JPH0475569B2 - - Google Patents
Info
- Publication number
- JPH0475569B2 JPH0475569B2 JP58186758A JP18675883A JPH0475569B2 JP H0475569 B2 JPH0475569 B2 JP H0475569B2 JP 58186758 A JP58186758 A JP 58186758A JP 18675883 A JP18675883 A JP 18675883A JP H0475569 B2 JPH0475569 B2 JP H0475569B2
- Authority
- JP
- Japan
- Prior art keywords
- magnetic
- shield layer
- magnetic shield
- layer
- magnetoresistive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000000758 substrate Substances 0.000 claims description 15
- 230000035699 permeability Effects 0.000 claims description 2
- 230000005415 magnetization Effects 0.000 description 28
- 229910000889 permalloy Inorganic materials 0.000 description 11
- 239000004020 conductor Substances 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 230000007423 decrease Effects 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 239000000696 magnetic material Substances 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 229910052755 nonmetal Inorganic materials 0.000 description 1
- 238000000059 patterning Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000001259 photo etching Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000001552 radio frequency sputter deposition Methods 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
- G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
- G11B5/3903—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects using magnetic thin film layers or their effects, the films being part of integrated structures
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Magnetic Heads (AREA)
Description
【発明の詳細な説明】
〔発明の利用分野〕
本発明は、電流バイアス方式による磁気抵抗効
果型再生ヘツドに係わり、特に、磁気シールド部
材を通してバイアス電流を流すようにした磁気抵
抗効果型再生ヘツドに関する。DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a magnetoresistive reproducing head using a current bias method, and more particularly to a magnetoresistive reproducing head in which a bias current is caused to flow through a magnetic shield member. .
近年、磁気抵抗効果素子を用いた再生ヘツドす
なわち、磁気抵抗効果型再生ヘツドが注目される
ようになつてきた。これは、磁界の強さに応じて
電気抵抗値（以下、単に抵抗値という）が変化す
るという、磁気抵抗効果素子の作用を利用するも
のであつて、磁気記録媒体上に形成されたトラツ
ク上の磁化パターンに応じて変化する磁界を、磁
気抵抗効果素子の抵抗値の変化として検出するこ
とにより、該トラツクに記録された情報信号を再
生することができるようにしたものである。
In recent years, read heads using magnetoresistive elements, that is, magnetoresistive read heads, have been attracting attention. This utilizes the effect of the magnetoresistive element, in which the electrical resistance value (hereinafter simply referred to as resistance value) changes depending on the strength of the magnetic field, and it is used on tracks formed on the magnetic recording medium. By detecting a magnetic field that changes according to the magnetization pattern of the track as a change in the resistance value of the magnetoresistive element, it is possible to reproduce the information signal recorded on the track.
ところで、磁気抵抗効果素子には、自発磁化
（以下、単に磁化という）が生じており、この磁
化の方向は、磁気抵抗効果素子に磁界が加えられ
ていない（以下、無磁界状態という）ときには、
磁気抵抗効果素子の磁化容易軸に平行である。こ
の場合、磁化容易軸方向の抵抗値をみると、かか
る無磁界状態では、大きな値となる。 By the way, spontaneous magnetization (hereinafter simply referred to as magnetization) occurs in the magnetoresistive element, and the direction of this magnetization is as follows when no magnetic field is applied to the magnetoresistive element (hereinafter referred to as a no-magnetic field state).
It is parallel to the easy axis of magnetization of the magnetoresistive element. In this case, when looking at the resistance value in the direction of the easy axis of magnetization, it becomes a large value in such a non-magnetic field state.
いま、この磁化容易軸方向と垂直な方向に磁界
を印加すると、この磁界の強さに応じて磁気抵抗
効果素子における磁化の方向は磁化容易軸に垂直
な方向へと変化する。そして、磁化容易軸方向の
抵抗値は、磁化の方向が磁化容易軸に垂直な方向
に近づくほど小さくなる。 Now, when a magnetic field is applied in a direction perpendicular to this easy axis direction, the direction of magnetization in the magnetoresistive element changes to a direction perpendicular to the easy axis depending on the strength of this magnetic field. The resistance value in the easy axis direction becomes smaller as the direction of magnetization approaches the direction perpendicular to the easy axis.
第１図はかかる磁気抵抗効果素子の磁界−電気
抵抗特性を示す特性図であつて、横軸に磁気抵抗
素子の磁化容易軸に垂直な方向の磁界の強さを、
また、縦軸にこの容易軸方向の抵抗値をとつてい
る。 FIG. 1 is a characteristic diagram showing the magnetic field-electrical resistance characteristics of such a magnetoresistive element, in which the horizontal axis represents the strength of the magnetic field in the direction perpendicular to the axis of easy magnetization of the magnetoresistive element.
Furthermore, the resistance value in the easy axis direction is plotted on the vertical axis.
同図から明らかなように、磁界の強さが零のと
きには、磁気抵抗効果素子は最大の抵抗値を呈
し、磁界の強さが増加するとともに、磁界の方向
には関係なく抵抗値は減少する。そして、磁界の
強さがある値以上になると、抵抗値は飽和して最
小の抵抗値を呈する。 As is clear from the figure, when the magnetic field strength is zero, the magnetoresistive element exhibits the maximum resistance value, and as the magnetic field strength increases, the resistance value decreases regardless of the direction of the magnetic field. . Then, when the strength of the magnetic field exceeds a certain value, the resistance value is saturated and exhibits the minimum resistance value.
この抵抗値が飽和するのは、磁気抵抗効果素子
の磁化の方向が磁化容易軸に垂直であることによ
るものである。 This resistance value is saturated because the direction of magnetization of the magnetoresistive element is perpendicular to the axis of easy magnetization.
そこで、かかる磁気抵抗効果素子を用いて磁気
抵抗効果型再生ヘツドを形成し、磁気記録媒体上
のトラツクを、その磁化パターンによる磁界の方
向が磁気抵抗効果素子の磁化容易軸に垂直になる
ようにして再生走査を行なうと、上記磁化パター
ンによる磁界の強さに応じて磁気抵抗効果素子の
抵抗値が変化し、また、上記の磁化パターンは情
報信号に応じたものであるから磁気抵抗効果素子
の磁化容易軸の方向に電流を流すことにより、上
記トラツクに記録されている情報信号を電流の変
化として再生することができる。 Therefore, a magnetoresistive reproducing head is formed using such a magnetoresistive element, and a track on a magnetic recording medium is formed such that the direction of the magnetic field due to the magnetization pattern is perpendicular to the axis of easy magnetization of the magnetoresistive element. When performing reproduction scanning, the resistance value of the magnetoresistive element changes depending on the strength of the magnetic field due to the magnetization pattern, and since the magnetization pattern above corresponds to the information signal, the resistance value of the magnetoresistive element changes depending on the strength of the magnetic field due to the magnetization pattern. By passing a current in the direction of the axis of easy magnetization, the information signal recorded on the track can be reproduced as a change in current.
以上が磁気抵抗効果型再生ヘツドの原理であ
る。 The above is the principle of the magnetoresistive read head.
ところで、かかる磁気抵抗効果型再生ヘツドに
より、磁気記録媒体から情報信号を再生する場合
についてみると、磁気記録媒体上のトラツクの磁
化パターンによる磁界のみにより、磁気抵抗素子
の抵抗値を変化させる場合には、この磁気をH1
とすると、第２図において、特性曲線の点Ａを中
心として抵抗値が変化し、ΔR1の抵抗値変化が得
られる。この抵抗値変化ΔR1は磁界H1の１周期
の変化に対して２周期の変化として表われる。 By the way, in the case of reproducing information signals from a magnetic recording medium using such a magnetoresistive reproducing head, when the resistance value of the magnetoresistive element is changed only by the magnetic field caused by the magnetization pattern of the tracks on the magnetic recording medium, converts this magnetic field to H 1
Then, in FIG. 2, the resistance value changes around point A of the characteristic curve, and a resistance value change of ΔR 1 is obtained. This resistance value change ΔR 1 appears as a two-cycle change for one-cycle change in the magnetic field H 1 .
これに対して、第２図において、特性曲線の直
線部分の中心点Ｂを中心として、抵抗値が変化す
るようにすると、上記磁化パターンによる同じ磁
界H1の変化に対して、抵抗値変化はΔR2となる。
この抵抗値変化ΔR2は、磁界H1の１周期の変化
に対して同じく、周期の変化として表われ、か
つ、点Ａを動作点とした場合よりもその変化の割
合が大きい。 On the other hand, in FIG. 2, if the resistance value is made to change around the center point B of the straight line portion of the characteristic curve, the resistance value will change for the same change in magnetic field H1 due to the above magnetization pattern. ΔR 2 .
This resistance value change ΔR 2 appears as a periodic change in the same manner as a one-period change in the magnetic field H 1 , and the rate of change is larger than when the point A is the operating point.
そこで、磁気抵抗効果型再生ヘツドの磁気抵抗
効果素子に、その磁化容易軸に平行に電流（以
下、この電流を検出用電流という）を流したと
き、上記の抵抗値変化によつて検出用電流が変化
するが、第２図の点Ａを動作点としたときには、
検出用電流の変化が小さく、かつ、この変化はト
ラツクに記録された情報信号の周波数の２倍の周
波数となり、この情報信号を忠実に再生すること
はできない。これに対して、第２図の点Ｂを動作
点とすると、検出用電流の変化は非常に大きく、
また、トラツクに記録された情報信号を忠実に表
わしている。 Therefore, when a current (hereinafter referred to as the detection current) is passed through the magnetoresistive element of the magnetoresistive playback head in parallel to its axis of easy magnetization, the detection current changes due to the above resistance value change. changes, but when point A in Figure 2 is taken as the operating point,
The change in the detection current is small, and this change has a frequency twice that of the information signal recorded on the track, making it impossible to faithfully reproduce this information signal. On the other hand, if point B in Fig. 2 is taken as the operating point, the change in the detection current is very large.
It also faithfully represents the information signals recorded on the track.
このことから、従来、磁気抵抗効果型再生ヘツ
ドにおいては、第２図に示す点Ｂを最適動作点と
している。この最適動作点Ｂは、磁気抵抗効果素
子の異方性磁界をHKとすると、約0.5HK〜0.7HK
であり、このとき、磁気抵抗効果素子の磁化の方
向は、磁化容易軸に対して45゜傾いている。なお、
第２図の磁界が負の領域の特性曲線の直線部分の
中心点B′も同様に最適動作点となり、この最適
動作点B′は約−0.5HK〜−0.7HKである。 For this reason, point B shown in FIG. 2 has conventionally been set as the optimum operating point in magnetoresistive read heads. This optimum operating point B is approximately 0.5H K to 0.7H K , where H K is the anisotropic magnetic field of the magnetoresistive element.
In this case, the direction of magnetization of the magnetoresistive element is inclined at 45 degrees with respect to the axis of easy magnetization. In addition,
Similarly, the center point B' of the linear portion of the characteristic curve in the region where the magnetic field is negative in FIG. 2 is the optimum operating point, and this optimum operating point B' is about -0.5H K to -0.7H K.
かかる最適動作点Ｂ（あるいはB′）を設定する
ためには、磁気抵抗効果素子に予じめその磁化容
易軸に垂直な方向に一定のバイアス磁界Hb（第２
図）を印加しなければならない。このバイアス磁
界を発生させるようにした従来からよく知られて
いる代表的な方式は、バイアス導体にバイアス電
流を流し、このバイアス電流によつて生ずる磁界
をバイアス磁界とするもの（すなわち、電流バイ
アス方式）である。この電流バイアス方式の磁気
抵抗効果型再生ヘツドは、さらに、外部磁界を遮
断するのに設けられた磁気シールド層をバイアス
導体とするものと、新たにバイアス導体を設ける
ものとがある。 In order to set such an optimal operating point B (or B'), a constant bias magnetic field H b (second
Figure) must be applied. A conventional and well-known typical method for generating this bias magnetic field is one in which a bias current is passed through a bias conductor and the magnetic field generated by this bias current is used as a bias magnetic field (i.e., current bias method). ). The current bias type magnetoresistive read head further includes one in which a magnetic shield layer provided to block an external magnetic field is used as a bias conductor, and another in which a bias conductor is additionally provided.
第３図は磁気シールド層をバイアス導体とした
従来のマルチトラツク用磁気抵抗効果型再生ヘツ
ドを示すものであつて同図ａはテープ摺動面側か
らみた正面図、同図ｂはテープ摺動面に垂直な断
面図であり、１は磁性基板、２は下部ギヤツプ、
３は磁気抵抗効果素子、４は上部ギヤツプ、５は
磁気シールド層である。 Figure 3 shows a conventional multi-track magnetoresistive playback head in which the magnetic shield layer is used as a bias conductor. 1 is a sectional view perpendicular to the plane, 1 is a magnetic substrate, 2 is a lower gap,
3 is a magnetoresistive element, 4 is an upper gap, and 5 is a magnetic shield layer.
同図ａにおいて、Ni−Zoフエライトなどの磁
性材からなる磁性基板１上に、MiO2などの非磁
性絶縁材からなる下部ギヤツプ２が形成され、こ
の下部ギヤツプ２上にトラツク幅Ltの複数個の磁
気抵抗効果素子３が形成されている。この磁気抵
抗効果素子３としては、膜厚が約0.05μｍで、テ
ープ摺動面に垂直な方向の幅が２〜7μｍのパー
マロイ薄膜が用いられ、一般には、図示するよう
に、その磁化容易軸Ｍがテープ摺動面に平行で、
かつ、トラツク幅方向に平行になるように形成さ
れている。また、磁気抵抗効果素子３には、図示
しない導体が接続され、この導体から磁気抵抗効
果素子３に、その磁化容易軸Ｍと平行な方向に検
出用電流ipが流される。 In the same figure a, a lower gap 2 made of a non-magnetic insulating material such as MiO 2 is formed on a magnetic substrate 1 made of a magnetic material such as Ni - Zo ferrite, and a track width L t is formed on this lower gap 2. A plurality of magnetoresistive elements 3 are formed. As this magnetoresistive effect element 3, a permalloy thin film with a film thickness of approximately 0.05 μm and a width of 2 to 7 μm in the direction perpendicular to the tape sliding surface is used, and generally, as shown in the figure, its easy magnetization axis is M is parallel to the tape sliding surface,
Moreover, it is formed so as to be parallel to the track width direction. Further, a conductor (not shown) is connected to the magnetoresistive element 3, and a detection current i p is passed from this conductor to the magnetoresistive element 3 in a direction parallel to its axis of easy magnetization M.
下部ギヤツプ２上には、さらに、磁気抵抗効果
素子３を完全に覆うように、SiO2などの上部ギ
ヤツプ４が形成され、その上部ギヤツプ４上に磁
気シールド層５が形成されている。磁気シールド
層５は、膜厚が約2μｍでテープ摺動面に垂直な
方向の幅が30〜50μｍのパーマロイ薄膜が用いら
れ、バイアス導体も兼ねて一定のバイアス電流ib
が流される。 Further, an upper gap 4 made of SiO 2 or the like is formed on the lower gap 2 so as to completely cover the magnetoresistive element 3, and a magnetic shield layer 5 is formed on the upper gap 4. The magnetic shield layer 5 is a permalloy thin film with a film thickness of about 2 μm and a width of 30 to 50 μm in the direction perpendicular to the tape sliding surface, and also serves as a bias conductor and carries a constant bias current i b
is washed away.
バイアス電流ibは、磁気抵抗効果素子３のトラ
ツク幅方向に流れており、いま、第３図ｂに示す
方向に流れているとすると、バイアス磁界Hbは、
磁気シールド層５に関して図面上反時計方向に生
じ、磁気抵抗効果素子３中テープ摺動面の方向の
向きで生ずる。したがつて、このバイアス磁界
Hbにより、磁気抵抗効果素子３の磁化の向きは
磁化容易軸Ｍ（第３図ａ）に平行な方向からテー
プ摺動面の方向に傾き、磁気抵抗効果素子３の磁
化容易軸Ｍの方向の抵抗値が低下する。バイアス
電流ibの大きさは、磁気抵抗効果素子３の動作点
が第２図に示した最適動作点ＢあるいはB′とな
るようなバイアス磁界Hbが生ずるように、設定
される。 The bias current i b is flowing in the track width direction of the magnetoresistive element 3, and if it is now flowing in the direction shown in FIG. 3b, the bias magnetic field H b is
It occurs counterclockwise in the drawing with respect to the magnetic shield layer 5, and occurs in the direction of the tape sliding surface in the magnetoresistive element 3. Therefore, this bias magnetic field
Due to H b , the direction of magnetization of the magnetoresistive element 3 is tilted from the direction parallel to the easy axis M of magnetization (Fig. 3 a) toward the tape sliding surface, and the direction of the magnetization of the magnetoresistive element 3 is tilted in the direction of the easy axis M of magnetization. resistance value decreases. The magnitude of the bias current i b is set so as to generate a bias magnetic field H b that brings the operating point of the magnetoresistive element 3 to the optimum operating point B or B' shown in FIG.
以上のようにして、上記従来の磁気抵抗効果型
再生ヘツドにおいては、歪みがなくて忠実に大き
い再生出力信号が得られる。 As described above, in the conventional magnetoresistive reproducing head described above, a large reproduced output signal can be obtained faithfully and without distortion.
しかし、かかる従来の磁気抵抗効果型再生ヘツ
ドにおいては、磁気抵抗効果素子３の動作点を最
適動作点ＢあるいはB′に設定するためにはバイ
アス電流ibとして、150〜250ｍＡと非常に大きな
電流でなければならず、このために、磁気シール
ド層５が発熱して磁気抵抗効果型再生ヘツド自体
が加熱される。この加熱によつて磁気抵抗効果素
子３などに熱雑音が生じ、この結果、再生信号の
Ｓ／Ｎが劣化することになる。 However, in such a conventional magnetoresistive read head, in order to set the operating point of the magnetoresistive element 3 to the optimum operating point B or B', a very large current of 150 to 250 mA is required as the bias current i b . Therefore, the magnetic shield layer 5 generates heat and the magnetoresistive read head itself is heated. This heating causes thermal noise in the magnetoresistive element 3, etc., and as a result, the S/N of the reproduced signal deteriorates.
本発明等の電流バイアス方式磁気抵抗効果型再
生ヘツドに関する系統的研究の結果、最適動作点
ＢあるいはB′にバイアスするために必要なバイ
アス電流ibは、磁気シールド層５の反磁界（ある
いは反磁界係数）に密接に関係していることがわ
かつた。 As a result of systematic research on current bias type magnetoresistive read heads such as those of the present invention, it has been found that the bias current i b necessary for biasing to the optimum operating point B or B' is It was found that it is closely related to the magnetic field coefficient).
第４図は磁気シールド層のテープ摺動面に垂直
な方向の反磁界係数と磁気抵抗効果素子を最適動
作点に設定するためのバイアス電流密度との関係
を示すグラフ図であつて、横軸に上記反磁界係数
hd、縦軸に上記バイアス電流密度ibpをとつてい
る。 FIG. 4 is a graph showing the relationship between the demagnetizing field coefficient in the direction perpendicular to the tape sliding surface of the magnetic shield layer and the bias current density for setting the magnetoresistive element to the optimum operating point, with the horizontal axis The above demagnetizing field coefficient
h d and the bias current density i bp is plotted on the vertical axis.
同図から明らかなように、磁気シールド層５の
上記反磁界係数（したがつて、反磁界）が大きい
程、磁気抵抗効果素子を最適動作点に設定するた
めのバイアス電流密度ibpが大きくなる傾向があ
ることがわかる。 As is clear from the figure, the larger the demagnetizing field coefficient (therefore, the demagnetizing field) of the magnetic shield layer 5, the larger the bias current density i bp for setting the magnetoresistive element to the optimum operating point. It can be seen that there is a tendency.
ところで、一般に、短冊状薄膜試料の反磁界係
数は、この試料の幅をｗ，膜厚をｔとすると近似
的にｔ／ｗで与えられる。したがつて、第３図
ａ，ｂにおいて、磁気シールド層５のテープ摺動
面に垂直な方向の幅を大きくすることにより、磁
気シールド層５の反磁界係数を小さくすることが
でき、磁気抵抗効果素子３を最適動作点に設定す
るための磁気シールド層５のバイアス電流密度
ibpを減少させることができる。 By the way, in general, the demagnetizing field coefficient of a strip-shaped thin film sample is approximately given by t/w, where w is the width of the sample and t is the film thickness. Therefore, in FIGS. 3a and 3b, by increasing the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface, the demagnetizing field coefficient of the magnetic shield layer 5 can be reduced, and the magnetoresistive Bias current density of the magnetic shield layer 5 for setting the effect element 3 to the optimum operating point
i bp can be decreased.
しかし、一方では、磁気シールド層５は、その
テープ摺動面方向の幅を増加させたことにより、
その断面積は増加し、結局、バイアス電流密度
ibpとこの断面積の積であるバイアス電流ibはほと
んど減少していないことになる。 However, on the other hand, by increasing the width of the magnetic shield layer 5 in the tape sliding surface direction,
Its cross-sectional area increases and eventually the bias current density
This means that the bias current i b , which is the product of i bp and this cross-sectional area, has hardly decreased.
このように、従来の磁気抵抗効果型再生ヘツド
においては、バイアス電流を大きくせざるを得
ず、このために、再生信号のＳ／Ｎが劣化すると
いう欠点があつた。 As described above, in the conventional magnetoresistive read head, the bias current has to be increased, which has the disadvantage that the S/N ratio of the read signal deteriorates.
本発明の目的は、上記従来技術の欠点を除き最
適動作点に設定するためのバイアス電流が小さ
く、良好なＳ／Ｎの再生信号を得ることができる
ようにした磁気抵抗効果型再生ヘツドを提供する
にある。
SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetoresistive playback head that eliminates the drawbacks of the prior art described above, requires a small bias current for setting the optimum operating point, and is capable of obtaining a playback signal with a good S/N ratio. There is something to do.
この目的を達成するために、本発明は、磁気シ
ールド層のテープ摺動面方向の幅を等価的に拡大
して該磁気シールド層の反磁界係数を減少せしめ
るようにした点に特徴がある。
In order to achieve this object, the present invention is characterized in that the width of the magnetic shield layer in the tape sliding surface direction is equivalently increased to reduce the demagnetizing field coefficient of the magnetic shield layer.
以下、本発明の実施例を図面について説明す
る。
Embodiments of the present invention will be described below with reference to the drawings.
第５図は本発明による磁気抵抗効果型再生ヘツ
ドの一実施例を示す断面図であつて、６は非磁性
絶縁ギヤツプ、７は磁性層であり、第３図ｂに対
応する部分には同一符号をつけている。 FIG. 5 is a sectional view showing an embodiment of the magnetoresistive read head according to the present invention, in which 6 is a non-magnetic insulating gap, 7 is a magnetic layer, and the parts corresponding to FIG. 3b are the same. It is marked with a sign.
第５図において、上部ギヤツプ４上には、81％
Niのパーマロイからなる磁気シールド５ととも、
この磁気シールド層５と非磁性絶縁ギヤツプ６を
挾み、テープ摺動面に垂直な方向に関して磁気シ
ールド層５よりも広幅の81％のNiのパーマロイ
からなる磁性層７が設けられている。非磁性絶縁
ギヤツプ６は、下部ギヤツプ２、上部ギヤツプ４
と同様に、SiO2からなつてギヤツプ長ｌが0.3μｍ
に設定される。 In Figure 5, above the upper gap 4, 81%
Along with the magnetic shield 5 made of Ni permalloy,
A magnetic layer 7 made of 81% Ni permalloy and having a wider width than the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface is provided between the magnetic shield layer 5 and the non-magnetic insulating gap 6. The non-magnetic insulating gap 6 is connected to the lower gap 2 and the upper gap 4.
Similarly, the gap length l of S i O 2 is 0.3 μm.
is set to
バイアス電流は磁気シールド層５のみに流れ
る。磁気シールド層５は、磁性層７により、等価
的にテープ摺動面に垂直な方向の幅が大きくな
り、このために、この方向の反磁界係数が、磁性
層７を設けない場合よりも減少し、磁気抵抗効果
素子３を最適動作点に設定するためのバイアス電
流密度が小さくなる。バイアス電流は上記のよう
に、磁気シールド層５のみに流れるから、結局、
磁気抵抗効果素子３を最適動作点に設定するため
のバイアス電流は、磁性層７を設けない場合より
も、小さくなる。 The bias current flows only through the magnetic shield layer 5. The magnetic shield layer 5 has a width equivalently increased in the direction perpendicular to the tape sliding surface due to the magnetic layer 7, and therefore the demagnetizing field coefficient in this direction is reduced compared to when the magnetic layer 7 is not provided. However, the bias current density for setting the magnetoresistive element 3 to the optimum operating point becomes smaller. As mentioned above, the bias current flows only through the magnetic shield layer 5, so in the end,
The bias current for setting the magnetoresistive element 3 to the optimum operating point is smaller than when the magnetic layer 7 is not provided.
一例として、磁気シールド層５のテープ摺動面
に垂直な方向の幅を40μｍとし、同じく磁性層７
の幅を約130μｍとし、また、磁気シールド層５
と磁性層７との重なり部分の幅を約5μｍとした
ところ、上記のバイアス電流は約80ｍＡであつ
て、第３図ａ，ｂに示した従来技術におけるバイ
アス電流の1/2〜1/3であつた。この結果、磁気シ
ールド層５の発熱によるノイズは約３〜6dB程度
減少し、再生信号のＳ／Ｎが向上した。 As an example, the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface is 40 μm, and the width of the magnetic shield layer 5 is 40 μm.
The width of the magnetic shield layer 5 is approximately 130 μm, and the magnetic shield layer 5
Assuming that the width of the overlapping portion between the magnetic layer 7 and the magnetic layer 7 is about 5 μm, the above bias current is about 80 mA, which is 1/2 to 1/3 of the bias current in the conventional technology shown in FIGS. 3a and 3b. It was hot. As a result, the noise caused by the heat generated by the magnetic shield layer 5 was reduced by about 3 to 6 dB, and the S/N of the reproduced signal was improved.
第６図は本発明による磁気抵抗効果型再生ヘツ
ドの他の実施例を示す断面図であつて、第５図に
対応する部分には同一符号をつけている。 FIG. 6 is a sectional view showing another embodiment of the magnetoresistive reproducing head according to the present invention, and parts corresponding to those in FIG. 5 are given the same reference numerals.
この実施例は、上部ギヤツプ４上に磁気シール
ド層５と磁性層７とを間隔l′を設けて形成したも
のであつて、第５図の実施例と同様に、磁性層７
により、磁気シールド層５の反磁界係数が減少す
る。バイアス電流は磁気シールド層５のみに流
れ、結局、磁気抵抗効果素子３を最適動作点に設
定するためのバイアス電流は、上記従来技術に比
べて極めて小さい。 In this embodiment, a magnetic shielding layer 5 and a magnetic layer 7 are formed on the upper gap 4 with a distance l' between them.Similar to the embodiment shown in FIG.
As a result, the demagnetizing field coefficient of the magnetic shield layer 5 decreases. The bias current flows only through the magnetic shield layer 5, and as a result, the bias current for setting the magnetoresistive element 3 to the optimum operating point is extremely small compared to the above-mentioned conventional technology.
因みに、磁気シールド５と磁性層７との間隔
l′を約1μｍとし、他の条件を第５図に示した実施
例と同一にしたとき、第５図に示した実施例と同
様の再生信号のＳ／Ｎが得られた。 Incidentally, the distance between the magnetic shield 5 and the magnetic layer 7
When l' was set to about 1 μm and other conditions were made the same as in the embodiment shown in FIG. 5, the same S/N ratio of the reproduced signal as in the embodiment shown in FIG. 5 was obtained.
なお、上記第５図および第６図に示した実施例
において、磁性層７の材料は、軟磁性材料であれ
ば金属、非金属を問わないし、磁気シールド層５
と同一材料であつても、異なる材料であつてもよ
い。また、磁性層７は各磁気抵抗効果素子に共通
となるように形成しても、各磁気抵抗効果素子毎
に独立に形成してもよい。 In the embodiments shown in FIGS. 5 and 6 above, the material of the magnetic layer 7 can be either metal or non-metal as long as it is a soft magnetic material, and the material of the magnetic shield layer 5
It may be the same material as or a different material. Further, the magnetic layer 7 may be formed in common to each magnetoresistive element, or may be formed independently for each magnetoresistive element.
第７図は本発明による磁気抵抗効果型再生ヘツ
ドのさらに他の実施例を示す断面図であつて７′
は磁性層であり、第５図に対応する部分には同一
符号をつけている。 FIG. 7 is a sectional view showing still another embodiment of the magnetoresistive read head according to the present invention.
is a magnetic layer, and parts corresponding to those in FIG. 5 are given the same reference numerals.
この実施例は、上部ギヤツプ４上に、磁気シー
ルド層５と磁性層７′とを、テープ摺動面に垂直
方向に互いに結合するに、配列形成したものであ
つて、磁性層７′の一部が磁気シールド５の一部
と重なつている。この磁性層７′により、磁気シ
ールド層５のテープ摺動面に垂直な方向の幅が等
価的に大きくなつて反磁界係数が減少する。磁気
シールド層５は、比抵抗が磁性層７′の比抵抗よ
りも小さい磁性材料からなる。このために、バイ
アス電流は主に磁気シールド層５に流れ、上記の
ように、磁気シールド層５の反磁界係数が減少し
たことから、磁性層７′を設けない場合よりもバ
イアス電流は小さくなる。 In this embodiment, a magnetic shield layer 5 and a magnetic layer 7' are arranged on an upper gap 4 so as to be coupled to each other in a direction perpendicular to the tape sliding surface. The portion overlaps with a portion of the magnetic shield 5. This magnetic layer 7' equivalently increases the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface, thereby reducing the demagnetizing field coefficient. The magnetic shield layer 5 is made of a magnetic material whose specific resistance is smaller than that of the magnetic layer 7'. For this reason, the bias current mainly flows through the magnetic shield layer 5, and as described above, since the demagnetizing field coefficient of the magnetic shield layer 5 has decreased, the bias current becomes smaller than when the magnetic layer 7' is not provided. .
この実施例では、磁性基板１、下部ギヤツプ
２、磁気抵抗効果素子３および上部ギヤツプ４
は、第５図および第６図に示した実施例と同様で
あり、磁気シールド層５は膜厚約2μｍの81％Ni
パーマロイ層とし、磁性層７′は膜厚2μｍの（４
％Mp＋79％Ni）パーマロイ層とした。 In this embodiment, a magnetic substrate 1, a lower gap 2, a magnetoresistive element 3, and an upper gap 4 are used.
is the same as the embodiment shown in FIGS. 5 and 6, and the magnetic shield layer 5 is made of 81% Ni with a thickness of about 2 μm .
The magnetic layer 7' is a permalloy layer with a thickness of 2 μm (4
%M p +79%N i ) permalloy layer.
かかる構成において、磁気シールド層５のテー
プ摺動面に垂直な方向の幅を30μｍとし、磁性層
７′の同方向の幅を70μｍとしたところ、両者の
抵抗値比は約１：２となつた。この場合、バイア
ス電流の約2/3が磁気シールド層５を流れること
になる。そして、この場合の磁気抵抗効果素子３
を最適動作点に設定するためのバイアス電流は約
100ｍＡであつて、上記従来技術に比べて半減し、
磁気シールド層５の発熱によるノイズは約３〜
6dB程度減少して再生信号のＳ／Ｎが大幅に向上
した。 In this configuration, when the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface is 30 μm, and the width of the magnetic layer 7' in the same direction is 70 μm, the resistance value ratio between the two is approximately 1:2. Ta. In this case, about 2/3 of the bias current will flow through the magnetic shield layer 5. In this case, the magnetoresistive element 3
The bias current to set the optimum operating point is approximately
100mA, which is half that of the conventional technology mentioned above.
The noise due to heat generated by the magnetic shield layer 5 is approximately 3~
The S/N ratio of the reproduced signal was significantly improved with a decrease of about 6 dB.
第８図に示した実施例は、磁気シールド層５の
一部に磁性層７′の一部を重ねたものであつたが、
第８図に示すように、逆に、磁性層７′の一部に
磁気シールド層５の一部を重ねるようにしても同
様の作用効果が得られる。 In the embodiment shown in FIG. 8, a part of the magnetic layer 7' is overlapped with a part of the magnetic shield layer 5.
As shown in FIG. 8, the same effect can be obtained even if a portion of the magnetic shield layer 5 is overlapped with a portion of the magnetic layer 7'.
第７図および第８図に示す実施例では、磁気シ
ールド層５と磁性層７′とは材料が異なり、前者
の比抵抗が後者の比抵抗の1/2以下とする。そし
て、磁気シールド層５の抵抗値が磁性層７′の抵
抗値よりも小さくなるように夫々を形成し、バイ
アス電流が主として磁気シールド層５に流れるよ
うにした。 In the embodiments shown in FIGS. 7 and 8, the magnetic shield layer 5 and the magnetic layer 7' are made of different materials, and the specific resistance of the former is set to be less than half that of the latter. The magnetic shield layer 5 is formed so that its resistance value is smaller than the resistance value of the magnetic layer 7', so that the bias current mainly flows through the magnetic shield layer 5.
第９図は本発明による磁気抵抗効果型再生ヘツ
ドのさらに他の実施例を示す断面図であり、第５
図に対応する部分には同一符号をつけている。 FIG. 9 is a sectional view showing still another embodiment of the magnetoresistive read head according to the present invention, and FIG.
Parts corresponding to the figures are given the same reference numerals.
この実施例は、磁気シールド層５を磁性基板１
と直接接合したものであり、これによつて、磁気
シールド層５のテープ摺動面に垂直な方向の幅が
等価的に大きくなり、したがつて、磁気シールド
層５の反磁界係数は減少する。バイアス電流は磁
気シールド層５のみに流れ、このために、磁気抵
抗効果素子３を最適動作点に設定するためのバイ
アス電流は、上記従来技術よりも充分小さくな
る。 In this embodiment, the magnetic shield layer 5 is connected to the magnetic substrate 1.
As a result, the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface is equivalently increased, and the demagnetizing field coefficient of the magnetic shield layer 5 is therefore decreased. . The bias current flows only through the magnetic shield layer 5, and therefore the bias current for setting the magnetoresistive element 3 to the optimum operating point is sufficiently smaller than in the prior art described above.
この実施例では、磁性基板１、下部ギヤツプ
２、上部ギヤツプ４は第５図ないし第８図に示し
た実施例と同様であり、磁気抵抗効果素子３は膜
厚0.05μｍの81％Niパーマロイ層とし、磁気シー
ルド層５は膜厚約5μｍの81％Niパーマロイ層と
した。 In this embodiment, the magnetic substrate 1, lower gap 2, and upper gap 4 are the same as those in the embodiments shown in FIGS. 5 to 8, and the magnetoresistive element 3 is made of 81% N The magnetic shield layer 5 was an 81% Ni permalloy layer with a thickness of about 5 μm.
かかる構成において、磁気シールド層５のテー
プ摺動面に垂直な方向の幅を約40μｍとしたとこ
ろ、磁気抵抗効果素子３を最適動作点に設定する
ためのバイアス電流は約80ｍＡであつて上記従来
技術の1/2〜1/3に減少し、磁気シールド層５の発
熱によるノイズは３〜6dB減少して再生信号の
Ｓ／Ｎが著しく向上した。 In this configuration, when the width of the magnetic shield layer 5 in the direction perpendicular to the tape sliding surface is about 40 μm, the bias current for setting the magnetoresistive element 3 to the optimum operating point is about 80 mA, which is different from the conventional method described above. The noise due to heat generation in the magnetic shield layer 5 has been reduced by 3 to 6 dB, and the S/N of the reproduced signal has been significantly improved.
以上、本発明の実施例について説明したが、こ
れらの実施例において、多結晶Ni−Zoフエライ
トを磁性基板１とし、その表面をメカノケミカル
研摩して下部ギヤツプ２を形成した。SiO2の下部
ギヤツプ２、上記ギヤツプ４および非磁性絶縁ギ
ヤツプ６（第５図）はRFスパツタリング法によ
り、81％Niパーマロイの磁気抵抗効果素子３は
真空蒸着法により、また、81％Niパーマロイの
磁気シールド層５、81％Niパーマロイの磁性層
７（第５図，第６図）および（４％Mp＋79％Ni）
パーマロイの磁性層７′はDC対向スパツタリング
法により夫々形成した。各部のパターニングに関
しては、通常のフオトエツチング法を用いた。 The embodiments of the present invention have been described above. In these embodiments, polycrystalline Ni - Zo ferrite was used as the magnetic substrate 1, and the lower gap 2 was formed by mechanochemically polishing the surface thereof. The lower gap 2 of S i O 2 , the above gap 4 and the non-magnetic insulating gap 6 (Fig. 5) were formed by RF sputtering method, and the magnetoresistive element 3 of 81% N i permalloy was formed by vacuum evaporation method. Magnetic shielding layer 5 of Ni permalloy, magnetic layer 7 of 81% Ni permalloy (Figures 5 and 6) and (4%M p +79%N i )
The permalloy magnetic layer 7' was formed by DC facing sputtering method. Regarding patterning of each part, a normal photoetching method was used.
なお、上記夫々の実施例においては、数値、材
料、製造方法などを具体的に示したが、本発明は
これらに特に制限されるものではなく、また、マ
ルチトラツク用に限られるものではない。 Although numerical values, materials, manufacturing methods, etc. are specifically shown in each of the above embodiments, the present invention is not particularly limited to these, and is not limited to multi-track applications.
さらに、磁性基板１は、基板としての機能を有
しているが、磁気シールド層５とともに外部磁界
に対するシールド効果も奏するものである。しか
し、本発明は、かかる構成にとらわれることな
く、特にマルチトラツク用の場合、基板を別個の
ものとし、該基板上に各磁気抵抗効果素子毎に高
透磁率磁性層を設け、これと磁気シールド層とで
各磁気抵抗効果素子毎に磁気シールドしてもよ
い。 Furthermore, although the magnetic substrate 1 has a function as a substrate, it also has a shielding effect against external magnetic fields together with the magnetic shield layer 5. However, the present invention is not limited to such a structure, and particularly in the case of multi-track use, a separate substrate is provided, a high permeability magnetic layer is provided for each magnetoresistive element on the substrate, and a magnetic shield is provided on the substrate. Each magnetoresistive element may be magnetically shielded by a layer.
以上説明したように、本発明によれば、磁気シ
ールド層の反磁界係数を、そのテープ摺動面に垂
直な方向の幅を等価的に増加させて減少せしめ、
かつ、バイアス電流が主として流れる断面積を小
さく制限するものであるから、該磁気シールド層
に流れるバイアス電流を大幅に小さくすることが
でき、このために、熱雑音の発生を抑圧すること
ができて再生信号のＳ／Ｎが大幅に向上し、上記
従来技術の欠点を除いて優れた機能の磁気抵抗効
果型再生ヘツドを提供することができる。
As explained above, according to the present invention, the demagnetizing field coefficient of the magnetic shield layer is reduced by equivalently increasing the width in the direction perpendicular to the tape sliding surface,
In addition, since the cross-sectional area through which the bias current mainly flows is limited to a small value, the bias current flowing through the magnetic shield layer can be significantly reduced, and therefore the generation of thermal noise can be suppressed. The S/N ratio of the reproduced signal is greatly improved, and it is possible to provide a magnetoresistive effect type reproduction head with excellent functions, except for the drawbacks of the prior art described above.
第１図は磁気抵抗効果素子の磁界の強さに対す
る抵抗値を示す特性図、第２図は電流バイアス方
式磁気抵抗効果型再生ヘツドの作用を示す説明
図、第３図ａ，ｂは従来の磁気抵抗効果型再生ヘ
ツドの一例を示す正面図および断面図、第４図は
第３図ａ，ｂの磁気シールド層の反磁界係数と磁
気抵抗効果素子を最適動作点に設定するためのバ
イアス電流密度との関係を示すグラフ図、第５図
は本発明による磁気抵抗効果型再生ヘツドの一実
施例を示す断面図、第６図ないし第９図は夫々本
発明による磁気抵抗効果型再生ヘツドの他の実施
例を示す断面図である。
１…磁性基板、２…下部ギヤツプ、３…磁気抵
抗効果素子、４…上部ギヤツプ、５…磁気シール
ド層、６…非磁性絶縁線ギヤツプ、７，７′…磁
性層。
Fig. 1 is a characteristic diagram showing the resistance value of the magnetoresistive element with respect to the strength of the magnetic field, Fig. 2 is an explanatory diagram showing the action of the current bias type magnetoresistive playback head, and Fig. 3 a and b are the conventional A front view and a cross-sectional view showing an example of a magnetoresistive read head, and FIG. 4 shows the demagnetizing field coefficient of the magnetic shield layer shown in FIGS. 3a and b and the bias current for setting the magnetoresistive element to the optimum operating point. FIG. 5 is a sectional view showing an embodiment of the magnetoresistive reproducing head according to the present invention, and FIGS. 6 to 9 are graphs showing the relationship with density, respectively. FIG. 7 is a sectional view showing another embodiment. DESCRIPTION OF SYMBOLS 1... Magnetic substrate, 2... Lower gap, 3... Magnetoresistive element, 4... Upper gap, 5... Magnetic shield layer, 6... Non-magnetic insulated wire gap, 7, 7'... Magnetic layer.
Claims (1)
に設けられた磁気抵抗効果素子を最適動作点に設
定するために、磁気シールド層に所定のバイアス
電流を流すようにした磁気抵抗効果型再生ヘツド
において、該磁気シールド層のテープ摺動面に垂
直な方向の幅を等価的に拡大する手段を有し、該
磁気シールド層の反磁界係数を減少することがで
きるように構成したことを特徴とする磁気抵抗効
果型再生ヘツド。 ２ 特許請求の範囲第１項において、前記手段は
磁性層からなり、該磁性層は、前記磁気シールド
層に対し、前記テープ摺動面に垂直な方向に所定
の間隔で配置したことを特徴とする磁気抵抗効果
型再生ヘツド。 ３ 特許請求の範囲第１項において、前記手段は
前記磁気シールド層よりも抵抗値が大きい磁性層
からなり、該磁性層は、前記磁気シールド層に対
し、前記テープ摺動面に垂直な方向に配置され、
かつ、前記磁気シールド層と一部重なつて直接接
合したことを特徴とする磁気抵抗効果型再生ヘツ
ド。 ４ 特許請求の範囲第１項において、前記手段は
前記磁性基板であつて、前記磁気シールド層の少
なくとも一部が直接前記磁性基板に接合されてな
ることを特徴とする磁気抵抗効果型再生ヘツド。[Claims] 1. In order to set the magnetoresistive element provided between the high permeability magnetic substrate and the magnetic shield layer to the optimum operating point, a predetermined bias current is caused to flow through the magnetic shield layer. The magnetoresistive read head has a means for equivalently expanding the width of the magnetic shield layer in the direction perpendicular to the tape sliding surface, so that the demagnetizing field coefficient of the magnetic shield layer can be reduced. A magnetoresistive playback head characterized in that it is configured as follows. 2. In claim 1, the means comprises a magnetic layer, and the magnetic layer is arranged at a predetermined interval in a direction perpendicular to the tape sliding surface with respect to the magnetic shield layer. Magnetoresistive playback head. 3. In claim 1, the means comprises a magnetic layer having a higher resistance value than the magnetic shield layer, and the magnetic layer extends in a direction perpendicular to the tape sliding surface with respect to the magnetic shield layer. placed,
A magnetoresistive read head characterized in that the magnetic shield layer is partially overlapped with and directly bonded to the magnetic shield layer. 4. The magnetoresistive read head according to claim 1, wherein the means is the magnetic substrate, and at least a portion of the magnetic shield layer is directly bonded to the magnetic substrate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18675883A JPS6079509A (en) | 1983-10-07 | 1983-10-07 | Magneto-resistance effect type reproducing head |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18675883A JPS6079509A (en) | 1983-10-07 | 1983-10-07 | Magneto-resistance effect type reproducing head |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6079509A JPS6079509A (en) | 1985-05-07 |
| JPH0475569B2 true JPH0475569B2 (en) | 1992-12-01 |
Family
ID=16194123
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP18675883A Granted JPS6079509A (en) | 1983-10-07 | 1983-10-07 | Magneto-resistance effect type reproducing head |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6079509A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5311385A (en) * | 1991-12-18 | 1994-05-10 | Minnesota Mining And Manufacturing Company | Magnetoresistive head with integrated bias and magnetic shield layer |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS53138380A (en) * | 1977-05-09 | 1978-12-02 | Nec Corp | Magnetic field detecting element |
| JPS53138830A (en) * | 1977-04-30 | 1978-12-04 | Ichirou Kubota | Driving device for cutter knife on mower |
| JPS5715222A (en) * | 1980-07-01 | 1982-01-26 | Mitsubishi Electric Corp | Magnetic head |
-
1983
- 1983-10-07 JP JP18675883A patent/JPS6079509A/en active Granted
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS53138830A (en) * | 1977-04-30 | 1978-12-04 | Ichirou Kubota | Driving device for cutter knife on mower |
| JPS53138380A (en) * | 1977-05-09 | 1978-12-02 | Nec Corp | Magnetic field detecting element |
| JPS5715222A (en) * | 1980-07-01 | 1982-01-26 | Mitsubishi Electric Corp | Magnetic head |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6079509A (en) | 1985-05-07 |
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