Dynamic magnetic information storage or retrieval – Head – Coil
Reexamination Certificate
2000-09-22
2002-01-01
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Coil
C029S603230
Reexamination Certificate
active
06335846
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a vertical magnetic head with integrated coil and its manufacturing process.
It finds privileged application in video recording by the general public. But it may also be used in other areas, such as data backup or computer memories.
STATE OF THE PRIOR ART
A magnetic recording medium for video recording, data backup or computer memory comprises numerous tracks on which information is written in the form of magnetic fields.
To increase information density, not only can the amount of information per unit length be increased, but also the number of tracks. To achieve this purpose, track width is reduced and, simultaneously, the distance between them is reduced until the tracks abut one another.
To avoid any crosstalk problems on reading, the information on two adjacent tracks is written at opposite angles. The head angle must be most precise (for example 20±0.15° in the new so-called DVC standard or <<Digital rodeo Cassette >>.
To meet these requirements, so-called <<sandwich >> heads can be currently found on the market of which an example of embodiment is illustrated in
FIG. 1
appended hereto. The head shown comprises a substrate
2
carrying a magnetic circuit
4
made up of a magnetic layer placed on the top surface of the substrate, this circuit having two polar parts
5
and
7
at the front separated by an air gap
6
which is formed by a nonmagnetic spacer. This head also comprises, above the magnetic circuit, a nonmagnetic substrate
2
′. An opening
8
is pierced through the whole unit to allow the passage of a conductor coil
9
surrounding the magnetic circuit.
The head shown in
FIG. 1
is intended to co-operate with a recording medium S oriented perpendicular to the substrate (in other words parallel to the latter's edge)
Such heads may be described as <<vertical >> in the sense that the active surface is perpendicular to the general surface of the substrate.
The width of the air gap, called
1
, is calculated perpendicular to the substrate (parallel to the recording medium). This Width
1
substantially corresponds to the respective width of the tracks in the medium. The length of the air gap, called L, is calculated in the direction of the relative movement of the head and recording medium. The height of the air gap, called h, is calculated parallel to the surface of the substrate carrying the magnetic circuit.
As soon as track width becomes narrow (less than approximately 10 micrometers), these heads become very difficult to fabricate (problems relating to precision alignment of the two polar parts during glass welding, low efficiency due to magnetic circuit length, difficult coil production, which is an added part and cannot be adapted easily to a package production process etc.)
The abstract of Japanese patent, vol. 13, No. 98 (P-840) (3446) of Mar. 8, 1989, describes a different magnetic head with planar coiling. This head is shown in
FIG. 2
appended hereto. It comprises two polar parts
12
a
,
12
b
separated by an air gap
13
, a twin spiral coil
14
a
,
14
b
placed over the two limbs of the magnetic circuit, two connection pads
15
a
,
15
b
and a magnetic bridge
15
closing the magnetic circuit.
This head still has disadvantages connected firstly with its coil structure which is long and therefore resistant producing thermal noise and, secondly with its magnetic circuit which is relatively long and therefore has reduced efficiency.
EP-A-0,467,263 discloses a head which partly avoids these drawbacks. This type of head can be seen in appended
FIGS. 3 and 4
. They show a nonmagnetic substrate
21
, a first insulating layer
22
, a second insulating layer
29
, a magnetic circuit
30
, a conductor coil
38
of solenoid type wound Ground the magnetic circuit; electric connection strips
33
and connection pads
34
.
FIG. 4
also shows the two front polar parts
25
and
27
separated by an air gap g. Also, an insulating layer
35
covering the entire unit and a protective layer
36
or superstrate complete the unit and make the contact surface symmetrical with the recording medium.
Although satisfactory from certain viewpoints, it this structure has the disadvantage of giving rise to a very large head thickness in the zone lying between substrate
21
and superstrate
36
. Such thickness corresponds to the lower part of coil
33
, polar parts
25
,
27
and insulating layers
22
,
29
,
32
,
35
. This thickness may give rise to friction problems with the recording medium leading to problems of differential wear of the various materials. Moreover, this large thickness gives rise to a considerable risk of delamination or bulging owing to intrinsic constraints in the layers, constraints of thermal origin etc.
Also, the process for manufacturing a head in accordance with
FIGS. 3 and 4
is hardly compatible with package processes, in particular for the production of the azimuth for the air gap using a diamond instrument, or for certain planarization stages of the insulators deposited on large thicknesses of metallic patterns, which leads to problems of step overlay with breaks on the edge of the patterns.
The purpose of the present invention is precisely to remedy such drawbacks.
DISCLOSURE OF THE INVENTION
For this purpose, the invention suggests integrating part of the coil winding into she substrate, namely the lower sheet of conductors. In practice, the lower sheet is placed in a chamber made in the substrate. In this way, the head thickness can be reduced and, correlatively, the problems described above come to be solved.
In precise manner, the purpose of the invention is a vertical magnetic head comprising a solid substrate, a magnetic circuit with at east one first and one second polar part placed side by side and separated by a nonmagnetic air gap, this magnetic circuit comprising at least one non-embedded part in the substrate, a conductor coil surrounding that part of the magnetic circuit which is not embedded in the substrate, this head being characterized in that the conductor coil is formed by a lower sheet of conductors placed in at least one chamber made in the substrate and by an upper sheet of conductors astride the non-embedded part.
According to a first embodiment, the magnetic circuit comprises a rear magnetic closing part and a first and second side magnetic part magnetically connected to the rear magnetic closing part and to the first and second polar parts respectively, the first and second side magnetic parts each forming a non-embedded part of the magnetic circuit, and characterized in that the conductor coil comprises at least one winding coiled around at least the first and/or second side magnetic parts, this winding comprising a lower sheet of conductors passing under the first and/or second side magnetic parts, this lower sheet being integrated into the substrate, and an upper sheet astride the first and/or second side polar parts.
The side magnetic parts are directly connected to the other components of the magnetic circuit (rear closing part and polar parts) or via an insulating layer of controlled thickness (for example SiO
2
or alumina 0.1 to 0.2 &mgr;m thick). The use of an insulating layer is preferable for high frequency operation.
Advantageously, the polar parts are also integrated into the substrate.
Still preferably, the rear magnetic closing part is also integrated into the substrate.
If the substrate is not in insulating material, either because it is conductive or semi-conductive, the integration of the lower sheet of conductors can be achieved by etching said chambers in the substrate, said chambers being filled with insulating material in which the conductors are subsequently fabricated. This is the case in particular for a silicone substrate.
In another embodiment, the magnetic circuit comprises a rear closing part forming the non-embedded part of the circuit, and the conductor coil comprises a winding coiled around this rear closing part, with a lower sheet of conductors passing under the rear closing part
Di Gioia Michel
Gaud Pierre
Sibuet Henri
Commissariat a l'Energie Atomique
Renner Craig A.
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