STTMRAM Free Layer Doping for Low Switching Current
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Solution Overview
Problem
Spin-transfer torque magnetic random access memory (STTMRAM) faces challenges in reducing programming current density while maintaining high thermal stability, which is crucial for scaling below 65 nm and ensuring long-term data retention, as conventional materials with perpendicular anisotropy lead to high switching current density and tunneling barrier degradation.
Innovation Solution
A spin-torque transfer memory (STTMRAM) element with a composite free layer made of an iron platinum alloy doped with specific materials like boron, phosphorous, or tantalum, which reduces the damping constant and magnetic anisotropy, allowing for lower switching current density and high thermal stability, along with a bidirectional electric current for switching between parallel and anti-parallel states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional materials with perpendicular anisotropy are used, then thermal stability is improved, but switching current density increases
Solution Approach 1:
The patent changes the material composition parameters of the free layer by doping FePt with elements like B, P, C, or N at controlled concentrations (e.g., 1-20 atomic percent). This modifies the magnetic anisotropy constant and saturation magnetization, achieving an optimal balance between thermal stability and switching current density. The doped FePt maintains perpendicular magnetic anisotropy while reducing the damping constant and switching current requirements.
Solution Approach 2:
The patent creates a composite magnetic layer by combining FePt with dopant elements (B, P, C, or N) to form a doped FePt alloy. This composite material structure leverages the high anisotropy of FePt for thermal stability while the dopants reduce the damping constant and switching current, achieving both high thermal stability and low switching current density simultaneously.
2Area of moving object
If cell size is reduced for scaling, then memory density is improved, but thermal stability deteriorates
Solution Approach 1:
The patent modifies the magnetic layer composition by doping FePt with elements that reduce saturation magnetization and damping constant while maintaining perpendicular anisotropy. This allows smaller cell sizes to maintain sufficient thermal stability (KuV/kT > 40) by optimizing the anisotropy-to-volume ratio through material composition control rather than relying solely on larger dimensions.
3Use of energy by moving object
If programming current is reduced, then power consumption is improved, but thermal stability deteriorates
Solution Approach 1:
The patent optimizes the magnetic layer's material parameters by doping FePt to achieve a specific combination of anisotropy constant, saturation magnetization, and damping constant. This creates a material system where low switching current (reduced programming current) and high thermal stability can coexist, as the doped material requires less energy to switch while maintaining stable magnetic states for data retention.
4Area of moving object
If MTJ element size is shrunk, then device density is improved, but write current increases
Solution Approach 1:
The patent changes the intrinsic magnetic properties of the free layer by doping FePt with elements that reduce the damping constant and saturation magnetization. This allows smaller MTJ elements to be switched with lower write currents because the doped material has reduced magnetic moment and damping, requiring less spin-transfer torque to induce magnetization switching, thereby decoupling the scaling relationship between size and write current.
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 a switching current density of less than 1 MA/cm² and maintains high thermal stability, enabling smaller cell sizes and improved scalability for STTMRAM, while ensuring reliable single domain switching and enhanced tunnel magnetoresistance performance.
Implementation Method 1
spin-transfer torque magnetic random access memory (STTMRAM)
Implementation Method 2
tunneling magneto-resistance (TMR) performance
Implementation Method 3
current-induced-magnetization-switching having reduced switching current
Data Source
AI summary
A spin-torque transfer memory random access memory (STTMRAM) element includes a fixed layer formed on top of a substrate and a tunnel layer formed upon the fixed layer and a composite free layer formed upon the tunnel barrier layer and made of an iron platinum alloy with at least one of X or Y material, X being from a group consisting of: boron (B), phosphorous (P), carbon (C), and nitride (N) and Y being from a group consisting of: tantalum (Ta), titanium (Ti), niobium (Nb), zirconium (Zr), tungsten (W), silicon (Si), copper (Cu), silver (Ag), aluminum (Al), chromium (Cr), tin (Sn), lead (Pb), antimony (Sb), hafnium (Hf) and bismuth (Bi), molybdenum (Mo) or rhodium (Ru), the magnetization direction of each of the composite free layer and fixed layer being substantially perpendicular to the plane of the substrate.