Nd-Fe-B Thin Film Magnet on Silicon Substrate
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Solution Overview
Problem
The challenge is to deposit a rare earth thin-film magnet of Nd—Fe—B on a silicon substrate without film separation and substrate fracture, especially at thicknesses exceeding 20 μm, due to thermal expansion differences and increased stress, which existing methods struggle to address effectively.
Innovation Solution
Optimizing the Nd content in the Nd—Fe—B film deposited via pulsed laser deposition, with specific atomic ratios depending on film thickness, and performing pulsed laser deposition and heat treatment to achieve a coercive force of 1000 kA/m or more, residual magnetization of 0.4 T or more, and a maximum energy product of 40 kJ/m3 or more, without the need for a strain buffer layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a Nd—Fe—B film is directly deposited on a Si substrate, then the deposition process is simplified, but film separation occurs during heat treatment due to thermal expansion differences
Solution Approach 1:
The patent introduces a strain buffer film as an intermediary layer between the Si substrate and the Nd—Fe—B film. This buffer film has intermediate thermal expansion properties that mediate between the Si substrate and the magnet film, reducing thermal stress during heat treatment and preventing film separation while maintaining process simplicity.
Solution Approach 2:
The patent optimizes the thickness of the strain buffer film and the composition of the Nd—Fe—B film to control thermal expansion parameters. By carefully adjusting these parameters, the thermal stress is minimized, allowing direct deposition without complex additional processes while maintaining film adhesion.
2Length of stationary object
If the Nd—Fe—B film thickness is increased to at least 10 μm to extract sufficient magnetic field, then the magnetic field extraction is improved, but film separation occurs more easily due to increased stress
Solution Approach 1:
The strain buffer film serves as a mediator that distributes and reduces the stress generated by thick Nd—Fe—B films during heat treatment. This allows the patent to achieve the required 10 μm or greater film thickness for sufficient magnetic field extraction without causing film separation.
Solution Approach 2:
The patent carefully controls the thickness parameter of the strain buffer film and the composition parameters of the Nd—Fe—B film to optimize the stress distribution. This enables the deposition of thick films (10 μm or more) while maintaining film adhesion through parameter optimization.
3Reliability
If a Ta film is used as strain buffer to prevent separation up to 20 μm thickness, then film adhesion is improved, but separation occurs and substrate fracture happens when thickness exceeds 20 μm
Solution Approach 1:
The patent optimizes the thickness parameter of the strain buffer film and the composition parameters of the Nd—Fe—B film to extend the usable thickness range. By adjusting these parameters, the patent achieves stable deposition up to 160 μm thickness, significantly exceeding the 20 μm limitation of conventional approaches.
Solution Approach 2:
The patent uses a composite structure consisting of a Si substrate, a strain buffer film, and a Nd—Fe—B film with optimized composition. This composite material system allows for better stress management and enables thicker film deposition without separation or substrate fracture.
4Reliability
If a strain buffer layer is used to prevent film separation, then film adhesion is improved, but production cost increases
Solution Approach 1:
The patent optimizes the thickness and material composition parameters of the strain buffer film to achieve the minimum effective configuration. This parameter optimization reduces the amount of additional material and processing required, thereby lowering production costs while maintaining film adhesion.
Solution Approach 2:
The strain buffer film is applied only where necessary - as a thin intermediate layer between the substrate and the magnet film. This localized application provides the needed stress relief without adding excessive complexity or cost to the overall manufacturing process.
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 method allows for the stable deposition of a Nd—Fe—B film up to 160 μm thickness on a Si substrate, maintaining favorable magnetic properties and reducing production costs by eliminating the need for a strain buffer layer, while preventing film separation and substrate fracture.
Implementation Method 1
a rare earth thin-film magnet of a Nd—Fe—B film formed via pulsed laser deposition (PLD)
Implementation Method 2
a neodymium-iron-boron (Nd—Fe—B)-based magnet exhibits the highest maximum energy product among existing magnets
Data Source
AI summary
A rare earth thin-film magnet of a Nd—Fe—B film deposited on a Si substrate, wherein, when the film thickness of the rare earth thin film is 70 μm or less, the Nd content satisfies the conditional expression of 0.15≤Nd/(Nd+Fe)≤0.25 in terms of an atomic ratio; when the film thickness of the rare earth thin film is 70 μm to 115 μm (but excluding 70 μm), the Nd content satisfies the conditional expression of 0.18≤Nd/(Nd+Fe)≤0.25 in terms of an atomic ratio; and when the film thickness of the rare earth thin film is 115 μm to 160 μm (but excluding 115 μm), the Nd content satisfies the conditional expression of 0.20≤Nd/(Nd+Fe)≤0.25 in terms of an atomic ratio. An object of the present invention is to provide a rare earth thin-film magnet having a maximum film thickness of 160 μm and which is free from film separation and substrate fracture, and a method of producing such a rare earth thin-film magnet by which the thin film can be stably deposited.