WO1990004846A1 - Scanning unit for a magnetic disk - Google Patents

Abstract

A scanning unit (2, 7) for a magnetic disk with a storage medium (1) disposed optically in the radial direction comprises, in addition to a magnetic write/read head (2, 7'), an optical sensor (2) which detects the actual position for dynamic track following. The optical sensor (2) is designed as a beam waveguide arrangement with a DFB (distributed feedback) laser (21) as the radiation source. A beam splitter (22) splits the emitted laser beam into two equivalent partial beams which scan the storage disk at a distance (D) apart which is a multiple of the track spacing. A detector element (27) is arranged in the path of each of the two partial beams reflected by the storage disk. The difference signal derived from their output signals is an index of the track position. The optical sensor (2) and a thin-film magnetic head (7') are preferably arranged on a common substrate (28).

Description

Scanning unit for a magnetic disk memory

The invention relates to a scanning unit for a magnetic disk memory according to the preamble of claim 1.

In the case of magnetic disk memories, it is known that a scanning unit carrying a magnetic head, in particular, is positioned radially to the surface of at least one disk via preferably concentric information tracks for carrying out read / write operations. There are basically two different positioning methods for setting the position of the scanning unit.

"Dedicated servo" positioning is the method in which track and other control information is recorded on a separate surface of a storage disk, the so-called servo surface. A servo magnetic head is assigned to this servo surface and is designed as a read head. In a disk stack with several storage disks, the remaining surfaces of the storage disks are assigned read / write heads which are mechanically rigidly coupled to the servo head via the positioning device. To perform

The servo head scans the track information for read / write operations in the magnetic disk memory and thus generates an actual value for the current radial position with respect to the servo surface. This actual value is compared in a positioning control loop with a target value and a control value for driving the positioning device is derived therefrom, which sets the servo head radially over the center of the selected servo track. The read / write heads assigned to the data surfaces of the magnetic disk memory inevitably follow the movements of the servo head, so that information tracks are thus indirectly defined on the data surfaces.

This positioning method has the advantage of being complete Decoupling of position control and data information. Furthermore, the servo information can be written in by the manufacturer with great accuracy and cannot be erased, which, with high operational reliability and appropriate technology, enables a high track density in magnetic disk memories. A disadvantage of this positioning principle is the indirect positioning of the actual read / write heads, which set limits on the track density that can actually be achieved because of the possible mechanical and thermal tolerances when operating the magnetic disk memory.

In contrast, the read / write heads of a magnetic disk memory are positioned directly in the "embedded servo" positioning. In this positioning method, the track information in connection with other control information is embedded directly along the information tracks on a data surface of a magnetic disk between the actual data information. In this case, the storage disk is preferably formatted, ie data and servo sectors which successively follow one another in the circumferential direction and in which data information or control information is stored. This positioning method offers the possibility of individually positioning each of the scanning units assigned to the surfaces of the storage disks radially and thus absorbing mechanical and thermal tolerances. This positioning method has the disadvantage of possible interference between lane control and data signals, and it must also be prevented in any case that the lane control information can be accidentally overwritten. At the current state of development in the field of magnetic disk storage, it is assumed that the inherent possibilities of this type of storage have not yet been fully exhausted and that a further increase in storage density in both the circumferential and radial directions is possible. One of the possibilities for improving the tracking of magnetic disk memories is seen, among other things, in optically closing the surface of the disk in the radial direction structure that there is an optically scannable ring-shaped grid, which essentially represents the track information.

In this context, it is known, for example from US-A-A, 663,451, to apply a magnetic layer to the carrier of a magnetic storage disc first in conventional technology, which magnetic layer represents the actual storage medium for data information to be stored. A cover layer arranged above serves first to protect the magnetic storage layer and is designed as an optical storage layer. Similar to optical memories, bit-wise information in the form of local focal spots is burned into this cover layer with the help of a laser. H. not registered for deletion. This information is used here as control information for the track positioning of a scanning unit in which an optical sensor is arranged on a missile next to a magnetic read / write head. This optical sensor contains a laser diode, the optical cover layer of the storage plate acting as a reflector, which influences the laser function or the operating characteristic. the laser diode modulated.

From "IEEE Transactions on Magnetics, Vol. MAG-16, No. 5, Sept. 1980, p. 631 ff." a similar solution is known. Here the carrier of a magnetic storage disk is an aluminum substrate, the surface of which is anodically oxidized. By coloring this surface in places in the form of concentric circular rings, the width and spacing of which corresponds to a track width, an optical pattern representing the track information is formed. A magnetically effective storage layer is placed over this layer. The magnetic storage layer has a layer thickness in the range of micrometers and is transparent, so that the optical track pattern underneath can be scanned through it. In this known solution, because of their weight and volume, the essential optical elements of an optical sensor are in the massive support arm of a positioning device shifted and provided in the missile glass fiber bundle for transporting a scanning light beam or a reflected light beam. Accordingly, it is known to construct a scanning unit for a magnetic disk memory in the form of a combination of a magnetic scanning head and an optical sensor. The advances in magnetic head technology probably make it possible to construct the magnetic read / write head as a thin-film magnetic head with low mass and suitable for high storage densities. This is more difficult with regard to the optical sensor, since conventional discrete optical elements often do not appear to be suitable because of their mass and their volume. The present invention is therefore based on the object to provide a scanning unit of the type mentioned, the optical sensor is designed such that it can be arranged together with the magnetic read / write head on the missile of the scanning unit, without thereby disadvantages for the operating parameters of the Magnetic disk storage in relation to conventional magnetic disk storage must be accepted.

This object is achieved in a scanning unit of the type mentioned by the features described in the characterizing part of claim 1.

This solution takes advantage of advances in the field of integrated optics, which allow such a sensor to be made compact and low-mass. This optical sensor, which is designed as an optical waveguide, has a high optical resolution and can be built up with an accuracy that corresponds to that of magnetic heads in thin-film technology. Such a scanning unit can therefore be used for magnetic disk memories with a high, previously unattained track density for both longitudinal and vertical recording. According to a particularly advantageous development of the invention, there is the possibility of arranging the magnetic head designed as a thin film head and an epitaxial optical sensor together on a substrate at a predetermined, defined distance from one another. In addition to the compactness in the construction of all the essential elements of the scanning unit, the particular advantage of this development of the invention is that it creates an adjustment-free scanning unit, since the geometrical position assignment of the magnetically active part and the optically active part of the scanning unit is clearly defined from the outset and thus Assembly errors are eliminated.

This creates an essential prerequisite for using the scanning unit designed according to the invention in accordance with another development of the invention in connection with a structured magnetic storage disk in which magnetic areas forming a track of information on a substrate with low reflectance are arranged in a radial direction separated from one another by non-magnetic areas . In contrast to conventional magnetic storage layers which are constructed completely uniformly apart from magnetic preferred directions, it is to be expected that such a structuring of the magnetic storage layer reduces such undesired couplings between adjacent magnetic areas which can lead to demagnetization. In addition, the useful / interference ratio in writing or reading processes is improved. Finally, it should be pointed out that a scanning unit according to the invention is suitable both for use in linear positioners and in rotary positioners. In the case of rotary positioners, however, it must be taken into account that the geometrical position of the connecting line between the magnetic head and the optical sensor with respect to the radial rays of the storage plate changes due to the pivoting-in process of the scanning unit over the surface of the associated storage plate. at An equidistant arrangement of the information tracks on the storage disk systematically results in a certain track division error, which is, however, in a range of a few percent.

If even this error appears to be no longer negligible, then according to a further development of the invention, this systematic error can be eliminated by using a scanning unit designed according to the invention in a rotary positioner in connection with a structured magnetic storage disk, the track density of which is inversely proportional to the variation of the skew angle that occurs when the rotary positioner is swiveled into the magnetic disk.

An embodiment of the invention is explained in more detail below with reference to the drawing, in which:

1 shows a schematic illustration of a section of a structured magnetic storage disk with an optical sensor arranged above the surface thereof and designed according to the invention as part of a scanning unit for a magnetic disk storage, FIG. 2 and FIG. 3 each show a basic illustration for a linear or a rotary positioner,

4 shows a side view of an embodiment for such a scanning unit, in which an optical sensor according to FIG. 1 is constructed together with a thin-film magnetic head on a common substrate,

5 shows a schematic view of the arrangement of FIG. 4 along the section line V-V,

6 shows the variation of the geometric position of the scanning stone on the basis of a section of a storage disk in two positions unit when used in a radial positioner to explain the systematic skews.

A partial cross section through a magnetic storage disk 1 is shown schematically in FIG. Basically, in this case it makes no difference whether the storage medium is intended for longitudinal or vertical recording, since in the present case the recording method as such does not play an essential role. In the present exemplary embodiment, the storage medium is intended to be suitable for vertical recording, and the magnetic storage disk 1 therefore has, for example, a substrate 101 made of transparent glass. The surface of the substrate 101 is structured, i. H. Magnetic areas are applied to it in the form of concentric circular rings, which are separated from one another by non-magnetic intermediate areas. The magnetic regions consist of a carrier layer 102 deposited on the substrate 101 and a cover layer which forms the magnetic storage layer 103. The magnetic storage layer can consist, for example, of a cobalt-chromium alloy.

The technology for the production of the magnetic disk 1 is not important in the present case. It is only important here that the magnetic areas 102, 103 are separated from each other by a track width w by an intermediate area and thus have a predetermined distance g from one another. The magnetic regions 102, 103 have a different reflectivity than the intermediate regions in which the transparent substrate 101 is exposed.

The magnetic areas 102, 103 of the magnetic disk 1 represent their information tracks, which are designated by the reference symbol 103 '. Because of this different reflectivity, the tracks can be recognized for optical scanning. In FIG 1, an optical sensor 2 is shown schematically as a means for detecting the tracks, which in the technology of integrated optics as light waves conductor arrangement is constructed. It has a DFB (Distributed Feedback) laser 21 as the radiation source. This type of laser is known, for example, from the book M. Young "Optics and Lasers-Including Fibers and Optical Wavtguides", 3rd edition 1986, page 234. It consists of an active material that has the shape of a waveguide on the surface of a substrate. In contrast to conventional lasers with reflecting mirrors at the opposite ends of the active material, in this type of laser, as is also indicated schematically in FIG. 1, in the surface of the short waveguide, a reflection grating with a reflection grating adapted to the wavelength of the laser and the refractive index of the active material Grid constant provided. Under this secondary condition, the grating leads to a reflection in the opposite direction distributed over the length of the waveguide and thus replaces the reflection mirrors in conventional lasers. Such a type of laser is therefore particularly suitable for arrangements in integrated optics, since it can be built up epitaxially on a substrate.

The DFB laser 21 emits radiation in this application, which is fed directly into a waveguide channel 22. A beam splitter 23 is connected to this and splits the emitted laser radiation into two equivalent partial waves. These partial waves are guided in partial wave channels 24 and leave the optical sensor at anti-reflective exit windows 25.

If this optical sensor 2 forms part of the scanning unit of a magnetic disk memory, for example if it is mounted on the missile of a movable magnetic head arrangement of a magnetic disk memory, the distance a of the exit surface of the optical sensor 2 from the surface of the magnetic disk disk 1 is usually less than 1 in the operating state of the magnetic disk memory μm, preferably about 0.5 μm.

If a partial wave emerging from one of the partial wave channels 24 strikes the magnetic medium under these conditions layer 103, it is reflected there and coupled back into the corresponding partial wave channel 24. For the extension w (a) of the partial wave in the vicinity of the exit surface at the anti-reflective channel ends 25 approximately applies to the relationship:

Here λ is the wavelength of the laser beams and w _o the diameter of a partial wave channel 24 at the exit window 25. If, for example, λ = 830 nm, w _o = 1.5 μm and a = 1 μm, the relationship (1) w (a) = w _o . 1.11. The partial wave only widened by 11% when it struck the magnetic storage layer 103, so that a substantial proportion of the emitted partial wave is fed back into the optical sensor 2.

According to FIG. 1, the feedback partial waves re-enter the optical sensor 2 via the exit windows 25 and are each supplied to one of two detector elements 27 via reflection wave channels 26. As shown in FIG. 1, the detector elements 27 can be manufactured as discrete photodetectors and glued onto the optical sensor 2 or can be integrated directly into the optical sensor 2 with a somewhat higher manufacturing effort.

An essential, function-determining variable of the optical sensor 2 is the mutual center distance D of the anti-reflective exit window 25. As shown schematically in FIG. 1, this center distance D should satisfy the relationship:

(2) D = g + n. (w + g) are sufficient. Here w denotes the track width of the information tracks 103 ', g the mutual spacing of these tracks and n an integer, positive number. As shown in FIG. 1, the operating point of the optical sensor 2 is set at a relative position with respect to the magnetic storage disk 1 when both beams emerging from the exit windows 25 are each reflected half by the magnetic storage layer 103 of the magnetic storage disk 1. With the same sensitivity of the photodetector elements 27, the difference between the photodiode currents is 0 in this case. If the optical sensor 2 is shifted radially to the left or right from the target position shown in FIG. 1, ie radially with respect to the magnetic disk 1, the two partial waves are different strongly reflected. This then results in a non-zero difference signal from the detector elements 27, the sign of which denotes the direction of the radial displacement.

In conventional magnetic disk memories, the scanning unit that is movable radially to magnetic disk 1 is usually a magnetic read / write head, which is preferably mounted on an end face of a missile. The missile is resiliently attached to a support arm of a positioning device, which can be designed as a linear or as a rotary positioner. Such positioning devices for magnetic disk storage are known per se well. To avoid the

 Description in the given context of details which are in themselves insignificant is therefore shown only schematically in FIG. 2 and in FIG. 3 the structure of a linear or a rotary positioner.

The linear positioner shown in FIG. 2 has a fixed permanent magnet 3, to which a moving coil 4 is assigned. This is fixed on a carriage 5 which is radially movable with respect to rotating magnetic storage disks 1. The carriage has support arms 6 which are arranged parallel to the magnetic storage disks 1 and which support spring-articulated magnetic heads 7. When the plunger 4 is excited, it is moved relative to the permanent magnet - as indicated by arrows - together with the carriage 5, and the magnetic heads 7 are thus positioned radially with respect to the magnetic storage disks 1. 3 shows the principle of a rotary positioner. In this case, when a magnet coil 8 is excited, a rotating body 9 is pivoted in or out with respect to the magnetic storage disk 1, depending on the sign of this excitation, as is schematically indicated by corresponding arrows. A missile 11 is resiliently articulated on the rotating body 9 via a support arm 10, which is designed to be resilient. As indicated schematically, a magnetic head 7 is arranged on an end face of this missile 11. When the rotary body 9 pivots, the missile 11 is moved together with the magnetic head 7 essentially radially with respect to the schematically indicated recording tracks 103 'of the magnetic disk 1 and thus the magnetic head 7 is positioned with respect to these recording tracks.

As explained in summary above with reference to FIGS. 2 and 3, the scanning unit in conventional magnetic disk memories usually consists of a magnetic head 7 fixed to an end wall of a missile 11, which is designed as a read / write head. Since, in the present case, however, storage information is magnetically written or read, track control information, on the other hand, is determined with the aid of the optical sensor 2 described by FIG. 1, in this case the scanning unit consists of a combination of a magnetic read / write head and an optical sensor.

FIG. 4 shows an integrated embodiment for such a combined scanning unit in a front view and in FIG. 5 in a view from below. The optical sensor 2, which has already been described in detail above with reference to FIG. 1, is built up epitaxially on a common substrate 28, for example consisting of gallium arsenide. In contrast to the embodiment of FIG. 1, however, the detector elements 27 are not designed as discrete elements, but are integrated in the optical sensor. 5 shows a view of the scanning unit in the direction of the arrows V / V of FIG. 4. In this view, only those of the optical sensor 2 are shown Exit window 25 of the partial wave channels 24 can be seen. A passivation layer 29 is placed over the optical sensor, on which a thin-film magnetic head 7 ', which is only shown schematically in FIG. 4, is then built, for example using conventional sputtering technology. 4 schematically shows the outline of a magnetic coil 71, vertically lying an outer core half 72 with a through-hole 73 to the lower core half and a pole tongue 74. In FIG. 5, an air gap 75 of the thin-film magnetic head 7 'is schematically indicated in the region of the pole tongue 74.

As illustrated in FIG. 5, due to this construction technique, a distance d is unavoidable in the plane perpendicular to the surface of the substrate 28 of the scanning unit between the position of the air gap 75 and the center of the exit windows 25 of the partial wave channels 24. In the plane perpendicular to it, i.e. H. A center distance R between the optical sensor 2 and the thin-film magnetic head 7 ′ is defined parallel to the surface of the substrate 28. FIG. 4 shows both the optical sensor 2 and the thin-film magnetic head 7 'in their desired position with respect to the recording tracks 103' of the magnetic disk 1. It follows from this that the relationship (3) is given for the center distance R of the optical sensor 2 from the thin-film magnetic head 7 ':

(3) R = nw + g (n + 1/2)

Here w is the track width, g is the mutual distance between the recording tracks 103 'of the magnetic disk 1 and n is a positive, integer number. With the precision of mask technology that can be achieved today, it can be ensured that this center distance R can be maintained with an accuracy that is below 1 μm. This tolerance is negligible compared to the track width w, so that the combined scanning unit as such is free of adjustment.

With appropriately structured magnetic storage disks 1 The scanning unit described with reference to FIGS. 4 and 5 can be used directly in linear positioners with a basic structure according to FIG. In this application, the combined scanning unit is only to be fixed on an end face of the associated missile instead of a conventional single read / write head.

With rotary positioners, on the other hand, there is the difficulty that the locus, which the scanning points of the magnetic heads during insertion or. Describe pivoting of the rotary positioner

 Circular ring section around the pivot point of the rotary positioner. This circular ring section is only ever approachable with restrictions to a radial beam to the magnetic storage disk 1. Due to this type of pivoting movement, the position of the scanning unit with respect to the respective track tangent also changes over the area to be scanned, ie. H. a skew occurs. FIG. 6 schematically attempts to clarify these geometrical relationships. A broken line shows a locus 12 of the scanning unit consisting of an optical sensor 2 and a thin-film magnetic head 7.

Details of the rotary positioner are not shown in FIG. 6 for reasons of clarity. The position of this locus 12 is - not in full agreement with practice - chosen so that the desired relationships are clear.

6 shows two pairs of information tracks 103 'approximately in an outer or an inner edge area of the magnetic storage disk 1. For the outer edge area, the locus 12 of the scanning unit 2, 7' is selected such that it is essentially parallel to a radial beam of the magnetic storage disk 1 is aligned. In this case, the distance between the track tangents of these outer information tracks 103 'corresponds to the center distance R between the optical sensor 2 and the thin-film magnetic head 7'. The position of the scanning unit 2, 7 'with respect to the track tangents of the inner information tracks 103' is shown in dashed lines in dashed lines poses. With respect to the corresponding radial beam 104, the scanning unit 2, 7 'is rotated by the skew angle α, so that the effective distance S between the optical sensor 2 and the thin-film magnetic head 7', seen parallel to this radial beam, is then also shortened. The relationship for this effective distance S results from the geometric view:

As mentioned, the illustration in FIG. 6 is intended to clarify the variation of the effective distance S between the optical sensor 2 and the thin-film magnetic head 7 '. In practice, the systematically determined skew angle is not so pronounced. If, for example, α = 17º and R = 100 μm is assumed, then R - S = 4.4 μm is calculated according to relationship (4). The variation of the effective distance S is, in relative terms, only a few percent, which, however, can no longer be neglected. In practice, the distance d between the optical sensor 2 and the thin-film magnetic head 7 ', viewed perpendicular to the substrate surface, also contributes to such an offset. It leads to an additional shift T according to the relationship:

(5) T = d sinα The variation of the effective distance S and the shift T can be compensated for if the track density 9 is varied accordingly over the surface of the disk. The following equation can be used for a local track density: (6) (S - T). = const.

Even with very high track densities, such a scanning unit combined from an optical sensor 2 and a thin-film magnetic head 7 'can then be used in rotary positioners, without the systematically predetermined skew here possibly leading to erroneous evaluations. Reference list

1 magnetic disk

 101 substrate from 1

 102 carrier layer

 103 magnetic storage layer

w track width

g mutual distance between the magnetic regions 102, 103

2 optical sensor

 21 DFB lasers

 22 waveguide channel

 23 beam splitters

 24 partial wave channels

 25 anti-reflective exit windows

a Distance from sensor to disk

 26 reflection wave channels

 27 detector elements

 D Center distance of the exit windows

 3 permanent magnet

 4 plunger

5 sledges

 6 support arms

 7 magnetic heads

 8 solenoid

 9 rotating body

 10 support arm

 11 missiles

 28 Substrate of the scanning unit

 29 passivation layer

7 'thin film magnetic head

 71 solenoid

 72 core half

 73 plated-through hole

 74 pole tongue

 75 air gap of 7 '

d Distance between optical sensor and thin-film magnetic head in

Vertical direction R corresponding center distance in the horizontal direction

12 locus of the scanning unit

 104 Radial beam to the magnetic disk

α Skew angle

 S effective effective distance R

 T shift

 Track density

Claims

Claims 1. scanning unit for a magnetic disk memory, in which on a missile (11) a magnetic head (7) and for tracking control an optical sensor (2) are provided with which the Surface of an associated storage disk (1) optically structured for the positional identification of information tracks (103 ') in the radial direction can be scanned, so that the optical sensor (2) is designed as an optical waveguide arrangement, which is a DFB  (Distributed feedback) laser (21) as the radiation source, a beam splitter (22) for splitting the emitted laser beam into two equivalent partial beams scanning the storage plate (1) at a distance (D) corresponding to a multiple of the track pitch, and two detector elements (27 ), which are each arranged in the beam path of one of the partial beams reflected by the storage plate. 2. Scanning unit according to claim 1, so that the optical sensor (2) is constructed as a hybrid circuit in which the detector elements (27) are designed as discrete components and are connected to the integrated optical waveguide arrangement. 3. Scanning unit according to claim 1, so that the detector elements (27) of the optical sensor (2) are integrated in the optical waveguide arrangement. 4. Scanning unit according to one of claims 1 to 3, characterized in that the thin-film magnetic head (7 ') formed read / write head and the epitaxially constructed sensor (2) together on a substrate (28) at a predetermined defined distance (R) are arranged from each other. 5. scanning unit according to claim 4, dadurchge indicates that the epitaxially constructed sensor (2) is covered by a passivation layer (29) on which the thin-film magnetic head (7 ') is formed using sputtering technology. 6. Scanning unit according to claim 4 or 5, characterized by its use in connection with a structured magnetic storage disk (1), in which on a substrate (101) low reflectance each magnetic information (103 ') forming an information track (103') by non-magnetic areas are arranged offset from each other in the radial direction. 7. scanning unit according to one of claims 4 to 6, g e k e n n z e i c h n e t d u r c h their use in a linear positioner. 8. Scanning unit according to one of claims 4 to 6, characterized by its use in a rotary positioner in connection with a structured magnetic disk (1), the track density (ς) of which is inversely proportional to the variation of the skew angle (α) which occurs when the positioner is pivoted into the magnetic disk is.