TMR Seed Layer Hf Segmentation for Pin Dispersion
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Solution Overview
Problem
Conventional seed layers in Magnetic Tunneling Junction (MTJ) elements, such as Ta/NiCr composite, are sensitive to surface conditions and result in inconsistent growth, leading to high pin dispersion and suboptimal magnetic properties like high interlayer coupling fields and low exchange coupling fields, which are detrimental to achieving high performance in MRAM and TMR applications.
Innovation Solution
A composite seed layer comprising a lower Ta layer, a middle Hf layer, and an upper NiFe layer with a Ni content of at least 30 atomic % is used, which promotes smoother growth and denser crystal structures in overlying layers, reducing interlayer coupling fields and enhancing exchange coupling fields, thereby stabilizing the magnetoresistive sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional Ta/NiCr composite seed layer is used, then the device structure is simple and easy to manufacture, but the surface is rough and results in high pin dispersion and inconsistent growth
Solution Approach 1:
The seed layer is divided into three distinct sub-layers: a lower Ta layer (5-20 nm) for adhesion and surface preparation, a middle Hf layer (5-20 nm) for promoting smooth crystal growth and reducing pin dispersion, and an upper NiFe layer (10-30 nm) for achieving the desired magnetic properties. This segmentation allows each layer to perform its specific function optimally, resulting in a smooth surface and consistent growth of overlying layers.
Solution Approach 2:
The invention uses a composite seed layer structure combining Ta, Hf, and NiFe materials. Each material contributes unique properties: Ta provides good adhesion and low cost, Hf promotes smooth crystal growth and reduces pin dispersion, and NiFe provides the necessary magnetic properties. This composite approach achieves surface smoothness and consistent growth while maintaining manufacturability.
2Reliability
If the seed layer promotes smooth growth, then the tunnel barrier layer quality improves and TMR ratio increases, but the manufacturing process becomes more complex
Solution Approach 1:
The seed layer is segmented into three functional sub-layers, each contributing to specific aspects of performance. The lower Ta layer ensures adhesion, the middle Hf layer promotes smooth growth, and the upper NiFe layer provides magnetic properties. This segmentation enables the achievement of high TMR ratio through smooth growth promotion while keeping the overall structure manageable and manufacturable.
3Reliability
If a thicker tunnel barrier layer is used to achieve high RA value, then the breakdown voltage increases, but the junction resistance becomes too high to match transistor resistivity
Solution Approach 1:
The invention optimizes the tunnel barrier layer thickness parameter to achieve the desired balance between breakdown voltage and junction resistance. By carefully controlling the thickness parameter within a specific range, the device achieves both high reliability through adequate breakdown voltage and proper resistance matching for circuit integration.
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 composite seed layer enables a more stable and efficient MTJ element with improved magnetic properties, including lower interlayer coupling fields and higher exchange coupling fields, resulting in enhanced performance and reduced pin dispersion, thus addressing the limitations of conventional seed layers.
Implementation Method 1
The composite seed layer comprises a lower Ta layer, a middle Hf layer, and an upper NiFe layer
Implementation Method 2
The thin tunnel barrier layer above the pinned layer is usually comprised of a dielectric material such as AlOx or MgO and is so thin that a current through it can be established by quantum mechanical tunneling of conduction electrons
Implementation Method 3
The pinned layer has a magnetic moment that is fixed in the 'x' direction, for example, by exchange coupling with the adjacent AFM layer that is also magnetized in the 'x' direction
Implementation Method 4
A MTJ element in a magnetic device such as a read head may be based on a tunneling magneto-resistance (TMR) effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer
Data Source
AI summary
A MTJ structure is disclosed in which the seed layer is made of a lower Ta layer, a middle Hf layer, and an upper NiFe or NiFeX layer where X is Co, Cr, or Cu. Optionally, Zr, Cr, HfZr, or HfCr may be employed as the middle layer and materials having FCC structures such as CoFe and Cu may be used as the upper layer. As a result, the overlying layers in a TMR sensor will be smoother and less pin dispersion is observed. The Hex/Hc ratio is increased relative to that for a MTJ having a conventional Ta/Ru seed layer configuration. The trilayer seed configuration is especially effective when an IrMn AFM layer is grown thereon and thereby reduces Hin between the overlying pinned layer and free layer. Ni content in the NiFe or NiFeX middle layer is above 30 atomic % and preferably >80 atomic %.