MTJ Device Partial Milling Anti-Parallel Coupled Free Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
During the manufacturing process of magnetic tunnel junction (MTJ) devices, the tunnel barrier layer is often unintentionally eroded, leading to a loss of tunnel magnetoresistance due to shunting and redeposited material, which affects the sensitivity and output of the devices.
Innovation Solution
A magnetic tunnel junction device design that includes a pinned ferromagnetic layer with a free ferromagnetic stack surrounded by a hard bias material, where the skirt extending from the stack is integral to the lower free sublayer and made of the same material, preventing the upper free sublayer and AP-coupling layer from extending beyond the vertical edges, and a method of forming the device by partially milling the lower free sublayer to create a skirt that radially extends beyond the upper sublayer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion milling is used to remove the free layers during manufacturing, then the free layers can be precisely removed down to the barrier, but the tunnel barrier layer is unintentionally eroded causing loss of tunnel magnetoresistance
Solution Approach 1:
A cap layer is deposited over the entire structure before ion milling to protect the tunnel barrier layer. This preliminary protective action prevents the barrier from being eroded during the subsequent milling process, while still allowing precise removal of the free layers through the cap layer.
Solution Approach 2:
The cap layer acts as an intermediary protective layer between the ion mill and the tunnel barrier. It absorbs the erosive effect of ion milling, preventing direct contact between the milling ions and the barrier, thus preserving barrier integrity while enabling precise material removal.
2Stability of the object's composition
If the hard bias layer is positioned to surround the free stack for stabilization, then magnetic stability is improved, but the layer alignment becomes difficult to center precisely
Solution Approach 1:
The cap layer is deposited beforehand to establish a reference surface and structural framework. This preliminary structure serves as a guide for subsequent alignment steps, making it easier to center the hard bias layer accurately around the free stack, thus improving both stability and alignment precision.
Solution Approach 2:
The cap layer and underlying structures are designed to self-align during deposition. The geometric constraints and material properties cause subsequent layers to automatically center themselves, reducing the need for complex external alignment procedures and improving manufacturing precision.
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 solution stabilizes the MTJ device by maintaining the tunnel barrier integrity, enhancing the magnetic properties and preventing erosion, thereby improving the sensitivity and output of the MTJ devices.
Implementation Method 1
the tunneling current perpendicularly through the layers depends on the relative orientation of the magnetizations in the two ferromagnetic layers
Implementation Method 2
the free layer may be established by two sublayers that are separated from each other by an antiparallel coupling (AP-coupling) layer. Since the magnetic fields of the two free sublayers are antiparallel to each other
Data Source
AI summary
In a magnetic tunnel junction (MTJ) device having a pinned layer and upper and lower antiparallel-coupled free sublayers, to avoid loss in tunnel magnetoresistance, etching or milling of the free sublayer layer materials is stopped in the lower free sublayer. The total thickness of the free sublayers may be large to ease manufacture because the effective magnetic thickness of the free layer combination may be as small as desired by appropriately establishing a small difference between the thicknesses of the AP-coupled free sublayers. A contiguous hard bias material is centered on the free sublayers for stabilization.