MTJ Sidewall Passivation Layer for Oxygen Diffusion Protection
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Solution Overview
Problem
Magnetic tunnel junctions (MTJs) in MRAM and spin-torque MRAM devices are susceptible to sidewall damage during etching, deposition, and annealing processes, particularly due to oxygen diffusion and redeposition of metal layers, leading to reduced device performance and yield.
Innovation Solution
A protective passivation layer made of B, C, or Ge is deposited on MTJ sidewalls using RF magnetron sputtering or atomic layer deposition, which is amorphous and non-crystalline to prevent diffusion of reactive materials, and is oxidized or nitridated to enhance protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric layer is deposited on MTJ sidewalls to insulate adjacent MTJs, then electrical insulation is improved, but sidewall damage occurs due to oxygen diffusion and metal redeposition
Solution Approach 1:
A protective passivation layer is deposited as an intermediary between the MTJ sidewall and the dielectric layer. This passivation layer (composed of materials such as Ru, Ir, Pt, or their alloys) acts as a barrier that prevents oxygen diffusion and metal redeposition during dielectric deposition, while allowing the dielectric layer to be formed on its outer surface for electrical insulation.
Solution Approach 2:
The protective passivation layer is deposited on the MTJ sidewalls before the dielectric layer deposition process. This preliminary protective action ensures that the sidewalls are shielded from harmful effects during subsequent processing steps, including oxygen diffusion prevention and metal redeposition protection.
2Reliability
If high temperature annealing at 400°C is applied to improve CMOS quality, then device performance is improved, but sidewall damage is exacerbated
Solution Approach 1:
The protective passivation layer serves as a thermal and chemical barrier between the MTJ sidewall and the harsh annealing environment. During high temperature annealing at 400°C, this passivation layer prevents direct exposure of the sidewall to oxidizing conditions and thermal stress, thereby protecting against sidewall damage while allowing the CMOS devices to benefit from the annealing process.
3Ease of manufacture
If the MgO tunnel barrier layer is exposed to atmosphere during dielectric deposition, then dielectric layer formation is enabled, but the tunnel barrier degrades due to poor corrosion properties
Solution Approach 1:
The protective passivation layer is deposited to completely cover and encapsulate the MgO tunnel barrier layer before dielectric deposition. This intermediary layer prevents direct exposure of the MgO to atmospheric conditions during dielectric layer formation, thereby preventing corrosion and degradation of the tunnel barrier while enabling standard dielectric deposition processes.
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 passivation layer significantly improves the resistance of MTJs to sidewall damage, maintaining device integrity during high-temperature annealing and dielectric layer deposition, resulting in improved performance and yield of memory devices.
Implementation Method 1
A protective passivation layer made of B, C, or Ge is deposited on MTJ sidewalls using RF magnetron sputtering
Implementation Method 2
A protective passivation layer made of B, C, or Ge is deposited on MTJ sidewalls using atomic layer deposition
Implementation Method 3
which is amorphous and non-crystalline to prevent diffusion of reactive materials, and is oxidized or nitridated to enhance protection
Implementation Method 4
which is amorphous and non-crystalline to prevent diffusion of reactive materials, and is oxidized or nitridated to enhance protection
Data Source
AI summary
A spin torque oscillator (STO) device includes a main pole, a trailing shield, an STO stack disposed between the main pole and the trailing shield, a passivation layer disposed on a sidewall of the STO stack, and a dielectric layer disposed on the passivation layer. The passivation layer is non-magnetic and includes one or more layers that is selected from the group consisting of a B-containing layer, a C-containing layer, and a Ge-containing layer.