Fluxgate Sensor Magnetic Core Annealing
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Solution Overview
Problem
Conventional integrated fluxgate sensors face significant across-wafer variation in magnetic alignment due to as-deposited magnetic layers, which can be exacerbated by magnetic field annealing post-formation, leading to structural defects like cracks and delamination from thermal expansion mismatches.
Innovation Solution
Encapsulating the magnetic core in a nonmagnetic metal or alloy layer, such as titanium, to reduce stress and prevent delamination, followed by magnetic field annealing with a strength of at least 0.1 T at 150°C to improve alignment uniformity without causing structural defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If magnetic field annealing is applied right after forming the magnetic core to maximize alignment improvement, then magnetic alignment uniformity is improved, but structural defects including cracks and delamination occur due to thermal expansion mismatches
Solution Approach 1:
The patent applies preliminary action by forming an encapsulation layer of nonmagnetic metal or metal alloy over the magnetic core before performing magnetic field annealing. This encapsulation layer is deposited in advance to protect the magnetic core during the subsequent thermal annealing process, preventing thermal expansion mismatches from causing cracks and delamination while still allowing the annealing to improve magnetic alignment uniformity.
Solution Approach 2:
The encapsulation layer acts as an intermediary between the magnetic core and the external environment during annealing. This nonmagnetic metal or metal alloy layer mediates the thermal stress by providing a buffer that reduces the direct impact of thermal expansion mismatches on the magnetic core structure, thereby preventing structural defects while enabling the beneficial magnetic alignment effects of annealing.
2Measurement precision
If the magnetic core dimensions are increased to improve sensor performance, then sensitivity is improved, but stress cracking increases
Solution Approach 1:
The patent applies this principle by using a thin encapsulation layer of nonmagnetic metal or metal alloy that conforms to the magnetic core structure. This thin film or shell provides flexible stress distribution across the magnetic core, allowing larger core dimensions for improved sensitivity while preventing stress concentration that would lead to cracking.
Solution Approach 2:
The patent creates a composite structure combining the magnetic core material with a nonmagnetic metal or metal alloy encapsulation layer. This composite material approach allows the magnetic core to be optimized for sensitivity with larger dimensions while the encapsulation layer provides stress management to prevent cracking, achieving both improved measurement precision and structural reliability.
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 encapsulation method allows for larger magnetic core dimensions and significantly reduces stress cracking, achieving uniform magnetic alignment across the wafer with minimal defects, comparable to annealing immediately after core formation.
Implementation Method 1
Magnetic field annealing has the capability to reduce the across-wafer variation of magnetic alignment
Implementation Method 2
magnetic alignment can have a strong beneficial impact on key parameters of fluxgate sensors
Implementation Method 3
annealing right after forming the magnetic core can cause structural defects including cracks and delamination of the magnetic core due to thermal expansion mismatches
Data Source
AI summary
A method of magnetic forming an integrated fluxgate sensor includes providing a patterned magnetic core on a first nonmagnetic metal or metal alloy layer on a dielectric layer over a first metal layer that is on or in an interlevel dielectric layer (ILD) which is on a substrate. A second nonmagnetic metal or metal alloy layer is deposited including over and on sidewalls of the magnetic core. The second nonmagnetic metal or metal alloy layer is patterned, where after patterning the second nonmagnetic metal or metal alloy layer together with the first nonmagnetic metal or metal alloy layer encapsulates the magnetic core to form an encapsulated magnetic core. After patterning, the encapsulated magnetic core is magnetic field annealed using an applied magnetic field having a magnetic field strength of at least 0.1 T at a temperature of at least 150° C.