ULTRASOUND ARRAY TRANSDUCER MANUFACTURING

Abstract

Described herein is a method for manufacturing, or for use in manufacturing a flexible ultrasonic transducer array and the resultant ultrasonic transducer array. The method includes providing a layer of piezoelectric material onto a foil substrate and using additive techniques to apply at least one electrode to a surface of the piezoelectric material such that the electrodes are arranged in an electrode array. The method also includes using the additive techniques to applying a plurality of electrical conduction tracks and a plurality of electrical connectors to the surface of the piezoelectric material or to a layer of dielectric material provided on the surface of the piezoelectric material, such that respective electrical conduction tracks electrically connect a respective electrode to a respective electrical connector. The additive techniques comprise at least one of: masking, deposition, photo patterning, printing or patterned coating. Optionally layer of piezoelectric material comprises a layer of inorganic piezoelectric material that has been deposited onto the foil.

Claims

1. A method for manufacturing, or for use in manufacturing, a flexible ultrasonic transducer for imaging and non-destructive testing, the method comprising: providing a layer of piezoelectric material on a foil substrate; using additive techniques to apply a plurality of electrodes to a surface of the piezoelectric material and to apply a plurality of electrical conduction tracks and a plurality of electrical connectors to the surface of the piezoelectric material or to a layer of dielectric material provided on the surface of the piezoelectric material, wherein the electrodes are arranged in an electrode array, and respective electrical conduction tracks electrically connect a respective electrode to a respective electrical connector; wherein the additive techniques comprise at least one of: masking, deposition, photo patterning, printing or patterned coating.

2. The method of claim 1 in which at least the electrode(s), electrical conduction track(s) and electrical connector(s) are all integrally formed using the one or more additive techniques.

3. The method of claim 1 comprising: applying a resist material to the surface of the layer of piezoelectric material; providing a mask defining an open pattern reflecting or imaging the shape of the electrodes, the conduction tracks and/or the connectors; applying radiation to the resist material via the mask so that only selected areas of the resist material receive the radiation, as governed by the open pattern of the mask such that the received radiation selectively crosslinks or otherwise modifies or reacts the selected areas of the resist material that receive the radiation; removing parts of the layer of resist material according to whether or not hey have received the radiation; and applying a conductive material at least to parts of the piezoelectric material that are not covered by resist material to form the at least one electrode (e.g. the electrodes of the electrode array), the at least one electrical conduction track and/or the at least one electrical connector.

4. The method of claim 1, wherein the at least one electrode of the electrode array is elongate.

5. The method of claim 1, wherein the at least one electrode of the electrode array is between 0.1 and 10 mm long and between 0.01 and 1 mm wide and spaced from each other by between 0.01 and 0.1 mm.

6. The method of claim 1, wherein at least part of one or more or each of the at least one electrical conduction tracks extends away from, spreads or fans out from one or more or each other electrical conduction track.

7. The method of claim 6, wherein the separation between the electrical connectors is greater than the separation between the electrodes of the electrode array.

8. The method of claim 1, wherein the electrode array comprises from 8 to 256 electrodes.

9. The method of claim 1 comprising providing an encapsulating material on, around and/or between at least part or all of the electrical conduction tracks and/or the at least one electrode (e.g, the electrodes of the array of electrodes).

10. The method of claim 9, wherein the encapsulation material is an electrically insulating dielectric material.

11. A flexible ultrasonic transducer array comprising: a layer of piezoelectric material on a metallic foil substrate; and a plurality of electrodes on a surface of the piezoelectric material; a plurality of electrical conduction tracks and a plurality of electrical connectors on the surface of the piezoelectric material or on a layer of dielectric material that is on the surface of the piezoelectric material layer; wherein respective electrical conduction tracks electrically connect a respective electrode to a respective electrical connector; the respective electrode is integral with the respective electrical conduction track.

12. The ultrasonic transducer array of claim 11, wherein at least one or each electrode of the electrode array is between 0.1 and 10 mm long and between 0.01 and 1 mm wide and spaced from each other by between 0.01 and 0.1 mm.

13. The ultrasonic transducer array of claim 12, wherein at least part of at least one or each of the electrical conduction tracks extends away from, spreads or fans out from at least one or each other electrical conduction track.

14. The ultrasonic transducer array of claim 11, wherein the separation between the electrical connectors is greater than the separation between the electrodes of the electrode array.

15. The ultrasonic transducer array of claim 11, wherein the ultrasonic transducer array comprises an electrically insulating dielectric encapsulating material on, around and/or between at least part or all of the electrical conduction tracks and/or the electrodes of the array of electrodes.

16. A set of computer readable instructions or computer code configured such that, when processed by additive manufacturing equipment, permit, control or cause the additive manufacturing equipment to: use additive techniques to apply a plurality of electrodes, a plurality of electrical conduction tracks and a plurality of electrical connectors to a surface of a layer of piezoelectric material on a foil substrate, or to a layer of dielectric material provided on the surface of the piezoelectric material; wherein the electrodes are arranged in an electrode array, and respective electrical conduction tracks electrically connect a respective electrode to a respective electrical connector; and the additive techniques comprise at least one of: masking, deposition, photo patterning, printing or patterned coating.

17. An ultrasonic non-destructive testing or imaging device comprising the ultrasonic transducer array of claim 11 configured to produce and emit ultrasonic waves and/or receive reflections of the emitted ultrasonic waves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying Figures, in which:

[0058] FIG. 1 is a schematic planar view of an ultrasonic transducer array;

[0059] FIG. 2 is schematic side view of the transducer array of FIG. 1;

[0060] FIG. 3 is a flowchart showing a method of producing the transducer array of FIGS. 1 and 2;

[0061] FIGS. 4 to 10 are schematic illustrations of steps of the method of FIG. 3, where the Figures suffixed with A are side cross sectional views and the Figures suffixed with B are plan views of the object that will become the ultrasonic transducer array of FIGS. 1 and 2 during stages of manufacture;

[0062] FIG. 11 is a schematic of an additive manufacturing system;

[0063] FIG. 12 is an alternative ultrasound transducer array that can be produced using the method of FIG. 3;

[0064] FIG. 13 is another alternative ultrasound transducer array that can be produced using the method of FIG. 3;

[0065] FIG. 14 is another alternative ultrasound transducer array that can be produced using the method of FIG. 3; and

[0066] FIG. 15 is another alternative ultrasound transducer array that can be produced using the method of FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

[0067] FIG. 1 shows a schematic planar view of an ultrasonic transducer array 5 and FIG. 2 shows a schematic side view of the ultrasonic transducer array 5. The ultrasonic transducer array 5 comprises an electrically conductive substrate 10 in the form of a metal foil, in this case an aluminium foil, and a layer of crystalline piezoelectric material 15 disposed on one planar surface of the substrate 10. The substrate 10 acts to support the layer of piezoelectric material 15 and also functions as a counter electrode and ultrasonic wave radiation surface from which ultrasonic waves are emitted from the transducer array in use. The substrate 10 is much thicker (i.e. in the order of magnitude of 10 times thicker) than the layer of piezoelectric material 15 and in this example, the substrate 10 is between 20 and 200 m thick and the layer of piezoelectric material 15 is between 2 and 20 m thick. In this example, the piezoelectric material is ZnO but it will be appreciated that other suitable piezoelectric materials such as AlN may be used.

[0068] An array of metallic (in this case gold) elongate working electrodes 20 are provided on a surface of the layer of piezoelectric material 15 that is on an opposite side of the layer of piezoelectric material 15 to the substrate 10. The working electrodes 20 are linearly distributed in the example shown but may be distributed in two dimensions in other embodiments. Each of the working electrodes 20 is connected to a corresponding electrically conductive track 25. The tracks 25 from each of the working electrodes fan out and become increasingly distant from each other as they extend away from the working electrodes 20. An end of the respective tracks 15 that is distal to the associated working electrode 20 is electrically connected to an associated electrical connector 30. In this way, each working electrode 20 in the array is individually operable/addressable by electrically driving/addressing the corresponding connector 30. Since the conductive tracks 25 fan out between the working electrodes 20 and the connectors 30, a high resolution ultrasonic transducer array may be provided by the closely spaced working electrodes 20 but at the same time, the connectors 30 are spaced for easy connection, e.g. by matching a standard connector configuration.

[0069] In examples, between 16 and 128 working electrodes 20 are provided in the array, where each electrode is 1 mm long by 0.1 mm wide with a gap of 0.05 mm between electrodes 20. In contrast, the connectors 30 have a pitch of 0.5 mm. Cured electrically insulating cross linked resist material such as SU-8 epoxy is provided between the working electrodes 20, between the tracks 25 and between the connectors 30, which may help to prevent electrical cross talk.

[0070] An electrically insulating dielectric encapsulating material 35 is provided over and around the electrodes 20 and the conductive tracks 25. However, the connectors 30 are left exposed to allow electrical connections to a controller or processing device to be made. The radiating surface of the substrate 10 (i.e. the surface of the substrate opposite to the piezoelectric material 15) is also left exposed and clear of encapsulation material.

[0071] In order to generate the ultrasound, the alternating electrical driving current is applied to the appropriate connector 30 or connectors 30 and thereby via the conductive tracks 25 to the corresponding working electrode 20 or electrodes 20. The working electrodes 20 form a couple with the conductive substrate that acts as a counter or ground electrode in order to apply an alternating electrical current across the corresponding sections of the piezoelectric material 15. This in turn causes the corresponding sections of piezoelectric material to vibrate at high frequency along with the corresponding portion of the substrate to thereby generate ultrasonic waves, which are emitted from portions of the outer surface of the substrate that correspond to the driven working electrode(s) 20.

[0072] The ultrasonic transducer 5 of FIGS. 1 and 2 can be conveniently and beneficially produced using additive manufacturing. One possible example of a suitable additive manufacturing process for producing the ultrasonic transducer 5 is shown in FIGS. 3 to 10. FIG. 3 shows a flowchart of the additive manufacturing process. FIGS. 4A, 5A, 6A, 7A, 8A, 9A and 10A show side cross sectional views of what will become the ultrasonic transducer array 5 during various stages of the additive manufacturing process. FIGS. 4B, 5B, 6B, 7B, 8B, 9B and 10B show corresponding plan views of what will become the ultrasonic transducer array 5 during various stages of the additive manufacturing process.

[0073] As shown in FIGS. 4A and 4B, the process starts with the substrate 10 in the form of a metal foil, such as aluminium foil. The substrate can be from 20 to 200 m thick. As indicated in step 305 of FIG. 3 and shown in FIGS. 5A and 5B, the substrate 10 is coated on one side with a thin layer of polycrystalline piezoelectric material 15, such as zinc oxide (ZnO) or aluminium nitride (AlN). The layer of piezoelectric material 15 is of the order of a 10.sup.th of the thickness of the substrate 10, e.g. from 2 to 20 m thick. The layer of piezoelectric material 15 can be deposited by a range of suitable techniques such as sputter coating, chemical vapour deposition and/or the like. For example, the piezoelectric material 15 could be deposited using closed field magnetron sputtering or high power impulse magnetron sputtering, which may optimize the piezoelectric properties of the film and/or the growth morphology.

[0074] As indicated in step 310 of FIG. 3 and as shown in FIGS. 6A and 6B a surface of the layer of piezoelectric material 15 that is opposite the substrate 10 is then covered by a layer of photoresist 40 such as SU-8. Then, as indicated in step 315 of FIG. 3 and as shown in FIGS. 7A and 7B, the photoresist 40 is exposed to radiation via a patterned mask 45.

[0075] Openings in the mask 45 serve to let radiation 50 through and solid portions of the mask 45 serve to block portions of the radiation 50. The radiation 50 is such that it changes the state of the parts of the photoresist 40 that are exposed to radiation 50. For example, in a negative photoresist 40 the radiation 50 crosslinks the photoresist 40 such that is becomes insoluble whereas the portions of the photoresist that haven't been exposed to the radiation remain soluble in a suitable solvent. Alternatively, a positive photoresist could be used. The patterning and shape of the mask 45 imparts the image of the electrodes 20, the conductive tracks 25 and the contacts 30 in the photoresist 40 by masking the radiation 50.

[0076] As indicated in step 320 of FIG. 3 and as shown in FIGS. 8A and 8B, the suitable solvent is applied to the photoresist 40 in order to remove the sections of the photoresist 40 corresponding to the electrodes 20, the conductive tracks 25 and the contacts 30 as imaged in the photoresist 40 by the radiation 50 using the mask 45. Removal of the photoresist 40 exposes corresponding portions of the layer of piezoelectric material 15.

[0077] As indicated in step 325 of FIG. 3 and as shown in FIGS. 9A and 9B, a layer of metal 55 is deposited such that it is deposited onto the exposed portions of the piezoelectric material 15. In this way, the metal 55 on the exposed portions of the piezoelectric material 15 form the array of working electrodes 20, the conductive tracks 25 and the contacts 30.

[0078] The electrically insulating cured photoresist 40 remains between each of the electrodes 20 of the electrode array, between the conductive tracks 25 and between the contacts 25 and acts to help prevent crosstalk. In addition, as indicated in step 330 of FIG. 3 and as shown in FIGS. 10A and 10B, the electrically insulating encapsulating material 35 is provided over and around the outer surface of the electrodes 20 and the conductive tracks 25 in order to protect and insulate them. The encapsulating material 35 can be any suitable dielectric material. However, the contacts 30 are left exposed so that they can form an electrical connection to a suitable controller, signal generator and/or processing device.

[0079] Although a beneficial example of an additive manufacturing method to form the ultrasonic transducer array is shown in, and described in relation to, FIGS. 3 to 10, it will be appreciated that other suitable additive manufacturing techniques could be used. For example, the masking, photo-patterning, selective removal of photoresist and metal deposition of steps 310 to 325 may be replaced by directly 3D printing or otherwise applying the metal 55 in the appropriate pattern to form the electrodes 20, the conductive tracks 25 and/or the contacts 30, using a 3D printer or other additive manufacturing apparatus 1205, as shown in FIG. 11. Other suitable additive manufacturing techniques could be apparent to a skilled person.

[0080] Although specific examples are described above in relation to the Figures, it will be appreciated that variations on the above examples are possible. As such, the scope of protection is defined by the claims and not by the above specific examples.

[0081] For example, although examples of piezoelectric materials being ZnO or AlN are given above, it will be appreciated that other piezoelectric materials could be used instead. In addition, although various thicknesses, dimensions, numbers and geometric arrangements of electrodes, conductive tracks and contacts are given above, it will be appreciated that other thicknesses, dimensions, numbers and geometric arrangements of electrodes, conductive tracks and contacts could be used. Indeed, although the electrodes are all shown as the same size and shape, it will be appreciated that at least some or all of the electrodes may be of different sizes and/or shapes. Furthermore, the electrodes in the electrode array need not be arranged linearly. Some examples of alternate electrode arrangements are shown in FIGS. 12 to 15. FIG. 12 shows an ultrasonic transducer array 5 that is similar to that shown in FIGS. 1 and 2 but with the electrodes 20 distributed in two dimensions rather than linearly. In the example of FIG. 12, the electrodes 20 are distributed in a grid arrangement and the electrodes are square but other two dimensional distributions of electrodes and/or other electrode shapes or sizes could be used. FIG. 13 shows an ultrasonic transducer array 5 that is similar to that shown in FIGS. 1 and 2 with the electrodes 20 arranged linearly and being rectangular. FIG. 14 shows an embodiment having annular electrodes 20 with a circular electrode 20 in the centre. In this example, the electrodes 20 are arranged concentrically but need not be. Similarly, the nested/concentric principle shown in FIG. 14 can be applied to other shapes and arrangements of electrodes. FIG. 15 shows an electrode arrangement in a tree format in this case having circular electrodes. However, the scope of coverage includes other arrangements of electrodes 20, connectors 25 and contacts 30, including but not limited to any suitable combinations of features of any of the embodiments shown and/or described herein, and/or other suitable configurations that would be apparent based on the present teaching. Employing the methods described herein make it easier of the designer of the ultrasonic transducer array 5 to provide arrangements, numbers, sizes and shapes of electrodes 20 to produce ultrasonic radiation best suited to the intended application.