Fabrication of nanoscale Bi Hall sensors by lift-off techniques for applications in scanning probe microscopy

Bismuth Hall effect sensors with active sizes in the range of 0.1-2 μm have been fabricated by electron beam lithography and lift-off techniques for applications in scanning Hall probe microscopy. The Hall coefficients, offset resistances and minimum detectable fields of the sensors have been systematically characterised as a function of device size. The minimum detectable field of 100 nm probes at 300 K and dc currents of 5 μA was found to be B=0.9 mT Hz with scope for up to a factor of ten reduction by using higher Hall probe currents. This is significantly lower than in similar samples fabricated by focused ion beam (FIB) milling of continuous Bi films, suggesting that the elimination of FIB damage and Ga ion incorporation through the use of lift-off techniques leads to superior figures of merit. A number of ways in which the room temperature performance of our sensors could be further improved are discussed.