Cross-Point MRAM Selector Rails With Notched MTJ Isolation
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Solution Overview
Problem
Current magnetic memory devices face challenges in efficiently manufacturing cross-point magnetoresistive random access memory arrays with selector rails, particularly in forming a two-dimensional periodic array of magnetic tunnel junctions and selector-containing notched rail structures that maintain proper electrical isolation and structural integrity.
Innovation Solution
The solution involves forming vertical stacks of electrically conductive lines and selector rails over a substrate, patterning magnetic tunnel junction material layers to create a two-dimensional array of magnetic tunnel junctions and periodic notches in the selector rails, and depositing a dielectric matrix layer that surrounds the magnetic tunnel junction pillar structures, ensuring proper electrical isolation and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-dimensional periodic array of magnetic tunnel junctions and selector-containing notched rail structures is formed, then the memory device achieves proper electrical isolation and structural integrity, but the manufacturing process becomes complex and time-consuming
Solution Approach 1:
The selector rail structure is segmented into notched sections, where the notches create discrete electrical isolation regions. This segmentation allows the formation of multiple magnetoresistive devices along a continuous rail while maintaining electrical isolation between adjacent devices, reducing the need for individual processing steps for each device.
Solution Approach 2:
The patent combines multiple functions into the selector rail structure: it serves as both a common electrode for multiple MTJs and an electrical isolation structure through its notched design. This merging reduces the total number of separate components and processing steps required compared to fully discrete device structures.
2Reliability
If selector rails with periodic notches are formed to isolate magnetic tunnel junctions, then electrical isolation is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The notches in the selector rail are formed with periodic spacing, creating a repeating pattern that can be manufactured using standard photolithography and etching processes. This periodic structure allows for consistent electrical isolation using established manufacturing techniques rather than requiring custom high-precision processes for each notch.
Solution Approach 2:
The electrical isolation is achieved by controlling the depth and spacing parameters of the notches rather than requiring extremely precise lateral positioning. By adjusting the etch depth and notch spacing, adequate electrical isolation can be achieved with standard manufacturing tolerances.
3Device complexity
If vertical stacks of conductive lines and selector rails are formed, then the cross-point memory array structure is achieved, but the manufacturing time and process steps increase
Solution Approach 1:
The selector rails and conductive lines are formed as vertical stacks in a preliminary structuring step, establishing the three-dimensional cross-point array framework before depositing the magnetic tunnel junction materials. This preliminary action allows subsequent processing to focus only on the active memory elements rather than forming the entire array structure from scratch.
Solution Approach 2:
The patent transitions from planar device formation to three-dimensional vertical stacking, where selector rails and conductive lines are formed at different heights and positions in the vertical dimension. This dimensional change enables higher device density and more efficient use of fabrication space compared to traditional planar approaches.
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 the effective formation of a cross-point magnetoresistive memory array with improved electrical isolation and structural integrity, enhancing the reliability and performance of the memory device.
Implementation Method 1
Spin-transfer torque (STT) refers to an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve is modified by a spin-polarized current
Implementation Method 2
A spin polarized current is one in which electrons have a net non-zero spin due to a preferential spin orientation distribution. A spin-polarized current can be generated by passing electrical current through a magnetic polarizer layer
Implementation Method 3
When the spin-polarized current flows through a free layer of a magnetic tunnel junction or a spin valve, the electrons in the spin-polarized current can transfer at least some of their angular momentum to the free layer, thereby producing a torque on the magnetization of the free layer
Implementation Method 4
A resistance differential of a magnetic tunnel junction between different magnetization states of the free layer can be employed to store data within the magnetoresistive random access memory (MRAM) cell depending if the magnetization of the free layer is parallel or antiparallel to the magnetization of the polarizer layer
Data Source
AI summary
A method of forming a memory device includes forming vertical stacks each including a respective first electrically conductive line and a respective selector rail over a substrate, such that the vertical stacks laterally extend along a first horizontal direction and are laterally spaced apart from each other along a second horizontal direction, forming magnetic tunnel junction material layers over the vertical stacks, and patterning the magnetic tunnel junction material layers and an upper portion of each of the selector rails to form a two-dimensional array of magnetic tunnel junctions and periodic notches at least in an upper portion of each of the selector rails.