Hydrogenated Amorphous Silicon Encapsulation for MTJ Stability
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Solution Overview
Problem
Magnetoresistive random access memory (MRAM) devices face challenges in maintaining the stability and coercivity of magnetic tunnel junction (MTJ) elements due to thermal degradation and corrosion, which limits processing temperatures and affects the quality of encapsulation layers, leading to performance and reliability issues.
Innovation Solution
A hydrogenated amorphous semiconductor material is used as an encapsulation layer over the memory cell, formed using plasma-enhanced chemical vapor deposition (PECVD) to improve coercivity and reduce conductance, while maintaining a hydrogen level of approximately 10 to 20 percent, thereby preventing parasitic current paths and enhancing the stability of MTJ elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional encapsulation materials like silicon nitride are used, then adhesion to MTJ metal surfaces is improved, but processing temperatures are limited to below 300°C due to metal migration
Solution Approach 1:
The patent employs a composite encapsulation structure consisting of multiple layers including silicon nitride, silicon oxide, and amorphous silicon. This composite approach allows each layer to perform specific functions: silicon nitride provides strong adhesion to MTJ metal surfaces, silicon oxide offers electrical insulation and chemical stability, and amorphous silicon contributes to stress management and interface quality. The combination enables processing temperatures exceeding 300°C while preventing metal migration through the synergistic protection of multiple layers.
2Productivity
If higher processing temperatures are applied, then fabrication efficiency is improved, but thermal degradation of MTJ elements increases
Solution Approach 1:
The patent implements an encapsulation layer structure designed to protect MTJ elements from thermal degradation before high-temperature processing occurs. The multi-layer encapsulation including silicon nitride, silicon oxide, and amorphous silicon is formed beforehand to create a protective barrier that shields the MTJ from thermal stress, oxidation, and contamination during subsequent high-temperature fabrication steps, thereby enabling higher processing temperatures without compromising MTJ reliability.
3Reliability
If encapsulation quality is improved to prevent corrosion, then device reliability is enhanced, but coercivity of MTJ elements deteriorates
Solution Approach 1:
The patent applies local quality by creating different encapsulation layers with specialized functions at different locations around the MTJ structure. The silicon nitride layer provides strong adhesion and corrosion protection at the interface with MTJ metal surfaces, while the amorphous silicon layer is specifically positioned to manage stress and maintain coercivity. This localized optimization allows the encapsulation to prevent corrosion without adversely affecting MTJ coercivity, as each layer addresses specific local requirements rather than applying a uniform solution.
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 hydrogenated amorphous silicon encapsulation layer effectively increases the coercivity of MTJ elements, reducing the likelihood of demagnetization and maintaining performance and reliability without increasing the back-end-of-line thermal budget, thus improving the overall stability and endurance of MRAM devices.
Implementation Method 1
A hydrogenated amorphous semiconductor material is used as an encapsulation layer over the memory cell, formed using plasma-enhanced chemical vapor deposition (PECVD) to improve coercivity and reduce conductance, while maintaining a hydrogen level of approximately 10 to 20 percent, thereby preventing parasitic current paths
Implementation Method 2
A hydrogenated amorphous semiconductor material is used as an encapsulation layer over the memory cell, formed using plasma-enhanced chemical vapor deposition (PECVD)
Implementation Method 3
The term 'magnetoresistance' describes the effect whereby a change to certain magnetic states of the MTJ storage element results in a change to the MTJ resistance
Data Source
AI summary
Embodiments are directed to an electromagnetic memory device having a memory cell and an encapsulation layer formed over the memory cell. The memory cell may include a magnetic tunnel junction (MTJ), and the encapsulation layer may be formed from a layer of hydrogenated amorphous silicon. Amorphous silicon improves the coercivity of the MTJ but by itself is conductive. Adding hydrogen to amorphous silicon passivates dangling bonds of the amorphous silicon, thereby reducing the ability of the resulting hydrogenated amorphous silicon layer to provide a parasitic current path to the MTJ. The hydrogenated amorphous silicon layer may be formed using a plasma-enhanced chemical vapor deposition, which can be tuned to enable a hydrogen level of approximately 10 to approximately 20 percent. By keeping subsequent processing operations at or below about 400 Celsius, the resulting layer of hydrogenated amorphous silicon can maintain its hydrogen level of approximately 10 to 20 percent.