Doped Oxide Capping Layer for Thermally Stable STT-MRAM
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Solution Overview
Problem
Existing STT-MRAM devices face challenges in maintaining high perpendicular magnetic anisotropy (PMA) and thermal stability due to the resistance contribution and diffusion of oxygen and other species through the Hk enhancing layer, which degrades the free layer properties during CMOS processes at elevated temperatures.
Innovation Solution
Incorporating a dopant into the Hk enhancing layer with a non-stoichiometric oxidation state to create conducting pathways and block oxygen diffusion, thereby reducing resistance and species diffusion, while maintaining interfacial PMA and thermal stability up to 400°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Hk enhancing layer with non-stoichiometric oxidation state is used to reduce resistance, then electrical resistance decreases, but oxygen diffusion increases causing degradation of free layer properties
Solution Approach 1:
A tantalum (Ta) barrier layer is introduced as an intermediary between the Hk enhancing layer and the free layer. This Ta layer serves dual functions: it maintains the low-resistance property of the non-stoichiometric Hk enhancing layer while blocking oxygen diffusion to the free layer, preventing degradation of the free layer's magnetic properties during CMOS processing
Solution Approach 2:
The structure combines multiple materials (Hk enhancing layer with non-stoichiometric oxidation state + Ta barrier layer) to achieve properties that neither material could provide alone. The composite structure leverages the low resistance of the non-stoichiometric oxide while the Ta layer provides oxygen blocking, solving both electrical and stability requirements
2Productivity
If temperature is increased during CMOS processes to improve manufacturing, then manufacturing efficiency increases, but thermal stability of free layer properties decreases due to oxygen diffusion
Solution Approach 1:
The Ta barrier layer is deposited beforehand to create a protective cushion between the Hk enhancing layer and the free layer. This pre-established barrier prevents oxygen diffusion during subsequent high-temperature CMOS processing steps, protecting the free layer's magnetic properties from thermal degradation
3Object-affected harmful factors
If a fully oxidized Hk enhancing layer is used to block oxygen diffusion, then oxygen diffusion decreases, but electrical resistance increases significantly
Solution Approach 1:
The Hk enhancing layer structure is segmented into two functional parts: a non-stoichiometric oxidation state region that provides low electrical resistance, and a Ta barrier layer that provides oxygen diffusion blocking. This segmentation allows each layer to optimize its specific function without compromising the other
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 doped Hk enhancing layer enhances PMA and thermal stability, ensuring a magnetoresistive ratio above 1 and preserving free layer properties during CMOS processes.
Implementation Method 1
Incorporating a dopant into the Hk enhancing layer with a non-stoichiometric oxidation state to create conducting pathways and block oxygen diffusion, thereby reducing resistance
Implementation Method 2
Incorporating a dopant into the Hk enhancing layer with a non-stoichiometric oxidation state to create conducting pathways and block oxygen diffusion
Implementation Method 3
STT-MRAM has a MTJ cell based on a tunneling magnetoresistance (TMR) effect wherein a MTJ stack of layers has a configuration in which two ferromagnetic layers are separated by a thin insulating tunnel barrier layer
Implementation Method 4
STT-MRAM technology for writing of memory bits was described by C. Slonczewski in 'Current driven excitation of magnetic multilayers'
Implementation Method 5
One practical way to obtain strong PMA is through interfacial PMA at an interface between an iron rich free layer and a MgO tunnel barrier layer
Data Source
AI summary
A magnetic tunnel junction (MTJ) is disclosed wherein a free layer (FL) interfaces with a metal oxide (Mox) layer and a tunnel barrier layer to produce interfacial perpendicular magnetic anisotropy (PMA). The Mox layer has a non-stoichiometric oxidation state to minimize parasitic resistance, and comprises a dopant to fill vacant lattice sites thereby blocking oxygen diffusion through the Mox layer to preserve interfacial PMA and high thermal stability at process temperatures up to 400° C. Various methods of forming the doped Mox layer include deposition of the M layer in a reactive environment of 02 and dopant species in gas form, exposing a metal oxide layer to dopant species in gas form, and ion implanting the dopant. In another embodiment, where the dopant is N, a metal nitride layer is formed on a metal oxide layer, and then an anneal step drives nitrogen into vacant sites in the metal oxide lattice.