Octagonal Write Pole for MAMR Breakage Prevention
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Solution Overview
Problem
The challenge in manufacturing high-density magnetic recording devices is the breakage of write poles with critical dimensions less than 50 nm during fabrication, which is exacerbated by the difficulty in achieving precise shape control and self-alignment of spin transfer oscillators (STO) and write poles for microwave-assisted magnetic recording (MAMR) applications.
Innovation Solution
An octagonal shaped write pole design is introduced, featuring three sections on each side with specific angles and thicknesses to enhance structural integrity, along with a method of fabrication that includes ion beam etching and chemical mechanical polishing to maintain self-alignment with the STO structure, allowing for precise control of dimensions and preventing breakage during ion milling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a write pole with critical dimension less than 50 nm is used for high-density recording, then recording density is improved, but the write pole becomes prone to breakage during fabrication
Solution Approach 1:
The write pole is divided into three distinct sections along its length: a first section with a first width, a second section with a second width greater than the first, and a third section with a third width. This segmentation allows each section to have optimized dimensions for its specific function, with the middle section providing structural support to prevent breakage while the end sections maintain the narrow profile needed for high-density recording.
Solution Approach 2:
Different sections of the write pole are given different local properties: the middle section has a larger width for structural integrity during fabrication, while the first and third sections have narrower widths for high-density recording. This local differentiation allows the structure to simultaneously satisfy both the need for small dimensions and structural robustness.
2Device complexity
If self-alignment of STO and write pole is achieved, then manufacturing complexity is reduced, but shape control precision becomes difficult to maintain
Solution Approach 1:
The write pole is segmented into three sections with progressively different widths, which provides multiple geometric features for alignment reference. The STO can be aligned to any of these sections with different tolerance requirements, making the overall alignment process more robust while maintaining shape control precision.
Solution Approach 2:
The problem is solved by adding the dimensional variation along the write pole length as an additional degree of freedom for alignment. Instead of relying solely on lateral alignment precision, the design uses the longitudinal dimension (different widths at different positions) to provide alignment references, effectively distributing the alignment tolerance across multiple dimensions.
3Ease of manufacture
If ion milling is used for fabrication, then manufacturing capability is improved, but write pole breakage increases
Solution Approach 1:
The middle section of the write pole is designed with a larger width before the ion milling process, providing a cushion of material that absorbs the mechanical stress and potential breakage during fabrication. This pre-engineered structural reserve allows the use of aggressive ion milling techniques while protecting the critical narrow sections from damage.
Solution Approach 2:
The width parameter of the write pole is varied along its length, creating a non-uniform cross-section. This parameter change provides a structural gradient where the middle section has sufficient material thickness to withstand ion milling stresses, while the end sections maintain the narrow profile needed for high-density recording after fabrication.
Data Source
AI summary
A microwave assisted magnetic recording writer is disclosed with an octagonal write pole having a top portion including a trailing edge that is self aligned to a spin transfer oscillator (STO). Leading and trailing edges are connected by two sidewalls each having three sections. A first section on each side is coplanar with the STO sidewalls and is connected to a sloped second section at a first corner. Each second section is connected to a third section at a second corner where the distance between second corners is greater than the distance between first corners. A method of forming the writer begins with a trapezoidal shaped write pole in an insulation layer. Two ion beam etch (IBE) steps are used to shape top and middle portions of the write pole and narrow the pole width to <50 nm without breakage. Finally, a trailing shield is formed on the STO.