TMR Sensor Dual Films Maximize Magnetoresistance Range
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Solution Overview
Problem
Existing TMR-based Wheatstone bridges for magnetic field sensing do not utilize the full range of magnetoresistance, resulting in reduced output voltage and sensitivity due to the ±45° orientation of sensor stripes, which limits the efficiency of the magnetic sensor design.
Innovation Solution
A TMR sensor device is designed with four resistors, where the first and fourth resistors comprise a synthetic anti-ferromagnetic pinned layer with a magnetization direction orthogonal to the free layer, and the second and third resistors comprise a double synthetic anti-ferromagnetic pinned layer with a magnetization direction opposite to the first TMR film's reference layer, all disposed in the same plane, allowing for different magnetoresistance responses and maximizing output voltage and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all four resistors are made with the same TMR material and ±45° stripe orientations, then the Wheatstone bridge characteristics are enabled, but the full range of magnetoresistance change cannot be utilized, resulting in reduced output voltage and sensitivity
Solution Approach 1:
The patent divides the TMR sensor into four separate resistors, each with its own TMR film having distinct magnetization directions (0°, 90°, 180°, 270°). This segmentation allows each resistor to contribute differently to the bridge output, enabling full utilization of the magnetoresistance range while maintaining Wheatstone bridge characteristics.
Solution Approach 2:
Each TMR film is given a unique local quality in terms of magnetization direction (0°, 90°, 180°, or 270°). This local differentiation allows each resistor to respond differently to applied magnetic fields, maximizing the differential output voltage and sensitivity of the bridge while maintaining structural feasibility.
2Power
If the first and fourth resistors use a single synthetic anti-ferromagnetic pinned layer while the second and third resistors use a double synthetic anti-ferromagnetic pinned layer, then opposite magnetization directions are achieved for maximum differential output, but the fabrication process becomes more complex
Solution Approach 1:
The patent changes the parameter of magnetization direction for each TMR film (0°, 90°, 180°, 270°) to achieve opposite resistance-field dependencies in different resistors. This parameter variation allows maximum differential output voltage while using a systematic approach to fabrication that, although more complex than uniform structures, follows a repeatable pattern.
Solution Approach 2:
The patent employs composite TMR film structures with different pinned layer configurations (single SAF vs. double SAF) to achieve the desired magnetization directions. These composite structures combine multiple magnetic layers with specific orientations to produce the required opposite magnetization directions for maximum bridge differential output.
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 configuration enables the TMR sensor device to operate within the full magnetoresistance range, achieving maximum output voltage and sensitivity by utilizing the distinct magnetoresistance responses of the two different TMR films, thereby enhancing the magnetic sensor's performance.
Implementation Method 1
The TMR based magnetic sensor has a very high sensitivity compared to other magnetic sensors. The first TMR film comprises a synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to a free layer. The second TMR film comprises a double synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to the magnetization of a free layer, but opposite to the magnetization direction of the reference layer of the first TMR film.
Implementation Method 2
The first TMR film comprises a synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to a free layer. The second TMR film comprises a double synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to the magnetization of a free layer, but opposite to the magnetization direction of the reference layer of the first TMR film.
Data Source
AI summary
A tunneling magnetoresistance (TMR) sensor device is disclosed that includes four or more TMR resistors. The TMR sensor device comprises a first TMR resistor comprising a first TMR film, a second TMR resistor comprising a second TMR film different than the first TMR film, a third TMR resistor comprising the second TMR film, and a fourth TMR resistor comprising the first TMR film. The first, second, third, and fourth TMR resistors are disposed in the same plane. The first TMR film comprises a synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to a free layer. The second TMR film comprises a double synthetic anti-ferromagnetic pinned layer having a magnetization direction of the reference layer orthogonal to the magnetization of a free layer, but opposite to the magnetization direction of the reference layer of the first TMR film.