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MMM 2022

November 07, 2022

Minneapolis, United States

Magnetic tunnel junctions for positioning systems with down to 100 nm resolution

Positioning systems with high resolution are in a high demand for robotics, operating in a wide scales of positioning ranges from tens of meters in heavy machine industry, down to few nanometers in high-precision electronics. A promising approach for a robust positioning at nanoscale is integration of magnetic field sensors into the positioning electronics and detection of magnetized objects by their induced magnetic fields. In this work, we introduce an approach for magnetic-based positioning, in which the displacement of a magnetized micro-object is detected by magnetic field sensor, as a variation of magnetic field, associated with this displacement. For the purpose to have higher resolution in positioning, magnetic sensor was composed of an array of magnetic tunnel junctions, having magnetoresistance of ~ 170 percent, whereas the geometry of the magnetized object was optimized to have a higher gradient of magnetic field along the positioning direction. The magnet-sensor configuration was optimized as follows: i) magnetization direction in the magnetized object, as well as the displacement direction were varied in respect to field sensing direction of the MTJ sensor, to achieve high linearity of the sensor signal variations with the displacements of the object, ii) the shape of the magnetized object was optimized to improve sensitivity of the MTJ sensor array to positioning displacements of this object, iii) the distance between the MTJ sensor array and the magnetized object was optimized to have largest dynamic range of MTJ output voltage variations, without oversaturating the sensor, iv) the lateral and transversal dimensions of the MTJ sensor array were optimized to improve sensitivity to gradient of magnetic field, induced by the micromagnet.
With the optimized configuration the positioning sensitivity of the sensor platform was tested with a micromagnet, placed on a nano-positioning piezo-stage, operating in a closed-loop feedback mode with 10 nm step resolution. The tests in open environment demonstrate robust operation of the magnetic tunnel junction sensor-based platform as a positioning sensor for displacements of magnetized objects with a resolution down to 100 nm.

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