Encased MTJ Free Layer Structure for MRAM Electrical Isolation
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Solution Overview
Problem
Conventional methods for fabricating magnetic tunnel junction (MTJ) pillars in MRAM devices face challenges such as electrical shorts due to re-sputtering of conductive metal layers during etching and void formation in inter-layer dielectrics, leading to reduced device reliability.
Innovation Solution
A stepwise method is employed to form MTJ pillars, where the bottom electrode and reference layer are patterned first, followed by dielectric encapsulation, then the tunnel barrier and free layer are formed, encasing the free layer's bottom and sidewall surfaces within the dielectric, reducing the risk of electrical shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional etching methods are used to form MTJ pillars, then manufacturing efficiency is maintained, but re-sputtering of conductive metal layers occurs causing electrical shorts
Solution Approach 1:
The patent applies preliminary action by forming the tunnel barrier layer and free layer structure before completing the pillar etching process. Specifically, the tunnel barrier layer is deposited on the bottom electrode, and the free layer is formed within a recessed area of the reference layer before the final etching steps. This sequence prevents re-sputtering of conductive metal layers during subsequent etching operations, as the protective tunnel barrier layer is already in place.
Solution Approach 2:
The tunnel barrier layer serves as an intermediary protective layer between the conductive bottom electrode and the etching environment. This intermediate layer prevents direct exposure of the conductive metal to re-sputtering during etching operations, thereby eliminating the harmful effect of re-sputtering while maintaining manufacturing efficiency.
2Reliability
If conventional fabrication methods are used, then process simplicity is maintained, but void formation occurs in inter-layer dielectrics
Solution Approach 1:
The patent employs preliminary action by forming the tunnel barrier layer and free layer structure before the final dielectric filling and planarization steps. The tunnel barrier layer is deposited first, followed by free layer formation within the recessed area. This sequence ensures that the MTJ structure is fully formed and encapsulated before inter-layer dielectric materials are deposited, preventing void formation in the dielectric layers while maintaining process simplicity.
3Productivity
If the free layer is fully exposed during fabrication, then manufacturing steps are reduced, but electrical shorts occur between neighboring devices
Solution Approach 1:
The patent applies the nested doll principle by placing the free layer within a recessed area of the reference layer, effectively nesting the free layer structure within the reference layer. The tunnel barrier layer is deposited on the bottom electrode and extends to line the recessed area, creating a nested structure where the free layer is enclosed by the tunnel barrier layer. This nesting prevents electrical shorts between neighboring devices while maintaining manufacturing efficiency by integrating multiple functions into a single structural element.
Data Source
AI summary
A magnetic tunnel junction device and formation thereof. The magnetic tunnel junction device includes a magnetic tunnel junction pillar formed above a bottom electrode. The magnetic tunnel junction pillar includes a reference layer formed on top of the bottom electrode, a dielectric layer formed on top of the reference layer, a free layer formed within the dielectric layer and partially within a recessed area of the reference layer, and a tunnel barrier layer separating the reference layer from the free layer, where the tunnel barrier layer covers bottom and sidewall surfaces of the free layer. The magnetic tunnel junction pillar device further includes a top electrode formed above the magnetic tunnel junction pillar.