A Si-micromachined 48-stage Knudsen pump for on-chip vacuum

• Published in: Journal of micromechanics and microengineering Vol. 22; no. 10; pp. 105026 - 8
• Main Authors: Gupta, Naveen K, An, Seungdo, Gianchandani, Yogesh B
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.10.2012; Institute of Physics
• Subjects: Applied sciences; Asymptotic properties; Compression ratio; Encapsulation; Exact sciences and technology; Gages; Gauges; High vacuum; Holes; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated Pirani gauge; Mechanical engineering. Machine design; Micropump; Physics; Pump and compressors (turbocompressors, fans, etc.); Pumping; Pumps; Thermal transpiration; Vacuum apparatus and techniques; Vacuum pumps; Aluminium oxide; Hermetic sealing; Patterning; Micromachining; Pirani gages; Vacuum pump; System on a chip; High vacuum; Inorganic compound; Atomic layer epitaxial growth; Finite element method; Nitrides; Engraving; Knudsen number; Manufacturing process; Silicon; PECVD
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/22/10/105026

This paper describes a thermal transpiration-driven multistage Knudsen pump for vacuum pumping applications. This type of pump relies upon the motion of gas molecules from the cold end to the hot end of a channel in which the flow is restricted to the free molecular or transitional regimes. To achieve a high compression ratio, 48 stages are cascaded in series in a single chip. A five-mask, single silicon wafer process is used for monolithic integration of the designed Knudsen pump. The pump has several monolithically integrated Pirani gauges to experimentally measure the vacuum pumping characteristics of the pump. It has a footprint of 10.35 × 11.45 mm2. For an input power of 1350 mW, the fabricated pump self-evacuates the encapsulated cavities from 760 to 50 Torr, resulting in a compression ratio of 15. It also pumps down from 250 to 5 Torr, resulting in a compression ratio of 50. Each integrated Pirani gauge requires 3.9 mW of power consumption, and its response is sufficiently sensitive in the operating pressure range of 760-1 Torr.