Chromium Capping Layer for MRAM Thermal Stability
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Solution Overview
Problem
Magnetoresistive random access memory (MRAM) technologies face challenges in achieving high tunnel magneto-resistance ratio (TMR) and magnetic anisotropy stability, particularly at elevated temperatures during the back-end-of-line (BEOL) processing, leading to degradation of magnetic tunnel junction (MTJ) performance.
Innovation Solution
A method involving the formation of a Cr-including capping layer above the pinning layer in a magnetic tunnel junction structure, followed by an anneal step that allows Cr to diffuse into the pinning and reference layers, enhancing thermal robustness and maintaining the TMR/RA ratio during high thermal budget processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MTJ structures are used without Cr diffusion, then the device structure remains simple, but the magnetic anisotropy and TMR ratio degrade at elevated temperatures during BEOL processing
Solution Approach 1:
Chromium is pre-deposited in the pinning layer before BEOL processing, and a preliminary anneal step is performed to initiate Cr diffusion into the reference layer. This preliminary action ensures that the Cr concentration gradient is established before the device undergoes subsequent high-temperature BEOL processing, preventing magnetic anisotropy degradation without requiring complex in-situ control during later steps
Solution Approach 2:
The invention changes the chemical composition parameter by introducing chromium into the pinning layer and controlling its diffusion into the reference layer. By adjusting the Cr concentration and distribution through controlled annealing, the magnetic anisotropy and TMR ratio are enhanced and stabilized against thermal degradation during BEOL processing
2Reliability
If Cr is diffused into the pinning and reference layers, then thermal stability and TMR ratio are improved, but the fabrication process becomes more complex
Solution Approach 1:
The Cr diffusion anneal step is merged with existing process steps such as magnetization reversal annealing or stress relaxation annealing. By combining multiple functions into a single thermal processing step, the invention achieves Cr diffusion for thermal stability improvement without adding significant process complexity
Solution Approach 2:
The pinning layer serves as an intermediary that contains the chromium source. The Cr diffuses from the pinning layer through the tunnel barrier into the reference layer, with the tunnel barrier acting as a controlled diffusion path. This intermediary structure enables precise control over Cr distribution and concentration, improving thermal stability while maintaining fabrication simplicity
3Manufacturing precision
If high TMR ratio is achieved through Cr diffusion, then the magnetic anisotropy is improved, but the junction resistance area product increases
Solution Approach 1:
The chromium concentration is optimized locally in different regions: higher Cr content in the pinning layer to provide stable magnetic anisotropy, and controlled Cr diffusion into the reference layer to enhance TMR ratio. The tunnel barrier thickness is also locally optimized to balance TMR enhancement with resistance control, achieving high magnetic anisotropy precision while minimizing junction resistance increase
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
This approach improves the magnetic anisotropy and coercivity of the reference layer, maintains the TMR/RA ratio, and increases the thermal stability of the magnetoresistive device, preventing degradation at elevated temperatures.
Implementation Method 1
performing an anneal step wherein Cr diffuses from the capping layer into at least the pinning layer
Implementation Method 2
performing an anneal step wherein Cr diffuses from the capping layer into at least the pinning layer
Data Source
AI summary
The disclosed technology generally relates to a magnetoresistive device and more particularly to a magnetoresistive device comprising chromium. According to an aspect, a method of forming a magnetoresistive device comprises forming a magnetic tunnel junction (MTJ) structure over a substrate. The MTJ structure includes, in a bottom-up direction away from the substrate, a free layer, a tunnel barrier layer and a reference layer. The method additionally includes forming a pinning layer over the MTJ structure, wherein the pinning layer pins a magnetization direction of the reference layer. The method additionally includes forming capping layer comprising chromium (Cr) over the pinning layer. The method further includes annealing the capping layer under a condition sufficient to cause diffusion of Cr from the capping layer into at least the pinning layer. According to another aspect, a magnetoresistive device is formed according to the method.