MTJ Current Sensor Bridge Temperature Compensation
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Solution Overview
Problem
Current sensors using Hall, AMR, and GMR effects face issues with low sensitivity, high power consumption, and limited linear range, while requiring large and heavy magnetic flux concentrators or complex manufacturing processes, and temperature compensation is necessary for high accuracy.
Innovation Solution
A current sensor utilizing magnetic tunnel junction (MTJ) elements for both sensing and temperature compensation, with MTJ elements connected in series and configured as a half or full bridge, providing high sensitivity, wide linear range, low power consumption, and excellent thermal stability without additional magnetic flux concentrators or reset coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall elements are used in current sensors, then the sensor can measure current, but the sensitivity is very low requiring additional magnetic flux concentrator structures
Solution Approach 1:
The patent replaces Hall effect-based mechanical/magnetic field sensing with MTJ-based magnetoresistive sensing. The MTJ elements directly sense magnetic field changes through resistance changes without requiring external magnetic flux concentrators, thereby improving sensitivity while reducing structural complexity
Solution Approach 2:
The patent changes the sensing mechanism from Hall voltage measurement to magnetoresistive resistance measurement. By utilizing the TMR effect in MTJ elements, the sensor achieves higher sensitivity through resistance changes that are more pronounced than Hall voltage changes for the same magnetic field variation
2Measurement precision
If magnetic flux concentrators are added to Hall sensors, then sensitivity increases, but the size and weight of the current sensor increase
Solution Approach 1:
The patent eliminates the need for magnetic flux concentrators by using MTJ elements that inherently provide high sensitivity through the TMR effect. This substitution removes the heavy magnetic flux concentrator structures while maintaining or improving sensitivity
Solution Approach 2:
The patent uses composite MTJ structures consisting of multiple thin magnetic layers (pinned layer, free layer, tunnel barrier) that work together to achieve high sensitivity without requiring additional magnetic flux concentrator materials, thereby reducing overall sensor weight
3Measurement precision
If magnetic flux concentrators are added to Hall sensors, then sensitivity increases, but linearity degrades
Solution Approach 1:
The patent replaces Hall effect sensing with MTJ-based magnetoresistive sensing, which provides a more linear response characteristic. The resistance change in MTJ elements with magnetic field strength follows a more linear relationship compared to the nonlinear Hall voltage response, especially without magnetic flux concentrators
4Measurement precision
If Hall elements are used in current sensors, then the sensor can measure current, but power consumption is high
Solution Approach 1:
The patent replaces Hall effect-based current sensing with MTJ-based magnetoresistive sensing. The MTJ structure operates passively with resistance changes directly indicating magnetic field strength, eliminating the need for high current drive required by Hall elements and their associated magnetic flux concentrators, thereby reducing power consumption
5Measurement precision
If AMR sensors are used, then sensitivity is much higher than Hall sensors, but the linear range is narrower and set/reset coils are required
Solution Approach 1:
The patent replaces AMR sensing with MTJ-based magnetoresistive sensing. The MTJ structure inherently provides wide linear range without requiring external set/reset coils, eliminating the complex coil structures needed for AMR sensors while maintaining high sensitivity
Solution Approach 2:
The patent uses composite MTJ structures with engineered magnetic layers that provide both high sensitivity and wide linear range through the TMR effect, eliminating the need for additional set/reset coil structures required by AMR sensors
6Measurement precision
If GMR sensors are used, then sensitivity is higher than Hall sensors, but the linear range is narrow
Solution Approach 1:
The patent replaces GMR sensing with MTJ-based magnetoresistive sensing. The TMR effect in MTJ elements provides both high sensitivity and wide linear range, overcoming the limited linear range characteristic of GMR sensors while maintaining enhanced sensitivity
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 MTJ-based current sensor achieves high sensitivity, wide linear range, low power consumption, and improved temperature stability, effectively compensating for temperature drift and reducing sensor size and complexity.
Implementation Method 1
They use the tunneling magnetoresistance (TMR) effect of a multilayered magnetic material stack to sense the magnitude and direction of a magnetic field
Implementation Method 2
MTJ elements have a resistance which changes in response to an applied magnetic field
Data Source
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AI summary
This patent discloses a current sensor comprising a sensor bridge (14), which consists of several magnetic tunnel junction (MTJ) elements (R11, R12, R21, R22), a MTJ temperature compensation resistor (16), and a current lead (20), which are integrated onto the same chip. The current lead (20) is positioned close to the sensor bridge (14), and it is used to carry the test current (19). A permanent magnet (17) is arranged at the periphery of the MTJ temperature compensation resistor (16). The permanent magnet (17) rigidly aligns the magnetization direction (7) of the free layer of the MTJ temperature compensation resistor (16) anti-parallel to the magnetization direction (8) of a pinning layer; so that the MTJ temperature compensation resistor (16) remains in a high resistance state providing a resistance value that changes as a function of temperature. The sensor bridge (14) is connected in series with the MTJ temperature compensation resistor (16) in order to temperature compensate the sensor bridge (14). A magnetic field (21) generated by the test current (19) produces an output voltage at the output of the temperature compensated sensor bridge that is proportional to the test current value. As a result of this temperature compensated structure, the current sensor has the advantages of high sensitivity, wide linear range, low power consumption, and excellent temperature stability.