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Proceedings Paper

Zigzag-shaped AMR magnetic sensors: Transfer characteristics and noise
Author(s): L. Jiang; Aisha Gokce; F. C. S. da Silva; E. R. Nowak
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Paper Abstract

Microfabricated magnetoresistive zigzag-shaped elements based on the anisotropic magnetoresistance effect were studied for use as magnetic field sensors. Images taken using scanning electron microscopy with polarization analysis show that the magnetization in the devices tends to follow the edges of the device, thereby providing a geometrical (45°) bias that alternates along length of the sensor. It was found that these devices are primarily sensitive to magnetic fields applied along the long axis; a flat response is observed for perpendicular fields. The alternating magnetization bias provides the directionality of the sensor because the angles in adjacent zigzag blocks scissor for fields parallel to the long axis and rotate for perpendicular fields. This results in resistances that either add or cancel, respectively. A single-domain, coherent rotation description provides an estimate for the qualitative behavior of these zigzag structures and indicates the possible role of exchange in the shape of the transfer curves. Noise measurements were also taken on these devices. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated magnetic state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in the saturated state depends in a nontrivial way on the quality and processing of the magnetic element, showing a trend for lower normalized noise in elements having higher sensitivity. In the most sensitive elements (magnetoresistance > 1%) the 1/f noise level is comparable to that found in nonmagnetic metals. We attribute the origin of noise to defect motion. In the unsaturated state, the excess noise is found to track the dc resistance susceptibility. For particular values of applied field we also observed large random telegraph signals in the time domain. The telegraph noise was extremely sensitive to the applied field, becoming active and inactive in our measurement bandwidth for changes in field of only a few Oersteds. This behavior indicates a magnetic origin to the excess noise. The variation of the excess noise level with applied dc magnetic field can be explained qualitatively using a model based on thermal excitation of the magnetization direction and/or domain wall hopping between pinning sites.

Paper Details

Date Published: 23 May 2005
PDF: 13 pages
Proc. SPIE 5846, Noise and Information in Nanoelectronics, Sensors, and Standards III, (23 May 2005); doi: 10.1117/12.609572
Show Author Affiliations
L. Jiang, Univ. of Delaware (United States)
Aisha Gokce, Univ. of Delaware (United States)
F. C. S. da Silva, Univ. of Colorado (United States)
E. R. Nowak, Univ. of Delaware (United States)

Published in SPIE Proceedings Vol. 5846:
Noise and Information in Nanoelectronics, Sensors, and Standards III
Janos A. Bergou; Janusz M. Smulko; Mark I. Dykman; Lijun Wang, Editor(s)

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