Spin valve sensors

Abstract

This paper demonstrates spin valve sensor applications as read elements in storage systems, or, when in a Wheatstone bridge configuration, as rotational speed control devices (for ABS systems), high current monitoring devices for power lines, and positioning control devices in robotic systems. For recording heads, shielded spin valve sensors are adequate for high linear density recording. A tape head was fabricated with output 400 μV per micron of trackwidth, with a D50 value of 100 kfci, and signal loss of −0.34 dB/kfci. For rotational speed measurement, spin valve bridge sensors with flux guides were used, yielding a 400-mVpp amplitude, and square wave output with rise/fall times below 70 μs, when excited by a magnetized wheel. Amplitude is independent of speed (0–3000 rpm), and of sensor to wheel separation (0.5–2.0 mm). For power line applications, currents up to 2100 A (at 50 Hz) could be measured with a sensitivity of 35 μVrms/A and deviations from linearity of ±1.5%. In robot position control, a maximum error of ±9 μm over a ±0.5-mm span was obtained. In the two last cases, bridges without flux guides are used to maximize linear response.