A monolithic Si-micromachined four-stage Knudsen pump for µGC applications

Abstract

This paper reports the design, microfabrication, and experimental evaluation of a monolithic Si-micromachined four-stage Knudsen pump (KP) suitable for microscale gas chromatography (µGC) applications. Without moving parts, KPs generate gas flow by leveraging free molecular flow against a temperature gradient in narrow channels. In this work the KP consists of four monolithically integrated stages that are fabricated by a five-mask lithographic process; each pump stage is micromachined into a silicon-on-insulator wafer and fluidically connected to adjacent stages by channels etched into glass wafers that are bonded above and below the silicon wafer. The pumping channels are densely arrayed, vertically oriented, 1.2 µm-wide rectangular channels with 10 nm thick Al2O3 sidewalls. The four-stage KP has a footprint of 5 × 7.5 mm2. While operating at ambient atmospheric pressure, the pump provides a blocking pressure of ≈3.3 kPa and a maximum air flow rate of ≈0.75 sccm with 1.2 W input power. (The experimental results match the modeling with <30% discrepancy.) Such performance is suitable for providing gas flow in µGCs.