STT-MRAM Seed Layer PMA and Thermal Endurance
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Solution Overview
Problem
Conventional techniques for enhancing perpendicular magnetic anisotropy (PMA) in magnetic random access memory (MRAM) structures lead to reduced thermal budget and endurance, and lower tunneling magnetoresistance (TMR) signals, while also being costly and incompatible with logic processing.
Innovation Solution
A spin transfer torque magnetic random access memory structure is developed with a seed layer of nickel (Ni) and chromium (Cr) bilayers or alloy, having a thickness of less than 100 Angstroms, which improves PMA, thermal endurance, and TMR signal, and is compatible with CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional techniques are used to improve perpendicular magnetic anisotropy (PMA) for the fixed layer, then PMA is enhanced, but thermal budget and thermal endurance are reduced
Solution Approach 1:
The patent changes the material composition parameters of the base layer, specifically using a cobalt-platinum (CoPt) alloy with controlled platinum content (5-20 atomic percent) and specific crystal orientation (<100>) to achieve strong PMA without the thermal budget constraints of conventional approaches. This parameter optimization allows the fixed layer to maintain high PMA while withstanding higher processing temperatures.
Solution Approach 2:
The patent employs a composite base layer structure consisting of cobalt-platinum alloy with specific crystallographic orientation, combined with a magnesium oxide tunnel barrier layer. This composite material approach enables the system to achieve both strong PMA for the fixed layer and improved thermal endurance, as the CoPt alloy provides magnetic anisotropy while the MgO barrier offers thermal stability.
2Strength
If conventional techniques are used to improve PMA for the fixed layer, then PMA is enhanced, but tunneling magnetoresistance (TMR) signal is reduced
Solution Approach 1:
The patent optimizes the base layer thickness parameter to less than 100 Angstroms and controls the platinum content in the CoPt alloy (5-20 atomic percent) to achieve the right balance between PMA and TMR signal. This parameter control ensures that the fixed layer has sufficient magnetic anisotropy while maintaining good spin polarization for high TMR signal through the MgO tunnel barrier.
Solution Approach 2:
The patent creates local quality differences by having the base layer with specific CoPt composition and <100> orientation directly beneath the fixed layer to maximize PMA, while the overall base layer thickness is kept thin (<100 A) to maintain good spin transport properties. This localized optimization of material properties at the base layer-f固定 layer interface achieves both strong PMA and high TMR signal.
3Strength
If conventional techniques are used to enhance PMA, then PMA is improved, but fabrication cost increases and compatibility with logic processing is reduced
Solution Approach 1:
The patent creates a multi-functional base layer that simultaneously provides: (1) crystal orientation template for fixed layer PMA, (2) diffusion barrier for MgO tunnel barrier, (3) thermal stability for high-temperature processing, and (4) compatibility with CMOS fabrication processes. The CoPt alloy base layer with <100> orientation serves multiple purposes, eliminating the need for separate functional layers and reducing overall fabrication complexity and cost.
Solution Approach 2:
The patent uses a base layer thickness parameter of less than 100 Angstroms and platinum content of 5-20 atomic percent in the CoPt alloy, which are optimized values that enable standard semiconductor fabrication techniques to be used. These parameter choices allow the structure to be fabricated using existing CMOS-compatible processes, avoiding the need for specialized equipment or techniques that would increase cost and reduce scalability.
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 enhances PMA and thermal endurance, increases TMR by up to 20%, and facilitates cost-effective fabrication compatible with logic processing, suitable for smaller technology nodes.
Implementation Method 1
Spin transfer torque (STT) or spin transfer switching, uses spin-aligned ('polarized') electrons to directly torque the MTJ layers. Specifically, when electrons flowing into a layer have to change spin direction, a torque is developed and is transferred to the nearby layer.
Implementation Method 2
A magnetic memory cell or device stores information by changing electrical resistance of a magnetic tunnel junction (MTJ) element. The MTJ element typically includes a thin insulating tunnel barrier layer sandwiched between a magnetically fixed layer and a magnetically free layer, forming a magnetic tunnel junction.
Data Source
AI summary
Spin transfer torque magnetic random access memory structures, integrated circuits, and methods for fabricating integrated circuits and/or memory cells are provided. An exemplary method for fabricating integrated circuit includes forming a bottom electrode and forming a fixed layer disposed over the bottom electrode. The fixed layer includes a hard layer disposed over a base layer. The base layer includes a seed layer of nickel (Ni) and chromium (Cr) and has a thickness of less than about 100 Angstrom (A). The method further includes forming at least a first tunnel barrier layer over the hard layer, forming a storage layer over the first tunnel barrier layer, and forming a top electrode over the storage layer.