MRAM Shield Vias for Magnetic Interference
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Solution Overview
Problem
Current magnetic shielding methods for MRAM chips are inadequate due to limited success in positioning large volume soft-magnetic shielding material close to the MTJ bearing surface, leading to ineffective field cancellation and increased costs, especially with full-wrap-around shields and thin shield deposition in the wafer process.
Innovation Solution
Incorporating one or more soft-magnetic shields with vias for bonding wires, allowing minimal spacing between the shield and chip, and using a ferro-fluid to form a hardened shield, which can be laminated or externally attached, to achieve effective magnetic field cancellation while maintaining low costs and flexibility during packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sheet shields are positioned close to the MRAM chip to improve shielding effectiveness, then magnetic field cancellation is enhanced, but bonding wires cannot pass through and must route around, increasing complexity and reducing shielding effectiveness
Solution Approach 1:
The shield is segmented by creating via holes that divide the shield into regions, allowing bonding wires to pass through the via holes while maintaining shield continuity around the wires. This segmentation resolves the conflict between needing close shield placement for effectiveness and needing wire routing paths.
Solution Approach 2:
The via holes act as intermediaries that provide pathways for bonding wires to pass through the shield without compromising the shield's magnetic field cancellation capability. The shield material is configured to maintain continuity around the via holes, allowing wires to pass through while preserving shielding effectiveness.
2Reliability
If partial-wrap-around or full-wrap-around shields are used to improve magnetic field cancellation, then shielding effectiveness is enhanced, but packaging process cost and difficulty increase
Solution Approach 1:
The shield is implemented as a planar structure with via holes rather than a wrap-around configuration. This segmentation into a flat shield with through-holes simplifies the packaging process while maintaining effective magnetic field cancellation through the via hole pathways.
Solution Approach 2:
The complex wrap-around geometry is extracted and replaced with a simpler planar shield structure. The essential shielding function is retained through the via hole configuration, eliminating the manufacturing complexity of wrap-around shields.
3Ease of manufacture
If coating or electro-depositing shield material onto chip or wafer surface is used to simplify packaging, then manufacturing complexity is reduced, but additional wafer manufacturing cost is incurred and sufficiently large thickness cannot be achieved
Solution Approach 1:
The shield structure with via holes is prepared in advance as a separate component before final assembly with the chip. This preliminary preparation allows optimization of the shield geometry and via hole placement without adding complexity to the wafer fabrication process, while achieving sufficient thickness.
Solution Approach 2:
The via holes are integrated into the shield structure, nesting the wire routing function within the shield itself. This nested configuration allows the shield to maintain sufficient thickness while providing pathways for bonding wires, avoiding the need for thin deposited layers.
4Ease of manufacture
If the shield's physical dimension is smaller than the MRAM chip size to reduce cost, then manufacturing cost is reduced, but the cancelling field at the chip edge is limited and usable area for MRAM data storage is reduced
Solution Approach 1:
The shield provides enhanced local magnetic field cancellation at critical regions through the via hole configuration, allowing effective shielding with a smaller overall shield footprint. This localized quality enhancement maintains usable chip area while providing adequate shielding where most needed.
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 proposed solution effectively reduces external magnetic field interference with MRAM chips by positioning large volume soft-magnetic shielding material close to the MTJ bearing surface, enhancing shielding strength and reducing costs associated with full-wrap-around shields and wafer deposition processes.
Implementation Method 1
The shields, under the external magnetic fields, are supposed to produce a counteracting field at the MTJ locations of the MRAM chip and reduce the total field on the MTJ
Implementation Method 2
one or more soft-magnetic shields shaped into blocks or sheets are positioned close to STT-MRAM chip
Data Source
AI summary
Chip packages are described with soft-magnetic shields that are included inside or attached externally to the package containing a MRAM chip. In one group of embodiments a single shield with vias for bonding wires is affixed to the surface of the MRAM chip having the contact pads. The limitation of shield to chip distance due to bonding wire is eliminated by VIA holes according to the invention which achieves minimal spacing between the shield and chip. A second shield without vias can be positioned on the opposite side of the chip from the first shield. In one group of embodiments a hardened ferro-fluid shield can be the only shield or the structure can include a shield with or without vias. One group of embodiments includes an external shield with vias for solder access to the package contact pads affixed to the outer surface of the package.