Method for producing stretchable conductive devices and devices obtained thereby

Abstract

The invention relates to a method for producing a device consisting of an elastomeric polymer substrate on which there is a metal film that maintains conductive properties even during the stretching and relaxation cycles of the substrate. The invention also relates to the stretchable conductive device thus obtained.

Description

Technical Field

[0001] This invention relates to a method for fabricating devices consisting of an elastic polymer substrate on which a metal film is present, the elastic polymer substrate maintaining conductive properties even during stretching and relaxation cycles. The invention also relates to the resulting stretchable conductive device. Background Technology

[0002] In many technical fields, it is necessary to establish stable electrical connections through conductors that, in addition to being flexible, are also stretchable, meaning they can withstand (reversible) elongation in the conductive direction. This specification and the claims define such conductors (those capable of elongating along the primary conductive direction while maintaining their conductivity) as stretchable conductive devices or even simply stretchable conductors.

[0003] While such conductors can be used in any application requiring a conductor, their primary intended application is the fabrication of electrodes implantable in the human (and animal) body. This requires the electrodes to be able to adapt to all deformations at their implantation site, including elongation and recovery to their initial length, without loss of continuity and key electrical properties. Such applications include, for example, implantable neural interfaces (e.g., described in WO 2009 / 090398 A2), deep brain stimulation devices (e.g., described in WO 2008 / 035344 A2), spinal cord stimulation devices for treating paralysis, and, for example, actuators that typically stimulate or replace muscle movement (referred to as “artificial muscles”). Given the importance of this latter application, reference will be made to implantable products and devices throughout the remainder of the specification; however, it should be understood that the products of this invention are also applicable to all other applications requiring stretchable conductors.

[0004] The first proposed method for preparing conductors with these characteristics involves fabricating a metal wire (conductor or thin deposit) with a wavy pattern within a biocompatible elastic polymer, exposing one or more electrical contacts from the polymer surface at predetermined points depending on the intended application; the wavy shape of the metal wire allows it to elongate or shorten when the polymer is stretched. Such conductors are described, for example, in patents US 7,085,605 B2 and US 7,265,298 B2. However, the methods in these patents are not entirely satisfactory. First, they are quite laborious and therefore unsuitable for transfer to industrial-scale production; second, products obtained by these methods resist traction only in the average direction of the trace (i.e., the direction of the centerline of the wavy or wrinkled pattern).

[0005] The second method, described in patent US 9,107,592 B2, involves depositing metallic traces (by known methods) on a prestressed elastomer; after deposition, the elastomer is allowed to recover its "rest" dimensions, and the metallic deposit geometrically reorganizes to follow its contraction. However, in this case, the metallic deposit is compressed within the resting elastomer; this may first involve changes in the mechanical properties of the elastomer surface on which the metallic deposit forms, subsequently triggering its fracture during the repeated stretching and relaxation cycles the product will endure. Furthermore, products obtained by these methods resist traction only in the direction of the initial prestress of the elastomer, and the maximum elongation is equal to that prestress.

[0006] Another method is described in the applicant's international patent application WO 2011 / 121017 A1. According to this method, conductive wires are formed by implanting nanoscale aggregates of a metal (e.g., titanium) into an elastic polymer; the embodiments described in the application demonstrate that electrical continuity is maintained despite the deposit consisting of discrete particles, and this continuity is preserved even after the conductor undergoes tens of thousands of stretching / shortening cycles. The method described in this application also includes the possibility of growing a continuous metal layer (e.g., by electrochemical (electroplating) deposition) on a deposit obtained through nanoparticle implantation (if the deposit appears on a substrate surface); in this case, the conductive layer obtained through particle implantation allows for connection to external circuitry to provide the electrons required for electrochemical deposition. However, the method described in this document is not readily scalable for industrial production.

[0007] Finally, the last method for producing conductive deposits on elastomeric substrates is to employ deposition techniques such as physical vapor deposition (PVD), particularly a variant known as electron beam evaporation, which enables high deposition rates. This technique and the results obtained are illustrated in, for example, the articles “Stretchable conductors: thin gold films on silicone elastomer,” SP Lacour et al., Mat. Res. Soc. Symp. Proc. Vol. 795 (2004); “Extended cyclic uniaxial loading of stretchable gold thin-films on elastomeric substrates,” IM Graz et al., Applied Physics Letters 94, 071902 (2009); “Stretchable gold conductors embedded in PDMS and patterned by photolithography: fabrication and electromechanical characterization,” T. Adrega et al., J. Micromech. Microeng. 20 (2010) 055025; and “Mechanisms of reversible stretchability.” The term "reversible stretching mechanism of thin metal films on elastomeric substrates" is described in SP Lacour et al., Applied Physics Letters 88, 204103 (2006).In all the articles, the systems prepared were consistently formed from gold deposits on a silicone rubber substrate, and it is unclear whether the described methods are equally applicable to other systems (especially metals other than gold). Furthermore, to ensure the adhesion of the gold deposits to the elastomer, it is necessary to deposit an intermediate thin chromium layer, which makes these systems unsuitable for implantation applications in humans or animals. Finally, the metal films obtained using these techniques can only be stretched at extremely low thicknesses, as acknowledged in the aforementioned article "Stretchable Conductor: Thin Gold Films on Silicone Rubber Elastomers," whose abstract states that deposits thicker than 100 nm will undergo electrical fracture under approximately 1% traction deformation. Summary of the Invention

[0008] The object of the present invention is to provide a method for fabricating stretchable conductive devices to overcome the problems of the prior art, and to provide devices obtained by said method.

[0009] This invention achieves this and other objectives, and its first aspect relates to a method for fabricating a stretchable conductive device, comprising the following steps:

[0010] a) Prepare an elastomer substrate having a first metal deposit with a thickness of 10 nm to 200 nm obtained by a dry process on its surface; b) Forming a second metal deposit on top of the first metal deposit by solution chemical or electrochemical deposition; The characteristic feature is that the solution deposition and ultrasonic treatment are performed simultaneously, or after the ultrasonic treatment.

[0011] In a second aspect, the present invention relates to a stretchable conductive device formed from an elastomer substrate having one or more discontinuous metal deposits on its surface, wherein components of these deposits are in contact with each other. Attached Figure Description

[0012] Figure 1 This image shows a photograph of the gold deposit of the sample of the present invention in a static state, obtained by scanning electron microscopy (SEM). Figure 1 .a), and three photographs of the same sample under tensile conditions at different magnifications ( Figure 1 .b-1.d); Figure 2 A top view of a device prepared by the method of the present invention is shown, wherein four gold metal traces are present on an elastomer substrate; Figure 3 The metal deposition geometry of the sample prepared for measuring the resistance as a function of stretching / relaxation cycles is shown. Figure 4 The image shown is a photograph of the gold deposits on the surface of the sample of the present invention obtained by optical microscopy; Figure 5 It shows the use of and Figure 4 Photographs obtained on non-invention samples using the same instruments and magnification; Figure 6 A photograph of the platinum deposits on the surface of the sample of the present invention, obtained by optical microscopy, is shown; Figure 7 A photograph of iridium deposits on the surface of the sample of the present invention, obtained by optical microscopy, is shown; Figure 8 This is a photograph of the device used to perform resistivity measurements during a stretching / relaxation cycle. Figure 9 The graph shows the trend of surface resistivity (Ω / □) of samples obtained using gold, platinum, and iridium deposits as a function of elongation %

[0013] Figure 10 The graph shows the trend of surface resistivity (Ω / □) as a function of elongation % for two gold deposit samples obtained according to the method of the present invention and one gold deposit sample not obtained according to the method of the present invention. Detailed Implementation

[0014] The applicant unexpectedly discovered that by performing chemical or electrochemical deposition on the surface of an elastomer in a metal film solution, and by subjecting the elastomer substrate to ultrasonic treatment during or after the deposition, the resulting deposits would fracture, but when the elastomer substrate was at rest, the components of the deposits would be in contact with each other, and when the elastomer substrate was subjected to tensile deformation, at least some of its edge regions would remain in contact, thus maintaining its electrical conductivity.

[0015] In its first aspect, the present invention relates to a method for preparing a stretchable conductive device.

[0016] The first step of the method, a), includes providing a substrate made of an elastomeric polymer, on the surface of which a first metal deposit obtained by a dry process is present.

[0017] The polymer material of the substrate can be any elastomeric polymer, such as polyolefin-based elastomers, elastic fluoropolymers, polybutadiene (BR), styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), nitrile rubber (NBR), acrylate rubber (ACM), isobutylene-isoprene rubber (IIR), copolyesters, chloroprene rubber (polychloroprene), polyurethane rubber, and polysiloxane (silicone rubber). For the preferred purpose of this invention, namely, to prepare devices for implantation in the human or animal body, the polymer must be biocompatible; in this case, silicone rubber is preferred, and polydimethylsiloxane (PDMS) is particularly preferred.

[0018] The first metal deposit can be prepared using any technique known for this purpose, such as those described in the background discussion. These known techniques for preparing the first deposit are all of the "dry" type, mainly falling into two categories: evaporation and injection. Specifically, the first deposit can be prepared using chemical deposition techniques (such as chemical vapor deposition (CVD)), physical deposition techniques (such as thermal evaporation, electron beam evaporation, or sputtering), or cluster deposition techniques (such as CBD (Cluster Beam Deposition), SCBD (Supersonic Cluster Beam Deposition), or SCBI (Supersonic Cluster Beam Injection)).

[0019] CVD technology is well-known in the field of materials science. It involves the thermal decomposition of volatile compounds (typically organometallic compounds) of a metal of interest on a substrate surface (which may be obtained by means of a mask to obtain a deposit with the desired geometry).

[0020] Physical techniques such as evaporation or sputtering are well-known in the field of materials science and need not be elaborated here.

[0021] According to the present invention, a preferred technique for forming the first metal deposit is known as supersonic cluster electron beam injection (SCBI); in this case, the first deposit is produced in the form of a nanoparticle layer. A method for preparing a nanoparticle layer on an elastomer surface using this technique is described in detail in the cited patent application WO 2011 / 121017 A1, with further details provided therein. In short, the technique includes the steps of: generating an electron beam of nanoscale neutral aggregates of the desired material, wherein the aggregates have an average velocity of 100 m / s to 10,000 m / s and a size less than 50 nm; and impinging the electron beam onto the surface of the elastomer material in a vacuum chamber. The present invention prefers the SCBI technique because the inventors have noted that the first deposit in nanoparticle form is more effective than a continuous deposit in promoting the subsequent formation of a second deposit, particularly when formed by chemical deposition.

[0022] Compared to using the aforementioned dry techniques alone, the advantage of this invention is that the latter has a relatively low deposition yield in terms of the thickness of the deposit formed per unit time; therefore, obtaining a thickness with, for example, resistivity values ​​suitable for practical purposes using these techniques would require excessively long industrial production times. Conversely, in this invention, the aforementioned techniques for forming the first deposit are used only for a short time to produce a low-thickness metal deposit, upon which a second, thicker deposit is grown using techniques with higher yields.

[0023] Furthermore, thin films obtained using some of the techniques in the background art (e.g., the method in the paper mentioned by Lacour et al.) are not stretchable when the thickness is greater than about 100 nm; however, this results in high resistivity values, which limits the applicability of the resulting thin films.

[0024] Furthermore, the greater thickness allowed by this invention also results in stronger corrosion resistance over time.

[0025] The inventors observed that the device of the present invention can withstand an elongation of up to 70% of its rest length for thousands of cycles without performance degradation.

[0026] The metal used to form the first deposit can vary depending on the intended use of the final device. For general applications, virtually all transition metals can be used, provided they are chemically resistant in the chemical or electrochemical deposition solution used in subsequent operations of the method of the invention. In the case of articles intended for implantation in the human body, inert or biocompatible metals, particularly noble metals or titanium, are preferred, even if the first deposit is subsequently covered by a second metal deposit. Platinum is a preferred metal for preparing the first deposit (whether in continuous or nanoparticle layer form).

[0027] When the final device is used for general purposes as a stretchable conductor, the first deposit can be uniformly formed on the surface of an elastomer substrate. However, for most applications, particularly for implantable devices, the first deposit is preferably present in the form of traces, which allows for the individual and selective conduction of different electrical signals to different points on the device. The formation of metal deposits with trace-shaped geometry can be achieved using methods known from the semiconductor industry, namely by using stencil masks or photolithography techniques to deposit and selectively remove layers of polymeric material (which can be removed at the end of the deposition process of the desired material). In cases where the device is intended for implantation, the extremely high resolution (orders of magnitude of 1 micrometer or less for the lateral dimensions of traces or structures) typically is not required for semiconductor devices; the lateral dimensions of traces can be on the order of millimeters or tenths of a millimeter, which can also be achieved using stencil masks. Figure 2 An embodiment of a device prepared using the method of the present invention is shown, wherein four independent metal traces exist on an elastomer substrate: the minimum width of the traces is 0.7 mm, and at the closest point, they are separated by a gap of 0.3 mm in width.

[0028] Since the first metal deposit does not function as a primary conductor in the final device, but only serves as a deposition electrode for subsequent electrochemical deposition and as anchoring the metal deposit to the elastomer substrate (regardless of whether the metal deposit is obtained by chemical deposition or electrochemical deposition), the first deposit has a submicron thickness, preferably 10 nm to 200 nm.

[0029] Following step a), especially when a considerable time has passed before proceeding to step b), the first deposit may be chemically cleaned (similar to pickling in the metal industry). This cleaning may be performed using reducing agents such as formic acid, hydrazine, alcohols, or the like. The aim is to remove the passivation layer that forms on the metal surface of the first deposit due to air exposure. This procedure is applicable even to noble metal nanoparticles obtained via SCBI, as their large surface area makes them more reactive than bulk forms of the same metal.

[0030] The second step b) of the method includes forming a second metal deposit on the first metal deposit obtained in the previous step by chemical or electrochemical deposition in a desired metal precursor solution; the second metal deposit may be formed while ultrasound is being applied or under static conditions, and then the deposit thus formed is subjected to ultrasound treatment.

[0031] In this step, a single metal can be deposited, or a mixture of two metals can be deposited if the two metals have similar chemical or electrochemical properties.

[0032] Solution chemical deposition is known in this field as “electroless deposition” or its abbreviation “ELD”, which will be used below.

[0033] This method involves immersing an elastomeric substrate containing a first deposit surface layer into a plating bath containing a salt or complex of the metal to be formed into a second deposit; a reducing agent is added to the same plating bath (solution) that is capable of providing electrons for the overall reaction of the following type: M n+ + ne → M 0 In this process, metals that initially exist as n+ oxidized ions (free, solvated, or complexed) are reduced to neutral metals.

[0034] In this case, the first metal deposit on the substrate acts as a catalyst or nucleation center for the metal reduction reaction; therefore, the reduction reaction that accompanies the formation of the second metal deposit occurs only on the first deposit.

[0035] The following are examples of reactions that reduce metal ions or complexes to the corresponding metals, applicable to gold, platinum, and iridium respectively:

[0036] In these reactions, the reducing agent for gold is hydrogen peroxide, while the reducing agent for platinum and iridium is hydrazine. In the above reactions of platinum and iridium, the complexes used as starting reagents are formed in situ: for platinum, they are formed by the reaction of hexachloroplatinic acid with ammonia in the presence of hydrazine; for iridium, they are formed by the reaction of hexachloroiridic acid with hydrazine.

[0037] ELD deposition can be carried out at temperatures ranging from 5°C to 80°C, preferably from 15°C to 70°C, with a concentration of the metal ions to be reduced (in free, solvated, or complex form) ranging from 0.01 g / L to 10 g / L. The concentration of the reducing agent varies with the metal ion concentration, and a stoichiometric excess of reducing agent is typically used, with a typical molar ratio of reducing agent to metal ions to be reduced ranging from 1:10 to 1:1000. The deposition reaction typically lasts from 10 minutes to one hour.

[0038] Various additives can also be present in the solution.

[0039] Some available additives, such as: - Surfactants, acting as brighteners for metal deposits, improve the diffusion of ultrasound in the deposition solution and inhibit chemical deposition in the solution; these compounds are believed to "incorporate" metal nuclei that may form in solution through micelles or similar structures, isolating them from the solution and preventing further growth and failure of the electroplating solution. For the purposes of this invention, preferred surfactants are polyvinyl alcohols, particularly the Mowiol® series (a trademark of Kuraray Specialties Europe AG); - Halogen ions, usually added by salting the metal to be deposited, act as regulators of the reduction rate; - Or pH adjusters, such as NaOH or HCl, also act as regulators of the reduction rate.

[0040] Solution electrochemical deposition is a well-known electroplating deposition technique in which the electrons required for the reduction of the metal ions of interest are provided by an external circuit; this deposition technique is also referred to in the field as the abbreviation ED (derived from "electrodeposition"). In this case, the first deposit present on the substrate is connected to the external circuit and serves as the electrode for the reduction to occur; naturally, in this case, the second metal deposit is formed corresponding to the first deposit, whether in a continuous form or a trace form.

[0041] Electrochemical deposition of metals, and the plating solution compositions used for various metal depositions, are well known in the art and need not be described in detail here. The same plating solutions used for the above-described chemical deposition can also be used for electrochemical deposition without the addition of chemical reducing agents.

[0042] Electrochemical deposition can be performed in a two-electrode or three-electrode system.

[0043] A three-electrode electrolytic cell consists of a working electrode (in the case of this invention, a first metal deposit on an elastomer substrate), a reference electrode (which allows control of the electrolytic cell's potential relative to an external potential reference), and a counter electrode that serves as a current collector.

[0044] The two-electrode electrolytic cell is similar to the former, but in this case, the reference electrode and the counter electrode are short-circuited. In this case, the circulating current in the electrolytic cell can be controlled, but the read potential is independent of the external reference.

[0045] In the case of ELD and ED, the thickness of the second metal deposit is preferably 50 nm to 1000 nm; when the thickness is low, the resistivity is high due to the small cross-sectional area of ​​the metal deposit; while when the thickness is high, the elastic deformation capability of the device will deteriorate.

[0046] A key feature of this invention is the application of ultrasound to form a second metal deposit: whether in the case of electroless or electrochemical deposition, ultrasound can be applied to the solution during the deposition operation, or applied after the second deposit has been obtained via ELD or ED, through a treatment process. For effective ultrasound application, the sample must be immersed in a liquid: if ultrasound is applied during ELD or ED deposition, the liquid is naturally the deposition solution itself; if ultrasound is applied after the formation of the second metal deposit, the liquid can be any liquid phase, as long as it is chemically compatible with the substrate polymer and the metals of both the first and second deposits; for devices intended for implantation, it is preferable to rinse the finished device with distilled water to remove residual traces of process solvents or dissolving chemicals.

[0047] Whether ultrasound is applied during or after the formation of the second metal deposit, the effect is to obtain a microcracked deposit; it is this characteristic that allows the resulting device to maintain conductivity even after the sample is stretched.

[0048] This phenomenon is as follows Figure 1 As shown. Figure 1 The images in .a-1.d are SEM images of gold deposits on silicone rubber obtained using ultrasound during ELD deposition. Figure 1 .a shows the sample in a static state (i.e., not under tension), while Figure 1 .b-1.d shows the same sample being stretched from left to right in the photograph at progressively increasing magnification. For example... Figure 1 As shown in .a, the metal deposit uniformly covers the sample surface, but the film exhibits a cracked appearance and forms an "island" structure along all its edges; under stretching ( Figure 1(b-1.d) The sediment “islands” are separated from each other, exposing the underlying elastomeric substrate (the darker area in the photo), but there are always contact points between these islands, which form a continuous permeation path parallel to the substrate surface, maintaining the conductivity of the sediment even when stretched. Figure 1 The .d diagram illustrates some possible continuous paths that allow charge to be transferred along the sample elongation direction (from right to left in the diagram).

[0049] The inventors observed that the suitable ultrasonic frequency range for the purposes of this invention is 25 kHz to 80 kHz: at frequencies below 25 kHz, strong cavitation effects occur in the liquid immersed in the second deposit (forming or already formed), posing a high risk of damaging the sample; at frequencies above 80 kHz, cavitation is weak, and the sample may not be able to form the microcracks required to maintain tensile conductivity. The optimal ultrasonic frequency is 30 kHz to 50 kHz, preferably about 40 kHz.

[0050] Preferably, during the application of ultrasound, the substrate is moved relative to its average position to achieve uniform treatment of the second metal deposit that is forming or has already formed; in practice, in some cases, standing wave conditions may form in the liquid, where the positions of the wave nodes remain constant over time, so the regions of the sample corresponding to these nodes are hardly treated by ultrasound. The movement of the substrate can be linear and reciprocating at speeds of 5 mm / s to 20 mm / s. Alternatively, the substrate can be rotated about its own axis at speeds of 10 rpm to 50 rpm, preferably 20 rpm to 30 rpm. To further improve the uniformity of the ultrasonic field on the substrate surface, linear and rotational motions can be combined.

[0051] The present invention will be further illustrated by the following embodiments.

[0052] Materials, Instruments and Methods The materials used for testing in implementing the embodiments are as follows: - NuSil® MED silicone rubber, 6033, 4930, 4950, 4970 and 6640 series, by Avantor TM The company produces and sells; - Elkem Siliconi Italia srl ​​(LSR 4370 silicone rubber from CaronnoPertusella (VA)); - Tetrachloroauric acid, hexachloroplatinic acid and hexachloroiridic acid were purchased from METALOR Technologies SA, Marin (Switzerland); - Mowiol® 4-88 was purchased from Sigma-Aldrich. - The first metal deposit formed in the silicone rubber substrate (on which a second deposit is subsequently grown) exists in the form of a layer of nanoparticles prepared by the SCBI technique according to the method described in the applicant's patent application WO 2011 / 121017 A1; in all cases, the metal of the nanoparticles is Pt; - The electrolytic cell used to produce metal deposits is a self-assembled three-electrode electrolytic cell, including a reference electrode Ag / AgCl IS-AG / AGCL.AQ.RE.1 (manufactured and sold by PalmSens BV (Netherlands)) and a graphite counter electrode BASI-MW-4131 (PalmSens BV); the electrodes are connected to a PalmSens-04 potentiostat. - Resistivity measurements were performed using an Agilent 34410A / 11A 6½ digital multimeter; - Using Avantor TM The Elmasonic P 120 H plating solution sold generates ultrasonic waves; - SEM images were acquired using a Zeiss LEO 1525 instrument; - Optical microscope images were acquired using an ASH OMNI 3 instrument.

[0053] Example 1 This embodiment relates to the preparation of gold deposits by chemical plating with ultrasonic waves applied during the deposition process.

[0054] A silicone rubber substrate was prepared by polymerization of NuSil® MED 6033 precursor at 115°C for 1 hour. The substrate had a thickness of 0.1 mm and a lateral dimension of 20 × 40 mm.

[0055] A layer of Pt nanoparticles is formed on one surface of the substrate. The deposit has... Figure 3 The geometry shown is obtained through a template mask. The deposit 11 obtained on substrate 10 has the shape shown in the figure, referred to in the art as a "dog bone" shape, consisting of two large lateral portions (each 5 × 12 mm) connected by a central portion 20 mm long and 1.5 mm wide. This shape is suitable for subsequent stress resistance measurements of the sample, where the two large lateral portions allow for easy electrical connection of the sample to the ohmmeter's fixture, while the central portion is the area of ​​tensile stress concentration.

[0056] The average thickness of the obtained nanoparticle layer was 63 nm, which was determined by measuring the thickness of the corresponding layer deposited on the silicone rubber substrate using a stylus profilometer (KLATencor P-17, with a resolution of up to 0.5 Å).

[0057] A gold deposition bath was prepared by adding 35 mL of a 0.2 g / L tetrachloroauric acid solution to a beaker and then adding hydrogen peroxide until the concentration of the compound reached 0.002 M. The temperature was maintained at 35°C using a constant-temperature bath.

[0058] The previously prepared substrate was suspended by a metal wire and moved vertically for 10 mm at a speed of 10 mm / s in the plating solution, while ultrasound with a frequency of 37 kHz was applied to the plating solution.

[0059] The process lasted 15 minutes.

[0060] Gold deposition occurs only in the regions where the Pt nanoparticle layer previously formed, thus the final deposit exhibits similar characteristics to... Figure 3 Same geometry.

[0061] The obtained samples were examined under an optical microscope, and the results were obtained. Figure 4 The photomicrograph shown.

[0062] In the image, the brighter lines represent the crack lines between island regions of the gold deposit, while the darker areas represent the island regions of the deposit, i.e., the continuous parts within it.

[0063] Example 2 (Comparative) The test of Example 1 was repeated, except that ultrasound was not applied to the deposition solution during the gold deposition process. Figure 5 It shows the relationship with Figure 4 Micrographs obtained at the same magnification: It can be noted that in this case, the surface of the sediment exhibits a generally uniform appearance without microcracks, similar to the sediment obtained in Example 1.

[0064] Example 3 This embodiment relates to the preparation of platinum deposits by chemical plating deposition in which ultrasound is applied during the deposition process.

[0065] Repeat the steps of Example 1 until a Pt nanoparticle layer is obtained on the silicone rubber substrate.

[0066] The substrate thus prepared is immersed in a plating bath maintained at 35°C, the plating bath containing hexachloroplatinic acid at a concentration of 0.3 g / L, hydrazine chloride at a concentration of 2.5 g / L, ammonia at a concentration of 35 g / L, and potassium chloride at a concentration of 15 g / L.

[0067] During platinum deposition, 37 kHz ultrasound was applied to the plating bath while the substrate moved vertically 10 mm at a speed of 10 mm / s and rotated at a speed of 25 rpm. Deposition lasted for 25 minutes.

[0068] Figure 6 The image shown is an optical microscope image illustrating the surface of the metal deposit: as shown, the surface has... Figure 4 The samples from Zhongjin have the same microcrack structure.

[0069] Example 4 This embodiment relates to the preparation of iridium deposits by chemical plating with ultrasonic waves applied during the deposition process.

[0070] Repeat the steps of Example 3, but use a plating solution containing 0.2 g / L hexachloroiridium acid, 0.1 g / L hydrazine chloride, and 0.005 g / L sodium hydroxide; the plating solution is maintained at 70°C during the iridium deposition process, which lasts for 30 minutes.

[0071] Figure 7 The image shown is an optical microscope image illustrating the surface of the metal deposit: as shown, the surface has... Figure 4 The samples from Zhongjin have the same microcrack structure.

[0072] Example 5 This embodiment relates to the preparation of gold deposits by chemical plating with the application of ultrasound after deposition.

[0073] Repeat the steps of Example 1 until a Pt nanoparticle layer is obtained on the silicone rubber substrate.

[0074] The substrate thus prepared is immersed in a plating bath maintained at 25°C, the plating bath containing 0.09 g / L tetrachloroauric acid, 0.44 M hydrogen peroxide, 0.5 g / L potassium chloride, and 2.0 g / L Mowiol® 4-88.

[0075] The deposition reaction lasted for 30 minutes.

[0076] The sample remained stationary during the deposition process, while the plating solution was stirred using a magnetic stirrer.

[0077] At the end of the gold deposition step, the sample was inserted into a second beaker containing deionized water and moved vertically 10 mm at a speed of 10 mm / s for 5 minutes, while ultrasound at a frequency of 37 kHz was applied to the liquid phase.

[0078] The characteristics of the obtained sample are similar to those of the sample obtained in Example 1.

[0079] Example 6 This embodiment relates to measuring the conductivity of the deposit sample of the present invention during a stretching / relaxation cycle.

[0080] The surface resistivity of the samples obtained in Examples 1, 3, and 4 was measured under tensile conditions and during the subsequent recovery to the initial size (relaxation).

[0081] To measure the relationship between resistance and traction force, a method such as... Figure 8 The self-assembly apparatus shown consists of two electrically insulated clamps 1 and 2, with clamp 1 fixed to a sliding surface 3 so that it can be moved away from or towards clamp 2. The lower parts of clamps 1 and 2 have metal components (not shown) that serve both to hold the stretched sample and to electrically connect it to a ohmmeter (multimeter) via a lateral region of the metal deposit; the central portion of the deposit, indicated by reference numeral 11, undergoes elongation during the test. Measurements are performed using a linear motor coupled to the ohmmeter. The movement of the movable surface 3 is controlled by software edited in LabVIEW; the test consists of 100 consecutive cycles of elongation followed by relaxation at the desired percentage of elongation, while the resistance of the sample is recorded.

[0082] Test results are as follows Figure 9 As shown in the figure, this graph illustrates the relationship between the surface resistivity value (Ω / □) and the percentage elongation of the sample after 100 cycles.

[0083] Example 7 (Comparative) The tests of Example 6 were repeated on the samples obtained in Example 2. The metal deposits underwent electrical fracture when the elongation was less than 10%, such as... Figure 10 As shown in curve 1, this figure shows the relationship between the surface resistivity value (Ω / □) of the sample and the elongation percentage; for comparison, the same figure shows the surface resistivity trend curves of the sample of Example 1 (gold deposit prepared by ultrasonication during deposition, curve 2) and the sample of Example 5 (gold deposit prepared by ultrasonication after deposition, curve 3).

Claims

1. A method for fabricating a stretchable conductive device, the method comprising the following steps: a) Prepare an elastomer substrate, the surface of which has a first metal deposit with a thickness of 10 nm to 200 nm obtained by a dry process; b) Forming a second metal deposit on top of the first metal deposit by solution chemical or electrochemical deposition; The characteristic feature is that the solution deposition and ultrasonic treatment are performed simultaneously, or after the ultrasonic treatment.

2. The method according to claim 1, wherein, The elastomer substrate is made of polymer materials selected from the following: polyolefin elastomers, fluoropolymer elastomers, polybutadiene (BR), styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), nitrile rubber (NBR), acrylate rubber (ACM), isobutylene-isoprene rubber (IIR), copolyesters, chloroprene rubber (polychloroprene), polyurethane rubber, and polysiloxane (silicone rubber).

3. The method according to any one of claims 1 or 2, wherein, The polymer material is polydimethylsiloxane (PDMS).

4. The method according to any one of the preceding claims, wherein, Step a) is performed using a dry method selected from evaporation and cluster deposition techniques.

5. The method according to claim 4, wherein, The evaporation technology is selected from chemical vapor deposition (CVD), thermal evaporation, electron beam evaporation and sputtering, and the cluster deposition technology is selected from CBD (cluster electron beam deposition), SCBD (supersonic cluster electron beam deposition) and SCBI (supersonic cluster electron beam injection).

6. The method according to any one of the preceding claims, wherein, The metal in the first deposit is platinum.

7. The method according to any one of the preceding claims, wherein, Step b) is performed by solution chemical reduction of the metal salt or complex of the second deposit using a reducing agent.

8. The method according to claim 7, wherein the metal of the second deposit is selected from gold, platinum and iridium; tetrachloroauric acid, hexachloroplatinic acid and hexachloroiridium acid are used as metal precursors respectively; when selected from gold, the reducing agent is hydrogen peroxide, and when selected from platinum and iridium, the reducing agent is hydrazine.

9. The method according to any one of claims 7 and 8, wherein, Step b) is carried out at a temperature of 5°C to 80°C, preferably 15°C to 70°C, with the concentration of the metal ion to be reduced being 0.01 g / L to 10 g / L, and the molar ratio of the reducing agent to the metal ion to be reduced being 1:10 to 1:1000.

10. The method according to any one of claims 7 to 9, wherein, The solution in step b) also contains one or more additives selected from surfactants, halide ions and pH adjusters.

11. The method according to any one of claims 1 to 6, wherein, Step b) is carried out by electrochemical reduction in a solution of a metal salt or complex of the second deposit.

12. The method of claim 11, wherein the metal of the second deposit is selected from gold, platinum and iridium; and tetrachloroauric acid, hexachloroplatinic acid and hexachloroiridium acid are used as metal precursors, respectively.

13. The method according to any one of claims 7 to 12, wherein the thickness of the second metal deposit is 50 nm to 1000 nm.

14. The method according to any one of claims 7 to 13, wherein, The frequency of the ultrasound applied during or after the formation of the second metal deposit is from 25 kHz to 80 kHz.

15. The method according to claim 14, wherein, The frequency is from 30 kHz to 50 kHz.

16. The method according to claim 15, wherein, The frequency is approximately 40 kHz.

17. The method according to any one of claims 7 to 16, wherein, During the application of ultrasound, the substrate moves linearly relative to its average position at a speed of 5 mm / s to 20 mm / s, and / or rotates at a speed of 10 rpm to 50 rpm.

18. The method according to claim 17, wherein, The base rotates at a speed of 20 rpm to 30 rpm.

19. The method according to any one of the preceding claims, wherein, Between steps a) and b), a reducing agent selected from formic acid, hydrazine, and alcohol is used to perform a chemical cleaning operation on the first deposit.

Images