Z-axis Magnetoresistive Sensor with On-Chip Calibration Coil
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Solution Overview
Problem
Current single chip Z-axis linear magnetoresistive sensors face challenges in precision and repeatability due to complex external magnetic field generation systems, imprecise magnetic field application, and irreversible magnetization state changes, leading to hysteresis and increased measurement costs.
Innovation Solution
Integration of a calibration/initialization coil on the chip generates precise current-induced magnetic fields to adjust and restore the magnetization state of magnetoresistive sensing units, eliminating hysteresis and improving measurement efficiency and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complex external magnetic field generation system is used for calibration, then measurement precision can be improved, but device complexity and measurement costs increase
Solution Approach 1:
The patent integrates the calibration coil directly into the sensor chip structure, merging the calibration function with the sensing function. The calibration coil is formed as part of the chip fabrication process, eliminating the need for external magnetic field generation systems and reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The sensor chip performs self-calibration using the integrated calibration coil. The calibration coil generates magnetic fields that can be controlled by on-chip circuitry, allowing the sensor to calibrate itself without requiring external calibration equipment. This self-service approach reduces both device complexity and measurement costs.
2Measurement precision
If external magnetic field generation systems are used for calibration, then measurement precision can be improved, but measurement time and efficiency decrease
Solution Approach 1:
By combining the calibration coil with the sensor chip, the patent enables simultaneous calibration and measurement operations. The integrated structure allows the calibration coil to be activated during or between measurement cycles without requiring separate external calibration equipment, thereby reducing measurement time and improving efficiency.
3Measurement precision
If initialization coil is added to eliminate hysteresis, then measurement precision and repeatability improve, but device complexity increases
Solution Approach 1:
The patent merges the initialization coil with the calibration coil, combining both functions into a single integrated component. This dual-function coil can generate magnetic fields for both calibration and initialization purposes, eliminating the need for separate initialization coil while maintaining measurement precision and repeatability.
Solution Approach 2:
The calibration coil is designed to serve multiple functions: calibration, initialization, and potentially hysteresis elimination. By making the coil multi-functional, the patent reduces device complexity while achieving the desired measurement precision and repeatability without requiring additional dedicated components.
4Stability of the object's composition
If bridge structure is used to compensate temperature dependence, then temperature stability improves, but intrinsic magnetic performance temperature dependence cannot be completely suppressed
Solution Approach 1:
The patent implements a feedback mechanism using the calibration coil to compensate for temperature-dependent magnetic performance changes. By monitoring the sensor output and adjusting the calibration coil current accordingly, the system can dynamically compensate for temperature effects on the intrinsic magnetic performance, achieving better temperature stability than passive bridge structures alone.
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 solution enhances measurement precision and efficiency by allowing precise control of magnetic fields and restoring the initial magnetization state, thereby improving the repeatability and accuracy of Z-axis magnetic field measurements.
Implementation Method 1
a chip-level calibration coil to generate a magnetic field along the sensing direction of the sensor
Implementation Method 2
a high-performance magnetoresistive sensor generally needs another coil to provide a periodic saturation field for the sensing elements in order to eliminate magnetic domains
Implementation Method 3
the soft ferromagnetic flux concentrators 2 distort the Z-direction magnetic field into two magnetic field components that have X-axis and -X-axis magnetic field components
Implementation Method 4
A Magnetic Tunnel Junction (MTJ) sensor is advantageous in terms of high sensitivity, small size, low cost, low power consumption
Data Source
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Figure 5~6
AI summary
A single chip Z-axis linear magnetoresistive sensor with a calibration/initialization coil comprises a single chip Z-axis linear magnetoresistive sensor, and a calibration coil and/or an initialization coil. The calibration coil and the initialization coil are planar coils or three-dimensional coils. The planar coils (101, 102) are located above a substrate and below a magnetoresistive sensing unit, between a magnetoresistive sensing unit and a soft ferromagnetic flux concentrator (2), above a soft ferromagnetic flux concentrator (2), or in a gap of the soft ferromagnetic flux concentrator (2). The three-dimensional coil is wound around the soft ferromagnetic flux concentrator and the magnetoresistive sensing unit. The calibration coil and the initialization coil respectively comprise straight wires (10, 11, 12, 13) which are parallel to a magnetization direction of a pinned layer/free layer, wherein the calibration coil generates an equivalent calibration magnetic field parallel/anti-parallel to the direction of the pinned layer of a push or a pull magnetoresistive unit string (4, 5), and the initialization coil generates a uniform initializing magnetic field in the direction of the free layer at all magnetoresistive sensing units. By controlling the current in the calibration coil/initialization coil, calibration and magnetic state initialization of the single chip Z-axis linear magnetoresistive sensor can be achieved. The sensor has advantages of being highly efficient, quick, and convenient.