Polycrystalline Tungsten Seed Layer for STT-MRAM Crystallinity
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Solution Overview
Problem
The existing magnetic tunnel junctions in STT-MRAM devices have low crystallinity and thermal stability, leading to delayed magnetization changes and reduced current flow, which hinders the development of high-speed memory devices.
Innovation Solution
A memory device structure is introduced with a magnetic tunnel junction comprising first and second free layers separated by a polycrystalline conductive separation layer, where the separation layer and seed layer are formed using tungsten, allowing for improved crystallinity and thermal stability even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous seed layer and amorphous magnetic tunnel junction are used, then device fabrication is simplified, but crystallinity is low leading to delayed magnetization changes and reduced operation speed
Solution Approach 1:
The patent changes the physical state parameter of the seed layer from amorphous to polycrystalline by controlling the crystallization process. This parameter change enables the seed layer to promote crystal growth in the magnetic tunnel junction, thereby improving crystallinity and magnetization change speed without significantly complicating the fabrication process
Solution Approach 2:
The patent performs preliminary crystallization of the seed layer before forming the magnetic tunnel junction. By pre-establishing a polycrystalline structure in the seed layer, the subsequent magnetic tunnel junction inherits improved crystallinity, which accelerates magnetization changes while maintaining fabrication efficiency
2Speed
If heat treatment is performed to improve crystallinity, then magnetization change speed increases, but thermal stability deteriorates at high temperatures
Solution Approach 1:
The patent creates a composite structure where a polycrystalline seed layer (e.g., tungsten) is combined with the magnetic tunnel junction layers. This composite configuration provides two key benefits: the polycrystalline seed layer promotes crystal growth for fast magnetization changes, while the specific material composition maintains thermal stability at high temperatures during subsequent processing
Solution Approach 2:
The patent uses a seed layer that can be sacrificial or temporary in nature - it performs its primary function of promoting crystallinity during and after formation, then its role is completed. The seed layer material (such as tungsten) is chosen to be stable and non-interfering, allowing the magnetic tunnel junction to function independently with improved properties
3Ease of manufacture
If amorphous magnetic tunnel junction is used, then fabrication process is simpler, but perpendicular magnetic anisotropy is reduced leading to operation errors
Solution Approach 1:
The patent changes the structural parameter of the magnetic tunnel junction from amorphous to polycrystalline by controlling the crystallization process. This parameter change enhances perpendicular magnetic anisotropy through improved crystal orientation, thereby improving operation reliability while maintaining fabrication simplicity through a straightforward crystallization step
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
This configuration enables rapid magnetization direction changes, enhancing read/write operation speed and maintaining perpendicular magnetic anisotropy, thus improving the reliability and performance of the memory device.
Implementation Method 1
the magnetic tunnel junction includes free layers consisting of first and second free layers and a separation layer, a tunneling barrier and a pinned layer
Implementation Method 2
a spin-transfer torque (STT) phenomenon generated by electron injection and discriminates a resistance difference before and after magnetization inversion
Implementation Method 3
the free layer and the pinned layer must have perpendicular magnetization values. When the perpendicular magnetization values are symmetrical with respect to 0 according to the intensity and direction of a magnetic field, and a squareness (S) shape becomes clear (S=1), perpendicular magnetic anisotropy (PMA) is considered to be excellent
Implementation Method 4
allowing for improved crystallinity and thermal stability even at high temperatures
Implementation Method 5
the magnetic tunnel junction includes free layers consisting of first and second free layers and a separation layer, a tunneling barrier and a pinned layer
Data Source
AI summary
The present invention provides a memory device in which lower electrodes, a buffer layer, a seed layer, a magnetic tunnel junction, a capping layer, synthetic exchange diamagnetic layers, and an upper electrode are formed on a substrate in a laminated manner. According to the present invention, the lower electrodes and the seed layer are formed of a polycrystalline conductive material, and the perpendicular magnetic anisotropy of the magnetic tunnel junction is maintained upon heat treatment at a high temperature of 400° C. or more.