Tapered PMR Write Pole with Vertical Side Walls
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Solution Overview
Problem
PMR writers face significant write pole width variations due to trailing edge taper milling and back end lapping processes, which affect writability and areal density in hard disk drives.
Innovation Solution
A PMR writer design with a trailing edge taper write pole and a fabrication process involving a stack of dielectric and metal layers, where reactive ion etching forms an opening with controlled sidewall angles to minimize pole width variations, including a seed layer for electroplating the main pole layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trailing edge taper is applied to the write pole to improve writability at narrow track widths, then write field gradient is improved, but pole width variation increases due to sensitivity to lapping and milling variations
Solution Approach 1:
The patent applies different geometric characteristics to different portions of the write pole: the trailing edge portion has a tapered shape with angle between 10-45 degrees to improve writability, while the leading edge portion has substantially vertical sidewalls to minimize sensitivity to lapping variations. This local differentiation allows each portion to optimize its function without compromising the other.
Solution Approach 2:
The write pole is segmented into two distinct portions: a trailing edge portion and a leading edge portion. The trailing edge portion extends from the air bearing surface to a first height and has a tapered shape, while the leading edge portion extends from the air bearing surface to a second height greater than the first height and has substantially vertical sidewalls. This segmentation allows independent optimization of each portion's geometry.
2Ease of manufacture
If conventional plating and CMP processes are used to form the write pole, then manufacturing is simplified, but pole width control deteriorates due to width reduction from sloped sidewalls during polishing
Solution Approach 1:
The patent forms the main pole layer with the desired final shape (tapered trailing edge with vertical leading edge) before the CMP process. By pre-defining the pole geometry through selective etching and plating, the subsequent CMP process only needs to planarize the surface without significantly altering the pole width, thereby maintaining both manufacturing simplicity and width control precision.
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 solution reduces pole width variations by maintaining the write pole width independent of taper angle and lapping processes, enhancing writability and reducing sensitivity to neck height variations, thereby improving areal density and yield.
Implementation Method 1
reactive ion etching forms an opening with controlled sidewall angles
Implementation Method 2
including a seed layer for electroplating the main pole layer
Data Source
AI summary
A main pole layer with a tapered trailing side is disclosed that has three sections each with a write pole portion along the ABS and a yoke portion. A lower section has a bottom surface including a leading edge at the write pole tip and sidewalls with a bevel angle between 4 and 20 degrees. The middle section has essentially vertical sidewalls with a tapered side starting at the trailing edge and extending to a back side of the write pole and into the yoke. An upper section includes a portion of the tapered side and a top surface of the main pole layer and has a sidewall with a bevel angle from 0 to 45 degrees. The thickness of the middle section is greater than the pole height variation caused by variations in back end processes including ion milling and lapping to reduce erase width (EW) variations.