Monolithic MEMS quadrupole mass spectrometers by deep silicon etching

A wafer-scale, batch fabrication process for constructing quadrupole mass spectrometers using microelectromechanical systems (MEMS) technology is described. The device is formed from two bonded silicon-on-insulator (BSOI) substrates, which are attached together to form a monolithic block. Deep etched features and springs formed in the outer silicon layers are used to locate cylindrical metal electrode rods, while similar features formed in the inner silicon layers' are used to define integrated ion entrance and exit optics. The precision of the assembly is determined by lithography and. deep etching, and by the mechanical definition of the bonded silicon layers. Mass filtering is demonstrated, with a mass range of approximate to 400 a.m.u. and a mass resolution of I a.m.u. at 219 a.m.u., using quadrupoles with rods of 500 pm diameter and 30 mm length, operating at 6 MHz RF frequency.