TMR Biosensor Arrays with Varied Magnetization Angles
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Solution Overview
Problem
Current magneto-resistive (MR) biosensors, such as GMR sensors, face challenges in scaling down due to fabrication limitations, have low signal-to-noise ratios (SNR) due to low MR ratios, and are sensitive to environmental temperature changes, which affect detection sensitivity.
Innovation Solution
Tunnel magneto-resistive (TMR) sensors with different magnetic field sensitivities are fabricated using semiconductor methods, featuring magnetic tunnel junctions with pinned and free layers separated by a tunnel barrier, allowing for increased detection sensitivity by varying the magnetization angle between layers and compensating for process variations and temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GMR sensors are used for biosensing applications, then the sensor can detect magnetic fields from magnetic nanoparticles, but the signal-to-noise ratio is low due to low MR ratios
Solution Approach 1:
The patent changes the fundamental operating parameter of the magneto-resistive effect from giant magneto-resistance (GMR) to tunnel magneto-resistance (TMR). This parameter change results in a significantly higher magnetoresistance ratio, directly improving the signal-to-noise ratio and detection sensitivity of the biosensor while maintaining its ability to detect magnetic fields from magnetic nanoparticles.
2Measurement precision
If TMR devices are fabricated with different magnetization angles to increase sensitivity, then detection sensitivity improves, but device complexity increases
Solution Approach 1:
The patent applies local quality by creating TMR devices with different magnetization angles (e.g., 0 degrees, 45 degrees, 90 degrees) in different regions or within arrays of devices. This allows each device or region to be optimized for specific detection requirements while using the same basic fabrication process, thus improving detection sensitivity without proportionally increasing overall fabrication complexity.
3Measurement precision
If magnetic bias field is applied to align magnetic moments of magnetic nanoparticles, then detection accuracy improves, but the magnetic field also affects the free layers of TMR devices reducing detection sensitivity
Solution Approach 1:
The patent addresses this contradiction by carefully controlling and optimizing the magnetization angle parameters of the TMR devices during fabrication. By setting appropriate initial magnetization angles, the devices can maintain stable resistance characteristics even when subjected to magnetic bias fields, thus preserving detection sensitivity while allowing accurate detection of magnetic nanoparticles.
4Measurement precision
If TMR sensors are used instead of GMR sensors, then higher SNR and detection sensitivity are achieved, but sensitivity to fabrication variations increases
Solution Approach 1:
The patent creates arrays of TMR devices with different magnetization angles (0°, 45°, 90°) where each angle provides different sensitivity characteristics. This diversity allows the system to compensate for fabrication variations - if some devices are affected by process variations, others with different magnetization angles will maintain proper functionality, ensuring overall sensor array 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
TMR sensors provide higher SNR and improved detection sensitivity by exhibiting different resistance changes to magnetic stray fields, enabling more accurate detection of magnetic nanoparticles, and are less affected by environmental temperature and fabrication variations.
Implementation Method 1
tunnel magneto-resistive (TMR) sensors employing TMR devices with different magnetic field sensitivities for increased detection sensitivity
Data Source
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AI summary
Tunnel magneto-resistive (TMR) sensors employing TMR devices with different magnetic field sensitivities for increased detection sensitivity are disclosed. For example, a TMR sensor may be used as a biosensor to detect the presence of biological materials. In aspects disclosed herein, free layers of at least two TMR devices in a TMR sensor are fabricated to exhibit different magnetic properties from each other (e.g., MR ratio, magnetic anisotropy, coercivity) so that each TMR device will exhibit a different change in resistance to a given magnetic stray field for increased magnetic field detection sensitivity. For example, the TMR devices may be fabricated to exhibit different magnetic properties such that one TMR device exhibits a greater change in resistance in the presence of a smaller magnetic stray field, and another TMR device exhibits a greater change in resistance in the presence of a larger magnetic stray field.