Demagnetized Bias Layer Tails Reduce Magnetic Coupling in CPP Sensors
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Solution Overview
Problem
As track widths narrow in magnetic data recording, thermal vibrations increase noise, limiting the signal-to-noise ratio (SNR) in current perpendicular to plane (CPP) magnetoresistive heads, and the need for a thinner read gap to enhance data density is hindered by magnetic coupling between hard bias structures and shields.
Innovation Solution
A magnetic sensor design featuring demagnetized tail portions of magnetic bias layers, which prevents magnetic coupling with the upper shield, reducing signal noise and allowing for a thinner non-magnetic gap, thereby improving SNR and data density without the need for a thick non-magnetic spacer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick non-magnetic gap is used to prevent magnetic coupling between hard bias structure and upper shield, then magnetic coupling is reduced, but read gap thickness increases
Solution Approach 1:
The patent extracts the magnetic coupling problem by removing the magnetic moment from the bias layer tail portion through demagnetization. This eliminates the harmful magnetic interaction with the upper shield without requiring a thick non-magnetic gap, thus solving both the magnetic coupling issue and maintaining a thin read gap structure
Solution Approach 2:
The patent changes the magnetic parameter of the bias layer tail portion by demagnetizing it, transforming it from a magnetically active state to a magnetically inactive state. This parameter change prevents magnetic coupling with the upper shield while allowing the read gap to remain thin, resolving the contradiction between magnetic isolation and gap thickness
2Productivity
If track width is narrowed to increase data density, then data density improves, but thermal vibration noise increases
Solution Approach 1:
The patent applies local quality by demagnetizing only the tail portion of the bias layer while maintaining the magnetic properties of other critical regions. This localized treatment reduces thermal vibration noise in the specific area where it affects the free layer, allowing narrow track widths to be used without excessive noise, thus enabling higher data density
3Measurement precision
If magnetic biasing is applied to reduce thermal vibration noise, then signal-to-noise ratio improves, but magnetic coupling with upper shield increases
Solution Approach 1:
The patent segments the bias layer into functionally distinct regions: a magnetically active head portion that provides biasing to improve signal-to-noise ratio, and a demagnetized tail portion that prevents magnetic coupling with the upper shield. This segmentation allows both benefits to coexist without contradiction
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 demagnetization of magnetic bias layer tails reduces signal noise, increases the signal-to-noise ratio, and allows for a thinner read gap, enhancing data density without increasing the read gap thickness.
Implementation Method 1
magnetic coupling between a magnetic bias layer and an upper magnetic shield
Implementation Method 2
first nonmagnetic protective layers 308, 318 respectively disposed between the upper magnetic shield 306 and first and second magnetic bias layers 302, 314
Implementation Method 3
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor, or a Tunnel Junction Magnetoresisive (TMR) sensor
Data Source
AI summary
A magnetic sensor having reduced read gap thickness, reduced signal noise and improved signal to noise ratio. The sensor includes a sensor stack and hard bias structures formed at either side of the sensor stack for biasing the free layer of the sensor. A protective layer is formed over a portion of the hard bias structure, however a portion of the hard bias structure extends upward toward the upper shield and is disposed between the protective layer and the sensor stack as a result of the process used to form the magnetic bias structure. This portion of the hard bias structure that extends toward the upper shield has a reduced magnetization relative to the rest of the hard bias structure so that it will not magnetically couple with the upper shield.