Magnetic Tunnel Junction Oxide Stack for Stable PMA Switching
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Solution Overview
Problem
Existing magnetic tunneling junction devices face challenges in achieving fast operating speeds and stable perpendicular magnetic anisotropy, which are crucial for improving the performance of memory devices like STT-MRAM.
Innovation Solution
The introduction of a second oxide layer with a higher oxygen affinity than the non-magnetic metal in the free layer, combined with a stoichiometrically oxygen-deficient first oxide layer and a capping metal layer, enhances interface perpendicular magnetic anisotropy (IPMA) and prevents oxygen interdiffusion, thereby stabilizing the free layer's magnetization and increasing operating speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional magnetic tunneling junction device structure is used, then the device can operate, but the operating speed is slow (greater than or equal to 10 ns) and the perpendicular magnetic anisotropy is unstable
Solution Approach 1:
The oxide barrier layer is segmented into a first oxide layer and a second oxide layer with different compositions and functions. The first oxide layer (oxygen-deficient) stabilizes the interface with the pinned layer, while the second oxide layer (higher oxygen affinity) stabilizes the interface with the free layer and prevents oxygen interdiffusion. This segmentation allows each layer to optimize its function, achieving both fast operating speed and stable perpendicular magnetic anisotropy simultaneously.
Solution Approach 2:
Different regions of the oxide barrier layer are given different oxygen concentrations and compositions. The first oxide layer has oxygen-deficient composition to match the pinned layer interface, while the second oxide layer has higher oxygen affinity to match the free layer interface. This local quality variation optimizes the perpendicular magnetic anisotropy at each interface, resulting in overall device performance improvement with operating speed less than 10 ns and stable PMA.
2Ease of manufacture
If oxygen is allowed to interdiffuse between layers during manufacturing, then the process is simpler, but the perpendicular magnetic anisotropy becomes unstable and operating speed decreases
Solution Approach 1:
The second oxide layer acts as an intermediary barrier between the free layer and the external environment. Its higher oxygen affinity creates a thermodynamic barrier that prevents oxygen from diffusing into the free layer during high-temperature processing. This intermediary layer protects the magnetization stability without complicating the manufacturing process, as it can be deposited using standard sputtering techniques.
Solution Approach 2:
The oxide barrier layer is constructed as a composite structure with two different oxide materials having distinct oxygen affinities. This composite structure provides both the functional benefits of oxygen diffusion prevention and compatibility with standard manufacturing processes, achieving reliable perpendicular magnetic anisotropy without sacrificing ease of manufacture.
3Reliability
If the oxide layer has high oxygen content, then oxygen diffusion is prevented, but the interface perpendicular magnetic anisotropy is reduced and operating speed slows down
Solution Approach 1:
The oxide barrier layer exhibits local quality variation with the first oxide layer having oxygen-deficient composition near the pinned layer interface to enhance IPMA and enable fast switching, while the second oxide layer has higher oxygen affinity near the free layer interface to prevent oxygen interdiffusion. This spatial differentiation of oxygen content allows simultaneous optimization of both switching speed and magnetization stability.
Solution Approach 2:
By dividing the oxide barrier layer into two segments with different oxygen characteristics, the device achieves both fast operating speed (through the oxygen-deficient first oxide layer) and oxygen diffusion prevention (through the high oxygen-affinity second oxide layer). This segmentation resolves the contradiction between speed and reliability.
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 results in a magnetic tunneling junction device with an operating speed of less than 10 ns and stable perpendicular magnetic anisotropy, improving the performance and reliability of memory devices.
Implementation Method 1
The metal oxide of the second oxide layer may have an oxide formation energy greater than that of the oxide of the non-magnetic metal in the free layer
Implementation Method 2
enhances interface perpendicular magnetic anisotropy (IPMA) and prevents oxygen interdiffusion, thereby stabilizing the free layer's magnetization
Implementation Method 3
The resistance of the magnetic tunneling junction device varies with the magnetization direction of a free layer. For example, when the magnetization direction of the free layer is the same as the magnetization direction of a pinned layer, the magnetic tunneling junction device may have low resistance, and when the magnetization directions are opposite to each other, the magnetic tunneling junction device may have high resistance
Data Source
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AI summary
Provided are a magnetic tunneling junction device (100a) having more stable perpendicular magnetic anisotropy (PMA) and/or increased operating speed, and/or a memory device including the magnetic tunneling junction device. The magnetic tunneling junction device includes a free layer (103) having a first surface and a second surface opposite the first surface; a pinned layer (101) facing the first surface of the free layer; a first oxide layer (102) between the pinned layer and the free layer; and a second oxide layer (104) on the second surface of the free layer. The free layer includes a magnetic material X doped with a non-magnetic metal. The second oxide layer includes ZOx which is an oxide of a metal Z. An oxygen affinity of the metal Z is greater than an oxygen affinity of the non-magnetic metal X.