Progress toward a thousandfold reduction in 1∕f noise in magnetic sensors using an ac microelectromechanical system flux concentrator (invited)

The potential advantage of some magnetic sensors having a large response is greatly decreased because of the 1∕f noise. We are developing a device, the microelectromechanical system (MEMS) flux concentrator, that will mitigate the effect of this 1∕f noise. It does this by placing flux concentrators on MEMS structures that oscillate at kilohertz frequencies. By shifting the operating frequency, the 1∕f noise will be reduced by one to three orders of magnitude depending upon the sensor and the desired operating frequency. We have succeeded in fabricating the necessary MEMS structures and observing the desired kilohertz normal-mode resonant frequencies. Only microwatts are required to drive the motion. We have used spin valves for our magnetic sensors. The measured field enhancement provided by the flux concentrators agrees to within 4% with the value estimated from finite element calculations. No difference was detected in noise measurements on spin valves with and without the flux concentrators. This resul...