Importance of Magnetic Field Sensing Technology

Applied Tech Review | Tuesday, March 16, 2021

Magnetic field identification has vastly expanded as the industry has used several magnetic sensors to identify the presence, strength, or direction of magnetic fields.

FREMONT, CA: Magnetic sensors differ from most other detectors in that they do not measure the physical property of interest. Devices that monitor properties like temperature, strain, pressure, or flow offer an output that directly reports the desired parameter. Magnetic sensors identify changes, or disturbances, in magnetic fields that have been created or modified and from them derive information on properties like direction, rotation, presence, angle, or electrical currents. The output signal of these sensors needs some signal processing for translation into the desired parameter. Although magnetic detectors are somewhat complex, they offer accurate and reliable data without physical contact.

A magnetic field is the vector quantity with magnitude and direction. The scalar sensor quantifies the field's total magnitude but not its direction. The omnidirectional sensor gauges the magnitude of the component of magnetization that lies along its sensitive axis. The bidirectional sensor comprises direction in its measurements. The magnetic vector sensor combines two or three bidirectional detectors. Some magnetic sensors have a threshold and generate an output only when it is surpassed. Low-field sensors tend to be bulky and expensive compared to magnetic devices. Care must be there to account for the Earth's field's impacts, whose daily variations may exceed the sensor's measurement range. The devices are leveraged for medical applications and military surveillance.

Smart sensors with sensing elements and electronics like amplification and signal conditioning are the current trend. GMR materials are sputtered onto wafers and can be directly combined with semiconductor operations. The small sensing elements fit well with semiconductor structures and are applied after the semiconductor fabrication operations. Because of the topography launched by the many layers of polysilicon, metal, and oxides over the transistors, areas must be reserved with no underlying transistors or connections. These areas will have GMR resistors. The GMR materials are deposited over the whole wafer, but the etched sensor elements remain only on these reserved, smooth areas on the wafers.

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