JP2004039160A - Method and device for measuring magnetic head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic head measuring method capable of evaluating the characteristics of a head element when electric discharge is generated in an environment in which the head element is practically integrated into a device. <P>SOLUTION: An insulating sheet 12 is arranged on a grounded ground plane 11 and a magnetic tape cut in a prescribed length is fixed on the sheet 12. A voltage is applied to the recording surface of a magnetic tape 1 by a voltage source 13 to charge the recording surface with electricity. Immediately after stopping the voltage application, the surface of the MR head 2 is brought into contact with the recording surface of the magnetic tape 1. Consequently electric charge is discharged from the magnetic tape 1 to the ground potential through the MR head 20 and the discharged current is measured with an oscilloscope 14. <P>COPYRIGHT: (C)2004,JPO

Description

【００３０】
表１で示した４種類の磁気テープＡ、Ｂ、ＣおよびＤは、いずれもデジタルビデオ用のＭＥ（Ｍｅｔａｌ　Ｅｖａｐｏｒａｔｅｄ）テープと呼ばれるものであり、樹脂ベース上に磁性体粒子が蒸着されて記録面が形成されている。表１ではこれらの磁気テープＡ〜Ｄにおける磁性層の厚さと表面抵抗が示されている。磁気テープＤは、他の磁気テープＡ〜Ｃと比較して５倍以上の表面抵抗を有している。
【００３１】
次に、これらの磁気テープＡ〜Ｄを用いて上記の測定装置により測定を行った結果を、表２に示す。
【００３２】
【表２】

【００３３】
ここでは、磁気テープＡ〜Ｄのそれぞれに対して、電圧源１３により３０Ｖの電圧を印加したときの、同じ仕様のＭＲヘッド２に対する放電現象について測定している。なお、この測定では実際のＭＲヘッド２の代わりに３０Ωの抵抗を取り付けて測定を行った。また、磁気テープＡ〜Ｄをすべて長さ２５ｃｍに切断して使用した。
【００３４】
表２において、磁気テープＡ〜Ｄの静電容量および電荷量は、抵抗へ放電させる前と同じ条件で磁気テープＡ〜Ｄに電圧を印加させたときに、ナノクーロンメータを用いて測定した値である。この測定結果によれば、磁気テープＡ〜Ｄの間で、静電容量および電荷量に大きな差は見られない。しかし、これらの磁気テープＡ〜Ｄから抵抗に放電させた場合には、抵抗を通じて流れる電流のピーク値は、磁気テープＤについての値が他の磁気テープＡ〜Ｃの１／５以下となっている。
【００３５】
ここで、図３は、放電時に抵抗を通じて流れた電流の波形の測定例を示すグラフである。なお、図３では例として、磁気テープＣおよびＤを用いた場合の電流波形を挙げる。図３（Ａ）は磁気テープＣ、（Ｂ）は磁気テープＤを使用して測定した場合について示す。
【００３６】
この図３によれば、磁気テープＣおよびＤを用いた場合のいずれでも、放電電流がピーク値を示している時間は５ｎｓ以下であり、各磁気テープＣおよびＤに蓄積されていた電荷は、放電から５０ｎｓ以内にほぼ放出されている。また、図示しないが、磁気テープＡおよびＢを用いた場合でも同様な結果が得られた。
【００３７】
以上の測定では、磁気テープ１の記録面における表面抵抗が、ＭＲヘッド２への放電時に流れる放電電流の値に大きな影響を与えることがわかる。ただし、上記のように電圧源１３により３０Ｖの電圧を印加した場合では、いずれの磁気テープＡ〜Ｄを用いて実際のＭＲヘッド２に放電させた場合でも、ＭＲヘッド２の特性にはほとんど影響を与えなかった。
【００３８】
ところで、磁気テープ１からの放電が行われたＭＲヘッド２の特性を評価する方法としては、例えば、ＭＲヘッド２の抵抗を測定してＭＲ素子の破壊の有無を調べる方法や、ＭＲヘッド２に磁界を印加してその感度を測定する方法等がある。
【００３９】
そこで、次に、電圧源１３による印加電圧をさらに高めて、磁気テープ１に蓄積させる電荷量を大きくした場合のＭＲヘッド２の特性を、抵抗の測定によって行う。ここでは例として、上記の磁気テープＡ〜Ｄのうち磁気テープＣおよびＤを使用して測定を行う。
【００４０】
なお、以下の測定では、３０Ωの抵抗値を有する実際のＭＲヘッド２を使用している。また、ＭＲヘッド２を通じた放電電流が流れる接続線は、ＭＲヘッド２の具備する２つの配線電極の双方に結線させている。
【００４１】
図４は、磁気テープＣ上に蓄積された電荷量と、この電荷を放電させた後のＭＲヘッド２の抵抗値との関係を示したグラフである。また、図５は、磁気テープＣ上に蓄積された電荷量に応じたＭＲヘッド２における放電電流の波形を示したグラフである。
【００４２】
図４では、電圧源１３による印加電圧を変化させて、磁気テープＣに蓄積させる電荷量を変化させた場合のそれぞれについて、放電後にＭＲヘッド２の抵抗値を測定した値を示している。ＭＲヘッド２の抵抗値の測定は、放電後にＭＲヘッド２の具備する２つの配線電極間の抵抗を測定することによって行っている。また、図５では、磁気テープＣの蓄積電荷量を変化させるごとに、放電時にオシロスコープ１４で測定された電流波形を示している。
【００４３】
図４によれば、磁気テープＣにおける電荷量が１５ｎＣ以下の場合には、ＭＲヘッド２の抵抗値の変化はほとんど見られないが、電荷量が２０ｎＣの場合ではＭＲヘッド２の抵抗値が落ち込んでおり、放電によってＭＲ素子が破壊されたことが観測されている。また、図５によれば、蓄積された電荷量が２０ｎＣの場合の放電電流は、３００ｍＡ以上に達していることがわかる。
【００４４】
図６は、磁気テープＤ上に蓄積された電荷量と、この電荷を放電させた後のＭＲヘッド２の抵抗値との関係を示したグラフである。また、図７は、磁気テープＤ上に蓄積された電荷量に応じたＭＲヘッド２における放電電流の波形を示したグラフである。
【００４５】
図６および図７は、上記の図４および図５に対応する測定を磁気テープＤを使用して行った場合の測定値を示している。図６によれば、磁気テープＤにおける電荷量が１００ｎＣに達した場合にも、ＭＲヘッド２の抵抗値の変化はほとんど見られず、放電によるＭＲ素子の破壊が発生していない。図７によれば、蓄積された電荷量が１００ｎＣの場合の放電電流は９０ｍＡ程度となっており、磁気テープＤでは磁気テープＣと比較して、放電電流が大幅に抑制されることがわかる。
【００４６】
以上の測定例により、高電圧の印加により磁気テープ１に大量の電荷が帯電した場合でも、磁気テープ１の記録面の表面抵抗が高いほど、この磁気テープ１からＭＲヘッド２への放電時に流れる放電電流が抑制されることが確認された。従って、表面抵抗の高い磁気テープ１を使用した方が、ＭＲヘッド２の安全性が保たれると言える。
【００４７】
ところで、上記の磁気テープＡ〜Ｄを実際に樹脂製のテープカートリッジに収めた状況では、通常の使用時に上記のように数十ｎＣの電荷が磁気テープＡ〜Ｄに帯電することは少ない。例えば、磁気テープをテープカートリッジに収め、このテープカートリッジの表面をナイロン手袋で摩擦した場合の磁気テープに帯電した電荷量は、表３のようになる。
【００４８】
【表３】

【００４９】
表３の測定結果において、（Ａ）は磁気テープＣを用いた場合、（Ｂ）は磁気テープＤを用いた場合を示している。また、各磁気テープＣおよびＤについて、異なる気温および湿度の環境下で、テープカートリッジの摩擦とその後の電荷測定を３回ずつ行った。
【００５０】
この表３によれば、気温１０度〜２５度の環境においては磁気テープＣに帯電する電荷量は５ｎＣに達しない。同様に、磁気テープＤの場合では、電荷量は３ｎＣにも達しない。従って、通常の取り扱いによりテープカートリッジに静電気が帯電した状態で、ＭＲヘッド２によるデータの再生が行われるような環境では、上記の磁気テープＡ〜ＤとＭＲヘッド２とを含むシステムは、ＭＲヘッド２におけるＥＳＤ破壊の発生に対して大きなマージンを有していると言える。
【００５１】
このように、上記の測定装置では、実際に使用する磁気テープ１を使用して、この磁気テープ１とＭＲヘッド２が接触した場合の放電現象をシミュレートすることができ、実際の使用環境により近い条件でＭＲヘッド２の性能評価を行うことが可能となる。例えば、テープシステムの開発時において、テープドライブ内の条件を考慮した、ＭＲヘッドのＥＳＤ破壊に対するシステム設計の指針を与えることができる。また、より実際のテープシステムに近い状態でのＥＳＤ破壊に対するマージンを測定できる。従って、より信頼性の高いテープシステムの開発を行うことが可能となる。
【００５２】
また、上記の測定装置を用いることにより、ＭＲヘッドや磁気テープの仕様の基準値を明確にすることができ、品質の安定した製品の供給のために貢献することができる。なお、例えば、ＭＲヘッドに対する磁気テープの特性の測定に本発明を利用する場合には、上述したように、ＭＲヘッドの代わりに同じ抵抗値を有する抵抗を使用して放電させることで、効率のよい測定が可能となる。
【００５３】
また、上記の測定例のように、ＡＭＲ素子を用いた磁気ヘッドの場合は、現状のシステムにおいてＥＳＤ破壊に対する十分なマージンを有しているが、今後、ＥＳＤ破壊現象がより発生しやすいＧＭＲ素子やＴＭＲ素子が用いられた場合には、磁気ヘッドや磁気テープの仕様基準がさらに厳密なものとされる。その場合に、本発明のように、実際の仕様環境により近い条件で正確な特性評価を行うことの重要性がさらに高まると考えられる。
【００５４】
ところで、図１に示した測定装置は基本的な要素のみで構成されており、実際にはこの他に、ＭＲヘッドの特性測定用の構成や、測定条件を変化させるための構成等を付加することが望ましい。以下、このような要素が付加された測定装置の一例を挙げる。
【００５５】
図８は、本発明の第２の実施の形態である測定装置の構成の一部を示す図である。なお、図８では、図１で示した測定装置と対応する構成要素には同じ符号を付して示しており、その説明は省略する
図８に示す測定装置では、ＭＲヘッド単体での測定に加えて、ＭＲヘッドをヘッドドラムに装着した状態での測定が可能となっている。図８では、ＭＲヘッドをヘッドドラム２０に装着した状態での測定例を示している。
【００５６】
この測定装置において、ヘッドドラム２０は昇降機構１５のホルダ１５ａに装着されている。ヘッドドラム２０は、ＭＲヘッドのヘッド摺動面が磁気テープ１側に向くように装着されて、昇降機構１５により、磁気テープ１の記録面に対して垂直に移動して、ヘッド摺動面が磁気テープ１の記録面に接触するようになっている。なお、磁気テープ１は、図示の測定装置と同様に、グランドプレーン１１上に配置された絶縁シート１２の上に、記録面を上にした状態で固定される。
【００５７】
また、ホルダ１５ａは、ヘッドドラム２０またはＭＲヘッドを保持するとともに、これらの具備する配線電極に外部の接続線１５ｂ、１５ｃおよび１５ｄを切り換えて接続する機能を有している。
【００５８】
接続線１５ｂの他端は接地されており、この接地電位とホルダ１５ａとの間には、オシロスコープ１４のプローブ１４ａ、ナノクーロンメータ１６のプローブ１６ａ、およびインピーダンス調整回路１７が接続されている。ナノクーロンメータ１６は、接続線１５ｂに流れる電流に基づいて、磁気テープ１に帯電した電荷量を測定する。インピーダンス調整回路１７は、内部に抵抗やコンデンサ、コイル等の回路を具備して、接続線１５ｂのインピーダンスを任意に調整することが可能となっている。
【００５９】
接続線１５ｃには、抵抗測定装置１８が接続されている。接続線１５ｃは例えば２本の導線によってなり、ＭＲヘッドにおいてＭＲ素子に接続された２つの配線電極のそれぞれの導線が接続されて、これにより抵抗測定装置１８は、ＭＲ素子の抵抗を測定することが可能となっている。
【００６０】
接続線１５ｄには、磁気特性測定装置１９が接続されている。磁気特性測定装置１９は、磁界印加装置１９ａと電圧測定装置１９ｂによって構成される。磁界印加装置１９ａは、例えば測定対象に磁界を印加するための磁気コアに巻き線がされ、この巻き線に交流電流が流される構造を有している。
【００６１】
ホルダ１５ａに装着されたヘッドドラム２０またはＭＲヘッドは、昇降機構１５の動作により磁気特性測定装置１９の磁界印加装置１９ａ内にセットされる。電圧測定装置１９ｂは、接続線１５ｄを通じてＭＲヘッド内のＭＲ素子に定電流を流し、磁界印加時の電圧を測定する。
【００６２】
なお、抵抗測定装置１８と、磁気特性測定装置１９内の電圧測定装置１９ｂは、同一の装置として実現されてもよい。また、図８では、磁気テープ１に電荷を帯電させるために電圧を印加する電圧源と、電圧印加のためのプローブについては図示を省略している。
【００６３】
このような測定装置による測定は、例えば以下のように行う。まず、昇降機構１５のホルダ１５ａでの接続を、接続線１５ｂに切り換えておく。そして、電圧源により磁気テープ１に電圧を所定の時間だけ印加し、電荷を帯電させる。
【００６４】
次に、電圧印加を停止し、その直後に昇降機構１５を作動させて、ヘッドドラム２０のヘッド摺動面を磁気テープ１の記録面に接触させる。これにより、磁気テープ１からヘッドドラム２０に対して放電が発生し、接続線１５ｂおよびインピーダンス調整回路１７を通じて接地電位に放電電流が流れる。このときの放電電流がオシロスコープ１４により測定されるとともに、ナノクーロンメータ１６では磁気テープ１に蓄積されていた電荷量が測定される。
【００６５】
またこの後、ホルダ１５ａでの接続を接続線１５ｃに切り換え、放電が行われたヘッドドラム２０内のＭＲ素子の抵抗値を、抵抗測定装置１８によって測定する。あるいは、ホルダ１５ａでの接続を接続線１５ｄに切り換えるとともに、昇降機構１５を作動させてヘッドドラム２０を磁気特性測定装置１９内の測定位置に移動させ、磁界印加装置１９ａによって磁界を印加させたときの電圧変化を電圧測定装置１９ｂによって測定する。これにより、放電後のＭＲヘッドの磁気に対する感度を測定できる。
【００６６】
以上の測定装置では、放電電流の流路上にオシロスコープ１４とナノクーロンメータ１６を直列に挿入したことにより、放電時にＭＲ素子に流れる電流と、磁気テープ１上の電荷量とを同時に測定することが可能となる。また、この流路上にインピーダンス調整回路１７を設けたことにより、例えばＭＲヘッドの配線電極に実際に接続されるアンプ等の回路のインピーダンスに応じて、放電時のインピーダンスを合致させて測定を行うことができ、より実際のシステムに近い条件でのシミュレーションが可能となる。
【００６７】
さらに、ホルダ１５ａにおいてＭＲヘッドの配線電極との接続が切り換えられることにより、放電が行われた後のＭＲヘッドの抵抗値や電圧変化量を、抵抗測定装置１８や磁気特性測定装置１９を用いて容易に測定することが可能となる。従って、ＭＲヘッドの特性評価を効率よく行うことができる。
【００６８】
また、このホルダ１５ａでは、単体のＭＲヘッドだけでなくヘッドドラムを装着できるため、ＭＲヘッドをヘッドドラムに搭載した状態でのシミュレーションが可能となる。
【００６９】
また、上記の昇降機構１５、オシロスコープ１４、ナノクーロンメータ１６、抵抗測定装置１８、磁気特性測定装置１９と、図示しない電圧源の動作を一括して制御し、これらを用いた測定工程を自動的に行うようにすることが望ましい。特に、測定の自動化により、磁気テープ１への電圧の印加後にＭＲヘッドを接触させるタイミングを一定にすることで、放電電流の測定を正確に行うことができる。
【００７０】
【発明の効果】
以上説明したように、本発明の磁気ヘッドの測定方法では、記録または再生システムに実際に使用される磁気テープを使用して、この磁気テープから磁気ヘッドへ放電させた際に、磁気ヘッドを通じて流れる電流を測定することができる。従って、磁気テープの特性に対して、実際の使用環境に即した正確な評価を行うことが可能となる。
【００７１】
また、本発明の磁気ヘッドの測定装置では、記録または再生システムに実際に使用される磁気テープを使用して、この磁気テープから磁気ヘッドへ放電させた際に、磁気ヘッドを通じて流れる電流を測定することができる。従って、磁気テープの特性に対して、実際の使用環境に即した正確な評価を行うことが可能となる。
【図面の簡単な説明】
【図１】本発明の実施の形態例である測定装置の全体構成を示す。
【図２】測定装置を用いた測定工程例を示すフローチャートである。
【図３】表面抵抗の異なる磁気テープを使用した場合に、放電時に抵抗を通じて流れた電流の波形の測定例を示すグラフである。
【図４】磁気テープＣ上に蓄積された電荷量と、この電荷を放電させた後のＭＲヘッドの抵抗値との関係を示したグラフである。
【図５】磁気テープＣ上に蓄積された電荷量に応じたＭＲヘッドにおける放電電流の波形を示したグラフである。
【図６】磁気テープＤ上に蓄積された電荷量と、この電荷を放電させた後のＭＲヘッドの抵抗値との関係を示したグラフである。
【図７】磁気テープＤ上に蓄積された電荷量に応じたＭＲヘッドにおける放電電流の波形を示したグラフである。
【図８】本発明の第２の実施の形態である測定装置の構成の一部を示す図である。
【図９】ＨＢＭを用いてＭＲヘッドのＥＳＤ破壊現象をシミュレートする装置の回路構成を示す図である。
【図１０】ＨＢＭを用いた場合のＭＲヘッドにおける電圧測定例を示すグラフである。
【図１１】ＨＢＭを用いた場合のＧＭＲヘッドの感度の測定例を示すグラフである。
【符号の説明】
１……磁気テープ、２……ＭＲヘッド、１１……グランドプレーン、１２……絶縁シート、１３……電圧源、１３ａ……プローブ、１４……オシロスコープ、１４ａ……プローブ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic head measuring method and a magnetic head measuring method for measuring characteristics of a magnetic head when a discharge occurs on a head sliding surface with respect to a magnetic tape, and is particularly suitable for measuring a magnetoresistive (MR) head. The present invention relates to a method and an apparatus for measuring a magnetic head.
[0002]
[Prior art]
In recent years, in a magnetic recording / reproducing apparatus which records and reproduces data using a magnetic tape, a further improvement in recording density is desired as the amount of information to be handled is increased. It is indispensable to employ an MR (Magneto Resistive) head instead of the inductive type head. An MR head is a magnetic head that reads a signal recorded on a magnetic recording medium by using a magnetoresistive effect by an MR element, and has a high signal detection sensitivity and a large reproduction output. The width can be easily reduced, and the recording density in the linear direction can be increased, so that high-density recording and reproduction can be performed.
[0003]
This MR head generally has a property that it is more susceptible to static electricity and heat than an inductive head. For example, when an MR head is applied to a system using a magnetic tape, the MR element is directly contacted with the magnetic tape without a protective film on the head sliding surface. At this time, the charge on the magnetic tape flows as a discharge current to the MR head, and there is a possibility that ESD (Electrostatic Discharge) destruction occurs in the MR element. For this reason, in the development of the MR head, it is important to measure the ESD breakdown phenomenon in the MR head in accordance with actual use conditions.
[0004]
As a method for measuring an ESD breakdown phenomenon in an MR head, there have conventionally been some standardized methods such as a HBM (Human Body Model) and a CDM (Charged Device Model). These methods assume a human body, a charged object, a machine, or the like as an environment in which a device is handled, replace these environments with an equivalent circuit, and simulate and evaluate an ESD breakdown phenomenon.
[0005]
FIG. 9 is a diagram showing a circuit configuration of an apparatus for simulating the ESD breakdown phenomenon of the MR head by using the HBM.
The circuit shown in FIG. 9 is an equivalent circuit for reproducing a case where a discharge phenomenon occurs in the MR head due to electric charges charged on a human body. In this circuit, a capacitor 33 having substantially the same capacitance as that of a human body and having a capacitance of 100 pF is connected in series to a voltage source 31 via a changeover switch 32, so that electric charges can be stored in the capacitor 33 by the voltage source 31. Has become.
[0006]
When the changeover switch 32 is switched after the capacitor 33 is charged, the MR head 35 to be measured is connected in series to the capacitor 33 via the 1.5 kΩ resistor 34, and the accumulated charge is grounded through the MR head 35. Discharged to potential. By measuring the resistance value and the like of the MR head 35 after this discharge, the ESD breakdown phenomenon in the MR head 35 can be evaluated in a pseudo manner.
[0007]
FIG. 10 is a graph showing an example of voltage measurement in an MR head using the above circuit. FIG. 10A shows a measurement result for an AMR (Anisotropic Magneto Resistive) head, and FIG. 10B shows a measurement result for a GMR (Giant Magneto Resistive) head.
[0008]
The graph shown in FIG. 10 shows the relationship between the voltage of the voltage source 31 and the resistance of the MR head 35 when the above-described circuit is used. According to these graphs, it can be seen that the resistance value greatly changes at about 230 to 240 V in the case of the AMR head and about 35 to 40 V in the case of the GMR head, and the ESD breakdown of the MR element is caused by the discharge. .
[0009]
FIG. 11 is a graph showing a measurement example of the sensitivity of the GMR head when the above circuit is used.
The graph of FIG. 11 shows the sensitivity of the GMR head after generating a discharge using the above-described circuit, as the amount of voltage change of the GMR head when a constant magnetic field is applied to the GMR head. According to this graph, it is understood that when the voltage generated by the voltage source 31 reaches about 30 V, the magnetic characteristics of the GMR head deteriorate.
[0010]
[Problems to be solved by the invention]
By the way, the above-described method for measuring ESD destruction involves taking out only a head portion using an MR element and measuring the ESD destruction phenomenon that has occurred alone. For this reason, there is a problem that it is not possible to simulate a use environment when the MR head is incorporated in an actual system using a magnetic tape.
[0011]
For example, the characteristic deterioration of the MR element actually occurs due to thermal fusing by an electric current. Also, in the case of a GMR head, the magnetic material of the GMR film is magnetized by an electric current to cause deterioration of characteristics. For this reason, when incorporated in an actual system, there is a possibility that the performance degradation of the MR element cannot be accurately known by the above-described measuring method.
[0012]
In particular, GMR elements and TMR (tunneling magneto-resistive) elements are more susceptible to ESD destruction than AMR elements. Therefore, in order to promote the spread of heads using these elements, strict measurement of head characteristics is required. It is even more important to do.
[0013]
The present invention has been made in view of such problems, and has a method of measuring a magnetic head capable of evaluating characteristics of a head element when a discharge occurs, according to an environment when the head element is actually incorporated in a device. The purpose is to provide.
[0014]
Another object of the present invention is to provide a magnetic head measuring method capable of evaluating the characteristics of a head element when a discharge occurs, according to an environment when the head element is actually incorporated in a device. .
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a method of measuring the characteristics of a magnetic head when discharge occurs on a head sliding surface with respect to a magnetic tape. A magnetic tape with the recording surface facing upward is fixed on the body, a voltage is applied to the magnetic tape to charge the magnetic tape, and immediately after the application of the voltage is stopped, the head sliding surface of the magnetic head is fixed to the magnetic tape. There is provided a method of measuring a magnetic head, wherein the magnetic head is brought into contact with a recording surface of a tape, and a current flowing from the magnetic head to a ground potential is measured before and after the magnetic head contacts the magnetic tape.
[0016]
In such a method of measuring a magnetic head, after a charge is applied to a magnetic tape by applying a voltage, the charge is discharged through the magnetic head by bringing the head sliding surface of the magnetic head into contact with the magnetic tape. The current flowing through the magnetic head as the phenomenon occurs is measured in real time.
[0017]
Further, according to the present invention, in a magnetic head measuring device for measuring characteristics of a magnetic head when discharge occurs on a head sliding surface with respect to a magnetic tape, a flat insulator disposed on a ground plane; A magnetic tape fixed on an insulator with a recording surface facing upward, voltage applying means for applying a voltage to the magnetic tape, and a head sliding surface contacting the recording surface of the magnetic tape. Current measuring means connected between the magnetic head and a ground potential for measuring the current flowing from the magnetic head to the ground potential before and after contact with the magnetic tape; And a magnetic head measuring device characterized by having the following.
[0018]
In such a magnetic head measuring device, the magnetic tape is charged by the application of the voltage by the voltage applying means. Then, by bringing the head surface of the magnetic head into contact with the charged magnetic tape, the charges are discharged through the magnetic head. The current measuring means measures, in real time, a current flowing through the magnetic head when a discharge phenomenon from the magnetic tape to the magnetic head occurs.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of a measuring device according to an embodiment of the present invention.
[0020]
The measuring device shown in FIG. 1 is a device for measuring a characteristic at the time of discharge in a magnetic head for recording or reproducing data on or from a magnetic tape 1. In the present embodiment, a reproducing device for reproducing data is particularly used as a magnetic head. An MR head 2 using an AMR element for a head portion is applied. This measuring device includes a ground plane 11, an insulating sheet 12, a voltage source 13, and an oscilloscope 14.
[0021]
The ground plane 11 has an electric resistivity of 10 ² Ω-10 ¹⁰ It is made of a so-called resistance conductive material of about Ωcm, and is set to the ground potential. The insulating sheet 12 is, for example, a sheet-like insulator having a thickness of 1 mm or less made of a glass epoxy board or the like. The insulating sheet 12 is disposed on the ground plane 11 and the magnetic tape 1 cut to a predetermined length is placed thereon. Is placed. The magnetic tape 1 is mounted such that the recording surface on which the magnetic layer is formed faces the opposite surface of the insulating sheet 12, and is fixed to the insulating sheet 12 with an adhesive tape or the like. It is desirable that the magnetic tape 1 be fixed so that the entire surface uniformly contacts the insulating sheet 12.
[0022]
On the recording surface side of the magnetic tape 1, a probe 13a connected to a voltage source 13 and an MR head 2 are arranged. The voltage source 13 applies a voltage to the magnetic tape 1 by bringing the probe 13 a into contact with the magnetic tape 1. The generated voltage is variable.
[0023]
The MR head 2 is a helical scan magnetic head that scans a magnetic tape in a helical manner and reads a recording signal. For example, an MR element, an insulating film, a shield film, and the like are formed as a thin film on a head substrate. Has a structure fixed on a base metal (not shown). The end surface on which the MR elements and the like are stacked is a surface on which the magnetic tape slides during data reproduction, and is formed in a cylindrical shape. In the above-described measuring device, the MR head 2 is moved up and down so that the head sliding surface correctly contacts the recording surface of the magnetic tape 1 at the same angle as during normal data reproduction.
[0024]
Further, two wiring electrodes are provided on the base metal of the MR head 2. These wiring electrodes are connected to both ends of the MR element in the width direction of the magnetic tape 1, and are used for connecting each wiring electrode to an external wiring to output a reproduction signal obtained by the MR element to the outside. Things. In the above-described measuring device, the probe 14a of the oscilloscope 14 is connected between one or both of these wiring electrodes and the ground potential, and the current waveform discharged to the ground potential through the MR head 2 can be measured. I have.
[0025]
Next, FIG. 2 is a flowchart showing a basic measuring process using this measuring device.
In step S21, the probe 13a is brought into contact with the recording surface of the magnetic tape 1 and a predetermined voltage is applied from the voltage source 13. In this measuring device, it can be considered that a capacitor is formed between the recording surface of the magnetic tape 1 and the ground plane 11. Therefore, by applying a voltage by bringing the probe 13 a of the voltage source 13 into contact with the magnetic tape 1, the charge amount obtained from the applied voltage V and the capacitance C of the capacitor is applied to the recording surface of the magnetic tape 1. The charge of Q (= C × V) is uniformly accumulated.
[0026]
After the voltage has been applied for a predetermined time, in step S22, monitoring of the waveform of the current flowing through the MR head 2 using the oscilloscope 14 is started. In step S23, the voltage application probe 13a is separated from the magnetic tape 1, and the voltage application is stopped. In step S24, the head sliding surface of the MR head 2 is brought into contact with the recording surface of the magnetic tape 1. Thereby, the electric charges accumulated in the magnetic tape 1 are discharged through the MR head 2. The waveform of the current flowing through the MR head 2 during this discharge is obtained by the oscilloscope 14. In order to prevent spontaneous discharge of electric charges, it is desirable that the intervals between the steps S23 and S24 be short.
[0027]
Thereafter, for example, a change in performance of the MR head 2 is evaluated by measuring a resistance value or the like of the discharged MR head 2.
In this measuring device, a resistor having the same resistance as the head element of the MR head 2 may be used instead of the MR head 2. In this case, the measurement is performed by connecting one end of the resistor to a connection line through which a discharge current flows, and bringing the other end into contact with the recording surface of the magnetic tape 1. In the case of the current MR head, for example, a resistance of 30Ω can be used. With such a configuration, for example, it is possible to easily perform measurement when the specifications of the magnetic tape to be used are changed for MR heads having the same resistance value.
[0028]
Next, an example of measurement using the above-described measuring device and an example of performance evaluation of the MR head 2 based on the measurement will be specifically described. The specifications of the magnetic tape 1 used in this measurement are shown in Table 1 below.
[0029]
[Table 1]

[0030]
The four types of magnetic tapes A, B, C, and D shown in Table 1 are all referred to as ME (Metal Evaporated) tapes for digital video, and magnetic particles are deposited on a resin base and the recording surface is formed. Is formed. Table 1 shows the thickness and surface resistance of the magnetic layers in these magnetic tapes A to D. The magnetic tape D has a surface resistance five times or more that of the other magnetic tapes A to C.
[0031]
Next, Table 2 shows the results of measurement using these magnetic tapes A to D by the above-described measuring device.
[0032]
[Table 2]

[0033]
Here, the discharge phenomena to the MR head 2 of the same specification when a voltage of 30 V is applied by the voltage source 13 to each of the magnetic tapes A to D is measured. In this measurement, the measurement was performed by attaching a 30Ω resistor instead of the actual MR head 2. Further, the magnetic tapes A to D were all cut to a length of 25 cm before use.
[0034]
In Table 2, the capacitance and the amount of charge of the magnetic tapes A to D are values measured using a nanocoulomb meter when a voltage is applied to the magnetic tapes A to D under the same conditions as before discharging to the resistor. It is. According to this measurement result, there is no large difference in the capacitance and the charge amount between the magnetic tapes A to D. However, when the magnetic tapes A to D are discharged to the resistor, the peak value of the current flowing through the resistor is such that the value for the magnetic tape D is 1/5 or less of the other magnetic tapes A to C. I have.
[0035]
Here, FIG. 3 is a graph showing a measurement example of a waveform of a current flowing through a resistor during discharging. FIG. 3 shows a current waveform when magnetic tapes C and D are used as an example. FIG. 3A shows a case where measurement was performed using a magnetic tape C, and FIG.
[0036]
According to FIG. 3, in each of the cases where the magnetic tapes C and D were used, the time during which the discharge current showed a peak value was 5 ns or less, and the electric charge accumulated in each of the magnetic tapes C and D was: It is almost emitted within 50 ns after the discharge. Although not shown, similar results were obtained when the magnetic tapes A and B were used.
[0037]
The above measurements show that the surface resistance of the recording surface of the magnetic tape 1 has a large effect on the value of the discharge current flowing when discharging to the MR head 2. However, when a voltage of 30 V is applied by the voltage source 13 as described above, the characteristics of the MR head 2 are hardly affected even when the actual MR head 2 is discharged using any of the magnetic tapes A to D. Did not give.
[0038]
By the way, as a method of evaluating the characteristics of the MR head 2 discharged from the magnetic tape 1, for example, a method of measuring the resistance of the MR head 2 to check whether or not the MR element is destroyed, There is a method of measuring the sensitivity by applying a magnetic field.
[0039]
Therefore, next, the characteristics of the MR head 2 in the case where the voltage applied by the voltage source 13 is further increased to increase the amount of charge stored in the magnetic tape 1 are measured by measuring the resistance. Here, as an example, the measurement is performed using the magnetic tapes C and D among the above magnetic tapes A to D.
[0040]
In the following measurement, an actual MR head 2 having a resistance value of 30Ω is used. The connection line through which the discharge current flows through the MR head 2 is connected to both of the two wiring electrodes of the MR head 2.
[0041]
FIG. 4 is a graph showing the relationship between the amount of charge accumulated on the magnetic tape C and the resistance value of the MR head 2 after discharging the charge. FIG. 5 is a graph showing a waveform of a discharge current in the MR head 2 according to the amount of charge accumulated on the magnetic tape C.
[0042]
FIG. 4 shows values obtained by measuring the resistance value of the MR head 2 after the discharge in each case where the amount of charge accumulated on the magnetic tape C is changed by changing the voltage applied by the voltage source 13. The measurement of the resistance value of the MR head 2 is performed by measuring the resistance between two wiring electrodes of the MR head 2 after discharging. FIG. 5 shows a current waveform measured by the oscilloscope 14 at the time of discharging each time the amount of charge stored on the magnetic tape C is changed.
[0043]
According to FIG. 4, when the charge amount of the magnetic tape C is 15 nC or less, the resistance value of the MR head 2 hardly changes, but when the charge amount is 20 nC, the resistance value of the MR head 2 drops. It has been observed that the discharge destroyed the MR element. Further, according to FIG. 5, it can be seen that the discharge current reaches 300 mA or more when the accumulated charge amount is 20 nC.
[0044]
FIG. 6 is a graph showing the relationship between the amount of charge accumulated on the magnetic tape D and the resistance value of the MR head 2 after discharging the charge. FIG. 7 is a graph showing a waveform of a discharge current in the MR head 2 according to the amount of charge accumulated on the magnetic tape D.
[0045]
FIGS. 6 and 7 show measured values obtained when the measurements corresponding to FIGS. 4 and 5 were performed using the magnetic tape D. According to FIG. 6, even when the amount of charge on the magnetic tape D reaches 100 nC, there is almost no change in the resistance value of the MR head 2 and no destruction of the MR element due to discharge has occurred. According to FIG. 7, when the accumulated charge amount is 100 nC, the discharge current is about 90 mA, and it can be seen that the discharge current is significantly suppressed in the magnetic tape D as compared with the magnetic tape C.
[0046]
According to the above measurement example, even when a large amount of electric charge is charged on the magnetic tape 1 by applying a high voltage, the higher the surface resistance of the recording surface of the magnetic tape 1 is, the more the magnetic tape 1 flows during discharge from the magnetic tape 1 to the MR head 2. It was confirmed that the discharge current was suppressed. Therefore, it can be said that the safety of the MR head 2 is maintained by using the magnetic tape 1 having a high surface resistance.
[0047]
By the way, in a situation where the magnetic tapes A to D are actually housed in a tape cartridge made of a resin, the electric charges of several tens nC rarely charge the magnetic tapes A to D during normal use as described above. For example, when a magnetic tape is housed in a tape cartridge and the surface of the tape cartridge is rubbed with nylon gloves, the amount of charge on the magnetic tape is as shown in Table 3.
[0048]
[Table 3]

[0049]
In the measurement results of Table 3, (A) shows the case where the magnetic tape C was used, and (B) shows the case where the magnetic tape D was used. The friction of the tape cartridge and the subsequent charge measurement were performed three times for each of the magnetic tapes C and D under different temperature and humidity environments.
[0050]
According to Table 3, the amount of charge on the magnetic tape C does not reach 5 nC in an environment where the temperature is 10 to 25 degrees. Similarly, in the case of the magnetic tape D, the charge amount does not reach 3 nC. Therefore, in an environment in which data is reproduced by the MR head 2 in a state in which static electricity is charged in the tape cartridge by normal handling, the system including the magnetic tapes A to D and the MR head 2 requires the MR head 2 2 has a large margin against the occurrence of ESD destruction.
[0051]
As described above, in the above-described measuring apparatus, it is possible to simulate a discharge phenomenon when the magnetic tape 1 and the MR head 2 come into contact with each other by using the magnetic tape 1 actually used. It is possible to evaluate the performance of the MR head 2 under close conditions. For example, during the development of a tape system, it is possible to provide a system design guide against the ESD destruction of the MR head in consideration of the conditions in the tape drive. In addition, a margin for ESD destruction in a state closer to an actual tape system can be measured. Therefore, it is possible to develop a more reliable tape system.
[0052]
In addition, by using the above-described measuring device, it is possible to clarify the standard values of the specifications of the MR head and the magnetic tape, and to contribute to the supply of products of stable quality. For example, when the present invention is used to measure the characteristics of a magnetic tape with respect to an MR head, as described above, the efficiency is improved by discharging using a resistor having the same resistance value in place of the MR head. Good measurement becomes possible.
[0053]
In the case of a magnetic head using an AMR element as in the above measurement example, the current system has a sufficient margin for ESD destruction, but a GMR element in which an ESD destruction phenomenon is more likely to occur in the future. When a TMR element or a TMR element is used, the specification standards for magnetic heads and magnetic tapes are stricter. In such a case, it is considered that the importance of performing accurate characteristic evaluation under conditions closer to the actual specification environment as in the present invention is further increased.
[0054]
By the way, the measuring device shown in FIG. 1 is composed of only basic elements, and actually, in addition to the above, a configuration for measuring the characteristics of the MR head, a configuration for changing the measurement conditions, and the like are added. It is desirable. Hereinafter, an example of a measuring device to which such an element is added will be described.
[0055]
FIG. 8 is a diagram showing a part of the configuration of the measuring apparatus according to the second embodiment of the present invention. In FIG. 8, components corresponding to those of the measuring apparatus shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
The measurement device shown in FIG. 8 can perform measurement in a state where the MR head is mounted on the head drum, in addition to the measurement using the MR head alone. FIG. 8 shows a measurement example in a state where the MR head is mounted on the head drum 20.
[0056]
In this measuring device, the head drum 20 is mounted on the holder 15a of the lifting mechanism 15. The head drum 20 is mounted so that the head sliding surface of the MR head faces the magnetic tape 1 side, and is vertically moved with respect to the recording surface of the magnetic tape 1 by the elevating mechanism 15 so that the head sliding surface is moved. It comes into contact with the recording surface of the magnetic tape 1. The magnetic tape 1 is fixed on an insulating sheet 12 disposed on a ground plane 11 with the recording surface facing up, as in the measuring device shown in the figure.
[0057]
The holder 15a has a function of holding the head drum 20 or the MR head, and switching and connecting external connection lines 15b, 15c and 15d to the wiring electrodes provided therein.
[0058]
The other end of the connection line 15b is grounded, and a probe 14a of the oscilloscope 14, a probe 16a of the nanocoulomb meter 16, and an impedance adjustment circuit 17 are connected between the ground potential and the holder 15a. The nanocoulomb meter 16 measures the amount of charge on the magnetic tape 1 based on the current flowing through the connection line 15b. The impedance adjustment circuit 17 includes a circuit such as a resistor, a capacitor, and a coil therein, and can arbitrarily adjust the impedance of the connection line 15b.
[0059]
The resistance measuring device 18 is connected to the connection line 15c. The connection line 15c is composed of, for example, two conductors, and the respective conductors of the two wiring electrodes connected to the MR element in the MR head are connected, whereby the resistance measuring device 18 measures the resistance of the MR element. Is possible.
[0060]
The magnetic characteristic measuring device 19 is connected to the connection line 15d. The magnetic property measuring device 19 includes a magnetic field applying device 19a and a voltage measuring device 19b. The magnetic field application device 19a has a structure in which, for example, a magnetic core for applying a magnetic field to a measurement target is wound around a magnetic core, and an alternating current flows through the winding.
[0061]
The head drum 20 or the MR head mounted on the holder 15a is set in the magnetic field applying device 19a of the magnetic property measuring device 19 by the operation of the elevating mechanism 15. The voltage measuring device 19b supplies a constant current to the MR element in the MR head through the connection line 15d, and measures a voltage when a magnetic field is applied.
[0062]
The resistance measuring device 18 and the voltage measuring device 19b in the magnetic property measuring device 19 may be realized as the same device. In FIG. 8, a voltage source for applying a voltage to charge the magnetic tape 1 with electric charges and a probe for applying the voltage are not shown.
[0063]
The measurement by such a measuring device is performed, for example, as follows. First, the connection of the lifting mechanism 15 by the holder 15a is switched to the connection line 15b. Then, a voltage is applied to the magnetic tape 1 by a voltage source for a predetermined time to charge the electric charge.
[0064]
Next, the application of the voltage is stopped, and immediately after that, the lifting mechanism 15 is operated to bring the head sliding surface of the head drum 20 into contact with the recording surface of the magnetic tape 1. As a result, a discharge is generated from the magnetic tape 1 to the head drum 20, and a discharge current flows to the ground potential through the connection line 15b and the impedance adjustment circuit 17. The discharge current at this time is measured by the oscilloscope 14, and the nanocoulomb meter 16 measures the amount of charge accumulated on the magnetic tape 1.
[0065]
After that, the connection in the holder 15a is switched to the connection line 15c, and the resistance value of the MR element in the head drum 20 where the discharge has been performed is measured by the resistance measuring device 18. Alternatively, when the connection in the holder 15a is switched to the connection line 15d, the head drum 20 is moved to the measurement position in the magnetic property measuring device 19 by operating the elevating mechanism 15, and the magnetic field is applied by the magnetic field applying device 19a. Is measured by the voltage measuring device 19b. Thus, the sensitivity of the MR head to magnetism after the discharge can be measured.
[0066]
In the above measuring device, by inserting the oscilloscope 14 and the nanocoulomb meter 16 in series on the flow path of the discharge current, the current flowing in the MR element at the time of discharge and the charge amount on the magnetic tape 1 can be measured simultaneously. It becomes possible. In addition, by providing the impedance adjustment circuit 17 on this flow path, it is possible to match the impedance at the time of discharge according to the impedance of a circuit such as an amplifier that is actually connected to the wiring electrode of the MR head and perform measurement. And simulation under conditions closer to the actual system becomes possible.
[0067]
Further, by switching the connection of the MR head to the wiring electrode in the holder 15a, the resistance value and the voltage change amount of the MR head after the discharge is performed can be measured by using the resistance measuring device 18 and the magnetic characteristic measuring device 19. It becomes possible to measure easily. Therefore, it is possible to efficiently evaluate the characteristics of the MR head.
[0068]
In addition, since the holder 15a can mount not only a single MR head but also a head drum, it is possible to perform a simulation with the MR head mounted on the head drum.
[0069]
In addition, the operation of the lifting mechanism 15, the oscilloscope 14, the nanocoulomb meter 16, the resistance measuring device 18, the magnetic characteristic measuring device 19, and the operation of a voltage source (not shown) are collectively controlled, and the measuring process using these is automatically performed. It is desirable to do so. In particular, by automating the measurement, the discharge current can be measured accurately by keeping the timing at which the MR head is brought into contact after the voltage is applied to the magnetic tape 1 constant.
[0070]
【The invention's effect】
As described above, in the magnetic head measuring method of the present invention, when a magnetic tape actually used in a recording or reproducing system is used and the magnetic tape is discharged to the magnetic head, the magnetic tape flows through the magnetic head. The current can be measured. Therefore, it is possible to accurately evaluate the characteristics of the magnetic tape in accordance with the actual use environment.
[0071]
In the magnetic head measuring apparatus of the present invention, a magnetic tape actually used in a recording or reproducing system is used to measure a current flowing through the magnetic head when the magnetic tape is discharged to the magnetic head. be able to. Therefore, it is possible to accurately evaluate the characteristics of the magnetic tape in accordance with the actual use environment.
[Brief description of the drawings]
FIG. 1 shows an overall configuration of a measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating an example of a measurement process using a measurement device.
FIG. 3 is a graph showing a measurement example of a waveform of a current flowing through a resistor during discharge when magnetic tapes having different surface resistances are used.
FIG. 4 is a graph showing the relationship between the amount of charge accumulated on a magnetic tape C and the resistance value of an MR head after discharging the charge.
FIG. 5 is a graph showing a waveform of a discharge current in an MR head according to an amount of electric charge accumulated on a magnetic tape C;
FIG. 6 is a graph showing the relationship between the amount of charge accumulated on a magnetic tape D and the resistance value of an MR head after discharging the charge.
FIG. 7 is a graph showing a waveform of a discharge current in an MR head according to an amount of charge accumulated on a magnetic tape D.
FIG. 8 is a diagram showing a part of a configuration of a measuring apparatus according to a second embodiment of the present invention.
FIG. 9 is a diagram showing a circuit configuration of an apparatus for simulating an ESD breakdown phenomenon of an MR head using an HBM.
FIG. 10 is a graph showing an example of voltage measurement in an MR head using an HBM.
FIG. 11 is a graph showing a measurement example of the sensitivity of a GMR head when an HBM is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Magnetic tape, 2 ... MR head, 11 ... Ground plane, 12 ... Insulating sheet, 13 ... Voltage source, 13a ... Probe, 14 ... Oscilloscope, 14a ... Probe

Claims (9)

In a magnetic head measuring method for measuring the characteristics of a magnetic head when discharge occurs on a head sliding surface with respect to a magnetic tape,
On a flat insulator placed on the ground plane, fix the magnetic tape with the recording surface facing up,
A voltage is applied to the magnetic tape to charge it,
Immediately after stopping the application of the voltage, the head sliding surface of the magnetic head is brought into contact with the recording surface of the magnetic tape,
Before and after contact of the magnetic head and the magnetic tape, measure a current flowing from the magnetic head to a ground potential,
A method for measuring a magnetic head, comprising: 2. The method according to claim 1, further comprising, when applying a voltage to the magnetic tape, further measuring an amount of charge on the magnetic tape. 2. The method according to claim 1, wherein a resistance value of a head element of the magnetic head is measured after the magnetic head is brought into contact with the magnetic tape. 2. The method according to claim 1, wherein after the magnetic head is brought into contact with the magnetic tape, a magnetic field is applied to the magnetic head to measure the sensitivity of the magnetic head to the magnetic field. 2. The method according to claim 1, wherein the magnetic head includes a head element made of a magnetoresistive element. In a magnetic head measuring device for measuring the characteristics of the magnetic head when discharge occurs on the head sliding surface with respect to the magnetic tape,
A flat insulator disposed on the ground plane,
A magnetic tape fixed with the recording surface facing upward on the insulator,
Voltage applying means for applying a voltage to the magnetic tape,
A magnetic head movably provided such that a head sliding surface contacts a recording surface of the magnetic tape,
Current measuring means connected between the magnetic head and ground potential, for measuring a current flowing from the magnetic head to ground potential before and after contact with the magnetic tape,
A measuring device for a magnetic head, comprising: 7. The magnetic head measuring apparatus according to claim 6, further comprising a charge amount measuring unit for measuring a charge amount charged on the magnetic tape. 7. The magnetic head measuring device according to claim 6, further comprising a resistance measuring means for measuring a resistance value of a head element of the magnetic head. 7. The magnetic head measuring apparatus according to claim 6, further comprising a sensitivity measuring unit that applies a magnetic field to the magnetic head and measures a sensitivity of the magnetic head to the magnetic field.

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