Single-Package MTJ Bridge Sensor for Orthogonal Field Detection
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Solution Overview
Problem
Existing magnetic sensors face challenges such as excessive size, inadequate sensitivity, and yield issues during mass production, particularly when integrating magnetic tunnel junction (MTJ) devices into semiconductor packages, and matching magnetoresistive responses for bridge sensors.
Innovation Solution
A single-package magnetic rotation sensor is developed, comprising two full-bridge sensors with MTJ or GMR magnetoresistive sensor chips aligned 90 degrees to each other, utilizing bar-shaped permanent magnets for biasing and wire bonding to a semiconductor package lead frame, encapsulated in plastic for a standard semiconductor package, allowing for precise measurement of magnetic field angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If MTJ devices are integrated into semiconductor packages using standard fabrication processes, then manufacturing cost is reduced and scalability is improved, but yield issues arise due to process difficulty and packaging challenges
Solution Approach 1:
The sensor is divided into separate half-bridge modules that can be independently fabricated and tested before final assembly. Each half-bridge contains a magnetoresistive element and associated circuitry, allowing modular integration into the full bridge configuration. This segmentation enables easier replacement of defective modules and simplifies the packaging process.
Solution Approach 2:
Magnetoresistive elements are pre-characterized and sorted before integration into the bridge configuration. Elements are tested individually to ensure they meet sensitivity and linearity specifications, and are grouped into matched pairs or sets before being assembled into half-bridges and full-bridges. This preliminary sorting ensures high yield by preventing assembly of mismatched components.
2Measurement precision
If bridge sensors are constructed by combining multiple magnetoresistive elements, then sensitivity and dynamic range are improved, but difficulty in matching magnetoresistive responses increases manufacturing complexity
Solution Approach 1:
Each magnetoresistive element is designed with localized compensation features, including individual trim resistors and adjustable bias circuits that can be tuned to match the specific characteristics of that element. This allows each element to be optimized independently rather than requiring all elements to have identical characteristics from fabrication.
Solution Approach 2:
The bridge circuit includes adjustable parameters such as excitation current levels, bias field strengths, and feedback gain that can be tuned to optimize the overall sensor response. These parameters can be adjusted during testing to compensate for variations in individual element characteristics, achieving matched performance without requiring perfectly matched components.
3Area of stationary object
If sensor size is reduced for better integration, then packaging density is improved, but sensitivity and dynamic range may be compromised
Solution Approach 1:
The bridge configuration uses asymmetric element arrangements where elements are positioned at different distances from the magnetic field source or oriented at different angles. This asymmetric layout allows the sensor to maintain sensitivity to a wide range of field strengths and directions while occupying a compact area, as elements strategically positioned closer to the excitation source provide high sensitivity without requiring large overall sensor dimensions.
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 configuration enhances sensitivity, reduces size, and improves yield, enabling cost-effective mass production of high-sensitivity magnetic sensors with improved reliability and dynamic range, effectively addressing the limitations of existing technologies.
Implementation Method 1
MTJ or GMR magnetoresistive sensor chips; each MTJ or GMR magnetoresistive sensor chip is a half-bridge, containing a reference resistor with a fixed resistance and a sensing resistor with a resistance varying in response to a magnetic field
Implementation Method 2
bar-shaped permanent magnets between MTJ or GMR sensor element rows to bias the magnetoresistive elements; the sensing resistors have a resistance that is linearly proportional to an applied magnetic field over a portion of their magnetoresistive transfer curves
Data Source
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AI summary
A single-package bridge-type magnetic-field angle sensor comprising one or more pairs of magnetic tunnel junction sensor chips rotated relative to each other by 90 degrees in order to detect two magnetic field components in orthogonal directions respectively is disclosed. The magnetic-field angle sensor may comprise a pair of MTJ full-bridges or half-bridges interconnected with a semiconductor package lead. The magnetic-field angle sensor can be packaged into various low-cost standard semiconductor packages.