| Summary: | 碩士 === 國立彰化師範大學 === 光電科技研究所 === 103 === The objective of this thesis is aiming to fabricate and analyze a planarized three-dimensional magnetic field sensor. A spin valve structure consisting of Ta (2nm)/ IrMn (10nm)/ CoFe (2.5nm)/ Cu(2.2nm)/ CoFe(1.5nm)/ NiFe (3nm)/ Ta (5nm)/ SiO2/Si is used as sensing material. The sensing device is designed to be a high aspect ratio of ellipse having the biasing direction along the short axis and the sensing magnetization is along the long axis due to the strong shape anisotropy. In such a design a linear transfer curve is obtained. Through many efforts in optimizing relevant parameters, such as MR ratio, linearity and dynamic range, a three-dimensional magnetic field sensor using spin valve structure is realized. For the fabrication procedures many key semiconductor processing techniques are employed, such as photo-lithography, electron beam lithography, thermal evaporation, ion beam sputtering and ion beam milling. The electrical characterization is carried out by using standard four-terminal measurements with the external magnetic field applied along the short axis of the device.
First of all, single spin valve ellipses with various aspect ratios, 3x10, 2x10, 1x10, 1x20, and 1x30 (unit in micro-meter), were made. In the results of these single ellipses, the highest MR ratio, up to 6.85%, is obtained in the ellipse with aspect ratio of 1x30. Thus, the optimized aspect ratio of 1x30 is then adopted for making a cascaded sensing device, having 13 identical spin valve ellipses in series. The gap, ranging from 1μm to 6μm, in between ellipses is varied for optimizing the sensing properties. It is found that the MR ratio is lower and center shift is greater with decreasing the gap distance, which is mainly due to stronger interaction between the spin valve ellipses. A highest MR ratio, up to 6.82%, in the cascaded ellipses is achieved with 6μm of gap distance. A complete three-dimensional magnetic field sensor is then fabricated in accordance with the aforementioned parameters, MR values are uniformly distributed throughout twelve sensing devices with MR all around 6-7% and sensitivity is up to 0.6 mV/V/Oe in the dynamic range of ± 50 Oe.
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