Buffer Layer Doping in STT-MRAM MTJ for Thermal Stability
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Solution Overview
Problem
Magnetic random access memory (MRAM) devices, particularly spin transfer torque magnetic random access memory (STT-MRAMs), face challenges in scalability due to thermal stability and writeability issues, and existing technologies struggle to achieve high tunnel magneto-resistance (TMR) while being easy to manufacture.
Innovation Solution
An MRAM device with a magnetic tunnel junction (MTJ) stack comprising a CoFeB magnetic reference layer, a MgO barrier layer, and a CoFeB magnetic free layer, where a buffer layer of Co, Fe, or CoFe doped with C or N is used to control diffusion and induce strain, allowing for improved crystalline quality, thermal robustness, and increased TMR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CoFeB/MgO/CoFeB MTJ stack is used to achieve high TMR, then thermal stability improves, but manufacturing complexity increases due to crystallization sequence requirements
Solution Approach 1:
A buffer layer comprising at least one of Co, Fe, CoFe and CoFeB is introduced between the MgO barrier layer and the CoFeB magnetic layer. This intermediary layer mediates the crystallization process by providing a nucleation site that allows MgO to crystallize first and transfer its 001 texture to the CoFeB, simplifying the manufacturing process while maintaining high TMR and thermal stability
Solution Approach 2:
The buffer layer changes the crystallization parameters of the CoFeB layer by controlling the sequence of crystallization. It enables the MgO layer to crystallize at a lower temperature first, establishing the 001 texture before CoFeB crystallizes, thereby avoiding the need for high-temperature processing and simplifying manufacturing
2Quantity of substance
If the CoFeB layer is made thinner to increase memory density, then device scaling improves, but interface degradation increases
Solution Approach 1:
The buffer layer acts as a protective intermediary between the MgO barrier layer and the thin CoFeB magnetic layer. It prevents direct interaction and degradation at the interface, allowing the use of thinner CoFeB layers (reducing memory cell size and increasing density) while maintaining interface quality and device reliability
Solution Approach 2:
The buffer layer is formed in advance before the final CoFeB layer is completed. It prepares the interface structure beforehand, preventing degradation during subsequent processing steps and enabling the use of thinner magnetic layers without compromising interface integrity
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 buffer layer enhances the thermal robustness and TMR of the MTJ, enabling a thinner CoFeB layer, reduced interface degradation, and increased memory density, while allowing for a wider process window during manufacturing, thus addressing the scalability and thermal stability limitations of STT-MRAMs.
Implementation Method 1
diffusion of B may affect or determine the crystallization process of CoFe. Thus, by adding B to the CoFe, so as to form CoFeB, the crystallization of CoFe can be delayed enough to let the MgO crystallize first
Implementation Method 2
The intermediate barrier layer is adapted to allow tunnelling of electrons between the reference layer and the free layer
Implementation Method 3
forming a buffer layer comprising at least one of Co, Fe, CoFe and CoFeB and being doped or provided with at least one of C and N
Data Source
AI summary
The disclosed technology generally relates to magnetic memory devices, and more particularly to spin transfer torque magnetic random access memory (STT-MRAM) devices having a magnetic tunnel junction (MTJ), and further relates to methods of fabricating the STT-MRAM devices. In an aspect, a magnetoresistive random access memory (MRAM) device has a magnetic tunnel junction (MTJ). The MTJ includes a magnetic reference layer including CoFeB, a magnetic free layer comprising CoFeB, and a barrier layer including MgO. The barrier layer is interposed between the magnetic reference layer and the magnetic free layer. The barrier layer has a thickness adapted to tunnel electrons between the magnetic reference layer and the magnetic free layer sufficient to cause a change in the magnetization direction of the variable magnetization under a bias. The MTJ further comprises a buffer layer comprising one or more of Co, Fe, CoFe and CoFeB, where the buffer layer is doped with one or both of C and N.