Double Magnetic Tunnel Junction Device via Ultra-High Vacuum Bonding

The patent divides the double magnetic tunnel junction device into two separate magnetic tunnel junction stacks that are formed independently and then bonded together. This segmentation allows each stack to be formed on its own grain erasing base layer, preventing the cumulative surface quality degradation that would occur if layers were formed sequentially on a single stack. The separation of the formation processes maintains high surface quality for both reference layers.

The patent applies grain erasing treatment to base layers before forming each magnetic tunnel junction stack. This preliminary action prepares the surface with high quality crystal orientation and surface morphology before deposition begins, ensuring optimal conditions for forming high-quality reference layers. By performing this preparation in advance for each separate stack, the invention avoids the surface quality degradation that would result from forming multiple layers sequentially.

The patent segments the device into two independent magnetic tunnel junction stacks, each with its own reference layer formed on a separate grain erasing base layer. This segmentation ensures that each reference layer maintains high crystal quality and surface morphology, which are critical for achieving high TMR ratios and write efficiency. The independent formation processes prevent the cumulative degradation that would occur in a single stacked structure.

The patent applies grain erasing treatment locally to each base layer before forming the corresponding magnetic tunnel junction stack. This local quality enhancement ensures that each reference layer formation occurs on a surface with optimal crystal orientation and morphology, thereby maintaining high TMR and write efficiency for both junctions independently, rather than having the quality degrade across the cumulative structure.

The patent divides the manufacturing process into separate formation of two magnetic tunnel junction stacks, which are then bonded together using ultra-high vacuum bonding. While this segmentation improves TMR and write efficiency by maintaining high surface quality for each reference layer, it does increase manufacturing process complexity. The segmentation enables independent optimization of each stack's formation process.

The patent combines two separately formed magnetic tunnel junction stacks into a single integrated device through ultra-high vacuum bonding. This merging step integrates the benefits of separate formation (high surface quality and performance) into a unified device structure, achieving both high TMR/write efficiency and functional integration despite the increased manufacturing complexity.