Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2002-08-27
2003-10-28
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S212000, C324S263000
Reexamination Certificate
active
06639400
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-264357, filed Aug. 31, 2001; and No. 2001-280638, filed Sep. 14, 2001, the entire contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head measuring apparatus for measuring a magnetic head.
2. Description of the Related Art
A magnetic force microscope (MFM) is often used in inspecting a magnetic head. For example, the following inspection method used in a thin-film magnetic head wafer inspection process is known. That is, with a plurality of thin-film magnetic heads formed on a wafer, a groove is formed in a surface on which a medium and the head gap of each thin-film magnetic head are in contact with each other. A probe of the MFM is inserted into this groove to inspect the shape of the head gap surface and the electromagnetic conversion characteristic of the thin-film magnetic head.
The MFM is a kind of a scanning probe microscope (SPM), and is an apparatus which detects a dynamic interaction between a pointed probe (MFM probe) which is a magnetic material, or a nonmagnetic material to which a magnetic material is adhered, and a magnetic field generated from a sample to be measured. The resolution is as very high as several tens of nm, although it depends upon the measurement method and the probe shape. Therefore, this MFM is very effective in magnetic characteristic evaluation on submicron order.
The MFM probe is supported by a leaf spring called a cantilever and has a mechanical resonance frequency determined by the mass of the MFM probe and the sprint constant of the cantilever. Accordingly, in MFM measurements in a normal mode, responses at frequencies higher than this mechanical resonance frequency (generally a few tens of kHz to a few hundred kHz) cannot be measured in the case where the response is measured by applying sinusoidal wave.
In the above inspection method, the MFM measurement is performed while applying a sinusoidal high-frequency electric current to the recording head. However, no desired response can be obtained from the measured MFM signal owing to the above limitation; a high-frequency component is contained in a DC signal. Also, the DC component of the measured MFM signal contains contribution from factors other than the head, e.g., an MFM interaction caused by a DC magnetic field generated from the head magnetic pole. Under the measurement conditions like this, the distribution of a true magnetic field generated from the magnetic head cannot be measured. In other words, strict magnetic head inspection is difficult to perform.
Furthermore, in MFM measurements, measurement values vary owing to tip variations when the MFM probes are changed (in some cases measurement values vary even for the same magnetic head as a sample to be measured). One reason is that the conditions (e.g., the shape, film thickness, and contamination) of a magnetic material at the tip of the MFM probe more or less change from one probe to another. Other reasons are variations in an optical system alignment for measuring the deflection of the cantilever supporting the MFM probe, and detection sensitivity variations caused by a difference in reflectance between thin metal films adhered to the back surface of the cantilever and required in the optical system alignment.
When the foregoing facts are taken into consideration, it is necessary to compensate for the influence of tip variations in the process of inspecting a large amount of magnetic heads. However, the above-mentioned references do not describe any method of solving this problem.
As described above, the conventional methods have the problems that no true high-frequency magnetic field can be measured, and the obtained measurement data have measurement variations caused by tip variations.
Also, electromagnetic conversion measurement for a magnetic head is conventionally performed using, e.g., a spin stand. This measurement must be performed with a magnetic head in the form of HGA (Head Gimbals Assembly). That is, since magnetic heads including defective ones are measured in the form of HGA, the yield cannot be improved unlimitedly.
From the foregoing, the presentation of a magnetic head inspection technology that can reduce measurement variations caused by tip variations and which can improve the yield is desired.
In the meantime, a magnetic recording-head as a sample to be measured by a magnetic head measuring device is, e.g., an inductive type thin-film head and has a magnetic gap that generates a recording magnetic field corresponding to a signal current applied to a coil. The magnetic head measuring device applies a high-frequency signal current to (the coil) of a head as a sample, and measures the distribution of a magnetic field generated from the magnetic gap. One practical measurement method is to detect the phase or deflection (dynamic interaction resulting from a head magnetic field) of a cantilever vibrating and, on the basis of this detection result, measure the force gradient or force acting between the probe and the sample. In this method, measurement is performed using the relationship that the phase of the cantilever approximates the force gradient and the deflection of the cantilever approximates the force.
This measurement method has wide variations. For example, R. Proksch et al., “Measuring the gigahertz response of recording heads with the magnetic force microscope”, (Digital Instruments et al.), Applied Physics Letters, Vol. 74, No. 9, March 1999, pp. 1308-1310 (to be referred to as prior art 1 hereinafter) discloses a technique which applies an amplitude-modulated electric current to a magnetic recording-head and matches the modulation frequency to the resonance frequency of the cantilever, thereby detecting the resonance frequency component of the deflection (or force) of the cantilever vibrating. This technique improves the sensitivity by using the Q value of the mechanical resonance frequency of the cantilever.
Also, Hiroyuki Ohmori, “Techniques of Evaluating and Analyzing Recording and Reproduction Heads”, SONY CORP., Journal of Japan Applied Magnetics Society, Vol. 23, No. 12, 1999, pp. 2111-2117 (to be referred to as prior art 2 hereinafter) discloses a technique which applies a high-frequency sinusoidal wave to a magnetic recording-head and measures the DC component of the phase change (force gradient) of the cantilever, resulting from a magnetic field generated around the head.
In prior art 1, however, the deflection of the cantilever is detected as magnetic field strength. Therefore, the vibration amplitude of the cantilever is not constant during probe scanning. In the case of the measurement which detects dynamic deflection of the cantilever such as the measurement in prior art 1, detected interaction on the probe depends on the cantilever amplitude, probe-sample distance, magnetic field and so on. Therefore, cantilever amplitude and probe-sample distance need to be constant during probe scanning, since magnetic field decays non-linearly. So an image reflecting a magnetic field cannot be measured. In addition, the sensitivity is improved by using the Q value of the mechanical resonance frequency of the cantilever. However, a high Q value may produce a response delay in a change of the cantilever.
On the other hand, prior art 2 measures the DC component of the phase change (force gradient) of the cantilever, resulting from a magnetic field generated around a head. However, this DC component contains contributions other than the high-frequency component, so the obtained data is difficult to analyze.
In either method, the frequency of a magnetic field generated from a magnetic recording-head is on the MHz order, i.e., much higher than the cantilever mechanical resonance frequency which determines the response speed of the scanning probe microscope. This makes it difficult to extract only a high-frequency response and measure this r
Aurora Reena
Kabushiki Kaisha Toshiba
Le N.
Pillsbury & Winthrop LLP
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