Silicon based quadrupole mass spectrometry using microelectromechanical systems

The conventional quadrupole mass spectrometer (QMS) arrangement uses circul ar metallic rods as the mass filter excited electrically at voltages up to 1 kV depending upon the application. If the size and voltages can be reduce d then the range of applications for QMS instruments would increase. The ap plication of microelectromechanical systems (MEMS) technology allows the fa brication of submillimeter versions of such structures. In this article the development of a miniature QMS is reported in which the conventional rod a rrangement has been replaced with a microengineered version. The structure is made in silicon with metallized specially drawn glass fibers of length 2 0-30 mm and diameter 0.5 mm to act as the quadrupole rods. This is about on e order of magnitude smaller than most conventional QMS filters, with the p otential for further reduction in size. The MEMS mass filter was mounted on to a commercial ion source, which was in turn attached to a vacuum flange a nd supplied by an electronic drive circuit at 6 MHz. Mass spectra in the ra nge 0-50 amu for a range of operating conditions have been obtained indicat ing a linear mass scale and a best resolution at 10% peak height of around 30. The use of pole bias applied to the rods is shown to be beneficial. Rel iable QMS operation was obtained up to a pressure of 10(-2) mbar. (C) 2001 American Vacuum Society.