Unshielded MTJ Sensor Design for Barkhausen Noise Suppression
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Solution Overview
Problem
Conventional magnetic field sensors face challenges such as high cost, large circuit area, high power consumption, inadequate sensitivity, and temperature-dependent resistance changes, particularly in mobile applications, due to the use of magnetic shields and complex magnetization techniques.
Innovation Solution
The development of a differential sensor using unshielded magnetic tunnel junction (MTJ) sensors with dynamically stabilized sense elements, where the sense layers are angled equally from a pinned layer, allowing for a single pinning direction and eliminating the need for magnetic shields, and the application of a stabilization field pulse to address field fluctuations and micro-magnetic domain issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic shields are used to suppress reference element response, then sensitivity is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes magnetic shields from the Wheatstone bridge structure, extracting the problematic component that caused complexity while maintaining sensitivity through alternative design approaches using unshielded MTJ sensors with carefully engineered magnetic layer configurations
Solution Approach 2:
The patent changes the magnetic properties and configuration of the MTJ sensor layers, specifically using pinned layers with perpendicular magnetization and sense layers with in-plane magnetization, along with controlled exchange coupling to achieve the desired reference element suppression without shields
2Measurement precision
If magnetic shields are used to suppress reference element response, then sensitivity is improved, but manufacturing cost increases
Solution Approach 1:
The patent eliminates magnetic shields from the manufacturing process, removing the need for thick shield deposits and careful NiFe seed and plating step tuning, thereby reducing manufacturing complexity and cost
Solution Approach 2:
The patent modifies the MTJ layer structure and magnetic properties to achieve shield-less operation, using perpendicular magnetization pinned layers and controlled exchange coupling to maintain performance without expensive shield manufacturing
3Measurement precision
If magnetic shields are used, then reference element suppression is improved, but power consumption increases
Solution Approach 1:
The patent removes magnetic shields that consume power and generate heat, reducing overall power consumption while maintaining reference element suppression through intrinsic MTJ layer design
4Device complexity
If unshielded MTJ sensors are used, then device complexity is reduced, but sensitivity decreases
Solution Approach 1:
The patent changes the magnetic configuration parameters of the MTJ layers, using perpendicular magnetization in pinned layers and in-plane magnetization in sense layers with specific thickness ratios and exchange coupling to maintain high sensitivity without shields
Solution Approach 2:
The patent uses composite magnetic layer structures combining CoFeB, CoFe, Ru, and other materials with specific magnetic properties to achieve the desired sensitivity and magnetic stability in unshielded configurations
5Measurement precision
If multiple pinning directions are implemented, then measurement accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The patent makes the pinned layer structure universal by using perpendicular magnetization that can serve multiple sensing directions, eliminating the need for separate pinning layers for each direction and simplifying manufacturing while maintaining measurement accuracy
Solution Approach 2:
The patent uses asymmetric magnetic layer configurations where the pinned layer has perpendicular magnetization and the sense layer has in-plane magnetization, creating the necessary magnetic anisotropy for accurate multi-directional sensing without complex manufacturing
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 simplifies manufacturing, reduces costs, and enhances sensitivity while minimizing power consumption, providing effective magnetic field measurement capabilities without residual magnetic moments and temperature compensation.
Implementation Method 1
CMOS-compatible magnetoelectronic field sensors used to sense magnetic fields
Implementation Method 2
two opposite anti-ferromagnetic pinning directions for each sense axis
Data Source
AI summary
A semiconductor process and apparatus provide a high-performance magnetic field sensor from two differential sensor configurations (201, 211) which require only two distinct pinning axes (206, 216), where each differential sensor (e.g., 201) is formed from a Wheatstone bridge structure with four unshielded MTJ sensors (202-205), each of which includes a magnetic field pulse generator (e.g., 414) for selectively applying a field pulse to stabilize or restore the easy axis magnetization of the sense layers (e.g., 411) to eliminate micromagnetic domain switches during measurements of small magnetic fields.