MTJ Insertion Layer Structure for Boron Diffusion Blocking
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Solution Overview
Problem
Conventional magnetic tunnel junction (MTJ) structures in magnetoresistive random access memory (MRAM) devices face challenges in achieving high perpendicular magnetic anisotropy, low damping, high spin transfer torque efficiency, small coercivity and critical voltage distribution, and high tunnel magneto-resistance ratio due to imperfections such as grain boundaries and diffusion of species from electrodes.
Innovation Solution
Incorporating a non-magnetic amorphous insertion layer with a tri-layer structure between the seed layer and the bottom electrode, comprising an amorphous magnetic film, a non-magnetic conductive film, and a non-magnetic metal film, which helps in preventing crystallinity and impurity diffusion, and improving the texture seeding and interface quality of the MTJ stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MTJ structure is used with a simple seed layer, then the device structure is simple and easy to manufacture, but the perpendicular magnetic anisotropy is insufficient and grain boundaries cause high damping and low TMR ratio
Solution Approach 1:
The seed layer is segmented into multiple functional layers: a non-magnetic amorphous insertion layer (bottom layer) directly on the bottom electrode, a non-magnetic conductive middle layer, and a conventional seed layer (top layer). This segmentation allows each layer to perform its specific function - the amorphous bottom layer provides texture seeding and prevents grain boundary formation, while the other layers provide conductivity and magnetic properties, thereby resolving the contradiction between improved reliability and increased complexity.
Solution Approach 2:
The invention uses a composite structure combining different material types in the seed layer: non-magnetic amorphous material (e.g., SiOx, Nx, or CoFeB with specific composition), non-magnetic conductive material (e.g., Ru, Rh, Ir), and conventional seed layer material (e.g., Pt, Co, Ir, Ru). This composite approach enables the system to achieve high perpendicular magnetic anisotropy and low damping by preventing grain boundary formation while maintaining electrical conductivity and magnetic properties.
2Reliability
If species diffusion from electrodes is allowed, then the manufacturing process is simpler without diffusion barriers, but the interface quality deteriorates and TMR ratio decreases
Solution Approach 1:
The non-magnetic amorphous insertion layer acts as an intermediary between the bottom electrode and the seed layer. It prevents direct contact and diffusion between the electrode and magnetic layers, thereby maintaining interface quality and high TMR ratio. The amorphous structure of this layer specifically blocks diffusion pathways while its texture properties promote beneficial (111) orientation in the MTJ stack, resolving the contradiction between improved reliability and increased complexity.
3Ease of manufacture
If crystalline seed layer is used directly on bottom electrode, then the deposition process is simpler, but grain boundaries form causing high damping and low spin transfer torque efficiency
Solution Approach 1:
The non-magnetic amorphous insertion layer is deposited first as a preliminary layer before the conventional seed layer. This preliminary action creates a texture-seeded amorphous foundation that promotes (111) orientation in subsequent layers and prevents grain boundary formation. By performing this texturing action in advance, the conventional seed layer can be deposited more easily without causing grain boundary issues, thus resolving the contradiction between manufacturing simplicity and torque efficiency.
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 the uniformity of radial resistance-area products and tunnel magnetoresistance, improves the (111) texture formation, and prevents boron diffusion, leading to improved thermal stability and performance of the MTJ structure.
Implementation Method 1
a non-magnetic amorphous insertion layer disposed between the seed layer and the bottom electrode
Implementation Method 2
A MTJ element is based on tunnel 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 or tunnel barrier layer. If the tunnel barrier layer is thin enough (typically a few angstroms to a few nanometers), electrons can tunnel from one ferromagnet into the other.
Implementation Method 3
the amorphous magnetic film comprises (CoxFe100-x)yB100-y, wherein 0≤x≤100 and 20≤y≤80
Data Source
AI summary
A semiconductor memory device includes a bottom electrode, a magnetic tunnel junction (MTJ) structure disposed over the bottom electrode, a seed layer disposed between the MTJ structure and the bottom electrode, and a non-magnetic amorphous insertion layer disposed between the seed layer and the bottom electrode.