SOI Through-Wafer Monolithic Knudsen Pumps for Microscale Gas Chromatographs

Passcode: 521323

Abstract:

The Knudsen pumps (KPs) are motionless, thermally-driven gas micropumps with high reliability and long lifetime, and are appealing for microscale gas chromatographs (μGC) and other such systems. In particular, silicon-on-insulator (SOI) through-wafer KPs are the most attractive type for their high performance with the implementation of numerous well-controlled and lithographically defined pumping channels. This thesis explores the design, microfabrication, and evaluation of two threads of SOI through-wafer KPs, suspended (Gen S) membrane structures and unsuspended (Gen U) structures, to provide high performance, reliability, and manufacturability for μGCs.

The Gen S KPs contain numerous (10³-10⁴) parallel pumping channels with 10 nm thick Al₂O₃ sidewalls. A suspended membrane above the pumping channels houses a thin-film metal heater and provides thermal isolation to the substrate. The Gen S KP provides a blocking pressure of ≈3.3 kPa and maximum flow rate of ≈0.75 sccm with 1.2 W applied power. Such performance is suitable for providing separation gas flow in μGCs.

The Gen U KPs significantly improve the mechanical robustness and simplify the microfabrication process compared to the Gen S KPs. The Gen U KP provides a blocking pressure of 0.62 kPa and maximum flow rate of 0.04 sccm with 2 W applied power. The fabrication simplicity and reliability of this mechanically robust KP can enable monolithic integration onto lab-on-a-chip systems.

Chair: Professor Yogesh Gianchandani and Dr. Yutao Qin