MTJ Magnetic Sensor Using Identical Junctions and Passive Resistors
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Solution Overview
Problem
Current magnetic field sensors using tunnel magnetoresistance (TMR) sensors require complex integration and etch schemes due to the need for four different MTJ structures, which complicates manufacturing and increases costs, while also requiring special annealing processes to orient magnetic fixed layers.
Innovation Solution
A magnetic field sensor design utilizing two identical MgO-based MTJ structures and two passive polysilicon resistors forming a Wheatstone bridge structure, eliminating the need for different MTJ types and simplifying the manufacturing process by using identical MTJ structures that respond similarly to magnetic field changes, with resistors providing a stable resistance that remains constant during field changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If four different MTJ structures are used to form a Wheatstone bridge structure, then magnetic field sensing capability is achieved, but device complexity and manufacturing complexity increase significantly
Solution Approach 1:
The patent uses four identical or substantially similar MTJ structures instead of four different MTJ structures with opposite resistance characteristics. All MTJ structures have the same magnetic fixed layer orientation and respond similarly to magnetic field changes, eliminating the need for complex differentiating designs while maintaining Wheatstone bridge functionality for magnetic field sensing
Solution Approach 2:
Instead of designing MTJ structures with opposite resistance characteristics (Type 1 and Type 2), the patent inverts the approach by using identical MTJ structures and achieving the required differential response through the Wheatstone bridge configuration itself, where adjacent arms provide the necessary resistance differentiation
2Measurement precision
If four different MTJ structures with opposite resistance characteristics are used, then magnetic field sensing is enabled, but manufacturing complexity and etch scheme complexity increase
Solution Approach 1:
The patent employs a unified fabrication process that deposits and patterns identical MTJ structures across the substrate. The same etch scheme and material layers are used for all four MTJ structures, eliminating the need for separate fabrication processes for different MTJ types and significantly simplifying manufacturing
Solution Approach 2:
A single MTJ structure design serves multiple functions in the Wheatstone bridge configuration. The identical MTJ structures are positioned in different locations and connected in specific patterns to achieve both the sensing function and the differential resistance response needed for bridge operation
3Measurement precision
If special annealing processes are used to orient magnetic fixed layers in different directions, then opposite resistance characteristics are achieved, but process complexity increases
Solution Approach 1:
The patent uses a single annealing process that orients the magnetic fixed layers in the same direction for all MTJ structures. This uniform thermal treatment simplifies the process significantly compared to multiple annealing steps required for different orientations, while the Wheatstone bridge configuration provides the necessary differential response through its circuit topology rather than through opposite material properties
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 design enhances magnetic sensitivity by two to three orders of magnitude compared to conventional Hall sensors, reduces manufacturing complexity, and eliminates the need for double processing steps, resulting in a cost-effective and highly sensitive magnetic field detection system.
Implementation Method 1
tunnel magnetoresistance (TMR) sensors have magnetic tunneling junction (MTJ) elements which have resistance changes with a parallel alignment or an anti-parallel alignment
Data Source
AI summary
The present disclosure relates to integrated circuits, and, more particularly, to a magnetic field sensor using magnetic tunneling junction (MTJ) structures and passive resistors, and methods of manufacture and operation. The structure includes: a first portion of a circuit including a first MTJ structure and a first resistor coupled in series between a first voltage source and a second voltage source; and a second portion of the circuit including a second MTJ structure and a second resistor coupled in series between the first voltage source and the second voltage source. The first portion and the second portion are coupled in parallel between the first voltage source and the second voltage source.