High-resolution giant magnetoresistance on-chip arrays for magnetic imaging

Arrays of micrometer-sized giant magnetoresistance (GMR) magnetic sensors with corresponding micrometer-sized spacing on a single chip are being used to detect very small magnetic fields with high spatial resolution. These very small magnetic fields, or changes in magnetic fields, are associated with magnetic biosensors, nondestructive evaluation, precision position sensing, document validation including currency and magnetic tape, and other magnetic imaging. By using a silicon substrate, the signal conditioning and logic capability of integrated circuits can be incorporated to optimize system performance. This integrated technique reduces the effect of noise and simplifies the sensor/signal-processing interface. GMR sensor arrays with sensor spacing as small as 5 micrometers as well as single-chip arrays with 128 sensors covering a 4 mm width have been constructed. The GMR sensors are made of multilayer material consisting of FeCo/Cu layers with 8% to 20% GMR and maximum sensitivities of 1.0 mV/V/G (100 nV/nT @10 V). The sensor elements are photolithographically patterned with 1.5 to 2 μm wide stripes for high resistance and directional sensitivity. These on-chip magnetic arrays are being applied to various forms of magnetic media as well as work with biosensors and nondestructive test.