I am fabricating the Hall bar (5 micron width and 35 micron length) of Ta(3nm)Co(4nm)Pt(5nm) using photolithoghaphy and sputtering. This Hall bar is connected by contact pads of Ti(10nm)/Au(60nm) using second layer of lithography and. Sputtering. But the resistance of Hall bar is showing in mega-ohm, which should be below 1000 ohm. What could be the problem with my fabrication process?