MTJ Pillar and SOT-Line Patterning for Self-Aligned Switching
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Solution Overview
Problem
The challenge in fabricating magnetic tunneling junction (MTJ) devices is the difficulty in aligning the spin-orbit torque (SOT) layer with the MTJ pillar during scaling, leading to current circumvention and reduced SOT-effect, which affects the switching efficiency of the free layer magnetization.
Innovation Solution
A method is developed to form self-aligned MTJ pillars and SOT-lines by using a combination of etch masks and sidewall spacers, allowing for precise control of dimensions and alignment, thereby minimizing current circumvention and enhancing the SOT-effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the SOT-layer is made larger than the cross-section of the MTJ pillar to ensure contact, then the alignment between SOT-layer and MTJ pillar is improved, but current circumvention occurs and SOT-effect is reduced
Solution Approach 1:
The patent introduces an intermediary patterning process with etch masks and sidewall spacers that acts as a mediator between the independently formed SOT-layer and MTJ pillar. This intermediary process enables precise alignment and size matching, preventing current circumvention while ensuring proper contact between the two components.
Solution Approach 2:
The patent applies preliminary patterning actions to both the SOT-layer and MTJ pillar structures before final assembly. By pre-defining the geometric boundaries and alignment features of both components separately, then combining them through controlled etching processes, the method ensures precise alignment without requiring one component to be oversized.
2Ease of manufacture
If independent patterning of MTJ pillar and SOT-layer is used to simplify fabrication, then manufacturing complexity is reduced, but alignment precision deteriorates
Solution Approach 1:
The patent employs self-aligned patterning where the etch masks and sidewall spacers automatically define the relative positions of the SOT-layer and MTJ pillar features. The process uses the structures themselves as alignment references, eliminating the need for complex external alignment procedures while maintaining high precision.
Solution Approach 2:
The patent segments the patterning process into distinct stages: forming etch masks, creating sidewall spacers, and performing controlled etching. This segmentation allows each step to be optimized independently, maintaining fabrication simplicity while achieving precise alignment through the cumulative effect of multiple controlled steps.
3Area of stationary object
If the SOT-layer size is increased to ensure coverage, then contact area with MTJ pillar is improved, but current circumvention increases and switching efficiency decreases
Solution Approach 1:
The patent changes the geometric parameters of the SOT-layer to precisely match the MTJ pillar cross-section dimensions. By controlling the size and shape parameters through controlled patterning rather than using a larger fixed size, the method ensures adequate contact area while preventing current circumvention, thereby maintaining high switching efficiency.
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 approach enables efficient magnetization switching of the free layer by ensuring proper alignment and contact between the SOT-layer and the MTJ pillar, improving the switching characteristics and reducing current circumvention, thus enhancing the performance of MTJ devices.
Implementation Method 1
The free layer magnetization direction may alternatively be controlled by a spin-orbit torque (SOT) effect wherein the magnetization direction is changed by passing a current through an additional SOT-generating layer arranged below the MTJ layer structure
Implementation Method 2
The data storing function of an MRAM device may be provided by magnetic tunneling junction (MTJ) devices
Data Source
AI summary
According to an aspect, there is provided a method of forming a magnetic tunneling junction (MTJ) device, including: forming a layer stack including an MTJ layer structure and a spin-orbit torque (SOT) layer below the MTJ layer structure; forming a first etch mask over the layer stack, the first etch mask including a first mask line extending in a first horizontal direction; patterning the layer stack to form an MTJ line extending in the first horizontal direction, the patterning including etching while the first etch mask masks the layer stack, and stopping etching on or above the SOT-layer; forming sidewall spacers on one or both sides of the MTJ line; while the sidewall spacers mask the SOT-layer, etching the SOT-layer to form a patterned layer stack including the MTJ line and a first patterned SOT-layer; forming a second etch mask over the patterned layer stack, the second etch mask including a second mask line extending in a second horizontal direction across the MTJ line; and patterning the patterned layer stack to form a twice patterned SOT-layer, the twice patterned SOT-layer including an SOT-line extending in the second horizontal direction, and to form an MTJ pillar on the SOT-line, the patterning including etching while the second etch mask masks the patterned layer stack.