Magnetic Encoder Using GMR Sensor With Nonlinear Response
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Solution Overview
Problem
Magnetic encoders face challenges in achieving high resolution and reliability due to insufficient sensitivity and stability in output caused by variations in the magnetic gap between the sensor and medium, particularly when using Spin-valve type GMR elements, which result in unintentional output setoff and reduced signal detection.
Innovation Solution
The use of magnetoresistive elements with nonlinear magnetoresistive properties, characterized by specific magnetic field requirements (H10-50 < H50-90) and locally nonuniform ferromagnetic interlayer coupling, along with annealing treatment under magnetic fields to deviate the magnetization direction of the ferromagnetic pinned layer, ensures high sensitivity in specific resistance change regions and suppresses output setoff.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the magnetized pitch of the magnetic medium is narrowed to achieve high resolution, then the resolution is improved, but the signal magnetic field from the surface of the magnetic medium decreases
Solution Approach 1:
The patent changes the magnetic field sensitivity parameter of the spin-valve type GMR element by adjusting the thickness of the ferromagnetic free layer and the interlayer coupling field strength. This enables the sensor to maintain high sensitivity to weak signal magnetic fields generated by narrowed magnetized pitch, thereby resolving the contradiction between high resolution and sufficient signal field strength.
2Measurement precision
If the pattern width of the magnetic sensor is narrowed to match the magnetized pitch, then the resolution is improved, but shape anisotropy increases and sensitivity to magnetic field decreases
Solution Approach 1:
The patent changes the magnetic anisotropy parameter by controlling the shape anisotropy through specific pattern width and length ratios, and compensates for sensitivity loss by optimizing the ferromagnetic free layer thickness and interlayer coupling field strength of the GMR element, thereby maintaining both high resolution and magnetic field sensitivity.
3Use of energy by stationary object
If spin-valve type GMR elements are used to achieve high MR ratio and low power consumption, then power consumption is reduced, but unintentional output setoff occurs and stability decreases due to variations in magnetic gap
Solution Approach 1:
The patent changes the magnetic field sensitivity parameter of the spin-valve type GMR element by optimizing the ferromagnetic free layer thickness and interlayer coupling field strength. This enables the sensor to maintain stable output characteristics across varying magnetic gap conditions while preserving low power consumption benefits, thereby resolving the contradiction between power efficiency and output stability.
4Use of energy by stationary object
If the thickness of the AMR film is increased to reduce element resistance and power consumption, then power consumption is reduced, but the MR ratio decreases and sensitivity is insufficient
Solution Approach 1:
The patent employs a composite multilayer structure consisting of ferromagnetic pinned layer, nonmagnetic intermediate layer, and ferromagnetic free layer in a spin-valve configuration. This composite structure achieves both low resistance and high MR ratio simultaneously, resolving the contradiction between power consumption and sensitivity that plagues single-layer AMR films.
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 enables a magnetic encoder with stable and high-resolution output, maintaining consistency across varying magnetic gaps, thereby enhancing reliability and reducing the impact of gap fluctuations on sensor performance.
Implementation Method 1
an element utilizing an antiferro-coupled giant magnetoresistive (hereinafter referred to simply as 'coupled GMR') film
Implementation Method 2
The direction of magnetization of the ferromagnetic pinned layer is unidirectionally pinned by an antiferromagnetic layer, which is formed adjacent to the ferromagnetic pinned layer to impart unidirectional magnetic anisotropy to the ferromagnetic pinned layer
Implementation Method 3
annealing treatment under magnetic fields to deviate the magnetization direction of the ferromagnetic pinned layer
Data Source
AI summary
The present invention provides a magnetic sensor suitable for high resolution and having high reliability by achieving stable output even at the occurrence of variations in a gap between a magnetic medium and the magnetic sensor, and a magnetic encoder using the magnetic sensor. The present invention uses a magnetoresistive element having magnetoresistive properties that satisfy the inequation, H10-50<H50-90, where H10-50 represents a magnetic field required for a resistance change from ΔR×10% to ΔR×50% with respect to a maximum amount of resistance change ΔR on a magnetoresitance effect curve, and H50-90 represents a magnetic field required for a resistance change from ΔR×50% to ΔR×90%.