US 8,133,439 B2Granted

GMR biosensor with enhanced sensitivity

AssigneeMagIC Technologies, Inc.

InventorsPo-Kang Wang, Xizeng Shi, Chyu-Jiuh Torng

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Abstract

A sensor array comprising a series connection of parallel GMR sensor stripes provides a sensitive mechanism for detecting the presence of magnetized particles bonded to biological molecules that are affixed to a substrate. The adverse effect of hysteresis on the maintenance of a stable bias point for the magnetic moment of the sensor free layer is eliminated by a combination of biasing the sensor along its longitudinal direction rather than the usual transverse direction and by using the overcoat stress and magnetostriction of magnetic layers to create a compensatory transverse magnetic anisotropy. By making the spaces between the stripes narrower than the dimension of the magnetized particle and by making the width of the stripes equal to the dimension of the particle, the sensitivity of the sensor array is enhanced.

A GMR sensor stripe formed as a lamination of horizontal planar layers of substantially identical horizontal shape and having a free layer bias point along a length dimension that is stable with respect to hysteresis, comprising:

a pinned layer having a magnetic moment;
a non-magnetic electrically conducting spacer layer formed on said pinned layer;
a free layer having a magnetic moment and characterized by magnetic anisotropies along said length dimension and along a perpendicular width dimension, wherein said free layer has a magnetostriction that is adjustable by variations in dimension and composition of said free layer, wherein said free layer is formed on said spacer layer and weakly coupled magnetically to said pinned layer across said spacer layer;
and
a capping layer formed on said free layer;
and wherein said layers have a length dimension that is greater than said width dimension, creating, thereby, a shape induced magnetic anisotropy in said length dimension of said free layer, maintaining a bias point of said free layer magnetic moment in a stable position along said length dimension while said free layer in a quiescent state not acted upon by external fields;
and
dielectric material contiguously surrounding said GMR sensor stripe
placing said free layer under tensile or compressional stresses along said width dimension whereby a stress-induced anisotropy is produced in said width dimension as a result of adjusting said magnetostriction thereby canceling effects of said shape induced anisotropy in directions away from said length dimension and permitting sensitive response of said free layer magnetic moment when said free layer is not in a quiescent state, and
wherein the magnetic moments of said pinned and free layers are aligned parallel to said length dimension with said stable bias point when said sensor is in a quiescent state yet whereby said free layer magnetic moment is responsive to external magnetic fields when said sensor is not in a quiescent state.

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Facts

Application

11/497,162Filed 1 Aug 2006

Published

US 2008/0032423 A17 Feb 2008

Granted

13 Mar 2012

Term ends

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Classification14 codes

G01R 33/0052
Arrangements or instruments for measuring magnetic variables: manufacturing aspects; Manufacturing of single devices, i.e. of semiconductor…
B82Y 25/00
Nanomagnetism
G01N 15/0656
Investigating concentration of particle suspensions: using electric, e.g. electrostatic methods or magnetic methods
G01N 27/745
Of fluids: for detecting magnetic beads used in biochemical assays

Abstract

Claims7