SOT Electrode Layer Protection in Magnetoresistive Devices
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Solution Overview
Problem
Magnetic tunnel junctions (MTJs) in spin-orbit-torque (SOT) magnetoresistive random access memory (MRAM) devices face issues with etch damage during the etching process, leading to reduced SOT electrode layer thickness, short spin diffusion length, and deteriorated tunnelling magnetoresistance (TMR) properties, especially when using conventional etching methods.
Innovation Solution
A magnetoresistive device structure with a spin-orbit-torque (SOT) electrode layer, an interface layer with a metal having a spin diffusion length greater than its thickness, and an etch stop layer composed of oxide or nitride material, which prevents over-etching and redeposition of the SOT electrode layer material, ensuring a thicker SOT electrode layer and improved spin current diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional etching process is used to etch the MTJ structure, then the etching speed is improved, but the SOT electrode layer thickness is reduced due to etch damage
Solution Approach 1:
An interface layer is introduced between the SOT electrode layer and the first magnetic layer. This interface layer acts as a mediator that protects the SOT electrode layer from direct exposure to the etching process, thereby preventing etch damage while allowing the etching to proceed at conventional speeds. The interface layer is selectively removed after the MTJ etching is complete.
Solution Approach 2:
The interface layer is formed in advance before the MTJ etching process. This preliminary action prepares a protective barrier that will prevent etch damage during the subsequent high-speed etching process, allowing the SOT electrode layer thickness to be maintained while achieving fast etching speeds.
2Manufacturing precision
If a highly selective etching process is used to reduce etch damage on SOT electrode layer, then the SOT electrode layer thickness is preserved, but the etching time is increased
Solution Approach 1:
The interface layer acts as a sacrificial intermediary that enables the use of conventional high-speed etching processes. By placing the interface layer between the etching process and the SOT electrode layer, the etching can proceed quickly without damaging the SOT electrode layer, thus preserving thickness while minimizing etching time.
3Device complexity
If the etch stop layer is not used, then the device complexity is reduced, but the platinum redeposition on MTJ side surface causes short circuit paths
Solution Approach 1:
The etch stop layer serves as an intermediary barrier between the SOT electrode layer and the MTJ side surface. During the etching process, this layer prevents platinum material from redepositing on the MTJ side surface by providing a physical barrier, thereby preventing short circuit paths while maintaining relatively simple device structure.
4Ease of manufacture
If conventional RIE method is used to etch MTJ, then the ease of manufacture is improved, but the patterned MTJ develops skirt shape due to insufficient etch selectivity
Solution Approach 1:
The interface layer acts as a mediator that enhances the effective etch selectivity between the MTJ and the underlying layers. By introducing this intermediate layer with distinct etching characteristics, the conventional RIE process can achieve better shape control and avoid skirt formation, while maintaining ease of manufacture.
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 proposed structure reduces etch damage, maintains a sufficient SOT electrode layer thickness for effective write current flow, prevents short circuits in the tunnel barrier, and enhances the TMR properties by suppressing over-etching and redeposition issues, allowing for more reliable and efficient operation of SOT-MRAM devices.
Implementation Method 1
The SOT-MRAM device is characterized in part by writing operations being performed as the result of a spin current generated from a current based on a spin hole effect (SHE)
Implementation Method 2
The interface layer comprises a metal having a spin diffusion length that is greater than a thickness of the interface layer
Implementation Method 3
the etch stop layer comprises an oxide or nitride material of the metal
Data Source
AI summary
A magnetoresistive device includes a spin-orbit-torque (SOT) electrode layer, and a first magnetic layer, a first non-magnetic layer, and a second magnetic layer sequentially stacked over the SOT electrode layer. An interface layer is located between the SOT electrode layer and the first magnetic layer, and an etch stop layer covers a surface portion of the SOT electrode layer and is located adjacent the interface layer. The interface layer includes a metal having a spin diffusion length that is greater than a thickness of the interface layer, and the etch stop layer includes an oxide or nitride material of the metal.