Paul Trap Mass Analyzer Consisting of Opposing Microfabricated Electrode Plates

We report the design and performance of a novel radio-frequency (RF) ion-trap mass analyzer, the planar Paul trap, in which a quadrupolar potential distribution is made between two electrode plates. Each plate consists of a series of concentric, lithographically deposited 100-microm-wide metal rings, overlaid with a thin resistive layer. A different RF amplitude is applied to each ring, such that the trapping field produced is similar to that of the conventional Paul trap. The accuracy and shape of the electric fields in this trap are not limited by electrode geometry nor machining precision, as is the case in traps made with metal electrodes. The use of two microfabricated plates for ion trap construction presents a lower-cost alternative to conventional ion traps, with additional advantages in electrode alignment, electric field optimization, and ion-trap miniaturization. Experiments demonstrate the effects of ion ejection mode and scan rate on mass resolution for several small organic compounds. The current instrument has a mass range up to approximately 180 Thomsons (Th), with better than unit mass resolution over the entire range.