Magnetic sensing has an extremely wide range of applications in modern industry and electronic products. It detects changes in corresponding physical quantities by converting changes in the magnetic properties of sensitive components caused by external factors such as magnetic field, electric current, stress-strain, temperature, light, etc. into electrical signals. Within the broad category of magnetic position sensors, magnetic sensors based on the Hall effect, AMR sensors based on the anisotropic magnetoresistive effect, GMR sensors based on the giant magnetoresistive effect, and TMR sensors based on the tunneling magnetoresistive effect are the core sensing technologies used in position sensing applications at present, and the latter three are also collectively referred to as magnetoresistive sensors.
Hall effect-based magnetic sensors are highly utilized in applications with mature technology, simple structure, small size and light weight, and high cost performance. Hall effect magnetic sensing is still widely used in high-end application scenarios such as automotive, robotics, and industrial automation. Among them, 3D Hall effect position sensors have attracted much attention in recent years. By placing three independent Hall elements in the three directions of X, Y and Z axes, it can simultaneously measure the magnetic field strength of the object in the three axes, realizing three-dimensional magnetic field sensing. 3D Hall sensors can provide multiple magnetic field ranges to cope with different strong magnetic field environments to ensure reliability, and the high-bandwidth measurements also improve the sensing speed. Currently, there are relatively few manufacturers on the market that can provide 3D Hall sensors, and it is difficult to transform traditional Hall to 3D Hall.
AMR, GMR and TMR three types of magnetoresistive sensing are based on the magnetoresistive effect, i.e., the conductor with current in the magnetic field under the action of the resistance value will change significantly. All three have increasing technical difficulty, structural complexity, cost and process difficulty, but at the same time have higher sensitivity and greater magnetoresistive effect. Taking the magnetoresistance ratio ΔR/Rmin as an example, AMR is around 3%, GMR is around 15%, and TMR is over 50%. These types of sensing have irreplaceable roles in magnetic field and current measurement in automotive sensing, smart grid, new energy and other fields.
There are more and more vendors in the related sensing technology track, and each vendor continues to enhance the strength of magnetoresistive sensing technology. For example, NXP has acquired the technology license of Crocus, a leading TMR vendor; TDK has acquired Micronas, a Hall sensing vendor; Infineon is exploring the fusion of magnetoresistive sensing xMR to take into account the advantages of magnetoresistive sensing; and MultiDimensional Technology continues to push forward the innovation of its TMR and AMR products; Allegro is focusing on the GMR track while exploring the TMR track. The popularity of magnetoresistive sensing is closely related to the automotive market. The development of automobiles towards electrification, intelligence and internet connectivity has led to a significant increase in the demand for magnetic sensing, and the rising number and value of magnetic sensors carried by a single automobile has accelerated the penetration of magnetoresistive sensing.
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