Study On Spin-Valve GMR Sensors

In the year of 1988, the discovery of the giant magnetoresistance (GMR) effectopened the door of a new discipline – Magnetic Electronics, and roused extensiveinterest in the scientific researches and applied technologies, especially brought the afar-reaching revolution of magnetic sensors. Compared with traditional magneticsensors, GMR sensor has many advantages - higher sensitivity under low field, lowerpower consumption, smaller size, and higher reliability even under harshenvironmental conditions. To obtain the high-quality GMR angle sensor and linearsensor is in the limelight of the academic circles and the industrial field. This thesisaims to obtain high-quality spin-valve GMR sensors after preparation of GMR thinfilms, design of sensor structure and fabrication of devices.Firstly, deposition process and MR performance of spin-valve GMR thin filmsare studied. With the DC magnetic sputtering method, top-pinned and bottom-pinnedspin-valve thin films are successfully obtained. By comparing the structure of the twotypes, the effect of buffer layer in a bottom-pinned spin-valve is discussed. Based onthe optimistic structure, the dependence of GMR properties on the annealing effectunder magnetic filed is extensively investigated. The spin-valve GMR thin film of 9%MR ratio is achieved. After annealing process under the magnetic field that is verticalof pinning direction, hysteresis of spin valve reduces to below 0.1Oe.Secondly, the GMR material has been integrated into sensors throughsemiconductor processing. As for the applications of angle detection and linearmeasurement, two basic sensor units, single GMR resistance and Wheatstone bridge,are proposed. The two types of sensor units with excellent performance have beenrealized with delicate design of layout and fabrication sequence. The GMR anglesensor can output standard sine curve, the error caused by hysteresis is less than 0.5degree within the range of overall 360 degrees;the GMR linear sensor has a transportcurve whose linearity is more than 99.9%, and its hysteresis is less than 0.1Oe withinthe range of ±10Oe.Based on the successful deposition and fabrication process of GMR material anddevices, the GMR chip for magnetic position gauge is designed. The compositivedesign with same phase and multi cycles deduces the error of measurement result, andthe proposal of extra resistance is helpful for adjusting the balance of Wheatstonebridge. Several fabrication runs have been conducted to increase the yield. With GMRchip, the precision of magnetic position gauge can reach the level of 10μm.