Co-Cr Seeded MTJ Structure for Low-RA High-TMR Memory Cells
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Solution Overview
Problem
Existing magnetic tunnel junction (MTJ) elements in MRAMs face issues with diffusion of metallic atoms and unwanted magnetic moments due to chemical potential differences, leading to performance degradation and reduced tunnel magnetoresistance (TMR) coefficient.
Innovation Solution
The MTJ element incorporates a laminated or alloyed Co and Cr films for the seed layer, along with a nitrogen-doped or chromium-alloyed Co-Hf film for the buffer layer, to minimize chemical potential differences and diffusion, enhancing the crystalline texture and reducing grain boundaries, thereby improving the TMR coefficient and lowering the product of resistance and area (RA).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional seed layers are used in MTJ elements, then manufacturing is simpler, but diffusion of metallic atoms and unwanted magnetic moments occur due to chemical potential differences, leading to performance degradation and reduced TMR coefficient
Solution Approach 1:
The patent applies composite materials by using a laminated structure of Co and Cr films in the seed layer. This composite structure minimizes chemical potential differences between adjacent layers, thereby preventing diffusion of metallic atoms and unwanted magnetic moments into the tunnel barrier layer, which resolves the contradiction between maintaining simple manufacturing and achieving high TMR coefficient reliability.
Solution Approach 2:
The patent changes the material parameters of the seed layer by incorporating specific compositions of Co and Cr films with controlled thicknesses. This parameter optimization reduces chemical potential gradients at interfaces, preventing atomic diffusion while maintaining manufacturing feasibility through established sputtering or deposition processes.
2Reliability
If conventional buffer layers are used in MTJ elements, then manufacturing is simpler, but chemical potential differences cause diffusion and unwanted magnetic moments, degrading device performance
Solution Approach 1:
The patent applies composite materials by using a laminated structure of Co and Cr films in the seed layer. This composite structure minimizes chemical potential differences between adjacent layers, thereby preventing diffusion of metallic atoms and unwanted magnetic moments into the tunnel barrier layer, which resolves the contradiction between maintaining simple manufacturing and achieving high TMR coefficient reliability.
Solution Approach 2:
The patent changes the material parameters of the seed layer by incorporating specific compositions of Co and Cr films with controlled thicknesses. This parameter optimization reduces chemical potential gradients at interfaces, preventing atomic diffusion while maintaining manufacturing feasibility through established sputtering or deposition processes.
3Use of energy by moving object
If MTJ elements with reduced RA are designed, then low-power write operations are enabled, but maintaining high yield and stability at elevated temperatures becomes more difficult
Solution Approach 1:
The patent uses composite Co-Cr laminated structures in both the buffer and seed layers, which provide thermal stability through minimized chemical potential differences. This composite approach maintains low RA for energy-efficient write operations while the structurally stable laminated configuration prevents thermal-induced diffusion and magnetic moment contamination, thereby achieving both low power consumption and high thermal reliability.
4Reliability
If grain boundaries are reduced in MTJ elements, then TMR coefficient increases, but manufacturing precision requirements become more stringent
Solution Approach 1:
The patent employs laminated Co and Cr films in the seed layer, where the composite structure promotes epitaxial growth with reduced grain boundaries. The alternating Co-Cr layers provide a template for crystalline alignment, achieving high TMR coefficient through improved crystalline texture while using standard thin-film deposition techniques that do not require excessive manufacturing precision.
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 improved MTJ element achieves lower RA and higher TMR coefficient, enabling low-power write operations with a broader read window and reduced bit-error-rate (BER), while maintaining high yield and stability at elevated temperatures.
Implementation Method 1
a tunnel barrier layer disposed over the reference layer and a free layer disposed over the tunnel barrier layer
Implementation Method 2
enhancing the crystalline texture and reducing grain boundaries, thereby improving the TMR coefficient
Implementation Method 3
minimize chemical potential differences and diffusion
Implementation Method 4
a nitrogen-doped or chromium-alloyed Co-Hf film for the buffer layer
Implementation Method 5
enhancing the crystalline texture and reducing grain boundaries
Data Source
AI summary
A magnetic tunnel junction (MTJ) element is provided. The MTJ element includes a buffer layer, a seed layer disposed over the buffer layer, a first ferromagnetic layer disposed over the seed layer, a tunnel barrier layer disposed over the first ferromagnetic layer and a second ferromagnetic layer disposed over the tunnel barrier layer. The seed layer includes a Cobalt (Co)-based film. The buffer layer includes cobalt (Co) and hafnium (Hf). The buffer layer is alloyed with chromium and has chromium content up to 20 at. %. The MTJ element in accordance with the present disclosure exhibits a low resistance desired for a low-power write operation, and a high TMR coefficient desired for a low bit-error-rate (BER) read operation.