High temperature micro-glassblowing process demonstrated on fused quartz and ULE TSG

Abstract

We report, for the first time, a MEMS fabrication process for building atomically smooth, symmetric 3-D wineglass and spherical shell structures, using low internal loss materials, namely fused quartz and ultra low expansion titania silicate glass (ULE TSG). The approach consists of three major steps: (1) a deep fused quartz cavity etch, (2) plasma activated bonding of fused quartz to fused quartz or TSG and (3) a high temperature (up to 1700 • C) micro-glassblowing process. An in-house process capability of 1800 • C glassblowing with a rapid cooling rate of 500 • C/min was developed. Feasibility of the process has been demonstrated by fabrication of fused quartz and TSG micro-glassblown structures. Spherical and inverted-wineglass shells with self-aligned stem structures were fabricated using this process. The approach may enable new classes of TSG and fused quartz MEMS devices with extremely low surface roughness (0.23 nm surface average), intrinsically low thermoelastic dissipation (QTED > 5E+10), and highly symmetric structures (radial error < 500 ppm).

3-Dimensional Blow Torch-Molding of Fused Silica Microstructures

“…Two-dimensional (2-D) cantilever resonators [13] and dog-bone resonators [15] have only moderate Q (<50,000). A micro-glass-blowing technology of ultra-low-expansion (ULE) glass or fused silica based on trapped gas expansion was reported [16], [17]. This method produced smooth surface quality but required hermetic bonding of a glass wafer to a support substrate with a higher melting temperature or the same material with a much larger thickness, which suffers from deformation of the support substrate while the shells are being blown.…”

“…It was previously described in [19], [29] and implemented by Senkal et al using ULE glass [16] and fused silica [17]. The anchor and the rest of the shell can be self-aligned, that is, they are fabricated simultaneously, which leads to better structural symmetry.…”

Metallic Glass Hemispherical Shell Resonators

“…For an ideal system, performance would be invariant of the clamping dynamics, as the resonance of the hemisphere is not coupled to the stem. Previous work done by the Shkel [12] group suggests that the diameter of the stem compared to the diameter of the vibratory element can greatly reduce anchoring losses. In their work, reducing the ratio of resonator diameter to stem diameter, the Q-factor increases from ∼10 2 to ∼10 7 .…”

“…These MEMS techniques include micro scale glass blow molding using quartz [12], Pyrex [13], and fused silica [14], as well as traditional silicon processing techniques followed by deposition of polysilicon [15], silicon nitride [16], alumina [17], or diamond [18] device layers. Most versatile in terms of shaping the resonator are the glass blowing techniques.…”

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

“…This leads to atomically smooth surfaces (0.23 nm Sa measured on glassblown shells using AFM [8]) and frequency splits ( ) that are uniformly low across the wafer. Table 1, shows summary of 5 borosilicate glass wineglasses on the same wafer, demonstrating ppm level frequency symmetry between the two degenerate n = 2 wineglass modes [9].…”