Magnetic Tunnel Junction Seed Layer Structure for High TMR
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Solution Overview
Problem
Existing magnetic tunneling junction devices and memory devices face challenges in achieving high tunneling magnetoresistance (TMR) ratios and exchange fields (Hex), with existing seed layers and manufacturing processes leading to deteriorated crystallinity and reduced performance.
Innovation Solution
Incorporation of amorphous seed layers, such as CoFeX and CoFeXTa, and anti-crystallized layers like YCoFeB, along with controlled heat treatments up to 500°C, to maintain amorphous states and improve crystallinity of the pinned and free layers, enhancing TMR ratios and Hex.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional seed layers are used in magnetic tunneling junction devices, then the manufacturing process is simple, but the crystallinity deteriorates and TMR ratio decreases
Solution Approach 1:
The seed layer is divided into multiple layers with different compositions and functions. The first seed layer (CoFeB) provides initial nucleation, the second seed layer (CoFeX) controls crystallization, and the third seed layer (CoFeXTa) optimizes interface properties. This segmentation allows each layer to be optimized for its specific function, improving overall crystallinity and TMR ratio while managing complexity through functional specialization.
Solution Approach 2:
The invention uses composite seed layer structures combining different materials (CoFeB, CoFeX, CoFeXTa) with specific compositional ratios. These composite structures leverage the advantageous properties of each material: CoFeB for low damping, CoFeX for crystallization control, and CoFeXTa for interface optimization. The composite approach achieves superior crystallinity and TMR performance that cannot be obtained with single-material seed layers.
2Manufacturing precision
If heat treatment temperature is increased to improve crystallinity, then TMR ratio improves, but amorphous layers may crystallize and degrade performance
Solution Approach 1:
The invention optimizes heat treatment parameters (temperature, time, atmosphere) to achieve the desired balance. By controlling the heat treatment temperature range and duration, the process promotes crystallization in the pinned and free layers while maintaining the amorphous state of the seed and anti-crystallized layers. This parameter optimization allows simultaneous achievement of high crystallinity in functional layers and amorphous stability in protective layers.
Solution Approach 2:
The anti-crystallized layer acts as an intermediary between the crystalline pinned layer and the amorphous seed layer. It prevents unwanted crystallization of the seed layer during heat treatment while allowing the pinned and free layers to achieve their desired crystalline structure. This intermediary layer mediates the thermal effects, protecting the amorphous phases from crystallizing at elevated temperatures.
3Reliability
If amorphous seed layers are used to maintain stability at high temperature, then TMR ratio improves, but the manufacturing process becomes more complex
Solution Approach 1:
Different regions of the seed layer structure are assigned different qualities and compositions. The first seed layer (CoFeB) has properties optimized for nucleation, the second layer (CoFeX) for crystallization control, and the third layer (CoFeXTa) for interface optimization. This local quality differentiation allows each region to perform its specific function optimally, achieving high reliability and TMR ratio while managing manufacturing complexity through localized optimization.
Solution Approach 2:
The multi-layer seed structure is prepared in advance with specific compositions and thicknesses to pre-establish the desired crystallization behavior during subsequent heat treatment. The preliminary configuration of the seed layers ensures that during heat treatment, the pinned and free layers will crystallize properly while the seed layers remain amorphous, eliminating the need for complex real-time control during manufacturing.
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 proposed structure and manufacturing process result in magnetic tunneling junction devices with significantly improved TMR ratios and Hex, maintaining stability under high external magnetic fields and enabling efficient data storage in memory devices.
Implementation Method 1
The seed layer includes at least one amorphous material selected from CoFeX and CoFeXTa... The seed layer and the anti-crystallized layer may be maintained in an amorphous state at a temperature of about 300° C. to about 500° C.
Implementation Method 2
performing a heat treatment for crystallizing the pinned layer... The heat treatment may be performed at a temperature of 300° C. to 500° C.
Implementation Method 3
a magnetic tunneling junction device may have low resistance, and when the magnetization directions are opposite to each other, e.g. are antiparallel with each other, the magnetic tunneling junction device may have high resistance
Data Source
AI summary
Provided are a magnetic tunneling junction device having a relatively high tunneling magnetoresistance (TMR) ratio; and a memory device including the magnetic tunneling junction device. The magnetic tunneling junction device includes: a pinned layer having a first surface and a second surface opposite the first surface; a seed layer disposed in contact with the first surface of the pinned layer; a free layer disposed to face the second surface of the pinned layer; and a tunnel barrier layer disposed between the pinned layer and the free layer, wherein the seed layer includes at least one amorphous material selected from CoFeX and CoFeXTa, and the X includes at least one element selected from niobium (Nb), molybdenum (Mo), tungsten (W), chromium (Cr), zirconium (Zr), and hafnium (Hf). The seed layer may not include boron.