Reconfigurable Spintronics Wheatstone Bridge Sensors With Offset Voltage Compensation at Wafer Level

摘要

Industrial requirements are continuously pushing the sensor limits toward higher signal-to-noise ratio under harsh environments, without compromising production costs by additional electronics. Non-full resistive Wheatstone bridge architectures arise as a compact and cheaper alternative to full-bridge measurement schemes, despite a lower output, linearity, and immunity to thermal drifts promoted by the replacement of the out-of-phase sensing elements by passive elements. However, the combination of state-of-the-art magnetoresistive (MR) sensors with thermally compatible materials used as tunable thin-film resistor at wafer level can lead to competitive prototypes for applications with high constraints. Therefore, the resistivity and the temperature coefficient of resistance (TCR) of Cr, Ti, and TiW thin films were evaluated as potential candidates for a thermal and electrical stable non-full MR bridge. Within a TCR around 1059 +/- 12 ppm/degrees C for a spin-valve sensor lying between the values observed for a Ti thickness range of 300 A up to 500 A (571.9 +/- 8.3 and 1347 +/- 69 ppm/degrees C, respectively), a sin/cos magnetic encoder was prototyped in a non-full-bridge architecture with a thermal offset drift of 51.48 +/- 0.25 nV/Vcc/degrees C and an offset voltage of 16 mV/Vcc.