MTJ Element Layer Inversion for MRAM Current Driving
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Solution Overview
Problem
Magnetic random access memory (MRAM) technologies face challenges in maintaining high current driving capability and reducing signal variations due to variations in the size of the free layer in MTJ elements, which affect data writing and storage performance.
Innovation Solution
The MTJ elements are configured with the pinned layer closest to the semiconductor substrate, and the tunnel barrier and free layer stacked in a specific order to reduce source voltage increase and maintain high current driving capability, while also minimizing variations in the free layer size through precise wiring and layout configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the MTJ element is configured with the free layer closest to the semiconductor substrate, then the processing alignment is easier, but the source voltage increases due to voltage drop when write current is applied, degrading the current driving capability of the cell transistor
Solution Approach 1:
The patent inverts the conventional MTJ element structure by placing the pinned layer closest to the semiconductor substrate and the free layer farthest from it. This inversion resolves the contradiction by preventing source voltage increase during write operations, thereby maintaining current driving capability while still achieving proper processing alignment through the inverted configuration.
2Ease of operation
If the MTJ element is configured with the pinned layer closest to the semiconductor substrate, then the source voltage increase is suppressed, but the lower free layer becomes separated from the mask during processing, causing variation in free layer size
Solution Approach 1:
The patent applies the inversion principle by swapping the positions of the pinned and free layers. This places the pinned layer (which serves as the reference layer for mask alignment) closest to the semiconductor substrate, ensuring accurate processing alignment, while the free layer is positioned farthest from the substrate, preventing source voltage increase and maintaining current driving capability.
3Reliability
If the free layer size varies among MTJ elements, then the signal variation among memory cells increases, but maintaining uniform free layer size requires complex processing control
Solution Approach 1:
The patent uses the homogeneity principle by ensuring that the pinned layer, which serves as the reference layer, is positioned closest to the semiconductor substrate and is formed with uniform thickness and properties across all MTJ elements. This reference layer uniformity propagates through the tunnel barrier to the free layer, ensuring consistent free layer dimensions and reducing signal variation among memory cells without requiring complex processing control.
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
This configuration enhances the MRAM's ability to efficiently change the state of MTJ elements and reduces signal variations among memory cells, enabling better data storage and retrieval performance with improved scalability.
Implementation Method 1
stores data by a change in a magnetic resistance caused by spin-polarized tunneling
Implementation Method 2
The MTJ element can be switched into a low resistance state or a high resistance state depending on the magnetization orientations of the two ferromagnetic layers
Data Source
AI summary
A memory includes MTJ elements. Active areas are separated to correspond to cell transistors, respectively, and extend in a first direction substantially orthogonal to an extending direction of gates of the cell transistors. The active areas are arranged in the first direction and constitute a plurality of active area columns. Two active area columns adjacent in a second direction are arranged to be half-pitch staggered in the first direction. As viewed from above surfaces of the active areas, each MTJ element is arranged to overlap with one end of each of the active areas. The first and second wirings extend while being folded back in a direction inclined with respect to the first and second directions in order to overlap with the MTJ elements alternately in the adjacent active area columns.