Ordered Alloy Free Layer for STT MRAM Switching
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Solution Overview
Problem
Current spin-transfer torque (STT) MRAM technologies face challenges with high switching current requirements and slow switching speeds in magnetic tunnel junction (MTJ) pillars, leading to potential write errors.
Innovation Solution
A multilayered magnetic free layer structure is introduced, featuring a first magnetic free layer composed of an ordered magnetic alloy with low moment but high magnetic Curie temperature, which reduces the switching current and enhances switching speed by using a non-magnetic layer to couple two magnetic free layers in parallel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a multilayered magnetic free layer structure with two magnetic free layers separated by a non-magnetic layer is used, then the magnetic coupling between layers provides stable parallel alignment, but the switching speed becomes too slow compared to the length of the applied voltage pulse
Solution Approach 1:
The magnetic free layer is divided into two separate magnetic free layers (16 and 20) separated by a non-magnetic layer (18). This segmentation allows each layer to be independently optimized - the first layer provides stability through magnetic coupling while the second layer enables faster switching response to voltage pulses, resolving the contradiction between stability and switching speed.
2Speed
If the magnetic free layer moment is reduced to enable fast switching, then the switching time decreases, but the activation energy decreases which compromises data retention
Solution Approach 1:
Two magnetic free layers are combined in a multilayered structure where the first magnetic free layer (16) has optimized moment for fast switching while the second magnetic free layer (20) contributes to maintaining sufficient activation energy. The magnetic coupling through the non-magnetic layer (18) merges their effects to achieve both fast switching and reliable data retention.
3Use of energy by moving object
If the magnetic damping of the magnetic free layer is lowered to reduce switching current, then the switching current decreases, but the switching speed may be affected
Solution Approach 1:
The first magnetic free layer (16) is designed with low magnetic damping to reduce switching current requirements, while the second magnetic free layer (20) is optimized for fast switching response. This local quality differentiation allows each layer to specialize in one aspect, resolving the contradiction between low switching current and fast switching speed.
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 significantly decreases the switching current needed and improves switching speed, thereby reducing write errors in STT MRAM devices.
Implementation Method 1
The ordered magnetic alloy provides a first magnetic free layer that has low moment (on order of 100 to 500 emu/cm3), but is strongly magnetic (i.e., has a magnetic Curie temperature, Tc, on the order of 200° C. or greater)
Implementation Method 2
The non-magnetic layer 18 is thin enough that the two magnetic free layers (16 and 20) are coupled together magnetically, so that in equilibrium the first and second magnetic free layers 16 and 20 are always parallel
Implementation Method 3
In STT MRAM, spin-transfer torque is used to flip (switch) the orientation of the magnetic free layer
Data Source
AI summary
A multilayered magnetic free layer structure is provided that includes a first magnetic free layer and a second magnetic free layer separated by a non-magnetic layer in which the first magnetic free layer is composed of an ordered magnetic alloy. The ordered magnetic alloy provides a first magnetic free layer that has low moment, but is strongly magnetic. The use of such an ordered magnetic alloy first magnetic free layer in a multilayered magnetic free layer structure substantially reduces the switching current needed to reorient the magnetization of the two magnetic free layers.