Perpendicular STTMRAM Scaling Thermal Stability
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Solution Overview
Problem
Current spin-torque transfer magnetic random access memory (STTMRAM) designs with in-plane magnetization struggle to scale below 65 nm due to thermal instability and higher costs, requiring a more stable and cost-effective solution for smaller feature sizes.
Innovation Solution
A multi-state STTMRAM with stacked magnetic tunnel junctions (MTJs) having at least one MTJ with a magnetization direction perpendicular to the plane, utilizing magnetic anisotropy to achieve lower switching currents and higher thermal stability, allowing for scalability down to 30 nm with circular or cylindrical bit shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If in-plane magnetization is used in STTMRAM, then the device structure is simpler, but thermal stability deteriorates and scaling below 65 nm becomes impossible
Solution Approach 1:
The patent transitions from in-plane magnetization to perpendicular magnetization, changing the dimension of magnetic anisotropy. This dimensional change enables thermal stability and scalability to below 65 nm while maintaining device functionality, directly resolving the contradiction between structural simplicity and thermal stability.
Solution Approach 2:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular orientation. This parameter change fundamentally alters the thermal stability characteristics and switching behavior, enabling the memory to achieve both stability and scalability without sacrificing device structure simplicity.
2Device complexity
If in-plane magnetization is used in STTMRAM, then the device structure is simpler, but scalability to smaller feature sizes below 65 nm deteriorates
Solution Approach 1:
By switching to perpendicular magnetization, the patent enables scaling to smaller feature sizes below 65 nm. The perpendicular orientation provides better thermal stability at reduced dimensions, directly improving scalability while the device structure remains relatively simple.
Solution Approach 2:
Changing the magnetic anisotropy from in-plane to perpendicular orientation fundamentally improves scalability. This parameter change allows the memory cells to maintain stability at smaller feature sizes, enabling continued miniaturization without compromising device structure simplicity.
3Reliability
If perpendicular magnetization is used in STTMRAM, then thermal stability and density increase, but device complexity increases
Solution Approach 1:
The perpendicular magnetization approach achieves high thermal stability and density through dimensional change rather than structural complexity. The bit shape and stacking arrangement provide the necessary stability without requiring complex device structures, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The patent employs circular or cylindrical bit shapes instead of elongated rectangular shapes. This curvature provides uniform magnetic properties and better thermal stability while simplifying the overall device structure, avoiding the need for complex elongated geometries to achieve the same stability.
4Quantity of substance
If perpendicular magnetization is used in STTMRAM, then density increases, but manufacturing challenges increase at lower lithography geometry
Solution Approach 1:
The circular or cylindrical bit shapes are inherently more manufacturable at lower lithography geometries compared to elongated rectangular shapes. The curved geometry is easier to define and control during fabrication, reducing manufacturing challenges while achieving high density through perpendicular magnetization.
Solution Approach 2:
By utilizing perpendicular magnetization, the patent achieves high density without relying on elongated in-plane geometries that are difficult to manufacture at small scales. The perpendicular orientation allows compact circular bit shapes that are easier to fabricate, resolving the contradiction between density and ease of manufacture.
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
The perpendicular STTMRAM design achieves lower switching currents, higher thermal stability, and increased density, enabling scalability to smaller feature sizes while reducing manufacturing challenges and costs.
Implementation Method 1
multi-state spin-torque transfer magnetic random access memory
Implementation Method 2
at least one MTJ having a storage layer with a magnetization direction being substantially perpendicular to the plane of the wafer (or substrate)
Data Source
AI summary
A multi-state spin-torque transfer magnetic random access memory (STTMRAM) is formed on a film and includes a first magnetic tunneling junctions (MTJ) having a first fixed layer, a first sub-magnetic tunnel junction (sub-MTJ) layer and a first free layer. The first fixed layer and first free layer each have a first magnetic anisotropy. The STTMRAM further includes a non-magnetic spacing layer formed on top of the first MTJ layer and a second MTJ formed on top of the non-magnetic spacing layer. The second MTJ has a second fixed layer, a second sub-MTJ layer and a second free layer. The second fixed and second free layers each have a second magnetic anisotropy, wherein at least one of the first or second magnetic anisotropy is perpendicular to the plane of the film.