Composite Write Shield for PMR Head Spacing Control
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Solution Overview
Problem
Current perpendicular magnetic recording (PMR) head designs face challenges in achieving optimal mechanical and magnetic performance due to the mismatch in thermal expansion coefficients (CTE) between different materials, leading to variations in writer and reader protrusion, which affect magnetic spacing and recording density.
Innovation Solution
A composite third write shield (pp3) structure is introduced, comprising a lower layer of CoNiFe alloy optimized for magnetic performance and an upper layer of CoFe alloy with low CTE, allowing for simultaneous optimization of mechanical and magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single magnetic alloy layer is used for the write shield, then magnetic performance is optimized, but mechanical performance and spacing control deteriorate due to thermal expansion mismatch
Solution Approach 1:
The write shield is constructed as a composite structure with a lower magnetic alloy layer (CoFeNi or CoNiFe) optimized for magnetic performance and an upper layer (CoFe or CoFeB) with low CTE for thermal stability. This composite approach allows simultaneous optimization of both magnetic properties and mechanical spacing control, resolving the contradiction between magnetic performance and spacing precision.
Solution Approach 2:
Different regions of the write shield are assigned different material properties: the lower layer near the pole tip uses high-moment magnetic alloy for optimal write field generation, while the upper layer uses low-CTE material for thermal expansion control. This local differentiation of material quality allows each region to fulfill its specific functional requirement.
2Productivity
If dynamic flying height power is applied to actuate the reader or writer, then recording density improves, but protrusion variations increase due to thermal expansion
Solution Approach 1:
The patent explicitly addresses thermal expansion effects by using a low-CTE material for the upper layer of the write shield. This material choice compensates for the thermal expansion caused by DFH power, maintaining stable protrusion and magnetic spacing even when dynamic flying height actuation is applied to improve recording density.
3Power
If writer protrusion is much greater than reader protrusion, then write field performance improves, but reader spacing increases reducing read back signal
Solution Approach 1:
The composite write shield structure allows independent optimization of protrusion parameters for both writer and reader functions. The low-CTE upper layer provides stable thermal expansion characteristics that enable precise control of the writer protrusion, while the overall shield geometry can be tuned to maintain optimal reader spacing, thus balancing write field strength and read back signal quality.
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 composite shield structure maintains high magnetic performance while providing better control over read/write head spacing, enhancing recording density and reliability by minimizing protrusion variations due to thermal expansion.
Implementation Method 1
coils that conduct a current and generate a magnetic flux in the main pole that exits through a write pole tip and enters a magnetic media
Implementation Method 2
an upper layer of CoFe alloy with low CTE, allowing for simultaneous optimization of mechanical and magnetic properties
Data Source
AI summary
A PMR writer in a read/write head is disclosed wherein an upper shield covering the coil layer is comprised of a magnetic layer optimized for magnetic performance and a second layer used for tuning mechanical protrusion. The composite layer simultaneously provides high saturation magnetization and high permeability from the magnetic layer and low CTE from the second layer which tunes the relative spacing between the writer, reader, and the rest of the slider. In one embodiment, first and second write shields are formed on a write gap layer and have front portions at the ABS and back portions in a back gap region. The upper write shield connects on one side with the second write shield at the ABS and on a second side with the back gap region. This design can yield better reader and writer spacing for the same physical clearance which enables products with higher recording density.