  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.
