Magnetic Oscillation Sensor for High-Density Recording

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Solution Overview

Problem

Conventional magnetic recording elements face limitations in achieving high recording density due to high magnetic white noise and signal-to-noise ratio (SNR) issues, particularly with TMR elements, which struggle to maintain reliability at reduced sizes and increased densities.

Innovation Solution

A magnetic sensor utilizing a magnetic oscillation element with a first and second magnetic resonance layer and a nonmagnetic layer, where a current is supplied perpendicularly to the layers to excite precession of magnetization, generating a high-frequency oscillation voltage that monitors changes in an external magnetic field, thereby improving SNR and enabling higher recording densities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the tunnel insulating layer is made thinner to reduce tunnel resistance and obtain required signal voltage, then the signal voltage increases, but the circuit between the upper and lower ferromagnetic layers shorts, lowering the MR ratio

Engineering Contradiction:

Improvesignal voltageVSAvoidMR ratio

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent changes the fundamental operating parameter from resistive detection (GMR/TMR) to dynamic magnetization detection. By applying a microwave frequency signal and detecting the change in resonance frequency caused by external magnetic fields, the system achieves high sensitivity without requiring thin tunnel insulating layers, thus avoiding short circuits while maintaining detection capability.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the element size is reduced to deal with increased recording density, then the recording density increases, but the magnetic white noise becomes predominant and degrades the SNR

Engineering Contradiction:

Improverecording densityVSAvoidmagnetic white noise

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent employs mechanical vibration analogously by using microwave frequency oscillations to drive the magnetization dynamics. The magnetic resonance layers are excited at their natural resonance frequency, and external magnetic fields are detected through changes in this oscillation frequency. This dynamic detection method is inherently more sensitive than static resistance measurement, allowing smaller element sizes without being dominated by magnetic white noise.

Inventive Principle:

Principle #18Mechanical vibration

3Measurement precision

If the TMR element is used to achieve higher magnetic recording density, then the MR ratio increases to about 100%, but the shot noise increases in proportion to the square root of tunnel resistance, failing to achieve high SNR

Engineering Contradiction:

ImproveMR ratioVSAvoidshot noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the electrical resistance-based detection system with a magnetic resonance-based detection system. Instead of measuring changes in electrical resistance (which generates shot noise), the system measures changes in the resonance frequency of magnetization precession. This substitution of the detection mechanism eliminates the shot noise problem entirely, as the measurement is based on frequency modulation rather than current fluctuation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The magnetic sensor effectively reduces magnetic white noise and enhances signal quality, allowing for recording densities of several hundred Gbpsi to over 1 Tbpsi without degrading sensitivity, even at reduced element sizes.

Implementation Method 1

a current is supplied perpendicularly to planes of the first resonance layer, the nonmagnetic layer and the second magnetic resonance layer to excite precession of magnetization

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

precession of magnetization in at least one of the first and second magnetic resonance layers caused by supplying the current

Methodology Applied

Scientific EffectMagnetization precession:

Implementation Method 3

determining a change in a high-frequency oscillation voltage generated across the magnetic oscillation element due to precession of magnetization

Methodology Applied

Scientific EffectMagnetic resonance:

Implementation Method 4

monitoring a change caused by an external magnetic field by determining a change in a high-frequency oscillation voltage

Methodology Applied

Scientific EffectFrequency modulation:

Data Source

PatentUS7602588B2Magnetic sensor using a magnetic oscillation element

Publication Date: 2009.10.13 KK TOSHIBA

AI summary

A magnetic sensor has a magnetic oscillation element including a first magnetic resonance layer, a second magnetic resonance layer, a nonmagnetic layer sandwiched between the first and second magnetic resonance layers, and a pair of electrodes which supply a current perpendicularly to planes of the first resonance layer, the nonmagnetic layer and the second magnetic resonance layer, and a monitor monitoring a change dependent on an external magnetic field in a change of a high-frequency oscillation voltage generated across the magnetic oscillation element due to precession of magnetization in at least one of the first and second magnetic resonance layers caused by supplying the current.