<title>Polysilicon xylophone bar magnetometers</title>

Abstract

The recently developed JHU/APL magnetometer, which is based on a free-free (xylophone) resonating bar, is simple, small, light weight, has a low power consumption and utilizes the Lorentz force to measure vector magnetic fields. The device is intrinsically linear and has a wide dynamic range such that it can measure magnetic field strengths from nanoteslas to teslas. Furthermore, its sensitivity is independent of size for resonating bars of the same material and aspect ratio. This makes it ideally suited for miniaturization using MEMS techniques.. Various polysilicon xylophone bars have been designed, processed, and characterized. The output response has verified the size-independent scaling law and sensitivities of the order of 100 nanoTesla have been achieved with drive currents as low as 20 microamps. This drive current is limited by the sheet resistance of the polysilicon support electrodes and directly affects the sensitivity The electrodes also have a dramatic effect on the resonant frequency since they act as torsional stiffening members on the resonating bar. For example, for a 500x50 micron xylophone the resonant frequency varies from the designed 69kHz to over 95 kHz for 10 micron wide support electrodes. The electrodes do not affect the mechanical Q-factors observed and values in excess of 20,000 at reduced pressures have been routinely obtained.