WO2011001323A1

WO2011001323A1 - Fibers including electronic elements

Info

Publication number: WO2011001323A1
Application number: PCT/IB2010/052793
Authority: WO
Inventors: Frank Anton Van Abeelen; Peter Douglas Fairley; Steffen Reymann; Ian French; Nigel David Young
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-06-29
Filing date: 2010-06-21
Publication date: 2011-01-06

Abstract

A fiber suitable for incorporation into a woven, knitted, braided or crocheted fabric or a fiberglass laminate structure is disclosed. The fiber comprising an elongate substrate arrangement having a length direction parallel to the axis of the fiber, the elongate substrate arrangement including a substrate formed of a plastics material and thin film electronic elements arranged over the substrate. The fiber also comprises a cladding layer formed of a plastics material and encapsulating the substrate arrangement. The substrate and the electronic elements are surrounded by the cladding layer along at least a portion of the length of the substrate arrangement, the cladding layer defining a rounded outer cross sectional shape. The substrate may be twisted about the fiber axis, in which case the fiber cross-section may be round. The cladding layer may be electrically conductive in discrete regions corresponding to positions of contact pads along the length of the substrate arrangement.

Description

Fibers including electronic elements

FIELD OF THE INVENTION

This invention relates to fibers which include electronic elements within their structure, and particularly such fibers for incorporation into a woven, knitted, braided or crocheted fabric or for incorporation into a fiber reinforced composite structure, such as a fiberglass laminate structure. A fabric constructed in this way may be conformable and therefore suitable for incorporation into clothing. A fiber reinforced composite structure, in particular one that is shaped, may benefit from the conformability of the fibers.

The invention also relates to a method of manufacturing fibers which include electronic elements within their structure.

BACKGROUND OF THE INVENTION

There is increasing interest in electronic devices which can be integrated into fabrics, particularly woven, knitted, braided or crocheted fabrics. Such devices, for example display devices, can then be integrated into various items of clothing or upholstery. There are a variety of uses for electronic devices integrated into items of clothing, including healthcare- related functions such as the sensing of body functions.

Known techniques for integrating electronic devices into fabrics generally either involve directly attaching the devices to the surface of the fabric or sandwiching the devices between layers of fabric to form a laminate structure. In either case, the level of integration of the electronic device into the fabric is somewhat limited. The resulting fabrics tend to be relatively stiff and unconformable, even when the electronic devices are inherently flexible. This can lead to discomfort when the devices are integrated into items of clothing.

It has also been proposed to incorporate electronic devices into woven or knitted fabrics by replacing some of the ordinary textile fibers with elongate substrates carrying thin film electronic elements. To provide a degree of mechanical flexibility, the elongate substrates are formed of a plastics material and manufactured using a so-called EPLaR (electronics on plastic by laser release) process.

According to the EPLaR process, a plastics material such as polyimide is spin coated onto a rigid carrier to define a plastic substrate. Thin film electronic circuitry and a cover layer are then formed over the plastic substrate before the rigid carrier is released by directing an ultraviolet laser at the rear surface of the plastic substrate. To form elongate substrates suitable for incorporation in a woven or knitted fabric, the plastic substrate is cut into narrow strips before the rigid carrier is released.

Textile fibers used for woven or knitted fabrics typically have a diameter of

200μm or less. By comparison, it has been found that elongate substrates having widths as low as 50μm or less may provide sufficient space for forming power lines, data lines and active electronic elements.

Fig. 1 is a cross sectional view showing an elongate substrate 1 manufactured by the EPLaR process described above. The elongate substrate 1 is provided with thin film electronic circuitry 3 and a cover layer 5 is formed over the circuitry 3 for support purposes. Fig. 2 is a plan view of a woven fabric 7 in which elongate substrates 1 manufactured by the EPLaR process has been substituted for a number of the ordinary textile fibers.

A problem associated with incorporating electronics devices into woven fabrics in this way is that the elongate substrates cannot be processed using standard textile manufacturing equipment. In particular, it has been found that the elongate substrates are easily damaged as they pass through the equipment, for example by cracking or delamination of the layers. Furthermore, it has been found that the sharp longitudinal edges of the elongate substrates tend to abrade adjacent textile fibers, leading to damage of the fabric.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a fiber for incorporation into a fabric, the fiber comprising (i) an elongate substrate arrangement having a length direction parallel to the axis of the fiber, the elongate substrate arrangement including a substrate formed of a plastics material and thin film electronic elements arranged over the substrate, and (ii) a cladding layer formed of a plastics material and encapsulating the substrate arrangement, wherein the substrate and the electronic elements are surrounded by the cladding layer along at least a portion of the length of the substrate arrangement, the cladding layer defining a rounded outer cross sectional shape.

By providing a cladding layer, the elongate substrate arrangement may be protected from damage during processing. Furthermore, the rounded shape of the cladding layer may reduce friction within the processing equipment and minimize damage to adjacent textile fibers. The meaning of the expression "rounded shape" will be clear to those skilled in the art, essentially referring to the absence of sharp corners (vertices). In embodiments, the outer cross sectional shape of the cladding layer may define a minimum radius of curvature of at least 5 μm, preferably at least 10 μm, and more preferably at least 20 μm.

The elongate substrate arrangement and/or the cladding layer may have a degree of inherent mechanical flexibility. The substrate, for example, may be formed of polyimide (PI) and the cladding layer may, for example, be formed of a polyester such as polyethylene terephthalate (PET) or poly trimethylene terephthalate (PTT).

The thin film electronic elements may comprise passive electronic elements, such as wiring, or active electronic elements, such as semiconductor-based sensors and display devices.

In a first group of embodiments, a width of the substrate arrangement may exceed a thickness of the substrate arrangement, and the cladding layer surrounding the substrate arrangement may define an outer cross-sectional shape which is non-circular. For example, the substrate arrangement may have a substantially oblong cross section and the cladding layer may have a substantially oval cross section. A fiber having this configuration may be suitable for incorporation in woven fabrics, since the fiber may align itself with the plane of the fabric such that the regular undulations in the fiber are accommodated in the thickness direction of the substrate arrangement.

In a second group of embodiments, the substrate arrangement may have any cross sectional shape and be twisted about the axis of the fiber, for example to form a helix. In this case, the cladding layer surrounding the substrate arrangement may define an outer cross sectional shape which is circular. A fiber having this configuration has the same mechanical flexibility in all bending directions (i.e. isotropic flexibility), and may therefore be suitable for incorporation in knitted, braided or crocheted fabrics.

In either case, the substrate arrangement may have a width of no more that 1 mm, preferably no more than 0.5 mm. The substrate arrangement may have a thickness of no more than 150 μm, preferably no more than 100 μm. As well as the substrate and thin film electronic elements, the substrate arrangement may further comprise a support layer arranged over the electronic elements.

In embodiments, the substrate arrangement may further comprise contact pads electrically connected to the electronic elements, the contact pads being spaced along the length of the substrate arrangement. In this case, the cladding layer may be formed to be electrically conductive in discrete regions corresponding to the positions of the contact pads. The discrete regions are each in contact with a respective contact pad, thereby enabling external circuit elements to be electrically connected to the electronic elements within the fiber.

The electrically conductive discrete regions of the cladding layer may be rendered electrically conductive by the presence of conductive particles, such as silver or carbon black particles. A number of other techniques may also be employed for providing the discrete regions and/or for minimizing the resistance of the connection between external circuit elements and the electronic elements within the fiber.

For example, the substrate arrangement may include discrete lateral extensions at the positions of the contact pads, the lateral extensions being folded along a line parallel to the length direction of the substrate arrangement. In this way, contact pads having a greater surface area may be provided, and portions of the contact pads may be brought closer to the external surface of the fiber.

Part or all of each electrically conductive discrete region of the cladding layer may be formed of an electrically conductive layer formed over each of the contact pads, the conductive layer extending through the cladding layer. Such a conductive layer may comprise a conventional conductive filler material in the form of a conductive plug. The conductive layer may be exposed at the surface of the fiber.

Another technique for reducing the resistance of the connection between external circuit elements and the electronic elements within the fiber is to form a plated metallic layer, such as a copper layer, over the fiber at locations corresponding to the discrete regions of the cladding layer.

In a specific embodiment of the invention, the thin film electronic elements comprise a solar cell. In this case, the substrate arrangement may further comprise metallic tracks arranged over a surface of the substrate opposite to the surface over which the solar cell is arranged. These metallic tracks may be connected to the solar cell through holes in the substrate and provide a low resistance conductive path over which current from the solar cell can be drawn. Such a configuration mitigates some of the problems associated with the very large aspect ratio of the solar cell surface.

According to another aspect of the invention, there is provided a woven fabric comprising (i) first fibers extending in a first direction, at least one of the first fibers being a fiber of the type described above which is electrically conductive in discrete regions, and (ii) second fibers extending in a second direction perpendicular to the first direction, a plurality of the second fibers being electrically conductive fibers, wherein the electrically conductive second fibers each contact a respective discrete region of the at least one first fiber.

This aspect of the invention provides a woven fabric in which the fibers may define a spatially distributed electrical circuit. In particular, electronic elements within the first fibers may be interconnected by the electrically conductive second fibers. Conductive or non-conductive stitching or conductive adhesive may be provided at the positions of the electrical connections between the first and second fibers.

According to yet another aspect of the invention, there is provided a method of manufacturing a fiber for incorporation into a fabric, the fiber comprising thin film electronic elements, the method comprising

(i) providing an elongate substrate arrangement including a substrate formed of a plastics material and thin film electronic elements arranged over the substrate, and

(ii) encapsulating the substrate arrangement in a cladding layer formed of a plastics material, such as polyester, wherein the substrate and the electronic elements are surrounded by the cladding layer along at least a portion of the length of the substrate arrangement, the cladding layer defining a rounded outer cross sectional shape.

The step of providing the elongate substrate arrangement may comprise:

forming the substrate by depositing a plastics material, such as polyimide (PI), over a rigid carrier, such as a glass support substrate; forming the thin film electronic elements over the polyimide substrate; cutting through the substrate to define an elongate shape and thereby form the substrate arrangement; and releasing the substrate arrangement from the rigid carrier.

In general, a plurality of the substrate arrangements may be formed together on a single rigid carrier. The substrate arrangements may be separated from each other by a laser cutting process prior to release from the rigid carrier.

The step of encapsulating the substrate arrangement in the cladding layer may comprise melting a plastics material and passing the melted plastics material and the substrate arrangement through an extrusion head, wherein the melted plastics material solidifies to form the cladding layer. The extrusion head may be a part of a spinneret apparatus.

The melted plastics material may be maintained at a temperature above that of its solidifying temperature, which is typically 300 ⁰C, but below the maximum processing temperature of the substrate arrangement, which is typically 450 ⁰C. The substrate arrangement, particularly the substrate and any cover layer, may be allowed to melt to a limited degree during the manufacturing process, provided the electronic elements remain unaffected by this.

Prior to passing the substrate arrangement through an extrusion head, discrete lengths of the substrate arrangement may be attached to each other, end-to-end, before being passed through the extrusion head.

For fibers in which the cladding layer of the fiber is electrically conductive in discrete regions corresponding to positions of contact pads of the substrate arrangement, the cladding layer may be made electrically conductive in the discrete regions by alternately passing an electrically conductive plastics material and a dielectric plastics material through the extrusion head to define the discrete regions and portions between the discrete regions, respectively, or intermittently adding an electrically conductive additive to the flow of plastics material passing through the extrusion head to define the discrete regions.

Additional features and advantages of the invention will become apparent from the detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a schematic cross sectional view of a known plastic substrate provided with thin film circuitry;

Fig. 2 is a schematic plan view of a woven fabric which includes the substrate shown in Fig. 1;

Fig. 3 is a schematic cross sectional view of a first fiber according the invention;

Fig. 4 is a schematic perspective view of a second fiber according to the invention;

Fig. 5 is a schematic cross sectional view of a third fiber according to the invention;

Figs. 6a and 6b are schematic cross sectional views, through first and second perpendicular planes respectively, of a portion of a fiber according to the invention at a position of a contact pad;

Figs. 7a and 7b are schematic cross section drawings, through first and second perpendicular planes respectively, of an alternative arrangement to that shown in Figs. 6a and 6b; Figs. 8a to 8d are schematic cross sectional views showing further alternative arrangements to that shown in Figs. 6a and 6b;

Fig. 9 is a schematic cross sectional view showing a variation on the arrangements shown in Fig. 7a and 7b and Figs. 8c and 8d;

Fig. 10 is a schematic perspective view showing a further variation on that shown in Figs. 7a and 7b;

Figs. 11a and 1 Ib are for use in describing the operating characteristics of a typical solar cell;

Figs. 12a to 12c are for use in describing the effect that the aspect ratio of a solar cell has on its performance;

Figs. 13a and 13b are schematic cross sectional views of a substrate arrangement which may form a part of a fiber according to the invention, the substrate arrangement functioning as a solar cell;

Figs. 14 and 15 are schematic plan and cross sectional views, respectively, of a woven fabric according to the invention;

Fig. 16 is a schematic view of stitching used in the fabric shown in Figs. 14 and 15;

Figs. 17a to 20 illustrate a method of manufacturing the fiber shown in Fig. 3; Fig. 21 to 23d illustrate methods for providing a fiber according to the invention with contact pads to which external circuit elements can be connected; and

Figs. 23a to 25b illustrate methods for making a cladding layer of a fiber according to the invention electrically conductive in discrete regions. DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a fiber for incorporation into a woven, knitted, braided or crocheted fabric. The fiber comprises an elongate substrate arrangement having a length direction parallel to the axis of the fiber. The elongate substrate arrangement includes a substrate formed of a plastics material and thin film electronic elements arranged over the substrate. The fiber also comprises a cladding layer formed of a plastics material and encapsulating the substrate arrangement. According to the invention, the substrate and the electronic elements are surrounded by the cladding layer along at least a portion of the length of the substrate arrangement, and the cladding layer defines a rounded outer cross sectional shape. The invention also provides a fabric comprising at least one of the fibers described above and a method for manufacturing the fiber described above.

Fig. 3 is a schematic cross sectional view of a first fiber 11 according the invention. The fiber 11 is particularly suitable for incorporation into a woven fabric, but may also be suitable for incorporation into other types of fabric. The fiber 11 essentially comprises an elongate substrate arrangement which forms a core of the fiber 11 and extends in a direction perpendicular to the plane of the drawing. The substrate arrangement is encapsulated along its length by a cladding layer 17.

The elongate substrate arrangement that forms the core of the fiber 11 comprises a flexible polyimide substrate 13. The polyimide substrate 13 provides a flat surface over which thin film electronic elements 15 are arranged. The electronic elements 15 define at least a part of an electronic circuit, and may include wiring and passive or active electronic devices, including sensors and display devices.

The polyimide substrate 13 is included in the fiber structure because it provides a suitable support surface on which to form the electronic elements 15 and by which the electronic elements 15 can be manipulated prior to and during encapsulation by the cladding layer 17. The polyimide substrate 13 typically has a width of 200 μm, which provides sufficient space for the electronic elements 15, including space for power and data lines if these are required.

The polyimide substrate typically has a thickness of 50 μm in order for the electronic elements 15 to be adequately supported while they are manipulated. In alternative embodiments, the electronic elements 15 may be sandwiched between a thinner polyimide layer and an additional plastic cover layer (not shown). As well as providing support, the cover layer may provide additional protection for the electronic elements.

The substrate arrangement may be formed using the so-called EPLaR

(Electronics on Plastic by Laser Release) process, described more fully hereinbelow.

The cladding layer 17 surrounds the substrate arrangement and, unlike the substrate arrangement, has a rounded outer cross-sectional shape. The cladding layer 17 is made from a polyester material, such as polyethylene terephthalate (PET) or poly

trimethylene terephthalate (PTT). These materials are preferred because they are

mechanically flexible and have solidification temperatures which are below a maximum processing temperature for the substrate arrangement.

The width of the substrate arrangement is greater than its thickness. That is, the substrate arrangement has a substantially oblong cross sectional shape. As a consequence, the outer cross sectional shape of the cladding layer 17, which is rounded, has a smaller radius of curvature adjacent to the "thickness" sides of the substrate arrangement than it has adjacent to the "width" sides of the substrate arrangement. The cladding layer 17 therefore has a substantially oval outer cross sectional shape.

The substantially oblong cross sectional shape of the substrate arrangement and the substantially oval outer cross sectional shape of the cladding layer 17 render the fiber 11 more bendable in the thickness direction of the substrate arrangement than in the width direction of the substrate arrangement. This behavior can be conveniently described as anisotropic flexibility.

When the fiber 11 according to the invention, shown in Fig. 3, is incorporated into a woven fabric it is forced to assume an undulating shape. In particular, fibers extending perpendicular to the fiber 11 according to the invention alternately pass over and under the fiber 11 according to the invention. As a result of its anisotropic flexibility, the fiber 11 according to the invention has a tendency to assume a consistent orientation in the fabric, with the fiber 11 orienting itself such that its width direction is parallel to the surface of the fabric. Such a configuration can be advantageous in maximizing the flexibility of the resulting woven fabric without compromising the integrity of the electronic elements. Such a configuration may also be advantageous in the case of fibers 11 which comprise electronic sensors or display devices that need to face away from the fabric.

Furthermore, the cladding layer 17 serves to protect the substrate arrangement, and particularly the electronic elements 15, as the fiber 11 passes through automated textile manufacturing equipment. When incorporated into a fabric, such as a woven fabric, the rounded outer cross sectional shape of the cladding layer 17 minimizes abrasion damage to adjacent textile fibers.

Fig. 4 is a schematic perspective view of a second fiber 21 according the invention. The fiber 21 is particularly suitable for incorporation into a coarsely knitted fabric, but may also be suitable for incorporation into other types of fabric. In common with the first fiber 11 shown in Fig. 3, the fiber 21 shown in Fig. 4 essentially comprises an elongate substrate arrangement which forms a core of the fiber 21 and extends in a direction along the axis of the fiber. The substrate arrangement is encapsulated along its length by a cladding layer 27.

The elongate substrate arrangement that forms the core of the fiber 21 comprises a flexible polyimide substrate 23. The polyimide substrate 23 provides a surface over which thin film electronic elements 25 are arranged. The electronic elements 25 define at least a part of an electronic circuit, and may include wiring and passive or active electronic devices, including sensors and display devices.

The polyimide substrate 23 is included in the fiber structure because it provides a suitable support surface on which to form the electronic elements 25 and by which the electronic elements 25 can be manipulated prior to and during encapsulation by the cladding layer 27. The polyimide substrate 23 typically has a width of 200 μm, which provides sufficient space for the electronic elements 25, including space for power and data lines if these are required.

The polyimide substrate typically has a thickness of 50 μm in order for the electronic elements 25 to be adequately supported while they are manipulated. In alternative embodiments, the electronic elements 25 may be sandwiched between a thinner polyimide layer as thin as 5 μm and an additional plastic cover layer (not shown). As well as providing support, the cover layer may provide additional protection for the electronic elements.

The substrate arrangement may be formed using a variation on the so-called EPLaR (Electronics on Plastic by Laser Release) process, described more fully hereinbelow.

The substrate arrangement of the second fiber 21 has a similar cross sectional shape to that of the first fiber 11 shown in Fig. 3. However, the substrate arrangement of the second fiber 21 differs substantially from that of the first fiber 11 in its overall shape. In particular, the substrate arrangement of the second fiber 21 is twisted about the axis of the fiber 21 to form a helix-like shape, as illustrated in Fig. 4. In contrast, the substrate arrangement of the first fiber 11 is not twisted and defines a substantially flat plate-like shape along its entire length.

The substrate arrangement of the second fiber 21 may be manufactured in an untwisted form and then twisted using its inherent flexibility. Encapsulation by the cladding layer 17 may then serve to "fix" the twisted shape of the substrate arrangement. In this case, the twisting pitch of the substrate arrangement is selected to be greater than a minimum twisting pitch that can be accommodated by the inherent flexibility of the substrate arrangement, so as to maintain some residual flexibility in the resulting fiber 21. For example, a twisting pitch of between 2.0 and 5.0 times the minimum twisting pitch may be suitable. The minimum twisting pitch may be obtained by the following relationship between the pitch/? and radius of curvature p for a helix:

(1)

where d is the diameter of the cylinder on which the helix lies. The minimum radius of curvature can be obtained either experimentally or by knowledge of the material properties.

The cladding layer 27 surrounds the substrate arrangement and, unlike the substrate arrangement, has a rounded outer cross-sectional shape. The cladding layer 27 is made from a polyester material, such as polyethylene terephthalate (PET) or poly

Although the substrate arrangement of the second fiber 21 has an oblong cross sectional shape, it is twisted into a helix-like shape having outer edges lying on a circular cylinder. In other words, an end view of the twisted substrate arrangement has a circular shape. As a consequence, the cladding layer 27 of the fiber 21 has a substantially circular outer cross sectional shape.

Over a reasonable length, the second fiber 21 is equally bendable in all directions. This behavior can be conveniently described as isotropic flexibility. Compared to the first fiber 11 shown in Fig. 3, some flexibility in a specific direction is sacrificed for more flexibility in other directions.

The second fiber 21 according to the invention lends itself to incorporation in fabrics in which bending in different directions is required, such as coarsely knitted fabrics.

In common with the first fiber 11 shown in Fig. 3, the cladding layer 27 of the second fiber 21 serves to protect the substrate arrangement, and particularly the electronic elements 25, as the fiber 21 passes through automated textile manufacturing equipment. When incorporated into a fabric, such as a knitted fabric, the rounded outer cross sectional shape of the cladding layer 27 minimizes abrasion damage to adjacent textile fibers.

Fig. 5 is a schematic cross sectional view of a third fiber 31 according to the invention. The third fiber 31 is similar to the first fiber 11 shown in Fig. 3, except that it comprises a pair of stacked substrate arrangements 33, 35 surrounded by a cladding layer 37. The substrate arrangements 33, 35 are arranged such that the polyimide substrates face towards each other and the thin film electronic elements face outwards.

The substrate arrangements 33, 35 may be bonded to each other, in which case the thickness of each substrate arrangement 33, 35 may be less than that of the substrate arrangement of the first fiber 11 shown in Fig. 3. The configuration illustrated in Fig. 5 enables more electronic circuitry to be included per unit length of the fiber 31. A similar technique may be applied to fibers having twisted substrate arrangements of the type schematically illustrated in Fig. 4.

Techniques for electrically connecting the electronic elements of the above described fibers to external circuit elements, such as power supplies, will now be described. Such connections may be facilitated by providing the substrate arrangements of the fibers with longitudinally spaced-apart contact pads, and by forming the cladding layer to be electrically conductive in discrete regions corresponding to positions of the contact pads.

Figs. 6a and 6b are schematic cross sectional views through a portion of a fiber 41 according to the invention. The fiber portions are suitable for electrically connecting the electronic elements 44 of the fiber 41 to external circuit elements. In the example shown, the external circuit element is a conductive wire 49 which directly contacts the fiber 41 and extends in a direction perpendicular thereto. Fig. 6a is view through a cross section extending parallel to the fiber 41 and Fig. 6b is a view through a cross section extending perpendicular to the fiber 41.

As shown in the Figures, the fiber 41 comprises a substrate arrangement which includes thin film electronic elements 44 formed over a polyimide substrate 43. The substrate arrangement is encapsulated by a cladding layer 47 having a rounded outer cross sectional shape, as described above.

The substrate arrangement is provided with a contact pad 45 for making an electrical connection between the electronic elements 44 and the external conductive wire 49. The contact pad 45 comprises a thin metallic film formed over the polyimide substrate 43. The contact pad 45 may be formed in a similar manner to and at the same time as the thin film electronic elements 44. The contact pad 45 is electrically connected to wiring of the electronic elements 44.

To provide the electrical connection between the contact pad 45 and the external wire 49, the cladding layer 47 is electrically conductive in a discrete region 48 corresponding to the longitudinal location of the contact pad 45. The cladding layer 47 is rendered conductive in the discrete region 48 by the inclusion of silver and/or carbon black particles throughout its volume. Thus, in the discrete region 48, the cladding layer 47 comprises a mixture of polyester and conductive particles. Away from the discrete region 48, the cladding layer 47 comprises polyester only, and therefore exhibits dielectric properties.

The discrete region 48 surrounds the substrate arrangement in an annular manner. That is, the discrete region 48 extends about the entire circumference of the fiber 41. In this way, an electrical connection between the contact pad 45 and the external wire 49 can be made regardless of the rotational orientation of the fiber 41. The connection arrangement shown in Figs. 6a and 6b is therefore suitable not only for fibers of the type shown in Fig. 3 but also for fibers of the type having a twisted substrate arrangement, as shown in Fig. 4.

Although a single contact pad 45 and discrete conductive region 48 are shown in the Figures, a plurality of the contact pads 45 are provided at spaced apart locations along the length of the fiber 41, together with a respective plurality of the discrete conductive regions 48 of the cladding layer 47. In this way, multiple electrical connections can be made between the electronic elements 44 and external circuit elements such as the wire 49. For example, connections may be made for both power lines and data lines. As explained above, the discrete conductive regions 48 of the cladding layer 47 are separated by regions exhibiting dielectric properties. The discrete conductive regions 48 may be positioned at predetermined distances from an end of the fiber 41 so that their respective functions, such as power and data, can be readily identified.

Figs. 7a and 7b are schematic cross section drawings, through first and second perpendicular planes respectively, of an alternative connection arrangement to that shown in Figs. 6a and 6b.

As shown in the Figures, the fiber 51 comprises a substrate arrangement which includes thin film electronic elements 54 formed over a polyimide substrate 53. The substrate arrangement is encapsulated by a cladding layer 57 having a rounded outer cross sectional shape, as described above. The substrate arrangement is also provided with a contact pad 55 of the type described above for making electrical connections between the electronic elements 54 and the external conductive wire 59.

To provide the electrical connection between the contact pad 55 and the external wire 59, a conductive metal film 58 is provided about the outer circumference of cladding layer 57 at a discrete longitudinal position corresponding to the contact pad 55. The conductive film 58, which surrounds the cladding layer 57 in an annular manner, is electrically connected to the contact pad 55 by a conductive plug 56. The conductive plug 56 is formed over the contact pad 55 and extends through the cladding layer 57. Suitable materials for the conductive plug 56 are conductive fillers and glues, for example silicone or epoxy-based glues which comprise silver particles.

The conductive metal film 58 may be formed by spray coating or electroless plating. In the case of spray coating, the fiber 51 is guided past a spray mouth. The spray mouth is selectively activated when it is adjacent to the contact pad 55. The metal coating is typically applied such that it covers the whole of the conductive plug 56, as shown in the Figures.

In the case of electroless plating, a catalyst-containing layer typically having a thickness of less than 3μm is deposited over the fiber at a position corresponding to the contact pad 55, for example by inkjet printing. At least the portion of the fiber having the contact pad 55 is then immersed in a metal- ion containing solution, for example a go Id- ion containing solution. The metal grows on the catalyst to form the conductive metal film 58. To ensure that the catalyst-containing layer, which is typically non-conducting, does not have a significant effect on the resistance of the connection arrangement, the catalyst-containing layer may be applied only to a part of the conductive plug surface, with another part of the conductive plug surface being left exposed. Then, when the fiber 51 is immersed in the metal- ion containing solution, the metal will also grow on metallic particles in the conductive plug 56, thereby bridging the catalyst containing layer.

The connection arrangement shown in Figs. 7a and 7b may provide a low resistance electrical connection between the electronic elements 54 and the external conductive wire 59. Furthermore, the arrangement has the advantage that the material properties of the cladding layer 57, such as flexibility and strength, are not significantly affected. Different processing requirements may also apply so that, for example, the material of the conductive plug 56 does not need to be capable of undergoing an extrusion or spinning process, which may be a requirement of the material of the cladding layer 57.

Figs. 8a to 8d are schematic cross sectional views showing further alternative connection arrangements to those shown in Figs. 6a and 6b and in Figs. 7a and 7b.

Fig. 8a shows a connection arrangement which differs from that shown in Figs. 6a and 6b in that the polyimide substrate 63 of the substrate arrangement includes a pair of laterally extending tabs positioned at the location of the contact pad 65. A thin metallic film 62, such as gold or aluminum, is arranged over each of the tabs and the tabs are folded about lines extending parallel to the axis of the fiber 61. The tabs are folded such that they are encapsulated close to the outer surface of the cladding layer 67. The metallic films 62 physically overlap edges of the contact pad 65 to provide an electrically connection therebetween.

The electrical resistance of the connection arrangement shown in Fig. 8a may be lower than that of the arrangement shown in Figs. 6a and 6b, since the contact pad 65 has a greater effective surface area and is generally positioned closer to the outer surface of the cladding layer 67. Fig. 8b shows a connection arrangement which is similar to that shown in Fig. 8 a, except that a single laterally extending tab and metallic film 72 are provided at the position of the contact pad 75. This arrangement provides some of the advantages of the arrangement shown in Fig. 8a, but has a simplified structure.

Fig. 8c shows a connection arrangement which combines features of the connection arrangements shown in Figs. 6a and 6b and in Figs. 7a and 7b. Thus, a conductive plug 86 is formed over the contact pad 85 and extends through the cladding layer 87.

Furthermore, the cladding layer 87 is electrically conductive in a discrete region

corresponding to the longitudinal location of the contact pad 85. The electrical resistance of the connection arrangement shown in Fig. 8c may be lower than that of either of the arrangements shown in Figs. 6a and 6b and Figs. 7a and 7b.

Fig. 8d shows a connection arrangement which is similar to that shown in Fig. 8c, and therefore includes a conductive plug 96 formed over the contact pad 96 and an electrically conductive region of the cladding layer 97. The arrangement of Fig. 8d further comprises the laterally extending tabs and metallic films 92 of the arrangement shown in Fig. 8a. The electrical resistance of the connection arrangement shown in Fig. 8c may therefore be lower than that of either of the arrangements shown in Figs. 8a and 8c.

Fig. 9 is a schematic cross sectional view showing a variation on the connection arrangements shown in Figs. 7a and 7b and in Figs. 8c and 8d.

The connection arrangements shown in Figs. 7a and 7b and in Figs. 8c and 8d have in common that a conductive plug is formed over the contact pad and extends through the cladding layer. With such arrangements there is a risk that bending and twisting of the fiber may cause the flexible cladding layer to push against the conductive plug in a lateral direction. As the side wall of the conductive plug tapers down towards the contact pad, prolonged exposure to such lateral forces could cause the conductive plug to detach and become separated from the contact pad, thereby increasing the resistance of the connection or even creating an open circuit. The risk of such a failure may be avoided by the arrangement shown in Fig. 9, in which the conductive plug 106 tapers down in the direction away from the contact pad 105. With this arrangement, lateral forces on the conductive plug 106 from the flexible cladding layer 107 serve only to push the conductive plug 106 towards the contact pad 105.

Fig. 10 is a schematic perspective view showing a further variation on the connection arrangement shown in Figs. 7a and 7b. The connection arrangement shown in Fig. 10 differs from that shown in Figs. 7a and 7b in that the conductive metal layer (not shown) is formed over the cladding layer 117 and directly over a portion of the contact pad 115 to provide an electrical connection thereto. The hole 116 in the cladding layer 117 exposing the contact pad 115 may be provided with tapered sidewalls to facilitate the deposition of a consistent thickness of the conductive metal layer. The conductive metal layer may be accurately formed to a desired pattern 118 using the electroless plating process described above with reference to Figs. 7a and 7b. Then, when the fiber is immersed in the metal- ion containing solution, the metal will also grow on the part of the contact pad that is not covered by the catalyst, thereby bridging the catalyst containing layer. With this arrangement, a direct connection is provided between the contact pad 115 and the outer conductive metal layer, thereby reducing the resistance of the arrangement. After the forming of the conductive metal layer, the hole 116 may be filled with a conductive filler material.

As mentioned above, fibers having various different types of electronic elements may be provided according to the invention. A particularly useful embodiment of the invention is a fiber having electronic elements in the form of solar cells, since such fibers may enable power supplies for electronic circuits to be integrated into fabrics, and particularly clothing. Such an embodiment will now be described.

A problem associated with the provision of solar cells on elongate substrates having widths of less that lmm is that the efficiency of a solar cell generally reduces as the aspect ratio of the cell increases. In particular, the use of a narrow substrate and a

conventional layout precludes the use of wide, relatively low resistance wiring tracks which are required for the efficient extraction of power from a solar cell.

Fig. 1 Ia is a diagram of a typical solar cell and Fig. 1 Ib is a plot of the current-voltage characteristic of the cell. As shown in Fig. 11a, the solar cell is connected to wiring tracks which present a series resistance R_senes to the cell. The effect of the series resistance is to reduce the efficiency of the solar cell. The magnitude of the series resistance is proportional to the length of the wiring tracks.

With reference to Fig. 1 Ib, the current-voltage characteristic of the solar cell is illustrated for three different series resistances. A first line 121 is the characteristic when the series resistance R_senesi is zero. A second line 123 is the characteristic when the series resistance R_senes2 is greater than R_senesi- A third line 125 is the characteristic when the series resistance R_senes3 is greater than R_senes2- The useful power that can be extracted at each series resistance is represented by the areas Al, A2 and A3 in the Figure. The solar cell is typically operated by adjusting a load current in order to operate at the peak power point.

It will be seen From Fig. 1 Ib that the series resistance of the solar cell must be minimized in order to efficiently extract power from the cell. A reasonable design guideline is that the series resistance should not be any greater than one tenth of the characteristic resistance of the solar cell. The characteristic resistance of the solar cell is that given by the short circuit current Isc and the open circuit voltage Voc (the reciprocal of the gradient of the line 127 in Fig. l ib).

Figs. 12a, 12b and 12c compare a conventional square solar cell 131 with conventional elongate cells 133, 135 having the same area. The Figures also schematically show the wiring tracks 137 required in order to comply with the design guideline of maintaining the series resistance at or below the one tenth of the characteristic resistance. For the square solar cell 131 shown in Fig. 12a, the track width is W₁. For the solar cell 133 shown in Fig. 12b, which has a length double that of the square cell 131, the track width w₂ is doubled. For the solar cell 135 shown in Fig. 12c, which has a length double that of the cell shown in Fig. 12b, the track width W₃ is again doubled and is therefore a factor of four times greater than the track width W₁ of the square cell 131.

It will be appreciated that in a conventional layout, in which the solar cell and the wiring tracks are formed on the same surface of the substrate, a lower limitation on the practical width of the solar cell is reached. Moreover, the relatively high resistivity of wiring tracks formed by conventional solar cell manufacturing techniques also implies a lower limitation on the practical width of the solar cell. This problem is solved by a specific embodiment according to the invention shown in Figs. 13a and 13b.

According to the embodiment shown in Figs. 13a and 13b, a substrate arrangement 141 for use in the fibers described above comprises a solar cell 143 formed on one surface of a substrate 145 and low resistivity wiring tracks 147 formed on the other surface of the substrate 145.

The solar cell 143 may be formed by a conventional solar cell manufacturing process and includes conventional wiring tracks 149 having a relatively high resistance. The conventional wiring tracks 149 of the solar cell 143 are electrically connected to the low resistivity wiring tracks 147 by vias extending through the substrate 145. Where the substrate 145 is formed of polyimide the vias may extend through holes in the substrate formed by a CO₂ laser, which is able to expose the conventional wiring tracks 149 of the solar cell without removing them. The low resistivity wiring tracks 147, and optionally the vias, may be formed by the electroless plating process described above with respect to Figs. 7a and 7b.

The low resistivity wiring tracks 147 serve to lower the effective series resistance of the solar cell and therefore facilitate a narrower substrate arrangement 141. In this way, a narrower fiber can be provided that can more easily be integrated into fabrics.

As mentioned above, the invention also provides a fabric into which at least one fiber having electronic elements is integrated. Such fabrics may generally be

manufactured using conventional textile processing equipment, since the cladding layer of the fibers having electronic elements prevents damage which may otherwise occur and reduces friction in the process. An embodiment of a fabric 151 according to the invention is shown in Figs. 14 and 15.

With reference to Figs. 14 and 15, a woven fabric 151 according to the invention comprises a plurality of first fibers 153 extending in a first direction. A number of the first fibers 153 each include electronic elements (not shown) and essentially comprise a substrate arrangement 157 carrying the electronic elements and a cladding layer

encapsulating the substrate arrangement. The first fibers 153 may be of the types described above with reference to Figs. 3 to 5. The first fibers 153 may be a mixture of the fibers having electronic elements and conventional textile fibers.

The first fibers having electronic elements are also provided with connection arrangements for facilitating external connections to the electronic elements. The connection arrangements are defined by discrete regions of the cladding layer that are electrically conductive and are spaced along the length of the fibers. The connection arrangements may be of the types described above with reference to Figs. 6a to 10.

The fabric 151 also comprises a plurality of second fibers 155 extending in a second direction perpendicular to the first direction. The second fibers 155 are interwoven with the first fibers 153. In other words one of the first and second fibers 153, 155 may define the "weft" fibers and the other of the first and second fibers 153, 155 may define the "warp" fibers.

A number of the second fibers 155 are electrically conductive. These conductive fibers may, for example, be uninsulated copper wires or insulated copper wires having portions of their insulation removed. The electrically conductive second fibers 155 cross the first fibers 153 at the location of connection arrangements (not shown). At these locations, an electrical connection is formed between the first and second fibers 153, 155. The electrical connections connect the first and second fibers 153, 155 to form at least a part of a spatially distributed electrical circuit.

An electrical connection between a first fiber 153 and a second fiber 155 is shown in Fig. 16. The second fiber 155 is centered on the connection arrangement 156 of the first fiber 153. Furthermore, to ensure that the connection is reliable, the first and second fibers 153, 155 are clamped together by stitching 159. The stitching may be sewn with conductive or non-conductive thread. In alternative embodiments the connection could additionally or alternatively be maintained by the localized application of a conductive adhesive.

Methods for manufacturing fibers according to the invention will now be described.

Figs. 17a to 19 show a process for forming a substrate arrangement for use in a fiber according to the invention. The process is essentially a variation on the known EPLaR (Electronics on Plastic by Laser Release) process for forming flexible electronic devices. The EPLaR process is described in greater detail in WO 2005050754, the entire contents of which are incorporated herein by reference, but a brief description of the process will be provided herein for completeness.

In a first step of the process, as shown in Fig. 17a, a rigid carrier 161 is provided. The rigid carrier 161 may be a glass substrate. In a second step, as shown in Fig. 17b, a polymer layer in the form of polyimide is spin coated over the flat surface of the rigid carrier 161 to define a flexible substrate 163. The polyimide is formed to a thickness of approximately 5μm on the rigid carrier 161.

In a third step of the process, thin film electronic elements 165 are formed over the polyimide substrate 163 using conventional techniques. The electronic elements 165 may comprise passive elements such as wiring and active elements such as semiconductor devices. In a specific embodiment, the electronic elements include TFT display devices, and a silicon nitride passivation layer is formed between the polyimide substrate 163 and the thin film elements 165.

The electronic elements 165 are arranged on the polyimide substrate 163 as a plurality of elongate groups of elements, which groups will subsequently form parts of different substrate arrangements. Contact pads are also formed over the polyimide substrate 163 at spaced apart locations

In a fourth step, a cover layer 167 is formed over the thin film electronic elements 165 and any exposed portions of the polyimide substrate 163. The cover layer 167 has a thickness of approximately 50 μm and is formed of a polymer such as polyester. The material of the cover layer 167 may be the same as that of the cladding layer which will later encapsulate the substrate arrangement. The cover layer 167 serves to protect the electronic elements 165 and to provide additional mechanical support to the relatively thin polyimide substrate 163. In an embodiment which includes TFT display devices, the cover layer may be an electrophoretic foil. In alternative embodiments a thicker polyimide substrate may be employed and the cover layer may be omitted.

In a fifth step of the process, as shown in Fig. 17e, the layers formed over the rigid carrier 161 are divided into a plurality of individual elongate substrate arrangements by laser cutting. The individual substrate arrangements are also released from the rigid carrier 161 by a laser release process.

The laser cutting process is illustrated in more detail in Fig. 18. The individual substrate arrangements each carry a number of the electronic elements 165 and contact pads. The substrate arrangements typically have a width of less than lmm and a length which depends on the size of the processing equipment. A typical length for the substrate arrangements is 0.7 m. A CO₂ laser 169 is used for the laser cutting process.

The laser release process is illustrated in more detail in Fig. 19. In this process, the individual substrate arrangements are released from the rigid carrier 161 by exposing the rear surface of the polyimide substrate 163 to laser light that can pass through the glass of the rigid carrier 161 but is strongly absorbed in polyimide. The laser light typically has a wavelength of 100 to 410 nm. The laser light is absorbed into a very thin layer of the polyimide substrate 163, which is ablated. This leaves a very thin layer of polyimide on the rigid carrier 161 and releases most of the polyimide substrate 163.

To form a fiber according to the invention one of the substrate arrangements described above is encapsulated by a cladding layer formed of a polyester material, such as poly ethylene terephthalate (PET) or poly trimethylene terephthalate (PTT). The substrate arrangement is encapsulated by drawing it with the melted polyester material through a spinneret head of a fiber spinning apparatus, as illustrated schematically in Fig. 20. As shown in the Figure, the substrate arrangement 171 and the melted polyester 173 are drawn through the spinneret 175 to form the fiber having the cladding layer 177. The spinneret 175 includes an extrusion head having a shape corresponding to the desired outer cross sectional shape of the fiber, which is typically circular or oval. The substrate arrangement 171 may be twisted as it is passed through the spinneret 175, in which case the resulting fiber has the configuration illustrated in Fig. 4. After formation of the fiber it is cooled and rolled onto a drum 179.

For processing efficiency, a plurality of the elongate substrate arrangements 171 may be joined together end-to-end before they are drawn through the spinneret 175 together. The joints may comprise adhesive bonds or laser welds. The joints may include electrical connections between the electrical elements of the substrate arrangements 171.

The maximum temperature in the spinneret is approximately 300 ⁰C, which temperature is required to maintain the melted state of the polyester material. This maximum temperature is well below the maximum processing temperature of the substrate arrangement 171, which is approximately 450 ⁰C. If the substrate arrangement 171 includes a cover layer, this may partially melt during the fiber spinning process.

Figs. 21 to 23d illustrate methods for providing a fiber according to the invention with contact pads to which external circuit elements can be connected.

With reference to Fig. 21, a contact pad 185 may be formed over the polyimide substrate 183 of a substrate arrangement 181 at the same time as the thin film electronic elements 184 are formed. Although only one contact pad 185 is illustrated, a plurality of contact pads 185 may be spaced along the substrate arrangement 181 and each electrically connected to respective electronic elements 184. As described above, a cover layer 187 may be formed over the thin film electronic elements 184 to provide protection and support for the electronic elements 184.

Although the cover layer 187 may partially melt during the spinning process which follows, there is a need to remove a portion of the cover layer 187 to expose the contact pad 185. It is only by removing the cover layer 187 that a reliable electrical connection to external circuit elements can be provided. The cover layer 187 is typically removed by forming a hole 189 using a CO₂ laser or photolithographic etching processes.

The hole 189 may be formed during the EPLaR (Electronics on Plastic by Laser Release) process used for forming the substrate arrangement. In particular, by forming the hole 189 prior to release of the substrate arrangement 181 from the rigid glass support (not shown), some of the problems relating to the accuracy of the alignment of the hole 189 with the contact pad 185 can be largely avoided.

In some embodiments of the invention, the effective area of the contact pad may be increased by extending the polyimide substrate to provide laterally extending tabs at the positions of the contact pads, as illustrated in Figs. 22a and 22b. As shown in the Figures, thin metallic films 191 may be formed over the tabs and the metallic films 191 may overlap opposite sides of the contact pad 193 to provide an electrical connection therebetween. The tabs may then be folded about lines parallel to the length direction of the substrate arrangement, as illustrated in Fig. 22c. The folded taps provide a cross section which can be encapsulated by the cladding layer. Gold and aluminum are particularly suitable as materials for the metallic films 191, since these metals are highly elastic.

Figs. 23a to 23d illustrate the steps by which a conductive plug may be formed over the contact pad to extend through the cladding layer.

In a first step of the method, as shown in Figure 23 a, a hole 205 is formed in the cover layer 203 of the substrate arrangement 201. In a second step, as shown in Fig. 23b, the hole is filled with a conductive filler to form a conductive plug 207. In a third step, as shown in Fig. 23c, the substrate arrangement 201 is passed through a spinning apparatus with a melted polyester material to encapsulate the substrate arrangement 201 in a cladding layer 209. In a fourth step, as illustrated in Fig. 23d, the conductive plug 207, which stands proud of the cladding layer 209, is polished until it is flush with the cladding layer 209.

Figs. 24a to 25b illustrate methods for making a cladding layer of a fiber according to the invention electrically conductive in discrete regions. Such electrical conductivity provides or improves an electrical connection between contact pads of the substrate arrangement and respective external circuit elements.

As shown in Fig. 24a and 25a, the cladding layer can be rendered electrically conductive in discrete regions along the length of the fiber 211 by varying the composition of melted material supplied to the spinneret during the spinning process. In particular, the composition is varied such that it includes conductive particles as a contact pad 213 passes through the spinneret and so that no conductive particles are present at other times. The portions of the composition having conductive particles then solidify to form the discrete regions of electrically conductive cladding layer.

In embodiments of the invention, the timing of passage of a contact pad 213 through the spinneret may be accurately determined by measuring light reflectance from the fiber 211. It has been found that the metallic material of the contact pads 213 in a substrate arrangement 215 has a higher reflectance that that of other parts of the substrate arrangement 215. Since the substrate arrangement 215 is drawn through the spinneret at a constant speed, measured reflectance data for the substrate arrangement can be used to determine the point in time at which a contact pad 213 passes through the spinneret, so that the composition of the melted material can be appropriately varied. Other techniques may be used to determine the position of contact pads, including capacitance measurement. In the arrangement shown in Fig. 24a, the supply of melted material to the spinneret is switched between a melted dielectric polymer 217 and a melted conductive polymer 219. The melted conductive polymer may be based on the same polymer as the melted dielectric material, but with conductive particles added. Flow valves are used to switch between the supplies of dielectric and conductive polymers such that the conductive polymer only is supplied to the spinneret as a contact pad 213 passes and such that the dielectric polymer is supplied to the spinneret at other times. The flow rate of the dielectric polymer 221 and the flow rate of the conductive polymer 223 as a function of time (or position) are illustrated in Fig. 24b.

In the arrangement shown in Fig. 25a, a supply of melted dielectric polymer

217 to the spinneret is maintained at all times. A conductivity promoting additive 225, such as a concentrated mixture of conductive particles, is then supplied to the spinneret only as a contact pad 213 passes. The flow of the conductivity promoting additive 225 is controlled by a flow valve. The flow rate of the conductivity promoting additive 227 as a function of time (or position) are illustrated in Fig. 25b.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the definite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

CLAIMS:

1. A fiber for incorporation into a fabric, the fiber comprising:

an elongate substrate arrangement having a length direction parallel to the axis of the fiber, the elongate substrate arrangement including a substrate formed of a plastics material and thin film electronic elements arranged over the substrate; and

- a cladding layer formed of a plastics material and encapsulating the substrate arrangement,

wherein the substrate and the electronic elements are surrounded by the cladding layer along at least a portion of the length of the substrate arrangement, the cladding layer defining a rounded outer cross sectional shape.

2. A fiber according to claim 1, wherein a width of the substrate arrangement exceeds a thickness of the substrate arrangement, and wherein the cladding layer surrounding the substrate and the electronic elements defines an outer cross-sectional shape which is non- circular.

3. A fiber according to claim 1, wherein the substrate arrangement is twisted about the axis of the fiber, and wherein the cladding layer surrounding the substrate arrangement defines an outer cross sectional shape which is circular.

4. A fiber according to claim 1, wherein the substrate arrangement has a width of no more that 1 mm and/or a thickness of no more than 150 μm.

5. A fiber according to claim 1, wherein the substrate arrangement further comprises a support layer arranged over the thin film electronic elements.

6. A fiber according to claim 1, comprising a further elongate substrate arrangement facing the substrate arrangement and having a length direction parallel to the axis of the fiber, the further elongate substrate arrangement including a further substrate formed of a plastics material and further thin film electronic elements arranged over the further substrate, wherein the cladding layer further encapsulates the further substrate arrangement.

7. A fiber according to claim 1, wherein:

- the substrate arrangement further comprises contact pads electrically connected to the electronic elements, the contact pads being spaced along the length of the substrate arrangement; and

the cladding layer is electrically conductive in discrete regions corresponding to the positions of the contact pads, the discrete regions each contacting a respective contact pad, the cladding layer being dielectric in between the discrete regions.

8. A fiber according to claim 7, wherein:

the discrete regions of the cladding layer each surround the substrate arrangement; and/or

- the substrate arrangement includes discrete lateral extensions at the positions of the contact pads, the lateral extensions being folded along a line parallel to the length direction of the substrate arrangement; and/or

an electrically conductive layer is formed over each of the contact pads, the conductive layer extending through the cladding layer and defining at least a part of the discrete region; and/or

the cladding layer is plated with a metallic layer at positions corresponding to the discrete regions.

9. A fiber according to claim 1, wherein the thin film electronic elements comprise a solar cell, and wherein the substrate arrangement further comprises metallic tracks arranged over a surface of the substrate opposite to the surface over which the solar cell is arranged.

10. A woven fabric comprising:

- first fibers extending in a first direction, at least one of the first fibers being a fiber according to claim 7 which is electrically conductive in discrete regions; and

second fibers extending in a second direction perpendicular to the first direction, a plurality of the second fibers being electrically conductive fibers, wherein the electrically conductive second fibers each contact a respective discrete region of the at least one first fiber.

11. A method of manufacturing a fiber for incorporation into a fabric, the fiber comprising thin film electronic elements, the method comprising:

providing an elongate substrate arrangement including a substrate formed of a plastics material and thin film electronic elements arranged over the substrate; and

encapsulating the substrate arrangement in a cladding layer formed of a plastics material,

12. A method according to claim 11, wherein providing the elongate substrate arrangement comprises:

forming the substrate by depositing a plastics material over a rigid carrier; forming the thin film electronic elements over the substrate;

cutting through the substrate to define an elongate shape and thereby form the substrate arrangement; and

- releasing the substrate arrangement from the rigid carrier.

13. A method according to claim 11, wherein encapsulating the substrate arrangement in the cladding layer comprises melting a plastics material and passing the melted plastics material and the substrate arrangement through an extrusion head, wherein the melted plastics material solidifies to form the cladding layer.

14. A method according to claim 13, wherein discrete lengths of the substrate arrangement are attached to each other, end-to-end, before being passed through the extrusion head.

15. A method according to claim 11, wherein the cladding layer of the fiber is electrically conductive in discrete regions corresponding to positions of contact pads of the substrate arrangement, and wherein the cladding layer is made to be electrically conductive in discrete regions by: alternately passing an electrically conductive plastics material and a dielectric plastics material through the extrusion head to define the discrete regions and portions between the discrete regions, respectively; or

intermittently adding an electrically conductive additive to the flow of plastics material passing through the extrusion head to define the discrete regions.