TMR Magnetic Sensor SNR via Interleaved Z-Axis Layout
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Solution Overview
Problem
Magnetic field sensors with high signal-to-noise ratio (SNR) require high power for operation, making them unsuitable for low power and high resolution magnetic sensing applications.
Innovation Solution
The implementation of a Wheatstone bridge circuit with identical sense elements, interleaved Z-axis layout, dual flux guides, and optimized reset line routing to reduce parasitic effects and enhance sense element packing density, thereby increasing the SNR of TMR magnetic field sensors without compromising sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high power is supplied to the magnetic field sensor, then the signal-to-noise ratio (SNR) is improved, but the power consumption increases making it unsuitable for low power applications
Solution Approach 1:
The sensor is divided into multiple sense elements arranged in a Wheatstone bridge circuit with four legs. Each leg contains an identical number of sense elements, allowing the total sensing function to be segmented across multiple components that work differentially to improve SNR while maintaining lower power requirements through balanced operation
Solution Approach 2:
A Z-axis layout is introduced by placing flux guides vertically between the pinned and free layers. This adds a dimensional element that concentrates magnetic flux through the sense elements, enhancing the magnetic field sensing capability and SNR without requiring increased power consumption
2Measurement precision
If more sense elements are packed into the sensor, then the SNR increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple sense elements are merged into integrated structures where adjacent elements share common connections and are fabricated using the same material layers and processes. The Wheatstone bridge configuration merges four legs of sense elements into a unified circuit that achieves high SNR through differential measurement while simplifying the overall device structure
Solution Approach 2:
The sense elements are designed with specific geometric parameters including aspect ratios between 1:2 and 1:5, and controlled spacing between adjacent elements. These parameter optimizations enable dense packing of sense elements while maintaining manufacturability through standard fabrication processes and achieving high SNR through increased element density
3Measurement precision
If sense elements are densely packed, then the SNR increases, but parasitic effects increase reducing measurement accuracy
Solution Approach 1:
The Wheatstone bridge circuit is designed with asymmetric current paths where adjacent sense elements carry currents in opposite directions. This asymmetry causes parasitic effects such as resistive drops and thermal noise to oppose each other, resulting in cancellation of harmful parasitic signals while the differential magnetic sensing signals add constructively
Solution Approach 2:
The parasitic effects that normally degrade sensor performance are converted into beneficial differential signals. By arranging sense elements to carry opposite currents, the parasitic voltage drops and thermal effects generate differential outputs that are indistinguishable from genuine magnetic field signals, allowing the measurement system to treat all differential signals as valid measurement data
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 effectively increases the SNR of TMR magnetic field sensors for low power and high resolution sensing, allowing for denser packing of sense elements and reduced noise, while maintaining sensitivity and power efficiency.
Implementation Method 1
Tunneling Magnetoresistance (TMR) is a promising magnetic sensing technology for handset applications due to its advantages in sensitivity, power, and process cost compared with other magnetic sensors
Implementation Method 2
dual flux guides are utilized for an optimal trench width while maintaining pitch and spacing constraints of a reference layer within a TMR sense element
Data Source
AI summary
Various means for improvement in signal-to-noise ratio (SNR) for a magnetic field sensor are disclosed for low power and high resolution magnetic sensing. The improvements may be done by reducing parasitic effects, increasing sense element packing density, interleaving a Z-axis layout to reduce a subtractive effect, and optimizing an alignment between a Z-axis sense element and a flux guide, etc.