Method of manufacturing a recording/reading matrix magnetic head

A matrix type magnetic recording/reading head made in integrated fashion, including an electrically non-conductive ceramic substrate having a first main face and a second main face, each provided with connection areas. The two areas of the two faces are interconnected in sets of two by internal connection elements. A layer with high magnetic permeability is deposited on the first face of the substrate. The substrate bears a first series of row conductors and a second series of column conductors intersecting the row conductors, each conductor being connected to a connection area of the first face. Pairs of magnetic poles are located substantially at the intersection of the row conductor and column conductors, the poles of each pair separated by a gap space and being magnetically coupled to the layer with high magnetic permeability in two opposite zones defined by the intersection of a row conductor and a column conductor.

BACKGROUND OF THE INVENTION 
The invention relates to a matrix type magnetic head for recording/reading 
that is applicable especially to the recording/reading of multiple-track 
magnetic tapes. 
The French patent applications 2 630 853 and 2 648 608 describe matrix type 
magnetic heads for recording and reading that can be used to carry out 
high-density recording/reading operations on a recording medium. For 
example, such magnetic heads are capable of recording on up to 1,024 
tracks in parallel on an 8 mm wide magnetic tape. 
These matrix heads can be made by hybrid technologies combining steps of 
sawing, winding, bonding, and thin-layer deposition. Methods of 
manufacture are described for example in the French patent 2 648 940. 
Furthermore, these matrix heads may be obtained entirely by the deposition 
of thin layers, using technologies known as "integrated" technologies. 
With integrated technologies, the conductors are no longer wound wires but 
etched conductor films. A number of patents describe this technology. 
A major constraint of integrated technologies is that the cost of 
manufacture of the heads is nearly proportional to their surface area. A 
major goal therefore is to reduce the surface area of the heads. 
When a thin-layer matrix type reading head is made, two alternatives emerge 
for the connection of this head to its electronic circuitry: 
Front-face connection system: wires are soldered directly to the thin-layer 
conductors. The excess thicknesses by this soldering precludes efficient 
contact between the tape and the head in the vicinity of the soldered 
wires. It then becomes necessary to take these solders to the exterior of 
the tape (on either side). The total height of the head is therefore 
dictated by this constraint. In certain configurations, this amounts to 
the considerable over-sizing of the real head. 
Rear-face connection: to avoid the drawbacks of the front-face connection 
system, it is possible to connect the writing head to the rear face by 
making conductive passages (for example, via holes) in the substrate. 
At present, the formation of holes in silicon substrates on an industrial 
scale has not been mastered. 
The invention provides a solution to this problem. 
SUMMARY OF THE INVENTION 
The invention therefore relates to a matrix type recording/reading head 
comprising: 
an electrically non-conductive ceramic substrate having a first main face 
and a second main face, each provided with connection areas, the two areas 
of the two faces being interconnected in sets of two by internal 
connection elements; 
a layer with high magnetic permeability deposited on the first face of the 
substrate and bearing a first series of row conductors and a second series 
of column conductors intersecting the row conductors, each conductor being 
connected to a connection area of the first face; 
pairs of magnetic poles located substantially at the intersection of a row 
conductor and a column conductor, the poles of a pair being separated by a 
gap space and being magnetically coupled to the layer with high magnetic 
permeability in two opposite zones defined by the intersection of a row 
conductor and a column conductor.

DETAILED DESCRIPTION 
Referring to FIG. 1, we shall first describe an exemplary embodiment of a 
magnetic head according to the invention. 
A substrate wafer SU made of an insulating material is covered on a face 
su2 with a layer MAG of material with high magnetic permeability. This 
layer has a first series of conductors L1, L2 (row conductors) and a 
second series of conductors C1, C2 (column conductors). The row conductors 
are not parallel to the column conductors and are separated from them by a 
layer of insulator IS1. 
According to the example of FIG. 1, the row conductors are parallel to one 
another and the column conductors are parallel to one another. 
If the layer MAG is conductive, an insulating layer IS2 insulates the row 
conductors and column conductors. 
The row conductors and column conductors form points of intersection. At 
each point of intersection there is provided a pair of magnetic poles P1, 
P2. Two poles P1, P2 are separated by a gap E1. The two poles are arranged 
so as to be oriented substantially along a line passing above the point of 
intersection. The two poles are coupled with the layer MAG at two zones 
that are substantially symmetrical with respect to the point of 
intersection. Preferably, the poles P1, P2 are in contact with the layer 
MAG by means of magnetic pads PM1, PM2. The magnetic circuit of an 
elementary magnetic head is thus formed by two poles P1, P2 separated by 
the gap E1, the two pads PM1, PM2 and the layer MAG. The passage of an 
electrical current in one conductor or the other or in both the row 
conductor and the column conductor will therefore induce the circulation 
of magnetic fluxes in the magnetic circuit. Depending on the directions of 
the currents in the two conductors, the fluxes induced will be added 
together or deducted from one another. 
A magnetic medium (not shown) placed in the vicinity of the gap will 
therefore be affected by these fluxes and could record magnetic 
information. 
The entire magnetic head is embedded in a material that is non-magnetic and 
electrically insulating. 
FIG. 1 shows only an elementary head (P1-P2). However, a matrix head may 
have several tens of row conductors and several tens of column conductors 
and have an elementary head at each point of intersection. 
The column conductors and row conductors are connected to connection areas 
such as C01, C02, located on the face su2 of the substrate. In order that 
this connection may be made, the magnetic layer MAG does not cover these 
connection areas or else holes are provided in the layer MAG to access 
these areas. 
The connection areas (C01, C02) are interconnected through the substrate SU 
to connection areas located on the surface su1 of the substrate. The 
substrate SU then has the form shown in FIGS. 2a and 2b. 
FIG. 2a shows the face su2 of the substrate. In the zone TM, there is shown 
the array of row conductors and column conductors on which the set of 
magnetic heads is made. Each row conductor and column conductor is 
connected to a connection area such a C01, C02. The contacts M1, M2 are 
the ground connections respectively common to the row conductors and to 
the column conductors. 
FIG. 2b shows the substrate seen from the face su1 side. A wafer of printed 
circuits CI is connected to this face. To the connection areas of the face 
su1 there correspond connection areas (e.g., CO'1 and CO') connected by 
internal connections to the connection areas of the face su2. 
Since the arrangements of the connection areas on the two faces of the 
substrate are not the same, it is necessary to plan for the distribution 
of the connections within the substrate. 
FIGS. 3a to 3g show the various connection within a substrate. 
FIG. 3a shows the substrate in a sectional view and brings out the fact 
that the substrate is a stack of layers. Each layer is crossed by as many 
connection elements as there are connection areas on a face. To reorganize 
the arrangement of the connection areas of a face with respect to the 
arrangement of the connection areas of the other face, internal conductors 
such as ci1 are provided between the different layers to enable the 
connection areas to be shifted. 
FIGS. 3b to 3g respectively show the face su2 of the substrate, the 
interfaces of the different layers 2-8 of the substrate, and the face su1. 
According to a preferred embodiment of the invention, the substrate is made 
of aluminium oxide. Each layer has a thickness of about 0.25 mm, which 
results in a substrate with a thickness of several millimeters (2 mm for 
example). 
The manufacturing method comprises a first stage of making the substrate by 
stacking different layers of aluminium oxide and making, at each stacking 
step, connection elements going through each layer and conductors (ci1) 
enabling the connection areas to be shifted. When the substrate has been 
made with connection areas C0'1, C0'2 on its face su1 and connection areas 
CO1, CO2 on its face su2, then all of the magnetic heads are made on the 
face su2. 
This set of magnetic heads is implemented as follows: 
polishing the substrate (face su2); 
making a base out of magnetic material such as sendust, permalloy, or any 
other alloy known for its high permeability (layer MAG); 
etching the base to bring out the connection areas C01, C02; 
providing electrical insulation (for example, SiO2 or polyimide) (layer 
IS2); 
depositing and etching of a line of row conductors (L1, L2) (for example, 
aluminum or gold or copper); 
insulating the row conductors with SiO2 or polyimide (layer IS1); 
depositing and etching a line of column conductors (C1, C2); 
insulating the column conductors (layer IS1); 
planarization; 
etching the insulating layers (IS1, IS2) up to the magnetic layer MAG; 
filling the holes with a magnetic material with high magnetic permeability; 
planarization; 
making the poles (P1, P2) and gap (E1). These poles are made, for example, 
according to the technique described in the French patent No. 2 605 783. 
The design of the conductors must take account of the constraints dictated 
by the construction of the magnetic head: for example, there must be a 
limited pitch between conductors (80 .mu.m for example). 
This layout also takes account of the constraints dictated by making the 
substrate, namely, typically there must be a pitch of 250 .mu.m between 
the connection elements going through the substrate (with a diameter of 
100 .mu.m). 
According to one embodiment, the substrate SU is made of a material with 
high magnetic permeability, for example ferrite. Therefore, there is no 
reason to plan for the layer MAG with high magnetic permeability. 
The invention has the advantage of giving a compact, integrated rigid 
matrix-type magnetic head that has dependable electrical connections and 
costs relatively little.