Study On Spin Valve Structure And GMR Sensor

In recent years, magnetic sensing techniques based on spin-valve magnetoresistance materials have been paid much attention in the field of magnitoelectronics and sensing techniques. In this dissertation, magnitoresistance characteristic and performance optimizing methods of conventional top-pinned spin-valve material and special spin-valve materials have been studied. A novel transverse annealing process, which reduces the coercivity of the spin-valve material dramatically, has been developed. And the single domain model of the spin-valve has been studied systematically. Based on the study of the single domain model, three kinds of GMR sensors have been fabricated on the semiconductor pilot line. After the transverse annealing process, the high performance GMR linear bridge sensor is on the top level in the world. Finally, three kinds of high precision detection systems based on the GMR sensors have been assembled.Firstly, the performance optimized method of the conventional top-pinned spin-valve material is studied. The high performance spin-valve material with high magnetoresistance and low coercivity is obtained by adjusting the thickness of spin-valve layers. Then ultilizing special structure such as NiFeCr accessorial buffer layer, SAF structure, etc., spin-valve materials with partial outstanding performance are obtained. The temperature characteristic of the spin-valve material is studied. To provide core elements of high-performance GRM sensor, the coercivity of the spin-valve material is reduced by a novel transverse annealing process.Secondly, the single domain model of spin-valve is investigated. The calculation results of the spin-valve magnetic behaviour using single domain model by energy minimizing method consist with the experimental results. The unparallel easy axis single domain model and the alterable applied field angle single domain model are developed based on the simple single domain model. The effect of transverse annealing process is explained using the unparallel easy axis single domain model,and the experiential fomula of the effect of transverse annealing process is achieved.Then, based on theoretical analysis of single domain model, layouts and process-flow designs of GMR single strip sensor, GMR magnetic grating vernier sensor and GMR linear bridge sensor are performed. Ultilizing high performance spin-valve material, these GMR sensors are fabricated using semiconductor process by three photolightprocesses method or five photolightprocesses method. Several fabrication runs are conducted to increase the yield. The coercivity of the GMR sensors is reduced by transverse annealing process. The magnetical response of the GMR sensors and the angle response, the uniformity and power spectrum density of noise of GMR single strip sensor are tested systematically. The results show that GMR single strip sensor and GMR magnetic grating vernier sensor have good performances, and the linear range, sensitivity and linearity of the GMR linear bridge sensor, which reaches the highest level in performances in the world, are 30.25Oe, 1.61mV/Oe-V and 99.952%, respectively.Finally, three kinds of detection systems including weak magnetic field linear detection system, magnetic grating vernier displacement detection system and biologic immune magnetic bead detection system are assembled. The magnetic grating vernier displacement detection system has been turned into commercial.