Spin Injection Write Magnetic Memory Device Cell Architecture
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Solution Overview
Problem
The scaling down of magnetic memory devices leads to unintended data writing in neighboring memory cells due to the magnetic field from write lines, and the magnetic field write method requires high current consumption, making it difficult to achieve high integration and low power consumption.
Innovation Solution
A spin-injection write type magnetic memory device is designed with memory cells and select transistors, where two adjacent memory cells share nodes connected to interconnects, allowing for bi-directional current flow without the need for magnetoresistance effect elements between write lines, thereby reducing unintentional writing and current requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic field write method is used, then writing capability is achieved, but unintentional write into neighboring memory cells occurs and power consumption increases
Solution Approach 1:
The patent replaces the magnetic field-based write mechanism with a spin-injection write mechanism. Instead of using current in write lines to generate magnetic fields that indirectly affect memory cells, the invention uses spin-polarized current injected directly into the magnetoresistance effect element through the select transistor. This direct electrical injection method eliminates the magnetic field interference that causes unintentional writes in neighboring cells while maintaining reliable writing capability.
2Reliability
If magnetic field write method is used, then writing function is implemented, but large current is required generating high power consumption
Solution Approach 1:
The patent substitutes the magnetic field generation approach with direct spin-injection current flow. By injecting spin-polarized current directly through the select transistor into the magnetoresistance effect element, the system achieves writing function with significantly reduced current requirements compared to the magnetic field write method, thereby lowering power consumption.
3Productivity
If scale-down of memory device is performed, then integration density increases, but magnetic field from write line unintentionally writes neighboring cells
Solution Approach 1:
The patent replaces the magnetic field-based writing mechanism with direct spin-injection through the select transistor. This substitution eliminates the magnetic field interference that becomes problematic at scaled-down dimensions where write lines are closer to memory cells. The direct current injection method maintains data integrity in high-density configurations where integration density is maximized.
Solution Approach 2:
The patent changes the fundamental parameter of the write mechanism from magnetic field generation to spin-injected current flow. This parameter change allows the system to maintain reliable writing operation at scaled-down dimensions where the magnetic field approach would cause unintentional writes in neighboring cells due to increased proximity and field coupling.
4Productivity
If spin-injection write method is used, then unintentional write is avoided and write speed increases, but bi-directional current requirement complicates arrangement of memory cells and interconnects
Solution Approach 1:
The patent segments the current flow path by introducing a select transistor that controls current direction into the magnetoresistance effect element. This segmentation allows the system to achieve bi-directional current capability through a single transistor switch rather than requiring complex multi-terminal structures, thereby managing the arrangement complexity while maintaining high write speed and preventing unintentional writes.
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 prevents unintentional writing in neighboring cells and reduces power consumption while enabling high-speed magnetization switching and high integration by using spin-injection write method effectively.
Implementation Method 1
A magnetic random access memory (MRAM) uses a magnetoresistance effect element as a memory cell. The magnetoresistance effect element includes a free layer (recording layer) having a free magnetization (spin) direction, and a pinned layer having a fixed magnetization direction. When the magnetization direction of the free layer is parallel with that of the pinned layer, the element exhibits the low resistance. On the other hand, when the magnetization direction of the free layer is antiparallel with that of the pinned layer, the element exhibits the higher resistance.
Implementation Method 2
spin-injection write (magnetization switching) has attracted interests (see U.S. Pat. No. 5,695,864). This write method involves carrying a current which is spin-polarized by a magnetic moment of a pinned layer to a free layer of a magnetoresistance effect element to change its magnetization direction to write data in accordance with the current direction.
Data Source
AI summary
A spin injection write type magnetic memory device includes memory cells which have a magnetoresistance effect element and a select transistor. The magnetoresistance effect element has one end connected to a first node. The select transistor has a first diffusion area connected to another end of the magnetoresistance effect element and a second diffusion area connected to a second node. A select line extends along a first direction and is connected to a gate electrode of the select transistor. A first interconnect extends along a second direction and is connected to the first node. A second interconnect extends along the second direction and is connected to the second node. Two of the memory cells adjacent along the first direction share the first node. Two of the memory cells adjacent along the second direction share the second node.