WO1989001685A1

WO1989001685A1 - Magnetic storage device with tracker system

Info

Publication number: WO1989001685A1
Application number: PCT/EP1988/000142
Authority: WO
Inventors: Eckhardt Hoenig; Heinrich Diepers; Herbert Schewe; Dietrich Stephani
Original assignee: Siemens Aktiengesellschaft
Priority date: 1987-08-17
Filing date: 1988-02-26
Publication date: 1989-02-23

Abstract

A magnetic storage device comprises a magnetizable storage disk, a write/read magnetic head arranged on a floating element, and a tracker system. This system comprises a servo head rigidly connected to the magnetic head and maintained on at least one guide track by electronic elements, connected downstream. The storage device is designed to ensure continuous guiding of the magnetic head. For this purpose, guide tracks (9, 10) are inscribed separately on the storage disk (2) along data tracks (40) each of which contains two parallel half-tracks (9a, 9b; 10a, 10b) with antiparallel magnetization directions (13a, 13b). The servo head (20) is arranged on the flat posterior side of the floating element and contains a magnetoresistive sensor (26) which is coupled magnetically to two magnet arms (22, 23) connected to at least one guide track (9, 10).

Description

Magnetic storage device with a tracking system

The invention relates to a magnetic storage device

- with a magnetizable storage plate,

- With at least one read / write magnetic head, which is arranged on an aerodynamically sliding over the moving storage disk missile and

with a track guidance system which contains a servo head rigidly connected to the magnetic head for guiding the magnetic head along a data track and which is to be kept on at least one guide track by means of a downstream electronics.

High-density storage of information (data) in disk-shaped recording media is known both according to the principle of longitudinal (horizontal) and in particular according to the principle of vertical (vertical) magnetization (cf., for example, "IEEE Transactions on Magnetics", Vol MAG-16, No. 1, January 1980, pages 71 to 76 or Vol. MAG-20, No. 5, September 1984, pages 657 to 662 and 675 to 680). The read / write magnetic heads to be used for these types of magnetization are advantageously formed using thin-film technology on non-magnetic substrates. The distance between a magnetic head and the surface of the storage disk should be kept extremely small and, in particular in the case of a vertical type of magnetization, should be less than 1 μm. Such small distances can practically only be ensured by designing the substrate carrying the magnetic head as a missile which aerodynamically over that flies away beneath it - the disk.

For this purpose, the substrate on its underside facing the recording medium is advantageously equipped with corresponding glide or flight skids (cf. e.g. EP-A-0 137 051). To guide such a flying read / write magnetic head of a corresponding magnetic storage device, a so-called track positioner and, in general, also a track keeping system are required. So-called linear or angular positioners in conjunction with a special servo plate are mainly used for track positioning. This servo plate carries a fixed, inscribed grid of guide tracks. These tracks are read with the aid of a suitable servo head which, in rigid mechanical connection with the read / write magnetic head, ensures that this track grid is transferred to the data surface of the actual data storage disk and is accordingly found again during the reading process can.

The limits of this guidance technology are given by the mechanical tolerances of the drive system for the memory and servo plate and the head positioner. A desired further increase in track density therefore requires, for example, a corresponding further development of the drive mechanism. However, the corresponding effort in production is very high and therefore cost-intensive. As an alternative to this, additional servo measures are known in which the storage disk itself is used for tracking. In the case of a corresponding device, also referred to as an “E bedded servo”, a previously firmly written servo information is read before each memory block and used for readjustment of the track positioning. A variant of this technique is described, for example, in "Electronics", November 13, 1986, pages 81 to 83. However, this servo principle presupposes that the interaction of drive mechanism and head positioner is limited of - 2 μm is reproducible. However, if one looks at the current development tendencies, which are aiming in particular for the principle of vertical magnetization, track widths in the range of 10 μm and possibly even below it, servo systems are required which continuously track the read / write magnetic head so-called "track locking".

The object of the present invention is therefore to design the magnetic storage device of the type mentioned at the outset in such a way that it can be used to ensure such a continuous tracking of its magnetic head.

According to the invention, this object is achieved in that guide tracks running separately along the data tracks are inscribed, each of which contains two parallel half tracks, which have antiparallel magnetization directions, and that the missile on its rear flat side with the servo Head is provided which contains a magnetoresistive sensor which is magnetically coupled to two magnetic legs which are assigned to at least one guide track.

The advantages associated with this configuration of the magnetic storage device are to be seen in particular in the fact that no additional servo plate is required for continuous guidance of the magnetic head, so that the drive system of the storage device and in particular the guidance of the magnetic head is correspondingly simplified. The two guide tracks provided for guidance along a data track, which run parallel to each long side of a data track, can be kept very narrow. Since these guide tracks lie within the always present distance zones between adjacent data tracks, there is no loss of memory area associated therewith. This measure can even lead to a Gain storage space due to the very narrow spacing zones. Due to the arrangement of the servo head on the rear surface of the missile, despite the relatively large expansion of the magneto-resistive sensor, the two magnetic legs of the servo head can be positioned precisely over the guide tracks. In this case, even slight tilting of the entire missile with respect to the longitudinal axis of a data track, such as is caused, for example, by rotary positioners, can be tolerated.

With the construction principle according to the invention there are the following further advantages:

- The permanent guidance system is in terms of its concrete design, e.g. regarding his

"Feedback frequency" can be adapted to the conditions of the respective storage device.

- The magnetic head can be easily positioned on a specific track by counting the guide tracks.

- A clear detection of the track deviation is possible because a linear characteristic of the sensor of the servo head can be obtained.

- Tracking in the submicrometer range can be realized, which essentially only depends on the positional accuracy of the

Leadership is.

Due to the exact tracking, tracking along non-circular tracks, such as those formed on plastic substrates, is also possible. - There are no high demands on radial tolerance dimensions of the drive and positioning mechanism as well as with regard to a constant temperature. For this reason, shorter positioning times can also be achieved, and the positioning mechanism can be designed with less weight. - "Soft sectoring", ie ultimately dispensing with sector division or a free choice of sector length is possible.

- Guide track and data track information are detected and processed with separate read heads. No special filter technology is therefore necessary, so that there is a correspondingly great freedom in the design of the magnetic heads for writing and / or reading data and in the design of the servo heads.

10

Advantageous refinements of the storage device according to the invention are evident from the subclaims.

To further explain the invention, reference is made below to the schematic drawing, which shows a storage disk in FIG. 1, a section of which is shown enlarged in FIG. FIG. 3 shows a double servo track in the storage disk. A missile with a servo head is indicated in FIG. FIG. 5 shows the arrangement of a part of this servo head over a storage disk. FIG. 6 shows an agneto-resistive sensor of this servo head, of which the characteristic curve is shown in FIG. Figure 8 shows an embodiment of a servo head with a magneto-resistive sensor. FIGS. 9 and 10 each show a section through the servo head shown in FIG. 8. Corresponding parts are provided with the same reference symbols in the figures.

FIG. 1 shows an oblique view of a storage disk 2 of a magnetic storage device according to the invention, which is not detailed. A section of the disk surface 3 of this disk 2 is shown in FIG.

For this in Figure 2 as a supervision of the disk upper ^; 35 The area shown in the section shows five data tracks 4a to 4e, which consist of a material suitable for the magnetization principle selected. According to the selected exemplary embodiment, it is assumed that CoCr is to be magnetized vertically. In the figure, a data track section 5 with correspondingly magnetizable data blocks 5a to 5e is indicated by the data track 4c. The width b of each data track perpendicular to the relative direction of movement v of a corresponding magnetic head with respect to the longitudinal direction of the track is in the order of approximately 10 μm. A narrow spacing zone 7 is formed between adjacent data tracks and has a transverse dimension a of approximately 3 to 4 μm. In this distance zone 7, which are also referred to as "lawn", guide tracks 8 to 11 are written in the longitudinal direction, each consisting of two parallel, continuous half tracks. The half-tracks are designated 8a, 8b to 11a, 11b and each have a transverse dimension q of a few μm. The half tracks are generally immediately next to each other and are magnetized vertically in the opposite direction. According to the invention, the two guide tracks adjacent to each data track are now to be used for track guidance by means of an appropriately designed servo head. Accordingly, as shown in FIG. 2, data track 4c, for example, is assigned the two guide tracks 9 and 10. The guide tracks which are adjacent to a data track in pairs can thus be viewed as a double servo track 12.

FIG. 3 shows a section which is made over two spacing zones 7 with the guide tracks 9 and 10 along a section line marked III-III in FIG. In FIG. 3, the opposite magnetization directions of the half tracks 9a, 9b and 10a, 10b forming the guide track 9 or 10 are illustrated by arrowed lines 13a and 13b. As can also be seen from the figure, alternating magnetization directions are advantageously provided from the guide track to the guide track. In the exemplary embodiment shown, the direction of magnetization of the half tracks 9a and 10b or 9b and 10a is the same.

Deviating from the design of the guide tracks 8 to 11 shown in FIGS. 2 and 3, these can also be divided into individual signal sections, one behind the other in the guide direction, slightly spaced apart. If such interrupted guide tracks are written at constant speed and constant frequency, it is advantageous to obtain an "on-track" trigger signal for stabilizing the speed in later use. This allows e.g. Reduce bitshift error.

FIG. 4 shows an oblique view of a substrate designed as a missile 15 made of, for example, non-magnetic material. At the bottom of this missile two Flugkufeπ 16 and 17 are formed, the aerodynamic sliding of the

Allow missile over a disk. A servo head 20 designed according to the invention is arranged in the area of the flight skids 16 and in the area of the flight skids 17 a known read / write magnetic head 21 is arranged on the rear flat side 18, seen in the relative movement direction v of the missile with respect to the storage disk. The servo head and the magnetic head 21 can advantageously be produced as thin-film structures in the same process, wherein the same magnetic materials can be used. Depending on the selected magnetization principle, for example vertically, the magnetic head can be used to write to or read out the storage disk that passes beneath it. The servo head 20 serves for an exact guidance of the missile 15 or its magnetic head 21 along a corresponding data track. This head is a resistive reading device Executed head and contains two magnetic legs 22 and 23, which lead up to the lower edge 24 of the fluid body 15 or its runner 16. A known agneto-resistive sensor 26 is arranged between the two magnetic legs 22 and 23.

FIG. 5 shows in an oblique view the positioning of the servo head 20 indicated in FIG. 4 over a storage disk 2 designed according to FIG. 3. Only the two ends 22a and 23a of its magnetic leg 22 facing the storage disk 2 are shown in FIG. 5 and 23 can be seen. The Ideal¬ position of this servo head 20 and the associated read / write magnetic head is given when the servo head d just above the two guide tracks 9 un ^'is 10 4c extending longitudinally to the data track and together the Form servo double track 12. Ie, the magnetic leg 22 is then located exactly above ^" the guide track 9 composed of the magnetization oppositely directed from the half-tracks 9a and 9b. Since these two half-tracks produce approximately equally strong, opposite magnetization relationships in the magnetic restaurant! 22, this is The total field recorded is practically zero. The same applies to the ideal position of the leg 23 shown in the figure above the guide track 10 with half tracks 10a and 10b of opposite magnetization. The figure also shows the distance between the data track and the respectively adjacent guide track designated by d The distance d is of the order of 1 μm.

An embodiment of a magnetoresistive sensor 26 for the servo head 20 according to FIG. 4 is illustrated in FIG. 6 in a top view. This sensor can advantageously be used in a

Known structure known as "Barber Poles" (see e.g.

"IEEE Transactions on Magnetics", Vol. MAG-11, No. 5, Sept.

1975, pages 1215 to 1217 or vol. MAG-17, no. November 6 1981, pages 2884 to 2889). The sensor 26 is one

Element formed, which is constructed in mirror image with respect to a plane of symmetry S and thus has an overall length L measured in the main direction of expansion with the same partial lengths 1, and 1 ₂ (cf., for example, "IEEE Transactions on Magnetics", vol. MAG-18, no 2, March 1982, pages 763 to 768). A corresponding element is characterized by a layer or surface 27 made of a magnetoresistive material such as a NiFe alloy. The layer 27 generally consists of several thin films made of the magnetoresistive material in a sandwich-like manner, these films being separated in each case by thin insulation films, for example made of SiO ₂ . On the surface 27 narrow strips 28 are applied of an electrically well-conducting material wi ^* e, for example, of Au or Cu. These conductor strips 28 are spaced apart from one another and are arranged at an angle σC of in particular 45 ° with respect to the easy axis of the magnetization M of the magnetoresistive material of the surface 27. A current I flowing perpendicularly between the conductor strips 28 is then forced to assume this angle with respect to the magnetization direction M. In the figure, the flow direction of this current I on side connecting conductors 30 and 31 and a central connecting conductor 32 is indicated by arrowed lines.

Typical dimensions of such an approximately 25 to 50 nm thick sensor are: total length L: approximately 100 to 200 μm; Width B: about 10 to 50 μm.

If a servo head 20 with such a sensor 26 is guided over a servo double track 12 according to FIG. 2, 3 or 5, voltage connections 30 to 32 occur on its connecting conductors, which can be read from the characteristic curve of its sensor shown in FIG are (see also "NTG Technical Reports", Volume 76, 1980, pages 69 to 75). This characteristic is in one 1 diagram ^" , the magnetic field H of a servo double track being entered on the abscissa and the signal or connecting voltage V occurring between the connecting conductors being entered on the ordinate. The servo head is exactly in its

5. Ideal position, where the fields of the two half-tracks of each guide track just cancel each other out, so no signal appears at the connecting conductor. As can be clearly seen from the figure, the connection voltage V is at least largely linear over a relatively wide range of the H field. Such a 10th characteristic curve can advantageously be used for exact tracking by means of electronics connected downstream of the sensor of the servo head.

The magnetic coupling of the device shown in FIG.

15 ^; showed sensors to a magnetic field, which is caused by a servo double track 12, which can be seen, for example, from FIG. It was assumed that the servo head 20 with its central plane ME, with respect to which its two magnetic legs 22 and 23 are arranged in mirror image, laterally

20. has shifted from the ideal position. This ideal position is indicated in the figure by a dashed line labeled IP. The magnetic leg 22 arranged above the guide track 9 of the servo double track 12 then essentially sees the magnetic field 13b caused by the half track 9b,

25 while the other magnetic leg 23 assigned to the guide track 10 registers the magnetic field 13a of the half track 10b. These magnetic fields are brought via the vertically aligned magnetic legs 22 and 23 to the magneto-resistive sensor 26, which isolates between the two magnetic legs

30 with the vertical main direction of expansion of its total length

L = 1, + 1 _{2 is} arranged and represents a bridge for the magnetic flux between these two legs. The magnetic flux conditions thus caused in the magnetic legs and in the sensor are shown by arrowed lines 34 in the figure

35 1 indicated. The connecting conductors 30 to 32 of the sensor 26 can also be seen from the figure. The center connection 32 can be guided away in an isolated manner via the sensor 26. A guide under or over one of the magnetic legs is also good

5 possible.

FIG. 9 shows a section which is laid across the servo head 20 along a section line marked IX-IX in FIG. FIG. 9 shows the structure of the magnetic leg 22

10 and, 23 can be seen from individual layers 35, which can advantageously be produced from the same material as the magnetic legs of the magnetic head 21 indicated in FIG. 4. The magnetic legs and the magnetoresistive sensor are made of a NiFe alloy

15 each have a gap 36 or 37 for electrical insulation of the sensor from the two magnetic legs. Stray flux coupling takes place via these columns 36 and 37.

Figure 10 shows a longitudinal section through the magnetic leg 22 20 along a section line marked XX in Figure 8. As can be seen from FIG. 10, the laminated magnetic legs of the servo head can advantageously be designed with multiple steps, their thickness increasing from their leg end 38 facing the recording medium to the opposite 25 leg end 39 up to a total thickness D of approximately 5 μm ¬ takes. The gradation can advantageously be optimized together with the ratio of 1 to 1 ₂ (see FIG. 8) and the location dependence of the columns 36, 37 (see FIG. 9).

A write operation for magnetizing the guide tracks can be carried out, for example, in a single run with a known magnetic head which is rotated by 90 ^* and is formed on its own missile. The shape of this missile can in particular be that of the one shown in FIG

* 35 Missile 15 correspond. The two magnetic legs of this special track disc head should advantageously generate an approximately equally strong, oppositely directed magnetic field. The thicknesses of the two magnetic legs of such a head essentially determine the respective transverse dimension q of the two half tracks of a guide track generated. A ring head with correspondingly wide, adjacent magnetic legs for writing the half tracks can also be provided. It is particularly advantageous if the special head for writing the guide tracks is arranged on one flight runner of a particular missile corresponding to the head 21 and a servo head 20 according to FIG. 8 is provided on the other flight runner at the predetermined distance. Then you can already write with servo control when writing the guide tracks.

According to the exemplary embodiments on which FIGS. 1 to 10 are based, it was assumed that the measures according to the invention should relate to a storage system which works on the principle of vertical magnetization. In principle, however, the measures according to the invention can also be used for the principle of longitudinal magnetization. In this (longitudinal) magnetization principle, too, each guide track should have two half tracks, which, however, are magnetized longitudinally (horizontally) and directed in opposite directions to one another. A servo head with a shape largely corresponding to the head 20 is then designed and guided such that its two magnetic legs are each assigned exactly one of the two half tracks in the ideal position. Of course, it is also possible that the two

Half tracks associated with magnetic legs lie in separate guide tracks, so that then as in the exemplary embodiments 1 according to Figures 2, 3 and 5, a servo double track is formed.

^* 5

10

15

20th

25

30

'35

Claims

1. Magnetic storage device

- With an agnetizable storage disk, - With at least one read / write magnetic head, the. is arranged on a missile which aerodynamically slides over the moving storage disk, and

- With a tracking system which contains a servo head rigidly connected to the magnetic head for guiding the magnetic head along a data track and which is to be kept on at least one guide track by means of downstream electronics, characterized in that in the storage disk (2) guide tracks (8 to 11) running separately along the data tracks (4a to 4e) are inscribed, each containing two parallel half tracks (8a, 8b to 11a, 11b), which have antiparallel magnetization directions (13a, 13b), and that Missile (15) is provided on its rear flat side (18) with the servo head (20) which contains a magneto-resistive sensor (26) which is magnetically coupled to two magnetic legs (22, 23), which at least are assigned to a guide track.

2. Storage device according to claim 1, dadurchge¬ indicates that the data tracks are to be magnetized longitudinally (horizontally) and that the two magnetic legs of the servo head are each assigned to a half track of a guide track or two guide tracks forming a servo double track .

3. Storage device according to claim 1, dadurchge¬ indicates that the data tracks (4a to 4e) are to be magnetized vertically (vertically) and that the two Magnetic legs (22, 23) of the servo head (20) are each assigned two guide tracks (8 to 11) which form a double servo track (12).

4. Storage device according to claim 3, dadurchge¬ indicates that the to a data track (4c) zu¬ assignable guide tracks (9, 10) contain half tracks (9a, 9b or 10a, 10b), the magnetization directions (13a, 13b) set so are that the half tracks (9b, 10a) facing the data track (4c) from both guide tracks (9, 10) have parallel magnetization directions (13b) (cf. FIG. 3).

5. Storage device according to one of claims 1 to 4, so that the guide tracks (8 to 11) are each arranged in a distance zone (7) between adjacent data tracks (4a to 4e).

6. Storage device according to one of claims 1 to 5, that the magneto-resistive sensor (26) of the servo head (20) is of the Barber-Pole type.

7. Storage device according to claim 6, so that the magnetoresistive sensor (26) is formed in mirror image with respect to a plane of symmetry (S).

8. Storage device according to one of claims 1 to 7, that the servo head (20) is designed as a thin-film structure.

9. Storage device according to one of claims 1 to 8, d a- characterized in that the read / write magnetic head (21) is designed as a thin-film structure.

10. Storage device according to one of claims 1 to 9, dadurchgeke nn zcichnet that the two magnetic legs (22, 23) of the servo head (20) extend substantially in the vertical direction with respect to the surface of the storage plate (2) and that the magneto-resistive sensor (26) is arranged between them in an electrically insulated manner.

11. Storage device according to one of claims 1 to 10, characterized in that the magnetic ^" gifts ^" (22, 23) of the servo head (20) from its the storage disk (2) facing end (38) to its opposite end (39) with increasing thickness (D) and multiple steps (see FIG. 10).

12. Storage device according to one of claims 1 to 11, d a d u r c h g e k e n n z e i c h n e t that on the rear flat side of another missile a writing head for writing the guide tracks and at a predetermined distance from it a servo head are arranged, this

The structure of the servo head corresponds to that of the servo head (20), which is used for guiding the read / write magnetic head (21).