TMR Sensor Self-Test Coil for High Field Factor
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Solution Overview
Problem
Magnetic field sensors, particularly those using Tunneling Magnetoresistance (TMR) technology, face challenges in minimizing power consumption and physical size while maintaining accurate self-test and calibration functions, which are essential for mobile electronic devices.
Innovation Solution
The implementation of a self-test coil configuration in TMR magnetic field sensors that utilizes multiple turns of self-test current lines routed in the same plane as a flux guide within a Z-axis sense element cell, allowing for a higher out-of-plane field factor and flexible design, with the coil split into interleaved coils for different operational modes to manage power constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-test current lines are routed to form a coil with multiple turns around the TMR elements, then the field factor for self-test is improved, but the physical size and power consumption increase
Solution Approach 1:
The patent applies local quality by configuring self-test current lines in the same plane as the flux guide within the Z-axis sense element cell, creating a localized high out-of-plane field factor region where needed for accurate self-test, while avoiding unnecessary in-plane fields at the flux guide center that would waste power
Solution Approach 2:
The patent transitions from conventional in-plane self-test fields to out-of-plane field generation by routing current lines in the same plane as the flux guide, achieving higher field factor in the Z-direction perpendicular to the sensor plane, thereby improving self-test accuracy without increasing lateral dimensions
2Measurement precision
If self-test current lines are routed to form a coil with multiple turns around the TMR elements, then the field factor for self-test is improved, but the physical size of the sensor increases
Solution Approach 1:
The self-test current lines are configured to generate concentrated out-of-plane magnetic flux density at the flux guide center where the TMR elements are located, achieving high field factor in a localized region without requiring large lateral coil dimensions
Solution Approach 2:
By generating out-of-plane fields perpendicular to the sensor plane rather than in-plane fields, the patent achieves high field factor without increasing the lateral footprint of the sensor, effectively utilizing the third dimension (Z-axis) for field generation
3Measurement precision
If the self-test coil is designed to achieve constant field over the sensor area, then measurement accuracy is improved, but the current and voltage requirements exceed drive circuit limits
Solution Approach 1:
The patent changes the field generation parameters by utilizing the flux guide structure to concentrate and direct magnetic flux, achieving constant out-of-plane field over the sensor area with moderate current levels that remain within drive circuit capabilities
Solution Approach 2:
The flux guide acts as an intermediary between the self-test current lines and the TMR elements, shaping and concentrating the magnetic flux to achieve uniform field distribution across the sensor area while reducing the current and voltage requirements compared to direct coil winding
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 reduces power consumption and physical size while ensuring accurate self-test and calibration functions, enabling effective performance testing and mitigation of spurious offset fields, and is applicable to various magnetic sensor technologies.
Implementation Method 1
The self-test coil in the sensor is used to generate controlled fields that are used to test the sensor performance in wafer/die level testing
Implementation Method 2
A TMR element is composed of two ferromagnetic layers separated by a non-magnetic, insulating tunnel barrier. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier is low. Conversely, when the magnetization directions are anti-parallel, the resistance is high. A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance
Implementation Method 3
The self-test current lines are arranged in the same plane as a flux guide within a Z-axis sense element cell. This leads to a higher out-of-plane field that is coupled in the flux guide
Data Source
AI summary
A magnetic field sensor includes built-in self-test coils in a configuration to provide magnetic field stimulation along three axes, with a high field factor, and thus, reduce a power budget of the sensor and physical size of the self-test coils. The magnetic field sensor comprises a first bridge circuit including a plurality of sense elements configured to sense a magnetic field. The magnetic field sensor further comprises re-configurable self-test current lines coupled to a self-test source to perform high field, high power wafer and die level testing and trim, as well as low power in-situ characterization and calibration of the sensor. The self-test current lines may be routed to form a coil with multiple turns around the TMR elements.