Preparation And Properties Of Stretchable Giant Magnetoresistance Magnetic Field Sensors

Compared with the traditional silicon component,flexible electronic devices own tensile,conformal molding,elastic deformation,light,not easily broken,high processing efficiency,low cost and many other advantages,have been widely used in curved display,flexible cell,biological sensors and e-skin etc various fields.Flexible magnetoelectronics and flexible spin electronic devices based on the magnetic metal films,because of the low temperature sputtering processes,and excellent malleability,sensitive and reliable for multi field response characteristics of magnetic,electrical and thermal and stress,etc.The devices have important research value and broad application prospect in flexible electronics.One of the most important applications of flexible magnetic thin films is the magnetic field sensor based on the flexible magnetic metallic multilayers.In the future,flexible magnetic field sensors will be widely used in wearable tracking and positioning system,electromagnetic pollution detection and protection devices,implantable medical devices,etc.So flexible magnetic field sensors are important components of flexible wearable devices.This paper will use polydimethylsiloxane(PDMS)and the top pinning spin valve(FeNi/FeCo/Cu/FeCo/IrMn)for the preparation of the tensile giant magnetic field sensors.We will carry out research on stretchable giant magnetoresistance magnetic field sensors.We use DC magnetron sputtering system to optimize the structure of the spin valve on silicon substrate.First,we should optimize the process of the ferromagnetic materials to obtain the small coercivity and good square property.Then,on the basis of spin valve(FeCo/Cu/FeCo),we obtained the appropriate process parameters of the nonmagnetic metal layer of Cu.In order to reduce the coercivity of the spin valve free layer and to improve the sensitivity of the spin valve magnetic field sensor,we further introduce FeNi magnetic thin film with small coercivity in the spin valve structure of the free layer.Through optimization of the thickness of the spin valve.Finally we get the spin valve structure with excellent comprehensive properties,high magnetoresistance ratio,high sensitivity and low coercivity of free layer,low saturation field.We prepared the spin valve structure on flexible substrate PDMS,and then study the effect of the stress applied to the flexible spin valve.We will obtain the spin valve structure grown on flexible substrate.The use of a stripe and curved mask can reduce cracks,we obtained flexible spin valve devices with self-assembly periodic wrinkle structure by the method of pre-strain.And the stress concentration generated by the tension is released on the substrate,which effectively avoids the adverse effects of stress anisotropy.Thus the magnetic field sensitivity of the sensor can maintain a good stability under large tensile deformation.The tensile range of the magnetic field sensor based on the spin valve giant magnetoresistance can be up to 50%,and it has good stability,the fatigue test shows that the device has good anti-fatigue properties.The spin valve devices prepared by using curved mask and pre-strain,due to the stress generated in the process of releasing cause cracks on the film surface,and then lead to device failure,so use the curved mask to prepare large stretchable spin valve film devices are restricted.