TMR Sensor Spacer Mitigates Etching Re-deposition
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Solution Overview
Problem
Existing tunnel magnetoresistance (TMR) sensor element fabrication methodologies face issues with low yield and poor magnetic performance due to re-deposition of metallic particles during etching, leading to shorting and non-uniform etching, which result in reduced TMR effect and increased manufacturing costs.
Innovation Solution
The use of a nitride or oxide spacer technique to protect the magnetic tunnel junction (MTJ) structure during etching processes, allowing for a robust and high-yield fabrication method that minimizes re-deposition and enables uniform etching of magnetic layers, thereby enhancing sensor performance and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching processes are used without protective spacers, then the etching speed is faster, but metallic particles re-deposit on the MTJ structure causing shorting and non-uniform etching
Solution Approach 1:
A nitride or oxide spacer layer is introduced as an intermediary protective barrier between the etching environment and the MTJ structure. This spacer prevents direct contact between metallic particles and the tunnel junction, eliminating the re-deposition problem while allowing fast etching to proceed.
Solution Approach 2:
The protective spacer is deposited on the MTJ structure before the etching process begins. This preliminary protective action ensures that when fast etching occurs, the MTJ structure is already shielded and cannot be damaged by metallic particle re-deposition.
2Reliability
If protective spacers are added to prevent re-deposition, then the yield and uniformity improve, but the device structure becomes more complex
Solution Approach 1:
The protective spacer is designed as a temporary structure that is discarded after serving its protective function during etching. After the etch process completes, the spacer is removed, leaving no permanent additional structure in the final device, thus avoiding increased device complexity.
3Manufacturing precision
If protective spacers are used during etching, then re-deposition is minimized and uniform etching is achieved, but additional process steps are required
Solution Approach 1:
The deposition of the protective spacer is merged with existing process steps in the fabrication sequence. By integrating the spacer deposition into the existing process flow and using standard deposition equipment, the additional process step does not significantly increase overall process complexity or manufacturing time.
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 approach results in improved magnetic sensor performance, increased yield, and cost savings by preventing shorting and ensuring uniform etching, allowing for the production of various magnetic stacks without additional process steps, leading to robust and reliable TMR sensor elements.
Implementation Method 1
depositing a protective layer over the TMR stack, performing a second etch process to remove the protective layer, wherein in response to the second etch process, a portion of the second magnetic layer is exposed from the protective layer and a spacer is formed from a remaining portion of the protective layer, the spacer surrounding sidewalls of the first magnetic layer and the tunnel junction
Implementation Method 2
performing a first ion beam etching process on a substrate having a tunnel magnetoresistance (TMR) stack formed on the substrate, the first ion beam etching process removing material portions of a first magnetic layer and a tunnel barrier layer of the TMR stack
Implementation Method 3
An MTJ structure includes a metal-insulator-metal layer sandwich in which the metal layers are ferromagnetic and the insulator layer is very thin. Electrically, this forms a tunnel diode in which electrons can tunnel from one ferromagnet into the other.
Implementation Method 4
Tunnel magnetoresistance (TMR) sensor elements exploit a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ) structure
Data Source
AI summary
A method includes performing an ion beam etching process on a tunnel magnetoresistance (TMR) stack to remove material portions of a first magnetic layer and a tunnel barrier layer of the TMR stack. The ion beam etching process stops at a top surface of a second magnetic layer of the TMR stack. A protective layer is deposited over the TMR stack. Another etch process is performed to remove the protective layer such that a portion of the second magnetic layer is exposed from the protective layer and a spacer is formed from a remaining portion of the protective layer. The spacer surrounds sidewalls of the first magnetic layer and the tunnel barrier layer. The portion of the second magnetic layer exposed from the protective layer is removed so that a TMR sensor element remains, where the TMR sensor element includes a bottom magnet, a top magnet, and a tunnel junction.