Bias structure for magnetic tunnel junction magnetoresistive sensor

A magnetic tunnel junction (MTJ) magnetoresistive sensor which has positive and negative readback signals about a bias point of a transfer curve upon sensing positive and negative magnetic incursions from a moving magnetic medium, said MTJ sensor comprising:

• a ferromagnetic free layer having a magnetization that is free to rotate in first and second directions from a position which corresponds to said bias point upon sensing positive and negative magnetic incursions, respectively;
• an antiparallel (AP)-pinned layer having a magnetization that is pinned in a pinned direction, said AP-pinned layer including:
• a first ferromagnetic (FM1) pinned layer;
• a second ferromagnetic (FM2) pinned layer;
• and
• an antiparallel coupling (APC) layer disposed between the FM1 layer and the FM2 layer;
• a ferromagnetic bias layer;
• an antiferromagnetic (AFM) layer disposed between the bias layer and the FM1 layer which pins the magnetization of the bias layer and the AP-pinned layer along said pinned direction;
• a tunnel barrier layer disposed between the free layer and the FM2 layer so that upon sensing positive and negative magnetic incursions the magnetization of the free layer rotates in said first and second directions relative to the pinned direction of the magnetization of the AP-pinned layer resulting in an increase or decrease, respectively, in the magnetoresistance of the MTJ sensor to a sense current;
• the direction of the magnetization of the free layer being influenced by a ferromagnetic coupling field (HFC) from the FM2 layer, a demagnetization field (HdmP) from the AP-pinned layer and a demagnetization field (HdmB) from the bias layer;
• and
• the demagnetization fields HdmP and HdmB adding together at the free layer and having such magnitude and direction that a net influence of HFC, HdmP and HdmB on the free layer is substantially zero.

A magnetic read/write head comprising:

• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor including:
• an antiparallel (AP)-pinned layer including a first ferromagnetic (FM1) layer, a second ferromagnetic (FM2) layer and an antiparallel coupling (APC) layer disposed between the FM1 and FM2 layers;
• a bias layer;
• an antiferromagnetic (AFM) layer disposed between said FM1 layer and said bias layer;
• a ferromagnetic free layer;
• and
• a tunnel barrier layer disposed between said FM2 layer and said free layer;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head;
• wherein said bias layer comprises:
• a ferromagnetic first bias layer;
• a ferromagnetic second bias layer adjacent to the AFM layer;
• and
• an antiparallel coupling (APC) layer disposed between the first and second bias layers.

A magnetic read/write head comprising:

• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor having having positive and negative readback signals about a bias point of a transfer curve upon sensing positive and negative magnetic incursions from a moving magnetic medium, said MTJ sensor comprising:
• a ferromagnetic free layer having a magnetization that is free to rotate in first and second directions from a position which corresponds to said bias point upon sensing positive and negative magnetic incursions, respectively;
• an antiparallel (AP)-pinned layer having a magnetization that is pinned in a pinned direction, said AP-pinned layer including:
• a first ferromagnetic (FM1) pinned layer;
• a second ferromagnetic (FM2) pinned layer;
• and
• an antiparallel coupling (APC) layer disposed between the FM1 layer and the FM2 layer;
• a ferromagnetic bias layer;
• an antiferromagnetic (AFM) layer disposed between the bias layer and the FM1 layer which pins the magnetization of the bias layer and the AP-pinned layer along said pinned direction;
• a tunnel barrier layer disposed between the free layer and the FM2 layer so that upon sensing positive and negative magnetic incursions the magnetization of the free layer rotates in said first and second directions relative to the pinned direction of the magnetization of the AP-pinned layer resulting in an increase or decrease, respectively, in the magnetoresistance of the MTJ sensor to a sense current;
• the direction of the magnetization of the free layer being influenced by a ferromagnetic coupling field (HFC) from the FM2 layer, a demagnetization field (HdmP) from the AP-pinned layer and a demagnetization field (HdmB) from the bias layer;
• and
• the demagnetization fields HdmP and HdmB adding together at the free layer and having such magnitude and direction that a net influence of HFC, and HdmP HdmB on the free layer is substantially zero;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head.

A disk drive system comprising:

• a magnetic recording disk;
• a magnetic read/write head for magnetically recording data on the magnetic recording disk and for sensing magnetically recorded data on the magnetic recording disk, said magnetic read/write head comprising:
• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor including:
• an antiparallel (AP)-pinned layer including a first ferromagnetic (FM1) layer, a second ferromagnetic (FM2) layer and an antiparallel coupling (APC) layer disposed between the FM1 and FM2 layers;
• a bias layer;
• an antiferromagnetic (AFM) layer disposed between said FM1 layer and said bias layer;
• a ferromagnetic free layer;
• and
• a tunnel barrier layer disposed between said FM2 layer and said free layer;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head;
• an actuator for moving said magnetic read/write head across the magnetic disk so that the read/write head may access different regions of the magnetic recording disk;
• and
• a recording channel coupled electrically to the write head for magnetically recording data on the magnetic recording disk and to the MTJ sensor of the read head for detecting changes in resistance of the MTJ sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the AP-pinned layer in response to magnetic fields from the magnetically recorded data;
• wherein said bias layer comprises:
• a ferromagnetic first bias layer;
• a ferromagnetic second bias layer adjacent to the AFM layer;
• and
• an antiparallel coupling (APC) layer disposed between the first and second bias layers.

A disk drive system comprising:

• a magnetic recording disk;
• a magnetic read/write head for magnetically recording data on the magnetic recording disk and for sensing magnetically recorded data on the magnetic recording disk, said magnetic read/write head comprising:
• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor including:
• an antiparallel (AP)-pinned layer including a first ferromagnetic (FM1) layer, a second ferromagnetic (FM2) layer and an antiparallel coupling (APC) layer disposed between the FM1 and FM2 layers;
• a bias layer;
• an antiferromagnetic (AFM) layer disposed between said FM1 layer and said bias layer;
• a ferromagnetic free layer;
• and
• a tunnel barrier layer disposed between said FM2 layer and said free layer;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head;
• an actuator for moving said magnetic read/write head across the magnetic disk so that the read/write head may access different regions of the magnetic recording disk;
• and
• a recording channel coupled electrically to the write head for magnetically recording data on the magnetic recording disk and to the MTJ sensor of the read head for detecting changes in resistance of the MTJ sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the AP-pinned layer in response to magnetic fields from the magnetically recorded data;
• wherein the FM2 layer has a thickness greater than the thickness of the FM1 layer and the first bias layer has a thickness greater than the thickness of the second bias layer.

A disk drive system comprising:

• a magnetic recording disk;
• a magnetic read/write head for magnetically recording data on the magnetic recording disk and for sensing magnetically recorded data on the magnetic recording disk, said magnetic read/write head comprising:
• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor including:
• an antiparallel (AP)-pinned layer including a first ferromagnetic (FM1) layer, a second ferromagnetic (FM2) layer and an antiparallel coupling (APC) layer disposed between the FM1 and FM2 layers;
• a bias layer;
• an antiferromagnetic (AFM) layer disposed between said FM1 layer and said bias layer;
• a ferromagnetic free layer;
• and
• a tunnel barrier layer disposed between said FM2 layer and said free layer;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head;
• an actuator for moving said magnetic read/write head across the magnetic disk so that the read/write head may access different regions of the magnetic recording disk;
• and
• a recording channel coupled electrically to the write head for magnetically recording data on the magnetic recording disk and to the MTJ sensor of the read head for detecting changes in resistance of the MTJ sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the AP-pinned layer in response to magnetic fields from the magnetically recorded data;
• wherein the FM1 layer has a thickness greater than the thickness of the FM2 layer and the second bias layer has a thickness greater than the thickness of the first bias layer.

A disk drive system comprising:

• a magnetic recording disk;
• a magnetic read/write head for magnetically recording data on the magnetic recording disk and for sensing magnetically recorded data on the magnetic recording disk, said magnetic read/write head comprising:
• a write head including:
• at least one coil layer and an insulation stack, the coil layer being embedded in the insulation stack;
• first and second pole piece layers connected at a back gap and having pole tips with edges forming a portion of an air bearing surface (ABS);
• the insulation stack being sandwiched between the first and second pole piece layers;
• and
• a write gap layer sandwiched between the pole tips of the first and second pole piece layers and forming a portion of the ABS;
• a read head including:
• a magnetic tunnel junction (MTJ) sensor and first and second shield layers, the MTJ sensor being sandwiched between the first and second shield layers, the MTJ sensor having having positive and negative readback signals about a bias point of a transfer curve upon sensing positive and negative magnetic incursions from a moving magnetic medium, said MTJ sensor comprising:
• a ferromagnetic free layer having a magnetization that is free to rotate in first and second directions from a position which corresponds to said bias point upon sensing positive and negative magnetic incursions, respectively;
• an antiparallel (AP)-pinned layer having a magnetization that is pinned in a pinned direction, said AP-pinned layer including:
• a first ferromagnetic (FM1) pinned layer;
• a second ferromagnetic (FM2) pinned layer;
• and
• an antiparallel coupling (APC) layer disposed between the FM1 layer and the FM2 layer;
• a ferromagnetic bias layer;
• an antiferromagnetic (AFM) layer disposed between the bias layer and the FM1 layer which pins the magnetization of the bias layer and the AP-pinned layer along said pinned direction;
• a tunnel barrier layer disposed between the free layer and the FM2 layer so that upon sensing positive and negative magnetic incursions the magnetization of the free layer rotates in said first and second directions relative to the pinned direction of the magnetization of the AP-pinned layer resulting in an increase or decrease, respectively, in the magnetoresistance of the MTJ sensor to a sense current;
• the direction of the magnetization of the free layer being influenced by a ferromagnetic coupling field (HFC) from the FM2 layer, a demagnetization field (HdmP) from the AP-pinned layer and a demagnetization field (HdmB) from the bias layer;
• and
• the demagnetization fields HdmP and HdmB adding together at the free layer and having such magnitude and direction that a net influence of HFC, and HdmP and HdmB on the free layer is substantially zero;
• and
• an insulation layer disposed between the second shield layer of the read head and the first pole piece layer of the write head;
• an actuator for moving said magnetic read/write head across the magnetic disk so that the read/write head may access different regions of the magnetic recording disk;
• and
• a recording channel coupled electrically to the write head for magnetically recording data on the magnetic recording disk and to the MTJ sensor of the read head for detecting changes in resistance of the MTJ sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the AP-pinned layer in response to magnetic fields from the magnetically recorded data.