Fabrication of micro fluidic cavities using Si-to-glass anodic bonding

Abstract

We demonstrate the fabrication of $\sim$1.08 $\mu$m deep microfluidic cavities with characteristic size as large as 7 mm $\times$ 11 mm or 11 mm diameter, using a silicon$-$glass anodic bonding technique that does not require posts to act as separators to define cavity height. Since the phase diagram of ${}^3$He is significantly altered under confinement, posts might act as pinning centers for phase boundaries. The previous generation of cavities relied on full wafer-bonding which is more prone to failure and requires dicing post-bonding, whereas the these cavities are made by bonding a pre-cut piece of Hoya SD-2 glass to a patterned piece of silicon in which the cavity is defined by etching. Anodic bonding was carried out at 425 ${}^{\circ }$C with 200 V, and we observe that pressurizing the cavity to failure ($>$ 30 bar pressure) results in glass breaking, rather than the glass-silicon bond separation. In this article, we discuss the detailed fabrication of the cavity, its edges, and details of the junction between the coin silver fill line and the silicon base of the cavity that enables a low internal-friction joint. This feature is important for mass coupling torsional oscillator experimental assays of the superfluid inertial contribution where a high quality factor ($Q$) improves frequency resolution. The surface preparation that yields well-characterized smooth surfaces to eliminate pinning sites, the use of transparent glass as a cover permitting optical access, low temperature capability and attachment of pressure-capable ports for fluid access may be features that are important in other applications.

arXiv comment10 figures

References in corpus (7)

• Thermodynamic properties of thin films of superfluid 3He-A
• Crystalline order in superfluid 3He films
• Drying by Cavitation and Poroelastic Relaxations in Porous Media with Macroscopic Pores Connected by Nanoscale Throats
• The A-B transition in superfluid 3He under confinement in a thin slab geometry
• Ultra-Low Dissipation Superfluid Micromechanical Resonator
• Anomalous Damping of a Micro-electro-mechanical Oscillator in Superfluid ${}^3$He-B
• Study of superfluid ${}^3$He under nanoscale confinement. A new approach to the investigation of superfluid ${}^3$He films

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• Thermal transport of helium-3 in a strongly confining channel
• Superfluid Optomechanics with Phononic Nanostructures
• Nanofluidic platform for studying the first-order phase transitions in superfluid helium-3
• Chiral superfluid helium-3 in the quasi-two-dimensional limit