Fabrication sequence for the capillaries: (a) photoresist mask is defined on one side of the wafer, (b) a narrow hole is etched, (c) the wafer is turned over and another etch mask containing a large hole is defined on the other side, (d) the large hole is etched until it meets the narrow hole, which then becomes the desired capillary, and (e) SEM image of the resulting silicon structure. The edge of the large hole is seen as the bright ring. The capillary, indicated by the arrow, is visible as a black dot in the bottom of the big hole.
Test structure showing an array of almost cylindrical holes etched into a silicon substrate: (a) cleaved across the holes and (b) cleaved parallel to the holes.
Flow through the capillaries as function of diameter. The points show experimental flow data for different diameters of the capillary. The curve is a plot of Eq. (4) for .
Measured flow dependence on temperature: The fit curve is a plot of Eq. (4). The inset shows a log-log plot of the same data.
Measured flow as function of the pressure. The fit curve is a plot of Eq. (4).
Model of the capillary showing the high-pressure side and the vacuum side. The regions with intermediate flow and molecular flow are indicated. The inlet pressure is and is the pressure at the vacuum side. At the pressure , the flow changes from intermediate to molecular.
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