SOLENOIDAL THIN FILM READ/WRITE HEAD FOR COMPUTER MASS STORAGE DEVICE AND METHOD OF MAKING SAME

Abstract: A new read/write head for use in a mass storage device in a digital data processing sys­ tem. The head is a thin-film head (10) having a solenoidal coil around one or both of the pole pieces. Sets of planar conductive traces (14, 16, 18, 20, 22, 24) are formed on planar layers of insulating material (36, 38, 40, 42, 46) on opposing sides of a pole piece (12), with vias (48, 50, 52, 54, 56) connecting the ends of selected traces to thereby form a solenoidal coil around the pole piece.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to the field of read/write heads for use in mass storage devices for digital data processing systems, and more particularly to such heads manufactured by thin film techniques. The invention provides a new thin film head which incorporates a solenoidal energizing coil, and a method of fabricating the new head. 2. Description of the Prior Art A typical modern digital data processing system comprises a hierarchy of memory devices, including a semiconductor main memory of relatively small capacity, and one or more mass storage devices, which have much greater capacity than the main memory, but which are also relatively much slower. The mass storage devices provide a back-up store for data which is in the main memory, and also for the voluminous amounts of data which will not fit into main memory but which can be called upon by the processor when it is needed. A processor typically only obtains information directly from the main memory, and so, when it needs information which is only in a mass storage device, it enables the mass storage device to copy the information to the main memory. Some time later, after it has processed the information, the processor enables the processed information to be stored in the mass storage device. This frees up storage in the main memory so that other information may be stored there. Typical mass strorage devices store information on magnetic disks, the information being recorded in the form of transitions in magnetic flux in the magnetic media generated by a read/write head. The information is organized into a plurality of tracks, each a selected radial distance from the center of the disk, and each track is divided into a plurality of sectors, with each sector subtending a predetermined angular portion of the disk. The read/write head is suspended from an arm, which is moved generally radially over the disk surface in a "sleek" operation to bring the read/write head into registration with a selected disk track. The disk is rotated in a "search" operation to bring the sector containing the desired information into angular registration with the read/write head, which reads the information contained in the sector, or writes information on the magnetic medium in the sector. Originally, read/write heads were generally toroidal in shape with a cut or gap, with the ends of the toroid at the gap being poles pieces. A wire coil was wound around the toroid and is energized to generate magnetic flux. The flux diverges between the pole pieces and impinges on the magnetic material of the disk. The density with which data may be written is directly related to the number of flux transitions, or changes in flux direction, which the heads may provide per unit of time. Since these heads have a relatively high electrical inductance to achieve a satisfactory rate of flux transitions, expensive driving circuitry is required. Furthermore, the high inductance results in increased "ringing," in which a signal, at a sharp transition, tends to fluctuate about the desired signal level. Too much ringing leads to uncertainty in the signal level for too long a time, which requires slowing down the system. More recently, thin film read/write heads have been developed which have much lower inductance than conventional read/write heads. Thin film read/write heads are fabricated by means of lithographic techniques that are generally similar to the techniques that are used in making integrated circuit chips. In such techniques, a planar pole piece is first formed and covered with an insulating material. A coil is then formed on the insulating material in the shape of a planar spiral over part of the pole piece, an insulating material is deposited over the spiral, and another pole piece is formed on top of the insulating material. However, because the coil, of a typical thin film read/write head has a planar spiral shape, a relatively long conductor is required to provide the number of turns in the coil that is required to generate the desired magnetic field during the write operation, or to intercept the magnetic field sensed by the head during a read operation. Since, in a planar spiral, the length of the conductor increases faster than the number of turns, the long sprial conductor results is a relatively large resistance, which, in turn, results in generation of a significant amount of heat. The increase in the resistance of the coil also results in a concomitant increase in the noise of the signal during the reading operation. Furthermore, when the coil has a spiral shape, the mutual inductance between turns also increases faster than the number of turns, and so a planar coil having a sufficient number of turns also has a relatively high inductance. The high inductance results in a relatively low effective resonant frequency, which, in turn, increases the amount of undesirable ringing that can occur in a signal applied to the coil. In addition, since the coil has a relatively high inductance, a high driving voltage is required during a write operation to provide the necessary write current. US Patent No. 3,662,119, entitled Thin Film Magnetic Transducer Head, issued May 9, 1972, to L. Romankiw, et al., discloses a thin film head having a solenoid coil formed around both pole pieces in the head to provide both a supply and a return path for electrical current which energizes the coil. The coil is formed in one layer around each pole piece using a complex fabrication method. Since coil layers are required around both pole pieces, the coil is not suitable for use in connection with vertical recording techniques now being developed, in which data is recorded vertically rather than horizontally on a disk surface. Attention is hereby directed toward two further prior art documents. JP-A-5545192 discloses a head according to the preamble of claim 1. GB-A-1216905 discloses a method for the manufacture of ferro-magnetically cored film type inductors using thick- or thin-film techniques This patent discloses the provision of a second coil an addition to a first coil on a different part of a magnetic core. SUMMARY OF THE INVENTION The invention provides a new and improved thin film read/write head for a disk storage unit in a digital data processing system, in which the energizing coil is in the form of a solenoid around at least one of the pole pieces, and a method of fabricating the head. The present invention provides a head according to claim 1 and a method of manufacturing it according to claim 12. BRIEF DESCRIPTION OF THE DRAWINGS This invention is pointed out with particularity in the appended claims. The above and further advantages of this invetion may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: Fig. 1A is a view representing a schematic layout of the various traces and the pole piece forming part of a read/write head constructed in accordance with this invention; Fig. 1B is a table that is useful in understanding Fig. 1A; and Fig. 1C is a schematic side sectional view, taken along axis 1C-1C, of the portion of the head illustrated schematically in Fig. 1A. DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT With reference to the Figures, a new read/write head 10 constructed in accordance with the invention includes a pole piece 12 and a plurality of traces of conductive material formed on layers of insulating material such as hard baked photoresist, silicon dioxide (SiO₂) and alumina (Al₂O₃). The traces are formed at predetermined angles with respect to a longitudinal axis 13 of the pole piece 12 and interconnected by conductive material deposited in vias in the conductive material as described below. The configuration of the conductive traces, that is, their placement and orientation relative to each other and to the pole piece 12, and of the vias, is selected so that they form a solenoidal coil around the pole piece. The head 10 includes four layers of conductive traces formed on planar layers of insulating material, with two layers being disposed under the pole piece 12 and two layers being disposed above pole piece 12. In particular, two of the layers of traces comprise a lower, or first, trace layer including three traces 14, 16 and 18 and an upper, or fourth, trace layer also including three traces 20, 22 and 24. As shown in Fig. 1B, the traces 14, 16, and 18 are all depicted in Fig. 1A by means of solid lines, with each pair of solid lines representing one trace. Similarly, the traces 20, 22 and 24 are all depicted in Fig. 1A by means of dashed lines with each pair of dashed lines representing one trace. The other two layers of traces include a second trace layer, comprising three traces 26, 28 and 30 situated between the first trace layer and the pole piece 12, and a third trace layer comprising two traces 32 and 34 situated between the fourth (upper) trace layer and the pole piece 12. As shown in Fig. 1B, the traces 26, 28 and 30 are all depicted in Fig. 1A by a dashed line having alternating long and short dashes, and traces 32 and 34 are depicted in Fig. 1A by a dashed line having alternating one long and two short dashes. As shown in Fig. 1C, the pole piece 12 and all of the traces are formed on and embedded in layers of insulating material. Six layers of insulating material are depicted in Fig. 1C, namely, layers 36, 38, 40, 42, 44 and 46. As explained below in greater detail, after insulating layer 36 and traces 14, 16 and 18 are formed, the sequential insulating layers 38, 40, 42, and 44 are deposited and the respective traces or pole piece 12 are formed thereon. The ends of the traces of the various trace layers are connected together appropriately, as described below, to form a solenoidal coil. In particular, ends of selected pairs of traces overly each other, and the overlying ends are connected together through the vias. After the upper trace layer, that is, traces 20, 22 and 24, has been formed, and all of the connections through the vias have been formed, an insulating layer 46 is applied thereto to cover the traces. Thereafter, a second pole piece (not shown) may be formed on the head 10 as appropriate. As has been mentioned, the traces are interconnected by appropriate vias which are formed through the insulating layers between the ends of the traces. These interconnections are such as to form a continuous circuit, with the traces and vias cooperating to effectively form a coiled electrical path around pole piece 12 from the upper end (as shown in Fig. 1) to the tip 74. One such via, namely via 48, connects the right end (as shown in Fig. 1A) of trace 14 in the lower trace layer, to the right end of trace 24 in the upper trace layer. Similarly, vias 50 and 52 interconnect the respective rights ends of the other traces 16 and 22, and 18 and 20, in the lower and upper trace layers. Similar vias 54 and 56 interconnect the left ends of respective pairs of traces 18 and 22, and 16 and 24, between the first (lowest) and fourth (uppermost) trace layers. The result is a solenoid coil around pole piece 12 which extends from the leftmost end of trace 14 near the top of pole piece 12 (as shown in Fig. 1A) to the leftmost end of trace 20 near the bottom of pole piece 12. The second and third trace layers are similarly interconnected by vias 58 (right end of traces 34 and 28), 60 (right end of traces 32 and 26), 62 (left end of traces 30 and 34), and 64 (left end of traces 28 and 32). This forms a solenoid coil around pole piece 12 which extends from the rightmost end of trace 30 near the top of pole piece 12 (as shown in Fig. 1A) to the leftmost end of trace 26 near the bottom of pole piece 12. The solenoid coil formed from the second and third trace layers is generally interior of the solenoid coil formed from the first and fourth trace layers. The two solenoid coils are connected together by a via 66 which conncects the leftmost end of trace 20, in the upper layer of traces, to the leftmost end of trace 26 in the second layer of traces. The result is a single solenoid coil having both a supply path and a return path for energizing current, with both paths being formed around a single pole piece 12. It is apparent that the new head does not require a coil to be formed around the other pole piece to provide a return current path, and so the new head may be particularly useful in conncection with vertical recording methods. However, it is also apparent that another coil may be formed around the second pole piece (not shown) if vertical recording is not to be used. Returning to Fig. 1A, the leftmost end of trace 14, and the rightmost end of trace 30 are connected, through vias 74 and 76, to bonding pads 70 and 72, respectively, which may be located on, for example, the uppermost (rightmost, as shown in Fig. 1C) surface of insulating layer 46. Conventional read/write signal generating and sensing circuitry (not shown) which generates writing current, or senses reading current generated in the head, is connected to the bonding pads in a known manner. The bonding pads may be located in any convenient location, but it is desirable that they be formed close to the ends of the traces to which they connect to minimize the resistance of the path between the line from the read/write signal generating and sensing circuitry. The method of fabricating the new read/write head is as follows. Initially, the first insulating layer 36 is formed as a base for traces 14, 16 and 18, and the traces are formed thereon using any conventional lithographic and metal deposition technique. Then, the second insulating layer 38 is formed, using a conventional technique, and the upper surface (the surface to the right as shown in Fig. 1C) may be smoothed. The upper surface of layer 38 forms the base for traces 26, 28 and 30, which are then formed. The third insulating layer 40 is then formed, and the pole piece 12 is formed. The pole piece may be formed using similar lithographic techniques, although the pole piece may be somewhat thicker than the traces. After the pole piece is formed, the fourth insulating layer 42 is formed and vias are formed to the second layers of traces. A metal layer is then deposited to form the third layer of traces which also services to fill the vias with conductive material and thereby form the inner solenoid coil. At the same time, vias, which, as described below, will be used later to interconnect the first layer of traces and a fourth layer of traces may be formed and filled with conductive material. The microlithographic technique using laser for fabrication of electronic components and the like, may be used to form the vias. After the third layer of traces have been formed and the interconnections have been formed through the vias bewteen the second and third layers of traces, the fifth layer of insulating material, layer 44, is formed, and the vias formed to the first layer of traces. A metal layer is then deposited to form the fourth layer of traces, that is traces 20, 22 and 24 which also serves to fill the vias conductive material to provide the outer solenoid coil. Thereafter, the top insulating layer 46 is deposited. The connections between the respective ends of traces 14 and 30 and the bonding pads 70 and 72 may be formed using the same method described above of interconnecting the ends of the respective traces. This may be done at any convenient point in the process. As has been noted above, a head including a pole piece and conductors as described above constructed in accordance with the invention is useful in disk drives incorporating either horizontal and vertical recording techniques. This is a result of the fact that the solenoid coil formed around one pole piece, including both the interior and the exterior coil layers, provides both a supply path and a return path for the energizing current. Thus, the head does not require a second coil around the other pole piece to provide a return current path. Furthermore, the new method of making the head simplifies fabrication of the head. It will be appreciated that a read/write head typically includes two pole pieces. In a head which is used in vertical recording, typically only one pole piece will be surrounded by a coil. However, if a head is to be used in longitudinal recording, one or both pole pieces may be surrounded by coils.

Claims: A head (10) for a magnetic storage device comprising a pole piece (12) disposed along a longitudinal axis (13) and having a distal end (74) adapted to be disposed adjacent to a storage medium of the magnetic storage device, and a plurality of electrically insulating layers (40,42) having generally planar opposing surfaces, said pole piece being disposed therebetween, a plurality of electrically conductive traces (14,16,18,20,22,24) separated from said pole piece (12) by said pair of insulating layers (40,42) and selectively interconnected by vias (48,50,52,54,56) through said insulating layers to form a solenoid around said pole piece, characterised in that said solenoid having a pair of ends (70,72) disposed adjacent to a proximal end of said pole piece (12) and being continuous between said ends to provide a generally helical path for the flow of energising current around said pole piece, a first portion (14,24,16,22,18) of said generally helical path extending from said proximal end to a region of said distal end of said pole piece, and a second portion (20,26,32,28,34,30) of said generally helical path returning from said region of said distal end to said proximal end of said pole piece (12) whereby the second portion serves to increase the flux linkage between said solenoid and said pole piece (12) relative to that provided by the first portion to increase the sensitivity of the head 10. The head of claim 1 wherein said pair of ends (70,72) are adapted to be connected to a signal source for supplying the energising current to and returning the energising current from said solenoid. The head of claim 2 wherein said plurality of traces (14-34) are disposed at skewed directions with respect to the longitudinal axis on opposing surfaces of said pair of insulating layers. The head of claim 1 wherein said plurality of electrically conductive traces includes: a first set of electrically conductive traces (14,16,18,26,28,30) disposed at an angle with respect to said longitudinal axis and separated from said pole piece by one of said insulating layers, and a second set of electrically conductive traces (20,22,24,32,34) disposed at an angle with respect to said longitudinal axis and separated from said pole piece by the other one of said insulating layers, wherein traces of said first and second sets of traces are selectively interconnected through said pair of insulating layers to form said solenoid. The magnetic head of claim 4 wherein said first set of traces comprises a first plurality of generally planar traces (14,16,18) disposed on a surface of said one of said insulating layers, said second set of traces comprises a second plurality of generally planar traces (20,22,24) disposed on a surface of said other one of said insulating layers, and said other one of said insulating layers and said first plurality of traces and said second plurality of traces being selectively interconnected by vias (48,54,50,56,52) disposed through said pair of insulating layers (40,42) to form said solenoid. The head of claim 1 wherein said electrically conductive traces are selectively interconnected to form a pair of solenoids, each one of which is electrically insulated from and disposed around said pole piece, each one of said pair of solenoids extending from said proximal end to said distal end region, said solenoids being serially coupled together in said distal end region to provide a path for the round trip flow of said energising current from said proximal end to said distal end region, and back to said proximal end, all around said pole piece. The head of claim 6 wherein: A. said first set of traces includes: i. a first plurality of generally parallel electrically conductive traces (14,16,18) disposed on an insulating substrate (36) in a first direction skewed with respect to the axis; ii. a third layer of insulating material (38) disposed over said first plurality of traces; and iii. a second plurality of generally parallel electrically conductive traces (26,28,30) disposed on said third insulating layer (38) in a second direction skewed with respect to said axis, the second direction being different from said first direction, the traces of the second plurality of traces (26,28,30) having a length that is generally shorter than the lengths of the traces of the first plurality of traces (14,16,18); and B. said second set of traces includes: i. a third plurality of generally parallel electrically conductive traces (32,34) disposed on said second one of the pair of insulating layers (42) in a direction skewed with respect to the axis and generally parallel to the first direction, the traces of the third plurality of traces (32,34) having a length similar to the length of the traces of the second plurality of traces (26,28,30); ii. a fourth layer of insulating material (44) disposed over said third plurality of traces (30,32); and iii. a fourth plurality of generally parallel electrically conductive traces (20,22,24) disposed on said fourth insulating layer (44) in a direction skewed with respect to the axis and generally parallel to the second direction, the traces of the fourth plurality of traces (20,22,24) having a length similar to the length of the traces of the first plurality of traces (14,16,18). The head of claim 7 wherein an end of at least one of the traces of the third plurality of traces (32,34) overlays an end of a trace of the second plurality of traces (26,28,30), an end of at least one of the traces of the fourth plurality of traces (20,22,24) overlays an end of a trace of the first plurality of traces (14,16,18), an end of a trace (20) of the fourth plurality of traces (20,22,24) overlays an end of a trace (26) of the second plurality of traces (26,28,30), and each overlaying end being electrically coupled to a respective underlaying end thereby to form said pair of solenoids, a first one of the pair of solenoids comprising the traces of the first and fourth plurality of traces (14-24) and a second one of the pair of solenoids comprising the traces of the second and third plurality of traces (26-34), with the second solenoid being generally interior of the first solenoid and the first and second coils being electrically coupled together to provide both said supply path and said return path for the energising current. The head of claims 1,4 or 6 further comprising a second pole piece disposed adjacent to said at least one pole piece (12) and insulated from said traces. The head of claim 9 wherein a proximal end of said at least one pole piece is electrically coupled to a proximal end of said second pole piece. The head of claim 10 wherein a distal end of said at least one pole piece is spaced closely to a distal end of said second pole piece relative to a spacing between said proximal end of said at least one pole piece and said proximal end of said second pole piece. A method of fabricating a head (10) for use in a magnetic storage device, the head being of the kind that includes: a pole piece (12) supported by a substrate (36), disposed along a longitudinal axis (13), and having a distal end (74) adapted to be disposed adjacent to a storage medium of the magnetic storage device; and first and second electrically insulating layers (40,42) having generally planar opposing surfaces, said pole piece being disposed therebetween, characterised in that said method includes the steps of: depositing a first set of electrically conductive traces (14,16,18,26,28,30) at an angle with respect to said axis (13) so that said first set of traces is disposed between said substrate (36) and said first insulating layer (40), depositing a second set of electrically conductive traces (20,22,24,32,34) over said second insulating layer (42) at an angle with respect to said axis, and selectively interconnecting traces of said first and second sets of traces through said insulating layers by means of vias (48,54,50,56,52,66,60,64,58,62) to form a pair of serially coupled solenoids that are each electrically insulated from and disposed around said pole piece (12), each of said solenoids extending from said proximal end of said pole piece to a region of a distal end (74) of said pole piece, said solenoids being serially coupled together in said region of said distal end to provide a generally helical path for the round trip flow of energising current from said proximal end to said region of said distal end (74), and back to said proximal end, all around said pole piece (12) whereby the connection of the solenoids serves to increase the flux linkage between said pole piece and said solenoids relative to that provided by one of said solenoids to increase the sensitivity of the head 10. The method of claim 12 wherein said vias (48-66) are produced using laser radiation. The method of claim 13 wherein: A. The step of depositing the first set of traces (14,16,18,26,28,30) comprises i. depositing a first plurality of generally parallel electrically conductive traces (14,16,18) on said substrate (36) in a first direction skewed with respect to the longitudinal axis (13), ii. depositing a third layer (38) of insulating material over said first plurality of traces (14,16,18), and iii. depositing a second plurality of generally parallel electrically conductive traces (26,28,30) on said third insulating layer (38) in a second, different direction skewed with respect to the longitudinal axis (13); B. the step of depositing the second set of traces (20,22,24,32,34) comprises i. depositing a third plurality of generally parallel electrically conductive traces (32,34) on said second insulating layer (42) in the first direction, and aligning ends of the traces of the third plurality of traces (22,34) with ends of the traces of the second plurality of traces (26,28,30). ii. depositing a fourth layer of insulating material (44) over the third plurality of traces (32,34), and iii. depositing a fourth plurality of generally parallel electrically conductive traces (20,22,24) over the fourth insulating layer (44) in the second direction, aligning ends of the traces of the fourth plurality of traces (20,22,24) with ends of the traces of the first plurality of traces (14,16,18), and aligning an end of a trace (20) of the fourth plurality of traces (20,22,24) with an end of a trace (26) of the second plurality of traces (26,28,30); and C. the interconnecting step comprises interconnecting the respective aligned ends (48-66) of the traces, thereby to form said pair of serially coupled solenoidal coils disposed around the pole piece (12), a first one of said coils comprising traces of the first and fourth plurality of traces and a second one of said coils comprising traces of the second and third plurality of traces. The method of claim 12 wherein said first set of traces (14,16,18,26,28,30) collectively comprise a first trace portion and said second set of traces (20,22,24,32,34) collectively comprise a second trace portion, said step of interconnecting further including producing vias between ends of said. traces of said first trace portion and ends of said traces of said second trace portion. The method of claim 15 wherein said first and second trace portions each includes a plurality of traces, said second trace portion being deposited so that an end of at least one of said traces of said second trace portion overlays an end of a trace of said first trace portion. The method of claim 15 wherein: A. the step of depositing the first trace portion includes the steps of: i. depositing a first plurality of generally parallel electrically-conductive traces (14,16,18) on said substrate in a first direction skewed with respect to the axis; ii. depositing a third layer of insulating material (38) over said first plurality of traces (14,16,18); and iii. depositing a second plurality of generally parallel electrically conductive traces (26,28,30) on said third insulating layer (38) in a second direction skewed with respect to said axis, the second direction being different from said first direction, the traces of the second plurality of traces (26,28,30) having a length that is generally shorter than the lengths of the traces of the first plurality of traces (14,16,18); and B. said step of depositing the second trace portion (20,22,24,32,34) includes the steps of: i. depositing a third plurality of generally parallel electrically-conductive traces (32,34) on said second insulating layer (42) in a direction skewed with respect to the axis and generally parallel to the first direction, the traces of the third plurality of traces (32,34) having a length similar to the length of the traces of the second plurality of traces (26,28,30); ii. depositing a fourth layer of insulating material (44) over said third plurality of traces (32,34); and iii. depositing a fourth plurality of generally parallel electrically conductive traces (20,22,24) on said fourth insulating layer (44) in a direction skewed with respect to the axis and generally parallel to the second direction, the traces of the fourth plurality of traces (20,22,24) having a length similar to the length of the traces of the first plurality of traces (14,16,18). The method of claim 17 wherein an end of at least one of the traces of the third plurality of traces (32,34) overlays an end of a trace of the second plurality of traces (26,28,30), and an end of at least one of the traces of the fourth plurality of traces (20,22,24) overlays an end of a trace of the first plurality of traces (14,16,18), and further that an end of at least one of the traces (20) of the fourth plurality of traces (20,22,24) overlays an end of a trace (26) of the second plurality of traces (26,28,30), the interconnecting step comprising electrically coupling each overlaying end to a respective underlaying end thereby to form said pair of solenoidal coils, a first coil comprising the traces from the first and fourth plurality of traces (14-24) and the second coil comprising the traces from the second and third plurality of traces (26-32), the first and second coils being serially coupled together in said region of said distal end to provide a path for the round trip flow of energising current from said proximal end to said distal end region, and back to said proximal end, all around said pole piece. The method of claim 15 wherein said vias (48-62) are produced using laser radiation, the first and second trace portions (14-34) being reflective and the first and second insulating layers (40,42) being non-reflective at the wavelengths of the laser radiation, the step of producing said vias comprising A. placing a reflective mask over the locations where the vias (48-62) are to be formed, the mask defining apertures at the locations where the vias are to be formed over the trace portion, B. illuminating the mask with the laser radiation to remove insulating material exposed by said apertures to expose selected points of said trace portion, such that when the insulating material exposed by the apertures is removed sufficiently to expose the trace portion, the trace portion stops the laser radiation, thereby to form recesses; and C. depositing conductive material in the recesses. The method of claim 12 wherein said first set of traces (14,16,18) are deposited to be disposed in a first skewed direction with respect to said axis and said second set of traces (20,22,24) are deposited in a second, different skewed direction with respect to said axis so that ends of traces of said second set overlay ends of traces of said first set, and further comprising the steps of: depositing a third electrically insulating layer (38) over said first set of traces, and depositing a third set of electrically conductive traces (26,28,30) in said second skewed direction between said third insulating layer (38) and said pole piece (12), said third set of traces being deposited so that an end of one of the traces (26) of said third set (26,28,30) is overlaid by an end of one of the traces of said second set (20), depositing a fourth electrically insulating layer (44) over said pole piece, and depositing a fourth set of electrically conductive traces (32,34) in said first skewed direction between said fourth insulating layer (44) and said second insulating layer (42), said fourth set of traces being deposited so that ends of traces of said fourth set overlay ends of traces of said third set (26,28,30), and applying laser radiation to produce vias (48-66) between the respective overlaying ends of said traces and electrically coupling said respective overlaying ends to form said pair of solenoids, one of said solenoids comprising the traces of said first and second sets of traces and the other one of said solenoids comprising the traces of said third and fourth sets of traces. The method of claims 12,15 or 20 further comprising disposing a second pole piece adjacent to said at least one pole piece (12) and insulated from said traces. The method of claim 21 further comprising electrically coupling a proximal end of said at least one pole piece to a proximal end of said second pole piece. The method of claim 21 further comprising spacing a distal end of said at least one pole piece close to a distal end of said second pole piece relative to a spacing between said proximal end of said at least one pole piece and said proximal end of said second pole piece.

Inventors: DAS, SHYAM, C.
Applicants: DIGITAL EQUIPMENT CORPORATION
Application year: 1988
Main classification: G11B5
IPC codes: G11B5