Magnetoresistive Element Alloy Cap Layer Thermal Stability
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Solution Overview
Problem
Conventional magnetic random access memory (MRAM) technologies face challenges in simultaneously achieving high thermal stability and a high magnetoresistive ratio (MR ratio) due to issues with element diffusion and abnormal oxidation in the cap layer of magnetic tunnel junction (MTJ) elements.
Innovation Solution
A magnetoresistive element is designed with a nonmagnetic alloy cap layer formed from materials with specific standard electrode potentials, where one metal material has a high ionization tendency to prevent abnormal oxidation and another with low ionization tendency to suppress diffusion, and optionally a diffusion suppressing layer to further enhance thermal stability and MR ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional cap layer is used to prevent element diffusion, then thermal stability is improved, but abnormal oxidation occurs and MR ratio decreases
Solution Approach 1:
The cap layer is segmented into multiple sub-layers with different materials and functions. The first cap layer (Ru) prevents oxidation, while the second cap layer (Ta) suppresses element diffusion. This segmentation allows each layer to specialize in one function, resolving the contradiction between preventing oxidation and suppressing diffusion.
Solution Approach 2:
The invention uses a composite cap layer structure combining Ru and Ta materials. Ru provides oxidation resistance while Ta provides diffusion suppression. The composite structure leverages the complementary properties of different materials to simultaneously achieve both thermal stability and high MR ratio.
2Stability of the object's composition
If the cap layer prevents element diffusion from upper layers, then thermal stability is improved, but element diffusion from the cap layer itself to the free layer occurs
Solution Approach 1:
The first cap layer (Ru) acts as an intermediary between the upper interconnection layer and the free layer. It provides a barrier that prevents element diffusion from the cap layer itself to the free layer, while also protecting against diffusion from upper layers. This intermediary layer resolves the contradiction by providing dual protection.
3Device complexity
If a single-material cap layer is used, then device complexity is reduced, but it cannot simultaneously achieve high thermal stability and high MR ratio
Solution Approach 1:
The cap layer is divided into two distinct sub-layers (Ru and Ta) with different thicknesses and functions. This segmentation enables the structure to achieve high thermal stability and high MR ratio simultaneously, overcoming the limitations of single-material cap layers.
Solution Approach 2:
The invention optimizes the thickness parameters of each cap layer sub-layer. The first cap layer has a thickness of 1-5 nm and the second cap layer has a thickness of 2-10 nm. These parameter optimizations ensure that each layer performs its intended function effectively while maintaining overall device performance.
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 solution effectively maintains high thermal stability while enhancing the MR ratio by controlling element diffusion and oxidation, thereby improving the performance of MTJ elements in MRAM.
Implementation Method 1
one metal material having a second standard electrode potential lower than the first standard electrode potential... having a high ionization tendency to prevent abnormal oxidation
Implementation Method 2
another with low ionization tendency to suppress diffusion
Implementation Method 3
a magnetoresistive ratio (MR ratio) of 20% or more can be obtained by a tunnel magneto-resistance (TMR) effect
Data Source
AI summary
A magnetoresistive element includes a first magnetic layer which includes a first surface and a second surface and has a first standard electrode potential, a second magnetic layer, a barrier layer which is provided between the second magnetic layer and the first surface of the first magnetic layer, and a nonmagnetic cap layer which contacts the second surface of the first magnetic layer and is formed from an alloy of a first metal material and a second metal material, the first metal material having a second standard electrode potential lower than the first standard electrode potential, the second metal material having a third standard electrode potential higher than the first standard electrode potential.