Magnetoresistive-based static tester for actuators

摘要

A static tester for precision actuators is proposed. It is intended to test the functioning of future actuators to be used in hard drive read heads. The design allows a simple fabrication of a nanometer-scale position measurement system that can measure lateral, vertical, and angular displacements. The tester consists of (a) a reference magnetic layer of CoCrPt, (150 X 100 / mu m~2, 600 nm thick) and (b) a sequence of four spin-valve sensors. The tested sensors have crossed anisotropies, 6.9 percent magnetoresistance with a linear response, 0.5 percent /mT sensitivity, coercive field less than 0.1 mT and resistance of 1680 OMEGA in the parallel state. A noise level of 6 nV/√Hz was measured at thermal background for 0.2 mA of applied current. The lateral displacement is measured by the two spin valves in the center. While the magnetic element is passing over these sensors, the measured signal on each of them varies in opposite directions, allowing a precise measurement of the center position. The two outer spin valves are sensitive to the angular orientation of the magnetic element. The relative movements of the spin valves and magnetic element are controlled by computer using piezoelectric crystals and step motors. Since the sensors are measuring the in-plane component of the field, the signal measured decreases rapidly with sensor-to-plane distance. An appropriate range for flight height is about 30 mu m. Simulations of the signal are in agreement with measurements.