TMR Sensor Bottom Lead Surface Roughness Reduction
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Solution Overview
Problem
The reliability and performance of Tunneling Magnetoresistive (TMR) sensors in Wheatstone bridge circuits are affected by surface roughness and fabrication methods, leading to inconsistent magnetoresistance responses.
Innovation Solution
A method involving chemical mechanical planarization (CMP) and multi-layer bottom leads with alternating conductive materials, such as copper and tantalum, to achieve a surface roughness of less than 2 Angstroms, enhancing the sensitivity and performance of TMR sensors in Wheatstone bridge arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-layer bottom lead is used, then the fabrication process is simpler, but the surface roughness is higher leading to poor TMR sensor performance
Solution Approach 1:
The bottom lead is divided into multiple alternating layers of conductive materials (e.g., copper and tantalum) with different polishing rates. This segmentation allows each layer to contribute differently to the final surface roughness, with slower-polishing layers effectively smoothing the surface by compensating for roughness from faster-polishing layers during CMP processing.
Solution Approach 2:
The bottom lead uses composite structure with alternating layers of different conductive materials having distinct polishing characteristics. The combination of materials with different polishing rates creates a synergistic effect where the slower-polishing layers act as a planarizing layer, reducing overall surface roughness below what could be achieved with a single material.
2Measurement precision
If chemical mechanical planarization (CMP) is applied to reduce surface roughness, then TMR sensor sensitivity improves, but the polishing rate varies by material leading to inconsistent results
Solution Approach 1:
The invention changes the material composition parameter of the bottom lead by using alternating layers of conductive materials with different polishing rates. This parameter change ensures that during CMP, the slower-polishing layers effectively planarize the surface by compensating for variations, achieving consistent sub-2 Angstrom surface roughness across different material compositions and processing conditions.
3Manufacturing precision
If multiple layers with different polishing rates are used, then surface roughness is reduced to sub-2 Angstroms, but the fabrication process becomes more complex
Solution Approach 1:
The bottom lead is divided into multiple alternating layers of conductive materials (e.g., copper and tantalum) with different polishing rates. This segmentation allows each layer to contribute differently to the final surface roughness, with slower-polishing layers effectively smoothing the surface by compensating for roughness from faster-polishing layers during CMP processing.
Solution Approach 2:
The alternating layer structure enables the bottom lead to self-planarize during CMP processing. The slower-polishing layers automatically compensate for surface irregularities created by faster-polishing layers, providing self-correcting planarization without requiring additional processing steps or external intervention.
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 approach results in a 40% improvement in magnetoresistance response and sensitivity, enabling a more reliable and accurate Wheatstone bridge design for magnetic field sensing.
Implementation Method 1
The bottom lead for the TMR sensor has a very small surface roughness due to not only chemical mechanical planarization (CMP) but also due to forming the bottom lead from multiple layers
Implementation Method 2
Magnetic sensors can include Hall effect magnetic sensors, anisotropy magnetoresistive sensors (AMR), giant magnetoresistive (GMR) sensors, and tunneling magnetoresistive (TMR) sensors
Data Source
AI summary
A Wheatstone bridge array comprising a tunneling magnetoresistive (TMR) sensor and a method for manufacturing is disclosed. The bottom lead for the TMR sensor has a very small surface roughness due to not only chemical mechanical planarization (CMP) but also due to forming the bottom lead from multiple layers. The multiple layers include at least a bottom first metal layer and a top second metal layer disposed on the first metal layer. The second metal layer generally has a lower surface roughness than the first metal layer. Additionally, the second metal layer has a slower polishing rate. Therefore, not only does the second metal layer reduce the surface roughness simply be being present, but the slower polishing rate enables the top second metal film to be polished to a very fine surface roughness of less than or equal to ˜2 Angstroms.