| From the mid of19th century, magnetic resistance has beenextensively studied and applied into all kinds of fields. Granularfilms magnetoresistance (MR) effect and tunnelingmagnetoresistance effect have been frequently used to fabricatemagnetic sensor, which can be applied to many areas of productiveresearch. There are many kinds of magnetic sensors, such as harddrives, current sensor, position sensor and angle sensor, etc.Although people have made great achievements in the area of MR,there are many problems to be resolved, such as, the sensor’ssensitivity of the GIG (nano-granular in gap) is too low, granulemembrane system MR ratio is small, poor stability; linear outputrange of linear magnetic sensor is too narrow, low sensitivity andsensor design is relatively complicated. These problems limit thepractical application of MR effect. In order to solve the above problems, we studied the MR effect of magneticmetal/semiconductor films, which will help us understand thephysics involved better and achieve a higher MR ratio at highertemperature for practical applications. We demonstrate a structureof MTJ sensor with ZnO or MgO barrier and use perpendicularanisotropy ferromagnet of L10-CoPt as the reference layer and inplane anisotropy ferromagnet of Co as the free layer.So, this thesis mainly studied the structure and design of MReffect sensor. The first part mainly studies the key element of GIG(nano-granular in gap) sensor. Resistance dependence of MR ingranular films. The granular films were deposited by sequentiallysputtering ultrathin Co layers and ZnO layers on glass substrates atRT. The film nominal structure is [Co (0.6)/ZnO (x)]60[denoted asCo/ZnO](thicknesses in nanometers), where x=0.3~2.5is thethickness of the ZnO layer. In this work, we studied a large numberof Co/ZnO films deposited at different sputtering pressures withdifferent ZnO thicknesses and make a lot of film samples whose MRratio is higher than8%. Then we found that the magnetic resistivityof the thin film in the room temperature has something to do withthe magnetic resistivity of the thin film. When0.08Ω cm<ρ<0.5Ω cm, the MR at room temperature is large, theresistivity of the film is too big or too small, the MR effect is significantly weakened, and we can adjust the resistivity of thinfilms to make high temperature magnetic resistivity of the film. TheMR effect is from electrons between magnetic metal nanoparticlestransport by tunneling through the barrier layer of semiconduc tor,electrons in metals and semiconductors, high-order jump andspin-independent connection between the magnetic particles willweaken MR film. According to conduction, the MR effect can beclassified into three regimes: the metallic, tunneling, and hoppingregimes. In the second part of the research we studied themagnetic tunnel junction MR linear sensor. A series of Ag/CoPt filmswere fabricated by DC magnetic sputtering system. And study thestructure and magnetic properties in term of different substrates,thicknesses of Ag and CoPt layer, and the annealing conditions. Weobtain L10-CoPt phase with large coercivity, high squareness ratioand nice continuous morphology for Ag(50nm)/CoPt(20nm) filmafter annealing at450oC. Coercive force and rectangular ratio isreaching15000Oe and1respectively, and then through depositionmethod step by step, make L10-CoPt and Co, respectively, as theupper and lower ferromagnetic layer, MgO or ZnO as the tunneljunction of intermediate barrier layer Ag/CoPt/MgO(ZnO)/Co.Hysteresis loop has a step change significantly, indicating that inthe process of making L10-CoPt-based tunnel junctions, deposition method step by step can avoid the diffusion between the layers andform the perfect interface structure between the layers.In this work we studied the resistivity dependence of MR ingranular films, design and make tunnel junction linear sensor, studythe structure and magnetic properties, which will further promotethe application of the MR effect in magnetic sensor devices. |
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