Rare Earth Thin Film Magnet With MoSi2 Buffer Layer
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Solution Overview
Problem
Existing methods for depositing Nd—Fe—B rare earth magnetic films on silicon substrates face challenges such as film separation and substrate breakage due to linear expansion coefficient differences, especially when the film thickness exceeds a few micrometers, limiting the magnetic field generation and mechanical stability.
Innovation Solution
A rare earth thin film magnet is produced by forming a Nd base film on a silicon substrate with a thermal oxide surface, followed by depositing a Nd—Fe—B film with a composition of 0.120≤Nd/(Nd+Fe)<0.150 using pulsed laser deposition, and subsequent heat treatment, which stabilizes the film and prevents separation even at thicker film thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Nd—Fe—B film is directly deposited on a Si substrate, then the magnetic field generation is improved, but film separation occurs due to linear expansion coefficient difference during heat treatment
Solution Approach 1:
A MoSi2 stress buffer film is introduced as an intermediary layer between the Si substrate and the Nd—Fe—B magnetic film. This buffer film has a linear expansion coefficient intermediate between Si and Nd2Fe14B, acting as a mediator to reduce the thermal expansion mismatch stress during heat treatment, thereby preventing film separation while allowing the magnetic film to function effectively
Solution Approach 2:
The linear expansion coefficient parameter is managed by introducing MoSi2 material with an intermediate expansion coefficient value. This changes the gradient of thermal expansion coefficients across the layered structure, reducing the overall stress accumulation during thermal processing and enabling stable film deposition
2Use of energy by moving object
If the film thickness is increased to generate sufficient magnetic field, then the magnetic field strength is improved, but film separation becomes more likely due to increased stress
Solution Approach 1:
The MoSi2 stress buffer film serves as a mediator that distributes and reduces the interfacial stress between the thick Nd—Fe—B film and the Si substrate. By having an intermediate linear expansion coefficient, it creates a more gradual transition in thermal expansion properties, allowing thicker magnetic films to be deposited without proportionally increasing separation risk
Solution Approach 2:
The stress buffer film is deposited beforehand on the Si substrate before the thick Nd—Fe—B magnetic film is formed. This pre-positioned buffer layer cushions the subsequent stress accumulation during heat treatment, preventing film separation even when the magnetic film thickness is increased to generate sufficient magnetic field strength
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 approach enables the production of rare earth thin film magnets with enhanced magnetic properties, including residual magnetization, coercive force, and maximum energy product, while preventing film separation and substrate breakage, allowing for thicker films without mechanical failure.
Implementation Method 1
the pulsed laser deposition (PLD) method
Implementation Method 2
by using the pulsed laser deposition method
Implementation Method 3
a thermal oxide surface
Implementation Method 4
stress is generated due to the linear expansion coefficient difference between the Si substrate and the Nd—Fe—B film during the heat treatment process
Data Source
AI summary
A rare-earth thin film magnet is provided which includes Nd, Fe and B as essential components, characterized by including a Si substrate having an oxide film present on a surface thereof, a Nd base film formed as a first layer over the Si substrate, and a Nd—Fe—B film formed as a second layer on the first layer. The rare earth thin film magnet and a production process therefor provides a rare earth thin film magnet suffering neither film separation nor substrate breakage and having satisfactory magnetic properties even when the second layer has composition in the range of 0.120 ≤Nd/(Nd+Fe)<0.150, which corresponds to a compositional range in the vicinity of a stoichiometric composition.