Synthetic Antiferromagnetic MRAM Reference Layer Design
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Solution Overview
Problem
Current magnetic random access memory (MRAM) devices face challenges in achieving high anneal temperature compatibility and sufficient activation energy for spin torque switching, with existing synthetic antiferromagnetic (SAF) structures losing pinning and magnetoresistance at temperatures below 400°C, and requiring high current densities.
Innovation Solution
The implementation of a synthetic antiferromagnetic device with specific layer structures, including ruthenium and cobalt iron boron layers, and a magnesium oxide spacer, which provides thermal stability and low switching currents, ensuring proper functioning at 400°C and reducing degradation of magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional SAF structures are used, then spin torque switching can be observed at anneal temperatures up to 350°C, but the current density required is too large for practical employment and activation energy is only 62 kT
Solution Approach 1:
The patent modifies the SAF structure by changing the thickness parameters of ruthenium layers (specifically the third Ru layer thickness of 0-18 Å) and cobalt iron boron layers to optimize magnetic coupling and anisotropy, achieving lower switching current density while maintaining thermal stability up to 400°C
Solution Approach 2:
The patent employs a composite multilayer structure consisting of alternating ruthenium and cobalt iron boron layers separated by magnesium oxide spacers, creating a synthetic antiferromagnetic structure that combines the benefits of strong exchange coupling with high thermal stability and reduced switching current
2Temperature
If conventional SAF structures are used, then spin torque switching can be observed at anneal temperatures up to 350°C, but activation energy reported was only 62 kT whereas MRAM applications require at least 80 kT
Solution Approach 1:
The patent adjusts the thickness of the third ruthenium layer (0-18 Å) and cobalt iron boron layers to optimize the magnetic coupling strength and perpendicular magnetic anisotropy, thereby increasing the activation energy from 62 kT to at least 80 kT while maintaining stability at 400°C anneal temperature
Solution Approach 2:
The patent transitions from in-plane magnetization to perpendicular magnetic anisotropy by engineering the multilayer thickness parameters, which provides higher thermal stability and increased activation energy suitable for non-volatile memory applications
3Temperature
If conventional SAF structures are used, then they can survive 400°C anneals with strong coupling, but devices lose pinning and magnetoresistance even for anneal temperatures below 400°C
Solution Approach 1:
The patent introduces magnesium oxide spacer layers as intermediaries between the reference and storage layers, which maintain the synthetic antiferromagnetic coupling while protecting the magnetoresistance effect from degradation during high-temperature annealing processes
Solution Approach 2:
The patent creates a composite structure with alternating ruthenium and cobalt iron boron layers separated by magnesium oxide spacers, where the Ru layers provide strong exchange coupling while the MgO spacers maintain structural integrity and magnetic properties during high-temperature processing
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 solution achieves thermal stability and appropriate switching characteristics with reduced current density, maintaining magnetoresistance and pinning at high anneal temperatures, meeting the requirements for MRAM devices with improved activation energy and coercivity.
Implementation Method 1
synthetic antiferromagnetic (SAF) freelayer and non-pinned reference layer for magnetic random access memory (MRAM) devices
Implementation Method 2
SAF storage layers are implemented in MRAM with certain advantages. For example, it appears that higher activation energy can be obtained for equivalent switching currents when using a SAF structure
Implementation Method 3
it is important that the process be compatible with existing CMOS fabrication requirements. In practice, this means that the MRAM device must be able to withstand high temperature annealing and processing, with temperatures in the range of 400° C. for 1 hour total exposure time
Implementation Method 4
a third ruthenium layer disposed on the cobalt iron boron layer, the third ruthenium layer having a thickness of approximately 0 angstroms to 18 angstroms
Data Source
AI summary
A synthetic antiferromagnetic device includes a reference layer having a first and second ruthenium layer, a magnesium oxide spacer layer disposed on the reference layer, a cobalt iron boron layer disposed on the magnesium oxide spacer layer and a third ruthenium layer disposed on the cobalt iron boron layer, the third ruthenium layer having a thickness of approximately 0 angstroms to 18 angstroms.