Thin-Film Magnetic Head Testing via Ferromagnetic Resonance Frequency
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Solution Overview
Problem
Existing methods for testing thin-film magnetic heads for high-temperature noise are time-consuming and complex, requiring temperature elevation to identify defective heads, which is inefficient and labor-intensive.
Innovation Solution
A testing method and apparatus that utilize an MR read head element with a multi-layered structure, including a magnetization-fixed layer, a magnetization-free layer, and a nonmagnetic intermediate layer, by measuring non-signal output versus frequency characteristics and comparing the frequency of the peak from ferromagnetic resonance with a threshold to determine if the head produces high-temperature noise, allowing for quick identification under room temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature elevation is used to test for high-temperature noise, then measurement accuracy is improved, but testing time and complexity increase significantly
Solution Approach 1:
The patent applies preliminary action by measuring the ferromagnetic resonance frequency of the magnetization-fixed layer at room temperature before any temperature elevation. This preliminary measurement serves as a predictive indicator of high-temperature noise behavior, allowing early identification of defective heads without subjecting all heads to time-consuming high-temperature testing. The room temperature FMR measurement is performed using a vector network analyzer to sweep through a frequency range and identify peak noise characteristics.
Solution Approach 2:
The patent uses copying by creating a correlation between room temperature ferromagnetic resonance characteristics and high-temperature noise performance. Instead of directly measuring high-temperature noise for every head, the method copies the diagnostic information from room temperature FMR measurements, which exhibit characteristic frequency shifts that predict high-temperature behavior. This allows the room temperature measurement to serve as a surrogate for high-temperature testing.
2Reliability
If temperature elevation is used to test for high-temperature noise, then reliable defect detection is improved, but device complexity and operational complexity increase
Solution Approach 1:
The patent applies taking out by extracting the essential diagnostic information (ferromagnetic resonance frequency characteristics) from the complex high-temperature noise measurement process. By isolating and measuring only the FMR characteristics at room temperature, the method extracts the critical predictive parameter without requiring the full high-temperature testing apparatus and procedure. This simplifies the testing setup while maintaining defect detection reliability.
Solution Approach 2:
The patent uses parameter changes by shifting the measurement parameter from high-temperature noise level to room temperature ferromagnetic resonance frequency. Instead of changing the physical state (temperature) of the device under test, the method changes the measurement parameter to FMR frequency, which exhibits characteristic variations that predict high-temperature noise behavior. This parameter substitution simplifies the testing procedure while maintaining diagnostic accuracy.
3Measurement precision
If comprehensive high-temperature testing is performed on all heads, then measurement accuracy is improved, but productivity decreases due to extended testing duration
Solution Approach 1:
The patent applies preliminary action by performing a quick room temperature ferromagnetic resonance frequency measurement on all heads before any high-temperature testing. This preliminary screening identifies defective heads based on characteristic FMR frequency shifts, allowing the testing process to be terminated early for defective units. Only heads that pass the preliminary FMR check proceed to high-temperature verification, significantly increasing testing throughput while maintaining measurement accuracy for final判定.
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
Enables easy and quick discrimination of defective thin-film magnetic heads producing high-temperature noise by comparing the frequency of the peak from ferromagnetic resonance with a threshold, reducing the need for elevated temperature testing and simplifying the evaluation process.
Implementation Method 1
measuring non-signal output versus frequency characteristics of the MR read head element over a frequency range that covers at least a ferromagnetic resonance (FMR) of the magnetization-free layer
Implementation Method 2
a magnetoresistive effect (MR) read head element having a multi-layered structure that includes a magnetization-fixed layer and a magnetization-free layer
Data Source
AI summary
A testing method of a thin-film magnetic head has an MR read head element with a multi-layered structure including a magnetization-fixed layer, a magnetization-free layer and a nonmagnetic intermediate layer or a tunnel barrier layer sandwiched between the magnetization-fixed layer and the magnetization-free layer. The method includes a step of feeding through the MR read head element a sense current, a step of measuring non-signal output versus frequency characteristics of the MR read head element over a frequency range that covers at least FMR of the magnetization-fixed layer, and a step of discriminating whether the thin-film magnetic head is a head providing high-temperature noises by comparing a frequency of a peak of the non-signal output resulting from FMR of the magnetization-fixed layer with a threshold.