TMR Sensor Bridge Cross-Axis Compensation
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Solution Overview
Problem
Magnetoresistive (MR) magnetic field sensors face challenges with cross-axis effects, which affect sensitivity and accuracy in determining the direction of the Earth's magnetic field, especially when combined with stray fields from phone materials, making precise in situ calibration difficult.
Innovation Solution
A tunneling magnetoresistive (TMR) magnetic field sensor bridge with a specific configuration of layers and connections between sense and reference legs, ensuring linear response and fully compensated cross-axis effect, independent of external magnetic field direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MR sensors are combined in a single device with high sensitivity and 3 orthogonal axes for use as geomagnetic magnetometers, then the sensor can determine the direction of the earth's magnetic field relative to the phone, but stray fields from magnetics and soft-iron materials in the phone superimpose on the earth's field and make in situ calibration difficult to do with high accuracy due to cross-axis effects
Solution Approach 1:
The sensor is divided into four separate sensing elements arranged in a bridge configuration, with each element responding differently to magnetic fields. This segmentation allows differential measurement that cancels out cross-axis effects while maintaining sensitivity to the primary measurement direction.
Solution Approach 2:
A reference element is introduced as an intermediary component that experiences the same cross-axis effects as the sensing elements but does not respond to the primary measurement field. This reference element serves as a mediator to cancel out the harmful cross-axis effects through differential measurement.
2Reliability
If advanced materials with very high TMR like MgO barriers are used, then the sensor achieves higher sensitivity, but the cross-axis effect becomes more pronounced and harder to compensate
Solution Approach 1:
The bridge configuration uses asymmetric arrangement of sensing elements with different magnetization orientations. Two elements have magnetization parallel to the pinned layer while two have magnetization perpendicular to it, creating asymmetric responses that when differenced eliminate cross-axis effects while preserving high TMR sensitivity.
Solution Approach 2:
The invention changes the magnetization orientation parameter of the free layers relative to the pinned layers. By setting specific elements with parallel magnetization and others with perpendicular magnetization, the system exploits parameter variation to achieve cross-axis effect cancellation while maintaining high sensitivity from advanced TMR materials.
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 TMR magnetic field sensor bridge provides high linearity and eliminates cross-axis effects, maintaining sensitivity regardless of applied direction, even with advanced materials like MgO barriers, as demonstrated by Matlab models and component current analysis.
Implementation Method 1
Known magnetoresistive (MR) magnetic field sensors are based on either Anisotropic Magnetoresistance (AMR), Giant Magnetoresistance (GMR), or Tunneling Magnetoresistance (TMR). The present disclosure is directed to a magnetoresistive (MR) magnetic field sensor bridge that in one embodiment is a tunneling MR (TMR) magnetic field sensor bridge.
Data Source
AI summary
In one embodiment, a magnetoresistive (MR) magnetic field sensor system includes a MR magnetic field sensor bridge. The MF magnetic field sensor bridge includes a sense leg with a sense element with a first layer with a first fixed magnetization orientation and, a second layer with a first free magnetization orientation, the first free magnetization orientation orthogonal to the first fixed magnetization orientation at a zero applied magnetic field. A reference leg of the MF magnetic field sensor bridge is electronically connected in parallel to the sense leg. The reference leg includes at least one reference element with a third layer with a second fixed magnetization orientation parallel to, and in the same direction as, the first fixed magnetization orientation, and a fourth layer with a second free magnetization orientation, the second free magnetization orientation parallel to the first fixed magnetization orientation at the zero applied magnetic field.