| Magnetic sensors are widely used in aerospace, automatic measurement, magneticstorage, biomedical etc and play an important role. As a new type of magnetic sensortechnology, giant magnetoimpedance (GMI) effect can make up for the insufficiency ofgiantmagnetoresistance (GMR) sensor to achieve a rapid and sensitive test with widetemperature range in weak magnetic field. While GMI effect is the only one able to meetinformation technology requirements of the sensor with high sensitivity, miniature size,fast response, low power consumption, no hysteresis, low production cost, easyminiaturization and integration. Compared to the film and ribbon material, the amorphouswire is easy to fabricate, easy to form an ideal magnetic anisotropy and easy to obtain anideal sensitivity and GMI performance, but wire material also has the obvious drawback:difficult to ensure repeatability of the sample performance in large quantities production,difficult for circuit welding and installation and uncompatible to large scale integratedcircuit (IC) technology. GMI performance and field sensitivity of film and ribbon materialhas been reached or even exceeded the amorphous wire through technical improvement,while the production process of them are compatible with IC, ensure the reproducibility ofthe sample performance in mass production, low production costs and the circuit weldingand installation are convenient. Some theoretic research works have been done toinvestigate the GMI effect in thin film and ribbon with single layered and multi-layeredstructure, but the theory model of GMI effect in meander structure is still lack. Inbiological detection, several investigations based on GMI sensing technology are carriedout, but so far, it has not seen one detection system based on giant magneto-impedanceeffect completely developed and clinical evaluation for specific pathogens. Meanwhile, thecurrent biological detection based on GMI effect still remain in the non-specific phase, only a small number of cells experiments have been done. The combination of cells andmagnetic particles in these experiments are phagocytosis and it can not be a specificdetection for a certain kind of cells.Based on the above considerations, systemically investigations for theory, fabricationand applications in biological detection of GMI micro sensors based on soft magnetic thinfilms and ribbon materials are carried out in this thesis. The GMI sensors with excellentperformance are picked out in order to establish a complete biological detection system forbiological testing and clinical application. The main research works of this thesis are asfollow:[1] From the Maxwell equations and the equation of magnetization motion, weestablish the theoritical model to calculate the impedance of ferromagnetic materials withsingle layered, meander and trilayered structure according to the distribution ofelectromagnetic field in ferromagnetic conductor and magnetization motion model at highfrequencies. In the model, many of parameters, such as the anisotropy field, the dampingcoefficient and the easy axis orientation etc, are considered. Coordinate system andboundary conditions are established according to the actual situation of the GMI sensor.The theoretical model is simplified consistent with the actual situation and ensuring thatthe theoretical results can be compared very well with the experimental data;[2] GMI effect in ferromagnetic materials with single layered, meander and trilayeredstructure are calculated using the established theoretical model. Symbolic and numericalcomputations are assisted by MATLAB software. Effects of the structure of the material,size effect, current frequency, magnetic field, anisotropy field, easy axis orientation and thedamping factor on the GMI effect are investigated by the theoretical calculation.Theoretical simulation results show that the sensor structure, current frequency, magnticfield, the sample size, the anisotropy field, easy axis orientation and the damping effecthave significant influences both on the magnitude and field sensitivity of the GMI effect.Also the GMI curves are changed by anisotropy field and easy axis orientation and todecide the size of the positive peak of GMI and the emergence or not;[3] Sputtered NiFe film and the commercialization Co-based amorphous ribbons were used for the GMI sensor materials. NiFe film was prepared by magnetron sputtering. Theinfluence of sputtering parameters, such as Ar gas flow rate, sputtering power andsputtering pressure, on magnetic properties of NiFe thin films are investigated and theoptimum sputtering conditions are obtained. Analysis method, such as X-rays, scanningelectron microscopy (SEM) and vibrating sample magnetometer (VSM), was adopted totest material component, surface microstructure and soft magnetic properties. The resultsshow that, NiFe and Co-based thin film materials exhabit excellent soft magneticproperties which guarantees to obtain high-performance of the GMI sensors;[4] NiFe film with different structure are fabricated by RF sputtering, lithography,electroplating and ion beam etching technology and the GMI effect of them are studied.The results show that: gas flow rate and sputtering pressure have a major impact on theGMI performance of thin film. The optimal parameter conditions are obtained through theexperiments: sputtering power 600W, Ar gas flow 14sccm, sputtering pressure5.4×10-3Torr; trilayered NiFe/Cu/NiFe with a three turns meander structure has GMI ratiois 34% and GMI field sensitivity was 1.5%/Oe;[5] Co-based amorphous ribbon with different structure are fabricated by bonding,lithography, chemical etching, and electroplating micro-fabrication process and the GMIeffect are studied. The results show that: the meander structure of ribbon with 3 turns hasmaximize GMI ratio of 204% with the magnetic field sensitivity of 17.8%/Oe, the linewidth of 3 turns structure is 800μm, the line spacing of 400μm. Meanwhile, experimentalGMI effects in Co-based amorphous ribbon are fit well with theoretical results;[6] Microbial typing system for HPV 16/18 virus is designed based on nano-magneticbeads marker. Conserved double-stranded amplified segment of HPV can be easilyseparated into single-stranded fragments by fully use of the good handling ofnano-magnetic magnetic microspheres. While the magnetic signal of the nano-magneticbeads labeled single-chain fragment was directly deteceed by GMI sensor and used forsubsequent genotyping. The separation and detection steps of previous typing method aremerged into one tag. DNA sequencing used as the gold standard in the clinical detection of132 cervical swab samples, the sensitivity of 95% and specificity of 100% of them; [7] RGD cyclic peptide used as the targeting ligands ofαvβ3 integrin in gastric cancercells, the surface modified Fe3O4 nanoparticles used as magnetic marker in detection.Targeted detection of different gastric cancer cells are carried out using GMI sensor, thetest results show that: GMI sensor can detect not only whether the cancer cells absorb themagnetic nanoparticles, but also can detect whether the target samples is gastric cancercells by targeting. Targeted gastric cancer cell, healthy cells and the gastric cancer cell toabsorb magnetic particles by phagocytosis can be recognized successfully. Compared withthe previous biological detection based on GMI effect, the GMI detection are improvedfrom the non-specific to the specific detection.
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