Magnetic Sensor Reset and Stabilization Control
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Solution Overview
Problem
Existing magnetic field sensors face challenges such as high cost, large size, high power consumption, and sensitivity issues due to the need for magnetic shields and complex magnetization techniques, which affect their performance in measuring low magnetic fields and are not suitable for mobile applications.
Innovation Solution
A method and apparatus for dynamically resetting and stabilizing magnetic sense elements using reset and stabilization field pulses, determined from the sensed external field component, to eliminate the need for hard bias layers and magnetic shields, allowing for a compact, cost-effective, and sensitive magnetic field sensor design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic shields are used to suppress the response of reference elements, then sensitivity is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent removes magnetic shields from the sensor structure entirely, using only unshielded MTJ sensors in a Wheatstone bridge configuration. This extraction of the magnetic shield component simplifies the device structure while maintaining sensitivity through the differential measurement approach of the bridge circuit.
Solution Approach 2:
The patent replaces the physical magnetic shield structure with an electrical/digital signal processing approach. The differential Wheatstone bridge circuit and associated electronics substitute for the mechanical magnetic shielding, achieving the same noise suppression function through circuitry rather than physical barriers.
2Measurement precision
If magnetic shields are used to suppress the response of reference elements, then sensitivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
By removing magnetic shields from the design, the patent eliminates the need for precise fabrication of thick magnetic shield layers and their associated NiFe seed and plating steps. This extraction reduces manufacturing precision requirements while maintaining sensor performance through the unshielded Wheatstone bridge configuration.
3Measurement precision
If magnetic shields are used, then sensitivity is improved, but power consumption increases
Solution Approach 1:
The patent removes magnetic shields that would require continuous power for active shielding or complex control circuits. The unshielded MTJ sensor design reduces power consumption by eliminating these additional power-hungry components while maintaining sensitivity through the differential bridge measurement technique.
4Measurement precision
If magnetic shields are used, then sensitivity is improved, but sensor size increases
Solution Approach 1:
The patent removes thick magnetic shield layers that occupy significant physical space. The unshielded MTJ sensor design reduces the sensor footprint by eliminating these bulky magnetic shielding structures, enabling more compact sensor integration while maintaining sensitivity through the Wheatstone bridge differential measurement approach.
5Measurement precision
If four different pinning directions are individually set for each wafer, then measurement accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The patent uses a single pinning direction for all MTJ sensors in the Wheatstone bridge, making the pinning layer universal for multiple sensing functions. This universal pinning approach simplifies manufacturing by eliminating the need for complex, wafer-specific magnetization techniques while maintaining measurement accuracy through the differential bridge configuration that inherently compensates for systematic errors.
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 enhances the signal-to-noise ratio, reduces manufacturing complexity and cost, and enables accurate measurement of low magnetic fields with minimal power consumption, making it suitable for mobile applications.
Implementation Method 1
each of which includes a magnetic field pulse generator for selectively applying a field pulse to stabilize or restore the easy axis magnetization of the sense layers
Implementation Method 2
detecting an external field component in the direction of the first stabilization field as sensed by the magnetic sense elements
Data Source
Figure 1~2
Figure 3~4
Figure 5~9
AI summary
A magnitude and direction of at least one of a reset current and a second stabilization current (that produces a reset field and a second stabilization field, respectively) is determined that, when applied to an array of magnetic sense elements, minimizes the total required stabilization field and reset field during the operation of the magnetic sensor and the measurement of the external field. Therefore, the low field sensor operates optimally (with the highest sensitivity and the lowest power consumption) around the fixed external field operating point. The fixed external field is created by other components in the sensor device housing (such as speaker magnets) which have a high but static field with respect to the low (earth's) magnetic field that describes orientation information.