the hypothesis that surface tension and pressure driven micro-glassblowing process may serve as an enabling mechanism for wafer-scale fabrication of extremely symmetric and atomically smooth degenerate mode CVGs, Fig 1. Micro-glassblowing process relies on viscous deformation of the device layer under the influence of surface tension and pressure forces to define the 3-D shell structure as opposed to conventional deposition, molding, or etching techniques, this leads to levels of smoothness and structural symmetry that is not available through conventional fabrication techniques.…”