Magnetoresistive (mr) sensors employing dual mr devices for differential mr sensing

Abstract

Magnetoresistive (MR) sensors employing dual MR devices for differential MR sensing are provided. These MR sensors may be used as biosensors to detect the presence of biological materials as an example. An MR sensor includes dual MR sensor devices that may be tunnel magnetoresistive (TMR) devices or giant magnetoresistive (GMR) devices as examples. The MR devices are arranged such that a channel is formed between the MR devices for receiving magnetic nanoparticles. A magnetic stray field generated by the magnetic nanoparticles causes free layers in the MR devices to rotate in opposite directions, thus causing differential resistances between the MR devices for greater sensing sensitivity. Further, as another aspect, by providing the channel between the MR devices, the magnetic stray field generated by the magnetic nanoparticles can more easily rotate the magnetic moment orientation of the free layers in the MR devices, thus further increasing sensitivity.

1 . A magnetoresistive (MR) sensing system, comprising:
 a plurality of MR sensors each comprising:
 a first MR device disposed in an encapsulation material, the first MR device having a first resistance; 
 a second MR device disposed in the encapsulation material a horizontal distance away from the first MR device, the second MR device having a second resistance; and 
 an external channel formed in a void in the encapsulation material between the first MR device and the second MR device, the external channel configured to capture magnetic nanoparticles; 
 the first resistance of the first MR device configured to increase in response to a presence of the magnetic nanoparticles in the external channel exerting a magnetic stray field on the first MR device; and 
 the second resistance of the second MR device configured to decrease in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second MR device; 
   a sensing circuit configured to:
 select a MR sensor among the plurality of MR sensors in response to a sense operation; 
 generate a first sensed voltage based on a change in the first resistance of the first MR device of the selected MR sensor; and 
 generate a second sensed voltage based on a change in the second resistance of the second MR device of the selected MR sensor; and 
   a sense amplifier configured to generate a differential output voltage indicative of the presence of the magnetic nanoparticles in the external channel based on a difference between the first sensed voltage and the second sensed voltage.   
     
     
         2 . The MR sensing system of  claim 1 , wherein, for each MR sensor among the plurality of MR sensors:
 the first MR device further comprises a first hard magnetic layer having a perpendicular magnetization disposed adjacent to the external channel, the first hard magnetic layer configured to generate a first magnetic bias field in the external channel to align a magnetic moment of the magnetic nanoparticles disposed in the external channel; and   the second MR device further comprises a second hard magnetic layer having the perpendicular magnetization disposed adjacent to the external channel, the second hard magnetic layer configured to generate a second magnetic bias field in the external channel to align the magnetic moment of the magnetic nanoparticles disposed in the external channel.   
     
     
         3 . The MR sensing system of  claim 1 , wherein each MR sensor among the plurality of MR sensors further comprises a hard magnetic layer having a perpendicular magnetization disposed below the external channel, the hard magnetic layer configured to generate a magnetic bias field in the external channel to align the magnetic moment of the magnetic nanoparticles disposed in the external channel. 
     
     
         4 . The MR sensing system of  claim 1 , wherein, for each MR sensor among the plurality of MR sensors, the first MR device comprises a first tunnel magnetoresistive (TMR) device, and the second MR device comprises a second TMR device. 
     
     
         5 . The MR sensing system of  claim 1 , wherein, for each MR sensor among the plurality of MR sensors, the first MR device comprises a first giant magnetoresistive (GMR) device, and the second MR device comprises a second GMR device. 
     
     
         6 . A method of detecting a presence of magnetic nanoparticles in a magnetoresistive (MR) sensor, comprising:
 receiving magnetic nanoparticles bound to a bioreceptor configured to capture a target analyte of interest in a MR biosensor chip in at least one external channel among a plurality of external channels each forming a biological active area, the MR biosensor chip comprising a plurality of MR sensors each comprising:
 a first MR device disposed in an encapsulation material, the first MR device having a first resistance; 
 a second MR device disposed in the encapsulation material a horizontal distance away from the first MR device, the second MR device having a second resistance; and 
 the at least one external channel among the plurality of external channels formed in a void in the encapsulation material between the first MR device and the second MR device, the at least one external channel configured to capture the magnetic nanoparticles; 
 the first resistance of the first MR device configured to increase in response to a presence of the magnetic nanoparticles in the at least one external channel exerting a magnetic stray field on the first MR device; and 
 the second resistance of the second MR device configured to decrease in response to the presence of the magnetic nanoparticles in the at least one external channel exerting the magnetic stray field on the second MR device; 
   selecting at least one MR sensor among the plurality of MR sensors in response to a sense operation;   generating a first sensed voltage based on a change in the first resistance of the first MR device of the selected at least one MR sensor;   generating a second sensed voltage based on a change in the second resistance of the second MR device of the selected at least one MR sensor; and   generating a differential output voltage indicative of the presence of the magnetic nanoparticles in the at least one external channel based on a difference between the first sensed voltage and the second sensed voltage.   
     
     
         7 . The MR sensing system of  claim 1 , wherein for at least one MR sensor among the plurality of MR sensors, a magnitude of the increase in the first resistance in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the first MR device is approximately equal to a magnitude of the decrease in the second resistance in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second MR device. 
     
     
         8 . The MR sensing system of  claim 1 , wherein:
 the first MR device of at least one MR sensor among the plurality of MR sensors comprises:
 a first pinned layer having a first magnetization in a first direction; 
 a first spacer disposed above the first pinned layer; and 
 a first free layer disposed above the first spacer having a first magnetization in a second axis orthogonal to the first direction; 
 the first free layer configured to rotate about the second axis in the first direction in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the first free layer; and 
   the second MR device of at least one MR sensor among the plurality of MR sensors comprises:
 a second pinned layer having the first magnetization in the first direction; 
 a second spacer disposed above the second pinned layer; and 
 a second free layer disposed above the second spacer having a second magnetization in a second direction; 
 the second free layer configured to rotate about the second axis in the second direction opposite of the first direction in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second free layer. 
   
     
     
         9 . The MR sensing system of  claim 1 , wherein:
 the first MR device comprises a first tunnel magnetoresistive (TMR) device;   the first spacer of the first TMR device comprises a first tunnel barrier;   the second MR device comprises a second TMR device;   the second spacer of the second TMR device comprises a second tunnel barrier;   the first resistance of the first TMR device is configured to increase in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the first TMR device in response to a TMR effect; and   the second resistance of the second TMR device is configured to decrease in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second TMR device in response to the TMR effect.   
     
     
         10 . The MR sensing system of  claim 1 , wherein:
 the first MR device comprises a first giant magnetoresistive (GMR) device;   the first spacer of the first GMR device comprises a first metal spacer;   the second MR device comprises a second GMR device;   the second spacer of the second GMR device comprises a second metal spacer;   the first resistance of the first GMR device is configured to increase in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the first GMR device in response to a GMR effect; and   the second resistance of the second GMR device is configured to decrease in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second GMR device in response to the GMR effect.   
     
     
         11 . The MR sensing system of  claim 1 , wherein:
 the first MR device of at least one MR sensor among the plurality of MR sensors comprises:
 a first free layer having a first magnetization in a second axis; 
 a first spacer disposed above the first free layer; and 
 a first pinned layer disposed above the first spacer, the first pinned layer having the first magnetization in a first direction orthogonal to the second axis; 
 the first free layer configured to rotate about the second axis in the first direction in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the first free layer; and 
   the second MR device of at least one MR sensor among the plurality of MR sensors comprises:
 a second free layer having the first magnetization in the second axis; 
 a second spacer disposed above the second free layer; and 
 a second pinned layer disposed above the second spacer, the second pinned layer having the first magnetization in the first direction orthogonal to the second axis; 
 the second free layer configured to rotate about the second axis in a second direction opposite of the first direction in response to the presence of the magnetic nanoparticles in the external channel exerting the magnetic stray field on the second free layer. 
   
     
     
         12 . The MR sensing system of  claim 11 , wherein the at least one MR sensor further comprises:
 a first access transistor comprising a first gate, a first electrode, and a second electrode, wherein:
 the first gate of the first access transistor is coupled to a word line; 
 the first electrode of the first MR device is coupled to the first electrode of the first access transistor; and 
 the second electrode of the first MR device is coupled to a selector line; 
   the first MR device configured to receive a first current between the first top electrode and the first bottom electrode based on the first resistance of the first MR device, in response to a control signal on the word line activating the first access transistor and a first voltage applied to the selector line; and   a second access transistor comprising a second gate, a third electrode, and a fourth electrode, wherein:
 the second gate of the second access transistor is coupled to the word line; 
 the third electrode of the second MR device is coupled to the first electrode of the second access transistor; and 
 the fourth electrode of the second MR device is coupled to the selector line; 
 the second MR device configured to receive a second current between the second top electrode and the second bottom electrode based on the second resistance of the second MR device in response to the control signal on the word line activating the second access transistor and a second voltage applied to the selector line. 
   
     
     
         13 . The MR sensing system of  claim 1 , wherein at least one MR sensor among the plurality of MR sensors further comprises:
 a first bottom electrode disposed below and in electrical contact with the first MR device;   a first top electrode disposed above and in electrical contact with the first MR device;   a second bottom electrode disposed below and in electrical contact with the second MR device; and   a second top electrode disposed above and in electrical contact with the second MR device;   the first MR device configured to carry a first current between the first bottom electrode and the first top electrode in response to a first voltage differential applied between the first bottom electrode and the first top electrode based on the first resistance of the first MR device; and   the second MR device configured to carry a second current between the second bottom electrode and the second top electrode in response to a second voltage differential applied between the second bottom electrode and the second top electrode based on the second resistance of the second MR device.   
     
     
         14 . The MR sensing system of  claim 2 , wherein the first hard magnetic layer is configured to generate the first magnetic bias field in the external channel having a south to north direction, and the second hard magnetic layer is configured to generate the second magnetic bias field in the external channel in a north to south direction. 
     
     
         15 . The MR sensing system of  claim 2 , wherein the first hard magnetic layer is configured to generate the first magnetic bias field in the external channel having a north to south direction, and the second hard magnetic layer is configured to generate the second magnetic bias field in the external channel in a south to north direction. 
     
     
         16 . The MR sensing system of  claim 1  comprising an MR biosensor configured to capture the magnetic nanoparticles bound to a bioreceptor bound to a target analyte of a biological sample. 
     
     
         17 . The MR sensing system of  claim 1  integrated into an integrated circuit (IC) chip. 
     
     
         18 . The MR sensing system of  claim 1  integrated into a device selected from the group consisting of: a wearable device, a point-of-care device, a bacteria infection diagnostic device, a cancer detection device, a heart disease diagnostic device, and a food safety monitoring device.