Magnetic Microimagers Based on Giant Magnetoresistance

Integrated-circuit imaging devices of a proposed type would contain planar arrays of microscopic sensors that would exploit giant magnetoresistance (GMR). Each GMR sensor in such a device would define one pixel in an image with a pixel pitch of the order of tens of microns. With the difference that the GMR sensors would respond to local magnetic fields instead of to locally incident light, they would perform essentially the same role as that played by photodetectors in familiar optoelectronic imaging devices. Indeed, the arrays of GMR sensors could be deposited on readout integrated circuits similar or identical to those on which, heretofore, visible and infrared photodetectors have been deposited. The proposed devices could be used, for example, as conventional magnetometers and gradiometers, magnetic microscopes for examining small ferromagnetic particles or cracks in ferromagnetic materials, imagers for mineralogical exploration, and readers of magnetic inks and magnetic cards.