JPH063644B2 - Pulse noise prevention method for thin film magnetic head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preventing pulsed noise in a thin film magnetic head for in-plane recording / reproducing or for perpendicular recording / reproducing, in which a protective film is formed after forming a thin film magnetic circuit. 270-4 before formation
By performing heat treatment under the temperature condition of 00 ° C., pulse noise such as popcorn noise or noise after writing can be dramatically reduced.

<Prior Art> Two types of thin film magnetic heads are known, one for in-plane recording / reproducing and the other for perpendicular recording / reproducing. FIG. 1 is a perspective view of a main part of an in-plane recording / reproducing thin-film magnetic head known from JP-A-55-84019, and FIG. 2 is a sectional view of the same part. 1 is a substrate, 2 is a lower magnetic film, 3
Is a gap film made of alumina or the like, 4 is an upper magnetic film, 5
Is a conductor coil film, 61 to 63 are insulating films made of an organic insulating resin such as novolac resin, 7 and 8 are lead-out lead portions,
Reference numeral 9 is an insulating film, and 10 is a protective film such as alumina.

The base 1 has a structure in which an insulating film 102 of Al ₂ O ₃ or the like is deposited on a ceramic structure 101 of Al ₂ O ₃ .TiC or the like. This type of thin-film magnetic head undergoes a manufacturing process in which a large number of thin-film magnetic head elements are formed on a wafer and then cut to take out each thin-film magnetic head element. Therefore, the substrate 1 is generally a wafer. is there.

The tip ends of the magnetic films 2 and 4 are pole portions 21 and 41 that face each other across the gap film 3 made of alumina or the like. Reading and writing are performed on the pole portions 21 and 41.

The conductor coil film 5 constitutes a thin film magnetic circuit together with the magnetic films 2 and 4 and the gap film 3. This conductor coil part 5
Has a structure in which a conductor film 5B made of Cu plating is laminated on a base conductor film 5A made of a Cu / Ti sputtered film, and a coupling portion of the yoke portions 22 and 42 of the magnetic films 2 and 4 is formed. It is formed in a spiral shape around.

The protective film 10 is provided to protect the thin film magnetic head element composed of the magnetic films 2 and 4, the gap film 3, the conductor coil film 5 and the interlayer insulating films 61 to 63.
It is formed as a sputtered film of alumina or the like. The perspective view of FIG. 1 shows a state before the protective film 10 is provided.

<Problems to be Solved by the Invention> However, in the conventional thin film magnetic head, when a read operation is performed after a time of about 10 μs to 20 μs is given after a write signal is applied, the read signal is usually Pulsed noise having a peak value significantly higher than that of the white noise of is generated. FIG. 3 is an oscilloscope waveform diagram showing pulse-like noise in white noise. The horizontal axis is a time scale represented by 0.5 μs per unit scale.
The vertical axis is a voltage scale represented by 30 μV per unit scale. Below the waveform diagram, a time chart of the write operation and the read operation is displayed with their time axes aligned. When the read operation is started at t ₀ after the write operation is stopped, the peak value is remarkably higher than the level of the white noise P _W when 1.5 μs to 2.5 μs has elapsed with respect to t _0. High pulse-like noise P _P occurs. Such noise P _P is called popcorn noise, access noise, or post-write noise by those skilled in the art.

Although the generation mechanism of the popcorn noise P _P is not always clear, it is presumed that the main factor is the delay in the formation of the magnetic domains in the magnetic films 2 and 4 when the write operation state shifts to the stationary state. The magnetic films 2 and 4 have magnetic anisotropy, and during writing operation, as shown in FIG. 4, the magnetic domain facing the hard axis direction H _H is shown in FIG. as shown in, 9 from the hard axis direction H _H
The direction is changed to the easy axis direction H _E rotated by 0 degree. The popcorn noise P _P is generated due to a time delay when the magnetic domain directions of the magnetic films 2 and 4 rotate from the hard axis direction H _H to the easy axis direction H _E.

The popcorn noise P _P reaches 100 μV _op when the peak value V _op is large, and cannot be distinguished from a normal read signal, resulting in a read error in the magnetic disk drive. This is an extremely important problem that may deny the practicality of the thin film magnetic head. However, at present, there is no effective solution. For example,
Although it is conceivable to increase the time (post.write.recovery.time) between the write operation and the read operation, it is necessary to change the system of the magnetic disk drive device in order to apply it. , Actually close to impossible. Moreover, post. Light. recovery. Taking a long time runs counter to the demand for high-density recording.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a method of a thin film magnetic head capable of dramatically reducing pulse noise such as popcorn noise.

<Means for Solving the Problems> In order to solve the problems described above, the present invention is a method for preventing pulse-like noise that may appear in a read signal at the time of a read operation of a thin film magnetic head. And, as shown in FIG. 2, after forming the thin film magnetic circuits 2 to 6 including the magnetic films 2 and 4 and the conductor coil film 5 on the substrate 1, the protective film 10 covering the thin film magnetic circuits 2 to 6 is formed. Before 270 ℃ ~
It is characterized in that the heat treatment is performed under a temperature condition of 400 ° C.

<Operation> When the heat treatment is performed under the temperature condition of 270 ° C. to 400 ° C. after forming the thin film magnetic circuits 2 to 6 and before forming the protective film 10 covering the thin film magnetic circuits, the reason is not clear.
It was found that the popcorn noise was significantly reduced.

At a temperature of 270 ° C. or lower, no remarkable effect can be obtained in reducing popcorn noise. At temperatures of 400 ° C. or higher, the characteristics of the magnetic films 2 and 4 formed as permalloy films deteriorate. Therefore, a temperature range of 270 ° C to 400 ° C is suitable.

When heat treatment is performed after forming the protective film 10, problems such as thermal stress between the protective film 10 and the magnetic film 4 and interface peeling occur. In order to avoid this problem, the above heat treatment is performed before forming the protective film 10.

The heat treatment time depends on the temperature conditions. Above temperature 27
In the range of 0 ° C to 400 ° C, a treatment time of 10 minutes to 120 minutes is suitable. If the heat treatment time is too long, the insulating film 61
A problem of film loss of about 63 occurs. As an example, 320
At a temperature of ℃, heat treatment time of about 60 minutes is suitable,
If the amount exceeds the limit, film loss will be unfavorable.

The above heat treatment is preferably performed in a vacuum having a vacuum degree of about 10 ^-2 to 10 ^-6 Torr. Insulating film 6 is used for the atmosphere treatment in vacuum.
This is to prevent carbonization of 1 to 63.

<Example> As shown in FIG. 1, after the thin film magnetic circuits 2 to 6 are formed on the substrate 1 which is a wafer, and before the protective film 10 is provided, heat treatment is performed at a temperature of 320 ° C. for 60 minutes. Was done.
The above heat treatment was performed in a vacuum having a vacuum degree of about 10 ^-3 to 10 ^{-5 Torr} . After that, a protective film 10 is formed by sputtering,
A thin film magnetic head having a structure as shown in FIG. 2 was obtained. In the obtained thin film magnetic head, the number of turns of the conductor coil film 5 is 32 and the resistance value is 30Ω.

FIG. 6 is a graph showing the popcorn noise number before and after the heat treatment of the above magnetic head. As shown in the figure, the popcorn noise, which was 1000 or more before the heat treatment, becomes almost zero after the heat treatment, and is dramatically reduced. In FIG. 6, the .smallcircle shows the case of setting the noise threshold voltage for the popcorn noise detection 40 uV _op, △ mark is popcorn frequency noise in the case of setting to 50μV _op. The effect of reducing the popcorn noise was the same for the thin film magnetic head on the wafer and the individual thin film magnetic heads after the wafer was piece-processed.

Next, the conditions set for obtaining the data in FIG. 6 will be described.

FIG. 7 is a time chart of write and read operations for obtaining the data of FIG. Write operation: Write current 40mA
_op and writing time were 1 ms. 10 μs after completion of writing operation
Post. Light. recovery. Time was taken and the read operation was performed. The read time is 16 ms. A test for 2 minutes was performed with the above as one cycle. The level of white noise assuming 30μV _op, noise threshold voltage 40 uV _op for popcorn noise detection, 50MyuV
_The test was conducted by setting each to _op .

FIG. 8 is a block diagram of the measurement circuit provided to obtain the data of FIG. In the figure, 11 is a thin film magnetic head, 12 and 13 are amplifiers, 14 is a filter, 15 is an operational amplifier, 16 is a comparator, 17 is a logic gate, 18 is a read / write switching controller, 19 is a gate controller, 20 is a gate. A timer, 21 is a logic gate, and 22 is a popcorn counter.

A switching signal applied from the switching controller 18 to the amplifier 12 switches between reading and writing according to the time chart shown in FIG. In the read operation, the signals output from the thin film magnetic head 11 are amplified by the amplifiers 12 and 13,
A necessary frequency component is extracted by the filter 14 and input to the comparator 16 through the operational amplifier 15. Comparator 16
Compares the signal supplied by the operational amplifier 15 with the noise threshold set by the Zener diode 23 for popcorn noise detection, and when the former is larger than the latter, produces a logic 1 output. This comparison output of logic 1 is passed through a logic gate 17 and popcorn noise. It is given to the counter 22 to count. Popcorn noise. The counting timing in the counter 22 is determined by the timing signal given from the gate controller 19 and the gate timer 20 through the logic gate 21.

<Advantages of the Invention> As described above, the present invention is a method of preventing pulse-like noise that may appear in a read signal during a read operation of a thin film magnetic head, and a magnetic film and a conductor coil film are provided on a substrate. After forming the thin film magnetic circuit including Pd, the heat treatment is performed under the temperature condition of 270 ° C. to 400 ° C. before forming the protective film covering the thin film magnetic circuit, so that pulse noise such as popcorn noise is almost generated. A thin film magnetic head can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an essential part of a thin film magnetic head, FIG. 2 is a sectional view of an essential part of a thin film magnetic head, FIG. 3 is an oscilloscope waveform diagram showing popcorn noise in white noise, and FIG. FIG. 5 is a diagram showing a magnetic domain structure during operation, FIG. 5 is a diagram showing a magnetic domain structure during a read operation, FIG. 6 is a graph showing popcorn noise numbers before and after heat treatment of a thin film magnetic head, and FIG. Is a time chart of write and read operations for obtaining the data of FIG. 6, and FIG. 8 is a block diagram of a measuring circuit provided for obtaining the data of FIG. 1 ... Substrate 2, 4 ... Magnetic film 5 ... Conductor coil film 10 ... Protective film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Shoko 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Inventor Tsutomu Koyanagi 1-13-11-1 Nihonbashi, Chuo-ku, Tokyo TDC Incorporated (72) Inventor Mikio Matsuzaki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Inventor Shinya Oyama 1-1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Corporation ( 72) Inventor Yoshiaki Tanaka, 13-1 Nihonbashi, Chuo-ku, Tokyo, TDC Corporation (56) Reference JP-A-2-83809 (JP, A)

Claims (2)

[Claims] 1. A method of preventing pulsed noise that may appear in a read signal during a read operation of a thin film magnetic head, comprising: forming a thin film magnetic circuit including a magnetic film and a conductor coil film on a substrate; A method for preventing pulsed noise in a thin film magnetic head, characterized in that heat treatment is performed under a temperature condition of 270 ° C. to 400 ° C. before forming a protective film covering the thin film magnetic circuit. 2. The method for preventing pulsed noise in a thin film magnetic head according to claim 1, wherein the heat treatment is performed for 10 minutes to 200 minutes.