Reserch On The Tunable Linear Sensor Based On Giant Magnetoresistance Effect

With the development of Internet of Things technology, the demand of the magnetic sensor is increasing rapidly. High sensitivity magnetoresistive sensor has the advantages of high sensitivity, small size, light weight, easy integration and so on.It has irreplaceable advantages to other sensors in the detection of weak magnetic signal.In this paper, a spin valve type magnetic sensor with high sensitivity is studied. On the basis of traditional spin valve type sensor thin film unit, an orthogonal double pinned spin valve sensor is developed.Utilizingthelinear tunable properties of the double pinned spin valve, we producedlinear tunable spin-valve linear sensor by microfabrication technology.Traditional two-pinned spin valve film needs twice annealing to achieve the exchange bias field orthogonal, and we propose a method of rotating magnetic field in situ to deposit thin films. It simplifies the manufacturing difficulty and improves the stability of the devices. In the study we first conducted the optimization of top and bottom pinned film properties, and found that the sputtering gas flow and CoFe thickness can change the exchange bias effect, and produced the exchange bias field up to 250 Oe top pinned film and the exchange b ias field up to 180 Oe bottom pinned film. On this basis, we studied the influence of sputtering gas flow, sputtering power and the thickness of CoFe and IrMn, on the exchange bias field and coercivity of pinned thin films, by the tunable magnetic field fixture. Simultaneously we studied the influence of the CoFe thickness of free layer and pinned layer, IrMn thickness and the C u layer of sputtering power and thickness, on the traditional spin-valve films. We produced a high magnetic resistance, lo w coercivity and high exchange bias field traditional spin- valve films. Based on the study of traditional spin- valve films, two pinned spin-valve film reference layer of CoFe thickness, sputtering gas flo w and sputtering power,have an impact on its the exchange bias field. By changing the three factors at the same time, the sensitivity of two-pinned spin valve film was tuned between 0.07% / Oe and 0.3% / Oe.Within this range the exchange bias field reached 200 Oe, and the maximum linear range reached 80 Oe and the minimum is better than 50 Oe.Finally, based on the study of two-pinned spin valve films, a four-terminal Wheatstone bridge magnetoresistive sensorwas produced by microfabrication technology. Its linear range is 40 Oe, and the sensitivity reached 0.61 mV / V / Oe, and the bias point is lowered to40 Oe, and linear fitting reaches 98.35%.