WO2007105009A2

WO2007105009A2 - Improvements in circuits comprising a substrate carrying a conductive track

Info

Publication number: WO2007105009A2
Application number: PCT/GB2007/001009
Authority: WO
Inventors: Keith Fawdington
Original assignee: Uvasol Limited
Priority date: 2006-03-16
Filing date: 2007-03-16
Publication date: 2007-09-20
Also published as: GB0605239D0; GB2436221A; GB0705101D0; WO2007105009A3

Abstract

Radio Frequency Identification Devices sometimes fail because of a break in the connection between a microchip mounted on a substrate sheet and a conductive track printed on the substrate and forming an antenna for the device. The problem is solved by forming the conductive track within a channel cut in the surface of the substrate and arranging the micro-circuit so that it is embedded in the channel or integrally formed in the substrate material.

Description

IMPROVEMENTS IN CIRCUITS COMPRISING A SUBSTRATE CARRYING A CONDUCTIVE TRACK

[0001] This invention relates to an electrical circuit comprising a substrate carrying an electrically conductive track.

[0002] The invention arose in connection with the design of an electronic transponder of the type sometimes known as a "Radio Frequency Identification Device" (RFID). Such a device comprises a microcircuit carried by a sheet of insulating material on which a conductive track is formed. This track is connected electrically to terminals on the chip and may form an antenna for transmission and reception of radio signals and/or an inductive loop in which current is induced by a magnetic field produced by a base station. The induced current can be employed to power the transponder for processing of information and transmission of data from the transponder and/or can be modulated to transmit data to the transponder.

[0003] The availability of inexpensive and very small integrated circuits suitable for the above functions has made it practicable to install transponders for identification and record purposes in a large variety of everyday items where they are likely to subjected to mechanical stresses. These stresses can cause failure of the very delicate electrical connections that need to be made between the integrated circuit chip and the conductive tracks. In some applications the transponder needs to be flexible and this accentuates the problem.

[0004] It has also been known to form electrical tracks on a substrate by cutting a channel in a substrate and then filling the channel with a conductive material. An example of such a process is described in patent specification WO 00/52975.

[0005] According to the invention there is provided an electrical circuit comprising a substrate carrying an electrical component and an electrically conductive track within a channel formed on a surface of the substrate characterised in that the electrical component is located in the channel or elsewhere within the substrate in electrical communication with the track.

[0006] In this way it becomes possible to overcome the problem described above by the simple expedient of positioning the integrated circuit in the channel (or elsewhere within the substrate before the latter is filled with conductive material. The integrated circuit can have terminals on opposite sides thereof making contact with the conductive track. If the integrated circuit is of the same width as the track it can form a seal with the sides of the channel, preventing the track from making a short circuit between terminals. Alternatively the integrated circuit can be fixed in the channel by an adhesive that forms a seal with the sides of the channel.

[0007] In one form of the invention the integrated circuit is formed using electrodes deposited on the substrate and organic semiconductor material deposited on those electrodes in situ in the channel. Using this technique it becomes possible to form the circuit as an integral part of the substrate. Thus, in accordance with a second aspect of the invention there is provided an identification device comprising an sheet of insulating substrate material, an electronic circuit formed as part of or embedded in the sheet, a groove or channel formed in the sheet, and electrically conductive material located in the channel and forming an antenna for the transmission and/or reception of signals and/or power from or to the circuit.

[0008] Because the electrical component such as an integrated circuit is held in the channel it is possible for it to be held securely in place, making a physical and electrical connection that is relatively unlikely to fail as a result of flexing of the substrate. In fact the invention can be employed with highly flexible substrates for use in circumstances where they are constantly subjected to flexing such as in clothing or as implants in living animal or vegetable bodies.

[0009] The channel can be formed in many different possible ways eg by printing a resist on the surface of the substrate and using a solvent to etch the channel. A preferred method however is to use a laser ablation since this has been found to form a surface to which conductive ink will readily adhere. Although, in some circumstances it may be necessary only to produce a channel to form a simple loop for use as an antenna or inductive device, in other circumstances it may be desired to form a complex circuit connecting many different circuit components.

[0010] For some circuits it may be required to employ two conductive tracks. For example, one track could be used as an inductive loop for the purpose of supplying power to the circuit in a manner well known in the field of contactless smart-cards, whilst the other track is used as an antenna for the transmission and/or reception of control signals and/ or data. In one design variation there are conductive tracks on both sides of the substrate with one or more holes through the substrate to allow the tracks to be connected together. These through-holes preferably open onto the base of the channel. In some situations it may be desirable for a component to be located in the channel immediately over such a hole, allowing an electrode at the base of the component to communicate electrically with a track on the opposite side of the substrate.

[0011] It is possible for the channel' to be made deeper at a specified region to form a recess for the reception of the electronic device and such recess can extent to the side of the substrate that is opposite the side on which the channel is formed. Likewise it is possible for the channel to be made wider at a specified region for the reception of the electronic device to one side of a main part of the channel. An electronic device located in such recesses adjoining the channel is still to be considered as being located in the channel for the purposes of interpreting the accompanying claims.

[0012] The conductive material is preferably an ink, applied in liquid form into the channel(s) and then allowed to set by solvent evaporation. Other techniques such as vapour deposition would be possible but the use of conductive ink has the advantage that it can be applied at low temperatures, avoiding damage to the electronic components. Application of the ink can be by ink jet or other conventional printing methods. However, because the shape of the track(s) is already defined by the channel(s), simpler methods may be possible eg by applying ink over the whole substrate surface and then wiping away any excess, not within the channels; or the surface of the substrate could be coated or otherwise treated so as to repel the ink, whilst the channel surfaces may be treated so as to adhere to the ink.

[0013] Three embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-

[0014] Fig 1 is a perspective view of an RF tag manufactured in accordance with the invention, but with its conductive ink removed to reveal details that would otherwise be hidden;

[0015] Fig 2 is a cross section through part of a modified version of the tag shown in Fig 1, the cross-section extending laterally across a channel; and

[0016] Fig 3 is a cross section taken longitudinally through the channel of another embodiment of the invention employing an organic semiconductor device

[0017] Referring to Fig 1, the illustrated tag comprises a substrate 1 formed from a sheet of flexible synthetic plastics material. Opening onto the top surface of this sheet 1 is a channel 2, formed by laser ablation, and defining, in this particular example, a closed loop. An integrated circuit chip 3, having a width identical to that of the channel 2, fits into the channel as shown and is held temporarily in position as an interference fit. The chip is designed so as to have electrodes 4 (only one shown) on opposite end surfaces, facing in opposite directions along the groove or channel 2.

[0018] After the chip 3 has been put into the position shown in Fig 1, electrically conductive ink (not shown) is applied using an ink jet printer to the top surface of the substrate 1 and fills the. channel 2. The ink covers the end surfaces of the chip 3, overlapping the electrodes and making a secure electrical connection therewith. The ink also acts as an adhesive, holding the chip permanently into the channel. In an alternative construction method the ink is deposited generally over the surface of the substrate and excess ink is wiped away leaving ink just in the channel 2. The ink dries to form a conductive track

[0019] In operation of the device, the loop of conductive ink forms an antenna for the transmission and reception of RF signals from and to the chip. When the device is in the vicinity of a base station equipped with appropriate facilities for providing a varying magnetic flux, an alternating current is induced in the loop and this is rectified in the chip and used as a power supply in a manner known in the field of contactless smart cards.

[0020] In the design variation of Fig 2, the chip 3 has a further electrode 5 on its lower surface aligned with a through-hole 6 and making contact with a conductive track 7 on the lower surface of the substrate. In some embodiments this lower conductive track can communicate through one or more further through-holes with the track on the upper surface.

[0021] The upper conductive track, formed in the channel 2, securely embeds the chip 3 in position, and the chip does not project from the surface of the substrate. This allows substantial and repeated flexing of the substrate to take place without risk of damaging the effectiveness of the electrical connection between the track and the electrodes 4.

[0022] Referring to Fig 3, there is shown another RF tag constructed in accordance with the invention and employing organic semiconductor technology. This device comprises a substrate 8 which is similar to that of Fig 1 and is formed with a channel by laser ablation. Fig 3 is a cross-section taken longitudinally through the channel.

[0023] One part of the channel, which may be widened for this purpose, receives an organic semiconductor circuit formed in situ on the substrate. This circuit, which is illustrated only schematically and not to scale, includes a pattern of conductors 9A and 9B printed onto the base of the channel using material known to be a good conductor and a good emitter. Some of the conductive parts 9Bhave organic semiconductor material 10 deposited over them to form a diode or other semiconductor device. The illustrated arrangement is formed as a transistor by the deposition of a dielectric 11 over the semiconductor followed by a conductor which forms the base. Notably, in the illustrated construction the base is formed by part of a conductive track 12which is applied by ink jet printing into the channel to form a loop, one end of which makes non-contact connection with the organic semiconductor material, the other end making electrical contact with one of the conductors 9A which is left uncovered by the dielectric 11 to act as a terminal.

[0024] The organic semiconductor device of Fig 2 will in practice usually be a complex circuit capable of utilising power from induced current in the conductive track and receiving and transmitting radio signals using the track as an antenna.

[0025] In a variation of the design shown in Fig 3 it would be possible for the organic semiconductor circuit to be formed as an integral part of the substrate sheet, the circuit having terminals that project into a conductor-filed channel or otherwise communicating with it eg as for the base connection of the transistor shown in Fig 3.

[0026] It is believed that tags constructed using the principles of the invention will be suitable for implantation in almost any product such as clothing and can also be inserted beneath the skin of animals, birds, humans and within trees for identification purposes without risk of failure of electrical connections when the tag is flexed.

Claims

[0001] An electrical circuit comprising a substrate carrying an electrical component and an electrically conductive track within a channel formed on a surface of the substrate characterised in that the electrical component is located in the channel or elsewhere within the substrate in electrical communication with the track.

[0002] An electrical circuit according to claim 1 characterised in that the electrically conductive track is formed from a conductive ink.

[0003] An electrical circuit according to any preceding claim 5 characterised in that the component is the same width as the channel so that it forms a seal with walls of the channel.

[0004] An electrical circuit according to claims 1 or 2 characterised in that the electrical component is held in the channel by an adhesive forming a seal with walls of the channel.

[0005] An electrical circuit according to any preceding claim characterised in that the electrical component has at least one electrical conductor in contact with the track.

[0006] An electrical circuit according to any preceding claim characterised by a non- contact electrical connection between the track and the electrical component.

[0007] An electrical circuit according to any preceding claim characterised in that the track defines a radio antenna.

[0008] An electrical circuit according to any preceding claim characterised in that the track forms an inductive loop and the electrical component includes a power supply designed to utilise current induced in the loop.

[0009] An electrical circuit according to any preceding claim characterised in that the electrical component is an integrated circuit which defines, with the antenna and the substrate, a.radio frequency identification device.

[0010] An electrical circuit according to any preceding claim characterised in that the substrate is flexible.

[0011] An electrical circuit according to any preceding claim characterised in that the channel is formed by laser ablation.

[0012] An electrical circuit according to any preceding claim characterised in that the electrical component includes an organic semiconductor device.

[0013] An electrical circuit according to claim 12 characterised in that the organic semiconductor device includes electrodes carried by the substrate.

[0014] An electrical circuit according to claim 12 or 13 characterised in that an electrode of the semiconductor device is defined by the track.

[0015] An electrical circuit according to any preceding claim characterised in that the track has a discontinuity defining two ends that make respective different contacts with the track.

[0016] An electrical circuit according to any preceding claim including two tracks.

[0017] An electrical circuit according to claim 16 characterised in that the tracks are on different sides of the substrate. [0018] An electrical circuit according to claim 16 characterised in that the tracks are on the same side of the substrate. [0019] An identification device comprising a sheet of insulating substrate material, an electronic circuit formed as part of or embedded in the sheet, a groove or channel formed in the sheet, and electrically conductive material located in the channel and forming an antenna for the transmission and/or reception of signals and/or power from or to the circuit.